At audio frequencies, switched-capacitor (SC) filters dominate over continuous-time filters. At video frequencies, however, they are limited by the need for high-gain large-bandwidth opamps. A design approach to realize high-frequency IIR SC filters addressing this problem is presented. The trade-off between speed-and-gain is overcome by designing a simple and compact amplifier with a limited but precisely controlled gain. The finite gain effect is taken into account in the filter design by adjusting the capacitor ratio. In addition, the filter uses nMOS-only switches, requiring a standard two-phase clock. Finally, the clock-to-bandwidth ratio is equal to 10, so fairly non-critical anti-aliasing filter is needed.
Baschirotto, A., Montecchi, F., Castello, R. (1995). A 150 Msample/s 20 mW BiCMOS switched-capacitor biquad using precise gain op amps. In Solid-State Circuits Conference, 1995. Digest of Technical Papers. 42nd ISSCC, 1995 IEEE International (pp.212-213). Piscataway, NJ, United States : IEEE [10.1109/ISSCC.1995.535527].
A 150 Msample/s 20 mW BiCMOS switched-capacitor biquad using precise gain op amps
BASCHIROTTO, ANDREA;
1995
Abstract
At audio frequencies, switched-capacitor (SC) filters dominate over continuous-time filters. At video frequencies, however, they are limited by the need for high-gain large-bandwidth opamps. A design approach to realize high-frequency IIR SC filters addressing this problem is presented. The trade-off between speed-and-gain is overcome by designing a simple and compact amplifier with a limited but precisely controlled gain. The finite gain effect is taken into account in the filter design by adjusting the capacitor ratio. In addition, the filter uses nMOS-only switches, requiring a standard two-phase clock. Finally, the clock-to-bandwidth ratio is equal to 10, so fairly non-critical anti-aliasing filter is needed.
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