A 4th-order active-Gm-RC low-pass filter with RC time constant auto-tuning for reconfigurable wireless receivers

Based on 0.18μm RF CMOS process, a 4th-order Butterworth low-pass filter (LPF) used in reconfigurable wireless receivers (for WCDMA and GPS/Galileo) is presented in this paper. The LPF adopts active-Gm-RC structure, and can satisfy both WCDMA and GPS/Galileo requirements, which maximizes hardware reuse. A RC time constant auto-tuning circuit is applied to improve the accuracy of bandwidth. The chip area occupies 0.78mm². The LPF is measured on wafer. With 1.8V power supply, the core circuit of the LPF consumes 1mW and 1.6 mW for WCDMA and GPS/Galileo respectively. The out of band attenuation rate is about -78dB/10 octave. The measured 1dB compression point is severally -3.0dBm and -5.1dBm.