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LT1204 4-Input Video Multiplexer with 75MHz Current Feedback Amplifier DESCRIPTIO
The LT1204 is a 4-input video multiplexer designed to drive 75 cables and easily expand into larger routing systems. Wide bandwidth, high slew rate, and low differential gain and phase make the LT1204 ideal for broadcast quality signal routing. Channel separation and disable isolation are greater than 90dB up to 10MHz. The channelto-channel output switching transient is only 40mVP-P, with a 50ns duration, making the transition imperceptible on high quality monitors. A unique feature of the LT1204 is its ability to expand into larger routing matrices. This is accomplished by a patent pending circuit that bootstraps the feedback resistors in the disable condition, raising the true output impedance of the circuit. The effect of this feature is to eliminate cable misterminations in large systems. The large input and output signal levels supported by the LT1204 when operated on 15V supplies make it ideal for general purpose analog signal selection and multiplexing. A shutdown feature reduces the supply current to 1.5mA.
FEATURES
s s s s s s s s s s s s
0.1dB Gain Flatness > 30MHz Channel Separation at 10MHz: 90dB 40mV Switching Transient, Input Referred - 3dB Bandwidth, AV = 2, RL = 150: 75MHz Channel-to-Channel Switching Time: 120ns Easy to Expand for More Inputs Large Input Range: 6V 0.04% Differential Gain, RL = 150 0.06 Differential Phase, RL = 150 High Slew Rate: 1000V/s Output Swing, RL = 400: 13V Wide Supply Range: 5V to 15V
APPLICATI
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S
Broadcast Quality Video Multiplexing Large Matrix Routing Medical Imaging Large Amplitude Signal Multiplexing Programmable Gain Amplifiers
TYPICAL APPLICATI
VIN 0 75 2 GND +1 1 VIN 0 +1
V+
16
15V 75 VOUT -20
+
CFA VO 15 V- 14 3 VIN 1
ALL HOSTILE CROSSTALK (dB)
VIN 1 75
-
-15V
RF 1k
-40
4
GND +1
FB 13 S/D 12
RG 1k
-60
VIN 2 75
5 VIN 2
-80
6
GND LOGIC +1
ENABLE 11 A1 10 A0 9
-100
VIN 3 75
7 VIN 3
-120 1 10 FREQUENCY (MHz) 100
LT1204 * TA02
8 6.8k
REF
LT1204 * TA01
8.2k -15V
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All Hostile Crosstalk
Surface Mount PCB Measurements
VS = 15V VIN 0 = GND VIN 1,2,3 = 0dBm RL = 100
1
LT1204 ABSOLUTE AXI U RATI GS
Operating Temperature Range ............... - 40C to 85C Storage Temperature Range ................ - 65C to 150C Junction Temperature (Note 4) ............................ 150C Lead Temperature (Soldering, 10 sec).................. 300C Supply Voltage ..................................................... 18V - Input Current (Pin 13) .................................... 15mA +Input and Control/Logic Current (Note 1) ........ 50mA Output Short-Circuit Duration (Note 2) ......... Continuous Specified Temperature Range (Note 3) ....... 0C to 70C
PACKAGE/ORDER I FOR ATIO
TOP VIEW VIN 0 GND VIN 1 GND VIN 2 GND VIN 3 REF 1 2 3 4 5 6 7 8 16 V + 15 VO 14 V - 13 FB 12 S/D 11 ENABLE 10 A1 9 A0
ORDER PART NUMBER LT1204CN*
N PACKAGE 16-LEAD PLASTIC DIP
TJMAX = 150C, JA = 70C/W
*See Note 3
ELECTRICAL CHARACTERISTICS
0C TA 70C, 5V VS 15V, VCM = 0V, Pin 8 grounded and pulse tested unless otherwise noted.
SYMBOL VOS PARAMETER Input Offset Voltage Offset Matching Input Offset Voltage Drift IIN+ IIN- en +in -in CIN COUT RIN Positive Input Bias Current Negative Input Bias Current Input Noise Voltage Noninverting Input Noise Current Density Inverting Input Noise Current Density Input Capacitance Output Capacitance Positive Input Resistance, Any Positive Input CONDITIONS Any Positive Input, TA = 25C
q
Between Any Positive Input, VS = 15V Any Positive Input Any Positive Input, TA = 25C
TA = 25C
q
f = 1kHz, RF = 1k, RG = 10, RS = 0 f = 1kHz f = 1kHz Input Selected Input Deselected Disabled, Pin 11 Voltage = 0V VS = 5V, VIN = - 1.5V, 2V, TA = 25C VS = 15V, VIN = 5V
q
2
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TOP VIEW VIN 0 1 GND 2 VIN 1 3 GND 4 VIN 2 5 GND 6 VIN 3 7 REF 8 S PACKAGE 16-LEAD PLASTIC SOL
TJMAX = 150C, JA = 90C/W
16 V + 15 VO 14 V - 13 FB 12 S/D 11 ENABLE 10 A1 9 A0
ORDER PART NUMBER LT1204CS*
MIN
TYP 5
MAX 14 16 5 8 10 50 75
UNITS mV mV mV V/C A A A A nV/Hz pA/Hz pA/Hz pF pF pF M M
q q q
0.5 40 3 10 7 1.5 40 3.0 3.5 8 5 4 20 20
LT1204
0C TA 70C, 5V VS 15V, VCM = 0V, Pin 8 grounded and pulse tested unless otherwise noted.
SYMBOL PARAMETER Input Voltage Range, Any Positive Input CONDITIONS VS = 5V, TA = 25C VS = 15V VS = 15V, Pin 8 Voltage = - 5V CMRR Common-Mode Rejection Ratio Negative Input Current Common-Mode Rejection PSRR AVOL ROL VOUT Power Supply Rejection Ratio Negative Input Current Power Supply Rejection Large-Signal Voltage Gain Transresistance VO /IIN- Output Voltage Swing VS = 5V, VCM = - 1.5V, 2V, TA = 25C VS = 15V, VCM = 5V VS = 5V, VCM = - 1.5V, 2V, TA = 25C VS = 15V, VCM = 5V VS = 4.5V to 15V VS = 4.5V to 15V VS = 15V, VOUT = 10V, RL = 1k VS = 5V, VOUT = 2V, RL = 150 VS = 15V, VOUT = 10V, RL = 1k VS = 5V, VOUT = 2V, RL = 150 VS = 15V, RL = 400, TA = 25C
q q q q q q q q q q q
ELECTRICAL CHARACTERISTICS
MIN 2.0 - 1.5 5.0 3.75 48 48
TYP 2.5 - 2.0 6.0 4.0 55 58 0.05 0.05
MAX
UNITS V V V V dB dB
1 1 5
A/V A/V dB A/V dB dB k k V V V V
60 57 57 115 115 12 10 3.0 2.5 35
76 0.5 73 66 310 210 13.5 3.7 55 19 19 1.5 125 24 24 3.5
VS = 5V, RL = 150, TA = 25C
q
IOUT IS
Output Current Supply Current (Note 5)
RL = 0, TA = 25C Pin 11 = 5V Pin 11 = 0V Pin 12 = 0V VS = 15V, Pin 11 = 0V, VO = 5V, RF = RG = 1k VS = 15V, Pin 11 = 0V, VO = 5V, RF = 2k, RG = 222
q q q q q
mA mA mA mA k k
Disabled Output Resistance
14 8
25 20
DIGITAL I PUT CHARACTERISTICS
SYMBOL VIL VIH IIL IIH PARAMETER Input Low Voltage Input High Voltage Input Low Current Input High Current Enable Low Input Current Enable High Input Current IS/D tsel tdis ten tS/D Shutdown Input Current Channel-to-Channel Select Time (Note 6) Disable Time (Note 7) Enable Time (Note 8) Shutdown Assert or Release Time (Note 9)
0C TA 70C, VS = 15V, RF = 2k, RG = 220, RL = 400 unless otherwise noted.
CONDITIONS Pins 9, 10, 11, 12 Pins 9, 10, 11, 12 Pins 9, 10 Voltage = 0V Pins 9, 10 Voltage = 5V Pin 11 Voltage = 0V Pin 11 Voltage = 5V Pin 12 Voltage 0V VS/D 5V Pin 8 Voltage = - 5V, TA = 25C Pin 8 Voltage = - 5V, TA = 25C Pin 8 Voltage = - 5V, TA = 25C Pin 8 Voltage = - 5V, TA = 25C
q q q q q q q
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MIN 2
TYP
MAX 0.8
UNITS V V A nA A A A ns ns ns s
1.5 10 4.5 200 20 120 40 110 1.4
6 150 15 300 80 240 100 200 3.4
3
LT1204
AC CHARACTERISTICS
SYMBOL t r , tf SR tS PARAMETER Small-Signal Rise and Fall Time Slew Rate (Note 10) Channel Select Output Transient Settling Time All Hostile Crosstalk (Note 11) Disable Crosstalk (Note 11) Shutdown Crosstalk (Note 11) All Hostile Crosstalk (Note 11) Disable Crosstalk (Note 11) Shutdown Crosstalk (Note 11) Differential Gain (Note 12) Differential Phase (Note 12)
TA = 25C, VS = 15V, RF = RG = 1k, unless otherwise noted.
CONDITIONS RL = 150, VOUT = 125mV RL = 400 All VIN = 0V, RL = 400, Input Referred 0.1%, VOUT = 10V, RL = 1k SO PCB #028, RL = 100, RS = 10 SO PCB #028, Pin 11 Voltage = 0V, RL = 100, RS = 50 SO PCB #028, Pin 12 Voltage = 0V, RL = 100, RS = 50 P-DIP PCB #029, RL = 100, RS = 10 P-DIP PCB #029, Pin 11 Voltage = 0V, RL = 100, RS = 50 P-DIP PCB #029, Pin 12 Voltage = 0V, RL = 100, RS = 50 VS = 15V, RL = 150 VS = 5V, RL = 150 VS = 15V, RL = 150 VS = 5V, RL = 150 500 MIN TYP 5.6 1000 40 70 92 95 92 76 81 76 0.04 0.04 0.06 0.12 MAX UNITS ns V/s mV ns dB dB dB dB dB dB % % DEG DEG
The q denotes specifications which apply over the specified operating temperature range. Note 1: Analog and digital inputs (Pins 1, 3, 5, 7, 9, 10, 11 and 12) are protected against ESD and overvoltage with internal SCRs. For inputs < 6V the SCR will not fire, voltages above 6V will fire the SCRs and the DC current should be limited to 50mA. To turn off the SCR the pin voltage must be reduced to less than 2V or the current reduced to less than 10mA. Note 2: A heat sink may be required depending on the power supply voltage. Note 3: Commercial grade parts are designed to operate over the temperature range of - 40C to 85C but are neither tested nor guaranteed beyond 0C to 70C. Industrial grade parts specified and tested over - 40C to 85C are available on special request. Consult factory. Note 4: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formulas: LT1204CN: TJ = TA + (PD x 70C/W) LT1204CS: TJ = TA + (PD x 90C/W) Note 5: The supply current of the LT1204 has a negative temperature coefficient. For more information see Typical Performance Characteristics. Note 6: Apply 0.5V DC to Pin 1 and measure the time for the appearance of 5V at Pin 15 when Pin 9 goes from 5V to 0V. Pin 10 Voltage = 0V. Apply 0.5V DC to Pin 3 and measure the time for the appearance of 5V at Pin 15 when Pin 9 goes from 0V to 5V. Pin 10 Voltage = 0V. Apply 0.5V DC to Pin 5 and measure the time for the
