Programmable L.F. Function Generator using High Frequency P.W.M. Techniques

The success of the application of switched mode techniques to d.c. power supplies has naturally led to developments of these techniques for the generation of a.c. voltages. Recently attention has been given to the use of microprocessors to program the outputs of these function generators. A low frequency programmable function generator has particular application in the telephone industry, where there is a requirement for sinusoidal tone wave forms at various frequencies between 16 2/3 Hz and 60 Hz to operate telephone ringing circuits. Other a.c. or pulsed d.c. functions may be required to operate relays in coin box mechanisms, and for automatic number identification. This paper discusses the concept of a bi-polar switching regulator and examines its properties in relation to the generation of d.c. and low frequency a.c. functions. Implementation problems are discussed, and the programmable function generator used in Northern Telecom´s DMS 100 is briefly described.