The HD155121F is a RF transceiver IC for GSM and PCN dual band cellular systems, and integrates most of the low power silicon functions of a transceiver. The HD155121F incorporates two bias circuits for RF LNAs, two first mixers, a second mixer, a programmable gain amplifier, and an IQ demodulator for the receiver, and an IQ modulator and offset PLL for the transmitter. Also, on chip are dividers for the phase splitter. Moreover the HD155121F includes control circuits to implement power saving modes. These functions can operate down to 2.7 V and are housed in a 48-pin LQFP SMD package. Hence the HD155121F can form a small size transceiver handset for dual band by adding a dual PLL frequency synthesizer IC, power amplifiers and some external components. The HD155121F is fabricated using a 0.6 m double-polysilicon Bi-CMOS process.