appearance of 5V at Pin 15 when Pin 9 goes from 5V to 0V. Pin 10 Voltage = 5V. Apply 0.5V DC to Pin 7 and measure the time for the appearance of 5V at Pin 15 when Pin 9 goes from 0V to 5V. Pin 10 Voltage = 5V. Note 7: Apply 0.5V DC to Pin 1 and measure the time for the disappearance of 5V at Pin 15 when Pin 11 goes from 5V to 0V. Pins 9 and 10 are at 0V. Note 8: Apply 0.5V DC to Pin 1 and measure the time for the appearance of 5V at Pin 15 when Pin 11 goes from 0V to 5V. Pins 9 and 10 are at 0V. Above a 1MHz toggle rate, ten reduces. Note 9: Apply 0.5V DC at Pin 1 and measure the time for the appearance of 5V at Pin 15 when Pin 12 goes from 0V to 5V. Pins 9 and 10 are at 0V. Then measure the time for the disappearance of 5V DC to 500mV at Pin 15 when Pin 12 goes from 5V to 0V. Note 10: Slew rate is measured at 5V on a 10V output signal while operating on 15V supplies with RF = 2k, RG = 220 and RL = 400. Note 11: VIN = 0dBm (0.223VRMS) at 10MHz on any 3 inputs with the 4th input selected. For Disable crosstalk and Shutdown crosstalk all 4 inputs are driven simultaneously. A 6dB output attenuator is formed by a 50 series output resistor and the 50 input impedance of the HP4195A Network Analyzer. RF = RG = 1k. Note 12: Differential Gain and Phase are measured using a Tektronix TSG120 YC/NTSC signal generator and a Tektronix 1780R Video Measurement Set. The resolution of this equipment is 0.1% and 0.1. Five identical MUXs were cascaded giving an effective resolution of 0.02% and 0.02.
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LT1204
TYPICAL AC PERFOR A CE
VS (V) 15 12 5 15 12 5V 15 12 5 AV 1 1 1 2 2 2 10 10 10 RL () 150 1k 150 1k 150 1k 150 1k 150 1k 150 1k 150 1k 150 1k 150 1k RF () 1.1k 1.6k 976 1.3k 665 866 787 887 750 845 590 649 866 1k 825 931 665 750
TRUTH TABLE
A1 0 0 1 1 X X A0 0 1 0 1 X X ENABLE 1 1 1 1 0 X SHUTDOWN 1 1 1 1 1 0 CHANNEL SELECTED VIN 0 VIN 1 VIN 2 VIN 3 High Z Output Off
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Measurements taken from SO Demonstration Board #028.
RG () None None None None None None 787 887 750 845 590 649 95.3 110 90.9 100 73.2 82.5 SMALL SIGNAL - 3dB BW (MHz) 88.5 95.6 82.6 90.2 65.5 68.2 75.7 82.2 71.9 77.5 58.0 62.1 44.3 47.4 43.5 46.3 37.2 39.3 SMALL SIGNAL 0.1dB BW (MHz) 48.3 65.8 49.1 63.6 43.6 42.1 45.8 61.3 45.0 52.1 32.4 42.7 28.7 30.9 27.2 32.1 22.1 27.8 SMALL SIGNAL PEAKING (dB) 0.1 0 0.1 0.1 0.1 0.1 0 0.1 0 0 0 0.1 0.1 0.1 0 0.1 0 0.1
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LT1204
TYPICAL PERFOR A CE CHARACTERISTICS
12V Frequency Response, AV = 1
4 3 2 1 PHASE VS = 12V RL = 150 RF = 976 0 -20 -40 -60
GAIN (dB)
GAIN (dB)
0 -1 -2 -3 -4 -5 -6 1M 10M 100M FREQUENCY (Hz) 1G
LT1204 * TPC01
12V Frequency Response, AV = 2
10 9 8 7
GAIN (dB)
PHASE
GAIN (dB)
6 5 4 3 2 1 0 1M 10M 100M FREQUENCY (Hz) 1G
LT1204 * TPC02
12V Frequency Response, AV = 10
24 23 22 21
GAIN (dB)
PHASE
GAIN (dB)
20 19 18 17 16 15 14 1M 10M 100M FREQUENCY (Hz) 1G
LT1204 * TPC03
6
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GAIN
5V Frequency Response, AV = 1
4 3 2 1
PHASE (DEG)
0 PHASE VS = 5V RL = 150 RF = 655 -20 -40 -60
PHASE (DEG)
-80 -100 -120 -140 -160 -180 -200
0 -1 -2 -3 -4 -5 -6 1M 10M 100M FREQUENCY (Hz) 1G
LT1204 * TPC04
-80 GAIN -100 -120 -140 -160 -180 -200
5V Frequency Response, AV = 2
0
10 9 8 7
PHASE (DEG)
0 VS = 5V RL = 150 RF = 590 RG = 590 -20 -40 -60
VS = 12V RL = 150 RF = 750 RG = 750
-20 -40 -60 -80
PHASE
PHASE (DEG)
6 5 4 3 2 1 0 1M 10M 100M FREQUENCY (Hz) 1G
LT1204 * TPC05
-80 GAIN -100 -120 -140 -160 -180 -200
GAIN
-100 -120 -140 -160 -180 -200
5V Frequency Response, AV = 10
24 23 22 21 PHASE VS = 5V RL = 150 RF = 665 RG = 73.2 0 -20 -40 -60
0 VS = 12V RL = 150 RF = 825 RG = 90.9 -20 -40 -60
PHASE (DEG)
PHASE (DEG)
-80 GAIN -100 -120 -140 -160 -180 -200
20 19 18 17 16 15 14 1M 10M 100M FREQUENCY (Hz) 1G
LT1204 * TPC06
-80 GAIN -100 -120 -140 -160 -180 -200
LT1204
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Undistorted Output vs Frequency
25 VS = 15V RL = 1k RFB = 1k
CAPACITIVE LOAD (pF)
20
1000
15 AV = 10
TOTAL HARMONIC DISTORTION (%)
OUTPUT VOLTAGE (VP-P)
10 AV = 1
5
AV = 2
0 1 10 FREQUENCY (MHz) 100
LT1204 * TPC07
15V All Hostile Crosstalk vs Frequency
-20 -30
ALL HOSTILE CROSSTALK (dB)
ALL HOSTILE CROSSTALK (dB)
ALL HOSTILE CROSSTALK (dB)
-40 -50 -60 -70 -80 -90 -100 -110 -120 1
VS = 15V RL = 100 RF = RG = 1k RS = 0 DEMO PCB #028
CH1 CH4 CH3
CH2
10 FREQUENCY (MHz)
Disable and Shutdown Crosstalk vs Frequency
-20 -30
