A compandor using junction transistors

A compandor for use on telephone speech circuits, which has a compression/expansion ratio of 2, and which gives a subjective improvement in signal/noise ratio of about 25 dB, is described. Junction transistors are used as variable-loss elements, control-current rectifiers and for temperature compensation, as well as for amplification. Use is made of the properties of the base-emitter junction of the transistor to achieve a closer approximation to the desired compression/expansion characteristic, over a wider range of signal levels than has been possible in the past, without the need for special selection or matching of the variable-loss circuit elements. A small number of compandors has been made and tested in the laboratory, and the performance of a typical unit is described.