A CMOS low-power widely programmable active RC filter based on a hybrid CS/D network

This paper presents an enhanced digital tuning approach for RC-active direct form circuits. By introducing a combined summing/dividing network for the current that flows from resistors to virtual grounds, an accurate frequency trimming is accomplished bringing out a linear dependence on the digital input code over a wide tuning range. Simulation results of a monolithic 12-bit 1.8 V–0.18 μm CMOS second order filter provide a 11.46-bit effective resolution to linearly control the frequency over three decades with distortion levels better than −70 dB for 1.5 Vp-p. The power consumption is below 0.5 mW with an active area of 0.087 mm
²
, which makes it suitable for battery-operated on-chip systems.