Current mirror and current cancellation circuit
First Claim
1. A circuit comprising:
- a first node and a second node;
a first current source coupled to the first node, the first current source configured to provide a first current source current;
a second current source coupled to the second node, the second current source configured to provide a second current source current;
a first current mirror coupled to a supply voltage, the first current mirror configured to provide a first current mirror reference current;
a second current mirror coupled to the supply voltage, the second mirror configured to provide a second current mirror reference current;
a first switch coupled to the first current mirror and the first node, the second switch configured to have a switch configuration;
a second switch coupled to the second current mirror and the second node and is configured to have the switch configuration;
a delta sigma modulator having an input and an output, the input coupled to the first node and the output configured to provide a discrete pulse density modulated output to control the switch configuration of the first switch and the second switch,wherein an average value of the discrete pulse density modulated output represents at least the first current source current as a function of the first current mirror reference current and the density modulated output is configured to control the second switch such that an equivalent current at the second node is a difference of the first current source current and the second current source current when the first current mirror current is at least approximately equal to the second current mirror current.
1 Assignment
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Accused Products
Abstract
Techniques are described to mirror currents and subtract currents accurately. In an implementation, a circuit includes a first current source coupled to a first node to provide a current IPD1 and a current mirror coupled to the first node through a first switch T1 to provide a current IREF1. In a closed configuration, the current IREF1 flows from the current mirror into the first node. A sigma delta modulator controls the switch T1 such that over a period of time an average current flowing from the current mirror into the first node is equal to the current IPD1 flowing out of the first node. The sigma delta modulator generates a digital output to control switch T2 to allow a current IREF2 into a second node, thus subtracting a portion of a current IPD2 at the second node over a period of time.
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Citations
14 Claims
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1. A circuit comprising:
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a first node and a second node; a first current source coupled to the first node, the first current source configured to provide a first current source current; a second current source coupled to the second node, the second current source configured to provide a second current source current; a first current mirror coupled to a supply voltage, the first current mirror configured to provide a first current mirror reference current; a second current mirror coupled to the supply voltage, the second mirror configured to provide a second current mirror reference current; a first switch coupled to the first current mirror and the first node, the second switch configured to have a switch configuration; a second switch coupled to the second current mirror and the second node and is configured to have the switch configuration; a delta sigma modulator having an input and an output, the input coupled to the first node and the output configured to provide a discrete pulse density modulated output to control the switch configuration of the first switch and the second switch, wherein an average value of the discrete pulse density modulated output represents at least the first current source current as a function of the first current mirror reference current and the density modulated output is configured to control the second switch such that an equivalent current at the second node is a difference of the first current source current and the second current source current when the first current mirror current is at least approximately equal to the second current mirror current. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A circuit comprising:
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a first node and a second node; a dark diode coupled to the first node, the dark diode configured to provide a first dark current; a photo sensor diode coupled to the second node, the photo sensor diode configured to provide a second dark current; a first current mirror coupled to a supply voltage, the first current mirror configured to provide a first current mirror reference current; a second current mirror coupled to the supply voltage, the second current mirror configured to provide a second current mirror reference current; a first switch coupled to the first current mirror and the first node, the first switch configured to have a switch configuration; a second switch coupled to the second current mirror and the second node, the second switch configured to have the switch configuration; a sigma delta modulator having an input and an output, the input coupled to the first node and the output configured to provide a discrete pulse density modulated output to control the switch configuration of the first switch and the second switch, wherein an average value of the discrete pulse density modulated output represents at least the first dark current as a function of the first current mirror reference current and the density modulated output is configured to control the second switch such that an equivalent current at the second node is a difference of the first dark current and the second dark current when the first current mirror current is at least approximately equal to the second current mirror current. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification