TONALSTRAR KRETS

摘要

An electronic tone ringer responds to ringing signals on a telephone line while being unresponsive to dialing pulses or other signals on the line. Powered directly from the telephone line the ringer uses current sources to provide a high impedance to the ringer circuitry and an insensitivity to line voltage variations so that reliable operation of the ringer is maintained on long loops and with multiple ringers terminated on the line. A multitone signal for activating an electroacoustic transducer (300) is provided by frequency modulating a single oscillator (500) within the tone ringer. Frequency stability of the oscillator is insured by the use of interrelated constant current sources that provide an insensitivity to supply voltage variations over a wide range. Two of the current sources determine the duty cycle by controlling the charge and discharge current of a capacitor in the circuit. A third current source determines the voltage swing on the capacitor. By varying the current output from the third current source, the generator circuit provides a variable frequency signal.