ca3280 Intersil Corporation, ca3280 Datasheet - Page 5

• Manufacturer Part Number: ca3280
• Description: Dual, 9mhz, Operational Transconductance Amplifier Ota
• Manufacturer: Intersil Corporation

Test Circuits and Waveforms
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
10k
10k
10k
10k
FIGURE 3A. EFFECTS OF DIODE LINEARIZATION, WITH DIODE PROGRAMMING TERMINAL ACTIVE
16
15
10
I
9
DIODE
I
5
DIODE
1/2
CA3280
1
1/2
CA3280
8
I
ABC
14
FIGURE 3B. WITH DIODE PROGRAMMING TERMINAL CUTOFF
3
V-
-15V
11
4
V+
15V
4
I
V+
15V
ABC
6
FIGURE 3. CA3280 TRANSFER CHARACTERISTICS
V-
-15V
13
(Continued)
12
1k
CA3280, CA3280A
1k
I
I
OUT
OUT
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
example, with an l
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
ABC
I
). With no diode bias current, the gain is merely g
ABC
I
ABC
= 650 A, I
= 650 A; I
Horizontal = 25mV/Div.
ABC
Horizontal = 1V/Div.
D
= 200 A; Vertical = 200 A/Div.;
D
of 1mA, the g
= 0; Vertical = 200 A/Div.;
V
V
IN
IN
M
is approximately 16mS.
M
R
L
. For