RADIO FREQUENCY INTEGRATED CIRCUIT FOR LOOP-BACK SELF-TEST

摘要

PROBLEM TO BE SOLVED: To provide a loop-back self-test circuit particularly applicable to cellular phone base stations.

SOLUTION: The components of the self-test circuit 10 are integrated on a common integrated circuit chip 20. The transmit signal and an LO signal are applied to a mixer 28 to convert the frequency of the transmitted signal to the frequency of a received signal. A VCO 56 generates the LO signal and a PLL 26 synchronizes the phase of the VCO signal to the phase of a reference signal. A divided reference signal and a divided VCO signal are applied to a phase comparator 52 that generates an error signal indicative of the phase difference between the reference signal and the VCO signal. The error signal is applied to a charge pump 60 that generates a current signal to tune a tank circuit 66. A voltage signal from a loop filter 62 is applied to the VCO 56 to tune it to the LO frequency.

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