-40 -50 -60 -70 -80 -90 -100 -110 -120 1
SPOT NOISE (nV/Hz or pA/Hz)
ALL HOSTILE CROSSTALK (dB)
OUTPUT IMPEDANCE ()
VS = 15V RL = 100 RF = RG = 1k RS = 50 DEMO PCB #028 ALL CHANNELS DRIVEN
SHUTDOWN CROSSTALK
DISABLE CROSSTALK
10 FREQUENCY (MHz)
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LT1204 * TPC10
LT1204 * TPC13
Maximum Capacitive Load vs Feedback Resistor
10000 RL = 1k AV = 2 TA = 25C 5dB PEAKING 0.1
Total Harmonic Distortion vs Frequency
VS = 15V RL = 400 RF = RG = 1k
0.01
VO = 6VRMS
VS = 5V 100
VS = 15V
VO = 1VRMS
10 0 2 1 FEEDBACK RESISTOR (k) 3
LT1204 * TPC08
0.001 10
100
1k 10k FREQUENCY (Hz)
100k
LT1204 * TPC09
5V All Hostile Crosstalk vs Frequency
-20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 100 1 10 FREQUENCY (MHz) 100
LT1204 * TPC11
All Hostile Crosstalk vs Frequency, Various Source Resistance
-30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 1 10 FREQUENCY (MHz) 100
LT1204 * TPC12
VS = 5V RL = 100 RF = RG = 1k RS = 0 DEMO PCB #028
VS = 15V RL = 100 RF = RG = 1k DEMO PCB #028
ANY CHANNEL
RS = 75 RS = 37.5 RS = 10 RS = 0
Spot Noise Voltage and Current vs Frequency
100 -in
100 1000
Amplifier Output Impedance vs Frequency
VS = 15V
10
en
10 RFB = RG = 2k 1 RFB = RG = 750
+in 1
100
10
100
1k 10k FREQUENCY (Hz)
100k
LT1204 * TPC14
0.1 10k
100k
1M 10M FREQUENCY (Hz)
100M
LT1204 * TPC15
7
LT1204
TYPICAL PERFOR A CE CHARACTERISTICS
Output Disable V-I Characteristic
100
DISABLED OUTPUT IMPEDANCE (k)
200 150
VS = 15V RF = RG = 1k
OUTPUT CURRENT (A)
100 50 0 -50 SLOPE = 1/18k
10
VOLTAGE ON PIN 8 (V)
-100 -150 -200
-5 -4 -3 -2 -1 0 1 2 3 OUTPUT VOLTAGE (V)
Input Voltage Range vs Pin 8 Voltage
6
INPUT VOLTAGE RANGE (V)
INPUT VOLTAGE RANGE (V)
4 2 0 -2 -4 -6 0 -1 -2 -3 -4 -5 -6 -7 VOLTAGE ON PIN 8 (V) -8 -9 -55C, 25C, 125C
4 2 0
25C -55C 125C 125C
POWER SUPPLY REFECTION (dB)
VS = 15V AV = 1
Output Saturation Voltage vs Temperature
V+
OUTPUT SHORT-CIRCUIT CURRENT (mA)
RL =
OUTPUT SATURATION VOLTAGE (V)
-0.5 -1.0
60
OUTPUT STEP (V)
1.0 0.5 V- -50 -25
50 25 75 0 TEMPERATURE (C)
8
UW
4 5
LT1204 * TPC16
Disabled Output Impedance vs Frequency
0 VS = 15V RF = RG = 1k -1 -2 -3 -4 -5 -6 -7 0 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M -8
Maximum Channel Switching Rate vs Pin 8 Voltage
VIN = 1VDC RL = 100 RFB = RG = 1k
1
1
1.5 2 3 3.5 2.5 CHANNEL SWITCHING RATE (MHz)
4
LT1204 * TPC16
LT1204 * TPC17
Input Voltage Range vs Supply Voltage
70 6 PIN 8 = 0V 60 50
Power Supply Rejection vs Frequency
VS = 15V RFB = RG = 1k POSITIVE 40 NEGATIVE 30 20 10 0 -10 10k
-2 -4 -6 2
-55C
25C
4
12 6 10 8 SUPPLY VOLTAGE (V)
14
16
100k
1M 10M FREQUENCY (Hz)
100M
LT1204 * TPC18
LT1204 * TPC19
LTC1204 * TPC20
Output Short-Circuit Current vs Temperature
80
Settling Time to 10mV vs Output Step
10 8 VS = 15V RF = RG = 1k
70
6 4 2 0 -2 -4 -6 -8
50
40
100
125
30 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
-10
30
40
60 50 SETTLING TIME (ns)
70
80
LT1204 * TPC21
LT1204 * TPC22
LT1204 * TPC23
LT1204
TYPICAL PERFOR A CE CHARACTERISTICS
Settling Time to 1mV vs Output Step
10 8 6 VS = 15V RF = RG = 1k
SUPPLY CURRENT (mA)
OUTPUT STEP (V)
4 2 0 -2 -4 -6 -8 -10 0 2 4 6 8 10 12 14 16 18 20 SETTLING TIME (s)
LT1204 * TPC24
19 18 17 16 15 14 13 12 0 2 4
SUPPLY CURRENT (mA)
APPLICATI
Logic Inputs
S I FOR ATIO
The logic inputs of the LT1204 are compatible with all 5V logic. All pins have ESD protection (> 2kV), and shorting them to 12V or 15V will cause excessive currents to flow. Limit the current to less than 50mA when driving the logic above 6V. Power Supplies The LT1204 will operate from 5V (10V total) to 15V (30V total) and is specified over this range. It is not necessary to use equal value supplies, however, the offset voltage and inverting input bias current will change. The offset voltage changes about 600V per volt of supply mismatch. The inverting bias current changes about 2.5A per volt of supply mismatch. The power supplies should be bypassed with quality tantalum capacitors. Feedback Resistor Selection The small-signal bandwidth of the LT1204 is set by the external feedback resistors and internal junction capacitors. As a result the bandwidth is a function of the supply voltage, the value of the feedback resistor, the closedloop gain and the load resistor. These effects are outlined in the resistor selection guide of the Typical AC Performance table. Bandwidths range as high as 95MHz and are
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Enabled Supply Current vs Supply Voltage
22 21 20 -55C 22 21 20 19 18 17 16 15 2 1 0 6 8 10 12 14 SUPPLY VOLTAGE (V) 16 18
