A Fully Integrated Single-Ended 1.5–15-Hz Low-Pass Filter With Linear Tuning Law

A second-order, single-ended, fully integrated low- pass filter with cut-off frequency tunable in the range 1.5-15 Hz is presented. The filter is based on a recently proposed CMOS transconductor topology, combining G_m values of the order of a few nS with large input ranges and suitability to single-ended filter architectures. The circuit has been designed and fabricated using 3.3-V 0.35-mum CMOS devices from the STMicroelectronics Bipolar-CMOS-DMOS process BCD6. The tested prototype occupies an area of 960 x 350 mum² and requires a supply current ranging from 50 to 500 muLambda, depending on tuning. Total harmonic distortion lower than 1% has been measured in a wide tuning range for 1-V peak-to-peak input signal amplitude. The effect of temperature on the tuning law in the interval 0-80degC is shown. A dynamic range in excess of 60 dB over the whole tuning range has been estimated from distortion and noise measurements.