A class of digitally programmable nth-order filters

A family of new high-order filters capable of providing all filter functions without changing the circuit topology is proposed for integrated circuit applications. The proposed filters are based on simple active elements, namely, digitally controlled current amplifiers (DCCAs) and unity gain voltage buffers (VBs). Gains of DCCAs are digitally programmed to adjust the coefficients of transfer functions. R2R ladders are also utilized to increase the tuning flexibility of the proposed filters. A filter replicating the famous KHN biquad is extended to realize general nth-order filters. Comparison with the recent works shows that the proposed approach results in more efficient realizations compared with its counterparts based on other current-mode active elements. Experimental results obtained from a fourth-order filter implemented using devices fabricated in a 0.35-μm CMOS process are provided.