LM1203AN National Semiconductor, LM1203AN Datasheet - Page 7

• 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

Figure 4 shows the block diagram of a typical analog RGB
Figure 4 block labeled ‘‘VIDEO AMPLIFICATION WITH
Figure 5 is a block diagram of one of the video amplifiers
Applications Information
color monitor The RGB monitor is used with CAD CAM
work stations PC’s arcade games and in a wide range of
other applications that benefit from the use of color display
terminals The RGB color monitor characteristics may differ
in such ways as sweep rates screen size CRT color trio
spacing (dot pitch) or in video amplifier bandwidths but will
still be generally configured as shown in Figure 4 Separate
horizontal and vertical sync signals may be required or they
may be contained in the green video input signal The video
input signals are usually supplied by coax cable which is
terminated in 75
coupled to the video amplifiers These input signals are ap-
proximately 1V peak to peak in amplitude and at the input of
the high voltage video section approximately 6V peak to
peak At the cathode of the CRT the video signals can be as
high as 60V peak to peak One important requirement of the
three video amplifiers is that they match and track each
other over the contrast and brightness control range The
GAIN AND DC CONTROL’’ describes the function of the
LM1203A which contains the three matched video amplifi-
ers contrast control and brightness control
Circuit Description
along with the contrast and brightness controls The con-
trast control is a DC-operated attenuator which varies the
AC gain of all three amplifiers simultaneously while not intro-
ducing any signal distortions or tracking errors The bright-
ness control function requires a ‘‘sample and hold’’ circuit
(black level clamp) which holds the DC bias of the video
amplifiers and CRT cathodes constant during the black level
reference portion of the video waveform The clamp com-
parator when gated on during this reference period will
charge or discharge the clamp capacitor until the plus input
of the clamp comparator matches that of the minus input
voltage which was set by the brightness control
at the monitor input and internally AC
FIGURE 4 Typical RGB Color Monitor Block Diagram
7
Figure 6 is a simplified schematic of one of the three video
VIDEO AMPLIFIER SECTION
amplifiers along with the recommended external compo-
nents The IC pin numbers are circled and all external com-
ponents are shown outside the dashed line The video input
is applied to pin 6 via a 10 F coupling capacitor DC bias
for the video input is through the 10k resistor connected to
the 2 8V reference at pin 11 The low frequency roll-off of
the amplifier is set by these two components Transistor Q1
buffers the video signal to the base of Q2 Q2’s collector
current is then directed to the V
through the 2k load resistor depending upon the differential
DC voltage at the bases of Q3 and Q4 This differential DC
voltage is generated by the contrast control circuit which is
described in the following sections A 0 01
capacitor in series with a 30
pins 2 and 3 to ensure high frequency isolation between the
three video amplifiers which share these common connec-
tions The video signal is buffered by Q5 and Q6 and DC
level shifted by the voltage drop across R5 The magnitude
of the current through R5 is determined by the voltage at pin
8 The voltage at pin 8 is set by the clamp comparator out-
put current which charges or discharges the clamp hold ca-
pacitor during the black level period of the video waveform
Transistors Q9 and Q10 are Darlington connected to ensure
a minimum discharge of the clamp hold capacitor during the
time that the clamp capacitor is gated off Q7 Q8 and R6
form a current mirror which sets a voltage at the base of
Q11 Q11 buffers the video signal to the base of Q12 which
provides additional signal gain The ‘‘Drive’’ pin allows the
user to trim the Q12 gain of each amplifier to correct for gain
differences in the CRT and high voltage cathode driver gain
stages A small capacitor (several pico-Farads) from the
‘‘Drive’’ pin to ground will cause high frequency peaking and
slightly improve the amplifier’s bandwidth
resistor is required between
CC1
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