Rf architecture for cellular multi-band telephones

Abstract

A multi-band RF architecture including a GSM quadrature modulator for modulating an intermediate frequency (IF) wherein the frequency of the modulated IF signal is changed such that each of the GSM, DCS 1800, and PCS 1900 bands have a respective IF. An intermediate frequency (IF) filter with a pass band that covers the GSM IF, the DCS 1800 IF, and the PCS 1900 IF is connected to the output of the modulator and outputs to a transmit phase lock loop, which translates the IF signal from the IF filter to either a GSM band radio frequency signal, a DCS 1800 band radio frequency signal, or a PCS 1900 band radio frequency signal, depending on the frequency of a local oscillator (LO). The receiver employs a down converter which provides a down converted output signal selected by high side injection for the GSM band an by low side injection for the DCS 1800 and PCS 1900 bands. The down converter outputs to an intermediate frequency (IF) receiver filter centered at 400 MHz designed to pass either the down converted GSM signal, the down converted DCS signal, or the down converted PCS signal to demodulation circuitry. A single phase lock loop circuit is used to supply, on a single output, the LO signal for down converting either the GSM receive band, the DCS 1800 receive band, or the PCS 1900 receive band, as well as the LO for the transmit phase lock loop.