Telephone voice frequencies generator - has two logic channels with common time base and filter to obtain sinusoidal signals

摘要

A voice frequency generator used with telecommunication systems is controlled by a numbered keyboard. The keyboard is connected to an encoder which gives for each key a high frequency and a low frequency logic level. It has two independent logic channels controlled by a common time base. Each channel has a logic part and an analogue part. The logic part comprises a frequency generator to give a signal proportional to a coded frequency. The analogue part comprises an active filter which transforms the logic signal from the generator into a sinusoidal signal. The signals from the filters are supplied to a mixer followed by an adaptation circuit which are current to a line.