Microwatt Switched Capacitor Circuit Design

The micropower CMOS implementation of the three basic components of switched capacitor circuits is discussed. Switches must be carefully designed to allow low voltage operation and compensation of clock feed-through by dummy transistors. Matched capacitors can be implemented in single polysilicon technologies primarily designed for digital micropower circuits. Excellent micropower amplifiers are realized by using simple one-stage circuits which take advantage of the special behaviour of MOS transistors in weak inversion. Noise is shown to be independent of current level which only influences the settling time. Various ways of improving the settling time while keeping a very low current drain are described. A method of calculating the noise of a biquadratic filter is followed by examples of a filter and of other switched capacitor circuits.

[1]  D.A. Hodges,et al.  All-MOS charge-redistribution analog-to-digital conversion techniques. II , 1975, IEEE Journal of Solid-State Circuits.

[2]  J. Fellrath,et al.  CMOS analog integrated circuits based on weak inversion operations , 1977 .

[3]  J. Fellrath Shot noise behaviour of subthreshold MOS transistors , 1978 .

[4]  H.J. De Man,et al.  An eight-channel 8 bit microprocessor compatible NMOS D/A converter with programmable scaling , 1980, IEEE Journal of Solid-State Circuits.

[5]  Francois Krummenacher,et al.  High-gain c.m.o.s. cascode operational amplifier , 1980 .

[6]  Eric A. Vittoz Micropower IC , 1980, ESSCIRC 80: 6th European Solid State Circuits Conference.

[7]  H. De Man,et al.  CMOS Adaptive Biasing Amplifier , 1981, ESSCIRC '81: 7th European Solid State Circuits Conference.

[8]  F. Krummenacher Micropower Switched Capacitor Biquadratic Cell , 1981, ESSCIRC '81: 7th European Solid State Circuits Conference.

[9]  F. Krummenacher High voltage gain CMOS OTA for micropower SC filters , 1981 .

[10]  M. Degrauwe,et al.  Class AB CMOS amplifier micropower SC filters , 1981 .