Tunable Current-Mode Capacitance Multiplication Circuit

A. Gupta, R. Suryanarayan, and T.N. Blalock (USA)


Active capacitor, current-mode, tunable,multiplication, CMOS, bandpass filter.


A tunable gm-based current-mode capacitance multiplication technique is presented. The technique increases the effective value of a capacitor up to three orders of magnitude. The new circuit dramatically reduces the area of low frequency active filters, and other circuits which require large values of capacitance. The circuit has been demonstrated in a 0.25 m CMOS process circuit where a 0.5 pF capacitor is multiplied to a value of 85 pF. The active capacitor circuit dissipates 10 W and uses 162 times less area than the equivalent physical FET-based capacitor. The implementation of this technique is also demonstrated in MOSFET-C and Gm-C low frequency bandpass filters with 100 times lower area than the same circuits implemented with equivalent FET based capacitors.

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