Browse Prior Art Database

CMOS Switched Capacitor Circuit that Emulates a Resistor

IP.com Disclosure Number: IPCOM000108989D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Grossman, B: AUTHOR

Abstract

Disclosed is a CMOS switched-capacitor circuit requiring only one clock signal as shown in the figure below. It is impractical to fabricate resistors on a VLSI chip from conductive materials, such as a doped polysilicon, diffusion, or metal lines. Physical resistors such as these occupy too much space for use on a VLSI chip and their accuracy is limited by the manufacturing tolerances of the resistivity and dimensions of the conductive material which, at best, is about 3 s = + 10%.

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CMOS Switched Capacitor Circuit that Emulates a Resistor

       Disclosed is a CMOS switched-capacitor circuit requiring
only one clock signal as shown in the figure below.  It is
impractical to fabricate resistors on a VLSI chip from conductive
materials, such as a doped polysilicon, diffusion, or metal lines.
Physical resistors such as these occupy too much space for use on a
VLSI chip and their accuracy is limited by the manufacturing
tolerances of the resistivity and dimensions of the conductive
material which, at best, is about 3 s = + 10%.

      Prior art for a circuit that emulates the characteristics of a
resistor is the switched-capacitor circuit implemented in either nMOS
or pMOS technology (see: J. Mavor, et al, Introduction to MOS LSI
Design, Addison-Wesley Co., 1983).  This prior approach requires two
MOSFETs, a capacitor, and two high-frequency, non-overlapping clock
signals.  The frequencies of the clock signals must be much higher
(>100X) than the signal placed across the emulated resistor. To
achieve maximum switching frequency, the two non-overlapping clock
pulses must be minimally spaced in time.

      In the circuit proposed in this article, a switched capacitor
circuit is implemented in a CMOS configuration requiring only one
high-frequency clock signal (>100X), a capacitor (C), and two
MOSFETs, as shown in the figure.  This CMOS implementation of a
switched-capacitor circuit eliminates the need for the additional
clock  signal requi...