Radio frequency integrated circuit for loopback self-test

Abstract

A loop-back self-test circuit () that has particular application for a cellular telephone base station, where the components of the self-test circuit () are integrated on a common integrated circuit chip (). The transmit signal and an LO signal are applied to a mixer () to convert the frequency of the transmit signal to the frequency of a receive signal. A VCO () generates the LO signal and a PLL () 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 () 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 () that generates a current signal to tune a tank circuit (). A voltage signal from a loop filter () is applied to the VCO () to tune it to the LO frequency.