A High-Accuracy Thin Film PCM Decoder Network Operating at 12 Mc

A precision tantalum nitride thin film integrated resistor network has been constructed to convert 9-bit parallel binary words to equivalent analog voltages at a rate of 12 megacycles per second. There are 35 precision resistors and 9 matched diode bridges that make up the decoder network. This paper concerns fabrication and performance of the resistor portion of the network. The network was fabricated on a 2x5.3 inch glazed ceramic substrate. Eighteen resistors dissipate 1/8 watt each at a power density of 9.5 watts per square inch of film. Aging tests at normal and accelerated rates show negligible resistance change and changes that occur with time or with temperature change are uniform for all resistors. The decoder network has been tested in its system application while transmitting a simulated full load of 600 telephone voice channels. The whole system converted signals with a signal to noise ratio only 1.6 db less than theoretical 9-bit performance.