Comparator with low supply current spike and input offset cancellation
First Claim
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1. A comparator comprising:
- a current source that provides a source current to a first node;
a first voltage supply terminal configured to receive a first supply voltage;
a first transistor coupled between the first node and the first voltage supply terminal along a first current path;
a second transistor coupled between the first node and the first voltage supply terminal along a second current path;
a third transistor coupled between the first node and the first voltage supply terminal along a third current path, wherein the first, second and third current paths are separate and parallel current paths between the first node and the first voltage supply terminal;
a first input terminal configured to receive a first differential input signal of the comparator, wherein the first input terminal is coupled to a gate of the first transistor;
a second input terminal configured to receive a second differential input signal of the comparator, wherein the second input terminal is coupled to gates of the second and third transistors;
a first capacitor coupled between the second input terminal and the first voltage supply terminal, wherein the first capacitor applies the second differential input signal to the comparator; and
means for sampling the first differential input signal on the first capacitor.
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Abstract
A current control circuit is coupled in parallel with the current paths of a differential comparator circuit to ensure that a substantially constant current is drawn from a current source during all operating phases of a comparator. The current control circuit is biased by a reference voltage, which is also used to bias a V− input terminal of the differential comparator circuit. The reference voltage is stored by a sample capacitor, which is charged by applying the reference voltage to a V+ input terminal of the differential comparator circuit while coupling an output terminal of the differential comparator circuit to the sample capacitor in a unity feedback configuration.
106 Citations
18 Claims
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1. A comparator comprising:
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a current source that provides a source current to a first node; a first voltage supply terminal configured to receive a first supply voltage; a first transistor coupled between the first node and the first voltage supply terminal along a first current path; a second transistor coupled between the first node and the first voltage supply terminal along a second current path; a third transistor coupled between the first node and the first voltage supply terminal along a third current path, wherein the first, second and third current paths are separate and parallel current paths between the first node and the first voltage supply terminal; a first input terminal configured to receive a first differential input signal of the comparator, wherein the first input terminal is coupled to a gate of the first transistor; a second input terminal configured to receive a second differential input signal of the comparator, wherein the second input terminal is coupled to gates of the second and third transistors; a first capacitor coupled between the second input terminal and the first voltage supply terminal, wherein the first capacitor applies the second differential input signal to the comparator; and means for sampling the first differential input signal on the first capacitor. - View Dependent Claims (4, 5, 6, 7)
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2. A comparator comprising:
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a current source that provides a source current to a first node; a first voltage supply terminal configured to receive a first supply voltage; a first transistor coupled between the first node and the first voltage supply terminal along a first current path; a second transistor coupled between the first node and the first voltage supply terminal along a second current path; a third transistor coupled between the first node and the first voltage supply terminal along a third current path, wherein the first, second and third current paths are separate and parallel current paths between the first node and the first voltage supply terminal; a first input terminal configured to receive a first differential input signal of the comparator, wherein the first input terminal is coupled to a gate of the first transistor; a second input terminal configured to receive a second differential input signal of the comparator, wherein the second input terminal is coupled to gates of the second and third transistors; a first capacitor coupled between the second input terminal and the first voltage supply terminal, wherein the first capacitor applies the second differential input signal to the comparator; an output terminal configured to receive an output signal of the comparator, wherein the output terminal is coupled to a drain of the second transistor; and a switch coupled between the output terminal and the second input terminal. - View Dependent Claims (3)
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8. A method of implementing a comparator comprising:
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sampling a reference voltage applied to a first input of a differential comparator circuit on a second input of the differential comparator circuit during a first operating phase; and
thenmaintaining the reference voltage on the second input of the differential comparator circuit and an input of a current control circuit during a second operating phase, wherein the current control circuit provides a current path in parallel with current paths of the differential comparator circuit; and applying a ramp voltage to the first input of the differential comparator circuit during the second operating phase. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification