Digital Tuning of Gm-C Baseband Filters in Configurable Radio Receivers

A master/slave technique which allows to digitally tune a G_m -C filter´s cutoff frequency is proposed in the context of multi-standard configurable filters for direct conversion architectures. The proposed scheme relies on an accurate transconductance division technique. It allows to fix the reference frequency independently from the filter cutoff frequency, and does not require to know the filter´s cutoff frequency tuning control law. This scheme has been implemented and measured with a G_m-C 5^th-order Butterworth low-pass filter in a 0.13mum 1.2-V CMOS process. It ensures a less than 5% error on a large tuning range, allowing its use in multimode mobile cellular applications. The chip area is 0.16mm² and its power consumption is reduced to less than 500μW.