A fully programmable sampled-data analog CMOS filter with transfer-function coefficients determined by timing

A CMOS analog signal processor which is as programmable as a digital one is discussed. This processor does not use known switched-capacitor techniques, nor does it contain any selectable capacitor (or resistor) arrays. Instead, it operates on a pulsewidth control principle in which the value of each branch gain is determined by the duty cycle of a single digitally controlled analog transmission gate. A 4-μm single-poly CMOS test IC containing all the critical analog functions was designed to demonstrate this principle at sampling frequencies up to 100 kHz. All of the processors described allow individual programming of each transfer function coefficient; one also features programmable topology, and another is capable of simultaneous multiple-signal multiple-transfer-function processing. A typical integrated fully programmable biquad shows 80-dB dynamic range.