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 highorder 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/ √ Hz.

Discrete-time Receivers, from N-Path to Charge Sharing Band-pass Filters: a Comparison

“…A CS version of the IIR filter is implemented in Fig. 6a, [24,[48][49][50][51]. In the circuit, the current i in is integrated over C S during T s creating a charge packet q in [n] defined by (3).…”

Low-Power Current Integrating Flat-Passband Infinite Impulse Response Filter for Sensor Read-Out Integrated Circuit in 65-nm CMOS Technology

“…In systems where current integrating filters are used, high sampling frequencies have been adopted [12][13][14]. In other words, when the sampling frequency increases, the signal bandwidth stretches, and thus the 3 dB cut-off frequency increases.…”

“…Likewise, to achieve the flat-passband frequency response, high sampling frequency for low-pass analog IIR filter is adopted [12][13][14]. Even though an analog baseband filter is used, sampling frequency is in the range of several hundred MHz.…”