A low-voltage III-order log-domain filter in standard CMOS technology with tunable frequency

This paper presents a third order low-pass filter realized using the log-domain principle and integrated in a standard 0.8 mum CMOS process, including the signal preconditioner and compressor and the subsequent output expander. It is able to operate with supply voltages down to 1.2 V. Class AB operation has been ensured to achieve a better dynamic range. Cut-off frequency is tunable from 17 KHz to 150 KHz, and the measured current consumption is less than 100 muA in idle mode with the maximum bias current. The measured dynamic range is about 50 dB, and the circuit is able to process input peak currents more than 10 times larger than the bias current. The effect of parasitic capacitances has been studied in order to highlight a basic tradeoff between the dynamic range and the filter bandwidth.