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LTC1992 Family Low Power, Fully Differential Input/Output Amplifier/Driver Family
FEATURES

DESCRIPTIO
Adjustable Gain and Fixed Gain Blocks of 1, 2, 5 and 10 0.3% (Max) Gain Error from -40C to 85C 3.5ppm/C Gain Temperature Coefficient 5ppm Gain Long Term Stability Fully Differential Input and Output CLOAD Stable up to 10,000pF Adjustable Output Common Mode Voltage Rail-to-Rail Output Swing Low Supply Current: 1mA (Max) High Output Current: 10mA (Min) Specified on a Single 2.7V to 5V Supply DC Offset Voltage <2.5mV (Max) Available in 8-Lead MSOP Package
The LTC(R)1992 product family consists of five fully differential, low power amplifiers. The LTC1992 is an unconstrained fully differential amplifier. The LTC1992-1, LTC1992-2, LTC1992-5 and LTC1992-10 are fixed gain blocks (with gains of 1, 2, 5 and 10 respectively) featuring precision on-chip resistors for accurate and ultrastable gain. All of the LTC1992 parts have a separate internal common mode feedback path for outstanding output phase balancing and reduced second order harmonics. The VOCM pin sets the output common mode level independent of the input common mode level. This feature makes level shifting of signals easy. The amplifiers' differential inputs operate with signals ranging from rail-to-rail with a common mode level from the negative supply up to 1.3V from the positive supply. The differential input DC offset is typically 250V. The railto-rail outputs sink and source 10mA. The LTC1992 is stable for all capacitive loads up to 10,000pF. The LTC1992 can be used in single supply applications with supply voltages as low as 2.7V. It can also be used with dual supplies up to 5V. The LTC1992 is available in an 8-pin MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S

Differential Driver/Receiver Differential Amplification Single-Ended to Differential Conversion Level Shifting Trimmed Phase Response for Multichannel Systems
TYPICAL APPLICATIO
Single-Supply, Single-Ended to Differential Conversion
10k 5V 10k 0V -5V 10k 0.01F INPUT SIGNAL FROM A 5V SYSTEM VIN 1 7 2 8 5V 3 5V 4 5V 2.5V 0V 5V 2.5V 0V OUTPUT SIGNAL FROM A SINGLE-SUPPLY SYSTEM
1992 TA01a
-+
VMID VOCM 6 10k
VIN (5V/DIV) +OUT (2V/DIV) -OUT
1992 TA01b
LTC1992 5
+-
U
0V -5V 5V 0V
1992f
U
U
1
LTC1992 Family
ABSOLUTE AXI U RATI GS
Total Supply Voltage (+V S to -V S) .......................... 12V Maximum Voltage on any Pin .......... (-VS - 0.3V) VPIN (+VS + 0.3V) Output Short-Circuit Duration (Note 3) ............ Indefinite Operating Temperature Range (Note 5) LTC1992CMS8/LTC1992-XCMS8/ LTC1992IMS8/LTC1992-XIMS8 ..........-40C to 85C LTC1992HMS8/LTC1992-XHMS8 .....-40C to 125C
PACKAGE/ORDER I FOR ATIO
TOP VIEW -IN 1 VOCM 2 +VS 3 +OUT 4 8 7 6 5 +IN VMID -VS -OUT
+ +-
-
MS8 PACKAGE 8-LEAD PLASTIC MSOP
TJMAX = 150C, JA = 250C/W
ORDER PART NUMBER LTC1992CMS8 LTC1992IMS8 LTC1992HMS8
MS8 PART MARKING LTYU LTZC LTAGR
Consult LTC Marketing for parts specified with wider operating temperature ranges.
2
U
U
W
WW
U
W
(Note 1)
Specified Temperature Range (Note 6) LTC1992CMS8/LTC1992-XCMS8/ LTC1992IMS8/LTC1992-XIMS8 ..........-40C to 85C LTC1992HMS8/LTC1992-XHMS8 .....-40C to 125C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
TOP VIEW -IN 1 VOCM 2 +VS 3 +OUT 4 8 7 6 5 +IN VMID -VS -OUT
- +-
+
MS8 PACKAGE 8-LEAD PLASTIC MSOP
TJMAX = 150C, JA = 250C/W
ORDER PART NUMBER LTC1992-1CMS8 LTC1992-1IMS8 LTC1992-1HMS8 LTC1992-2CMS8 LTC1992-2IMS8 LTC1992-2HMS8 LTC1992-5CMS8 LTC1992-5IMS8 LTC1992-5HMS8 LTC1992-10CMS8 LTC1992-10IMS8 LTC1992-10HMS8
MS8 PART MARKING LTACJ LTACM LTAFZ LTYV LTZD LTAGA LTACK LTACN LTAJH LTACL LTACP LTAJJ
1992f
LTC1992 Family
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Specifications applicable to all parts in the LTC1992 family.
SYMBOL VS IS PARAMETER Supply Voltage Range Supply Current VS = 2.7V to 5V
ELECTRICAL CHARACTERISTICS
CONDITIONS
ALL C AND I GRADE MIN TYP MAX 2.7 0.65 0.75 0.7 0.8 0.25 0.25 0.25 10 10 10 75 80 1 0.1 -85 0.5 1 2 10 10 10 (-VS)+0.5V 500 2 2.44 2.60 2.50 2.29 2.50 2.69 2.61 2.52 0.02 0.10 0.20 4.90 4.85 4.75 4.99 4.90 4.81 0.02 0.10 0.20 4.90 4.85 4.65 4.99 4.89 4.80 - 4.99 - 4.90 - 4.80 -4.90 -4.75 -4.65 0.10 0.25 0.35 0.10 0.25 0.35 2.56 11 1.0 1.2 1.2 1.5 2.5 2.5 2.5
ALL H GRADE MIN TYP MAX 2.7 0.65 0.8 0.7 0.9 0.25 0.25 0.25 10 10 10 72 80 1 0.1 -85 0.5 1 2 10 10 10 11 1.0 1.5 1.2 1.8 4 4 4
UNITS V mA mA mA mA mV mV mV V/C V/C V/C dB
VS = 5V
VOSDIFF
Differential Offset Voltage (Input Referred) (Note 7) Differential Offset Voltage Drift (Input Referred) (Note 7) Power Supply Rejection Ratio (Input Referred) (Note 7)
VS = 2.7V VS = 5V VS = 5V VS = 2.7V VS = 5V VS = 5V VS = 2.7V to 5V

VOSDIFF/T
PSRR GCM
VOSCM
Common Mode Gain(VOUTCM/VOCM) Common Mode Gain Error Output Balance (VOUTCM/(VOUTDIFF) VOUTDIFF = -2V to +2V Common Mode Offset Voltage VS = 2.7V VS = 5V (VOUTCM - VOCM) VS = 5V Common Mode Offset Voltage Drift VS = 2.7V VS = 5V VS = 5V
0.3 -60 12 15 18
0.35 -60 15 17 20
% dB mV mV mV V/C V/C V/C
VOSCM /T
VOUTCMR RINVOCM IBVOCM VMID VOUT
Output Signal Common Mode Range (Voltage Range for the VOCM Pin) Input Resistance, VOCM Pin Input Bias Current, VOCM Pin Voltage at the VMID Pin Output Voltage, High (Note 2) Output Voltage, Low (Note 2) Output Voltage, High (Note 2) Output Voltage, Low (Note 2) Output Voltage, High (Note 2) Output Voltage, Low (Note 2) VS = 2.7V, Load = 10k VS = 2.7V, Load = 5mA VS = 2.7V,Load = 10mA VS = 2.7V, Load = 10k VS = 2.7V, Load = 5mA VS = 2.7V, Load = 10mA VS = 5V, Load = 10k VS = 5V, Load = 5mA VS = 5V, Load = 10mA VS = 5V, Load = 10k VS = 5V, Load = 5mA VS = 5V, Load = 10mA VS = 5V, Load = 10k VS = 5V, Load = 5mA VS = 5V, Load = 10mA VS = 5V, Load = 10k VS = 5V, Load = 5mA VS = 5V, Load = 10mA VS = 2.7V to 5V
(+VS)-1.3V (-VS)+0.5V 500 2 2.43 2.60 2.50 2.29 2.50 2.69 2.61 2.52 0.02 0.10 0.20 4.90 4.80 4.70 4.99 4.90 4.81 0.02 0.10 0.20 4.85 4.80 4.60 4.99 4.89 4.80 -4.98 -4.90 -4.80
(+VS)-1.3V
V M pA

2.57
V V V V
0.10 0.25 0.41
V V V V V V
0.10 0.30 0.42
V V V V V V
-4.85 -4.75 -4.55
V V V
1992f
3
LTC1992 Family
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Specifications applicable to all parts in the LTC1992 family.
SYMBOL ISC PARAMETER Output Short-Circuit Current Sourcing (Notes 2,3) Output Short-Circuit Current Sinking (Notes 2,3) AVOL Large-Signal Voltage Gain CONDITIONS VS = 2.7V, VOUT = 1.35V VS = 5V, VOUT = 2.5V VS = 5V, VOUT = 0V VS = 2.7V, VOUT =1.35V VS = 5V, VOUT = 2.5V VS = 5V, VOUT = 0V

ELECTRICAL CHARACTERISTICS
ALL C AND I GRADE MIN TYP MAX 20 20 20 13 13 13 30 30 30 30 30 30 80
ALL H GRADE MIN TYP MAX 20 20 20 13 13 13 30 30 30 30 30 30 80
UNITS mA mA mA mA mA mA dB
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Specifications applicable to the LTC1992 only.
LTC1992CMS8 LTC1992ISM8 MIN TYP MAX

SYMBOL IB IOS RIN CIN en in VINCMR CMRR SR GBW
PARAMETER Input Bias Current Input Offset Current Input Resistance Input Capacitance
CONDITIONS VS = 2.7V to 5V VS = 2.7V to 5V
LTC1992HMS8 MIN TYP MAX 2 0.1 500 3 35 1 69 0.5 90 1.5 3.2 3.5
4.0
UNITS pA pA M pF nV/Hz fA/Hz V dB V/s MHz MHz MHz
2 0.1 500 3 35 1
250 100
400 150
Input Referred Noise Voltage Density f = 1kHz Input Noise Current Density Input Signal Common Mode Range Common Mode Rejection Ratio (Input Referred) Slew Rate (Note 4) Gain-Bandwidth Product (fTEST = 100kHz) TA = 25C LTC1992CMS8 LTC1992IMS8/ LTC1992HMS8 VINCM = -0.1V to 3.7V f = 1kHz

(-VS)- 0.1V (+VS)- 1.3V (-VS)- 0.1V (+VS)- 1.3V 69 0.5 3.0
2.5 1.9
90 1.5 3.2
3.0
3.5
4.0 4.0
3.0
1.9
1992f
4
LTC1992 Family
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Typical values are at TA = 25C. Specifications apply to the LTC1992-1 only.
