Switched-opamp: an approach to realize full CMOS switched-capacitor circuits at very low power supply voltages

• Published in: IEEE journal of solid-state circuits 1994-08, Vol.29 (8), p.936-942
• Main Authors: Crols, J., Steyaert, M.
• Format: Article
• Language: English
• Subjects: CMOS analog integrated circuits; CMOS process; Distortion measurement; Low voltage; Power harmonic filters; Power supplies; Signal processing; Switches; Switching circuits; Total harmonic distortion
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/4.297698

The implementation of analog CMOS circuits that operate in the very low power supply voltage range (1 V to 2 V) becomes more important nowadays. Most accurate filter circuits are designed in the switched-capacitor 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 which are turned on and off. This technique results in a true, very low voltage operation without the need for voltage multipliers. As an example, 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-/spl mu/m CMOS process with V/sub T/=/spl plusmn/0.9 V. It has a measured total harmonic distortion of -60 dB for a signal swing of 600 mV/sub ptp/ and a powerdrain of only 110 /spl mu/W.< >