A 28.8-MHz 23-dBm-IIP3 3.2-mW Sallen-Key fourth-order filter with out-of-band zeros cancellation

In this brief, a 28.8-MHz-3-dB frequency low-pass analog filter is presented. The filter synthesizes a fourth-order Butterworth transfer function, exploiting the well-known Sallen-Key (SK) biquadratic cell. The out-of-band zeros typically present in SK implementations are hereby completely canceled by using a low-power auxiliary path. This leads to a significant improvement of the stop-band rejection, at the cost of a small power for the same auxiliary path biasing. The design exhibits very large in-band IIP3 over the entire filter bandwidth (20 dBm at 10 MHz and 11 MHz), at 3.2-mW power consumption. The filter prototype has been designed in CMOS 0.18-μm technological node. The total area occupancy is 0.12 mm2 and the in-band integrated noise is 101 μVRMS.