LTC1992-1CMS8 LTC1992-1IMS8 MIN TYP MAX

ELECTRICAL CHARACTERISTICS
SYMBOL GDIFF
PARAMETER Differential Gain Differential Gain Error Differential Gain Nonlinearity Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-1HMS8 MIN TYP MAX 1 0.1 50 3.5 45 22 55 0.5 30 - 0.1V to 4.9V 60 1.5 3 0.35
UNITS V/V % ppm ppm/C nV/Hz k V dB V/s MHz
1 0.1 50 3.5 45 22.5 55 0.5 30 60 1.5 3
0.3
en RIN VINCMR CMRR SR GBW
Input Referred Noise Voltage Density (Note 7) f = 1kHz Input Resistance, Single-Ended +IN, -IN Pins Input Signal Common Mode Range Common Mode Rejection Ratio (Amplifier Input Referred) (Note 7) Slew Rate (Note 4) Gain-Bandwidth Product fTEST = 180kHz VS = 5V VINCM = -0.1V to 3.7V
37.5
38
- 0.1V to 4.9V
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Typical values are at TA = 25C. Specifications apply to the LTC1992-2 only.
LTC1992-2CMS8 LTC1992-2IMS8 MIN TYP MAX

SYMBOL GDIFF
PARAMETER Differential Gain Differential Gain Error Differential Gain Nonlinearity Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-2HMS8 MIN TYP MAX 2 0.1 50 3.5 45 22 55 0.7 30 - 0.1V to 4.9V 60 2 4 0.35
UNITS V/V % ppm ppm/C nV/Hz k V dB V/s MHz
2 0.1 50 3.5 45 22.5 55 0.7 30 60 2 4
0.3
en RIN VINCMR CMRR SR GBW
Input Referred Noise Voltage Density (Note 7) f = 1kHz Input Resistance, Single-Ended +IN, -IN Pins Input Signal Common Mode Range Common Mode Rejection Ratio (Amplifier Input Referred) (Note 7) Slew Rate (Note 4) Gain-Bandwidth Product fTEST = 180kHz VS = 5V VINCM = -0.1V to 3.7V
37.5
38
- 0.1V to 4.9V
1992f
5
LTC1992 Family
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Typical values are at TA = 25C. Specifications apply to the LTC1992-5 only.
LTC1992-5CMS8 LTC1992-5IMS8 MIN TYP MAX

ELECTRICAL CHARACTERISTICS
SYMBOL GDIFF
PARAMETER Differential Gain Differential Gain Error Differential Gain Nonlinearity Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-5HMS8 MIN TYP MAX 5 0.1 50 3.5 45 22 55 0.7 30 - 0.1V to 3.9V 60 2 4 0.35
UNITS V/V % ppm ppm/C nV/Hz k V dB V/s MHz
5 0.1 50 3.5 45 22.5 55 0.7 30 60 2 4
0.3
en RIN VINCMR CMRR SR GBW
Input Referred Noise Voltage Density (Note 7) f = 1kHz Input Resistance, Single-Ended +IN, -IN Pins Input Signal Common Mode Range Common Mode Rejection Ratio (Amplifier Input Referred) (Note 7) Slew Rate (Note 4) Gain-Bandwidth Product fTEST = 180kHz VS = 5V VINCM = -0.1V to 3.7V
37.5
38
- 0.1V to 3.9V
The denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. +VS = 5V, -VS = 0V, VINCM = VOUTCM = VOCM = 2.5V, unless otherwise noted. VOCM is the voltage on the VOCM pin. VOUTCM is defined as (+VOUT + -VOUT)/2. VINCM is defined as (+VIN + -VIN)/2. VINDIFF is defined as (+VIN - -VIN). VOUTDIFF is defined as (+VOUT - -VOUT). Typical values are at TA = 25C. Specifications apply to the LTC1992-10 only.
LTC1992-10CMS8 LTC1992-10IMS8 MIN TYP MAX

SYMBOL GDIFF
PARAMETER Differential Gain Differential Gain Error Differential Gain Nonlinearity Differential Gain Temperature Coefficient
CONDITIONS
LTC1992-10HMS8 MIN TYP MAX 10 0.1 50 3.5 45 11 55 0.7 15 - 0.1V to 3.8V 60 2 4 0.35
UNITS V/V % ppm ppm/C nV/Hz k V dB V/s MHz
10 0.1 50 3.5 45 11.3 55 0.7 15 60 2 4
0.3
en RIN VINCMR CMRR SR GBW
Input Referred Noise Voltage Density (Note 7) f = 1kHz Input Resistance, Single-Ended +IN, -IN Pins Input Signal Common Mode Range Common Mode Rejection Ratio (Amplifier Input Referred) (Note 7) Slew Rate (Note 4) Gain-Bandwidth Product fTEST = 180kHz VS = 5V VINCM = -0.1V to 3.7V
18.8
19
- 0.1V to 3.8V
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Output load is connected to the midpoint of the +VS and -VS potentials. Measurement is taken single-ended, one output loaded at a time. Note 3: A heat sink may be required to keep the junction temperature below the absolute maximum when the output is shorted indefinitely. Note 4: Differential output slew rate. Slew rate is measured single ended and doubled to get the listed numbers. Note 5: The LTC1992C/LTC1992-XC/LTC1992I/LTC1992-XI are guaranteed functional over an operating temperature of -40C to 85C. The LTC1992H/LTC1992-XH are guaranteed functional over the extended operating temperature of - 40C to 125C.
Note 6: The LTC1992C/LTC1992-XC are guaranteed to meet the specified performance limits over the 0C to 70C temperature range and are designed, characterized and expected to meet the specified performance limits over the -40C to 85C temperature range but are not tested or QA sampled at these temperatures. The LTC1992I/LTC1992-XI are guaranteed to meet the specified performance limits over the -40C to 85C temperature range. The LTC1992H/LTC1992-XH are guaranteed to meet the specified performance limits over the -40C to 125C temperature range. Note 7: Differential offset voltage, differential offset voltage drift, CMRR, noise voltage density and PSRR are referred to the internal amplifier's input to allow for direct comparison of gain blocks with discrete amplifiers.
1992f
6
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
1.0 0.9 0.8
SUPPLY CURRENT (mA)
125C 85C
DIFFERENTIAL VOS (mV)
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 1
25C -40C
0.2 0 -0.2 -0.4 VS = 5V -0.6 -0.8 -40 VS = 1.35V VS = 2.5V
COMMON MODE VOS (mV)
2345678 TOTAL SUPPLY VOLTAGE (V)
Common Mode Offset Voltage vs VOCM Voltage
5 125C 85C 25C VOCM VOS (mV) VOCM VOS (mV) -5 -40C
-5 5
0
VOCM VOS (mV)
-10
-15 +V = 2.7V S -VS = 0V VINCM = 1.35V -20 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 VOCM VOLTAGE (V)
1992 G04
Output Voltage Swing vs Output Load, VS = 2.7V
2.70 2.65 2.60
+SWING (V)
+SWING (V)
2.55 -40C 2.50 25C 2.45 85C 2.40 2.35 2.30 0 5 -20 -15 -10 -5 10 LOAD CURRENT (mA) 15 20 125C -40C 85C 25C
UW
9
1992 G01
Applicable to all parts in the LTC1992 family. Common Mode Offset Voltage vs Temperature
4 3 2 1 0 -1 -2 -3 -4 VS = 2.5V VS = 1.35V VINCM = 0V VOCM = 0V VS = 5V
Differential Input Offset Voltage vs Temperature (Note 7)
0.6 0.4 VINCM = 0V VOCM = 0V
10
85 25 TEMPERATURE (C)
125
1992 G02
-5 -40
25 85 TEMPERATURE (C)
125
1992 G03
Common Mode Offset Voltage vs VOCM Voltage
5 125C 0 85C 25C -40C -5 0
Common Mode Offset Voltage vs VOCM Voltage
125C 85C 25C -40C -10
-10
-15 +V = 5V S -VS = 0V VINCM = 2.5V -20 0 0.5 1 1.5 2 2.5 3 3.5 VOCM VOLTAGE (V)
4
4.5
5
-15 +V = 5V S -VS = -5V VINCM = 0V -20 -5 -4 -3 -2 -1 0 1 2 VOCM VOLTAGE (V)
3
4
5
1992 G05
1992 G06
Output Voltage Swing vs Output Load, VS = 5V
0.8 0.7 125C 0.6 0.5 0.4 0.3 0.2 0.1 0
-SWING (V)
5.00 4.95 4.90 4.85 4.80 4.75 4.70 4.65 4.60 4.55 4.50 -20 -15 -10 -5 0 5 10 LOAD CURRENT (mA) 15 20 125C -40C -40C 25C 85C 125C 85C 25C 1.0 0.9 0.8 0.7
-SWING (V)
0.6 0.5 0.4 0.3 0.2 0.1 0
1992 G07
1992 G08
1992f
7
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Swing vs Output Load, VS = 5V
5.0 4.9 -40C 4.8
+SWING (V)
VOCM INPUT BIAS CURRENT (A)
25C 4.7 85C 4.6 125C 4.5 4.4 5 10 0 -20 -15 -10 -5 LOAD CURRENT (mA) 125C 85C 25C -40C -4.8 -5.0 15 20 -4.4 -4.6
100E-12 85C 10E-12 -40C 1E-12 +VS = 5V -VS = 0V VINCM = 2.5V 0 0.5 1 1.5 2 2.5 3 3.5 VOCM VOLTAGE (V) 4 4.5 5 25C
DELTA VOS (V)
Differential Gain vs Time (Normalized to t = 0)
10 8 6
DELTA GAIN (ppm)
TEMP = 35C
4
0 -2 -4 -6 -8 -10 0 400 800 1200 TIME (HOURS) 1600 2000
1992 G12
1V/DIV
OUTPUTS
1V/DIV
2
Output Overdrive Recovery (Expanded View)
+VS = 2.5V, -VS = -2.5V, VOCM = 0V
1V/DIV
INPUTS
OUTPUTS
1V/DIV
LTC1992-2 SHOWN FOR REFERENCE 50s/DIV
1992 G15
8
UW
1992 G09
Applicable to all parts in the LTC1992 family. Differential Input Offset Voltage vs Time (Normalized to t = 0)
100 80 TEMP = 35C
VOCM Input Bias Current vs VOCM Voltage
-3.8 -4.0 -4.2
-SWING (V)
10E-9 125C
1E-9
60 40 20 0 -20 -40 -60 -80 -100 0 400 800 1200 TIME (HOURS) 1600 2000
1992 G11
100E-15
1992 G10
Input Common Mode Overdrive Recovery (Expanded View)
BOTH INPUTS (INPUTS TIED TOGETHER)
Input Common Mode Overdrive Recovery (Detailed View)
BOTH INPUTS (INPUTS TIED TOGETHER)
OUTPUTS +VS = 2.5V -VS = -2.5V VOCM = 0V LTC1992-10 SHOWN FOR REFERENCE
+VS = 2.5V -VS = -2.5V VOCM = 0V LTC1992-10 SHOWN FOR REFERENCE 50s/DIV
1992 G13
1s/DIV
1992 G14
Output Overdrive Recovery (Detailed View)
INPUTS
OUTPUTS
+VS = 2.5V -VS = -2.5V VOCM = 0V LTC1992-2 SHOWN FOR REFERENCE 5s/DIV
1992 G16
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Differential Gain vs Frequency, VS = 2.5V
12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 10 RIN = RFB = 10k
PHASE (DEG)
GAIN (dB)
GAIN (dB)
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G17
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 +VS = 2.7V -VS = 0V 1.5 VOCM = 1.35V DIFFERENTIAL VOS (mV)
2.0
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 COMMON MODE VOLTAGE (V)
1922 G20
-40C 125C 25C 85C
Common Mode Rejection Ratio vs Frequency (Note 7)
120 100 80
CMRR (dB)
70
PSRR (dB)
60 50 40 30 20 10
+VS
OUTPUT BALANCE (dB)
60 40 20 0 100
1k
10k 100k FREQUENCY (Hz)
UW
VAMPCM VAMPDIFF
1992 G23
Applicable to the LTC1992 only. Differential Phase Response vs Frequency
0 - 20 - 40 - 60 - 80 -100 -120 -140 -160 -180
10000
1992 G18
Single-Ended Input Differential Gain vs Frequency, VS = 2.5V
12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 10 RIN = RFB = 10k
RIN = RFB = 10k
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz)
CLOAD = 10pF 50pF 100pF 500pF 1000pF 5000pF 10000pF 10 100 FREQUENCY (kHz) 1000
1992 G37
Differential Input Offset Voltage vs Input Common Mode Voltage
+VS = 5V 1.5 -VS = 0V VOCM = 2.5V 1.0 0.5 0 - 0.5 -1.0 -1.5 -2.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 COMMON MODE VOLTAGE (V)
1922 G21
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 1.5 1.0 0.5 -40C 0 125C -0.5 -1.0 -1.5 -2.0 -5 -4 -3 -2 -1 0 1 2 3 COMMON MODE VOLTAGE (V) 4 5 25C 85C +VS = 5V -VS = -5V VOCM = 0V
-40C 125C 25C 85C
1922 G22
Power Supply Rejection Ratio vs Frequency (Note 7)
100 90 80 -VS VS VAMPDIFF
Output Balance vs Frequency
0 VOUTCM VOUTDIFF
-20
-40
-60
-80
0 1M 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G24
-100 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G25
1992f
9
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 1.5V -VIN = 1.5V CLOAD = 0pF GAIN = 1 0V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
