1
CA3280, CA3280A
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.
Pinout
CA3280
(PDIP, CERDIP)
TOP VIEW
Features
Low Initial Input Offset Voltage: 500
V (Max) (CA3280A)
Low Offset Voltage Change vs I
ABC
: <500
V (Typ)
for All Types
Low Offset Voltage Drift: 5
V/
o
C (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
14
15
16
9
13
12
11
10
1
2
3
4
5
7
6
8
I
D
, A1
EMITTER, A1
I
ABC
, A1
V-
NC
I
ABC
, A2
I
D
, A2
EMITTER, A2
+IN, A1
V+, A1
OUT, A1
OUT, A2
V+, A2
-IN, A2
+IN, A2
-IN, A1
-
+
A1
-
+
A2
Ordering Information
PART NUMBER
TEMP.
RANGE (
o
C)
PACKAGE
PKG.
NO.
CA3280AE
-55 to 125
16 Ld PDIP
E16.3
CA3280E
0 to 70
16 Ld PDIP
E16.3
CA3280AF3
-55 to 125
16 Ld CERDIP
F16.3
Data Sheet
September 1998
File Number
1174.4
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143
|
Copyright
Intersil Corporation 1999
2
.
Functional Diagram
4
14
2
3
1
16
15
13
-
+
10
9
8
6
12
7
11
2K
2K
1/2 CA3280
CA3280, CA3280A
3
Absolute Maximum Ratings
Thermal Information
Supply Voltage (Between V+ and V-) . . . . . . . . . . . . . . . . . . . . +36V
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V
Input Voltage Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V+ to V-
Input Current at I
D
= 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
A
Amplifier Bias Current (I
ABC
) . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
Output Short Circuit Duration (Note 1). . . . . . . . . . . . . . . . Indefinite
Linearizing Diode Bias Current, I
D
. . . . . . . . . . . . . . . . . . . . . . . 5mA
Peak Input Current with Linearizing Diode. . . . . . . . . . . . . . . . . .
I
D
Operating Conditions
Temperature Range
CA3280 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0
o
C to 70
o
C
CA3280A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55
o
C to 125
o
C
Supply Voltage Range (Typ) . . . . . . . . . . . . . . . . . . . . .
2V to
15V
Thermal Resistance (Typical, Note 2)
JA
(
o
C/W)
JC
(
o
C/W)
CERDIP Package . . . . . . . . . . . . . . . . .
65
16
PDIP Package . . . . . . . . . . . . . . . . . . .
100
N/A
Maximum Junction Temperature (CERDIP Package). . . . . . . . .175
o
C
Maximum Junction Temperature (Plastic Package) . . . . . . . .150
o
C
Maximum Storage Temperature Range . . . . . . . . . . -65
o
C to 150
o
C
Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . 300
o
C
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
For Equipment Design, at T
A
= 25
o
C, V
SUPPLY
=
15V, Unless Otherwise Specified
PARAMETER
SYMBOL
TEST CONDITIONS
CA3280
CA3280A
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
Input Offset Voltage
V
IO
I
ABC
= 1mA
-
-
3
-
-
0.5
mV
I
ABC
= 100
A
-
0.7
3
-
0.25
0.5
mV
I
ABC
= 10
A
-
-
3
-
-
0.5
mV
I
ABC
= 1mA to 10
A,
T
A
= Full Temp. Range
-
0.8
4
-
0.8
1.5
mV
Input Offset Voltage Drift
|
V
IO
|
I
ABC
= 1
A to 1mA
-
0.5
1
-
0.5
1
mV
I
ABC
= 100
A, T
A
= Full
Temperature Range
-
5
-
-
3
5
V/
o
C
Amplifier Bias Voltage
V
ABC
I
ABC
= 100
A
-
1.2
-
-
1.2
-
V
Peak Output Voltage
V
OM
+
I
ABC
= 500mA
12
13.7
-
12.5
13.7
-
V
V
OM
-
12
-14.3
-
-13.3
-14.3
-
V
V
OM
+
I
ABC
= 5
A
12
13.9
-
12.5
13.9
-
V
V
OM
-
12
-14.5
-
-13.5
-14.5
-
V
Common Mode Input Voltage
Range
V
ICR
I
ABC
= 100
A
-13
-
13
-13
-
13
V
Noise Voltage
e
N
I
ABC
= 500
A
