Telephone line interface circuit
First Claim
1. A communications medium interface circuit which couples data to a telephone line having at least one telephone connected thereto during all normal operating conditions of the line comprising:
- a first transistorized output state connected to the telephone line having a low bridging impedance operative when the associated telephone connected to the telephone line is off-hook;
a second transistorized output stage connected to the telephone line having a high bridging impedance operative when the associated telephone connected to the telephone line is on-hook; and
means connected to the telephone line and operatively connected to each of the output stages for sensing when the associated telephone is on-hook or off-hook and for switching the circuit between the first output stage and the second output stage in response to the condition of the telephone line such that data is operably coupled to the telephone line by the first stage when the telephone is off-hook and the data is operably coupled to the telephone line by the second stage when the telephone is on-hook.
1 Assignment
0 Petitions
Accused Products
Abstract
A circuit for coupling digital or analog data signals to a telephone line. A direct coupled transistorized circuit is disclosed having three different impedance conditions: on-hook, off-hook, and loop-test. Consequently, data can be transmitted regardless of the on-hook or off-hook status of the associated telephone sets and regardless of whether or not the telephone sets are in use. In addition, data transmission can range over a frequency spectrum of approximately d-c to frequencies in the data-over-voice range. Because of the variable bridging impedance, the drive impedance is not too low during on-hook ringing and the circuit need not be disconnected during ringing or testing.
133 Citations
15 Claims
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1. A communications medium interface circuit which couples data to a telephone line having at least one telephone connected thereto during all normal operating conditions of the line comprising:
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a first transistorized output state connected to the telephone line having a low bridging impedance operative when the associated telephone connected to the telephone line is off-hook; a second transistorized output stage connected to the telephone line having a high bridging impedance operative when the associated telephone connected to the telephone line is on-hook; and means connected to the telephone line and operatively connected to each of the output stages for sensing when the associated telephone is on-hook or off-hook and for switching the circuit between the first output stage and the second output stage in response to the condition of the telephone line such that data is operably coupled to the telephone line by the first stage when the telephone is off-hook and the data is operably coupled to the telephone line by the second stage when the telephone is on-hook. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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Specification