A variable gain high linearity low power baseband filter for WLAN

This paper presents a 4^th order low-pass baseband filter for WLAN applications, implemented in a 1.5V 3V 0.15μm CMOS process. The active-RC configuration uses single amplifier biquads (SABs) to save power and has resistor and capacitor arrays to provide variable gain and bandwidth trimming. The biquads are implemented using three-stage opamps and a hybrid π-to-tee transformation network for the resistor arrays, so that higher linearity than conventional Sallen-Key circuits may be obtained. The filter achieves a measured THD of -72 dB at 1 MHz.