10Hz
-
20
-
-
20
-
nV/
Hz
1kHz
-
8
-
-
8
-
nV/
Hz
10kHz
-
7
-
-
7
-
nV/
Hz
Input Offset Current
I
IO
I
ABC
= 500
A
-Z
0.3
0.7
-
0.3
0.7
A
Input Bias Current
I
IB
I
ABC
= 500
A
-
1.8
5
-
1.8
5
A
I
ABC
= 500
A, T
A
= Full
Temperature Range
-
3
8
-
3
8
A
Peak Output Current
I
OM
+
I
ABC
= 500
A
Source
350
410
650
350
410
650
A
I
OM
-
Sink
-350
-410
-650
-350
-410
-650
A
I
OM
+
I
ABC
= 5
A
Source
3
4.1
7
3
4.1
7
A
I
OM
-
Sink
-3
-4.1
-7
-3
-4.1
-7
A
CA3280, CA3280A
4
Peak Output Current Sink and
Source
I
OM
-,
I
OM
+
I
ABC
= 500
A, T
A
= Full
Temperature Range
350
450
550
350
450
550
A
Linearization Diodes
I
D
= 100
A
-
10
-
-
10
-
A
Offset Current
I
D
= 10
A
-
0.5
1
-
0.5
1
A
Dynamic Impedance
I
D
= 100
A
-
700
-
-
700
-
Diode Network Supply Current
I
ABC
= 100
A
250
400
800
250
400
800
A
Amplifier Supply Current
(Per Amplifier)
I+
I
ABC
= 500
A
-
2
2.4
-
2
2.4
mA
Amplifier Output Leakage Current
I
OL
I
ABC
= 0, V
O
= 0V
-
0.015
0.1
-
0.015
0.1
nA
I
ABC
= 0, V
O
= 30V
-
0.15
1
-
0.15
1
nA
Common Mode Rejection Ratio
CMRR
I
ABC
= 100
A
80
100
-
94
100
-
dB
Power Supply Rejection Ratio
PSRR
I
ABC
= 100
A
86
105
-
94
105
-
dB
Open Loop Voltage Gain
A
OL
I
ABC
= 100
A,
R
L
=
,
V
O
= 20V
P-P
94
100
-
94
100
-
dB
50
100
-
50
100
-
kV/V
Forward Transconductance
G
M
I
ABC
= 50
A, Large Signal
-
0.8
1.2
-
0.8
1.2
mS
g
M
I
ABC
= 1mA, Small Signal
-
16
22
-
16
22
mS
Input Resistance
R
I
I
ABC
= 10
A
0.5
-
-
0.5
-
-
M
Channel Separation
f = 1kHz
-
94
-
-
94
-
dB
Open Loop Total
Harmonic Distortion
THD
f = 1kHz, I
ABC
= 1.5mA,
R
L
= 15k
, V
O
= 20V
P-P
-
0.4
-
-
0.4
-
%
Bandwidth
f
T
I
ABC
= 1mA, R
L
= 100
-
9
-
-
9
-
MHz
Slew Rate, Open Loop
SR
I
ABC
= 1mA
-
125
-
-
125
-
V/
s
Capacitance
C
I
I
ABC
= 100
A
Input
-
4.5
-
-
4.5
-
pF
C
O
Output
-
7.5
-
-
7.5
-
pF
Output Resistance
R
O
I
ABC
= 100
A
-
63
-
-
63
-
M
Test Circuits and Waveforms
FIGURE 1. LEAKAGE CURRENT TEST CIRCUIT
FIGURE 2. CHANNEL SEPARATION TEST CIRCUIT
Electrical Specifications
For Equipment Design, at T
A
= 25
o
C, V
SUPPLY
=
15V, Unless Otherwise Specified (Continued)
PARAMETER
SYMBOL
TEST CONDITIONS
CA3280
CA3280A
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
1/2
+
-
13
CA3280
3
14
4
1
16
15
I
30V
0V
TEST
POINT
+30V
1/2
+
-
13
CA3280
4
14
3
15
16
V+
0.1
F
OUTPUT
10k
V+
V-
INPUT
30k
0.1
F
1k
1k
30k
CA3280, CA3280A
5
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.
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
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
(l
ABC
). With no diode bias current, the gain is merely g
M
R
L
. For
example, with an l
ABC
of 1mA, the g
M
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
FIGURE 3A. EFFECTS OF DIODE LINEARIZATION, WITH DIODE PROGRAMMING TERMINAL ACTIVE
FIGURE 3B. WITH DIODE PROGRAMMING TERMINAL CUTOFF
FIGURE 3. CA3280 TRANSFER CHARACTERISTICS
Test Circuits and Waveforms
(Continued)
1/2
13
CA3280
1
14
4
3
15
16
15V
I
DIODE
I
ABC
-15V
1k
V+
10k
10k
V-
I
OUT
V
IN
I
ABC
= 650
A, I
D
= 200
A; Vertical = 200
A/Div.;
Horizontal = 1V/Div.
1/2
12
CA3280
8
11
6
4
10
9
15V
I
DIODE
I
ABC
1k
V+
10k
10k
-15V
V-
I
OUT
V
IN
I
ABC
= 650
A; I
D
= 0; Vertical = 200
A/Div.;
Horizontal = 25mV/Div.
CA3280, CA3280A
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