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Low Cost, High Speed Differential Amplifier AD8132
FEATURES
High speed 350 MHz, -3 dB bandwidth 1200 V/s slew rate Resistor set gain Internal common-mode feedback Improved gain and phase balance -68 dB @ 10 MHz Separate input to set the common-mode output voltage Low distortion: -99 dBc SFDR @ 5 MHz, 800 load Low power: 10.7 mA @ 5 V Power supply range: +2.7 V to 5.5 V
PIN CONFIGURATION
-IN 1 VOCM 2 V+ 3 +OUT 4
AD8132
8 7 6 5
+IN NC V-
01035-001
-OUT
NC = NO CONNECT
Figure 1.
APPLICATIONS
Low power differential ADC drivers Differential gain and differential filtering Video line drivers Differential in/out level shifting Single-ended input to differential output drivers Active transformers
The AD8132 is also used as a differential driver for the transmission of high speed signals over low cost twisted pair or coaxial cables. The feedback network can be adjusted to boost the high frequency components of the signal. The AD8132 is used for either analog or digital video signals or for other high speed data transmission. The AD8132 is capable of driving either a Category 3 or Category 5 twisted pair or coaxial cable with minimal line attenuation. The AD8132 has considerable cost and performance improvements over discrete line driver solutions. Differential signal processing reduces the effects of ground noise that plagues ground-referenced systems. The AD8132 can be used for differential signal processing (gain and filtering) throughout a signal chain, easily simplifying the conversion between differential and single-ended components. The AD8132 is available in both SOIC_N and MSOP packages for operation over the extended industrial temperature range of -40C to +125C.
6 VS = 5V G = +1 VO, dm = 2V p-p RL, dm = 499
GENERAL DESCRIPTION
The AD8132 is a low cost differential or single-ended input to differential output amplifier with resistor set gain. The AD8132 is a major advancement over op amps for driving differential input ADCs or for driving signals over long lines. The AD8132 has a unique internal feedback feature that provides output gain and phase matching balanced to -68 dB at 10 MHz, suppressing harmonics and reducing radiated EMI. Manufactured using the next generation of Analog Devices, Inc.'s XFCB bipolar process, the AD8132 has a -3 dB bandwidth of 350 MHz and delivers a differential signal with -99 dBc SFDR at 5 MHz, despite its low cost. The AD8132 eliminates the need for a transformer with high performance ADCs, preserving the low frequency and dc information. The common-mode level of the differential output is adjustable by applying a voltage on the VOCM pin, easily level shifting the input signals for driving single-supply ADCs. Fast overload recovery preserves sampling accuracy.
3
0
GAIN (dB)
-3
-6
-9
1
10 100 FREQUENCY (MHz)
1k
Figure 2. Large Signal Frequency Response
Rev. F
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2006 Analog Devices, Inc. All rights reserved.
01035-002
-12
AD8132 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Pin Configuration............................................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 DIN to OUT Specifications...................................................... 3 VOCM to OUT Specifications ..................................................... 4 DIN to OUT Specifications...................................................... 5 VOCM to OUT Specifications ..................................................... 6 DIN to OUT Specifications...................................................... 7 VOCM to OUT Specifications ..................................................... 7 Absolute Maximum Ratings............................................................ 8 Thermal Resistance ...................................................................... 8 ESD Caution.................................................................................. 8 Pin Configuration and Function Descriptions............................. 9 Typical Performance Characteristics ........................................... 10 Test Circuits..................................................................................... 19 Operational Description................................................................ 20 Definition of Terms.................................................................... 20 Basic Circuit Operation ............................................................. 20 Theory of Operation ...................................................................... 21 General Usage of the AD8132 .................................................. 21 Differential Amplifier Without Resistors (High Input Impedance Inverting Amplifier) .............................................. 21 Other 2 = 1 Circuits ................................................................. 22 Varying 2 ................................................................................... 22 1 = 0............................................................................................ 22 Estimating the Output Noise Voltage ...................................... 22 Calculating Input Impedance of the Application Circuit ..... 23 Input Common-Mode Voltage Range in Single-Supply Applications ................................................................................ 23 Setting the Output Common-Mode Voltage .......................... 23 Driving a Capacitive Load......................................................... 23 Open-Loop Gain and Phase ..................................................... 23 Layout, Grounding, and Bypassing.............................................. 24 Circuits......................................................................................... 24 Applications..................................................................................... 25 Analog-to-Digital Driver .......................................................... 25 Balanced Cable Driver............................................................... 25 Transmit Equalizer ..................................................................... 26 Low-Pass Differential Filter ...................................................... 26 High Common-Mode Output Impedance Amplifier ........... 27 Full-Wave Rectifier .................................................................... 28 Outline Dimensions ....................................................................... 29 Ordering Guide .......................................................................... 29
REVISION HISTORY
11/06--Rev. E to Rev. F Updated Format..................................................................Universal Changes to Table 1............................................................................ 3 Changes to Table 4............................................................................ 6 Changes to Table 5............................................................................ 7 Changes to Ordering Guide .......................................................... 29 11/05--Rev. D to Rev. E Changes to Table 7, Thermal Resistance Section, Maximum Power Dissipation Section, and Figure 3....................................... 8 Changes to Ordering Guide .......................................................... 29 12/04--Rev. C to Rev. D Changes to General Description .....................................................1 Changes to Specifications.................................................................2 Changes to Absolute Maximum Ratings........................................8 Updated Outline Dimensions....................................................... 29 Changes to Ordering Guide .......................................................... 29 2/03--Rev. B to Rev. C Changes to Specifications.................................................................2 Addition to Estimating the Output Noise Voltage Section....... 15 Updated Outline Dimensions....................................................... 21 1/02--Rev. A to Rev. B Edits to Transmitter Equalizer Section........................................ 18
Rev. F | Page 2 of 32
AD8132 SPECIFICATIONS
DIN TO OUT SPECIFICATIONS
At TA = 25C, VS = 5 V, VOCM = 0 V, G = 1, RL, dm = 499 , RF = RG = 348 , unless otherwise noted. For G = 2, RL, dm = 200 , RF = 1000 , RG = 499 . Refer to Figure 56 and Figure 57 for test setup and label descriptions. All specifications refer to single-ended input and differential outputs, unless otherwise noted. Table 1.
Parameter DYNAMIC PERFORMANCE -3 dB Large Signal Bandwidth -3 dB Small Signal Bandwidth Bandwidth for 0.1 dB Flatness Slew Rate Settling Time Overdrive Recovery Time NOISE/HARMONIC PERFORMANCE Second Harmonic Conditions VOUT = 2 V p-p VOUT = 2 V p-p, G = 2 VOUT = 0.2 V p-p VOUT = 0.2 V p-p, G = 2 VOUT = 0.2 V p-p VOUT = 0.2 V p-p, G = 2 VOUT = 2 V p-p 0.1%, VOUT = 2 V p-p VIN = 5 V to 0 V step, G = 2 VOUT = 2 V p-p, 1 MHz, RL, dm = 800 VOUT = 2 V p-p, 5 MHz, RL, dm = 800 VOUT = 2 V p-p, 20 MHz, RL, dm = 800 VOUT = 2 V p-p, 1 MHz, RL, dm = 800 VOUT = 2 V p-p, 5 MHz, RL, dm = 800 VOUT = 2 V p-p, 20 MHz, RL, dm = 800 20 MHz, RL, dm = 800 20 MHz, RL, dm = 800 f = 0.1 MHz to 100 MHz f = 0.1 MHz to 100 MHz NTSC, G = 2, RL, dm = 150 NTSC, G = 2, RL, dm = 150 VOS, dm = VOUT, dm/2; VDIN+ = VDIN- = VOCM = 0 V TMIN to TMAX variation Differential Common mode Min 300 Typ 350 190 360 160 90 50 1200 15 5 -96 -83 -73 -102 -98 -67 -76 40 8 1.8 0.01 0.10 1.0 10 3 12 3.5 1 -4.7 to +3.0 -70 -3.6 to +3.6 +70 -70 3.5 7 Max Unit MHz MHz MHz MHz MHz MHz V/s ns ns dBc dBc dBc dBc dBc dBc dBc dBm nV/Hz pA/Hz % Degrees mV V/C A M M pF V dB V mA dB
1000
Third Harmonic
IMD IP3 Input Voltage Noise (RTI) Input Current Noise Differential Gain Error Differential Phase Error INPUT CHARACTERISTICS Offset Voltage (RTI) Input Bias Current Input Resistance Input Capacitance Input Common-Mode Voltage CMRR OUTPUT CHARACTERISTICS Output Voltage Swing Output Current Output Balance Error
VOUT, dm/VIN, cm; VIN, cm = 1 V; resistors matched to 0.01% Maximum VOUT; single-ended output VOUT, cm/VOUT, dm; VOUT, dm = 1 V
-60
Rev. F | Page 3 of 32
AD8132
VOCM TO OUT SPECIFICATIONS
At TA = 25C, VS = 5 V, VOCM = 0 V, G = 1, RL, dm = 499 , RF = RG = 348 , unless otherwise noted. For G = 2, RL, dm = 200 , RF = 1000 , RG = 499 . Refer to Figure 56 and Figure 57 for test setup and label descriptions. All specifications refer to single-ended input and differential outputs, unless otherwise noted. Table 2.
Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Slew Rate Input Voltage Noise (RTI) DC PERFORMANCE Input Voltage Range Input Resistance Input Offset Voltage Input Bias Current VOCM CMRR Gain POWER SUPPLY Operating Range Quiescent Current Power Supply Rejection Ratio OPERATING TEMPERATURE RANGE Conditions VOCM = 600 mV p-p VOCM = -1 V to +1 V f = 0.1 MHz to 100 MHz Min Typ 210 400 12 3.6 50 1.5 0.5 -68 1 Max Unit MHz V/s nV/Hz V k mV A dB V/V V mA A/C dB C
VOS, cm = VOUT, cm; VDIN+ = VDIN- = VOCM = 0 V VOUT, dm/VOCM; VOCM = 1 V; resistors matched to 0.01% VOUT, cm/VOCM; VOCM = 1 V
7
0.985 1.35 11
1.015 5.5 13 -60 +125
VDIN+ = VDIN- = VOCM = 0 V TMIN to TMAX variation VOUT, dm/VS; VS = 1 V
12 16 -70
-40
Rev. F | Page 4 of 32
AD8132
DIN TO OUT SPECIFICATIONS
At TA = 25C, VS = 5 V, VOCM = 2.5 V, G = 1, RL, dm = 499 , RF = RG = 348 , unless otherwise noted. For G = 2, RL, dm = 200 , RF = 1000 , RG = 499 . Refer to Figure 56 and Figure 57 for test setup and label descriptions. All specifications refer to single-ended input and differential outputs, unless otherwise noted. Table 3.
Parameter DYNAMIC PERFORMANCE -3 dB Large Signal Bandwidth -3 dB Small Signal Bandwidth Bandwidth for 0.1 dB Flatness Slew Rate Settling Time Overdrive Recovery Time NOISE/HARMONIC PERFORMANCE Second Harmonic Conditions VOUT = 2 V p-p VOUT = 2 V p-p, G = 2 VOUT = 0.2 V p-p VOUT = 0.2 V p-p, G = 2 VOUT = 0.2 V p-p VOUT = 0.2 V p-p, G = 2 VOUT = 2 V p-p 0.1%, VOUT = 2 V p-p VIN = 2.5 V to 0 V step, G = 2 VOUT = 2 V p-p, 1 MHz, RL, dm = 800 VOUT = 2 V p-p, 5 MHz, RL, dm = 800 VOUT = 2 V p-p, 20 MHz, RL, dm = 800 VOUT = 2 V p-p, 1 MHz, RL, dm = 800 VOUT = 2 V p-p, 5 MHz, RL, dm = 800 VOUT = 2 V p-p, 20 MHz, RL, dm = 800 20 MHz, RL, dm = 800 20 MHz, RL, dm = 800 f = 0.1 MHz to 100 MHz f = 0.1 MHz to 100 MHz NTSC, G = 2, RL, dm = 150 NTSC, G = 2, RL, dm = 150 VOS, dm = VOUT, dm/2; VDIN+ = VDIN- = VOCM = 2.5 V TMIN to TMAX variation Differential Common-mode Min 250 Typ 300 180 360 155 65 50 1000 20 5 -97 -100 -74 -100 -99 -67 -76 40 8 1.8 0.025 0.15 1.0 6 3 10 3 1 0.3 to 3.0 -70 1.0 to 4.0 50 -68 3.5 7 Max Unit MHz MHz MHz MHz MHz MHz V/s ns ns dBc dBc dBc dBc dBc dBc dBc dBm nV/Hz pA/Hz % Degrees mV V/C A M M pF V dB V mA dB
800
Third Harmonic
IMD IP3 Input Voltage Noise (RTI) Input Current Noise Differential Gain Error Differential Phase Error INPUT CHARACTERISTICS Offset Voltage (RTI) Input Bias Current Input Resistance Input Capacitance Input Common-Mode Voltage CMRR OUTPUT CHARACTERISTICS Output Voltage Swing Output Current Output Balance Error
VOUT, dm/VIN, cm; VIN, cm = 1 V; resistors matched to 0.01% Maximum VOUT; single-ended output VOUT, cm/VOUT, dm; VOUT, dm = 1 V
-60
Rev. F | Page 5 of 32
AD8132
VOCM TO OUT SPECIFICATIONS
At TA = 25C, VS = 5 V, VOCM = 2.5 V, G = 1, RL, dm = 499 , RF = RG = 348 , unless otherwise noted. For G = 2, RL, dm = 200 , RF = 1000 , RG = 499 . Refer to Figure 56 and Figure 57 for test setup and label descriptions. All specifications refer to single-ended input and differential outputs, unless otherwise noted. Table 4.
Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Slew Rate Input Voltage Noise (RTI) DC PERFORMANCE Input Voltage Range Input Resistance Input Offset Voltage Input Bias Current VOCM CMRR Gain POWER SUPPLY Operating Range Quiescent Current Power Supply Rejection Ratio OPERATING TEMPERATURE RANGE Conditions VOCM = 600 mV p-p VOCM = 1.5 V to 3.5 V f = 0.1 MHz to 100 MHz Min Typ 210 340 12 1.0 to 3.7 30 5 0.5 -66 1 Max Unit MHz V/s nV/Hz V k mV A dB V/V V mA A/C dB C
VOS, cm = VOUT, cm; VDIN+ = VDIN- = VOCM = 2.5 V VOUT, dm/VOCM; VOCM = 2.5 V 1 V; resistors matched to 0.01% VOUT, cm/VOCM; VOCM = 2.5 V 1 V
11
0.985 2.7 9.4
1.015 11 12 -60 +125
VDIN+ = VDIN- = VOCM = 2.5 V TMIN to TMAX variation VOUT, dm/VS; VS = 1 V
10.7 10 -70
-40
Rev. F | Page 6 of 32
AD8132
DIN TO OUT SPECIFICATIONS
At TA = 25C, VS = 3 V, VOCM = 1.5 V, G = 1, RL, dm = 499 , RF = RG = 348 , unless otherwise noted. For G = 2, RL, dm = 200 , RF = 1000 , RG = 499 . Refer to Figure 56 and Figure 57 for test setup and label descriptions. All specifications refer to single-ended input and differential outputs, unless otherwise noted. Table 5.
Parameter DYNAMIC PERFORMANCE -3 dB Large Signal Bandwidth -3 dB Small Signal Bandwidth Bandwidth for 0.1 dB Flatness NOISE/HARMONIC PERFORMANCE Second Harmonic Conditions VOUT = 1 V p-p VOUT = 1 V p-p, G = 2 VOUT = 0.2 V p-p VOUT = 0.2 V p-p, G = 2 VOUT = 0.2 V p-p VOUT = 0.2 V p-p, G = 2 VOUT = 1 V p-p, 1 MHz, RL, dm = 800 VOUT = 1 V p-p, 5 MHz, RL, dm = 800 VOUT = 1 V p-p, 20 MHz, RL, dm = 800 VOUT = 1 V p-p, 1 MHz, RL, dm = 800 VOUT = 1 V p-p, 5 MHz, RL, dm = 800 VOUT = 1 V p-p, 20 MHz, RL, dm = 800 VOS, dm = VOUT, dm/2; VDIN+ = VDIN- = VOCM = 1.5 V Min Typ 350 165 350 150 45 50 -100 -94 -77 -90 -85 -66 10 3 0.3 to 1.0 -60 Max Unit MHz MHz MHz MHz MHz MHz dBc dBc dBc dBc dBc dBc mV A V dB
Third Harmonic
INPUT CHARACTERISTICS Offset Voltage (RTI) Input Bias Current Input Common-Mode Voltage CMRR
VOUT, dm/VIN, cm; VIN, cm = 0.5 V; resistors matched to 0.01%
VOCM TO OUT SPECIFICATIONS
At TA = 25C, VS = 3 V, VOCM = 1.5 V, G = 1, RL, dm = 499 , RF = RG = 348 , unless otherwise noted. For G = 2, RL, dm = 200 , RF = 1000 , RG = 499 . Refer to Figure 56 and Figure 57 for test setup and label descriptions. All specifications refer to single-ended input and differential outputs, unless otherwise noted. Table 6.
