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

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-m BiCMOS technology, the filter
prototype has an area of about 1.6 mm2 and a power consumption
of 17 mW. The in-band noise density is 380 nV/pHz, and the
dynamic range is about 68 dB for a 3% IM.