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Dual conversion radio frequency transceiver

  • US 6,118,984 A
  • Filed: 04/08/1997
  • Issued: 09/12/2000
  • Est. Priority Date: 04/08/1997
  • Status: Expired due to Term
First Claim
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1. A dual conversion radio frequency (RF) transceiver comprising:

  • an antenna for transmitting and receiving RF signals;

    a low noise amplifier for amplifying the received RF signals from the antenna;

    a mixer for mixing the amplified RF signals from the low noise amplifier with first local oscillator signals to generate first IF (intermediate frequency) signals;

    an IF filter for filtering the first IF signals from the mixer;

    a local oscillator for providing second local oscillator signals;

    a demodulator for demodulating the filtered first IF signals from the IF filter into first baseband signals by using the second oscillator signals from the local oscillator;

    a baseband circuit for processing the first baseband signals from the demodulator and generating second baseband signals comprising I signals and Q signals to be transmitted;

    a modulator for modulating the second baseband signals from the baseband circuit into second IF signals by using the second local oscillator signals from the local oscillator, the modulator comprising a phase shifter for converting the second local oscillator signals into 90 degree phase-shifted signals, an I mixer for mixing the I signals with the phase-shifted signals, a Q mixer for mixing the Q signals with the second local oscillator signals, and an adder for adding the outputs from the I and Q mixers to generate the second IF signals;

    a frequency multiplier for multiplying the frequency of the second IF signals from the modulator by a predetermined factor to generate RF signals;

    a power amplifier for amplifying the RF signals from the frequency multiplier and passing the amplified RF signals to the antenna;

    wherein when the transceiver starts receiving the RF signals, the baseband circuit will produce a fixed baseband signal, the fixed baseband signal will be modulated into fixed frequency signals by the modulator by using the second local oscillator signals and setting the I signals of the second baseband signals to a non-zero constant value and setting the Q signals to zero, and the frequency of the fixed frequency signals will be multiplied by the frequency multiplier to generate the first local oscillator signals.

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