Design of switched-capacitor FIR filters with application to a low-power MFSK receiver

Finite impulse response (FIR) switched-capacitor (SC) filters for minimum frequency-shift keying (MFSK) demodulation techniques have been developed and are discussed. The proposed filters comprise combinations of the following building blocks: sample-and-hold circuits, even-odd delay circuits, Gillingham delay circuits, recharge memory elements, Lee-Martin summer circuits, recharge summer circuits, and rotator switches. These are described in the paper. Furthermore, composite SC filter structures are derived using a morphological approach. The FIR SC filter structures are compared and evaluated with respect to the required chip area when implemented in 3 μm CMOS technology, and, by computer simulation, with regard to bit error probability when used in an MFSK receiver. It is shown that the receiver performance is independent of the FIR filter structure used. Furthermore, using the FIR filters, and for a given bit error probability, the required signal-to-noise ratio (SNR) is actually 3 dB lower than for a typical commercial MFSK receiver (e.g. an MB87002).