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-μm BiCMOS process is presented. It has a nominal cutoff frequency of 320 kHz corresponding to a bias current of 1 μA and can be frequency tuned over almost three decades up to about 10 MHz. It operates with a nominal supply voltage of 1.2 V maintaining a dynamic range at 1% total harmonic 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 to companding systems, the class AB filter shows a measured SNR versus input signal that saturates to a maximum value which for this particular realization is 52.5 dB. It has an active area of 0.55 mm² and dissipates 65 μW, leading to a power consumption per pole and edge frequency of 67.7 pJ. These results demonstrate the potential of instantaneous companding filters for very low-voltage and low-power applications with moderate linearity and SNR requirements