Current mirror using resistor ratios in CMOS process
First Claim
1. A current control device for establishing a controlled current through an LED wherein the magnitude of the current through the LED is proportional to a reference current through a reference current sense resistor, the current control device comprising:
- a series combination of circuit elements including a controlled current sense resistor and a variation resistor responsive to a control signal applied to a control terminal thereof, the series combination being adapted for series coupling with said LED and between first and second voltage terminals; and
operational amplifier means having an output terminal coupled to said control terminal for providing said control signal, a first input terminal coupled to a sense point on said series combination, and a second input terminal receiving a substantially constant voltage signal corresponding to a voltage present at said sense point when the desired magnitude of current passes through said sense resistor, said substantially constant voltage signal being provided by a voltage divider network including first and second series coupled resistive elements;
wherein the reference current sense resistor is connected between the second operational amplifier input terminal and one of the first and second voltage terminals and wherein the current sense resistor and the second series coupled resistive elements are both fabricated in integrated circuit form so that a desired ratio of resistances therebetween may be accurately set.
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Accused Products
Abstract
An operational amplifier drives the gate of a voltage controlled variation resistor having a source terminal coupled in series to a reference voltage through a current sense resistor and a drain terminal coupled in series to a supply voltage via a current regulated component, e.g., a light emitting diode. Voltage across the current sense resistor feeds back to the inverting input of the operational amplifier. The non-inverting input receives a substantially constant voltage corresponding to a target voltage, the voltage at the current sense resistor when the desired current flows therethrough. The operational amplifier varies the resistance of the variation resistor to maintain the target voltage at the current sense resistor and establish the desired current flow.
35 Citations
4 Claims
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1. A current control device for establishing a controlled current through an LED wherein the magnitude of the current through the LED is proportional to a reference current through a reference current sense resistor, the current control device comprising:
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a series combination of circuit elements including a controlled current sense resistor and a variation resistor responsive to a control signal applied to a control terminal thereof, the series combination being adapted for series coupling with said LED and between first and second voltage terminals; and operational amplifier means having an output terminal coupled to said control terminal for providing said control signal, a first input terminal coupled to a sense point on said series combination, and a second input terminal receiving a substantially constant voltage signal corresponding to a voltage present at said sense point when the desired magnitude of current passes through said sense resistor, said substantially constant voltage signal being provided by a voltage divider network including first and second series coupled resistive elements; wherein the reference current sense resistor is connected between the second operational amplifier input terminal and one of the first and second voltage terminals and wherein the current sense resistor and the second series coupled resistive elements are both fabricated in integrated circuit form so that a desired ratio of resistances therebetween may be accurately set. - View Dependent Claims (2, 3, 4)
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Specification