A micropower class-AB CMOS log-domain filter for DECT applications

This paper presents a micropower second-order low-pass filter using the log-domain principle and integrated in a 0.35-mum CMOS process. It has been designed as an antialiasing filter for a DECT transceiver with a 45-kHz nominal cutoff frequency. The circuit uses transistors biased in weak inversion without requiring separate wells. It operates at 1.5-V supply voltage and its current consumption is 8 muA in idle mode. The log-domain filter is implemented with an on-chip conditioner which allows class-AB operation. It can process input currents at 5 kHz that are 25 times larger than the 200-nA bias current, Measurements up to 500 times the bias current have been done, since at 1 kHz the input current is only limited by the supply voltage.