A Charge-Sharing IIR Filter With Linear Interpolation and High Stopband Rejection

Abstract

This article introduces a new discrete-time (DT) charge-sharing (CS) low-pass filter (LPF) that achieves high-order filtering and improves its stopband rejection while maintaining a reasonable duty cycle of the main clock at 20%. It proposes two key innovations: 1) a linear interpolation of the sampling capacitor and 2) a charge re-circulation of the history capacitors for deep stopband rejection. Fabricated in 28-nm CMOS, the proposed IIR LPF demonstrates a 1–9.9-MHz bandwidth (BW) programmability and achieves a record-high 120-dB stopband rejection at 100 MHz while consuming merely 0.92 mW. The in/out-of-band IIP3 is +17.7 dBm/+26.6 dBm, and the input-referred noise is 3.5 nV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {\mathrm{ Hz}}$ </tex-math></inline-formula> .