Line powered modem
First Claim
Patent Images
1. A telephone line powered modem comprising:
- a first circuit for coupling to a telephone line and operative wholly in response to telephone line power to provide operating power for all modem circuits;
said first circuit including a solid state shunt regulator circuit providing a voltage which is substantially constant irrespective of variations in current from the telephone line, and a current source operating as a constant current source for AC and self adjusting for DC current and operative to provide a low DC resistance and high AC impedance such that audio frequency variations in line voltage cause no appreciable current change through the load;
a modem receiver subsystem powered by the first circuit and operative to provide data signals derived from signals received on the telephone line; and
a modem transmitter subsystem powered by the first circuit and operative in response to data from a source to provide modulated data signals to the telephone line.
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Accused Products
Abstract
A modem for coupling a data terminal or other apparatus to a telephone line and deriving its operating power for both transmitting and receiving operation from the telephone line, and providing electrical isolation between the telephone line and the data terminal.
89 Citations
20 Claims
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1. A telephone line powered modem comprising:
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a first circuit for coupling to a telephone line and operative wholly in response to telephone line power to provide operating power for all modem circuits; said first circuit including a solid state shunt regulator circuit providing a voltage which is substantially constant irrespective of variations in current from the telephone line, and a current source operating as a constant current source for AC and self adjusting for DC current and operative to provide a low DC resistance and high AC impedance such that audio frequency variations in line voltage cause no appreciable current change through the load; a modem receiver subsystem powered by the first circuit and operative to provide data signals derived from signals received on the telephone line; and a modem transmitter subsystem powered by the first circuit and operative in response to data from a source to provide modulated data signals to the telephone line. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. For use in a telephone line powered modem which includes a receiver operative to provide data signals derived from signals received on a telephone line, and a transmitter operative in response to data from a source to provide modulated data signals for transmission on the telephone line, a circuit operative wholly in response to telephone line power to provide operating power for itself and said transmitter and receiver, said circuit comprising:
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first means for providing substantially constant operating voltages for the modem and minimum current sufficient to hold the telephone line in an off hook condition; and second means providing a low DC resistance and a high AC impedance substantially matched to the telephone line impedance, wherein said second means includes; a solid state shunt regulator circuit operative to maintain substantially constant voltage across the modem circuits constituting the load, and to limit the voltage drop on the telephone line to ensure a predetermined minimum DC line current; and a current source operative as a constant current source for AC current and self-adjusting for DC current, and operative to pass DC current to maintain a predetermined AC impedance to match the telephone line. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification