This circuit is a video line driver specifically intended for use with a single-ended power supply. As a matter of fact, the synchronized outputs of a line driver for composite-video signals go negative with respect to ground. In order to be able to process these negative signals in a circuit powered from a single-ended supply, it is necessary to AC-couple the input of the opamp as well as level-shift the signal in the positive direction.
The input is terminated into a 75 Ω resistor (R1). From here, the signal passes through AC-coupling capacitor C2 and is applied to potential divider R2-R3, which provides the necessary DC-offset. The shift in the positive direction amounts to +1.7 V, with the values shown in the schematic. To avoid any misunderstandings we should add that this value is fairly critical. Deviating from the values shown can lead to distortion in the complementary input stage of the opamp that has been used here, and this, of course, has to be avoided.
Because we provided the circuit with its own voltage regulator circuit (IC2), just about any mains adapter will suffice for the power supply. The current consumption is less than 20 mA. The construction of the line driver using the accompanying printed circuit board layout is no more than a simple, routine job.
