High output swing comparator stage
AssigneeTexas Instruments Incorporated
InventorBrett E. Forejt
Life of this patent
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Abstract
A circuit and method is provided that provides an amplification stage to a comparator device that matches transistor transconductances to provide adequate amplification and employs diode coupled transistors to control the common mode output bias voltage. The circuit and method provides for a high gain comparator stage with control over output common mode voltage, while providing rail to rail output swing during differential mode without an external feedback to the comparator device.
Claims17
A high gain differential input and output stage circuit for a comparator device comprising:
- a first common mode setting portion coupled to a first differential output;
- and
- a second common mode setting portion coupled to a second differential output;
- wherein the first and second common mode setting portions have a first state in which the first and second common mode setting portions are coupled to the respective differential outputs for setting the common mode bias output voltage of the stage during a common mode condition and a second state in which the first and second common mode setting portions allow the respective differential outputs to swing rail to rail during a differential mode condition;
- the first common mode setting portion comprising a first diode coupled transistor selectively coupleable to the first differential output and the second common mode setting portion comprising a second diode coupled transistor selectively coupleable to a second differential output;
- the first common mode setting portion further comprising a first switch provided for selectively coupling the first differential output to the second diode coupled transistor and the second common mode setting portion further comprising a second switch provided for selectively coupling the second differential output to the second diode coupled transistor, the first switch being a transistor disposed between a drain and a gate of the first diode coupled transistor and the second switch being a transistor disposed between a drain and a gate of the second diode coupled transistor.
A method for controlling common mode voltage in a high gain differential stage circuit for a comparator device without an external feedback, comprising the steps of:
- providing a first diode coupled transistor selectively coupleable to a first differential output and a second diode coupled transistor selectively coupleable to a second differential output;
- coupling the first diode coupled transistor to the first differential output and coupling the second diode coupled transistor to the second differential output during common mode of the stage circuit;
- and
- alternating coupling and decoupling the first diode coupled transistor from the first differential output and the second diode coupled transistor from the second differential output during differential mode of the stage circuit, while providing a high impedance in place of the respective diode coupled transistor when it is decoupled.
A high gain differential input and output stage circuit for a comparator device without an external feedback, comprising:
- a first diode coupled transistor selectively coupleable to a first differential output;
- and
- a second diode coupled transistor selectively coupleable to a second differential output;
- wherein the first and second diode coupled transistors have a first state coupled to the respective differential outputs for setting the common mode bias output voltage of the stage and a second state alternating between a coupled and a decoupled state from the respective differential outputs, with a high impedance being provided in place of the respective diode coupled transistor when it is decoupled, for allowing rail to rail output swing during differential mode.
A high gain differential input and output stage circuit for a comparator device without an external feedback, comprising:
- a first diode coupled transistor selectively coupleable to a first differential output;
- and
- a second diode coupled transistor selectively coupleable to a second differential output;
- wherein the first and second diode coupled transistors have a first state coupled to the respective differential outputs for setting the common mode bias output voltage of the stage and a second state alternating between a coupled and a decoupled state from the respective differential outputs for allowing rail to rail output swing during differential mode;
- further comprising a first switch provided for selectively coupling the first differential output to the first diode coupled transistor and a second switch provided for selectively coupling the second differential output to the second diode coupled transistor, the first switch being a transistor disposed between a drain and a gate of the first diode coupled transistor and the second switch being a transistor disposed between a drain and a gate of the second diode coupled transistor.
A high gain differential input and output stage circuit for a comparator device without an external feedback, comprising:
- means for controlling output bias voltage in common mode, the means for controlling output bias voltage in common mode having a low output impedance;
- and
- means for providing a high output impedance during differential mode.
Dependencies are inferred from the claim text.