J. Crols et M. Steyaert, SWITCHED-OPAMP - AN APPROACH TO REALIZE FULL CMOS SWITCHED-CAPACITOR CIRCUITS AT VERY-LOW POWER-SUPPLY VOLTAGES, IEEE journal of solid-state circuits, 29(8), 1994, pp. 936-942
The implementation of analog CMOS circuits that operate in the very lo
w power supply voltage range (1 V to 2 V) becomes more important nowad
ays. Most accurate filter circuits are designed in the switched-capaci
tor technique. The existing design techniques require, however, the on
-chip generation of a higher voltage by means of a voltage multiplier.
In this paper, a novel technique, derived from the standard switched-
capacitor technique, is presented. It is called switched-opamp because
it is based on the replacement of the critical switches with opamps w
hich are turned on and off. This technique results in a true, very low
voltage operation without the need for voltage multipliers. As an exa
mple, a second order lowpass switched-capacitor filter is implemented
in the switched-opamp technique. This filter operates with only a 1.5
V power supply. It is realized in a 2.4-mum CMOS process with V(T) = /-0.9 V. It has a measured total harmonic distortion of -60 dB for a s
ignal swing of 600 mV(ptp) and a powerdrain of only 110 muW.