Gold Doped Silicon Compandor Diodes for N2 and N3 Carrier Systems

Compandors are a special application for a diode because the diodes are used as variolossers and the electrical parameter which must be controlled is the small signal forward impedance as a function of bias current. Furthermore, control of impedance is required over two orders of magnitude. Other requirements are low noise and good stability. The 484/489A and 484/489B diode pairs, which are electrically identical and differ only in mechanical out line, are silicon "planar" diodes which were designed for use in this application. The new devices were designed to replace two pairs of troublesome unpassivated "mesa" type devices in both the N2 and N3 carrier systems. A comprehensive diode design was not previously available for this application. Diodes were obtained by selection from available types at low yield. This paper discusses the theoretical and empirical design and the fabrication of the new diodes. 1451 1452 T H E BELL SYSTEM TECHNICAL .JOURNAL, SEPTEMBER 1«)«7 I I . C I R C U I T F U N C T I O N O F COMPANDORS