Call tone generator for radio telephony - has quartz oscillator coupled to programmable frequency divider

摘要

A call tone generator for radio telephony appts. has a quartz oscillator (1) attached to the call tone generator circuit (6). The circuit includes a quartz oscillator (1), a first divider (2), a phase difference detector (3) and a voltage controlled oscillator (4). The VCO output, which may be taken off directly is fed to a further divider (5). The quartz oscillator is in addition, coupled to a programmable divider (7) which is part of the call tone generator circuit. The divisor factor is selected by way of a number of inputs (7'). The programmable divider is connected to a further 2n:1 divider. The integer n is chosen so that the square wave output at all usable call tone frequencies has a 1:1 duty cycle.