Telephone loop current modulator
First Claim
1. For use with a telephone system including a telephone company central office for providing a loop current and a subscriber line which conducts said loop current, a transformerless loop current modulator responsive to an audio input signal for placing audio signals onto said subscriber line by modulating said loop current, comprising:
- variable resistance means connected across said subscriber line for modulating said loop current by conducting a variable current corresponding to a bias voltage;
biasing means for providing said bias voltage, said bias voltage biasing said variable resistance means in a linear operating region;
modulating means responsive to said audio input signal for modulating said bias voltage; and
switching means connected to said biasing means and responsive to a digital command signal for allowing said variable current to be conducted by enabling said variable resistance means.
12 Assignments
0 Petitions
Accused Products
Abstract
An improvement to automatic answering and call forwarding features used in telephone communications which allows a user to remotely activate, modify, and deactivate these features. The improvement describes a transformerless means for coupling signals to and from the telephone line without compromising the operation of the telephone line. The apparatus employs a microprocessor controller (11) with memory (12), a tone encoder (15), a toner decoder (14), a voice synthesizer (16), a timer (13), a cassette interface (17), an RS232C interface (20), a switching matrix (21), and a line interface (22). Audio, pulse dial, and tone signals are routed among the components and the telephone line (51) by the switching matrix (21) and line interface (22). The line interface (22) provides a transformerless means for coupling signals to and from the telephone line (51) and also analyzes the status of, and signals present on, the telephone line (51).
17 Citations
14 Claims
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1. For use with a telephone system including a telephone company central office for providing a loop current and a subscriber line which conducts said loop current, a transformerless loop current modulator responsive to an audio input signal for placing audio signals onto said subscriber line by modulating said loop current, comprising:
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variable resistance means connected across said subscriber line for modulating said loop current by conducting a variable current corresponding to a bias voltage; biasing means for providing said bias voltage, said bias voltage biasing said variable resistance means in a linear operating region; modulating means responsive to said audio input signal for modulating said bias voltage; and switching means connected to said biasing means and responsive to a digital command signal for allowing said variable current to be conducted by enabling said variable resistance means. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. For use with a telephone system including a telephone company central office for providing a loop current and a subscriber line which conducts said loop current, a transformerless loop current modulator responsive to an audio input signal for placing audio signals onto said subscriber line by modulating said loop current, comprising:
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a controllable current source connected across said subscriber line for modulating said loop current by sourcing a controlled current corresponding to a bias signal; biasing means for providing said bias signal, said bias signal biasing said controllable current source in a linear operating region; modulating means responsive to said audio input signal for modulating said bias signal; and switching means responsive to a digital command signal for allowing said controlled current to be sourced by enabling said controlled current source. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification