Radio frequency integrated circuit for loopback self-test

摘要

A loop-back self-test circuit ( 10 ) that has particular application for a cellular telephone base station, where 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 transmit signal to the frequency of a receive 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.