A 1.2-V LOW-POWER BICMOS CLASS AB LOG-DOMAIN FILTER

A third-order class AB current-mode Chebyshev filter based on the log- domain instantaneous companding principle and integrated in a 1-mu m B iCMOS process is presented, It has a nominal cutoff frequency of 320 k Hz corresponding to a bias current of 1 mu A and can be frequency tune d over almost three decades up to about 10 MHz. It operates with a nom inal supply voltage of 1.2 V maintaining a dynamic range at 1% total h armonic distortion (THD) of 65 dB, For cutoff frequencies in the range of 10 kHz, the supply voltage can be reduced down to 0.9 V, Typical t o companding systems, the class AB filter shows a measured SNR versus input signal that saturates to a maximum value which for this particul ar realization is 52.5 dB, It has an active area of 0.55 mm(2) and dis sipates 65 mu W, leading to a power consumption per pole and edge freq uency of 67.7 pJ, These results demonstrate the potential of instantan eous companding filters for very low-voltage and low-power application s with moderate linearity and SNR requirements.