EL2321C
Triple, Low Cost, Gain of 2, Video Op Amp
0.1 µF
0.32 VB 68K
RA
CB
V IN
4.7K
+
75
V OUT
0.64 VB
V AMP
1 V
RB
AMP
RO
-
1K
RF
Video
1 V
V1
+
–
+
–
5 V
Figure 1.
Input capacitive coupling will increase the needed
dynamic range of the amplifier. The standard NTSC
video signal is 1V peak to peak plus 143 mV for the
color AC peak. The video signal is made up of the -286
mV sync pulse plus the 714 mV picture signal which
may very from 0V to 714 mV. The video signal average
value for a black picture is about 28 mV (Figure 2) and
with a white picture level is about 583 mV (Figure 3).
This gives a maximum change in average value of about
555 mV. A direct coupled amplifier with an standard
NTSC video signal needs a dynamic range of 1.143V.
But with input capacitance coupling the dynamic range
requirements are the sum of the 1.143V video plus the
average picture value change of 0.555V or 1.698VP-P
.
At a gain of two this doubles to 3.394V. These amplifi-
ers do not have this much dynamic range so a gain of
less than 2 must be used to avoid waveform compression
under all conditions.
Gain = 2
1.8 V offset
Amp Out
Volts
Ý10
53 µs
1.428
1.166
2.062
1.8
0.714 V
0.6
0.583 V
0.867
0.0 V
-0.286 V
1.3 µs
0
+0.348
+0.062
-0.572
3.8 µs
5.1 µs
Figure 2. White Level Video
6
ELANTEC [ ELANTEC SEMICONDUCTOR ]