Disabled and Shutdown Supply Current vs Supply Voltage
125C
25C
25C -55C
125C
-55C, 25C, 125C
IS/D
0
2
4
6 8 10 12 14 SUPPLY VOLTAGE (V)
16
18
LT1204 * TPC25
LT1204 * TPC26
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specified over a very wide range of conditions. An advantage of the current feedback topology used in the LT1204 is well-controlled frequency response. In all cases of the performance table the peaking is 0.1dB or less. If more peaking can be tolerated, larger bandwidths can be obtained by lowering the feedback resistor. For gains of 2 or less, the 0.1dB bandwidth is greater than 30MHz for all loads and supply voltages. At high gains (low values of RG) the disabled output resistance drops slightly due to loading of the internal buffer amplifier as discussed in Multiplexer Expansion.
Small-Signal Rise Time, AV = 2
VS = 15V RL = 150
RF = 1k RG = 1k
LT1204 * AI01
9
LT1204
APPLICATI
S I FOR ATIO
Capacitance on the Inverting Input Current feedback amplifiers require resistive feedback from the output to the inverting input for stable operation. Take care to minimize the stray capacitance between the output and the inverting input. Capacitance on the inverting input to ground will cause peaking in the frequency response and overshoot in the transient response. Capacitive Loads The LT1204 can drive capacitive loads directly when the proper value of feedback resistor is used. The graph of Maximum Capacitive Load vs Feedback Resistor should be used to select the appropriate value. The value shown is for 5dB peaking when driving a 1k load at a gain of 2. This is a worst case condition. The amplifier is more stable at higher gains and driving heavier loads. Alternatively, a small resistor (10 to 20) can be put in series with the output to isolate the capacitive load from the amplifier output. This has the advantage that the amplifier bandwidth is only reduced when the capacitive load is present. The disadvantage is that the gain is a function of load resistance. Slew Rate The slew rate of the current feedback amplifier on the LT1204 is not independent of the amplifier gain the way slew rate is in a traditional op amp. This is because both the input and the output stage have slew rate limitations. In high gain settings the signal amplitude between the negative input and any driven positive input is small and the overall slew rate is that of the output stage. For gains less than 10, the overall slew rate is limited by the input stage. The input slew rate of the LT1204 is approximately 135V/ s and is set by internal currents and capacitances. The output slew rate is set by the value of the feedback resistors and the internal capacitances. At a gain of 10 with a 1k feedback resistor and 15 supplies, the output slew rate is typically 1000V/s. Larger feedback resistors will reduce the slew rate as will lower supply voltages, similar to the way the bandwidth is reduced. The graph, Maximum Undistorted Output vs Frequency, relates the slew rate limitations to sinusoidal inputs for various gain configurations.
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Large-Signal Transient Response
VS = 15V AV = 2 RF = 1k RG = 1k RL = 400
LT1204 * AI02
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Large-Signal Transient Response
VS = 15V AV = 10
RF = 910 RG = 100 RL = 400
LT1204 * AI03
Switching Characteristics and Pin 8 Switching between channels is a "make-before-break" condition where both inputs are on momentarily. The buffers isolate the inputs when the "make-before-break" switching occurs. The input with the largest positive voltage determines the output level. If both inputs are equal, there is only a 40mV error at the input of the CFA during the transition. The reference adjust (pin 8) allows the user to trade off positive input voltage range for switching time. For example, on 15V supplies, setting the voltage on pin 8 to - 6.8V reduces the switching transient to a 50ns duration, and reduces the positive input range from 6V to 2.35V. The negative input range remains unchanged at - 6V. When switching video "in picture," this short transient is imperceptible even on high quality
LT1204
APPLICATI
S I FOR ATIO
monitors. The reference pin has no effect when the LT1204 is operating on 5V, and should be grounded. On supply voltages above 8V, the range of voltages for pin 8 should be between - 6.5V and - 7.5V. Reducing pin 8 voltage below - 7.5V turns "on" the "off" tee switch, and the isolation between channels is lost.
