GB1378818A - Digital tone signal generator - Google Patents

Abstract

1378818 Counting apparatus ROCKWELL INTERNATIONAL CORP 24 March 1972 [27 Aug 1971] 13965/72 Heading G4D [Also in Division H4] A digital signal generator comprises a clockdriven variable ratio frequency dividing counter stepping a register arranged to cyclically generate digital representation of a waveform shape. In the dual tone telephone number sender shown depression of a push-button on a panel 2 enables via a diode matrix one wire each of sets 5 and 6. Counters 9 and 10, driven from a clock 72, on reaching predetermined counts recognized by AND gates 16 and 20 are set to counts characteristic of the depressed key and step associated shift registers 14 and 23, the frequency of stepping of the registers being characteristic of the key. Each register has its last stage connected back to its first stage such that with four stage registers four "ones" followed by four "zeros" pass through the registers. The ones enables drivers 36 to 39 and 45 to 48 supplying power to resistors having values 2R and R and having their outputs combined to produce at 4 the required dual tone digital representations. The drivers and logic gates may be field effect transistor circuits. The circuits may be integrated. High voltage P- channel devices, N-channel, silicon gate, CMOS and other types of field effect transistors and bipolar devices are suggested alternatives.