A low-voltage active-RC filter for wideband communication transceivers

A low -voltage wide-band active-RC filter for wireless communication transceivers is presented. It is the 5th-order Chebyshev-II low pass filter with the bandwidth of 20 MHz. To guarantee high linear characteristic at a low supply voltage, the input common-mode level shifting circuit is added at the inputstage of the operational amplifier so that the input common-mode levelof the amplifier can be set close to one of the supply rails. The measured result of the IIP3 (3rd-order input intercept point) is about 24 dBm. A fast and accurate frequency tuning circuit is included to compensate RC variation. The filter is fabricated in a 0.25-mum CMOS standard process and dissipates 30 mW for a supply voltage of 12 V.