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LM1203N データシート(PDF) 7 Page - National Semiconductor (TI) |
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LM1203N データシート(HTML) 7 Page - National Semiconductor (TI) |
7 / 16 page Circuit Description Figure 5 is a block diagram of one of the video amplifiers 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 introduc- ing any signal distortions or tracking errors The brightness 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 comparator 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 Figure 6 is a simplified schematic of one of the three video amplifiers along with the recommended external compo- nents The IC pin numbers are circled with all external com- ponents shown outside of the dashed line The video input is applied to pin 6 via the 10 mF coupling capacitor DC bias to the video input is through the 10 kX resistor which is connected to the 24V reference at pin 11 The low frequen- cy roll-off of the amplifier is set by these two components Transistor Q1 buffers the video signal to the base of Q2 The Q2 collector current is then directed to the VCC 1 sup- ply directly or through the 1k load resistor depending upon the differential DC voltage at the bases of Q3 and Q4 The Q3 and Q4 differential base voltage is determined by the contrast control circuit which is described below RF decou- pling capacitors are required at pins 2 and 3 to insure high frequency isolation between the three video amplifiers which share these common connections The black level dc voltage at the collector of Q4 is maintained by Q5 and Q6 which are part of the black level clamp circuit also described below The video signal appearing at the collector of Q4 is then buffered by Q7 and level shifted down by Z1 and Q8 to the base of Q9 which will then provide additional system gain TLH9178 – 5 FIGURE 5 Block Diagram of LM1203 Video Amplifier with Contrast and Black Level Control http www nationalcom 7 |
同様の部品番号 - LM1203N |
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同様の説明 - LM1203N |
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