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Design of General Multifunction Biquads and Their Comparative Study Using Log-Domain Technique
Nisar A. Shah and Farooq A. Khanday

Two general designs (GDs) for Single-Input-Multiple-Output (SIMO) log-domain Multi-Function Biquads (MFBs) are presented in this paper. The GDs yield eight configurations of SIMO log-domain MFBs. Most of the yielded designs are novel while a few are recently reported in the literature. The biquads realize three standard filter functions, that is, lowpass (LP), highpass (HP) and bandpass (BP). The other two filter functions, that is, band reject (BR) and allpass (AP) can be obtained from these functions by employing an additional summer that forms a weighted sum of these functions. The features of the circuits are: the circuit descriptions are very simple, consisting of merely few exponential transconductor cells and two grounded capacitors; without any external resistors and using only grounded elements, the circuits are good for absorbing the shunt parasitic capacitances; the filter parameters are electronically tunable and are suitable for monolithic integration. Furthermore, the biquad being designed by log-domain technique offers all its advantages. Last but not the least, a comparative study of the biquads is also carried in the paper which helps in the selection of better MFB for an application. Simulated results are obtained to prove the theoretical analyses.

Keywords: Analog integrated circuits, biquadratic filters, current mode filters, log-domain filters.

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