A 20-kHz~16-MHz Programmable-Bandwidth 4th Order Active Filter Using Gain-Boosted Opamp With Negative Resistance in 65-nm CMOS

This brief presents a 4th order 20-kHz~16-MHz programmable-bandwidth active RC filter. For high linearity performance, the gain-boosted opamp in the biquad adopts negative resistance in auxiliary amplifiers to achieve high-gain without requiring extra common-mode feedback amplflifier, thereby minimizing total current and design complexity. To further enhance the filter linearity, a source follower using native nMOS transistors generates common-mode output without adding extra resistive loading to the opamp output. The prototype filter is fabricated in 65-nm CMOS and occupies 0.098 mm
²
. It features three programmable cutoff frequencies of 20 kHz, 2 MHz, and 16 MHz and achieves IIP3 of 22.1 dBm while consuming 19 mW under 1.8-V supply. The measured figure-of-merit considering the linearity, power, bandwidth, noise, and silicon area shows that the presented filter achives best-in-line compromise among conflicting design metrics.