A 10.7-MHz BiCMOS high-Q double-sampled SC bandpass filter

Abstract

A fundamental block in telecommunication systems is the high-selectivity bandpass filter centered at the intermediate frequency (IF). In this paper, a BiCMOS high-Q (Q=29) 10.7-MHz switched-capacitor (SC) bandpass filter to be used in the FM receiver channel has been developed. The filter uses low-gain large-bandwidth opamps. The opamp finite gain effects have been compensated using an SC integrator suited for high-Q filters. The particular SC finite-gain compensation scheme allows the implementation of double sampling to relax opamp bandwidth requirements. To reduce total output noise, noisy T-cell networks (often used in other cases) have been avoided. The resulting large capacitors (the largest capacitor is 8.5 pF) are driven by a Class AB output buffer. In a 1.2-/spl mu/m BiCMOS technology, the filter prototype has an area of about 1.6 mm/sup 2/ and a power consumption of 17 mW. The in-band noise density is 380 nV//spl radic/Hz, and the dynamic range is about 68 dB for a 3% IM.