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High Speed RGB to YPBPR Converter

High Speed RGB to YPBPR Converter

An LT6559 and an LT1395 can also be used to map RGB signals into YPBPR “component” video. The LT1395 performs a weighted inverting addition of all three inputs. The LT1395 output includes an amplification of the R input by –324/1.07k = –0.3. The amplifi cation of the G input is by –324/549 = –0.59. Finally, the B input is amplified by –324/2.94k = – 0.11. Therefore the LT1395 output is –0.3R, –0.59G, –0.11B = –Y. This output is further scaled and inverted by –301/150 = –2 by LT6559 section A2, thus producing 2Y. With the division by two that occurs due to the termination resistors, the desired Y signal is generated at the load. The LT6559 section A1 provides a gain of 2 for the R signal, and performs a subtraction of 2Y from the section A2 output. The output resistor divider provides a scaling factor of 0.71 and forms the 75Ω back-termination resistance. Thus the signal seen at the terminated load is the desired 0.71(R – Y) = PR. The LT6559 section A3 provides a gain of 2 for the B signal, and also performs a subtraction of 2Y from the section A2 output. The output resistor divider provides a scaling factor of 0.57 and forms the 75Ω back-termination resistance. Thus the signal seen at the terminated load is the desired 0.57(B – Y) = PB. As with the previous circuit, to develop a normal sync on the Y signal, a normal sync must be inserted on each of the R, G, and B inputs or injected directly at the Y output with controlled current pulses.