Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-02-03
2001-01-09
Wrong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S313000
Reexamination Certificate
active
06172495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally directed to a current mirroring circuit. More specifically, the present invention is directed to a circuit and method for mirroring currents in application specific integrated circuits (ASICs) with an accuracy greater than previously obtainable using matched active devices.
2. Background
Various techniques are used to provide regulated current to a load circuit. One such technique involves a current mirroring circuit which is used to provide an output current equal to or proportional to a reference input current. Current mirroring is typically accomplished by putting current through an active reference device such as a bipolar or MOS device. The resulting gate to source voltage in a field-effect transistor (FET) for example, can then be applied to multiple other devices which closely match and are connected to the original reference device. Current which mirrors the reference current then flows through each of the other multiple devices to the extent these devices are identical. A total mirrored current which is larger than the reference current by the same number of times as there are multiple devices connected to the reference device is achieved by combining the device outputs.
An important aspect in the design of current mirroring circuits is achieving an optimum match between the input reference current and the output current of each mirroring device. Since this current mirroring accuracy assumes that the active mirroring devices are fabricated with similar traits, current mirroring circuits are commonly fabricated on monolithic substrates as part of an integrated circuit such as an ASIC. Additionally, nominally equal value resistors are sometimes added in series with the source of each active device to improve the mirroring accuracy. This technique is successful to the extent that the matching of the resistors is better that the matching of the active mirror devices.
Nevertheless, prior art methods of achieving current mirroring accuracy in ASICs or other monolithic integrated circuits continue to suffer from problems in matching active mirror devices, especially where mirroring ratios beyond two are desired. Where higher mirroring ratios are desired, the associated increase in the number of mirror devices precludes placing all the mirror devices directly adjacent to the reference device. Therefore, device mismatch is increased by the gradients of dimensional accuracy and doping as the mirror devices are spread across the chip. The result is a reduction in current mirroring accuracy when higher mirroring ratios are desired because of the necessary reliance on matching the active mirror devices.
Accordingly, there exists the need for a method of mirroring currents in application specific integrated circuits with an accuracy better than obtainable by mirroring with matched active devices.
SUMMARY OF THE INVENTION
A method and apparatus for mirroring currents in application specific integrated circuits provides higher current mirroring accuracy than previously obtainable with matched active devices by using small groups of resistors with local matching to create a summing node which represents the average voltage across the source resistors of the active output devices and by forming a reference resistor through the combination of resistors from the local resistor groups such that the reference resistor has properties which will largely cause cancellation of location gradients and initial value variation in the resistor groups. An error amplifier compares the voltage at the summing junction with the voltage across the reference resistor and adjusts its output voltage to drive the paralleled gates of each active mirror output device such that the summing junction and reference resistor voltages remain equal. The number of active devices forming an output array is typically an integer squared, and a local resistor group of three matched is resistors is provided for each active mirror device. The error amplifier output voltage driving the gates of the active output devices causes the current flowing through each device to mirror the reference input current flowing through the reference resistor. The result is that the current flowing from the output array of active devices is closely equal to the integer squared times the reference input current flowing in the reference resistor.
REFERENCES:
patent: 5107199 (1992-04-01), Vo et al.
patent: 5570009 (1996-10-01), Nakamura
patent: 5581174 (1996-12-01), Formen
patent: 5680037 (1997-10-01), Carobolante
patent: 5747978 (1998-05-01), Gariboldi et al.
patent: 5867014 (1999-02-01), Wrathall et al.
patent: 5877617 (1999-03-01), Ueda
patent: 5917311 (1999-06-01), Brokaw
LSI Logic Corporation
Vu Bao Q.
Wrong Peter S.
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