0V
CLOAD = 10000pF CLOAD = 1000pF
2s/DIV
1992 G26
20s/DIV
Single-Ended Input Large-Signal Step Response
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 4V -VIN = 2V CLOAD = 0pF GAIN = 1 2.5V
Single-Ended Input Large-Signal Step Response
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 4V -VIN = 2V GAIN = 1 2.5V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
CLOAD = 10000pF CLOAD = 1000pF 2s/DIV
1992 G28
20s/DIV
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 50mV -VIN = 50mV CLOAD = 0pF GAIN = 1 0V
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 50mV -VIN = 50mV GAIN = 1 0V
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
CLOAD = 10000pF CLOAD = 1000pF 1s/DIV
1992 G30
10s/DIV
10
UW
Applicable to the LTC1992 only. Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 1.5V -VIN = 1.5V GAIN = 1
1992 G27
1992 G29
1992 G31
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal Step Response
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 200mV -VIN = 100mV CLOAD = 0pF GAIN = 1 1s/DIV
1992 G32
THD + Noise vs Frequency
-40 -50 500kHz MEASUREMENT BANDWIDTH +VS = 5V -VS = -5V VOCM = 0V
THD + NOISE (dB)
THD + NOISE (dB)
-60 -70 VOUT = 1VP-PDIFF -80 VOUT = 2VP-PDIFF -90
-100 100
Differential Noise Voltage Density vs Frequency
1000
INPUT REFERRED NOISE (nVHz)
GAIN (dB)
100
10 10 100 1000 FREQUENCY (Hz) 10000
1922 G36
UW
Applicable to the LTC1992 only. Single-Ended Input Small-Signal Step Response
CLOAD = 10000pF CLOAD = 1000pF
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 200mV -VIN = 100mV GAIN = 1 10s/DIV
1992 G33
THD + Noise vs Amplitude
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V 50kHz -70 10kHz -80 -90 2kHz 1kHz 20 -100 0.1 1 10 INPUT SIGNAL AMPLITUDE (VP-PDIFF) 5kHz 20kHz
VOUT = 10VP-PDIFF VOUT = 5VP-PDIFF
-60
1k 10k FREQUENCY (Hz)
50k
1992 G34
1992 G35
VOCM Gain vs Frequency, VS = 2.5V
5 0 -5 -10 -15 -20 -25 -30 -35 10 100 1000 FREQUENCY (kHz) 10000
1992 G19
CLOAD = 10pF TO 10000pF
1992f
11
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Differential Gain vs Frequency, VS = 2.5V
12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 10
PHASE (DEG)
GAIN (dB)
GAIN (dB)
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G38
Differential Gain Error vs Temperature
0.025 0.020 0.015 GAIN ERROR (%) 0.010 GAIN (dB) 0.005 0 - 0.005 - 0.010 - 0.015 - 0.020 - 0.025 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
-25 -30 -35 -5 -10 -15 -20 5 0
Differential Input Offset Voltage vs Input Common Mode Voltage
5 +VS = 2.7V 4 -VS = 0V VOCM = 1.35V 3 2 1 0 -1 -2 -3 -4 -5 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 COMMON MODE VOLTAGE (V)
1922 G43
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
-40C 125C 25C 85C
12
UW
Applicable to the LTC1992-1 only. Differential Phase Response vs Frequency
0 -20 -40 -60 -80 CLOAD = 10pF 50pF 100pF 500pF 1000pF 5000pF 10000pF 10 100 FREQUENCY (kHz) 1000
1992 G40
Single-Ended Input Differential Gain vs Frequency, VS = 2.5V
12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 10
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G39
-100 -120 -140 -160 -180
VOCM Gain vs Frequency
CLOAD = 10pF TO 10000pF
10
100 1000 FREQUENCY (kHz)
10000
1992 G42
1992 G41
Differential Input Offset Voltage vs Input Common Mode Voltage
5 +VS = 5V 4 -VS = 0V VOCM = 2.5V 3 2 1 0 -1 -2 -3 -4 -5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 COMMON MODE VOLTAGE (V)
1922 G44
Differential Input Offset Voltage vs Input Common Mode Voltage
5 4 3 2 1 0 -1 -2 -3 -4 -5 -5 -4 -3 -2 -1 0 1 2 3 COMMON MODE VOLTAGE (V) 4 5 -40C 25C 125C 85C +VS = 5V - VS = -5V VOCM = 0V
-40C 25C 85C
125C
1922 G45
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 1.5V -VIN = 1.5V CLOAD = 0pF 0V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
0V
CMRR (dB)
CLOAD = 10000pF CLOAD = 1000pF
2s/DIV
1992 G46
20s/DIV
Single-Ended Input Large-Signal Step Response
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 4V -VIN = 2V CLOAD = 0pF 2.5V
Single-Ended Input Large-Signal Step Response
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 4V -VIN = 2V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
PSRR (dB)
2.5V
CLOAD = 10000pF CLOAD = 1000pF 2s/DIV
1992 G49
20s/DIV
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 50mV -VIN = 50mV CLOAD = 0pF 0V
Differential Input Small-Signal Step Response
0
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 50mV -VIN = 50mV
OUTPUT BALANCE (dB)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
0V
CLOAD = 10000pF CLOAD = 1000pF
1s/DIV
1992 G52
10s/DIV
UW
Applicable to the LTC1992-1 only. Common Mode Rejection Ratio vs Frequency
100 90 80 70 60 50 40 30 20 10
1992 G47
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 1.5V -VIN = 1.5V
VAMPCM VAMPDIFF 0 1k 100
10k 100k FREQUENCY (Hz)
1M
1992 G48
Power Supply Rejection Ratio vs Frequency
100 90 80 70 60 50 40 30 20 10 0 VS VAMPDIFF 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G51
-VS +VS
1992 G50
Output Balance vs Frequency
-20
-40
-60
-80 VOUTCM VOUTDIFF 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M
-100
1992 G53
1992 G54
1992f
13
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal Step Response
INPUT REFERRED NOISE (nVHz)
1992 G56
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 200mV -VIN = 100mV CLOAD = 0pF 1s/DIV
1992 G55
THD + Noise vs Frequency
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V THD + NOISE (dB)
THD + NOISE (dB)
-60 -70 VOUT = 1VP-PDIFF -80 VOUT = 2VP-PDIFF -90
-100 100
14
UW
Applicable to the LTC1992-1 only. Differential Noise Voltage Density vs Frequency
1000
Single-Ended Input Small-Signal Step Response
CLOAD = 10000pF CLOAD = 1000pF
2.5V
100
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 200mV -VIN = 100mV 10s/DIV
10 10 100 1000 FREQUENCY (Hz) 10000
1922 G57
THD + Noise vs Amplitude
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V 50kHz -70 10kHz -80 -90 2kHz 1kHz 20 -100 0.1 1 10 INPUT SIGNAL AMPLITUDE (VP-PDIFF) 5kHz 20kHz
VOUT = 10VP-PDIFF VOUT = 5VP-PDIFF
-60
1k 10k FREQUENCY (Hz)
50k
1992 G58
1992 G59
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Differential Gain vs Frequency, VS = 2.5V
18 12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 10
PHASE (DEG)
GAIN (dB)
GAIN (dB)
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G60
Differential Gain Error vs Temperature
0.05 0.04 0.03 0 -5 5
GAIN ERROR (%)
0.02
GAIN (dB)
0.01 0 - 0.01 - 0.02 - 0.03 - 0.04 - 0.05 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
Differential Input Offset Voltage vs Input Common Mode Voltage (Note 7)
2.0 +VS = 2.7V = 0V 1.5 -VS VOCM = 1.35V
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
0.5 0 -0.5 85C -1.0 -1.5 -2.0 0
-40C 25C
0.5 0 -0.5 -1.0 -1.5 85C
-40C 25C
DIFFERENTIAL VOS (mV)
1.0
125C
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 COMMON MODE VOLTAGE (V)
1992 G65
UW
Applicable to the LTC1992-2 only. Differential Phase Response vs Frequency
0 -20 -40 -60 -80 -100 -120 -140 -160
10000
1992 G61
Single-Ended Input Differential Gain vs Frequency, VS = 2.5V
18 12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 10
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz)
-180 10
CLOAD = 10pF 50pF 100pF 500pF 1000pF 5000pF 10000pF 100 FREQUENCY (kHz) 1000
1992 G62
VOCM Gain vs Frequency, VS = 2.5V
CLOAD = 10pF TO 10000pF
-10 -15 -20 -25 -30 10 100 1000 FREQUENCY (kHz) 10000
1992 G64
1992 G63
Differential Input Offset Voltage vs Input Common Mode Voltage (Note 7)
2.0 +VS = 5V 1.5 -VS = 0V VOCM = 2.5V 1.0 2.0
Differential Input Offset Voltage vs Input Common Mode Voltage (Note 7)
+VS = 5V 1.5 -VS = -5V VOCM = 0V 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 85C -40C 25C
125C
125C
-2.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 COMMON MODE VOLTAGE (V)
1992 G66
-5 -4 -3 -2 -1 0 1 2 3 COMMON MODE VOLTAGE (V)
4
5
1992 G67
1992f
15
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 750mV -VIN = 750mV CLOAD = 0pF 0V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
CMRR (dB)
0V
CLOAD = 10000pF CLOAD = 1000pF 2s/DIV
1992 G68
20s/DIV
Single-Ended Input Large-Signal Step Response
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 2V -VIN = 1V CLOAD = 0pF 2.5V
Single-Ended Input Large-Signal Step Response
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 2V -VIN = 1V
PSRR (dB)
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
2.5V
CLOAD = 10000pF CLOAD = 1000pF 2s/DIV
1992 G71
20s/DIV
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 25mV -VIN = 25mV CLOAD = 0pF 0V
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 25mV -VIN = 25mV
OUTPUT BALANCE (dB)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
0V
CLOAD = 10000pF CLOAD = 1000pF
2s/DIV
1992 G74
20s/DIV
16
UW
Applicable to the LTC1992-2 only. Common Mode Rejection Ratio vs Frequency (Note 7)
100 90 80 70 60 50 40 30 20 10
1992 G69
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 750mV -VIN = 750mV
0 100
VAMPCM VAMPDIFF 1k 10k 100k FREQUENCY (Hz) 1M
1992 G70
Power Supply Rejection Ratio vs Frequency (Note 7)
100 90 80 70 60 50 40 30 20 10 0 VS VAMPDIFF 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G73
-VS +VS
1992 G72
Output Balance vs Frequency
0
- 20
- 40
- 60
- 80 VOUTCM VOUTDIFF 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M
- 100
1992 G75
1992 G76
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal Step Response
INPUT REFERRED NOISE (nVHz)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 100mV -VIN = 50mV CLOAD = 0pF 2s/DIV
1992 G77
THD + Noise vs Frequency
-40 -50 THD + NOISE (dB)
THD + NOISE (dB)
-60 -70 -80 -90 VOUT = 1VP-PDIFF VOUT = 2VP-PDIFF VOUT = 5VP-PDIFF VOUT = 10VP-PDIFF 1k 10k FREQUENCY (Hz) 50k
1992 G80
-100 100
UW
Applicable to the LTC1992-2 only. Differential Noise Voltage Density vs Frequency
1000
Single-Ended Input Small-Signal Step Response
CLOAD = 10000pF CLOAD = 1000pF
2.5V
100
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 100mV -VIN = 50mV 20s/DIV
1992 G78
10 10 100 1000 FREQUENCY (Hz) 10000
1922 G79
THD + Noise vs Amplitude
