Duplex communication transceiver with modulation cancellation

• US 4,520,474 A
• Filed: 12/05/1983
• Issued: 05/28/1985
• Est. Priority Date: 12/05/1983
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Vilmur, Richard J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/558,685
• Time in Patent Office: 540 Days
• Field of Search: 370/24, 370/30, 370/32, 370/36, 455/63, 455/73, 455/86, 455/87, 455/76
• US Class Current: 370/278
• CPC Class Codes: H04B 1/408 the transmitter oscillator frequency being identical to the receiver local oscillator frequency

Abstract

A duplex FM communication transceiver 10 is disclosed in which a modulated transmit carrier signal is utilized as the receiver first mixer (32) injection signal. The receiver portion of the transceiver comprises dual conversion circuitry, and the transmit information signal used for modulating the transmit carrier signal is phase and amplitude adjusted and then utilized to modulate the receiver second injection local oscillator 41 which provides the input injection signal to the receiver second mixer 36. The second mixer substantially cancels all of the transmit information signal and provides just received information signals to a demodulator 43 which provides audio signals to a speaker 46.

Claims

1. A duplex communication transceiver comprising:

transmitter means for providing for information transmission an output signal comprising a first carrier signal having a first predetermined frequency and modulated by a first information signal;

receiver means, coupled to and simultaneously operable with said transmitter means, for receiving an input signal comprising a second carrier signal having a second predetermined frequency different from said first frequency and modulated by a second information signal different from said first information signal, said receiver means effectively demodulating said input signal and providing said second information signal in response thereto;

said receiver means including;

a first mixer means coupled to said transmitter means for receiving said modulated first and second carrier signals and for providing, in response thereto, a first IF signal modulated with said first and second information signals, said first IF signal having an IF frequency comprising an arithmetic combination of the frequencies of said first and second carrier signals,

a first IF means fixed tuned to said IF frequency and coupled to said first mixer means for receiving and passing said first IF signal and rejecting signals at substantially different frequencies,

a second mixer means coupled to said first IF means for receiving said passed modulated first IF signal therefrom and also receiving, from a local oscillator means, a local oscillator carrier signal having a predetermined local oscillator frequency and modulated by a signal related to said first information signal, and for providing in response thereto a modulated second IF signal having a second IF frequency comprising the arithmetic combination of said first IF frequency and said local oscillator frequency,

signal adjustment means coupled to said transmitter means and said local oscillator means for receiving said first information signal from said transmitter means and adjusting it to provide said modulating related signal such that said second mixer means cancels said first information signal modulation contained in said first IF signal so that said second IF signal substantially comprises a carrier signal at said second IF frequency modulated by just said second information signal, and

demodulator means coupled to said second mixer means for receiving said modulated second IF signal and providing said second information signal in response thereto.

2. A duplex communication transceiver according to claim 1 wherein said transmitter means includes apparatus for radiating said transmitter output signal at RF frequencies and wherein said receiver means includes apparatus for providing said modulated second carrier signal in response to received RF radiation.

3. A duplex communication transceiver according to claim 1 wherein said signal adjustment means comprises phase and amplitude adjustment apparatus to adjust the phase and amplitude relationship of said related signal to said first information signal to obtain the cancellation of said first information signal in said second IF signal.

4. A duplex communication transceiver according to claim 3 wherein the amount of phase and amplitude adjustment provided by said signal adjustment means compensates for the attenuation and phase adjustment provided to said first information signal by said first mixer means and said first IF means.

5. A duplex communication transceiver according to claim 4 wherein said transmitter means utilizes frequency modulation to modulate said first carrier signal with said first information signal and wherein said demodulator means utilizes frequency demodulation circuitry to provide said second information signal in response to said second IF signal.

6. A duplex communication transceiver according to claim 5 wherein said transmitter means includes a first carrier signal oscillator for receiving said first information signal and FM modulating said first carrier signal therewith to provide said transmitter output signal.

7. A duplex communication transceiver according to claim 6 wherein said receiver means includes a voltage controlled oscillator means for receiving said related signal and providing an FM modulated signal as said modulated local oscillator carrier signal which is coupled to said second mixer means.

8. A duplex communication transceiver according to claim 7 wherein said voltage controlled oscillator means provides a fixed frequency output signal in the absence of said related signal.

9. A duplex communication transceiver according to claim 6 wherein said transmitter means includes audio signal generator means for providing an audio information signal as said first information signal.

10. A duplex communication transceiver according to claim 1 wherein said signal adjustment means comprises a circuit network for receiving said first information signal and providing in response thereto said related signal, said network comprising a first operational amplifier stage having a preselected resistance in its feedback path to provide an amplitude adjustment and a second additional operational amplifier connected in series with said first operation amplifier having a preselected resistance coupled to a capacitor which together form an all pass filter connected in series with the input of said second operational amplifier to provide a phase adjustment.