el2257 Intersil Corporation, el2257 Datasheet - Page 14

• Manufacturer Part Number: el2257
• Description: 125mhz Single Supply, Clamping Op Amp
• Manufacturer: Intersil Corporation

Video Sync Pulse Remover Application
All CMOS Analog to Digital Converters (A/Ds) have a
parasitic latch-up problem when subjected to negative input
voltage levels. Since the sync tip contains no useful video
information and it is a negative going pulse, we can chop it
off. Figure 7 shows a unity gain connected amplifier A of an
EL2257. Figure 8 shows the complete input video signal
applied at the input, as well as the output signal with the
negative going sync pulse removed.
Propagation Delay vs Overdrive
EL2257 as a Comparator
FIGURE 5.
FIGURE 6.
FIGURE 4.
14
EL2257
Multiplexing with the EL2257
The ENABLE pins on the EL2257 allow for multiplexing
applications. Figure 9 shows an EL2257 with both outputs
tied together, driving a back terminated 75: video load. Two
sinewaves of varying amplitudes and frequencies are
applied to the two inputs. Logic signals are applied to each of
the ENABLE pins to cycle through turning each of the
amplifiers on, one at a time. Figure 10 shows the resulting
output waveform at V
50ns. Notice the outputs are tied directly together.
Decoupling resistors at each output are not necessary. In
fact, adding them approximately doubles the switching time
to 100ns.
CLK
V
IN
1.3V
7.5V
75:
1MHz
5MHz
1 of 2
coder
De-
P-P
P-P
OUT
1
2
3
4
5
6
7
1
2
3
4
5
6
7
FIGURE 8.
. Switching is complete in about
FIGURE 7.
FIGURE 9.
+
+
-
-
+
+
-
-
14
13
12
11
10
9
8
14
13
12
11
10
9
8
150:
V
150:
V
OUT
OUT
+5V
0.1µF 4.4µF