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CA3280, CA3280A
Data Sheet September 1998 File Number 1174.4
Dual, 9MHz, Operational Transconductance Amplifier (OTA)
The CA3280 and CA3280A types consist of two variable operational amplifiers that are designed to substantially reduce the initial input offset voltage and the offset voltage variation with respect to changes in programming current. This design results in reduced "AGC thump," an objectionable characteristic of many AGC systems. Interdigitation, or crosscoupling, of critical portions of the circuit reduces the amplifier dependence upon thermal and processing variables. The CA3280 has all the generic characteristics of an operational voltage amplifier except that the forward transfer characteristics is best described by transconductance rather than voltage gain, and the output is current, not voltage. The magnitude of the output current is equal to the product of transconductance and the input voltage. This type of operational transconductance amplifier was first introduced in 1969, and it has since gained wide acceptance as a gateable, gain controlled building block for instrumentation and audio applications, such as linearization of transducer outputs, standardization of widely changing signals for data processing, multiplexing, instrumentation amplifiers operating from the nanopower range to high current and high speed comparators. For additional application information on this device and on OTAs in general, please refer to Application Notes: AN6818, AN6668, and AN6077.
Features
* Low Initial Input Offset Voltage: 500V (Max) (CA3280A) * Low Offset Voltage Change vs IABC: <500V (Typ) for All Types * Low Offset Voltage Drift: 5V/oC (Max) (CA3280A) * Excellent Matching of the Two Amplifiers for All Characteristics * Internal Current-Driven Linearizing Diodes Reduce the External Input Current to an Offset Component * Flexible Supply Voltage Range. . . . . . . . . . . 2V to 15V
Applications
* Voltage Controlled Amplifiers * Voltage Controlled Oscillators * Multipliers * Demodulators * Sample and Hold * Instrumentation Amplifiers * Function Generators * Triangle Wave-to-Sine Wave Converters * Comparators * Audio Preamplifier
Pinout
CA3280 (PDIP, CERDIP) TOP VIEW
ID, A1 1 EMITTER, A1 2 IABC, A1 3 V- 4 NC 5 IABC, A2 6 EMITTER, A2 7 ID, A2 8 A2 16 +IN, A1 15 -IN, A1 14 V+, A1 13 OUT, A1 12 OUT, A2 11 V+, A2
Ordering Information
PART NUMBER CA3280AE CA3280E CA3280AF3 TEMP. RANGE (oC) -55 to 125 0 to 70 -55 to 125 PACKAGE 16 Ld PDIP 16 Ld PDIP 16 Ld CERDIP PKG. NO. E16.3 E16.3 F16.3
A1
+
-
+
10 -IN, A2 9 +IN, A2
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 321-724-7143 | Copyright (c) Intersil Corporation 1999
CA3280, CA3280A
.Functional
Diagram
1/2 CA3280 14 11
-
15 10 7 2
+ 16 9 2K 1 8 4 3 6 2K 13 12
2
CA3280, CA3280A
Absolute Maximum Ratings
Supply Voltage (Between V+ and V-). . . . . . . . . . . . . . . . . . . . +36V Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V Input Voltage Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V+ to VInput Current at ID = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100A Amplifier Bias Current (IABC) . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA Output Short Circuit Duration (Note 1). . . . . . . . . . . . . . . . Indefinite Linearizing Diode Bias Current, ID . . . . . . . . . . . . . . . . . . . . . . . 5mA Peak Input Current with Linearizing Diode. . . . . . . . . . . . . . . . . . ID
