Electronic Circuit Collection

The circuit diagram shows two LT1398’s from Linear Technology used to create buffered color-difference signals from RGB (red-green-blue) inputs. In this application, the R input arrives via 75? coax. It is routed to the non-inverting input of amplifier IC1a and to 1.07-k? resistor, R8. There is also an 80.6-? termination resistor R11, which yields a 75-? input impedance at the R input when considered in parallel with R8. R8 connects to the inverting input of a second LT1398 amplifier (IC1b), which also sums the weighted G and B inputs to create a –0.5Y output.
Yet another LT1398 amplifier, IC2a, then takes the –0.5Y output and amplifies it by a gain of –2, resulting in the +Y output. Amplifier IC1a is configured for a non-inverting gain of 2 with the bottom of the gain resistor R2 tied to the Y output. The output IC1a thus results in the color-difference output R–Y. The B input is similar to the R input. Here, R13 when considered in parallel with R10 yields a 75-? input impedance. R10 also connects to the inverting input of ampli?er IC1b, adding the B contribution to the Y signal as discussed above.
Source : www.extremecircuits.net