Bias circuit for switched capacitor applications

Details Bias circuit for switched capacitor applications Bias circuit for switched capacitor applications

1997-02-21

1998-11-17

Callahan, Timothy P.

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

With specific source of supply or bias voltage

327530, 327543, G05F 110

Patent

active

058381910

ABSTRACT:
An adaptive bias circuit for switched capacitor applications that compensates for temperature and process variations by maintaining a constant settling time of CMOS operational amplifiers is introduced. To this end, the adaptive bias circuit allows a dynamic trade-off between the slew-rate and the gain bandwidth product which allows the output of the operational amplifier to settle within a certain predetermined precision. A first aspect of the invention includes a current source providing a same current to a pair of transistors having different effective current densities. A resistor is coupled between the pair of transistors while from one end of the resistor, a constant bias current is drawn. In this manner, a voltage difference develops across the resistor which effectively indicates the change in the transconductance of the pair of transistors with respect to temperature and process variations. Another aspect of the invention allows the bias circuit to minimize the body effect, the back bias effect, the channel length modulation effect, as well as the dependence of circuit performance upon the power supply voltage.

REFERENCES:
patent: 4489282 (1984-12-01), Jett, Jr.
patent: 4714901 (1987-12-01), Jain et al.
patent: 5289058 (1994-02-01), Okamoto
patent: 5512855 (1996-04-01), Kimura
patent: 5543746 (1996-08-01), Kuo
patent: 5587674 (1996-12-01), Danstrom
B.Y. Kamath, R.G. Meyer, and P.R. Gray "Relationship between frequency response and settling time of operational amplifiers," IEEE Journal of Solid State Circuits, vol. SC-9, (6), pp. 347-352, Dec. 1974.
S.M. Sze, Physics of Semiconductor Devices, 2nd ed., New York: John Wiley & Sons, 1981 pp. 27-30.
Dennis M. Monticelli, "A Quad CMOS Single-Supply Op Amp with Rail-to-Rail Output Swing," IEEE Journal of Solid-State Circuits, vol. SC-21, No. 6, Dec. 1986.

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