Programmable CMOS switched-capacitor biquad using quasi-passive algorithmic DAC´s

This paper describes an electrically programmable switched-capacitor (SC) biquad using quasi-passive algorithmic digital-to-analog converters (DAC´s). Since only two equal-valued capacitors are needed for programming each capacitance value, the proposed technique offers compact, cost-effective programmability when compared to traditional programming techniques employing binary-weighted capacitor-arrays (C-arrays). A demonstration prototype chip realized in a 1.2 μm CMOS double-metal double-poly technology, and which implements an 8 b programmable SC biquad giving a wide range of lowpass, bandpass and highpass filtering functions, occupies an active area of only 0.38 mm²