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V 50kHz 20kHz -70 -80 -90 -100 0.1 1 INPUT SIGNAL AMPLITUDE (VP-PDIFF) 10 10kHz 5kHz 2kHz 1kHz
-60
1992 G81
1992f
17
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Differential Gain vs Frequency, VS = 2.5V
30 24 18 12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 10
30 24 18 12 6 0 -6 -12 -18 -24 -30 -36 -42 -48 -54 -60 10
PHASE (DEG)
GAIN (dB)
GAIN (dB)
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G82
Differential Gain Error vs Temperature
0.050 0.025 0
GAIN ERROR (%) GAIN (dB)
-0.025 -0.050 -0.075 -0.100 -0.125 -01.50 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 +VS = 2.7V -VS = 0V 1.5 VOCM = 1.35V DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
1.0 0.5 -40C 0 -0.5 -1.0 -1.5 -2.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 COMMON MODE VOLTAGE (V)
1922 G87
25C
125C 85C
18
UW
Applicable to the LTC1992-5 only. Differential Phase Response vs Frequency
0 -20 -40 -60 -80 -100 -120 -140 -160 -180 10000
1992 G83
Single-Ended Input Differential Gain vs Frequency, VS = 2.5V
CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz)
CLOAD = 10pF 50pF 100pF 500pF 1000pF 5000pF 10000pF 10 100 FREQUENCY (kHz) 1000
1992 G84
VOCM Gain vs Frequency
5 0 -5 -10 -15 -20 -25 -30 10 100 1000 FREQUENCY (kHz) 10000
1992 G86
CLOAD = 10pF TO 10000pF
1992 G85
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 +VS = 5V -VS = 0V 1.5 VOCM = 2.5V 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 COMMON MODE VOLTAGE (V)
1922 G88
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 1.5 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 -5 -4 -3 -2 -1 0 1 2 3 COMMON MODE VOLTAGE (V) 4 5 -40C +VS = 5V -VS = -5V VOCM = 0V
-40C 125C 85C
25C
85C
25C
125C
1922 G89
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 300mV -VIN = 300mV CLOAD = 0pF 0V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
0V
CMRR (dB)
CLOAD = 10000pF CLOAD = 1000pF 2s/DIV
1992 G90
20s/DIV
Single-Ended Input Large-Signal Step Response
Single-Ended Input Large-Signal Step Response
100
CLOAD = 10000pF CLOAD = 1000pF
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
PSRR (dB)
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 800mV -VIN = 400mV CLOAD = 0pF 2s/DIV
1992 G93
2.5V
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 800mV -VIN = 400mV 20s/DIV
1992 G94
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 10mV -VIN = 10mV CLOAD = 0pF 0V
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 10mV -VIN = 10mV
OUTPUT BALANCE (dB)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
0V
CLOAD = 10000pF CLOAD = 1000pF
5s/DIV
1992 G96
50s/DIV
UW
Applicable to the LTC1992-5 only. Common Mode Rejection Ratio vs Frequency (Note 7)
100 90 80 70 60 50 40 30 20 10
1992 G91
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 300mV -VIN = 300mV
VAMPCM VAMPDIFF 0 1k 100
10k 100k FREQUENCY (Hz)
1M
1992 G92
Power Supply Rejection Ratio vs Frequency (Note 7)
90 80 70 60 50 40 30 20 10 0 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G95
+VS -VS
VS VAMPDIFF
Output Balance vs Frequency
0
-20
-40
-60
-80 VOUTCM VOUTDIFF -100
1992 G97
1
10
100 1k 10k FREQUENCY (Hz)
100k
1M
1992 G98
1992f
19
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal Step Response
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 40mV -VIN = 20mV CLOAD = 0pF 5s/DIV
1992 G99
INPUT REFERRED NOISE (nVHz)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
THD + Noise vs Frequency
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V THD + NOISE (dB) VOUT = 1VP-PDIFF VOUT = 2VP-PDIFF VOUT = 5VP-PDIFF -80 -90 -100 100 VOUT = 10VP-PDIFF
-70
THD + NOISE (dB)
-60
20
UW
Applicable to the LTC1992-5 only. Differential Noise Voltage Density vs Frequency
1000
Single-Ended Input Small-Signal Step Response
CLOAD = 10000pF CLOAD = 1000pF
2.5V
100
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 40mV -VIN = 20mV 50s/DIV
1992 G100
10 10 100 1000 FREQUENCY (Hz) 10000
1922 G101
THD + Noise vs Amplitude
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V 50kHz -60 20kHz -70 -80 -90 -100 0.1 1 INPUT SIGNAL AMPLITUDE (VP-PDIFF) 5 10kHz 5kHz 2kHz 1kHz
1k 10k FREQUENCY (Hz)
50k
1992 G102
1992 G103
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Differential Gain vs Frequency, VS = 2.5V
40 30 20 10
GAIN (dB)
GAIN (dB)
0 -10 -20 -30 -40 -50 -60 10 CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G104
0 -10 -20 -30 -40 -50 -60 10 CLOAD = 10000pF CLOAD = 5000pF CLOAD = 1000pF CLOAD = 500pF CLOAD = 100pF CLOAD = 50pF CLOAD = 10pF 100 1000 FREQUENCY (kHz) 10000
1992 G105
PHASE (DEG)
Differential Gain Error vs Temperature
0.050 0.025 0
GAIN ERROR (%)
0 -5 5
-0.025
GAIN (dB)
-0.050 -0.075 -0.100 -0.125 -0.150 -0.175 -0.200 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 +VS = 2.7V - VS = 0V 1.5 VOCM = 1.35V 2.0
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
DIFFERENTIAL VOS (mV)
1.0 0.5 0 -0.5 25C -1.0 -1.5 -2.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 COMMON MODE VOLTAGE (V)
1922 G109
-40C 125C 85C
UW
Applicable to the LTC1992-10 only. Differential Phase Response vs Frequency
0 - 20 - 40 - 60 - 80 -100 -120 -140 -160 -180 10 CLOAD = 10pF 50pF 100pF 500pF 1000pF 5000pF 10000pF 100 FREQUENCY (kHz) 1000
1992 G106
Single-Ended Input Differential Gain vs Frequency, VS = 2.5V
40 30 20 10
VOCM Gain vs Frequency
CLOAD = 10pF TO 10000pF
-10 -15 -20 -25 -30 10 100 1000 FREQUENCY (kHz) 10000
1992 G108
1992 G107
Differential Input Offset Voltage vs Input Common Mode Voltage
+VS = 5V 1.5 - VS = 0V VOCM = 2.5V 1.0 0.5 0 -0.5 -1.0 -1.5 -2.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 COMMON MODE VOLTAGE (V)
1922 G110
Differential Input Offset Voltage vs Input Common Mode Voltage
2.0 1.5 1.0 0.5 -40C 0 -0.5 -1.0 -1.5 -2.0 -5 -4 -3 -2 -1 0 1 2 3 COMMON MODE VOLTAGE (V) 4 5 25C 85C 125C +VS = 5V - VS = -5V VOCM = 0V
-40C 125C 25C 85C
1922 G111
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LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 150mV -VIN = 150mV CLOAD = 0pF 0V
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
CMRR (dB)
0V
CLOAD = 10000pF CLOAD = 1000pF 2s/DIV
1992 G112
20s/DIV
Single-Ended Input Large-Signal Step Response
Single-Ended Input Large-Signal Step Response
100
CLOAD = 10000pF CLOAD = 1000pF
VOUTDIFF (1V/DIV)
VOUTDIFF (1V/DIV)
PSRR (dB)
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 400mV -VIN = 200mV CLOAD = 0pF 2s/DIV
1992 G115
2.5V
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 400mV -VIN = 200mV 20s/DIV
1992 G116
Differential Input Small-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 5mV -VIN = 5mV CLOAD = 0pF 0V
Differential Input Small-Signal Step Response
0
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 5mV -VIN = 5mV
OUTPUT BALANCE (dB)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
0V
CLOAD = 10000pF CLOAD = 1000pF 10s/DIV
1992 G118
100s/DIV
22
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Applicable to the LTC1992-10 only. Common Mode Rejection Ratio vs Frequency (Note 7)
100 90 80 70 60 50 40 30 20 10
1992 G113
Differential Input Large-Signal Step Response
+VS = 2.5V -VS = -2.5V VOCM = 0V +VIN = 150mV -VIN = 150mV
0 100
VAMPCM VAMPDIFF 1k 10k 100k FREQUENCY (Hz) 1M
1992 G114
Power Supply Rejection Ratio vs Frequency (Note 7)
90 80 70 60 50 40 30 20 10 0 VS VAMPDIFF 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G117
+VS -VS
Output Balance vs Frequency
-20 -40 -60 -80 -100 -120 VOUTCM VOUTDIFF 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M
1992 G119
1992 G120
1992f
LTC1992 Family TYPICAL PERFOR A CE CHARACTERISTICS
Single-Ended Input Small-Signal Step Response
2.5V +VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 20mV -VIN = 10mV CLOAD = 0pF 10s/DIV
1992 G121
2.5V
INPUT REFERRED NOISE (nVHz)
VOUTDIFF (50mV/DIV)
VOUTDIFF (50mV/DIV)
THD + Noise vs Frequency
-40 500kHz MEASUREMENT BANDWIDTH +VS = 5V -50 -VS = -5V VOCM = 0V THD + NOISE (dB) VOUT = 1VP-PDIFF VOUT = 2VP-PDIFF VOUT = 5VP-PDIFF -80 -90 -100 100
-40
THD + NOISE (dB)
-60 -70
UW
Applicable to the LTC1992-10 only. Differential Noise Voltage Density vs Frequency
1000
Single-Ended Input Small-Signal Step Response
CLOAD = 10000pF CLOAD = 1000pF
100
+VS = 5V -VS = 0V VOCM = 2.5V +VIN = 0V TO 20mV -VIN = 10mV 100s/DIV
1992 G122
10 10 100 1000 FREQUENCY (Hz) 10000
1922 G123
THD + Noise vs Amplitude
50kHz -50 -60 -70 -80 -90 -100 0.1 1 INPUT SIGNAL AMPLITUDE (VP-PDIFF) 2 20kHz 10kHz 5kHz 2kHz 1kHz
1k 10k FREQUENCY (Hz)
50k
1992 G124
1992 G125
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LTC1992 Family
PI FU CTIO S
-IN, +IN (Pins 1, 8): Inverting and Noninverting Inputs of the Amplifier. For the LTC1992 part, these pins are connected directly to the amplifier's P-channel MOSFET input devices. The fixed gain LTC1992-X parts have precision, on-chip gain setting resistors. The input resistors are nominally 30k for the LTC1992-1, LTC1992-2 and LTC1992-5 parts. The input resistors are nominally 15k for the LTC1992-10 part. VOCM (Pin 2): Output Common Mode Voltage Set Pin. The voltage on this pin sets the output signal's common mode voltage level. The output common mode level is set independent of the input common mode level. This is a high impedance input and must be connected to a known and controlled voltage. It must never be left floating. +VS, -VS (Pins 3, 6): The +VS and -VS power supply pins should be bypassed with 0.1F capacitors to an adequate analog ground or ground plane. The bypass capacitors should be located as closely as possible to the supply pins. +OUT, -OUT (Pins 4, 5): The Positive and Negative Outputs of the Amplifier. These rail-to-rail outputs are designed to drive capacitive loads as high as 10,000pF. VMID (Pin 7): Mid-Supply Reference. This pin is connected to an on-chip resistive voltage divider to provide a midsupply reference. This provides a convenient way to set the output common mode level at half-supply. If used for this purpose, Pin 2 will be shorted to Pin 7, Pin 7 should be bypassed with a 0.1F capacitor to ground. If this reference voltage is not used, leave the pin floating.