Parameter DC PERFORMANCE Input Offset Voltage Gain POWER SUPPLY Operating Range Quiescent Current Power Supply Rejection Ratio OPERATING TEMPERATURE RANGE Conditions VOS, cm = VOUT, cm; VDIN+ = VDIN- = VOCM = 1.5 V VOUT, cm/VOCM; VOCM = 0.5 V 2.7 VDIN+ = VDIN- = VOCM = 0 V VOUT, dm/VS; VS = 0.5 V -40 7.25 -70 +125 Min Typ 7 1 11 Max Unit mV V/V V mA dB C
Rev. F | Page 7 of 32
AD8132 ABSOLUTE MAXIMUM RATINGS
Table 7.
Parameter Supply Voltage VOCM Internal Power Dissipation Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering 10 sec) Junction Temperature Rating 5.5 V VS 250 mW -40C to +125C -65C to +150C 300C 150C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
The power dissipated in the package (PD) is the sum of the quiescent power dissipation and the power dissipated in the package due to the load drive for all outputs. The quiescent power is the voltage between the supply pins (VS) times the quiescent current (IS). The load current consists of the differential and common-mode currents flowing to the load, as well as currents flowing through the external feedback networks and the internal common-mode feedback loop. The internal resistor tap used in the common-mode feedback loop places a 1 k differential load on the output. Consider rms voltages and currents when dealing with ac signals. Airflow reduces JA. In addition, more metal directly in contact with the package leads from metal traces through holes, ground, and power planes reduces the JA. Figure 3 shows the maximum safe power dissipation in the package vs. the ambient temperature for the 8-lead SOIC_N (JA = 121C/W) and MSOP (JA = 142C/W) packages on a JEDEC standard 4-layer board. JA values are approximations.
1.75 1.50 1.25 1.00 0.75 MSOP 0.50 0.25 0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 AMBIENT TEMPERATURE (C)
01035-082
THERMAL RESISTANCE
JA is specified for the worst-case conditions, that is, JA is specified for the device soldered in a circuit board in still air. Table 8.
Package Type 8-Lead SOIC/4-Layer 8-Lead MSOP/4-Layer JA 121 142 Unit C/W C/W
Maximum Power Dissipation
The maximum safe power dissipation in the AD8132 packages is limited by the associated rise in junction temperature (TJ) on the die. At approximately 150C (the glass transition temperature), the plastic changes its properties. Even temporarily exceeding this temperature limit can change the stresses that the package exerts on the die, permanently shifting the parametric performance of the AD8132. Exceeding a junction temperature of 150C for an extended period can result in changes in the silicon devices, potentially causing failure.
MAXIMUM POWER DISSIPATION (W)
SOIC
Figure 3. Maximum Power Dissipation vs. Temperature
ESD CAUTION
Rev. F | Page 8 of 32
AD8132 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
-IN 1 VOCM 2 V+ 3 +OUT 4
AD8132
8 7 6 5
+IN NC V-
01035-004
-OUT
NC = NO CONNECT
Figure 4. Pin Configuration
Table 9. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 Mnemonic -IN VOCM V+ +OUT -OUT V- NC +IN Description Negative Input. Voltage applied to this pin sets the common-mode output voltage with a ratio of 1:1. For example, 1 V dc on VOCM sets the dc bias level on +OUT and -OUT to 1 V. Positive Supply Voltage. Positive Output. Note that the voltage at -DIN is inverted at +OUT (see Figure 64). Negative Output. Note that the voltage at +DIN is inverted at -OUT (see Figure 64). Negative Supply Voltage. No Connect. Positive Input.
Rev. F | Page 9 of 32
AD8132 TYPICAL PERFORMANCE CHARACTERISTICS
2 1 0 GAIN (dB) GAIN (dB) -1 -2 -3 -4 -5 VS = 5V VS = +3V
3 2 1 0 -1 -2 -3 -4
01035-006
VS = 5V VS = +3V VS = +5V
VS = +5V
VS = +3V
G = +1 VO, dm = 0.2V p-p RL, dm = 499
G = +1 VO, dm = 2V p-p FOR VS = 5V, +5V VO, dm = 1V p-p FOR VS = +3V RL, dm = 499
1
10 100 FREQUENCY (MHz)
1k
1
10 100 FREQUENCY (MHz)
1k
Figure 5. Small Signal Frequency Response (See Figure 56)
0.5 0.4 0.3 0.2 GAIN (dB) 0.1 0 -0.1 -0.2 -0.3 -0.4
01035-007
Figure 8. Large Signal Frequency Response; CF = 0 pF (See Figure 56)
2
G = +1 VO, dm = 0.2V p-p RL, dm = 499
VS = +3V 1 VS = +5V 0 GAIN (dB) -1 -2 -3 -4 -5 1 10 100 FREQUENCY (MHz) 1k G = +1 VO, dm = 2V p-p FOR VS = 5V, +5V VO, dm = 1V p-p FOR VS = +3V RL, dm = 499
01035-010 01035-011
VS = +3V VS = +5V VS = 5V VS = +3V
VS = 5V
-0.5 1 10 100 FREQUENCY (MHz) 1k
Figure 6. 0.1 dB Flatness vs. Frequency; CF = 0 pF (See Figure 56)
0.2 0.1 0
GAIN (dB)
Figure 9. Large Signal Frequency Response; CF = 0.5 pF (See Figure 56)
3 +85C +25C
VS = +3V
VS = +5V
2 1 0 -40C -1 -2 -3 -4
01035-008
-0.2 -0.3 -0.4 -0.5 1 10 100 FREQUENCY (MHz) 1k
GAIN (dB)
-0.1
VS = 5V
G = +1 VO, dm = 0.2V p-p RL, dm = 499
VS = 5V G = +1 VO, dm = 2V p-p RL, dm = 499
-5
1
10 100 FREQUENCY (MHz)
1k
Figure 7. 0.1 dB Flatness vs. Frequency; CF = 0.5 pF (See Figure 56)
Figure 10. Large Signal Frequency Response at Various Temperatures (See Figure 56)
Rev. F | Page 10 of 32
01035-009
-5
AD8132
3 2 1 5.9 0 -1 -2 -3 -4 -5 1 10 100 FREQUENCY (MHz) 1k VS = 5V G = +1 VO, dm = 2V p-p RL, dm = 499 RF = 249 RF = 499 RF = 348 6.0 6.1
GAIN (dB)
GAIN (dB)
5.8
5.7 VS = +3V, +5V, 5V G = +2 VO, dm = 0.2V p-p RL, dm = 200 1 10 100 FREQUENCY (MHz) 1k
01035-016 01035-018 01035-017
5.6
01035-012
5.5
Figure 11. Large Signal Frequency Response vs. RF (See Figure 56)
100
Figure 14. 0.1 dB Flatness vs. Frequency (See Figure 57)
7 VS = +5V, 5V VS = +3V
6
IMPEDANCE ()
10
5 GAIN (dB)
4
1
3
VS = +5V VS = 5V
01035-013
2
G = +2 VO, dm = 2V p-p FOR VS = 5V, +5V VO, dm = 1V p-p FOR VS = +3V RL, dm = 200
0.1
1 1 10 100 FREQUENCY (MHz) 1k
1
10 FREQUENCY (MHz)
100
Figure 12. Closed-Loop Single-Ended ZOUT vs. Frequency; G = 1 (See Figure 56)
7
Figure 15. Large Signal Frequency Response (See Figure 57)
7 RF = 1.5k
6
6 RF = 1.0k RF = 499 4
5 GAIN (dB)
VS = 5V, +5V GAIN (dB)
5
4 VS = +3V 3 G = +2 VO, dm = 0.2V p-p RL, dm = 200
3
2
2
VS = 5V G = +2 VO, dm = 0.2V p-p RL, dm = 200
01035-015
1
1
10 100 FREQUENCY (MHz)
1k
1 1 10 100 FREQUENCY (MHz) 1k
Figure 13. Small Signal Frequency Response (See Figure 57)
Figure 16. Small Signal Frequency Response vs. RF (See Figure 57)
