LM1203AN National Semiconductor, LM1203AN Datasheet - Page 10

• Manufacturer Part Number: LM1203AN
• Description: IC VIDEO AMP RGB 150MHZ 28DIP
• Manufacturer: National Semiconductor

Specifications of LM1203AN

• Applications: General Purpose
• Number Of Circuits: 3
• -3db Bandwidth: 70MHz
• Current - Supply: 73mA
• Current - Output / Channel: 28mA
• Voltage - Supply, Single/dual (±): 10.8 V ~ 13.2 V
• Mounting Type: Through Hole
• Package / Case: 28-DIP (0.600", 15.24mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM1203AN

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Figure 7 shows the input reference and contrast control cir-
Figures 8 and 9 show simplified schematics of the clamp
Circuit Description
INPUT REFERENCE AND CONTRAST CONTROL
SECTION
cuitry A temperature compensated 2 8V reference voltage
is made available at pin 11 The external DC biasing resis-
tors shown should not be larger than 10k because minor
differences in input bias currents of the individual video am-
plifiers may cause offsets in gain Figure 7 also shows how
the contrast control circuit is configured R21 R22 Q22
Q23 and Q24 establish a low impedance zero TC half sup-
ply voltage reference at the base of Q25 The differential
amplifier formed by Q27 Q28 and feedback transistor Q29
along with R28 and R29 establish a differential base voltage
for Q3 and Q4 in Figure 6 When externally adding or sub-
tracting current from the collector of Q28 a new differential
voltage is generated that reflects the change in the ratio of
currents in Q27 and Q28 To allow voltage control of the
current through Q28 resistor R27 is added between the
collector Q28 and pin 12 A capacitor should be connected
from pin 12 to ground to prevent noise from the contrast
control potentiometer from entering the IC
CLAMP GATE AND CLAMP COMPARATOR SECTION
gate and clamp comparator circuits The clamp gate circuit
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FIGURE 7 Simplified Schematic of LM1203A Video Input Reference and Contrast Control Circuits
(Continued)
10
(Figure 8) consists of a PNP input buffer transistor (Q46) a
PNP emitter coupled pair (Q47 and Q49) referenced on one
side to 2 1V and an output switch transistor Q53 When the
clamp gate input at pin 14 is high (
on and shunts the 200 A current from current source Q54
to ground When pin 14 is low (
and the 200
comprised of Q55 and Q36 (see Figure 9 ) Consequently
the clamp comparator comprised of the differential pair Q35
and Q37 is enabled The input of each clamp comparator is
similar to the clamp gate except than an NPN emitter cou-
pled pair is used to control the current that will charge or
discharge the clamp capacitors at pins 5 8 and 10 PNP
transistors are used at the inputs because they offer a num-
ber of advantages over NPNs PNPs will operate with base
voltages at or near ground and will usually have a greater
emitter base breakdown voltage (BVebo) Because the dif-
ferential input voltage to the clamp comparator during the
video scan period could be greater than the BVebo of NPN
transistors a resistor (R37) with a value one half that of R36
or R39 is connected between the bases of Q34 and Q38
The clamp comparator’s common mode range is from
ground to approximately 9V and the maximum differential
input voltage is V
A current is mirrored by the current mirror
CC
and ground
k
1 3V) the Q53 switch is off
l
1 5V) the Q53 switch is
TL H 11441 – 11