Method and apparatus for isolation in a data access...

Telephonic communications – Subscriber line or transmission line interface – Circuitry to provide a coder and decoder function

Reexamination Certificate

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Reexamination Certificate

active

07031458

ABSTRACT:
The present invention is directed toward a method and apparatus for transferring data across an isolation barrier using high speed analog encoded signals. A line side circuit interfaces with tip and ring contacts on one side of a capacitive isolation barrier that isolates the line side circuit from a modem side circuit. During an on-hook state, the line side circuit converts an analog line side voltage signal to a frequency signal and then encodes the frequency signal into a high frequency pulse-width-modulated (PWM) signal. The high frequency PWM signal is transmitted across the capacitive isolation barrier to the modem side circuit. During an off-hook state, the analog line side voltage is again encoded into a high frequency pulse-width-modulated (PWM) signal for transmission across the isolation barrier. The modem side circuit recovers the transmitted PWM signal and converts it into a digital count value that represents the amplitude of the analog voltage observed at the tip and ring. The digital count value may be directly processed by a processor on the modem side or may be converted back to an analog signal.

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Allen et al., “CMOS Analog Circuit Design,” HRW Series in Electrical and Computer Engineering, 349-357 (1987).
Copy of European Search Report established for EP 02024427.3.

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