Thermal Information
Thermal Resistance (Typical, Note 2) JA (oC/W) JC (oC/W) CERDIP Package. . . . . . . . . . . . . . . . . 65 16 PDIP Package . . . . . . . . . . . . . . . . . . . 100 N/A Maximum Junction Temperature (CERDIP Package). . . . . . . . .175oC Maximum Junction Temperature (Plastic Package) . . . . . . . .150oC Maximum Storage Temperature Range . . . . . . . . . . -65oC to 150oC Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300oC
Operating Conditions
Temperature Range CA3280 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0oC to 70oC CA3280A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55oC to 125oC Supply Voltage Range (Typ) . . . . . . . . . . . . . . . . . . . . . 2V to 15V
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES: 1. Short circuit may be applied to ground or to either supply. 2. JA is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications
PARAMETER Input Offset Voltage
For Equipment Design, at TA = 25oC, VSUPPLY = 15V, Unless Otherwise Specified CA3280 SYMBOL VIO TEST CONDITIONS IABC = 1mA IABC = 100A IABC = 10A IABC = 1mA to 10A, TA = Full Temp. Range MIN 12 12 IABC = 5A 12 12 IABC = 100A IABC = 500A 10Hz 1kHz 10kHz -13 -Z 350 -350 3 -3 TYP 0.7 0.8 0.5 5 1.2 13.7 -14.3 13.9 -14.5 20 8 7 0.3 1.8 3 410 -410 4.1 -4.1 MAX 3 3 3 4 1 13 0.7 5 8 650 -650 7 -7 MIN 12.5 -13.3 12.5 -13.5 -13 350 -350 3 -3 CA3280A TYP 0.25 0.8 0.5 3 1.2 13.7 -14.3 13.9 -14.5 20 8 7 0.3 1.8 3 410 -410 4.1 -4.1 MAX 0.5 0.5 0.5 1.5 1 5 13 0.7 5 8 650 -650 7 -7 UNITS mV mV mV mV mV V/oC V V V V V V nV/Hz nV/Hz nV/Hz A A A A A A A
Input Offset Voltage Drift
|VIO|
IABC = 1A to 1mA IABC = 100A, TA = Full Temperature Range
Amplifier Bias Voltage Peak Output Voltage
VABC VOM+ VOMVOM+ VOM-
IABC = 100A IABC = 500mA
Common Mode Input Voltage Range Noise Voltage
VICR eN
Input Offset Current Input Bias Current
IIO IIB
IABC = 500A IABC = 500A IABC = 500A, TA = Full Temperature Range
Peak Output Current
IOM+ IOMIOM+ IOM-
IABC = 500A
Source Sink
IABC = 5A
Source Sink
3
CA3280, CA3280A
Electrical Specifications
PARAMETER Peak Output Current Sink and Source Linearization Diodes Offset Current Dynamic Impedance Diode Network Supply Current Amplifier Supply Current (Per Amplifier) Amplifier Output Leakage Current I+ IOL For Equipment Design, at TA = 25oC, VSUPPLY = 15V, Unless Otherwise Specified (Continued) CA3280 SYMBOL IOM -, IOM+ TEST CONDITIONS IABC = 500A, TA = Full Temperature Range ID = 100A ID = 10A ID = 100A IABC = 100A IABC = 500A IABC = 0, VO = 0V IABC = 0, VO = 30V Common Mode Rejection Ratio Power Supply Rejection Ratio Open Loop Voltage Gain CMRR PSRR AOL IABC = 100A IABC = 100A IABC = 100A, RL = , VO = 20VP-P IABC = 50A, Large Signal IABC = 1mA, Small Signal IABC = 10A f = 1kHz THD fT SR CI CO Output Resistance RO IABC = 100A f = 1kHz, IABC = 1.5mA, RL = 15k, VO = 20VP-P IABC = 1mA, RL = 100 IABC = 1mA IABC = 100A Input Output MIN 350 250 80 86 94 50 0.5 TYP 450 10 0.5 700 400 2 0.015 0.15 100 105 100 100 0.8 16 94 0.4 9 125 4.5 7.5 63 MAX 550 1 800 2.4 0.1 1 1.2 22 MIN 350 250 94 94 94 50 0.5 CA3280A TYP 450 10 0.5 700 400 2 0.015 0.15 100 105 100 100 0.8 16 94 0.4 9 125 4.5 7.5 63 MAX 550 1 800 2.4 0.1 1 1.2 22 UNITS A A A A mA nA nA dB dB dB kV/V mS mS M dB % MHz V/s pF pF M
