Electronic ringing arrangements in telephone systems

Claim 1

IN A TELEPHONE SYSTEM INCLUDING A CENTRAL OFFICE HAVING A SOURCE OF DIRECT CURRENT AND A SOURCE OF LOW POWER VOICE FREQUENCY SIGNAL CURRENT INTERRUPTED IN AN ON-OFF PATTERN, AND A SUBSCRIBER LINES, AN ARRANGEMENT CONNECTED TO AND POWERED OVER SAID LINE BY SAID DIRECT CURRENT SOURCE FOR GENERATING AN AUDIBLE TONE THAT IS INDEPENDENT OF SAID SIGNAL FREQUENCY, SAID ARRANGEMENT COMPRISING: AN OSCILLATOR FOR GENERATING SAID AUDIBLE TONE, SAID OSCILLATOR INCLUDING A TRANSISTOR HAVING AN INPUT AND AN OUTPUT, AND A FIRST RESONANT CIRCUIT HAVING A SOUND TANSDUCER CONNECTED TO SAID OUTPUT OF SAID TRANSISTOR; A SECOND RESONANT CIRCUIT COUPLED TO SAID LINE, SAID SECOND RESONANT CIRCUIT BEING TUNED TO SAID LOW POWER VOICE FREQUENCY; MEANS CONNECTED TO SAID SECOND RESONANT CIRCUIT FOR RECTIFYING AND FILTERING SAID LOW POWER VOICE FREQUENCY SIGNALS AND FOR ISOLATING SAID SIGNALS FROM THE INPUT OF SAID TRANSISTOR; AND MEANS INTERPOSED BETWEEN SAID RECEITIFER AND FILTER MEANS AND SAID INPUT OF SAID TRANSISTOR FOR CONTROLLING THE OPERATION OF SAID OSCILLATOR IN ACCORDANCE WITH SAID ON-OFF PATTERN.