Low power and high efficiency voltage-to-current converter with improved power supply rejection
First Claim
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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Accused Products
Abstract
A low power and high efficiency voltage-to-current (V/I) converter designed with few parts and having improved power supply rejection. The V/I converter may include an op-amp, a MOSFET, and a first and second voltage dividers. The first voltage divider circuit may include a first, second, third, and fourth resistors. A source terminal of the MOSFET may be connected to a junction of the third and fourth resistors and the fourth resistor may be connected to a positive supply rail. Also, an inverting input terminal of the op-amp may be coupled to a junction of the second and third resistors. Additionally, the second resistor may be coupled to the first resistor, which may be connected to an input terminal of the V/I converter. The V/I converter typically has very good DC rejection of the power supply because the first and second voltage dividers are designed to have the same ratios.
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Citations
26 Claims
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1. A voltage-to-current (V/I) converter comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A measurement device comprising:
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one or more digital-to-analog converters (DACs) operable to convert received digital data into analog data; a voltage-to-current (V/I) converter coupled to the one or more DACs, the 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 and the drain terminal is coupled to the output terminal of the V/I converter; and 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; a protection circuit coupled to the V/I converter to prevent over-voltage and over-current conditions, wherein the protection circuit comprises; a first diode coupled between the drain terminal of the transistor and an output terminal of the protection circuit; 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 an 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. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A voltage-to-current (V/I) converter comprising:
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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 metal-oxide semiconductor field-effect transistor (MOSFET) 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 MOSFET 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; a second voltage divider circuit including a fifth resistor and a sixth resistor, wherein the non-inverting input terminal of the op-amp is coupled to a junction of the fifth and sixth resistors, and wherein the fifth resistor is also coupled to the positive supply rail and the sixth resistor is also coupled to ground; and a protection circuit coupled to the MOSFET to prevent over-voltage and over-current conditions, the protection circuit including; a Schottky diode coupled between the drain terminal of the MOSFET and the output terminal of the V/I converter; a pn-junction diode coupled to a junction of the drain terminal of the MOSFET and the Schottky diode, wherein the pn-junction diode is also coupled to a seventh 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 seventh 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 an eighth 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 eighth 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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26. A measurement device comprising:
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a voltage-to-current converter including; 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 metal-oxide semiconductor field-effect transistor (MOSFET) 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 and the drain terminal is coupled to the output terminal of the V/I converter; 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 MOSFET 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 second voltage divider circuit including a fifth resistor and a sixth resistor, wherein the non-inverting input terminal of the op-amp is coupled to a junction of the fifth and sixth resistors, and wherein the fifth resistor is also coupled to the positive supply rail and the sixth resistor is also coupled to ground; and a protection circuit coupled to the V/I converter to prevent over-voltage and over-current conditions, the protection circuit including; a Schottky diode coupled between the drain terminal of the MOSFET and an output terminal of the protection circuit; a pn-junction diode coupled to a junction of the drain terminal of the MOSFET and the Schottky diode, wherein the pn-junction diode is also coupled to a seventh 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 seventh 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 an eighth 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 eighth 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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Specification