IC Mask Design
Design of Analog CMOS Integrated Circuits
Design of Analog CMOS Integrated Circuits
Optimizing capacitance ratio assignment for low-sensitivity SC filter implementation
IEEE Transactions on Evolutionary Computation
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A critical issue in the design of switched-capacitor (SC) filters is the capacitance matching, because the filter coefficients depend on capacitance ratios. The most successful design method to achieve an accurate capacitance matching employs a parallel arrangement of identical unit capacitors to implement each filter capacitor. However, this procedure can be directly applied only if the filter coefficients can be written as rational numbers, since each capacitor is implemented as an integer number of unit capacitors in parallel. This paper presents a systematic procedure, with low computational effort, to approximate the filter coefficients by integer ratios causing acceptable errors in the filter frequency response, whereas keeping the total number of unit capacitors small, in order to save die area. This procedure was applied in the design of a sixth-order SC band-pass filter, which has been fabricated in a 0.35 μm CMOS technology. The fabricated filter occupies an area of 0.913 mm2, exhibits low sensitivity to fabrication process deviations and has an output dynamic range of 79.2 dB.