A wide tuning range 4 th-order Gm-C elliptic filter for wideband multi-standards GNSS receivers

A 4 ^th order Gm-C elliptic low-pass filter with a wide continuous tuning range is presented. The continuous tuning is achieved by means of a new tuning circuit which adjusts the bias current of the Gm cell´s input stage to control the cut-off frequency. With this tuning circuit, power efficiency is achieved by scaling down the power consumption proportionally to the cut-off frequency while keeping the linearity near constant over a wide range of frequencies. To extend the tuning range of the filter, Gm switching was employed which also acts on the Gm cell´s input stage without adding any switches in the signal path. The filter was fabricated using UMC 180-nm CMOS technology on an active area of 0.23 mm². Its cut-off frequency ranges continuously from 7.4 to 27.4 MHz. This wide range of possible tuning makes the filter suitable for modern wideband GNSS signals in zero-IF receivers. The filter consumes 2.1 and 7.5 mA (from 1.8 V) at its lowest and highest cut-off frequencies, respectively, and achieves a high input IP3 of up to -1.3 dBV_RMS.