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Low power and high efficiency voltage-to-current converter with improved power supply rejection

  • US 7,239,184 B2
  • Filed: 04/27/2005
  • Issued: 07/03/2007
  • Est. Priority Date: 04/27/2005
  • Status: Active Grant
First Claim
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1. A voltage-to-current (V/I) converter comprising:

  • a positive supply rail;

    an input terminal operable to receive a control voltage;

    an output terminal operable to provide an output current corresponding to the control voltage;

    an op-amp including an inverting input terminal, a non-inverting input terminal, and an output terminal;

    a transistor including a gate terminal, a source terminal, and a drain terminal, wherein the gate terminal is coupled to the output terminal of the op-amp;

    a first voltage divider circuit including a first resistor, a second resistor, a third resistor, and a fourth resistor, wherein the source terminal of the transistor is coupled to a junction of the third and fourth resistors, wherein the fourth resistor is also coupled to the positive supply rail, wherein the inverting input terminal of the op-amp is coupled to a junction of the second and third resistors, and wherein the second resistor is coupled to the first resistor and the first resistor is coupled to the input terminal of the V/I converter; and

    a protection circuit coupled to the transistor to prevent over-voltage and over-current conditions, the protection circuit including;

    a first diode coupled between the drain terminal of the transistor and the output terminal of the V/I converter;

    a second diode coupled to a junction of the drain terminal of the transistor and the first diode, wherein the second diode is also coupled to a fifth resistor;

    a first bipolar junction transistor (BJT) including a base terminal, an emitter terminal, and a collector terminal, wherein the emitter terminal of the first BJT is coupled to the fifth resistor and the base terminal of the first BJT is coupled to ground, wherein the collector terminal of the first BJT is coupled to a junction of the positive supply rail and a sixth resistor; and

    a second BJT including a base terminal, an emitter terminal, and a collector terminal, wherein the base terminal of the second BJT is coupled to the sixth resistor and the emitter terminal of the second BJT is coupled to the positive supply rail, wherein the collector terminal of the second BJT is coupled to the gate terminal of the transistor.

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