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Bias current generator

  • US 7,902,912 B2
  • Filed: 03/25/2008
  • Issued: 03/08/2011
  • Est. Priority Date: 03/25/2008
  • Status: Expired due to Fees
First Claim
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1. A bias current generator comprising:

  • a first amplifier having an inverting input, a non-inverting input and an output;

    a first bipolar transistor having a base-emitter voltage associated with a first one of the inverting or non-inverting inputs of the first amplifier;

    a load MOS transistor comprising a gate, a source, and a drain, wherein the load MOS transistor is associated with a second one of the inverting or non-inverting inputs of the first amplifier, wherein the gate of the load MOS transistor is operatively coupled to the output of the first amplifier;

    a second bipolar transistor operating at a lower collector current density than that of the first bipolar transistor, wherein a base-emitter voltage of the second bipolar transistor is also associated with the second one of the inverting or non-inverting inputs of the first amplifier such that the base-emitter voltage of the second bipolar transistor is arranged in series with a drain-source voltage of the load MOS transistor; and

    a biasing MOS transistor associated with the load MOS transistor, wherein the gate of the biasing MOS transistor is operatively coupled to the output of the first amplifier such that a gate to source voltage of the load MOS transistor and a gate to source voltage of the biasing MOS transistor are the same;

    wherein the first amplifier, the first bipolar transistor, the second bipolar transistor, the load MOS transistor, and the biasing MOS transistor are arranged in a feedback loop such that the biasing MOS transistor is biased to operate in the saturation region and the load MOS transistor is biased to operate in the triode region;

    wherein the first and second bipolar transistors are arranged relative to the load MOS transistor such that operation of the feedback loop develops a voltage across the drain-source resistance ron of the load MOS transistor equivalent to the base-emitter voltage difference Δ

    Vbe between the first bipolar transistor and the second bipolar transistor thereby generating a PTAT bias current.

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