309-µW 40-MHz 20-dB-Gain Analog Filter in 28nm-CMOS

This paper presents the design and the validation of a continuous-time 2nd-order analog filter with 40 MHz -3 dB cut-off frequency. The circuit synthesizes a pair of conjugated complex poles by leveraging the inductive behaviour of the source node of the folded branch of a differential amplifier. This circuital technique dominates noise power and harmonic distortion by a simple input MOS transistor pair of a differential stage, resulting in 7-nV/√Hz in-band Input Referred Noise power spectral density and 69 dB output Dynamic Range. Moreover, this solution enables the introduction of gain in the filter, relaxing gain, power, and bandwidth requirements of the following stages in cascade structure. A filter prototype is realized in 28 nm CMOS, consuming 309 µW from 1.1 V and performing -6 dBm in-band Input IP3 at 20 dB passband gain.