Circuit and method for switching active loads of operational amplifier input stage
First Claim
1. An amplifier having a wide input common mode voltage range, comprising:
- (a) first and second differential input transistor pairs, first electrodes of transistors of the first differential input transistor pair being coupled to a first tail current source, first electrodes of transistors of the second differential input transistor pair being coupled to a second tail current source, current flow through one of the first and second tail current sources being controlled by a common mode control circuit in response to an input signal of a differential input signal applied to the amplifier, the input signal including a differential component and a common mode component;
(b) an output stage having first and second inputs driven by the second and first differential input transistor pairs, respectively, the output stage producing an output signal representative of the differential component of the input signal; and
(c) a first controlled active load circuit connected to second electrodes of one of the first and second differential input transistor pairs and coupled to one of the first and second inputs of the output stage and operable in response to the common mode component of the input signal to divert part of a current through the one of the first and second differential input pairs away from the one of the first and second inputs of the output stage.
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Accused Products
Abstract
An operational amplifier having a wide input common mode voltage range includes first (2) and second (3) differential input transistor pairs coupled to first (14) and second (15) tail current transistors. At least one of the first and second tail current transistor pairs is controlled by a common mode control circuit (4). A gate of the first tail current transistor (14) is coupled to the common mode control circuit (4) to turn the first tail current transistor on and to turn the second tail current transistor off when the common mode input voltage is below a common mode threshold voltage (CMTHR). A folded cascode stage (5) is driven by the first and second differential input transistor pairs. Switched active load transistors are coupled to active load transistors of the folded cascode stage and are operable in response to the common mode control circuit to divert part of a current produced by one of the first and second differential input pairs from the folded cascode circuit, depending on whether the common mode input voltage is above or below the common mode threshold voltage.
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Citations
20 Claims
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1. An amplifier having a wide input common mode voltage range, comprising:
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(a) first and second differential input transistor pairs, first electrodes of transistors of the first differential input transistor pair being coupled to a first tail current source, first electrodes of transistors of the second differential input transistor pair being coupled to a second tail current source, current flow through one of the first and second tail current sources being controlled by a common mode control circuit in response to an input signal of a differential input signal applied to the amplifier, the input signal including a differential component and a common mode component; (b) an output stage having first and second inputs driven by the second and first differential input transistor pairs, respectively, the output stage producing an output signal representative of the differential component of the input signal; and (c) a first controlled active load circuit connected to second electrodes of one of the first and second differential input transistor pairs and coupled to one of the first and second inputs of the output stage and operable in response to the common mode component of the input signal to divert part of a current through the one of the first and second differential input pairs away from the one of the first and second inputs of the output stage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of operating an amplifier, comprising:
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(a) providing first and second differential input transistor pairs, first electrodes of transistors of the first differential input transistor pair being coupled to a first tail current transistor, first electrodes of transistors of the second differential input transistor pair being coupled to a second tail current transistor, (b) controlling flow of current in at least one of the first and second tail current transistors by means of a common mode control circuit in response to a common mode component of an input signal applied to the amplifier, the input signal including a differential component; (c) providing an output stage having first and second inputs driven by the first and second differential input transistor pairs, respectively, the output stage producing an output signal representative of the input signal; and (d) operating a first controlled active load circuit connected to second electrodes of one of the first and second differential input transistor pairs and coupled to one of the first and second inputs of the output stage in response to the common mode component of the input signal to divert part of a current through one of the first and second differential input transistor pairs away from one of the first and second inputs of the output stage. - View Dependent Claims (17, 18, 19)
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20. An amplifier including means for providing a wide input common mode voltage range, the amplifier comprising:
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(a) first and second differential input transistor pairs, first electrodes of transistors of the first differential input transistor pair being coupled to a first tail current transistor, first electrodes of transistors of the second differential input transistor pair being coupled to a second tail current transistor, (b) means for controlling flow of current through at least one of the first and second tail current transistor pairs by means of a common mode control circuit in response to a common mode component of an input signal applied to the amplifier, the input signal also having a differential component; (c) an output stage having first and second inputs driven by the first and second differential input transistor pairs, respectively, for producing an output signal representative of the input signal; and (d) controlled active load circuit means connected to second electrodes of one of the first and second differential input transistor pairs and coupled to one of the first and second inputs of the output stage in response to the common mode component of the input signal for diverting part of a current produced by one of the first and second differential input pairs away from the one of the first and second inputs of the output stage.
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Specification