BLOCK DIAGRA S
VMID 7 200k V- VOCM 2 - + A1 A2 - +
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+VS 3
+VS -IN 1 V+ 200k -VS
+ +
30k
4 +OUT
30k
+
+VS +IN 8
-
5 -OUT
1992 BD
-VS
6 -VS
1992f
LTC1992 Family
BLOCK DIAGRA S
PART LTC1992-1 LTC1992-2 LTC1992-5 LTC1992-10
RIN
RFB -VS 6 -VS 2 VOCM
30k 30k 30k 60k 30k 150k 15k 150k
APPLICATIO S I FOR ATIO
Theory of Operation
The LTC1992 family consists of five fully differential, low power amplifiers. The LTC1992 is an unconstrained fully differential amplifier. The LTC1992-1, LTC1992-2, LTC1992-5 and LTC1992-10 are fixed gain blocks (with gains of 1, 2, 5 and 10 respectively) featuring precision onchip resistors for accurate and ultra stable gain. In many ways, a fully differential amplifier functions much like the familiar, ubiquitous op amp. However, there are several key areas where the two differ. Referring to Figure 1, an op amp has a differential input, a high open-loop gain and utilizes negative feedback (through resistors) to set the closed-loop gain and thus control the amplifier's gain with great precision. A fully differential amplifier has all of these features plus an additional input and a complementary output. The complementary output reacts to the input signal in the same manner as the other output, but in the opposite direction. Two outputs changing in an equal but opposite manner require a common reference point (i.e., opposite relative to what?). The additional input, the VOCM pin, sets this reference point. The voltage on the VOCM input directly sets the output signal's com-
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+VS 3
+VS RIN 1 200k -VS VMID 7 +VS RIN +IN 8 RFB
-IN
-+ +-
RFB
4
+OUT
5
-OUT
200k
1992-X BD
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mon mode voltage and allows the output signal's common mode voltage to be set completely independent of the input signal's common mode voltage. Uncoupling the input and output common mode voltages makes signal level shifting easy. For a better understanding of the operation of a fully differential amplifier, refer to Figure 2. Here, the LTC1992 functional block diagram adds external resistors to realize a basic gain block. Note that the LTC1992 functional block diagram is not an exact replica of the LTC1992 circuitry. However, the Block Diagram is correct and is a very good tool for understanding the operation of fully differential amplifier circuits. Basic op amp fundamentals together with this block diagram provide all of the tools needed for understanding fully differential amplifier circuit applications. The LTC1992 Block Diagram has two op amps, two summing blocks (pay close attention the signs) and four resistors. Two resistors, RMID1 and RMID2, connect directly to the VMID pin and simply provide a convenient midsupply reference. Its use is optional and it is not involved in the operation of the LTC1992's amplifier. The LTC1992 functions through the use of two servo networks
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LTC1992 Family
APPLICATIO S I FOR ATIO
Op Amp
-IN
-
LTC1992 AO OUT
+IN
+
* DIFFERENTIAL INPUT * HIGH OPEN-LOOP GAIN * SINGLE-ENDED OUTPUT
Op Amp with Negative Feedback
RFB
RIN VIN
-
LTC1992 VOUT
+
R GAIN = - FB RIN
Figure 1. Comparison of an Op Amp and a Fully Differential Amplifier
RFB
LTC1992
RIN +VIN
-IN
1
INM V+ RMID1 200k
VMID 7 RMID2 200k V- VOCM 2 - + A1 A2 - +
RIN -VIN
+IN
8
INP
Figure 2. LTC1992 Functional Block Diagram with External Gain Setting Resistors
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Fully Differential Amplifier
-IN VOCM +IN
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LTC1992 AO
+OUT
+-
-OUT
* * * *
DIFFERENTIAL INPUT HIGH OPEN-LOOP GAIN DIFFERENTIAL OUTPUT VOCM INPUT SETS OUTPUT COMMON MODE LEVEL
Fully Differential Amplifier with Negative Feedback
RFB
RIN -VIN RIN +VIN
- +
VOCM RFB
+
LTC1992
+VOUT
VOCM
-
-VOUT R GAIN = - FB RIN
1992 F01
VOCM
+VS 3
+
SP
+
RCMP 30k
4
+OUT
+VOUT
RCMM 30k -OUT
+ -
SM 5
-VOUT
6 -VS RFB
1992 F02
LTC1992 Family
APPLICATIO S I FOR ATIO
each employing negative feedback and using an op amp's differential input to create the servo's summing junction. One servo controls the signal gain path. The differential input of op amp A1 creates the summing junction of this servo. Any voltage present at the input of A1 is amplified (by the op amp's large open-loop gain), sent to the summing blocks and then onto the outputs. Taking note of the signs on the summing blocks, op amp A1's output moves +OUT and -OUT in opposite directions. Applying a voltage step at the INM node increases the +OUT voltage while the -OUT voltage decreases. The RFB resistors connect the outputs to the appropriate inputs establishing negative feedback and closing the servo's loop. Any servo loop always attempts to drive its error voltage to zero. In this servo, the error voltage is the voltage between the INM and INP nodes, thus A1 will force the voltages on the INP and INM nodes to be equal (within the part's DC offset, open loop gain and bandwidth limits). The "virtual short" between the two inputs is conceptually the same as that for op amps and is critical to understanding fully differential amplifier applications. The other servo controls the output common mode level. The differential input of op amp A2 creates the summing junction of this servo. Similar to the signal gain servo above, any voltage present at the input of A2 is amplified, sent to the summing blocks and then onto the outputs. However, in this case, both outputs move in the same direction. The resistors RCMP and RCMM connect the +OUT and -OUT outputs to A2's inverting input establishing negative feedback and closing the servo's loop. The midpoint of resistors RCMP and RCMM derives the output's common mode level (i.e., its average). This measure of the output's common mode level connects to A2's inverting input while A2's noninverting input connects directly to the VOCM pin. A2 forces the voltages on its inverting and noninverting inputs to be equal. In other words, it forces the output common mode voltage to be equal to the voltage on the VOCM input pin. For any fully differential amplifier application to function properly both the signal gain servo and the common mode level servo must be satisfied. When analyzing an applications circuit, the INP node voltage must equal the INM node voltage and the output common mode voltage must equal the VOCM voltage. If either of these servos is taken
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out of the specified areas of operation (e.g., inputs taken beyond the common mode range specifications, outputs hitting the supply rails or input signals varying faster than the part can track), the circuit will not function properly. Fully Differential Amplifier Signal Conventions Fully differential amplifiers have a multitude of signals and signal ranges to consider. To maintain proper operation with conventional op amps, the op amp's inputs and its output must not hit the supply rails and the input signal's common mode level must also be within the part's specified limits. These considerations also apply to fully differential amplifiers, but here there is an additional output to consider and common mode level shifting complicates matters. Figure 3 provides a list of the many signals and specifications as well as the naming convention. The phrase "common mode" appears in many places and often leads to confusion. The fully differential amplifier's ability to uncouple input and output common mode levels yields great design flexibility, but also complicates matters some. For simplicity, the equations in Figure 3 also assume an ideal amplifier and perfect resistor matching. For a detailed analysis, consult the fully differential amplifier applications circuit analysis section.. Basic Applications Circuits Most fully differential amplifier applications circuits employ symmetrical feedback networks and are familiar territory for op amp users. Symmetrical feedback networks require that the -VIN/+VOUT network is a mirror image duplicate of the +VIN/-VOUT network. Each of these half circuits is basically just a standard inverting gain op amp circuit. Figure 4 shows three basic inverting gain op amp circuits and their corresponding fully differential amplifier cousins. The vast majority of fully differential amplifier circuits derive from old tried and true inverting op amp circuits. To create a fully differential amplifier circuit from an inverting op amp circuit, first simply transfer the op amp's VIN/VOUT network to the fully differential amplifier's -VIN/+VOUT nodes. Then, take a mirror image duplicate of the network and apply it to the fully differential amplifier's +VIN/-VOUT nodes. Op amp users can comfortably transfer any inverting op amp circuit to a fully differential amplifier in this manner.