Channel-to-Channel Switching
A0 PIN 9
VOUT PIN 15
VIN 0 AND VIN 1 CONNECTED TO 2MHz SINEWAVE PIN 8 VOLTAGE = -6.8V, VS = 15V
LT1204 * AI04
Transient at Input Buffer
A0 PIN 9
VIN 0 PIN 1
SWITCHING BETWEEN VIN 0 AND VIN 1 RS = 50, VREF = - 6.8V, VS 15V
LT1204 * AI05
Competitive video multiplexers built in CMOS are bidirectional and suffer from poor output-to-input isolation and cause transients to feed to the inputs. CMOS MUXs have been built with "break-before-make" switches to eliminate the talking between channels, but these suffer from output glitches large enough to interfere with sync circuitry. Multiplexers built on older bipolar processes that switch lateral PNP transistors take several s to settle and blur the transition between pictures.
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Competitive MUXs
CMOS MUX BIPOLAR MUX VIN 0 AND VIN 1 CONNECTED TO 2MHz SINEWAVE
LT1204 * AI06
W
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Crosstalk The crosstalk, or more accurately all hostile crosstalk, is measured by driving a signal into any 3 of the 4 inputs and selecting the 4th input with the logic control. This 4th input is either shorted to ground or terminated in an impedance. All hostile crosstalk is defined as the ratio in dB of the signal at the output of the CFA to the signal on the 3 driven inputs, and is input referred. Disable crosstalk is measured with all 4 inputs driven and the part disabled. Crosstalk is critical in many applications where video multiplexers are used. In professional video systems a crosstalk figure of - 72dB is a desirable specification. The key to the outstanding crosstalk performance of the LT1204 is the use of tee switches (see Figure 1). When the tee switch is on (Q2 off) Q1 and Q3 are a pair of emitter followers with excellent AC response for driving the CFA. When the decoder turns off the tee switch (Q2 on) the
V+ I1 Q3 VIN 0 TO LOGIC V- Q1 Q2
+
CFA
VOUT
-
RF I2 -V FB RG
LT1204 * F01
Figure 1. Tee Switch
11
LT1204
APPLICATI
S I FOR ATIO
emitter base junctions of Q1 and Q3 become reverse biased while Q2 emitter absorbs current from I1. Not only do the reverse biased emitter base junctions provide good isolation, but any signal at VIN 0 coupling to Q1 emitter is further attenuated by the shunt impedance of Q2 emitter. Current from I2 is routed to any on switch. Crosstalk performance is a strong function of the IC package, the PC board layout as well as the IC design. The die layout utilizes grounds between each input to isolate adjacent channels, while the output and feedback pins are on opposite sides of the die from the input. The layout of a PC board that is capable of providing -90dB all hostile crosstalk at 10MHz is not trivial. That level corresponds to a 30V output below a 1V input at 10MHz. A demonstration board has been fabricated to show the component and ground placement required to attain these crosstalk numbers. A graph of all hostile crosstalk for both the P-DIP and
All Hostile Crosstalk
-20 VS = 15V VIN 0 = GND VIN 1,2,3 = 0dBm RL = 100 P-DIP DEMO PCB #029
ALL HOSTILE CROSSTALK (dB)
-40
-60
-80 SOL DEMO PCB #028 -100
-120 1 10 FREQUENCY (MHz) 100
LT1204 * AI07
12
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SO packages is shown. It has been found empirically from these PC boards that capacitive coupling across the package of greater than 3fF (0.003pF) will diminish the rejection, and it is recommended that this proven layout be copied into designs. The key to the success of the SOL PC board #028 is the use of a ground plane guard around pin 13, the feedback pin.
P-DIP PC Board #029, Component Side
GND V- V+ VOUT VIN0 C2 + U1 VIN1 RF C4 R6 VIN2 R2 S/D R1 (408) 432-1900 LT1204 VIDEO MUX DEMONSTRATION BOARD R3 R0 R1 + C3 C1 ENABLE RO VIN3 REF
LT1204 * AI09
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LT1204
APPLICATI S I FOR ATIO U W U UO
SOL PC Board #028, Component Side
GND
V-
V+ VOUT
VIN0 ENABLE C4 VIN1 U1 RF RG R2 C3 A0 C2 C1 RO R3 A1
R1 VIN2
S/D (408) 432-1900 LT1204 VIDEO MUX DEMONSTRATION BOARD VIN3 REF
LT1204 * AI08
13
LT1204
APPLICATI
S I FOR ATIO
Demonstration PC Board Schematic
GND V - V+
VIN 0
1 2
VIN 0 GND VIN 1 GND LT1204 VIN 2 GND VIN 3 REF
4 VIN 2 5 6 VIN 3 7 8
FB S/D ENABLE A1 A0
13 12 11 10 9 R1 10k R2 10k REF
LT1204 * AI10
All Hostile Crosstalk Test Setup*
HP4195A NETWORK ANALYZER OSC 50 REF 50 VIN 50
50 SPLITTER 10 1 2 3 4 5 6 7 8 50 16 15 14 13 12 11 10 9 *SEE PC BOARD LAYOUT 10k -15V 1k 1k
VIN 0 GND VIN 1 GND LT1204 VIN 2 GND VIN 3 REF
V+ VO V- FB S/D ENABLE A1 A0
15V 50
10 1 2 3 50 4 5 50 6 7 50
LT1204 * AI11
LT1204 * AI12
14
+
VIN 1
3
U
V+ VO V- 16 15 14 C3 4.7F C4 0.1F RF 750
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+
C1 4.7F
C2 0.1F
RO 75
RG 750
R3 10k
SHUTDOWN ENABLE A1 A0 RESISTORS R1, R2 AND R3 ARE PULL-DOWN AND PULL-UP RESISTORS FOR THE LOGIC AND ENABLE PINS. THEY MAY BE OMITTED IF THE LT1204 IS DRIVEN FROM TTL LEVELS OR FROM 5V CMOS.