Forward Transconductance
GM gM
Input Resistance Channel Separation Open Loop Total Harmonic Distortion Bandwidth Slew Rate, Open Loop Capacitance
RI
Test Circuits and Waveforms
V+ +30V INPUT 16 30V 0V I TEST POINT 14 15 14 + 1/2 CA3280 0.1F OUTPUT 13 3 30k V30k 1k V+ 10k
1/2 CA3280 + 4 1 3 13 15
4
16
1k
0.1 F
FIGURE 1. LEAKAGE CURRENT TEST CIRCUIT
FIGURE 2. CHANNEL SEPARATION TEST CIRCUIT
4
CA3280, CA3280A Test Circuits and Waveforms
(Continued)
V+ 15V 14 10k 16 1/2 CA3280 10k 15 4 3 1 V-15V IABC IDIODE VIN 1k IOUT 13
IABC = 650A, ID = 200A; Vertical = 200A/Div.; Horizontal = 1V/Div.
FIGURE 3A. EFFECTS OF DIODE LINEARIZATION, WITH DIODE PROGRAMMING TERMINAL ACTIVE
V+ 15V 11 10k 9 1/2 CA3280 10k 10 6 4 8 IDIODE IABC V-15V VIN 1k 12 IOUT
IABC = 650A; ID = 0; Vertical = 200A/Div.; Horizontal = 25mV/Div. FIGURE 3B. WITH DIODE PROGRAMMING TERMINAL CUTOFF FIGURE 3. CA3280 TRANSFER CHARACTERISTICS
Application Information
Figures 4 and 5 show the equivalent circuits for the current source and linearization diodes in the CA3280. The current through the linearization network is approximately equal to the programming current. There are several advantages to driving these diodes with a current source. First, only the offset current from the biasing network flows through the input resistor. Second, another input is provided to extend the gain control dynamic range. And third, the input is truly differential and can accept signals within the common mode range of the CA3280. network requires ratio matching of 0.01% or trimming for 80dB of common-mode rejection. The CA3280, with its excellent common mode rejection ratio, is capable of converting a small (25mV) differential input signal to a single-ended output without the need for a matched resistor network. Figure 7 shows the CA3280 in a typical gain control application. Gain control can be performed with the amplifier bias current (lABC). With no diode bias current, the gain is merely gMRL. For example, with an lABC of 1mA, the gM is approximately 16mS. With the CA3280 operating into a 5k resistor, the gain is 80. The need for external buffers can be eliminated by the use of low value load resistors, but the resulting increase in the required amplifier bias current reduces the input impedance
Typical Applications
The structure of the variable operational amplifier eliminates the need for matched resistor networks in differential to single ended converters, as shown in Figure 6. A matched resistor 5
CA3280, CA3280A
of the CA3280. The linearization diode impedance also decreases as the diode bias current increases, which further loads the input. The diodes, in addition to acting as a linearization network, also operate as an additional attenuation system to accommodate input signals in the volt range when they are applied through appropriate input resistors. Figure 10 shows a triangle wave to sine wave converter using the CA3280. Two 100k resistors are connected between the differential amplifier emitters and V+ to reduce the current flow through the differential amplifier. This allows the amplifier to fully cut off during peak input signal excursions. THD is appropriately 0.37% for this circuit.
V+
RD = SMALL SIGNAL DIODE IMPEDANCE RD 70 52 ID(mA) x 1.34 = ID RD VOA VOA
IABC
ID
IABC
ID
V-
FIGURE 4. VOA SHOWING LINEARIZATION DIODES AND CURRENT DRIVE
FIGURE 5. BLOCK DIAGRAM OF LINEARIZED VOA
+15V
10VP-P INPUT 68k 600 1 10k 14 16 V+ SINGLEENDED OUTPUT 10k + 1/2 CA3280
V+ = +15V OUTPUT 21VP-P 14mV AGC FEEDTHRU 400V NOISE AT MAX GAIN 13 4 15k
68k 14 2k 16 DIFFERENTIAL INPUT 2k 15 3 + 1/2 CA3280
13
330k 100k V15
3
4 1
10k 20k V- = -15V
-15V
VOLTAGE CONTROL
FIGURE 6. DIFFERENTIAL TO SINGLE ENDED CONVERTER
FIGURE 7. TYPICAL GAIN CONTROL CIRCUIT
6
CA3280, CA3280A
3 +15V 2k 16 33pF 15 14 + 1/2 CA3280 13 1800pF 10k
51
-
2k 2k 9 6 + 1/2 CA3280 10k 12 300pF 4 8 1 100 -15V 0.05F 10k 1N914 OUTPUT 100k 3 1/2 CD4013 5 2 1 14 4 6 7
-15V
TO 10k 3 TO 10k 6
51
33pF 10
-
FIGURE 8. TWO CHANNEL LINEAR MULTIPLEXER
3.6k 14 16 200 15 200 910k V+ 100k V-
V+
V+ = +7.5V 0.1F 7 13 15 - 115pF 3 + CA3160 2 6 V+
100k VV+ 560k 3.3k 10 11 2.7k
+ 1/2 CA3280
3
1/2 CA3280 + 4 1
6 12 8
4 9 0.1F
VV- = -7.5V V+ 10k MAX FREQ. SET 5.6k 500 V1k MIN FREQ. SET 4 - 60pF 2k 1N914 1N914 3.3k
FIGURE 9. CA3280 USED IN CONJUNCTION WITH A CA3160 TO PROVIDE A FUNCTION GENERATOR WITH A TUNABLE RANGE OF 2Hz TO 1MHz
+15V 170mVP-P 2k 16
14 3 + 1/2 CA3280
30k
13 100k
15 0.1 F 1 6.8 M M
+15V 11
2 +15V 51
-15V +15V 1M
6 9 + 1/2 CA3280 7 12
200 100k
3.9 k
10 100k -15V 2k
4 -15V
FIGURE 10. TRIANGLE WAVE-TO-SINE WAVE CONVERTER
7
CA3280, CA3280A Typical Performance Curves
105 SMALL SIGNAL FORWARD TRANSCONDUCTANCE (mS) 104 103 102 101 1 IABC = 3mA IABC = 300A IABC = 30A IABC = 3.0A IABC = 0.3A TA = 25oC SUPPLY CURRENT (mA) 101 TA = 25oC VS = 15V
1
10-1
I = 0.03A 0.1 ABC 101 102 103
104
105
106
107
108
109
10-2 10-1
1
101 DIODE CURRENT (A)
102
103
FREQUENCY (Hz)
FIGURE 11. AMPLIFIER GAIN vs FREQUENCY
103 INPUT OFFSET CURRENT (nA)
FIGURE 12. SUPPLY CURRENT vs DIODE CURRENT
2 INPUT OFFSET VOLTAGE (mV) 1 0 -1 -2 -3 -4 -5 1 101 102 AMPLIFIER BIAS CURRENT (A) 103 TA = 125oC TA = 125oC TA = 25oC TA = -55oC
VS = 15V TA = -55oC TA = 25oC TA = 125oC
102
101
1 1
101
102
103
AMPLIFIER BIAS CURRENT (A)
FIGURE 13. INPUT OFFSET CURRENT vs AMPLIFIER BIAS CURRENT
FIGURE 14. INPUT OFFSET VOLTAGE vs AMPLIFIER BIAS CURRENT
16 15 PEAK OUTPUT VOLTAGE (V) 14 13 0 -13 -14 -15 -16 1 101 102 103 AMPLIFIER BIAS CURRENT (A) TA = 125oC TA = 25oC TA = -55oC VS = 15V
106 105 INPUT CURRENT (pA) 104 103 102 101 1 0 1 2 3 4 5 6 7 8 9 10 DIFFERENTIAL INPUT VOLTAGE (V) TA = 25oC
TA = 125oC
TA = 125oC TA = 25oC TA = -55oC
FIGURE 15. PEAK OUTPUT VOLTAGE vs AMPLIFIER BIAS CURRENT
FIGURE 16. INPUT CURRENT vs INPUT DIFFERENTIAL VOLTAGE
8
CA3280, CA3280A Typical Performance Curves
104 AMPLIFIER BIAS VOLTAGE (mV) 103 102 V9 = V10 = V12 = 30V
(Continued)
1800 1600 1400 1200 1000 800 600 400 TA = 100oC TA = 125oC TA = 25oC
VS = 15V TA = -55oC
LEAKAGE CURRENT (nA)
10 1 10-1 10-2 -75 V9 = V10 = V12 = 0V
-50
-25
0
25
50
75
100
125
150 175
1
101
102
103
TEMPERATURE (oC)
AMPLIFIER BIAS CURRENT (A)
FIGURE 17. LEAKAGE CURRENT vs TEMPERATURE
FIGURE 18. AMPLIFIER BIAS VOLTAGE vs AMPLIFIER BIAS CURRENT
24 22 1/ f NOISE VOLTAGE (nV/Hz) 20 18 16 14 12 10 8 6 4 2 0 101
TA = 25oC PEAK OUTPUT CURRENT (A)
103
VS = 15V
TA = -55oC TA = 25oC TA = 125oC
102
IABC = 500A
101 TA = 125oC TA = -55oC TA = 25oC 1 1 101 102 103
102
103 FREQUENCY (Hz)
104
105
AMPLIFIER BIAS CURRENT (A)
FIGURE 19. 1/f NOISE vs FREQUENCY
FIGURE 20. PEAK OUTPUT CURRENT vs AMPLIFIER BIAS CURRENT
106 SMALL SIGNAL FORWARD TRANSCONDUCTANCE (mS) TA = +25oC VS = +15V
105 104 103 102 101 1 10-1 10-3 TA = -55oC TA = 25oC TA = 125oC
DIODE RESISTANCE ()
105
104
103
102
101 10-1
1
101
102
103
104
10-2
10-1
1
101
102
103
104
DIODE CURRENT (A)
AMPLIFIER BIAS CURRENT (A)
FIGURE 21. DIODE RESISTANCE vs DIODE CURRENT
FIGURE 22. AMPLIFIER GAIN vs AMPLIFIER BIAS CURRENT
9
CA3280, CA3280A Typical Performance Curves
104 VS = 15V INPUT BIAS CURRENT (nA)
(Continued)
104 VS = 15V 103
SUPPLY CURRENT (A)
103
102 TA = 125oC 101 TA = -55oC, 25oC 1 10-1
102
TA = 125oC TA = 25oC
101 TA = -55oC
10-1
1
101
102
103
1 10-1
1
101
102
103
AMPLIFIER BIAS CURRENT (A)
AMPLIFIER BIAS CURRENT (A)
FIGURE 23. SUPPLY CURRENT vs AMPLIFIER BIAS CURRENT
FIGURE 24. INPUT BIAS CURRENT vs AMPLIFIER BIAS CURRENT
Metallization Mask Layout
Dimensions in parentheses are in millimeters and derived from the basic inch dimensions as indicated. Grid graduations are in mils (10-3 inch). The photographs and dimensions represent a chip when it is part of the wafer. When the wafer is cut into chips, the cleavage angles are 57o instead of 90o with respect to the face of the chip. Therefore, the isolated chip is actually 7 mils (0.17mm) larger in both dimensions.
10

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