Rev. F | Page 11 of 32
AD8132
25 20 15 10 G = +2, RF = 1k 5 0 -5 -10 -15 G = +1, RF = 499 G = +10, RF = 4.99k G = +5, RF = 2.49k
-30 -40 -50 DISTORTION (dBc) -60 -70 -80 -90 -100
01035-020
RL, dm = 800 VO, dm = 2V p-p
HD3 (V S = +5V)
HD2 (V S = 5V) HD3 (V S = 5V) HD2 (VS = +5V)
GAIN (dB)
VS = 5V VO, dm = 2V p-p RL, dm = 200 RG = 499 1 10 100 FREQUENCY (MHz) 1k
0
10
20
30 40 FREQUENCY (MHz)
50
60
70
Figure 17. Large Signal Frequency Response for Various Gains (See Figure 58)
-25 -30 -35 VS = 5V VO, dm = 2V p-p VO, cm/VO, dm
Figure 20. Harmonic Distortion vs. Frequency, G = 1 (See Figure 62)
-40 -50 -60
DISTORTION (dBc)
VS = 3V RL, dm = 800
HD3 (F = 20MHz)
RTI BALANCE ERROR (dB)
-40 -45 -50 -55 -60 G=2 -65 -70
01035-022
HD2 (F = 20MHz)
G=1
-70 -80 -90 -100 HD2 (F = 5MHz) HD3 (F = 5MHz)
01035-026
-75
1
10 100 FREQUENCY (MHz)
1k
-110 0.25
0.50 0.75 1.00 1.25 1.50 DIFFERENTIAL OUTPUT VOLTAGE (V p-p)
1.75
Figure 18. RTI Output Balance Error vs. Frequency (See Figure 59)
-40 -50 -60 DISTORTION (dBc) -70 -80 HD2 (VS = 5V) -90 -100 HD3 (V S = 5V)
01035-024
Figure 21. Harmonic Distortion vs. Differential Output Voltage, G = 1 (See Figure 62)
-40 VS = 5V RL, dm = 800
RL, dm = 800 VO, dm = 1V p-p HD3 (VS = 3V)
-50 -60
HD3 (F = 20MHz)
DISTORTION (dBc)
HD2 (VS = 3V)
-70 -80 -90 -100 -110 0 1 2 3 DIFFERENTIAL OUTPUT VOLTAGE (V p-p) 4 HD2 (F = 5MHz) HD2 (F = 20MHz)
HD3 (F = 5MHz)
01035-027
-110
0
10
20
30 40 FREQUENCY (MHz)
50
60
70
Figure 19. Harmonic Distortion vs. Frequency, G = 1 (See Figure 62)
Figure 22. Harmonic Distortion vs. Differential Output Voltage, G = 1 (See Figure 62)
Rev. F | Page 12 of 32
01035-025
-110
AD8132
-40 -50 -60 VS = 5V RL, dm = 800 HD2 (F = 20MHz) HD3 (F = 20MHz)
-60 -50 VS = 5V VO, dm = 2V p-p HD3 (F = 20MHz)
DISTORTION (dBc)
DISTORTION (dBc)
-70 HD2 (F = 20MHz) HD2 (F = 5MHz) -90
-70 -80 -90 -100 HD3 (F = 5MHz)
01035-028
-80
HD2 (F = 5MHz)
-100 HD3 (F = 5MHz)
-110
0
5 1 2 3 4 DIFFERENTIAL OUTPUT VOLTAGE (V p-p)
6
300
400
500
RLOAD ()
600
700
800
900
1000
Figure 23. Harmonic Distortion vs. Differential Output Voltage, G = 1 (See Figure 62)
-50 VS = 3V VO, dm = 1V p-p
Figure 26. Harmonic Distortion vs. RLOAD, G = 1 (See Figure 62)
-40
-60
HD3 (F = 20MHz)
-50 -60
RL, dm = 800 VO, dm = 1V p-p HD3 (VS = 3V)
DISTORTION (dBc)
HD2 (F = 20MHz)
DISTORTION (dBc)
-70
-70 -80 -90 -100 HD3 (V S = 5V) HD2 (VS = 5V)
-80
-90
HD3 (F = 5MHz)
HD2 (VS = 3V)
-100 HD2 (F = 5MHz)
01035-029
300
400
500
600 700 RLOAD ()
800
900
1000
0
10
20
30 40 FREQUENCY (MHz)
50
60
70
Figure 24. Harmonic Distortion vs. RLOAD, G = 1 (See Figure 62)
-50 VS = 5V VO, dm = 2V p-p HD3 (F = 20MHz)
Figure 27. Harmonic Distortion vs. Frequency, G = 2 (See Figure 63)
-20 -30 -40 RL, dm = 800 VO, dm = 4V p-p HD2 (VS = +5V) HD3 (VS = +5V)
-60
DISTORTION (dBc)
DISTORTION (dBc)
-70
-50 -60 -70 -80 HD3 (VS = 5V)
-80
HD2 (F = 20MHz) HD2 (F = 5MHz)
-90
-100
HD3 (F = 5MHz)
-90
01035-030
HD2 (VS = 5V)
300
400
500
600 700 RLOAD ()
800
900
1000
0
10
20
40 50 30 FREQUENCY (MHz)
60
70
80
Figure 25. Harmonic Distortion vs. RLOAD, G = 1 (See Figure 62)
Figure 28. Harmonic Distortion vs. Frequency, G = 2 (See Figure 63)
Rev. F | Page 13 of 32
01035-034
-110 200
-100
01035-033
-110 200
-110
01035-031
-110 200
AD8132
-40 -50 -60 VS = 5V RL, dm = 800 HD3 (F = 20MHz)
-60 HD2 (F = 20MHz)
DISTORTION (dBc)
-50
VS = 5V VO, dm = 2V p-p
HD3 (F = 20MHz)
DISTORTION (dBc)
-70 HD2 (F = 20MHz) -80 -90 HD2 (F = 5MHz) -100 -110 HD3 (F = 5MHz)
01035-035
-70
-80 HD2 (F = 5MHz) -90
-100
HD3 (F = 5MHz)
01035-038
-120
0
1 2 3 DIFFERENTIAL OUTPUT VOLTAGE (V p-p)
4
-110 200
300
400
500
700 600 RLOAD ()
800
900
1000
Figure 29. Harmonic Distortion vs. Differential Output Voltage, G = 2 (See Figure 63)
-40 -50 -60 VS = 5V RL, dm = 800 HD3 (F = 20MHz)
Figure 32. Harmonic Distortion vs. RLOAD, G = 2 (See Figure 63)
10 0 -10 POUT (dBm [Re: 50]) fC = 20MHz VS = 5V RL, dm = 800
HD2 (F = 20MHz)
DISTORTION (dBc)
-20 -30 -40 -50 -60 -70 -80
-70 -80 -90 HD3 (F = 5MHz) -100 -110 HD2 (F = 5MHz)
01035-036
0
4 1 2 3 5 DIFFERENTIAL OUTPUT VOLTAGE (V p-p)
6
20.0 FREQUENCY (MHz)
20.5
Figure 30. Harmonic Distortion vs. Differential Output Voltage, G = 2 (See Figure 63)
-50 VS = 5V VO, dm = 2V p-p -60 INTERCEPT (dBm [Re: 50]) HD3 (F = 20MHz) 40 45
Figure 33. Intermodulation Distortion, G = 1
VS = 5V, +5V RL, dm = 800
DISTORTION (dBc)
-70 HD2 (F = 20MHz) -80
35
30
-90
HD2 (F = 5MHz)
25
-100 HD3 (F = 5MHz)
01035-037
20
300
400
500
600 700 RLOAD ()
800
900
1000
0
10
20
30 40 FREQUENCY (MHz)
50
60
70
Figure 31. Harmonic Distortion vs. RLOAD, G = 2 (See Figure 63)
Figure 34. Third-Order Intercept vs. Frequency, G = 1
Rev. F | Page 14 of 32
01035-040
-110 200
15
01035-039
-90 19.5
AD8132
VS = 5V, +5V, +3V CF = 0pF VS = 5V VO, dm = 2V p-p
CF = 0.5pF
01035-041
40mV
5ns
400mV
5ns
Figure 35. Small Signal Transient Response, G = 1
Figure 38. Large Signal Transient Response, G = 1
CF = 0pF
VS = 3V VO, dm = 1.5V p-p
VO, dm V-OUT
CF = 0.5pF
V+OUT
V+DIN
01035-042
01035-045
300mV
5ns
1V
5ns
Figure 36. Large Signal Transient Response, G = 1
Figure 39. Large Signal Transient Response, G = 1
CF = 0pF
VS = 5V VO, dm = 2V p-p
VS = 5V, +5V, +3V
CF = 0.5pF
01035-043
400mV
5ns
40mV
5ns
Figure 37. Large Signal Transient Response, G = 1
Figure 40. Small Signal Transient Response, G = 2
Rev. F | Page 15 of 32
01035-046
01035-044
AD8132
VS = 3V VS = 5V G = +1 VO, dm = 2V p-p RL, dm = 499
01035-047
0.1%/DIV
2mV 0 5 10 15 20 25 5ns/DIV 30
5ns 35 40
01035-050 01035-052
300mV
5ns
Figure 41. Large Signal Transient Response, G = 2
Figure 44. 0.1% Settling Time
VS = +5V, 5V
CL = 0pF CL = 5pF
CL = 20pF
01035-048
400mV
5ns
400mV
5ns
Figure 42. Large Signal Transient Response, G = 2
0
VS = 5V
Figure 45. Large Signal Transient Response for Various Capacitor Loads (See Figure 60)
VO, dm VS
-10 -20
-PSRR
VO, dm
PSRR (dB)
-30 -40 -50 -60
+PSRR (VS = 5V, +5V) -PSRR (VS = 5V)
V-OUT
+PSRR
V+OUT
V+DIN
01035-049
-70 -80
1V
5ns
1
10 FREQUENCY (MHz)
100
1k
Figure 43. Large Signal Transient Response, G = 2
Figure 46. PSRR vs. Frequency
Rev. F | Page 16 of 32
01035-053
-90 0.1
AD8132
-20 VS = 5V VIN, cm = 2V p-p
-10 -20 -30
VOCM CMRR (dB)
VO, dm VOCM
VOCM = 600mV p-p
-30
-40
CMRR (dB)
VO, cm VIN, cm
VOCM = 2V p-p -40 -50 -60
-50
-60 VO, dm VIN, cm
-70
-70 -80
01035-055
1
10 100 FREQUENCY (MHz)
1000
1
10 100 FREQUENCY (MHz)
1000
Figure 47. CMRR vs. Frequency (See Figure 61)
6 3 0
VOCM GAIN (dB)
Figure 50. VOCM CMRR vs. Frequency
1k
VO, cm VOCM
VS = 5V
INPUT VOLTAGE NOISE (nV/Hz)
VOCM = 600mV p-p
100
-3 -6 -9 -12
VOCM = 2V p-p
10
8nV/Hz
01035-056
1
10 100 FREQUENCY (MHz)
1000
10
100
1k
10k 100k FREQUENCY (Hz)
1M
10M
100M
Figure 48. VOCM Gain Response
1k
VS = 5V VOCM = -1V TO +1V
Figure 51. Input Voltage Noise vs. Frequency
INPUT CURRENT NOISE (pA/Hz)
VO, cm
100
10
1.8pA/Hz
10
100
1k
10k 100k FREQUENCY (Hz)
1M
10M
100M
Figure 49. VOCM Transient Response
Figure 52. Input Current Noise vs. Frequency
Rev. F | Page 17 of 32
01035-060
400mV
5ns
01035-057
1
01035-059
-15
1
01035-058
-80
AD8132
0
DIFFERENTIAL OUTPUT OFFSET (mV)
VO, dm (0.5V/DIV)
-0.5
VS = +5V
VIN, sm (1V/DIV)
-1.0 VS = 5V -1.5
-20
0
20 40 TEMPERATURE (C)
60
80
100
Figure 53. Overdrive Recovery
15
Figure 55. Differential Output Offset Voltage vs. Temperature
13
SUPPLY CURRENT (mA)
VS = 5V 11 VS = +5V 9
7
-50
-30
-10
10 30 TEMPERATURE (C)
50
70
90
Figure 54. Quiescent Current vs. Temperature
01035-062
5
Rev. F | Page 18 of 32
01035-063
5ns
01035-061
VS = 5V VIN = 2.5V STEP G = +2 RF = 1k RL, dm = 200
-2.0
-2.5 -40
AD8132 TEST CIRCUITS
CF 348 348 49.9
49.9 RG 0.1F RL 24.9 RG RF
01035-005
RF RL
0.1F 348 348 CF
499
24.9
G = +1: RF = RG = 348, RL = 249 (RL, dm = 498) G = +2: RF = 1000, RG = 499, RL = 100 (RL, dm = 200)
Figure 56. Basic Test Circuit, G = 1
1000 499 49.9 0.1F 499 1000 200
Figure 59. Test Circuit for Output Balance
348 348 49.9 0.1F
01035-014
24.9 CL 24.9 348
01035-051
453
24.9
348 24.9
Figure 57. Basic Test Circuit, G = 2
RF 499 49.9 0.1F 499 RF 200
Figure 60. Test Circuit for Capacitor Load Drive
348 348 249 VO, dm 49.9
01035-019
VO, cm
24.9
348
249
01035-054
348 NOTES RESISTORS MATCHED TO 0.01%.
Figure 58. Test Circuit for Various Gains
Figure 61. CMRR Test Circuit
348 348 LPF 49.9 0.1F 348 348
2:1 TRANSFORMER 300 HPF ZIN = 50
24.9
Figure 62. Harmonic Distortion Test Circuit, G = 1, RL, dm = 800
1000 499 LPF 49.9 0.1F 499 1000 2:1 TRANSFORMER 300 HPF ZIN = 50
24.9
Figure 63. Harmonic Distortion Test Circuit, G = 2, RL, dm = 800
Rev. F | Page 19 of 32
01035-032
300
01035-023
300
01035-021
AD8132 OPERATIONAL DESCRIPTION
DEFINITION OF TERMS
Differential Voltage The difference between two node voltages. For example, the output differential voltage (or equivalently output differentialmode voltage) is defined as VOUT, dm = (V+OUT - V-OUT) where V+OUT and V-OUT refer to the voltages at the +OUT and -OUT terminals with respect to a common reference. Common-Mode Voltage The average of two node voltages. The output common-mode voltage is defined as VOUT, cm = (V+OUT + V-OUT)/2
CF RF RG +IN -OUT
Table 10. Differential and Common-Mode Gains
Input VIN, dm VIN, cm VOCM VOUT, dm RF/RG 0 0 VOUT, cm 0 (by design) 0 (by design) 1 (by design)
As listed in Table 10, the differential output (VOUT, dm) is equal to the differential input voltage (VIN, dm) times RF/RG. In this case, it does not matter if both differential inputs are driven, or only one output is driven and the other is tied to a reference voltage, such as ground. As seen from the two zero entries in the VOUT, dm column, neither of the common-mode inputs has any effect on this gain. The gain from VIN, dm to VOUT, cm is 0, and first-order does not depend on the ratio matching of the feedback networks. The common-mode feedback loop within the AD8132 provides a corrective action to keep this gain term minimized. The term balance error describes the degree that this gain term differs from 0.
+DIN VOCM -DIN
AD8132
RG -IN RF CF +OUT
RL, dm
VO, dm
The gain from VIN, cm to VOUT, dm directly depends on the matching of the feedback networks. The analogous term for this transfer function (used in conventional op amps) is common-mode rejecttion ratio (CMRR). Therefore, if it has a high CMRR, the feedback ratios must be well matched. The gain from VIN, cm to VOUT, cm is ideally 0 and is first-order independent of the feedback ratio matching. As in the case of VIN, dm to VOUT, cm, the common-mode feedback loop keeps this term minimized. The gain from VOCM to VOUT, dm is ideally 0 when the feedback ratios are matched only. The amount of differential output signal that is created by varying VOCM is related to the degree of mismatch in the feedback networks. VOCM controls the output common-mode voltage VOUT, cm with a unity-gain transfer function. With equal-ratio feedback networks (as previously assumed), its effect on each output is the same, that is the gain from VOCM to VOUT, dm is 0. If not driven, the output common-mode voltage is set with an internal voltage divider to a level that is nominally midsupply. It is recommended that a 0.1 F bypass capacitor be connected to VOCM. When unequal feedback ratios are used, the two gains associated with VOUT, dm become nonzero. This significantly complicates the mathematical analysis along with any intuitive understanding of how the part operates.
Figure 64. Circuit Definitions
BASIC CIRCUIT OPERATION
One of the more useful and easy to understand ways to use the AD8132 is to provide two equal-ratio feedback networks. To match the effect of parasitics, comprise these networks of two equal-value feedback resistors (RF) and two equal-value gain resistors (RG). This circuit is shown in Figure 64. Like a conventional op amp, the AD8132 has two differential inputs that can be driven with both differential-mode input voltage (VIN, dm) and common-mode input voltage (VIN, cm). There is another input (VOCM) that is not present on conventional op amps, but provides another input to consider on the AD8132. It is totally separate from the previous inputs. There are two complementary outputs whose response can be defined by a differential-mode output (VOUT, dm) and a commonmode output (VOUT, cm). Table 10 indicates the gain from any type of input to either type of output.
01035-064
Rev. F | Page 20 of 32
AD8132 THEORY OF OPERATION
The AD8132 differs from conventional op amps by the external presence of an additional input and output. The additional input, VOCM, controls the output common-mode voltage. The additional output is the analog complement of the single output of a conventional op amp. For its operation, the AD8132 uses two feedback loops as compared to the single loop of conventional op amps. Although this provides significant freedom to create various novel circuits, basic op amp theory can still be used to analyze the operation. One of the feedback loops controls the output common-mode voltage, VOUT, cm. Its input is VOCM (Pin 2) and the output is the common-mode, or average voltage, of the two differential outputs (+OUT and -OUT). The gain of this circuit is internally set to unity. When the AD8132 is operating in its linear region, this establishes one of the operational constraints: VOUT, cm = VOCM. The second feedback loop controls the differential operation. Similar to an op amp, the gain and gain shaping of the transfer function can be controlled by adding passive feedback networks. However, only one feedback network is required to close the loop and fully constrain the operation, but depending on the function desired, two feedback networks can be used. This is possible because there are two outputs that are each inverted with respect to the differential inputs. For each feedback network, a feedback factor can be defined as the fraction of the output signal that is fed back to the opposite sign input. These terms are
2 = RG2 (RG2 + R F2 )
The feedback factor, 1, is for the side that is driven, and the feedback factor, 2, is for the side that is tied to a reference voltage (ground). Note that each feedback factor can vary anywhere between 0 and 1. A single-ended-to-differential gain equation can be derived (this is true for all values of 1 and 2):
G= 2 (1 - 1)
1 = RG1 (R G1 + R F1 )
(1 + 2 )
This expression is not very intuitive, but some further examples can provide better understanding of its implications. One observation that can be made immediately is that a tolerance error in 1 does not have the same effect on gain as the same tolerance error in 2.
DIFFERENTIAL AMPLIFIER WITHOUT RESISTORS (HIGH INPUT IMPEDANCE INVERTING AMPLIFIER)
The simplest closed-loop circuit that can be made does not require any resistors and is shown in Figure 70. In this circuit, 1 is equal to 0, and 2 is equal to 1. The gain is equal to 2. A more intuitive method to figure the gain is by simple inspection. +OUT is connected to -IN, whose voltage is equal to the voltage at +IN under equilibrium conditions. Thus, +VOUT is equal to VIN, and there is unity gain in this path. Because -OUT has to swing in the opposite direction from +OUT due to the common-mode constraint, its effect doubles the output signal and produces a gain of 2. One useful function that this circuit provides is a high input impedance inverter. If +OUT is ignored, there is a unity-gain, high input impedance amplifier formed from +IN to -OUT. Most traditional op amp inverters have relatively low input impedances, unless they are buffered with another amplifier. VOCM is assumed to be at midsupply. Because there is still the constraint that +VOUT must equal VIN, changing the VOCM voltage does not change +VOUT (equal to VIN). Therefore, the effect of changing VOCM must show up at -OUT. For example, if VOCM is raised by 1 V, then -VOUT must increase by 2 V. This makes VOUT, cm also increase by 1 V, because it is defined as the average of the two differential output voltages. This means that the gain from VOCM to the differential output is 2.
GENERAL USAGE OF THE AD8132
Several assumptions are made here for a first-order analysis; they are the typical assumptions used for the analysis of op amps: * * * The input bias currents are sufficiently small so they can be neglected. The output impedances are arbitrarily low. The open-loop gain is arbitrarily large, and drives the amplifier to a state where the input differential voltage is effectively 0. Offset voltages are assumed to be 0.
*
Though it is possible to operate the AD8132 with a purely differential input, many of its applications call for a circuit that has a single-ended input with a differential output. For a single-ended-to-differential circuit, the RG of the input that is not driven is tied to a reference voltage. This is ground. Other conditions are discussed in the following sections. In addition, the voltage at VOCM, and therefore VOUT, cm, is assumed to be ground. Figure 67 shows a generalized schematic of such a circuit using an AD8132 with two feedback paths.
Rev. F | Page 21 of 32
AD8132
OTHER 2 = 1 CIRCUITS
The preceding simple configuration with 2 = 1 and its gain of 2 is the highest gain circuit that can be made under this condition. Since 1 was equal to 0, only higher 1 values are possible. The circuits with higher values of 1 have gains lower than 2. However, circuits with 1 equal to 1 are not practical because they have no effective input and result in a gain of 0. To increase 1 from 0, it is necessary to add two resistors in a feedback network. A generalized circuit that has 1 with a value higher than 0 is shown in Figure 69. A couple of different convenient gains that can be created are a gain of 1, when 1 is equal to 1/3, and a gain of 0.5, when 1 equals 0.6. With 2 equal to 1 in these circuits, VOCM serves as the reference voltage that measures the input voltage and the individual output voltages. In general, when VOCM is varied in circuits with unmatched feedback networks, a differential output signal is generated that is proportional to the applied VOCM voltage. With 2 equal to 0 in these circuits, the gain can theoretically be set to any value from close to 0 to infinity, just as it can with a conventional op amp in the inverting mode. However, practical real-world limitations and parasitics limit the range of acceptable gain to more modest values.
1 = 0
There is yet another class of circuits where there is no feedback from -OUT to +IN. This is the case where 1 = 0. The differential amplifier without a resistor described in the Differential Amplifier Without Resistors (High Input Impedance Inverting Amplifier) section meets this condition, but it was presented only with the condition that 2 = 1. Recall that this circuit had a gain equal to 2. If 2 decreases in this circuit from unity, a smaller part of +VOUT is fed back to -IN and the gain increases (see Figure 68). This circuit is very similar to a noninverting op amp configuration, except for the presence of the additional complementary output. Therefore, the overall gain is twice that of a noninverting op amp or 2 x (1 + RF2/RG2) or 2 x (1/2). Once again, varying VOCM does not affect both outputs in the same way; therefore, in addition to varying VOUT, cm with unity gain, there is also an effect on VOUT, dm by changing VOCM.
VARYING 2
Though the 2 = 1 circuit sets 2 to 1, another class of simple circuits can be made that sets 2 equal to 0. This means that there is no feedback from +OUT to -IN. This class of circuits is very similar to a conventional inverting op amp. However, the AD8132 circuits have an additional output and commonmode input that can be analyzed separately (see Figure 71). With -IN connected to ground, +IN becomes a virtual ground in the sense that the term is used for conventional op amps. Both inputs must maintain the same voltage for equilibrium operation; therefore, if one is set to ground, the other is driven to ground. The input impedance can also be seen to be equal to RG, just as in a conventional op amp. In this case, however, the positive input and negative output are used for the feedback network. Because a conventional op amp does not have a negative output, only its inverting input can be used for the feedback network. The AD8132 is symmetrical, therefore, the feedback network on either side can be used to produce the same results. Because +IN is a summing junction, by an analogy to conventional op amps, the gain from VIN to -OUT is -RF/RG. This holds true regardless of the voltage on VOCM, and since +OUT moves the same amount in the opposite direction from -OUT, the overall gain is -2(RF/RG). VOCM still governs VOUT, cm, so +OUT must be the only output that moves when VOCM is varied. Because VOUT, cm is the average of the two outputs, +OUT must move twice as far and in the same direction as VOCM to create the proper VOUT, cm. Therefore, the gain from VOCM to +OUT must be 2.
ESTIMATING THE OUTPUT NOISE VOLTAGE
Similar to the case of a conventional op amp, the differential output errors (noise and offset voltages) can be estimated by multiplying the input referred terms, at +IN and -IN, by the circuit noise gain. The noise gain is defined as
R GN = 1 + F RG
To compute the total output referred noise for the circuit of Figure 64, consideration must be given to the contribution of resistors, RF and RG. See Table 11 for estimated output noise voltage densities at various closed-loop gains. Table 11. Recommended Resistor Values and Noise Performance for Specific Gains
Output Noise AD8132 Only (nV/Hz) 16 24.1 48.4 88.9 Output Noise AD8132 + RG, RF (nV/Hz) 17 26.1 53.3 98.6
Gain 1 2 5 10
RG () 499 499 499 499
RF () 499 1.0 k 2.49 k 4.99 k
Bandwidth -3 dB (MHz) 360 160 65 20
Rev. F | Page 22 of 32
AD8132
When using the AD8132 in gain configurations where 1 2, differential output noise appears due to input-referred voltage noise in the VOCM circuitry according to the following formula:
offset values in the Specifications section assume the VOCM input is driven by a low impedance voltage source.
DRIVING A CAPACITIVE LOAD
A purely capacitive load can react with the pin and bond wire inductance of the AD8132, resulting in high frequency ringing in the pulse response. One way to minimize this effect is to place a small capacitor across each of the feedback resistors. The added capacitance must be small to avoid destabilizing the amplifier. An alternative technique is to place a small resistor in series with the amplifier outputs, as shown in Figure 60.
VOND = 2 VNOCM
1 - 2 1 + 2
where VOND is the output differential noise and VNOCM is the input-referred voltage noise on VOCM.
CALCULATING INPUT IMPEDANCE OF THE APPLICATION CIRCUIT
The effective input impedance of a circuit, such as that in Figure 64, at +DIN and -DIN, depends on whether the amplifier is being driven by a single-ended or differential signal source. For balanced differential input signals, the input impedance (RIN, dm) between the inputs (+DIN and -DIN) is simply
OPEN-LOOP GAIN AND PHASE
Open-loop gain and phase plots are shown in Figure 65 and Figure 66.
60 50 40 30 20 10 0 -10
01035-083 01035-084
RL, dm = 2k
R IN, dm = 2 x R G In the case of a single-ended input signal (for example, if -DIN is grounded and the input signal is applied to +DIN), the input impedance becomes
OPEN-LOOP GAIN (dB)
RIN, dm
RG = RF 1 - 2 x (RG + RF )
The circuit input impedance is effectively higher than it would be for a conventional op amp connected as an inverter because a fraction of the differential output voltage appears at the inputs as a common-mode signal, partially bootstrapping the voltage across the Input Resistor RG.
-20 0.1
1
10 FREQUENCY (MHz)
100
1000
Figure 65. Open-Loop Gain Plot
40 20 0
RL, dm = 2k
INPUT COMMON-MODE VOLTAGE RANGE IN SINGLE-SUPPLY APPLICATIONS
The AD8132 is optimized for level-shifting ground-referenced input signals. For a single-ended input, this implies that the voltage at -DIN in Figure 64 is 0 V when the amplifier's negative power supply voltage (at V-) was also set to 0 V.
OPEN-LOOP PHASE (Degrees)
-20 -40 -60 -80 -100 -120 -140 -160 -180 -200 0.1 1 10 FREQUENCY (MHz) 100 1000
SETTING THE OUTPUT COMMON-MODE VOLTAGE
The AD8132s VOCM pin is internally biased at a voltage approximately equal to the midsupply point (average value of the voltage on V+ and V-). Relying on this internal bias results in an output common-mode voltage that is within approximately 100 mV of the expected value. In cases where more accurate control of the output common-mode level is required, it is best practice that an external source or resistor divider (with RSOURCE < 10 k) be used. The output common-mode
Figure 66. Open-Loop Phase Plot
Rev. F | Page 23 of 32
AD8132 LAYOUT, GROUNDING, AND BYPASSING
As a high speed part, the AD8132 is sensitive to the PCB environment in which it operates. Realizing its superior specifications requires attention to various details of good high speed PCB design. The first requirement is a good solid ground plane that covers as much of the board area around the AD8132 as possible. The only exception to this is that the two input pins (Pin 1 and Pin 8) are kept a few millimeters from the ground plane and that ground be removed from inner layers and the opposite side of the board under the input pins. This minimizes the stray capacitance on these nodes and helps preserve the gain flatness vs. the frequency. Bypass the power supply pins as close as possible to the device to the nearby ground plane and use good high frequency ceramic chip capacitors. Do this bypassing with a capacitance value of 0.01 F to 0.1 F for each supply. Farther away, provide low frequency bypassing with 10 F tantalum capacitors from each supply to ground. Keep the signal routing short and direct to avoid parasitic effects. Wherever there are complementary signals, a symmetrical layout with matched lengths must be provided to the extent possible to maximize the balance performance. When running differential signals over a long distance, place the traces on the PCB close together or twist together any differential wiring to minimize the area of the loop that is formed. This reduces the radiated energy and makes the circuit less susceptible to interference.
CIRCUITS
RF1 RG1 +
RF2
Figure 67. Typical Four-Resistor Feedback Circuit
VIN +
RG2
Figure 68. Typical Circuit with 1 = 0
RF1 RG1 +
01035-067
Figure 69. Typical Circuit with 2 = 1
VIN +
01035-068
Figure 70. G = 2 Circuit with 1 = 0, Without Resistors
RF1 VIN RG1 +
01035-069
Figure 71. Typical Circuit with 2 = 0
Rev. F | Page 24 of 32
01035-066
RF2
01035-065
RG2
AD8132 APPLICATIONS
ANALOG-TO-DIGITAL DRIVER
Many of the newer high speed ADCs are single-supply and have differential inputs. Thus, the driver for these devices is able to convert from a single-ended signal to a differential signal and provide output common-mode level shifting in addition to having low distortion and noise. The AD8132 conveniently performs these functions when driving the AD9203, a 10-bit, 40 MSPS ADC. In Figure 73, a 1 V p-p signal drives the input of an AD8132 configured for unity gain. Both the AD8132 and the AD9203 are powered from a single 3 V supply. A voltage divider biases VOCM at midsupply and in turn drives VOUT, cm to half of the supply voltage. This is within the common-mode range of the AD9203. Between the ADC and the driver is a 1-pole, differential filter that helps to filter some of the noise and assists the switched-capacitor inputs of the ADC. Each of the ADC inputs is driven by a 0.5 V p-p signal that ranges from 1.25 V dc to 1.75 V dc. Figure 72 is an FFT plot of the performance of the circuit when running at a clock rate of 40 MSPS and an input frequency of 2.5 MHz.
BALANCED CABLE DRIVER
When driving a twisted pair cable, it is desirable to drive only a pure differential signal onto the line. If the signal is purely differential (that is, fully balanced), and the transmission line is twisted and balanced, there is minimum radiation of any signal. The complementary electrical fields are confined mostly to the space between the two twisted conductors and does not significantly radiate out from the cable. The current in the cable creates magnetic fields that radiate to some degree. However, the amount of radiation is mitigated by the twists, because for each twist, the two adjacent twists have an opposite polarity magnetic field. If the twist pitch is tight enough, these small magnetic field loops contain most of the magnetic flux, and the magnetic farfield strength is negligible.
10 0 -10 -20 -30 FUND
fS = 40MHz fIN = 2.5MHz
OUTPUT (dBc)
-40 -50 -60 -70 -80 -90 -100 -110 0 2.5 5.0 7.5 10.0 12.5 15.0 INPUT FREQUENCY (MHz) 17.5 20.0
01035-071
2ND 3RD 4TH
5TH
6TH
9TH 8TH 7TH
-120
Figure 72. FTT Response for AD8132 Driving AD9203
3V 10k
3V 0.1F + 10F 0.1F 60.4
8 3 5 25 28
3V
1V p-p
10k 348
348
0.1F
2
AVDD
DRVDD DIGITAL OUTPUTS
49.9 0.1F 348
1 6 2
20pF 20pF 60.4
AINN
AD8132
4
AD9203
AINP
26
AVSS
27
DRVSS
01035-070
24.9
348
1
Figure 73. AD8132 Driving AD9203, a 10-Bit, 40 MSPS ADC
Rev. F | Page 25 of 32
AD8132
+5V + +5V 10F 0.1F 49.9 1 100 49.9 1k 10F + 0.1F -5V TWISTED PAIR 2 3 4 5 10F 0.1F -5V + 10F 0.1F 1k 499 50 SOURCE 49.9 0.1F 523
AD8132
AD830
7 VOUT
+
Figure 74. Balanced Line Driver and Receiver Using AD8132 and AD830
VOUT/VIN (dB)
Any imbalance in the differential drive signal appears as a common-mode signal on the cable. This is the equivalent of a single wire that is driven with the common-mode signal. In this case, the wire acts as an antenna and radiates. Thus, to minimize radiation when driving differential twisted pair cables, make sure the differential drive signal is well balanced. The common-mode feedback loop in the AD8132 helps to minimize the amount of common-mode voltage at the output, and can therefore be used to create a well-balanced differential line driver. Figure 74 shows an application that uses an AD8132 as a balanced line driver and an AD830 as a differential receiver configured for unity gain. This circuit was operated with 10 meters of Category 5 cable.
20 10 0 -10 -20 -30 -40 -50 -60 -70
01035-074
-80 1 10 100 FREQUENCY (MHz) 1000
TRANSMIT EQUALIZER
Any length of transmission line attenuates the signals it carries. This effect is worse at higher frequencies than at lower frequencies. One way to compensate for this is to provide an equalizer circuit that boosts the higher frequencies in the transmitter circuit, so that at the receive end of the cable, the attenuation effects are diminished. By lowering the impedance of the RG component of the feedback network at a higher frequency, the gain can be increased at a high frequency. Figure 75 shows the gain of a two-line driver that has its RG resistors shunted by 10 pF capacitors. The effect of this is shown in the frequency response plot of Figure 76.
10pF VIN 49.9 24.9 10pF 499 499 49.9
Figure 76. Frequency Response for Transmit Boost Circuit
LOW-PASS DIFFERENTIAL FILTER
Similar to an op amp, various types of active filters can be created with the AD8132. These can have single-ended inputs and differential outputs that can provide an antialias function when driving a differential ADC. Figure 77 is a schematic of a low-pass, multiple feedback filter. The active section contains two poles, and an additional pole is added at the output. The filter was designed to have a -3 dB frequency of 1 MHz. The actual -3 dB frequency was measured to be 1.12 MHz, as shown in Figure 78.
2.15k
2k VIN 49.9
01035-072
953 953
33pF
549 200pF 200pF 54
01035-075
249 249
100 49.9
VOUT
100pF 100pF
VOUT
24.9
01035-073
2k
33pF 2.15k
Figure 75. Frequency Boost Circuit
Figure 77. 1 MHz, 3-Pole Differential Output, Low-Pass, Multiple Feedback Filter
Rev. F | Page 26 of 32
AD8132
10 0 -10 -20
Another way to look at this is that the circuit performs what is sometimes called transformer action. One main difference is that the AD8132 passes dc while transformers do not. A transformer can also be easily configured to have either a high or low common-mode output impedance. If the transformers center tap is connected to a solid voltage reference, it sets the commonmode voltage on the secondary side of the transformer. In this case, if one of the differential outputs is grounded, the other output has half of the differential output signal. This keeps the common-mode voltage at ground, where it is required to be due to the center tap connection. This is analogous to the AD8132 operating with a low output impedance common-mode (see Figure 80).
01035-078 01035-079
VOUT/VIN (dB)
-30 -40 -50 -60 -70 -80 100k 1M FREQUENCY (Hz) 10M 100M
01035-076
-90 10k
Figure 78. Frequency Response of 1 MHz Low-Pass Filter
VOCM
VDIFF
HIGH COMMON-MODE OUTPUT IMPEDANCE AMPLIFIER
Changing the connection to VOCM (Pin 2) can change the commonmode from low impedance to high impedance. If VOCM is actively set to a particular voltage, the AD8132 tries to force VOUT, cm to the same voltage with a relatively low output impedance. All the previous analysis assumed that this output impedance is arbitrarily low enough to drive the load condition in the circuit. However, there are some applications that benefit from a high common-mode output impedance. This is accomplished with the circuit shown in Figure 79.
RF 348 RG 348 10 1k 1k 10 RF 348
01035-077
Figure 80. Transformer with Low Output Impedance Secondary Set at VOCM
If the center tap of the secondary of a transformer is allowed to float as shown in Figure 81 (or if there is no center tap), the transformer has a high common-mode output impedance. This means that the common mode of the secondary is determined by what it is connected to and not by anything to do with the transformer itself. If one of the differential ends of the transformer is grounded, the other end swings with the full output voltage. This means that the common mode of the output voltage is one-half of the differential output voltage. However, this shows that the common mode is not forced via a low impedance to a given voltage. The common-mode output voltage can be easily changed to any voltage through its other output terminals. The AD8132 can exhibit the same performance when one of the outputs in Figure 79 is grounded. The other output swings at the full differential output voltage. The common-mode signal is measured by the voltage divider across the outputs and input to VOCM. This, then, drives VOUT, cm to the same level. At higher frequencies, it is important to minimize the capacitance on the VOCM node; otherwise, phase shifts can compromise the performance. The voltage divider resistances can also be lowered for better frequency response.
NC VDIFF
49.9 49.9
RG 348
Figure 79. High Common-Mode, Output Impedance, Differential Amplifier
VOCM is driven by a resistor divider that measures the output common-mode voltage. Thus, the common-mode output voltage takes on the value that is set by the driven circuit. In this case, it comes from the center point of the termination at the receive end of a 10 meter length of Category 5 twisted pair cable. If the receive end common-mode voltage is set to ground, it is well defined at the receive end. Any common-mode signal that is picked up over the cable length due to noise appears at the transmit end and must be absorbed by the transmitter. Thus, it is important that the transmitter have adequate common-mode output range to absorb the full amplitude of the common-mode signal coupled onto the cable and therefore prevent clipping.
Figure 81. Transformer with High Output Impedance Secondary
Rev. F | Page 27 of 32
AD8132
FULL-WAVE RECTIFIER
The balanced outputs of the AD8132, along with a couple of Schottky diodes, can create a very high speed, full-wave rectifier. Such circuits are useful for measuring ac voltages and other computational tasks. Figure 82 shows the configuration of such a circuit. Each of the AD8132 outputs drives the anode of an HP2835 Schottky diode. These Schottky diodes were chosen for their high speed operation. At lower frequencies (approximately lower than 10 MHz), a silicon signal diode, such as a 1N4148, can be used. The cathodes of the two diodes are connected together, and this output node is connected to ground by a 100 resistor.
+5V RG1 348 RT1 49.9 RT2 24.9 RG2 348 +5V 10k CR1 HP2835 RF2 348 -5V RL 100 VOUT RF1 348
If there is not enough forward bias (VOUT, cm too low), the lower sharp cusps of the full-wave rectified output waveform are rounded off. In addition, as the frequency increases, there tends to be some rounding of the lower cusps. The forward bias can be increased to yield sharper cusps at higher frequencies. There is not a reliable, entirely quantifiable means to measure the performance of a full-wave rectifier. Since the ideal waveform has periodic sharp discontinuities, it has (mostly even) harmonics that have no upper bound on the frequency. However, for a practical circuit, as the frequency increases, the higher harmonics become attenuated and the sharp cusps that are present at low frequencies become significantly rounded. When running the circuit at a frequency up to 300 MHz, though it stays functional, the major harmonic that remains in the output is the second. This looks like a sine wave at 600 MHz. Figure 83 is an oscilloscope plot of the output when driven by a 100 MHz, 2.5 V p-p input. Sometimes a second harmonic generator is useful for creating a clock to oversample a DAC by a factor of two. If the output of this circuit is run through a low-pass filter, it can be used as a second harmonic generator.
1V
VIN
Figure 82. Full-Wave Rectifier
Operate the diodes such that they are slightly forward-biased when the differential output voltage is 0. For the Schottky diodes, this is approximately 400 mV. The forward biasing is conveniently adjusted by CR1, which, in this circuit, raises and lowers VOUT, cm without creating a differential output voltage. One advantage of this circuit is that the feedback loop is never momentarily opened while the diodes reverse their polarity within the loop. This scheme is sometimes used for full-wave rectifiers that use conventional op amps. These conventional circuits do not work well at frequencies above approximately 1 MHz.
01035-080
100mV
2ns
Figure 83. Full-Wave Rectifier Response with 100 MHz Input
Rev. F | Page 28 of 32
01035-081
AD8132 OUTLINE DIMENSIONS
5.00 (0.1968) 4.80 (0.1890)
8
3.20 3.00 2.80
4.00 (0.1574) 3.80 (0.1497)
8 1
5 4
6.20 (0.2440) 5.80 (0.2284)
3.20 3.00 2.80 PIN 1
5
1
5.15 4.90 4.65
4
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) 0.25 (0.0099) 8 0 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157)
45
0.95 0.85 0.75
0.65 BSC 1.10 MAX 8 0 0.80 0.60 0.40
0.51 (0.0201) 0.31 (0.0122)
0.15 0.00
0.38 0.22 SEATING PLANE
0.23 0.08
COMPLIANT TO JEDEC STANDARDS MS-012-A A CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COPLANARITY 0.10
060506-A
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 84. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches)
Figure 85. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
ORDERING GUIDE
Model AD8132AR AD8132AR-REEL AD8132AR-REEL7 AD8132ARZ1 AD8132ARZ-RL1 AD8132ARZ-R71 AD8132ARM AD8132ARM-REEL AD8132ARM-REEL7 AD8132ARMZ1 AD8132ARMZ-REEL1 AD8132ARMZ-REEL71
1
Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C
Package Description 8-Lead SOIC_N 8-Lead SOIC_N, 13" Tape and Reel 8-Lead SOIC_N, 7" Tape and Reel 8-Lead SOIC_N 8-Lead SOIC_N, 13" Tape and Reel 8-Lead SOIC_N, 7" Tape and Reel 8-Lead MSOP 8-Lead MSOP, 13" Tape and Reel 8-Lead MSOP, 7" Tape and Reel 8-Lead MSOP 8-Lead MSOP, 13" Tape and Reel 8-Lead MSOP, 7" Tape and Reel
Package Option R-8 R-8 R-8 R-8 R-8 R-8 RM-8 RM-8 RM-8 RM-8 RM-8 RM-8
Branding
Ordering Quantity 2,500 1,000 2,500 1,000
HMA HMA HMA HMA# HMA# HMA#
3,000 1,000 3,000 1,000
Z = Pb-free part, # denotes lead-free product may be top or bottom marked.
Rev. F | Page 29 of 32
AD8132 NOTES
Rev. F | Page 30 of 32
AD8132 NOTES
Rev. F | Page 31 of 32
AD8132 NOTES
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C01035-0-11/06(F)
Rev. F | Page 32 of 32

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