A class of digitally programmable nth‐order filters

Abstract

SUMMARYA 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-m CMOS process are provided.

Highly linear wide‐swing continuous tuning of CMOS transconductors

“…However, these programmable current mirrors often provide limited linearity and reduce the output range available. A better approach in terms of linearity is using current splitting [11][12][13][14][15][16]. Unfortunately, this technique often limits the input and output range as will be shown below.…”

1.5 V square‐root domain universal biquad filters

“…An important subclass of second‐order filters is the universal biquads, denoted as the topologies which offer the five standard filter functions: lowpass (LP), highpass (HP), bandpass (BP), bandstop (BS), and allpass (AP). Universal biquads are widely used in realization of analog signal processing systems, such as three‐way crossover networks for high‐fidelity loudspeakers, touchtone telephone systems and phase‐locked loop FM stereo demodulators .…”