11
avoided because of their additional series inductance. Use
of sockets should also be avoided if possible. Sockets add
parasitic inductance and capacitance that can result in
compromised performance. Minimizing parasitic capacitance
at the amplifier’s inverting input pin is very important. The
feedback resistor should be placed very close to the
inverting input pin. Strip line design techniques are
recommended for the signal traces.
Typical Applications
VIDEO SYNC PULSE REMOVER
Many CMOS analog to digital converters 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
31 shows a gain of 2 connections for EL8302.
Figure
32 shows the complete input video signal applied at
the input, as well as the output signal with the negative going
sync pulse removed.
MULTIPLEXER
Besides the normal power down usage, the ENABLE pin of
the EL8302 can be used for multiplexing applications. Figure
33 shows two channels with the outputs tied together, driving
a back terminated 75
video load. A 2VP-P 2MHz sine wave
is applied to Amp A and a 1VP-P 2MHz sine wave is applied
to Amp B. Figure
34 shows the ENABLE signal and the
resulting output waveform at VOUT. Observe the break-
before-make operation of the multiplexing. Amp A is on and
VIN1 is passed through to the output when the ENABLE
signal is low and turns off in about 25ns when the ENABLE
signal is high. About 200ns later, Amp B turns on and VIN2 is
passed through to the output. The break-before-make
operation ensures that more than one amplifier isn’t trying to
drive the bus at the same time.
SINGLE SUPPLY VIDEO LINE DRIVER
The EL8302 is wideband rail-to-rail output op amplifiers with
large output current, excellent dG, dP, and low distortion that
allow them to drive video signals in low supply applications.
Figure
35 is the single supply non-inverting video line driver
configuration and Figure
36 is the inverting video ling driver
configuration. The signal is AC coupled by C1. R1 and R2
are used to level shift the input and output to provide the
largest output swing. RF and RG set the AC gain. C2 isolates
the virtual ground potential. RT and R3 are the termination
resistors for the line. C1, C2 and C3 are selected big enough
to minimize the droop of the luminance signal.
FIGURE 31. SYNC PULSE REMOVER
5V
1K
VOUT
VIN
75
+
-
75
1K
75
VS+
VS-
FIGURE 32. VIDEO SIGNAL
1V
0.5V
0V
1V
0.5V
0V
M = 10s/DIV
VOUT
VIN
FIGURE 33. TWO TO ONE MULTIPLEXER
+2.5V
1K
2MHz
75
+
-
1K
75
-2.5V
VOUT
75
1VP-P
B
+2.5V
1K
2MHz
+
-
1K
75
-2.5V
2VP-P
A
ENABLE
FIGURE 34.
0V
-0.5V
-1.5V
-2.5V
1V
0V
M = 50ns/DIV
A
ENABLE
B
-1V
EL8302