Integrated ringer for short telephone lines

Apparatus for coupling a subscriber line with a digital signal path in a telephone system, the apparatus receiving information including a ring command from said digital signal path, said subscriber line being coupled with a subscriber telephone device, said subscriber telephone device including a signal generator and hook switch, said subscriber line having a first conductor and a second conductor, said hook switch having a first state and a second state, said signal generator generating a ringing indication in response to a ringing signal on said subscriber line when said hook switch is in said second state, the apparatus comprising:

• an interface for coupling the apparatus with said subscriber line;
• a ringer coupled with said interface for providing said ringing signal to said subscriber line, said ringing signal including only a first time varying signal and a second time varying signal, said ringer providing said first time varying signal and said second time varying signal in response to said ring command;
• and
• a detector coupled with said interface for detecting only an AC impedance between said first conductor and said second conductor in the presence of said ringing signal, said AC impedance having a first value when said hook switch has said first state and a second value when said hook switch has said second state, said detector providing a ring trip indication when said AC impedance has one of said first value and said second value, said interface, said ringer and said detector being integrated in a common integrated circuit.

Apparatus for use with a subscriber line interface circuit in a telephone system, the subscriber line interface circuit being interposed between a telephone central office and a subscriber line, the subscriber line being coupled with a subscriber telephone device, the subscriber line having a first conductor and a second conductor, the apparatus comprising:

• a first interface circuit for coupling with said subscriber line;
• a second interface circuit for coupling with said telephone central office and receiving a ring command from said telephone central office;
• a ringing generator coupled with said first interface circuit, said ringing generator providing a first ringing signal to said first conductor and a second ringing signal to said second conductor in response to said ring command, said first ringing signal and said second ringing signal being balanced, time varying signals, said subscriber telephone device producing a ringing indication in response to said first ringing signal and said second ringing signal;
• and
• an AC impedance detector coupled with said first interface circuit, said AC impedance detector detecting only an AC impedance between said first conductor and said second conductor in the presence of said first ringing signal and said second ringing signal, said AC impedance detector providing a ring trip indication when said impedance is below a predetermined threshold;
• said first interface circuit, said second interface circuit, said ringing generator, and said AC impedance detector being integrated in a common integrated circuit.

An improved subscriber line interface circuit for coupling to a subscriber line, the subscriber line being coupled with a subscriber telephone device, the subscriber line having a first conductor and a second conductor, the subscriber line interface circuit comprising:

• a first interface circuit for coupling with said subscriber line;
• a second interface circuit for coupling with said telephone central office and receiving a ring command from said telephone central office;
• a ringing generator coupled with said first interface circuit, said ringing generator providing a first ringing signal to said first conductor and a second ringing signal to said second conductor in response to said ring command, said first signal and said second ringing signal being balanced, time varying signals, said subscriber telephone device producing a ringing indication in response to said first ringing signal and said second ringing signal;
• and
• an AC impedance detector coupled with said first interface circuit, said AC impedance detector detecting only an AC impedance between said first conductor and said second conductor in the presence of said first ringing signal and said second ringing signal, said AC impedance detector providing a ring trip indication when said impedance is below a predetermined impedance threshold;
• said first interface circuit, said second interface circuit, said ringing generator, and said AC impedance detector being integrated in a common integrated circuit.