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LM1203B データシート(PDF) 8 Page - National Semiconductor (TI) |
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LM1203B データシート(HTML) 8 Page - National Semiconductor (TI) |
8 / 16 page Circuit Description (Continued) VIDEO AMPLIFIER SECTION 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 and all external com- ponents are shown outside the dashed line The video input is applied to pin 6 via a 10 mF coupling capacitor and a 47X resistor The resistor is added to limit the current through the input pin should the applied voltage rise above VCC or drop below ground The performance of the LM1203B is not degraded by the 47X resistor However if EMI is a concern this resistor can be increased to well over 100X where the rise and fall times will become longer DC bias for the video input is through the 10k resistor connected to the 28V refer- ence at pin 11 The low frequency roll-off of the amplifier is set by the 10k resistor and the 10 mF capacitor Transistor Q1 buffers the video signal to the base of Q2 Q2’s collector current is then directed to the VCC1 supply directly or through the 4k 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 001 mF decoupling capacitor in series with a 30X resistor is required between 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 For individual gain adjustment of each video channel a 51X resistor in series with a 100X potentiometer should be used with the red and green channel drive pins A 91X resistor used with the blue channel drive pin sets the blue channel amplifier gain at approximately 62 The 100X potentiome- ters at the red and green channel drive pins allow a gain of 62 with g25% gain adjustment The video signal at the TLH11489 – 10 FIGURE 6 Simplified Schematic of LM1203B Video Amplifier Section with Recommended External Components http www nationalcom 8 |
同様の部品番号 - LM1203B |
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同様の説明 - LM1203B |
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