Interface circuit for telecommunications devices
First Claim
1. A circuit for adapting a telecommunications device having on-hook and off-hook states and a two-wire interface to a cellular mobile radiotelephone having an audio transmit interface, an audio receive interface, and a contact which controls cellular mobile radiotelephone muting, said circuit comprising:
- a two-wire bidirectional port for coupling to said telecommunications device two-wire interface;
a transmit port for coupling to said cellular mobile radiotelephone audio transmit interface;
a receive port for coupling to said cellular mobile radiotelephone audio receive interface;
a switchhook terminal for coupling to said muting control contact;
a first amplifier having an input coupled to said receive port and an output coupled to said bidirectional port, said first amplifier output supplying a received signal;
a second amplifier having a first input coupled to said first amplifier output, a second input coupled to said bidirectional port, and an output coupled to said transmit port, said second amplifier being configured so that said received signal as amplified through said first input substantially cancels said received signal as amplified through said second input; and
means, coupled to said bidirectional port and to said switchhook terminal, for detecting said off-hook state of said telecommunications device.
1 Assignment
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Accused Products
Abstract
An interface circuit which adapts an existing telecommunications device, such as a facsimile machine, to successfully operate through an existing cellular mobile radiotelephone. No significant modifications are required of the telecommunications device or of the cellular mobile radiotelephone. The interface circuit includes circuitry to convert a two-wire communication interface of the telecommunications device into a four-wire communication interface required by the cellular mobile radiotelephone. This circuitry includes a received signal altering circuit which permits controlling side tone cancellation independently of transmitted and received signal gain control. In addition, the interface circuit includes a switchhook status detector which monitors the switchhook state of the telecommunications device to control muting in the cellular mobile radiotelephone. The muting of the cellular mobile radiotelephone prevents contamination of transmitted data from the telecommunications device and protects a user from hearing displeasing sounds associated with handshaking signals and data communication.
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Citations
29 Claims
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1. A circuit for adapting a telecommunications device having on-hook and off-hook states and a two-wire interface to a cellular mobile radiotelephone having an audio transmit interface, an audio receive interface, and a contact which controls cellular mobile radiotelephone muting, said circuit comprising:
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a two-wire bidirectional port for coupling to said telecommunications device two-wire interface; a transmit port for coupling to said cellular mobile radiotelephone audio transmit interface; a receive port for coupling to said cellular mobile radiotelephone audio receive interface; a switchhook terminal for coupling to said muting control contact; a first amplifier having an input coupled to said receive port and an output coupled to said bidirectional port, said first amplifier output supplying a received signal; a second amplifier having a first input coupled to said first amplifier output, a second input coupled to said bidirectional port, and an output coupled to said transmit port, said second amplifier being configured so that said received signal as amplified through said first input substantially cancels said received signal as amplified through said second input; and means, coupled to said bidirectional port and to said switchhook terminal, for detecting said off-hook state of said telecommunications device. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A circuit for detecting an off-hook state of a remote telecommunications device which is coupled to a two-wire port having a signal terminal and a reference terminal, said circuit comprising:
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a supply terminal adapted to supply a first reference potential; a first resistor coupled between said signal terminal and said reference terminal; a second resistor coupled between said supply terminal and said signal terminal; a comparator having a first input coupled to said signal terminal and a second input adapted to receive a second reference potential, said second reference potential being between said first reference potential and a potential exhibited by said reference terminal. - View Dependent Claims (12, 13)
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14. A method of adapting a line signal, to which a telecommunications device couples, into a transmitted audio signal, a received audio signal, and into a muting control signal, to which signals a cellular mobile radiotelephone transceiver couples, said method comprising the steps of:
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buffering said received audio signal to supply a received signal; driving said line signal with said received signal so that said received signal forms at least a component of said line signal; altering the amplitude of said received signal in a manner which has substantially no influence on said received signal, said altering step generating an altered received signal; adding said line signal to said altered received signal to produce a summation signal in which said received signal component of said line signal substantially reduces said altered received signal; driving said transmitted audio signal with said summation signal; and monitoring said line signal to determine an off-hook condition at said telecommunications device and to provide an indication of said off-hook condition for control of muting in said cellular mobile radiotelephone. - View Dependent Claims (15, 16, 17, 18)
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19. An interface apparatus for coupling a facsimile machine to a control head associated with a cellular mobile radiotelephone (CMR) transceiver, the interface apparatus comprising:
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a two-wire, bidirectional port for coupling to the facsimile machine; a four-wire port for coupling to the control head, the four-wire port comprising a two-wire, unidirectional, RX port and comprising a two-wire, unidirectional, TX port; and muting means coupled between the two-wire, bidirectional port and the control head for providing a muting signal to the control head, which muting signal is developed in response to a predetermined operating condition of the facsimile machine so as to substantially effect the amplitude of a signal present at the RX port. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26)
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27. An interface circuit for interconnecting a two wire bi-directional port with both an audio transmit port and an audio receive port, comprising:
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receive amplifier means having an input coupled to the audio receive port and an output coupled to the bi-directional port for producing receive signals that contribute components of a signal present at the bi-directional port, transmit amplifier means having an input connected to the bi-directional port and an output coupled to the audio transmit port for producing a transmit signal, and altering means connected between the output of the receive amplifier and another input of the transmit amplifier for applying modified receive signals to the transmit amplifier whereby the receive signal components present upon different inputs to the transmit amplifier are reduced in the transmit signal produced by the transmit amplifier means. - View Dependent Claims (28, 29)
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Specification