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LTC1992 Family
APPLICATIO S I FOR ATIO
A -A VINDIFF 4AVP-PDIFF A -A 2AVP-P -VIN VINCM
2AVP-P +VIN
DIFFERENTIAL = V INDIFF = +VIN - -VIN INPUT VOLTAGE +VIN + -VIN INPUT COMMON = V INCM = 2 MODE VOLTAGE +VOUT = +VIN - -VIN * -VOUT = -VIN - +VIN * RFB VOUTDIFF = VINDIFF * R IN VAMPDIFF = VINP - VINM VAMPCM = VINP + VINM 2
( (
) )
1 RFB * + VOCM 2 RIN 1 RFB * + VOCM 2 RIN
VOUTCM = VOCM CMRR = VAMPCM ; +VIN = -VIN VAMPDIFF VOUTCM VOUTDIFF
2 2 NIN + rN WHERE: eNOUT = OUTPUT REFERRED NOISE VOLTAGE DENSITY eNIN = INPUT REFERRED NOISE VOLTAGE DENSITY
OUTPUT BALANCE = eNOUT = RFB +1 * RIN
( ) e
VOSDIFFOUT = VOSDIFFIN * VOSCM = VOUTCM - VOCM
()
RFB +1 RIN
Figure 3. Fully Differential Amplifier Signal Conventions (Ideal Amplifier and Perfect Resistor Matching is Assumed)
Single-Ended to Differential Conversion One of the most important applications of fully differential amplifiers is single-ended signaling to differential signaling conversion. Many systems have a single-ended signal that must connect to an ADC with a differential input. The ADC could be run in a single-ended manner, but performance usually degrades. Fortunately, all of basic applications circuits shown in Figure 4, as well as all of the fixed gain LTC1992-X parts, are equally suitable for both differential and single-ended input signals. For single-ended input signals, connect one of the inputs to a reference voltage (e.g., ground or midsupply) and connect the other to the signal path. There are no tradeoffs here as the part's performance is the same with singleended or differential input signals. Which input is used
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RFB RIN INM VOCM RIN INP
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-+
VOCM LTC1992
+VOUT VOUTCM -VOUT
B -B B -B
2BVP-P VOUTDIFF 4BVP-PDIFF 2BVP-P
+-
RFB
1992 F03
DIFFERENTIAL = VOUTDIFF = +VOUT - -VOUT OUTPUT VOLTAGE +VOUT + -VOUT OUTPUT COMMON = V OUTCM = 2 MODE VOLTAGE ; VOSCM = 0V ; VOSCM = 0V
RIN * RFB rN (0.13nV/Hz) R + R IN FB
(
)
(RESISTIVE NOISE IS ALREADY INCLUDED IN THE SPECIFICATIONS FOR THE FIXED GAIN LTC1992-X PARTS)
for the signal path only affects the polarity of the differential output signal. Signal Level Shifting Another important application of fully differential amplifier is signal level shifting. Single-ended to differential conversion accompanied by a signal level shift is very commonplace when driving ADCs. As noted in the theory of operation section, fully differential amplifiers have a common mode level servo that determines the output common mode level independent of the input common mode level. To set the output common mode level, simply apply the desired voltage to the VOCM input pin. The voltage range on the VOCM pin is from (-VS + 0.5V) to (+VS - 1.3V).
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LTC1992 Family
APPLICATIO S I FOR ATIO
RFB RIN VIN
-
VOUT
+
R GAIN = FB RIN RFB CIN VIN RIN
-
VOUT
+
C
RFB RIN VIN RIN -VIN VOUT RIN +VIN H(S) = HO * WHERE HO = P S + P
- +
R2 C1
R1 VIN
R3 C2
-
R4 VOUT C3
+
H(S) = HO
WHERE HO = R2 ; P = 1 ; O = R4C3 R1 Q= R1 * R2R3 * R1 R2 + R1 R2 + R2 R3
Figure 4. Basic Fully Differential Amplifier Application Circuits (Note: Single-Ended to Differential Conversion is Easily Accomplished by Connecting One of the Input Nodes, +VIN or -VIN, to a DC Reference Level (e.g., Ground))
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Gain Block
RIN -VIN RIN +VIN RFB
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-
+
+VOUT
VOCM LTC1992
+-
RFB
-VOUT
AC Coupled Gain Block
CIN -VIN CIN +VIN S H(S) = HO * S + P R 1 HO = FB ; P = RIN RIN * CIN RIN RIN
RFB
-
+
+VOUT
VOCM LTC1992
+-
RFB
-VOUT
Single Pole Lowpass Filter
C
RFB
-
+
+VOUT
VOCM LTC1992
+-
RFB C
-VOUT
RFB 1 ; = RIN P RFB * C
3-Pole Lowpass Filter
R2 C1
R1 -VIN
R3 C2 2 R3
-
+
R4 +VOUT C3 2 R4 -VOUT C1
VOCM LTC1992
R1 +VIN
+-
( )(
P S + P
O2 2 + S O + 2 S O Q
)
R2
1992 F04
1 R2R3C1C2 C2 C1
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LTC1992 Family
APPLICATIO S I FOR ATIO
The VOCM input pin has a very high input impedance and is easily driven by even the weakest of sources. Many ADCs provide a voltage reference output that defines either its common mode level or its full-scale level. Apply the ADC's reference potential either directly to the VOCM pin or through a resistive voltage divider depending on the reference voltage's definition. When controlling the VOCM pin by a high impedance source, connect a bypass capacitor (1000pF to 0.1F) from the VOCM pin to ground to lower the high frequency impedance and limit external noise coupling. Other applications will want the output biased at a midpoint of the power supplies for maximum output voltage swing. For these applications, the LTC1992 provides a midsupply potential at the VMID pin. The VMID pin connects to a simple resistive voltage divider with two 200k resistors connected between the supply pins. To use this feature, connect the VMID pin to the VOCM pin and bypass this node with a capacitor. One undesired effect of utilizing the level shifting function is an increase in the differential output offset voltage due to gain setting resistor mismatch. The offset is approximately the amount of level shift (VOUTCM - VINCM) multiplied by the amount of resistor mismatch. For example, a 2V level shift with 0.1% resistors will give around 2mV of output offset (2 * 0.1% = 2mV). The exact amount of offset is dependent on the application's gain and the resistor mismatch. For a detail description, consult the Fully Differential Amplifier Applications Circuit Analysis section. CMRR and Output Balance One common misconception of fully differential amplifiers is that the common mode level servo guarantees an infinite common mode rejection ratio (CMRR). This is not true. The common mode level servo does, however, force the two outputs to be truly complementary (i.e., exactly opposite or 180 degrees out of phase). Output balance is a measure of how complementary the two outputs are. At low frequencies, CMRR is primarily determined by the matching of the gain setting resistors. Like any op amp, the LTC1992 does not have infinite CMRR, however resistor mismatching of only 0.018%, halves the circuit's CMRR. Standard 1% tolerance resistors yield a CMRR of about 40dB. For most applications, resistor matching
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dominates low frequency CMRR performance. The specifications for the fixed gain LTC1992-X parts include the on-chip resistor matching effects. Also, note that an input common mode signal appears as a differential output signal reduced by the CMRR. As with op amps, at higher frequencies the CMRR degrades. Refer to the Typical Performance plots for the details of the CMRR performance over frequency. At low frequencies, the output balance specification is determined by the matching of the on-chip RCMM and RCMP resistors. At higher frequencies, the output balance degrades. Refer to the typical performance plots for the details of the output balance performance over frequency. Input Impedance The input impedance for a fully differential amplifier application circuit is similar to that of a standard op amp inverting amplifier. One major difference is that the input impedance is different for differential input signals and single-ended signals. Referring to Figure 3, for differential input signals the input impedance is expressed by the following expression: RINDIFF = 2 * RIN For single-ended signals, the input impedance is expressed by the following expression:
RINS-E = RIN RFB 1- 2 * (RIN + RFB )
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The input impedance for single-ended signals is slightly higher than the RIN value since some of the input signal is fed back and appears as the amplifier's input common mode level. This small amount of positive feedback increases the input impedance. Driving Capacitive Loads The LTC1992 family of parts is stable for all capacitive loads up to at least 10,000pF. While stability is guaranteed, the part's performance is not unaffected by capacitive loading. Large capacitive loads increase output step response ringing and settling time, decrease the bandwidth
1992f
LTC1992 Family
APPLICATIO S I FOR ATIO
and increase the frequency response peaking. Refer to the Typical Performance plots for small-signal step response, large-signal step response and gain over frequency to appraise the effects of capacitive loading. While the consequences are minor in most instances, consider these effects when designing application circuits with large capacitive loads. Input Signal Amplitude Considerations For application circuits to operate correctly, the amplifier must be in its linear operating range. To be in the linear operating range, the input signal's common mode voltage must be within the part's specified limits and the rail-torail outputs must stay within the supply voltage rails. Additionally, the fixed gain LTC1992-X parts have input protection diodes that limit the input signal to be within the supply voltage rails. The unconstrained LTC1992 uses external resistors allowing the source signals to go beyond the supply voltage rails. When taken outside of the linear operating range, the circuit does not perform as expected, however nothing extreme occurs. Outputs driven into the supply voltage rails are simply clipped. There is no phase reversal or oscillation. Once the outputs return to the linear operating range, there is a small recovery time, then normal operation proceeds. When the input common mode voltage is below the specified lower limit, on-chip protection diodes conduct and clamp the signal. Once the signal returns to the specified operating range, normal operation proceeds. If the input common mode voltage goes slightly above the specified upper limit (by no more than about 500mV), the amplifier's open-loop gain reduces and DC offset and closed-loop gain errors increase. Return the input back to the specified range and normal performance commences. If taken well above the upper limit, the amplifier's input stage is cut off. The gain servo is now open loop; however, the common mode servo is still functional. Output balance is maintained and the outputs go to opposite supply rails. However, which output goes to which supply rail is
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random. Once the input returns to the specified input common mode range, there is a small recovery time then normal operation proceeds. The LTC1992's input signal common mode range (VINCMR) is from (-VS - 0.1V) to (+VS - 1.3V). This specification applies to the voltage at the amplifier's input, the INP and INM nodes of Figure 2. The specifications for the fixed gain LTC1992-X parts reflect a higher maximum limit as this specification is for the entire gain block and references the signal at the input resistors. Differential input signals and single-ended signals require a slightly different set of formulae. Differential signals separate very nicely into common mode and differential components while single ended signals do not. Refer to Figure 5 for the formulae for calculating the available signal range. Additionally, Table 1 lists some common configurations and their appropriate signal levels. The LTC1992's outputs allow rail-to-rail signal swings. The output voltage on either output is a function of the input signal's amplitude, the gain configured and the output signal's common mode level set by the VOCM pin. For maximum signal swing, the VOCM pin is set at the midpoint of the supply voltages. For other applications, such as an ADC driver, the required level must fall within the VOCM range of (-VS + 0.5V) to (+VS - 1.3V). For singleended input signals, it is not always obvious which output will clip first thus both outputs are calculated and the minimum value determines the signal limit. Refer to Figure 5 for the formulae and Table 1 for examples. To ensure proper linear operation both the input common mode level and the output signal level must be within the specified limits. These same criteria are also present with standard op amps. However, with a fully differential amplifier, it is a bit more complex and old familiar op amp intuition often leads to the wrong result. This is especially true for single-ended to differential conversion with level shifting. The required calculations are a bit tedious, but are necessary to guarantee proper linear operation.
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APPLICATIO S I FOR ATIO
A -A VINDIFF 4AVP-PDIFF A -A
2AVP-P -VIN VINCM
INM RIN NODE VOCM RIN INP NODE
2AVP-P +VIN
INPUT COMMON MODE LIMITS A. CALCULATE VINCM MINIMUM AND MAXIMUM GIVEN RIN, RFB AND VOCM 1 VINCM(MAX) = (+VS - 1.3V) + (+VS - 1.3V - VOCM) G 1 VINCM(MIN) = (-VS - 0.1V) + (-VS - 0.1V - VOCM) G OR B. WITH A KNOWN VINCM, RIN, RFB AND VOCM, CALCULATE COMMON MODE VOLTAGE AT INP AND INM NODES (VINCM(AMP)) AND CHECK THAT IT IS WITHIN THE SPECIFIED LIMITS. V + VINM 1 G = V + V VINCM(AMP) = INP 2 G + 1 INCM G + 1 OCM OUTPUT SIGNAL CLIPPING LIMIT VINDIFF(MAX)(VP-PDIFF) = THE LESSER VALUE OF 4 4 (+VS - VOCM) OR (VOCM - -VS) G G
INM RIN NODE VINREF VOCM A VREF -A RIN 2AVP-P VINSIG INP NODE
INPUT COMMON MODE LIMITS (NOTE: FOR THE FIXED GAIN LTC1992-X PARTS, VINREF AND VINSIG CANNOT EXCEED THE SUPPLIES) VINSIG(MAX) = 2 VINSIG(MIN) = 2 OR VINSIGP-P = 2
( (
V 1 +VS - 1.3V - VOCM +VS - 1.3V - INREF + 2 G V 1 -VS - 0.1V - INREF + -VS - 0.1V - VOCM 2 G 1 (+VS - -VS) - 1.2V G
(
(+VS - -VS) - 1.2V +
OUTPUT SIGNAL CLIPPING LIMIT VINSIG(MAX) = THE LESSER VALUE OF VINREF + 2 2 (+VS - VOCM) OR VINREF + (VOCM - -VS) G G 2 2 VINSIG(MIN) = THE GREATER VALUE OF VINREF + (-VS - VOCM) OR VINREF + (VOCM - +VS) G G
Figure 5. Input Signal Limitations
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Differential Input Signals
RFB
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-+
VOCM LTC1992
+VOUT VOUTCM -VOUT R G = FB RIN
B -B B -B
2BVP-P VOUTDIFF 4BVP-PDIFF 2BVP-P
+-
RFB
Single End Input Signals
RFB
-+
VOCM LTC1992
+VOUT VOUTCM -VOUT R G = FB RIN
B -B B -B
2BVP-P VOUTDIFF 4BVP-PDIFF 2BVP-P
+-
RFB
)( )( )(
) )
)
1992 F05
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LTC1992 Family
APPLICATIO S I FOR ATIO
Table 1. Input Signal Limitations for Some Common Applications Differential Input Signal, VOCM at Midsupply. (VINCM must be within the Min and Max table values and VINDIFF must be less than the table value)
+VS (V) 2.7 2.7 2.7 2.7 5 5 5 5 5 5 5 5 -VS (V) 0 0 0 0 0 0 0 0 -5 -5 -5 -5 GAIN (V/V) 1 2 5 10 1 2 5 10 1 2 5 10 VOCM (V) 1.35 1.35 1.35 1.35 2.5 2.5 2.5 2.5 0 0 0 0 VINCM(MAX) (V) 1.450 1.425 1.410 1.405 4.900 4.300 3.940 3.820 7.400 5.550 4.440 4.070 VINCM(MIN) (V) -1.550 -0.825 -0.390 -0.245 -2.700 -1.400 -0.620 -0.360 -10.200 -7.650 -6.120 -5.610 VINDIFF(MAX) (VP-PDIFF) 5.40 2.70 1.08 0.54 10.00 5.00 2.00 1.00 20.00 10.00 4.00 2.00 VOUTDIFF(MAX) (VP-PDIFF) 5.40 5.40 5.40 5.40 10.00 10.00 10.00 10.00 20.00 20.00 20.00 20.00
Differential Input Signal, VOCM at Typical ADC Levels. (VINCM must be within the Min and Max table values and VINDIFF must be less than the table value)
+VS (V) 2.7 2.7 2.7 2.7 5 5 5 5 5 5 5 5 -VS (V) 0 0 0 0 0 0 0 0 -5 -5 -5 -5 GAIN (V/V) 1 2 5 10 1 2 5 10 1 2 5 10 VOCM (V) 1 1 1 1 2 2 2 2 2 2 2 2 VINCM(MAX) (V) 1.800 1.600 1.480 1.440 5.400 4.550 4.040 3.870 5.400 4.550 4.040 3.870 VINCM(MIN) (V) -1.200 -0.650 -0.320 -0.210 -2.200 -1.150 -0.520 -0.310 -12.200 -8.650 -6.520 -5.810 VINDIFF(MAX) (VP-PDIFF) 4.00 2.00 0.80 0.40 8.00 4.00 1.60 0.80 12.00 6.00 2.40 1.20 VOUTDIFF(MAX) (VP-PDIFF) 4.00 4.00 4.00 4.00 8.00 8.00 8.00 8.00 12.00 12.00 12.00 12.00
U
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33
LTC1992 Family
APPLICATIO S I FOR ATIO
Table 1. Input Signal Limitations for Some Common Applications Midsupply Referenced Single-Ended Input Signal, VOCM at Midsupply. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)
+VS (V) 2.7 2.7 2.7 2.7 5 5 5 5 5 5 5 5 -VS (V) 0 0 0 0 0 0 0 0 -5 -5 -5 -5 GAIN (V/V) 1 2 5 10 1 2 5 10 1 2 5 10 VOCM (V) 1.35 1.35 1.35 1.35 2.5 2.5 2.5 2.5 0 0 0 0 VINREF (V) 1.35 1.35 1.35 1.35 2.5 2.5 2.5 2.5 0 0 0 0 VINSIG(MAX) (V) 1.550 1.500 1.470 1.460 7.300 5.000 3.500 3.000 10.000 5.000 2.000 1.000 VINSIG(MIN) (V) -1.350 0.000 0.810 1.080 -2.500 0.000 1.500 2.000 -10.000 -5.000 -2.000 -1.000 VINSIGP-P(MAX) (VP-P AROUND VINREF) 0.40 0.30 0.24 0.22 9.60 5.00 2.00 1.00 20.00 10.00 4.00 2.00 VOUTDIFF(MAX) (VP-PDIFF) 0.40 0.60 1.20 2.20 9.60 10.00 10.00 10.00 20.00 20.00 20.00 20.00
Midsupply Referenced Single-Ended Input Signal, VOCM at Typical ADC Levels. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)
+VS (V) 2.7 2.7 2.7 2.7 5 5 5 5 5 5 5 5 -VS (V) 0 0 0 0 0 0 0 0 -5 -5 -5 -5 GAIN (V/V) 1 2 5 10 1 2 5 10 1 2 5 10 VOCM (V) 1 1 1 1 2 2 2 2 2 2 2 2 VINREF (V) 1.35 1.35 1.35 1.35 2.5 2.5 2.5 2.5 0 0 0 0 VINSIG(MAX) (V) 2.250 1.850 1.610 1.530 6.500 4.500 3.300 2.900 6.000 3.000 1.200 0.600 VINSIG(MIN) (V) -0.650 0.350 0.950 1.150 -1.500 0.500 1.700 2.100 -6.000 -3.000 -1.200 -0.600 VINSIGP-P(MAX) (VP-P AROUND VINREF) 1.80 1.00 0.52 0.36 8.00 4.00 1.60 0.80 12.00 6.00 2.40 1.20 VOUTDIFF(MAX) (VP-PDIFF) 1.80 2.00 2.60 3.60 8.00 8.00 8.00 8.00 12.00 12.00 12.00 12.00
34
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LTC1992 Family
APPLICATIO S I FOR ATIO
Table 1. Input Signal Limitations for Some Common Applications Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Midsupply. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)
+VS (V) 2.7 2.7 2.7 2.7 5 5 5 5 -VS (V) 0 0 0 0 0 0 0 0 GAIN (V/V) 1 2 5 10 1 2 5 10 VOCM (V) 1.35 1.35 1.35 1.35 2.5 2.5 2.5 2.5 VINREF (V) 0 0 0 0 0 0 0 0 VINSIG(MAX) (V) 2.700 1.350 0.540 0.270 5.000 2.500 1.000 0.500 VINSIG(MIN) (V) -2.700 -1.350 -0.540 -0.270 -5.000 -2.500 -1.000 -0.500 VINSIGP-P(MAX) (VP-P AROUND VINREF) 5.40 2.70 1.08 0.54 10.00 5.00 2.00 1.00 VOUTDIFF(MAX) (VP-PDIFF) 5.40 5.40 5.40 5.40 10.00 10.00 10.00 10.00
Single Supply Ground Referenced Single-Ended Input Signal, VOCM at Typical ADC Reference Levels. (The VINSIG Min and Max values listed account for both the input common mode limits and the output clipping)
+VS (V) 2.7 2.7 2.7 2.7 5 5 5 5 -VS (V) 0 0 0 0 0 0 0 0 GAIN (V/V) 1 2 5 10 1 2 5 10 VOCM (V) 1 1 1 1 2 2 2 2 VINREF (V) 0 0 0 0 0 0 0 0 VINSIG(MAX) (V) 2.000 1.000 0.400 0.200 4.000 2.000 0.800 0.400 VINSIG(MIN) (V) -2.000 -1.000 -0.400 -0.200 -4.000 -2.000 -0.800 -0.400 VINSIGP-P(MAX) (VP-P AROUND VINREF) 4.00 2.00 0.80 0.40 8.00 4.00 1.60 0.80 VOUTDIFF(MAX) (VP-PDIFF) 4.00 4.00 4.00 4.00 8.00 8.00 8.00 8.00
Fully Differential Amplifier Applications Circuit Analysis All of the previous applications circuit discussions have assumed perfectly matched symmetrical feedback networks. To consider the effects of mismatched or asymmetrical feedback networks, the equations get a bit messier. Figure 6 lists the basic gain equation for the differential output voltage in terms of +VIN, -VIN, VOSDIFF, VOUTCM and the feedback factors 1 and 2. The feedback factors are simply the portion of the output that is fed back to the input summing junction by the RFB-RIN resistive voltage divider. 1 and 2 have the range of zero to one. The VOUTCM term also includes its offset voltage, VOSCM, and its gain mismatch term, KCM. The KCM term is determined by the matching of the on-chip RCMP and RCMM resistors in the common mode level servo (see Figure 2).