Alternate All Hostile Crosstalk Setup*
HP4195A NETWORK ANALYZER OSC 50 REF 50 VIN 50
50 SPLITTER
VIN 0 GND VIN 1 GND LT1204 VIN 2 GND VIN 3 REF
V+ VO V- FB S/D ENABLE A1 A0
16 15 14 13 12 11 10 9 -15V
15V 50
1k 1k
10k
8
*SEE PC BOARD LAYOUT
LT1204
APPLICATI
S I FOR ATIO
Multiplexer Expansion Pin 11 and Pin 12 To expand the number of MUX inputs, LT1204s can be paralleled by shorting their outputs together. The multiplexer disable logic has been designed to prevent shootthrough current when two or more amplifiers have their outputs shorted together. (Shoot-through current is a spike of power supply current caused by both amplifiers being on at once.)
Monitoring Supply Current Spikes
V+ TEK CT-1 1 3 5 7 13 TO SCOPE
+ + + + -
1k
16 LT1204 EN 11 14 15 75
VIN 1 TEE SWITCH
V-
1k 74HC04 5V O OSCILLATOR 1 3 5 7 13 V+ 16 11 EN LT1204 15 75 75
V-
+ + + + -
14 V - 1k
LT1204 * AI13
1k
Timing and Supply Current Waveforms
74HC04 OUTPUT 5V/DIV OSCILLATOR 5V/DIV
VOUT 1V/DIV
IS 10mA/DIV
LT1204 * AI14
U
The multiplexer uses a circuit to ensure the disabled amplifiers do not load or alter the cable termination. When the LT1204 is disabled (pin 11 low) the output stage is turned off and an active buffer senses the output and drives the feedback pin to the CFA (Figure 2). This bootstraps the feedback resistors and raises the true output impedance of the circuit. For the condition where RF = RG = 1k, the Disable Output Resistance is typically raised to 25k and drops to 20k for AV = 10, RF = 2k and RG = 222 due to loading of the feedback buffer. Operating the Disable feature with RG < 100 is not recommended.
VIN 0 TEE SWITCH AV = +1
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+
VIN 2 TEE SWITCH CFA "OFF"
VOUT
-
VIN 3 TEE SWITCH FB RG RF
75
75
CABLE
75 LT1204 "ON"
LT1204 * F02
Figure 2. Active Buffer Drives FB Pin 13
A shutdown feature (pin 12 low) reduces the supply current to 1.5mA and lowers the power dissipation when the LT1204 is not in use. If the part is shut down, the bootstrapping is inoperative and the feedback resistors will load the output. If the CFA is operated at a gain of +1, however, the feedback resistor will not load the output even in shutdown because there is no resistive path to ground, but there will be a - 6dB loss through the cable system. A frequency response plot shows the effect of using the disable feature versus using the shutdown feature. In this example 4 LT1204s were connected together at their outputs forming a 16-to-1 MUX. The plot shows the effect of the bootstrapping circuit that eliminates the
15
LT1204
APPLICATI S I FOR ATIO
improper cable termination due to feedback resistors loading the cable. The limit to the number of expanded inputs is set by the acceptable error budget of the system.
16-to-1 MUX Response Using Disable vs Shutdown
4 VS = 15V RL = 100 RF = RG = 1k DISABLE SHUTDOWN -2
2
GAIN (dB)
0
-4
-6 1 10 FREQUENCY (MHz) 100
LT1204 * AI16
16-to-1 Multiplexer All Hostile Crosstalk
-20 VS = 15V RL = 100 RF = RG = 1k RS = 0
ALL HOSTILE CROSSTALK (dB)
-40
-60 SHUTDOWN CROSSTALK -80 DISABLE CROSSTALK
75 1V REQ VOUT 75
LT1204 * AI18
-100
-120 1 10 FREQUENCY (MHz) 100
LT1204 * AI17
16
U
For a 64-to-1 MUX we need 16 LT1204s. The equivalent load resistance due to the feedback resistor REQ in Disable is 25k/15 = 1.67k. See Figure 3.
VO = 75REQ , V = 0.489V 75(75) + 150REQ O
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This voltage represents a 2.1% loading error. If the shutdown feature is used instead of the disable feature, then the LT1204 could expand to only an 8-to-1 MUX for the same error. As a practical matter the gain error at frequency is also set by capacitive loading. The disabled output capacitance of the LT1204 is about 8pF, and in the case of 16 LT1204s, it would represent a 128pF load. The combination of 1.67k and 128pF correspond to about a 0.3dB roll-off at 5MHz.
