Modified folded cascode amplifier
First Claim
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1. An amplifier circuit, comprising:
- a differential pair circuit that is arranged to steer a tail current between first and second nodes in response to a differential signal;
a current mirror circuit that is coupled to the first and second nodes, wherein the current mirror circuit is arranged to provide a reflected current to the second node when activated by at least a portion of the tail current, wherein the current mirror circuit includes;
a sixth transistor that is coupled to the first node, and a fifth transistor that is coupled to the second node, wherein the fifth and sixth transistors are commonly controlled by a signal from the first node; and
a cascode circuit that is biased by a cascode current, wherein the cascode circuit is coupled between a cascode output node and the second node such that second node is isolated from the cascode output node by the cascode circuit, wherein the amplifier is arranged to provide an output current to the cascode output node.
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Abstract
A folded-cascode amplifier is arranged with a differential pair circuit, a current mirror circuit, and a cascode circuit. The differential pair is coupled to the current mirror circuit, while the cascode circuit is only coupled to one half of the current mirror circuit. A minimum number of transistors are employed such that overall speed is improved. An output stage with a compensation circuit may be coupled to an output of the cascode circuit. The cascode circuit is configured such that the compensation capacitor is driven with a current of approximately +/−2*I when slewing in the positive and negative directions.
16 Citations
19 Claims
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1. An amplifier circuit, comprising:
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a differential pair circuit that is arranged to steer a tail current between first and second nodes in response to a differential signal;
a current mirror circuit that is coupled to the first and second nodes, wherein the current mirror circuit is arranged to provide a reflected current to the second node when activated by at least a portion of the tail current, wherein the current mirror circuit includes;
a sixth transistor that is coupled to the first node, and a fifth transistor that is coupled to the second node, wherein the fifth and sixth transistors are commonly controlled by a signal from the first node; and
a cascode circuit that is biased by a cascode current, wherein the cascode circuit is coupled between a cascode output node and the second node such that second node is isolated from the cascode output node by the cascode circuit, wherein the amplifier is arranged to provide an output current to the cascode output node. - View Dependent Claims (2, 3, 4, 5, 8, 9, 10)
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6. An amplifier circuit, comprising:
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a differential pair circuit that is arranged to steer a tail current between first and second nodes in response to a differential signal;
a current mirror circuit that is coupled to the first and second nodes, wherein the current mirror circuit is arranged to provide a reflected current to the second node when activated by at least a portion of the tail current, wherein the current mirror circuit includes a fourth transistor that is coupled between the first node and an input of the current mirror such that the current mirror circuit is cascoded; and
a cascode circuit that is biased by a cascode current, wherein the cascode circuit is coupled between a cascode output node and the second node such that second node is isolated from the cascode output node by the cascode circuit, wherein the amplifier is arranged to provide an output current to the cascode output node, wherein the cascode circuit further includes a second current source that is arranged to provide the cascode current, and a third transistor that is coupled between the cascode output node and the second node, wherein the third transistor is biased by a cascode bias signal, wherein the third and fourth transistors have associated sizes, and wherein the size associated with the third transistor is related to the size associated with the fourth transistor such that the third and fourth transistors operate with similar current densities.
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7. An amplifier circuit, comprising:
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a differential pair circuit that is arranged to steer a tail current between first and second nodes in response to a differential signal;
a current mirror circuit that is coupled to the first and second nodes, wherein the current mirror circuit is arranged to provide a reflected current to the second node when activated by at least a portion of the tail current; and
a cascode circuit that is biased by a cascode current, wherein the cascode circuit is coupled between a cascode output node and the second node such that second node is isolated from the cascode output node by the cascode circuit, wherein the amplifier is arranged to provide an output current to the cascode output node, wherein the cascode circuit further includes a second current source that is arranged to provide the cascode current, and a third transistor that is coupled between the cascode output node and the second node, wherein the third transistor is biased by a cascode bias signal, wherein the cascode circuit further includes a seventh transistor that is coupled between the second current source and the third transistor, wherein the seventh transistor is biased by another cascode bias signal such that the cascode output node is isolated from the second current source.
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11. An amplifier circuit comprising:
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a differential pair circuit that is arranged to steer a tail current between first and second nodes in response to a differential signal;
a current mirror circuit that is coupled to the first and second nodes, wherein the current mirror circuit is arranged to provide a reflected current to the second node when activated by at least a portion of the tail current;
a cascode circuit that is biased by a cascode current, wherein the cascode circuit is coupled between a cascode output node and the second node such that second node is isolated from the cascode output node by the cascode circuit, wherein the amplifier is arranged to provide an output current to the cascode output node;
an output stage that is arranged to provide an output signal at an output node in response to an input signal at the cascode output node; and
a capacitor that is coupled between the second node and the output node, wherein the amplifier has a slew rate that corresponds to +/−
2*I/C, wherein the tail current and the cascode current have a magnitude of I, and the capacitor has a value of C.
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12. An apparatus comprising:
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a differential pair circuit that includes a first current source that is coupled to a third node, a first transistor that is coupled between a first node and the third node, a second transistor that is coupled between a second node and the third node, wherein the first and second transistors are arranged to steer a tail current from the first current source to the first and second nodes in response to a differential signal;
a current mirror circuit that is coupled to the first and second nodes, wherein the current mirror circuit includes a fourth transistor that is coupled between the first node and a fourth node, a fifth transistor that is coupled to the first node and the second node, and a sixth transistor that is coupled to the first node and the fourth node, wherein the fifth and sixth transistor are commonly controlled by a signal from the first node such that a reflected current is provided to the second node when the sixth transistor is activated by at least a portion of the tail current; and
a cascode circuit that includes a second current source that is coupled to a fifth node, and a third transistor that is coupled between the fifth node and the second node, wherein the third transistor is biased by a cascode bias signal such that the amplifier is arranged to provide a cascode output current to the fifth node. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification