Methods and apparatus for a track and hold amplifier
AssigneeSemiconductor Components Industries, LLC
InventorShankar Ramakrishnan
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Abstract
Various embodiments of the present technology may comprise methods and apparatus for a track-and-hold amplifier configured to sample and amplify an analog signal. Methods and apparatus for a track-and-hold amplifier according to various aspects of the present invention may comprise an isolation circuit configured to isolate transient current in a track-and-hold capacitor during a track phase. According to various embodiments, selective activation of the isolation circuit provides a settling time that is independent of the gain of the amplifier.
Claims19
A track-and-hold amplifier circuit configured to be coupled to a supply voltage and a first reference voltage and receive an input signal, comprising:
- a gain setting element coupled to the input signal;
- a cascode circuit coupled to the gain setting element;
- a track-and-hold capacitor comprising:
- a first capacitor terminal coupled to the gain setting element at a first node;
- and
- a second capacitor terminal;
- and
- an isolation circuit, coupled to the second capacitor terminal of the track-and-hold capacitor and the cascode circuit, and configured to selectively isolate transient current in the track-and-hold capacitor and redirect the transient current through at least a portion of the cascode circuit,
- wherein the isolation circuit comprises:
- a third transistor comprising:
- a first terminal;
- and
- a second terminal;
- wherein:
- the first terminal is directly coupled to the second capacitor terminal at a third node;
- and
- the second terminal is directly coupled to the cascode circuit.
A method for improving an output signal settling time for a track-and-hold amplifier, comprising:
- during a tracking phase:
- supplying a first current to a cascode circuit comprising a first transistor and a second transistor;
- tracking an input signal at a first terminal of a track-and-hold capacitor;
- supplying a second current to a third transistor coupled to a second terminal of the track-and-hold capacitor;
- and
- directing a transient current through the track-and-hold capacitor to a reference voltage through one of:
- the first transistor and a clamp device;
- during a holding phase:
- selectively coupling the third transistor to the reference voltage;
- stopping the first current;
- and
- supplying a dynamic voltage to the third transistor.
An imaging system, comprising:
- a plurality of pixel columns;
- a plurality of track-and-hold amplifiers, wherein:
- each pixel column is coupled to one track-and-hold amplifier;
- and
- each track-and-hold amplifier comprises:
- a gain setting element coupled to the input signal;
- a cascode circuit, coupled to the gain setting element at a second node and a bias voltage, comprising:
- a first transistor;
- and
- a second transistor;
- a track-and-hold capacitor, comprising:
- a first terminal;
- and
- a second terminal;
- a first current source, coupled to the cascode circuit and the gain setting element at a first node, and selectively coupled to the track-and-hold capacitor;
- a third transistor, comprising:
- a first terminal;
- a second terminal;
- and
- a third terminal;
- wherein:
- the first terminal of the third transistor is coupled to the second terminal of the track-and-hold capacitor at a third node;
- the second terminal of the third transistor is coupled to the cascode circuit at a fourth node;
- and
- the third terminal of the third transistor is coupled to a dynamic voltage;
- a switch coupled between the second terminal of the third transistor and a reference voltage;
- and
- a second current source coupled to the third node.
Dependencies are inferred from the claim text.