OFF 75 LT1204 CABLE ON LT1204 1V 75
VOUT 75
Figure 3. Equivalent Loading Schematic
LT1204
TYPICAL APPLICATI
Programable Gain Amplifier (PGA) Two LT1204s and seven resistors make a Programable Gain Amplifier with a 128-to-1 gain range. The gain is proportional to 2N where N is the 3-bit binary value of the select logic. An input attenuator alters the input signal
Programable Gain Amplifier Accepts Inputs from 62.5mVP-P to 8VP-P
VIN = 62.5mVP-P TO 8VP-P 499 249 124 1 3 5 7 13
+ + LT1204 + #1 + -
1.5k
124
100 VOUT = 1VP-P 1 3 5 7 13
+ + + LT1204 + #2 -
1.5k
LT1204 * AI19
TWISTED PAIR 68
CABLE 1k* 1k* 1k
*OPTIONAL
UO
S
by 1, 0.5, 0.25 and 0.125 to form an amplifier with a gain of 16, 8, 4, 2, when LT1204 #1 is selected. LT1204 #2 is connected to the same attenuator. When enabled (LT1204 #1 disabled), it results in gain of 1, 0.5, 0.25 and 0.125. The wide input common-mode range of the LT1204 is needed to accept inputs of 8VP-P. 4-Input Differential Receiver LT1204s can be connected inverting and noninverting as shown to make a 4-input differential receiver. The receiver can be used to convert differential signals sent over a low cost twisted-pair to a single-ended output or used in video loop-thru connections. The logic inputs A0 and A1 are tied together because the same channels are selected on each LT1204. By using the Disable feature, the number of differential inputs can be increased by adding pairs of LT1204s and tying the outputs of the noninverting LT1204s (#1) together. Switching transients are reduced in this receiver because the transient from LT1204 #2 subtracted from the transient of LT1204 #1.
4-Input Differential Receiver
A0 A1 S/D EN
IN 1 IN 2 IN 3 IN 4
+A0 + A1 S/D + LT1204 EN + #1 -
1k
75 VOUT 75
68
-IN 1 -IN 2 1k* 1k* -IN 3 -IN 4
+A0 + A1 S/D + LT1204 EN + #2 -
1k
LT1204 * AI20
1k
17
LT1204
TYPICAL APPLICATI
Differential Receiver Switching Waveforms
CABLE OUTPUT
LT1204 #2 OUTPUT
A0 PIN 9
Differential Receiver Response
DIFFERENTIAL RECEIVER RESPONSE (dB)
20 VS = 15V RL = 100 DIFFERENTIAL MODE RESPONSE
0
-20
-40
COMMON-MODE RESPONSE
-60 10k 100k 1M 10M FREQUENCY (Hz) 100M
LT1204 * AI22
VIN 0 VIN 1 75 VIN 2 VIN 3
1k
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+ + + + - + -
S
4-Input Twisted-Pair Driver It is possible to send and receive color composite video signals appreciable distances on a low cost twisted-pair. The cost advantage of this technique is significant. Standard 75 RG-59/U coaxial cable cost between 25 and 50 per foot. PVC twisted-pair is only pennies per foot. Differential signal transmission resists noise because the interference is present as a common-mode signal. The LT1204 can select one of four video cameras for instance, and drive the video signal on to the twisted-pair. The circuit uses an LT1227 current feedback amplifier connected with a gain of - 2, and an LT1204 with a gain of 2. The 47 resistors back-terminate the low cost cable in its characteristic impedance to prevent reflections. The receiver for the differential signal is an LT1193 connected for a gain of +2. Resistors R1, R2 and capacitors C1, C2 are used for cable compensation for loss through the twisted-pair. Alternately, a pair of LT1204s can be used to perform the differential to single-ended conversion.
LT1204 * AI09
4-Input Twisted-Pair Driver/Receiver
LT1204
1k
47
1000 FT OF TWISTED-PAIR 91
+
75
2k
47
- + -
18 680pF 390 300pF 300 200
LT1193
LT1227
300
LT1204 * AI23
LT1204
TYPICAL APPLICATI
Multiburst Pattern Passed Through 1000 Feet of Twisted-Pair, No Cable Compensation
INPUT
PACKAGE DESCRIPTIO
0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
)
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.
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Multiburst Pattern Passed Through 1000 Feet of Twisted-Pair, with Cable Compensation
OUTPUT
INPUT
OUTPUT
LT1204 * AI24
LT1204 * AI25
Dimensions in inches (millimeters) unless otherwise noted.
N Package 16-Lead Plastic DIP
0.770 (19.558) MAX 16 15 14 13 12 11 10 9
0.260 0.010 (6.604 0.254)
1 0.130 0.005 (3.302 0.127)
2
3
4
5
6
7
8
0.045 - 0.065 (1.143 - 1.651)
0.015 (0.381) MIN
0.065 (1.651) TYP
0.125 (3.175) MIN
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
0.018 0.003 (0.457 0.076)
N16 0492
19
LT1204
PACKAGE DESCRIPTIO U
Dimensions in inches (millimeters) unless otherwise noted. S Package 16-Lead Plastic SOL
0.398 - 0.413 (10.109 - 10.490) (NOTE 2) 16 15 14 13 12 11 10 9
NOTE 1
0.394 - 0.419 (10.007 - 10.643)
0.005 (0.127) RAD MIN
0.291 - 0.299 (7.391 - 7.595) (NOTE 2) 0.010 - 0.029 x 45 (0.254 - 0.737)
1
2
3
4
5
6
7
8
0.093 - 0.104 (2.362 - 2.642)
0.037 - 0.045 (0.940 - 1.143)
0 - 8 TYP 0.050 (1.270) TYP
0.009 - 0.013 (0.229 - 0.330)
NOTE 1 0.016 - 0.050 (0.406 - 1.270)
0.004 - 0.012 (0.102 - 0.305)
NOTE: 1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS. 2. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
0.014 - 0.019 (0.356 - 0.482) TYP
SOL16 0392
20
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 1093 10K REV 0 * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1993

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