Programmable direct digital tuning circuit for a continuous-time filter

Direct tuning techniques of continuous-time filters for mobile radio receivers are discussed. Different design aspects are considered. A single-shot tuning is proposed especially for cases (CDMA) where sufficient time cannot be allocated for feedback based tuning as in time-division multiplexed radio systems (TDMA). A digital tuning circuit for the corner frequency of a continuous-time filter was designed and implemented. The chip was implemented using 0.35 µm CMOS technology. Because of the programmability the same circuit can be used to tune baseband filters in different mobile phone systems. Experimental results on GSM and WCDMA LP-filters are presented.