U
While mathematically correct, the basic signal equation does not immediately yield any intuitive feel for fully differential amplifier application operation. However, by nulling out specific terms, some basic observations and sensitivities come forth. Setting 1 equal to 2, VOSDIFF to zero and VOUTCM to VOCM gives the old gain equation from Figure 3. The ground referenced, single-ended input signal equation yields the interesting result that the driven side feedback factor (1) has a very different sensitivity than the grounded side (2). The CMRR is twice the feedback factor difference divided by the feedback factor sum. The differential output offset voltage has two terms. The first term is determined by the input offset term, VOSDIFF, and the application's gain. Note that this term equates to the formula in Figure 3 when 1 equals 2. The amount of signal level shifting and the feedback factor mismatch determines the second term. This term
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LTC1992 Family
APPLICATIO S I FOR ATIO
-VIN VINDIFF +VIN - -VIN +VIN VOCM RIN1
VOUTDIFF = WHERE: 1 =
2[+VIN * (1 - 1) - (-VIN) * (1 - 2)] + 2VOSDIFF + 2VOUTCM (1 - 2) 1 + 2 ; VOSDIFF = AMPLIFIER INPUT REFERRED OFFSET VOLTAGE VOUTCM = KCM * VOCM + VOSCM 0.999 < KCM < 1.001
RIN1 RIN2 ; 2 = RIN1 + RFB1 RIN2 + RFB2
* FOR GROUND REFERENCED, SINGLE-ENDED INPUT SIGNAL, LET +VIN = VINSIG AND -VIN = 0V VOUTDIFF = 2 * VINSIG * (1 - 1) + 2VOSDIFF + 2VOUTCM (1 - 2) 1 + 2
* COMMON MODE REJECTION: SET +VIN = -VIN = VINCM, VOSDIFF = 0V, VOUTCM = 0V CMRR = VINCM 1 + 2 =2 ; OUTPUT REFERRED 2 - 1 VOUTDIFF
* OUTPUT DC OFFSET VOLTAGE: SET +VIN = -VIN = VINCM VOSDIFFOUT = VOSDIFF 2 - 1 2 + (VOUTCM - VINCM) 2 1 + 2 1 + 2
Figure 6. Basic Equations for Mismatched or Asymmetrical Feedback Applications Circuits
quantifies the undesired effect of signal level shifting discussed earlier in the Signal Level Shifting section. Asymmetrical Feedback Application Circuits The basic signal equation in Figure 6 also gives insight to another piece of intuition. The feedback factors may be deliberately set to different values. One interesting class of these application circuits sets one or both of the feedback factors to the extreme values of either zero or one. Figure 7 shows three such circuits. At first these application circuits may look to be unstable or open loop. It is the common mode feedback loop that enables these circuits to function. While they are useful circuits, they have some shortcomings that must be considered. First, do to the severe feedback factor asymmetry, the VOCM level influences the differential output voltage with about the same strength as the input signal. With this much gain in the VOCM path, differential output offset and noise increase. The large VOCM to VOUTDIFF gain also necessitates that these circuits are largely limited to
36
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RFB2 RIN2
W
UU
-+
VOCM LTC1992
+VOUT VOUTDIFF +VOUT - -VOUT -VOUT
+-
RFB1
dual, split supply voltage applications with a ground referenced input signal and a grounded VOCM pin. The top application circuit in Figure 7 yields a high input impedance, precision gain of 2 block without any external resistors. The on-chip common mode feedback servo resistors determine the gain precision (better than 0.1 percent). By using the -VOUT output alone, this circuit is also useful to get a precision, single-ended output, high input impedance inverter. To intuitively understand this circuit, consider it as a standard op amp voltage follower (delivered through the signal gain servo) with a complementary output (delivered through the common mode level servo). As usual, the amplifier's input common mode range must not be exceeded. As with a standard op amp voltage follower, the common mode signal seen at the amplifier's input is the input signal itself. This condition limits the input signal swing, as well as the output signal swing, to be the input signal common mode range specification. The middle circuit is largely the same as the first except that the noninverting amplifier path has gain. Note that
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LTC1992 Family
APPLICATIO S I FOR ATIO
-+
VOCM VIN
VOCM LTC1992
+-
RFB
RIN
-+
VOCM VIN VOCM LTC1992
+-
-+
VOCM RIN VIN VOCM LTC1992
+-
RFB
1992 F07
Figure 7. Asymmetrical Feedback Application Circuits (Most Suitable in Applications with Dual, Split Supplies (e.g., 5V), Ground Referenced Single-Ended Input Signals and VOCM Connected to Ground)
once the VOCM voltage is set to zero, the gain formula is the same as a standard noninverting op amp circuit multiplied by two to account for the complementary output. Taking RFB to zero (i.e., taking to one) gives the same formula as the top circuit. As in the top circuit, this circuit is also useful as a single-ended output, high input impedance inverting gain block (this time with gain). The input common mode considerations are similar to the top circuit's, but are not nearly as constrained since there is now gain in the noninverting amplifier path. This circuit, with VOCM at ground, also permits a rail-to-rail output swing in most applications.
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+VOUT VOUTDIFF = 2(+VIN - VOCM) -VOUT SETTING VOCM = 0V VOUTDIFF = 2VIN +VOUT VOUTDIFF = 2 +VIN
W
UU
(
1 - VOCM
)
;=
RIN RIN + RFB
-VOUT
SETTING VOCM = 0V RFB 1 VOUTDIFF = 2VIN = 2VIN 1 + R IN
() (
)
;= RIN RIN + RFB
+VOUT
VOUTDIFF = 2 +VIN
(
1- + VOCM
)
-VOUT
SETTING VOCM = 0V RFB 1- VOUTDIFF = 2VIN = 2VIN R IN
() ()
The bottom circuit is another circuit that utilizes a standard op amp configuration with a complementary output. In this case, the standard op amp circuit has an inverting configuration. With VOCM at zero volts, the gain formula is the same as a standard inverting op amp circuit multiplied by two to account for the complementary output. This circuit does not have any common mode level constraints as the inverting input voltage sets the input common mode level. This circuit also delivers rail-to-rail output voltage swing without any concerns.
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LTC1992 Family
TYPICAL APPLICATIO S
Interfacing a Bipolar, Ground Referenced, Single-Ended Signal to a Unipolar Single Supply, Differential Input ADC (VIN = 0V Gives a Digital Mid-Scale Code)
5V 0.1F 10k 1F
2.5V VIN -2.5V
0V 5V 13.3k 40k
2.5V VIN 0V
38
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40k 13.3k
3 10k 1 7 2 10k 8
1 4 100 100pF 100 5 3 -IN GND 4 10k 2 +IN VREF
8 VCC SCK SDO CONV 7 6 5 SERIAL DATA LINK
-+
VMID VOCM 6
LTC1992
LTC1864
+-
1992 TA02a
0.1F
Compact, Unipolar Serial Data Conversion
5V 1F 0.1F 1 7 2 8 3 1 4 100 100pF 100 5 3 -IN GND 4
1992 TA03a
8 VCC SCK SDO CONV 7 6 5 SERIAL DATA LINK
-+
VMID VOCM
2
+IN
VREF
LTC1992-2
LTC1864
+-
6
0.1F
Zero Components, Single-Ended Adder/Subtracter
+VS 0.1F 1 2 8 3
VA VB VC
-+ +-
6 -VS
4
V1 = VB + VC - VA
VOCM LTC1992-2 5 V2 = VB + VA - VC
0.1F
1992 TA04
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LTC1992 Family
TYPICAL APPLICATIO S
Single-Ended to Differential Conversion Driving an ADC
2.2F 10F 10 36 5V 10F 5V 10F
3 VREF
5V 47F 0.1F 3 1 7 2 VIN 8
4
REFCOMP 4.375V 1.75X
7.5k
+
2.5V REF
RD 30 BUSY 27 OVDD 29
-+
VMID VOCM
4
100
1 AIN+ 100pF 2 AIN-
+ -
16-BIT SAMPLING ADC AGND 6 B15 TO B0 OUTPUT BUFFERS
OGND 28 16-BIT PARALLEL BUS 11 TO 26
1992 TA06a
5V OR 3V 10F
LTC1992-1 5
D15 TO D0
+-
6
AMPLITUDE (dB)
100 0.1F
AGND 5
AGND 7
AGND VSS 8 34
-5V -5V
+
10F
PACKAGE DESCRIPTIO
MS8 Package 8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
0.889 0.127 (.035 .005) 0.254 (.010) 5.23 (.206) MIN 3.20 - 3.45 (.126 - .136) GAUGE PLANE 0.53 0.152 (.021 .006) 0.42 0.038 (.0165 .0015) TYP DETAIL "A" 0 - 6 TYP 1.10 (.043) MAX 0.86 (.034) REF 3.00 0.102 (.118 .004) (NOTE 3)
0.65 (.0256) BSC
DETAIL "A" 0.18 (.007) SEATING PLANE 0.22 - 0.38 (.009 - .015) TYP 0.127 0.076 (.005 .003)
4.90 0.152 (.193 .006)
RECOMMENDED SOLDER PAD LAYOUT NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
0.65 (.0256) BSC
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
+
U
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+
35 AVDD
+
9
+
FFT of the Output Data
10 DGND SHDN 33 CS 32 CONVST 31 P CONTROL LINES
0 -10 - 20 - 30 - 40 - 50 - 60 - 70 - 80 - 90 -100 -110 -120 -130 -140 0 fIN = 10.0099kHz fSAMPLE = 333kHz SNR =85.3dB THD = -72.1dB SINAD = -72dB
AVDD
DVDD
LTC1603
CONTROL LOGIC AND TIMING
10 20 30 40 50 60 70 80 90 100 FREQUENCY (kHz)
1992 TA06b
8
7 65
0.52 (.0205) REF
3.00 0.102 (.118 .004) (NOTE 4)
MSOP (MS8) 0603
1
23
4
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LTC1992 Family
TYPICAL APPLICATIO U
SAMPLER 2kHz LOWPASS FILTER 5V 0.1F 0.1F 4 3 V+ 4 7 8 13 1/2 LTC1043 6 120pF 5 14 16 9.53k CLK - V 17 0.1F 0.1F VOCM
1992 TA05a
Balanced Frequency Converter (Suitable for Frequencies up to 50kHz)
60kHz LOW PASS FILTER
9.53k 120pF 9.53k 8.87k 330pF BNC VINP 9.53k 8.87k
0.1F 390pF 11 37.4k 60.4k 180pF 12 37.4k 60.4k
75k
1 7 2 8
-+
VMID VOCM
1 7 2 8
3
BNC 4 VOUTP BNC VOUTM
-+
VMID VOCM
LTC1992
LTC1992 5
+-
+-
6
390pF 0.1F
75k
10k
0.1F
-5V CLK
0V
VINP = 24kHz (1V/DIV) CLK = 25kHz (LOGIC SQUARE WAVE) (5V/DIV) VOUTP = 1kHz (0.5V/DIV) VOUTM = 1kHz (0.5V/DIV)
0V 0V 0V
200s/DIV
1992 TA05b
RELATED PARTS
PART NUMBER LT1167 LT1990 LT1991 LT1995 LT6600-X DESCRIPTION Precision Instrumentation Amplifier High Voltage, Gain Selectable Difference Amplifier Precision Gain Selectable Difference Amplifier High Speed Gain Selectable Difference Amplifier Differential In/Out Amplifier Lowpass Filter COMMENTS Single Resistor Sets the Gain 250V Common Mode, Micropower, Selectable Gain = 1, 10 Micropower, Pin Selectable Gain = -13 to 14 30MHz, 1000V/s, Pin Selectable Gain = -7 to 8 Very Low Noise, Standard Differential Amplifier Pinout
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT/TP 0105 1K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2005

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