A receiver front-end with variable-gain control for WiMAX applications

A receiver front-end for WiMAX applications has been designed and fabricated on 90-nm CMOS technique. The front-end circuit covers the frequency range from 2.3GHz to 2.7GHz. In this design, the components included a single-to-differential low-noise amplifier (LNA), demodulator, a divided-by-2 circuit, and buffers. The LNA, with a variable-gain control, respects the input-signal power to match the specific requirement of linearity. This LNA structure can avoid the signal distortion caused by insufficiency of linearity. As for demodulator, it consists of a gm-stage (transconductor amplifier), a passive mixer, and a transimpedance amplifier. This demodulator adopts a current-mode structure to overcome transfer-power loss resulted from voltage transfer. The receiver front-end provides variable-gain range from 4dB to 30dB. The maximum gain and noise figure of this circuit achieve 30dB and 4.5dB, respectively. The chip consumes 22mW from a 1.2-V power supply.