Four-terminal power MOSFET switch having reduced threshold voltage and on-resistance
First Claim
1. A method of switching a current on and off comprising the steps of:
- providing a MOSFET, the MOSFET comprising first and second regions of a first conductivity type formed in a semiconductor substrate and separated by a body region of a second conductivity type, and a gate separated from channel region within the body region by a dielectric layer, neither of the first and second regions being shorted to the body region;
applying a voltage VDS across the first and second regions;
applying a voltage VG (on) to the gate so as to cause a current to flow between the first and second regions through the channel region;
applying a voltage VB to the body region so as to forward-bias a PN junction between the body region and the second region, the voltage VG being set at a level such that a resulting forward-bias across the PN junction is not sufficient to cause a substantial current to flow across the PN junction;
applying a voltage VG (off) to the gate so as to terminate the flow of current between the first and second regions through the channel region; and
removing the voltage VB from the body region.
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Accused Products
Abstract
The threshold voltage and on-resistance of a four-terminal power MOSFET switch are reduced by partially forward-biasing (to, for example, 0.5 V) the junction between the body and electrical source of the MOSFET. Preferably, as the MOSFET is switched on and off to control the current to a load, the body is switched synchronously with the gate so that the source-body junction is partially forward-biased (i.e., biased at a level that is insufficient to cause a forward current to flow through the junction) when the MOSFET switch is turned on and the body is shorted to the source when the MOSFET switch is turned off, thereby reducing the leakage current through the MOSFET in its off state. The body bias may be derived directly from the gate voltage or from a separate voltage supply line. A current-limiting device and a voltage clamp may be used to limit the body current and voltage, respectively.
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Citations
28 Claims
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1. A method of switching a current on and off comprising the steps of:
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providing a MOSFET, the MOSFET comprising first and second regions of a first conductivity type formed in a semiconductor substrate and separated by a body region of a second conductivity type, and a gate separated from channel region within the body region by a dielectric layer, neither of the first and second regions being shorted to the body region; applying a voltage VDS across the first and second regions; applying a voltage VG (on) to the gate so as to cause a current to flow between the first and second regions through the channel region; applying a voltage VB to the body region so as to forward-bias a PN junction between the body region and the second region, the voltage VG being set at a level such that a resulting forward-bias across the PN junction is not sufficient to cause a substantial current to flow across the PN junction; applying a voltage VG (off) to the gate so as to terminate the flow of current between the first and second regions through the channel region; and removing the voltage VB from the body region. - View Dependent Claims (2, 3, 4)
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5. A power MOSFET switch for switching a current to a load, the power MOSFET switch comprising:
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a four-terminal MOSFET having first, second gate and body terminals, no one of the terminals being shorted to any of the other terminals; a first switch connected between the first and gate terminals; a second switch connected between the first and body terminals; wherein the first and second switches are ganged together, the first switch passing a voltage VG (on) to the gate terminal and the second switch passing a voltage VB to the body terminal when the first and second switches are in a first position, the first switch passing a voltage VG (off) to the gate terminal and the second switch removing the voltage VB from the body terminal when the first and second switches are in a second position. - View Dependent Claims (6)
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7. A power MOSFET switch arrangement comprising:
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a four-terminal power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; and a resistor connected between the gate and body terminals. - View Dependent Claims (8, 9, 10, 11)
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12. A power MOSFET switch arrangement comprising:
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a four-terminal power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; and a depletion-mode MOSFET connected between the gate and body terminals, the depletion-mode MOSFET having source, body and gate terminals shorted together. - View Dependent Claims (13, 14, 15, 16)
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17. A power MOSFET switch arrangement comprising:
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a four-terminal power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; a resistor connected between the gate and body terminals; and a depletion-mode MOSFET connected between the source and body of the power MOSFET, the depletion-mode MOSFET having source and body terminals shorted together and a gate terminal connected to the gate of the power MOSFET. - View Dependent Claims (18, 19, 20)
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21. A power MOSFET switch arrangement comprising:
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a power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; a voltage supply line; a first inverter having an output terminal connected to the gate terminal and a power input terminal connected to the voltage supply line; and a second inverter having an output terminal connected to the body terminal and a power input terminal connected through a resistor to the voltage supply line. - View Dependent Claims (22, 23)
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24. A power MOSFET switch arrangement comprising:
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a power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; a voltage supply line; a first inverter having an output terminal connected to the gate terminal and a power input terminal connected to the voltage supply line; a second inverter having an output terminal connected to an input terminal of the first inverter and a power input terminal connected to the voltage supply line; and third and fourth MOSFETs connected in series between the voltage supply line and ground, a common node between the third and fourth MOSFETs being connected to the body terminal of the power MOSFET, the output terminal of the first inverter being connected to the gate of the third MOSFET and the output terminal of the second inverter being connected to the gate of the fourth MOSFET. - View Dependent Claims (25)
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26. A power MOSFET switch arrangement comprising:
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a power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; a voltage supply line; a first inverter having an output terminal connected to the gate terminal and a power input terminal connected to the voltage supply line; a second inverter having an output terminal connected to the body terminal; and a voltage divider connected to the voltage supply line, a midpoint of the voltage divider being connected to a power input terminal of the second inverter. - View Dependent Claims (27)
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28. A power MOSFET switch arrangement comprising:
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a power MOSFET having source, drain, gate and body terminals, no one of the terminals being shorted to any of the other terminals; a voltage supply line; a first inverter having an output terminal connected to the gate terminal and a power input terminal connected to the voltage supply line; a second inverter having an output terminal connected to the body terminal; and a linear regulator connected to the voltage supply line, an output terminal of the linear regulator being connected to a power input terminal of the second inverter.
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Specification