A 94.7-dB Dynamic Range Fully Passive Switched-Capacitor Low-Pass Filter With Enhanced Selectivity

Abstract

In this article, a passive gain-boosting technique is employed to improve the bandpass gain, input-referred noise, and area usage of a charge-rotation switched-capacitor (CRSC) filter. In addition, a passive feedback network is introduced, creating a sharp transition between the passband and stopband, thereby enhancing noise and linearity performance compared to prior work employing active feedback. Furthermore, the utilization of the pipeline technique raises the sampling frequency to match the clock frequency. The proposed filter is fabricated in 0.18- $\mu $ m CMOS technology. Operating from 1.8 V, the measured power dissipation of the filter is 1.52 mW. By applying a 250-MHz clock, the cutoff frequency of the filter can be tuned from 428 kHz to 6.75 MHz, while the dc gain is fixed at 1.33 dB under different bandwidth settings. For a 3-dB cutoff frequency of 2.35 MHz, the measured in-band IIP3 and IIP2 are 25 and 56 dBm, while the out-of-band IIP3 and IIP2 are 22.4 and 71.4 dBm, respectively. The input-referred integrated noise over 110 kHz–2.35 MHz is $8.58{\mu }$ Vrms. Compared to prior art, the proposed filter presents competitive noise performance, area usage, and dynamic range (DR).