A 100 tap FIR/IIR analog linear-phase lowpass filter

Abstract

A 5 kHz linear-phase lowpass filter is implemented in a 2-/spl mu/m BiCMOS technology as a combination of a sigma-delta front-end, a digital shift register, an SC summer circuit of 50 input capacitors and an SC biquad running at a 1 MHz clock. The measured group delay variation in the passband is less than 1 /spl mu/s and the measured THD is -80 dB for an input sine wave amplitude of 0.7 V at 1 kHz.