Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-09-11
2001-07-24
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S312000
Reexamination Certificate
active
06265859
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to electronic circuitry and in particular, to current mirroring circuitry and methods.
2. Description of the Related Art
Current mirrors have many applications, including those in analog circuits such as operational amplifiers, comparators, band gap references, and the like. In one common current mirroring technique, a reference current is generated and then replicated (mirrored) through parallel weighted current paths using a set of matched transistors of appropriate aspect ratios. The resulting set of graduated currents can then, for example, be used to bias or drive other circuits in the device in varying ratios.
One of the drawbacks of using parallel transistors in current mirrors is their sensitivity to such factors as power supply variation, operating temperature variation, and fabrication process tolerances. Temperature and power supply variation can cause the currents to drift from their nominal design values, unless suitable compensation is provided for making the current paths track with the temperature and power supply changes. Fabrication process variations can cause the conductance of the transistors, and hence the accuracy in the current mirroring, to vary from wafer to wafer or even between circuits on the same wafer. For example, even if the channel width to length ratios of the transistors are held well within design tolerances, other factors such as differences in oxide thickness, carrier mobility and carrier doping levels can still cause variation in transistor conductivity.
Given the usefulness of current mirrors in a wide range of electronic circuit applications, better techniques are needed for compensating for temperature, process, and/or power supply variation in circuits employing current mirrors.
SUMMARY OF THE INVENTION
According to the principles of the present invention, a current mirror is disclosed which includes a current mirroring transistor having a selected aspect ratio for conducting a mirrored current of a selected mirroring ratio with respects to a reference current. A plurality of reference current transistors are disposed in parallel with the current mirroring transistor, each of the reference current transistors having a current path coupled to a source of the reference current and a selected aspect ratio. A switch is coupled to a control terminal of a selected one of the reference current transistors for selectively turning on and turning off the selected reference current transistor to adjust the mirroring ratio.
The inventive concepts provide an efficient mechanism for compensating for fabrication process, variation in current sourcing devices. Among other things, these concepts can be used to tune the mirroring ratios in a current mirror such that a precise current mirroring is possible. Additionally, these concepts can be implemented using a minimum amount of additional hardware and can be applied on a device by device basis.
REFERENCES:
patent: 5625281 (1997-04-01), Lambert
patent: 5684394 (1997-11-01), Marshall
patent: 5877616 (1999-03-01), Wan et al.
patent: 5936392 (1999-08-01), Taylor
patent: 6188211 (2001-02-01), Ricon-Mora et al.
Datar Rajendra
Soman Manoj
Cirrus Logic Inc.
Murphy, Exq. James J.
Vu Bao Q.
Winstead Sechrest & Minick
Wong Peter S.
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