The Picturephone System: Station Set Components

The Picturephone station set1 is one of the most sophisticated items of station equipment ever provided a Bell System customer for switched two-way communications. In concept, the Picturephone station set resembles a commercial closed circuit transmitter and receiver. However, the operating conditions are markedly different and impose special requirements on many of the components. To provide the optical to electrical conversion in the transmitter and the inverse in the receiver, as well as the audio and control functions, requires over 900 electrical components in the station set. These range from simple passive discrete resistors to the silicon diode array camera tube which contains over 500,000 diodes in its approximately 0.2 square inch active target area. Combinations of hybrid integrated circuits utilizing both silicon and tantalum technologies, silicon monolithic circuits, discrete solidstate devices, and discrete passive components are incorporated on the various circuit boards. Additional components consist of the camera and display tubes and two active non-solid-state devices which are used in the high-voltage power supply. The active components used in the display, control, and service units are shown in Fig. 1. To develop the complex station set circuitry in an orderly fashion, it was necessary to decide early in the design which portions of the circuitry were to be realized in integrated form. Some circuits re313