SWITCHED-OPAMP - AN APPROACH TO REALIZE FULL CMOS SWITCHED-CAPACITOR CIRCUITS AT VERY-LOW POWER-SUPPLY VOLTAGES

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.