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Bias circuit and differential amplifier having stabilized output swing

  • US 5,451,898 A
  • Filed: 11/12/1993
  • Issued: 09/19/1995
  • Est. Priority Date: 11/12/1993
  • Status: Expired due to Term
First Claim
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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:

  • 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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