A 4MHz Gm-C filter with on-chip frequency automatic tuning

A fifth-order elliptic low-pass Gm-C filter used in monolithic DAB receiver is presented, the filter integrates an on-chip frequency automatic tuning circuit based on PLL to control the cutoff frequency. The filter has been implemented in 0.25/spl mu/um CMOS process. The measurement results show that the frequency tuning error is within 1%, the dynamic range is 54dB, the stop-band rejection rate is greater than 40dB. The filter draws 13mA current from a 3.3V power supply.