Integrated interface circuit for driving a subscriber line

An integrated interface circuit for a telephone subscriber line, comprising:

• a switching circuit having an output, first and second switch inputs, and a control terminal, the switching circuit being responsive to a control signal at the control terminal to selectively couple the first or second input to the output;
• a storage circuit coupled to the switching circuit output;
• a charging circuit coupled to the first switch input;
• a discharging circuit coupled the second switch input;
• a phase splitter coupled to the storage circuit and responsive to produce a pair of inverse output signals at respective first and second splitter outputs in response to the voltage of the storage circuit;
• a comparing circuit having a first input coupled to the first splitter output, a second input coupled to the second splitter output, and a compare output, the comparator being responsive to produce a first compare signal at the compare output in response to the voltage of the first splitter output being greater than the voltage of the second splitter output and to output a second compare signal in response to the voltage of the first splitter output being less than the voltage of the second splitter output;
• and
• a control circuit having a logic input coupled to the compare output and a logic output coupled to the control terminal, the control circuit producing the control signal in response to the first or second compare signal.

A method of reversing polarity in an integrated interface circuit in response to a reversal signal, comprising the steps of:

• charging a storage capacitor at a predetermined charging rate for a first interval in response to the reversal signal;
• producing a pair of inverse signals indicative of a capacitor voltage;
• comparing the inverse signals;
• in response to a first of the inverse signals exceeding the second inverse signal, discharging the capacitor at a predetermined discharging rate;
• in response to the first of the inverse signals being less than the second inverse signal, charging the capacitor at a predetermined charging rate;
• in response to the first of the inverse signals being less than the second inverse signal, outputting the first inverse signal at a first output terminal;
• and
• in response to the first of the inverse signals exceeding the second inverse signal, outputting the second inverse signal at a first output terminal.