Bias circuit and differential amplifier having stabilized output swing
First Claim
1. A differential amplifier circuit which receives as input a first input voltage and a second input voltage and outputs a differential output voltage indicative of which input voltage is greater, said circuit comprising:
- a differential pair of transistors coupled to receive the first input voltage and second input voltage;
first and second load transistors, each load transistor coupled between a first supply voltage and a respective transistor of the differential pair of transistors;
first and second output nodes for providing the differential output voltage, said first output node coupled between a first transistor of the differential pair of transistors and the first load transistor and the second output node coupled between a second transistor of the differential pair of transistors and the second load transistor;
a bias circuit comprising;
a bias load transistor coupled to the first supply voltage, said transistor having gate, first and second nodes, the gate node of the bias load transistor being connected to gate nodes of the first and second load transistors and the first node coupled to the first supply voltage,a feedback loop coupled to the bias load transistor to maintain a predetermined voltage at said second node of the bias load transistor and a predetermined current through a feedback path loop, said feedback loop maintaining said predetermined voltage at the second node of the bias load transistor independent of variations of said first supply voltage and transconductance of transistors in the circuit, anda current mirror coupled to receive the current through the feedback path, said current mirror further coupled to the differential pair of transistors to provide a constant current value through said differential pair of transistors;
wherein the differential output is stabilized against variations in supply voltage and transconductance of transistors in the circuit.
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Accused Products
Abstract
A differential circuit is provided that generates a differential output voltage ΔV that does not vary when the power supply voltage changes and/or when the field effect transistor conductance changes. The bias circuit connected to the differential amplifier stabilizes the output voltage swing ΔV to be insensitive to change in supply voltage and/or transconductance. A feedback loop is provided to drive the voltage to a predetermined voltage dependent upon the threshold voltage of the transistors used (e.g., the threshold voltage of a PMOS transistor). The voltage stabilizes the current source of the differential amplifier via a current mirror coupled to the feedback loop. Therefore, the resultant differential output voltage ΔV is equal to the transistor threshold voltage. As the transistor threshold voltage is independent of the power supply voltage and device transconductance, the differential amplifier output ΔV is stabilized against variations in power supply voltage and transconductance.
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Citations
33 Claims
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1. A differential amplifier circuit which receives as input a first input voltage and a second input voltage and outputs a differential output voltage indicative of which input voltage is greater, said circuit comprising:
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a differential pair of transistors coupled to receive the first input voltage and second input voltage; first and second load transistors, each load transistor coupled between a first supply voltage and a respective transistor of the differential pair of transistors; first and second output nodes for providing the differential output voltage, said first output node coupled between a first transistor of the differential pair of transistors and the first load transistor and the second output node coupled between a second transistor of the differential pair of transistors and the second load transistor; a bias circuit comprising; a bias load transistor coupled to the first supply voltage, said transistor having gate, first and second nodes, the gate node of the bias load transistor being connected to gate nodes of the first and second load transistors and the first node coupled to the first supply voltage, a feedback loop coupled to the bias load transistor to maintain a predetermined voltage at said second node of the bias load transistor and a predetermined current through a feedback path loop, said feedback loop maintaining said predetermined voltage at the second node of the bias load transistor independent of variations of said first supply voltage and transconductance of transistors in the circuit, and a current mirror coupled to receive the current through the feedback path, said current mirror further coupled to the differential pair of transistors to provide a constant current value through said differential pair of transistors; wherein the differential output is stabilized against variations in supply voltage and transconductance of transistors in the circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. In a differential amplifier circuit comprising a pair of amplifier transistors having load transistors, said circuit receives as input a first input voltage and a second input voltage and outputs a differential output voltage indicative of which input voltage is greater, a bias circuit that stabilizes the differential output against variations in a first supply voltage and transistor transconductance, said bias circuit comprising:
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a bias load transistor approximately equal in size to sizes of the load transistors, a gate node of the bias load transistor coupled to gate nodes of the load transistors; a feedback loop to maintain a predetermined voltage at a first node of the bias load transistor and a current through a feedback path, said feedback loop maintaining said predetermined voltage at the first node of the bias load transistor independent of variations of said first supply voltage and transconductance of transistors in the circuit, and a current mirror coupled to the feedback loop to receive the current through the feedback path, said current mirror further coupled to the differential pair of transistors to provide a constant current value through said differential pair of transistors; wherein the differential output is stabilized against variations in said first supply voltage and transistor transconductance. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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33. In a differential amplifier circuit comprising a pair of amplifier transistors having load transistors, said circuit receives as input a first input voltage and a second input voltage and outputs a differential output voltage indicative of which input voltage is greater, a method for biasing the circuit that stabilizes the differential output against variations in supply voltage and transistor transconductance, said method comprising the steps of:
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connecting a bias load transistor to the load transistors, said bias load transistor approximately equal in size to sizes of the load transistors, a gate node of the bias load transistor coupled to gate nodes of the load transistors; maintaining a predetermined voltage at a first node of the bias load transistor and a current through a feedback path, said feedback loop maintaining said predetermined voltage at the first node of the bias load transistor independent of variations of said supply voltage and transconductance of transistors in the circuit, and mirroring the current to the pair of amplifier transistors to provide a constant current value through said pair of amplifier transistors; wherein the differential output is stabilized against variations in said supply voltage and transistor transconductance.
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Specification