ca3256 Intersil Corporation, ca3256 Datasheet - Page 6

• Manufacturer Part Number: ca3256
• Description: 25mhz, Bimos Analog Video Switch Amplifier
• Manufacturer: Intersil Corporation

buffer amplifier. The T-switch, together with the input
impedance of the buffer, is typically 10k , and has an inser-
tion loss of approximately 0.8dB. The T-switch was designed
to handle up to 3V
T-switches of the CA3256 conform to a break-before-make
format; hence, shorting to ground is eliminated.
The amplifier is programmable for gain and, typically, can
provide a gain of 1 into a 75 load or a gain of 5 into a 1k
load. The maximum output signal swing with linearity is
greater than 5V
12V, while the maximum output current is approximately
20mA. The amplifier has base-current compensation to
reduce offset and a temperature compensated 5V zener ref-
erenced bias. Other features include LED-selector indicators
for channels 1 through 4. The fifth channel is independently
Typical Applications
CHANNEL 1
CHANNEL 5
OUTPUT
INPUT
INPUT/
SHOWN
INPUTS
2 OF 5
FIGURE 2. TYPICAL APPLICATION WITH DIRECT-COUPLED OUTPUT AND V- = -5V (DIP PINOUT)
P-P
100K
P-P
CHANNEL
ENABLE
for (V+ to V-) greater than or equal to
1-4
input signal with low distortion. The
100K
13
15
17
1
3
4.7K
6
100K
CHAN 1-4
ENABLE
SELECT
TG-1
AND
LLC
4.7K
-5V
TG-2
V-
5
5
TG-3
CHANNEL
16
SELECT
A
BIAS
REG
1-4
V+
14
14
TG-4
18
+7V TO +12V
B
CA3256
TG-5
4.7K
V- +5V
CHANNEL
SELECT
2
1
3
4
8-6
5
10K
10K
selectable for use as a separate input or output in parallel
with any on channel, and may be used as a monitor, or for
pass-through, signal summing, or parallel distribution.
In the application, the user has the option to specify V- = -5V
for the switch and a ground reference for the amplifier input
and output. Alternatively, the CA3256 may be used with a
single +12V supply. The logic select for channels 1 through 4
is controlled by the A, B and Inhibit lines with ground to V+
logic switching. The logic threshold is approximately
(V+ - V-)/2 referenced to ground. DC coupling may also be
used at the output (when V- is returned to a -5V supply). For
the circuit of Figure 3, AC coupling is used at the output and
input. The switching bias arrangement shown provides for
stable bias across each switch when in the off position to
minimize transients when the input is switched.
7
C
8
1K
OUTPUT
4.7K
+
-
AMP
R
F
4
GND
10
12
2
9
11
LED INDICATOR CHANNEL 1
LED INDICATOR CHANNEL 2
LED INDICATOR CHANNEL 3
LED INDICATOR CHANNEL 4
75
WHERE AMPLIFIER GAIN:
A V
i.e., FOR A
=
1
R
+
F
R
----------------------
= 9k
F
10K
+
V
AMPLIFIER
1K
TO CABLE
= 1.8
OUTPUT
x
0.9
75
V
LED
OUT