MOS differential amplifier with offset compensation
AssigneeNational Semiconductor Corporation
InventorPaul Mike Henry
Life of this patent
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Abstract
A differential amplifier with adjustable offset includes a differential pair, a controller, an offset adjuster and an output stage. The differential pair and the output stage can be standard implementations such as, for example, a source-coupled PFETs and a folded-cascode output stage. The offset adjuster includes transistors that can be selectively enabled to form a composite transistor that is connected in parallel with at least one transistor of the differential pair to, in effect, increase the size of the transistor of the differential pair. The controller can reduce offset by causing the offset adjuster to increase the effective size of the appropriate transistor of the differential pair to compensate for device mismatch in the differential amplifier.
Claims21
An differential amplifier, comprising:
- a differential pair including a first transistor and a second transistor, the first transistor having a terminal couplable to receive a first input signal and the second transistor having a terminal couplable to receive a second input signal, the first and second input signals forming a differential signal;
- an offset adjuster coupled to the differential pair, wherein the offset adjuster is configurable to adjust a relative size between the first and second transistors;
- an output stage coupled to the differential pair;
- and
- a controller having a control line that is couplable to the offset adjuster, wherein the controller is configured to provide a control signal to the offset adjuster to cause the offset adjuster to change the relative size between the first and second transistors to compensate for offset in the differential amplifier.
A comparator, comprising:
- a differential pair including a first transistor and a second transistor, the first transistor having a terminal couplable to receive a first input signal and the second transistor having a terminal couplable to receive a second input signal;
- an offset adjuster coupled to the differential pair, wherein the offset adjuster is configurable to adjust a relative size between the first and second transistors;
- an output stage coupled to the differential pair, wherein the output stage is configured to output a digital signal in response to the first and second input signals;
- and
- a controller having a control line that is couplable to the offset adjuster, wherein the controller is configured to provide a control signal to the offset adjuster to cause the offset adjuster to change the relative size between the first and second transistors to compensate for offset in the differential amplifier.
A bandgap reference, comprising:
- a differential pair including a first transistor and a second transistor, the first transistor having a first terminal couplable to receive a first input signal and the second transistor having a second terminal couplable to receive a second input signal;
- an offset adjuster coupled to the differential pair, wherein the offset adjuster is configurable to adjust a relative size between the first and second transistors;
- an output stage coupled to the differential pair, wherein the output stage is configured to output a signal as a function of a difference between the first and second input signals;
- a controller having a control line that is couplable to the offset adjuster, wherein the controller is configured to provide a control signal to the offset adjuster to cause the offset adjuster to change the relative size between the first and second transistors to compensate for offset in the differential amplifier;
- a third transistor coupled to the first terminal of the differential pair;
- a fourth transistor coupled to the second terminal of the differential pair through a resistor, the third and fourth transistors having different sizes;
- and
- a current source coupled to the output lead of the output stage and the third and fourth transistors, wherein the current source is configured to provide a current with a level that is responsive to the output signal of the output stage.
An differential amplifier, comprising:
- a differential pair including a first transistor and a second transistor, the first transistor having a terminal couplable to receive a first input signal and the second transistor having a terminal couplable to receive a second input signal, the first and second input signals forming a differential signal;
- adjuster means, coupled to the differential pair, for adjusting a relative size between the first and second transistors;
- an output stage coupled to the differential pair;
- and
- a controller having a control line that is couplable to the adjuster means, wherein the controller is configured to provide a control signal to the adjuster means to cause the adjuster means to change the relative size between the first and second transistors to compensate for offset in the differential amplifier.
Dependencies are inferred from the claim text.