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Intermediate frequency circuit for cellular telephone transceiver using surface acoustic wave filter

  • US 5,170,500 A
  • Filed: 08/03/1990
  • Issued: 12/08/1992
  • Est. Priority Date: 08/03/1990
  • Status: Expired due to Term
First Claim
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1. An IF circuit for use in a cellular telephone receiver, comprising in combination:

  • (a) a first mixer circuit receiving an rf signal from a low noise input amplifier and a first local oscillator signal from a first local oscillator circuit and producing in response thereto a first signal;

    (b) a first amplifier receiving the first signal and producing an amplified second signal;

    (c) a first impedance matching circuit connected to receive the second signal and match the second signal to a first impedance;

    (d) a double-mode resonator SAW bandpass filter with a bandwidth of approximately 30 kilohertz and having an input connected to receive the second signal and producing a filtered third signal;

    (e) a second impedance matching circuit connected to receive the third signal after it is filtered by the double-mode resonator SAW bandpass filter and impedance match it to a second input impedance;

    (f) a second amplifier receiving the third signal after it has been impedance matched, and producing in response thereto a fourth signal;

    (g) a second mixer circuit receiving the fourth signal and a second local oscillator signal, and producing an IF signal in response to the fourth signal and that second local oscillator signal;

    (h) a first IF filter connected to receive and filter the IF signal;

    (i) a third amplifier connected to receive and apply the IF signal to produce an amplified IF signal;

    (j) a detector circuit connected to produce an audio frequency output signal in response to the amplified IF signal.

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