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    mosfet parastic

    hi, why is the parasitic diode of the MOSFET exist?

    •   Alt30th July 2007, 05:07

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    MOSFET Parasitic Diode

    Parasitic diode is because a MOSFET does not have a PN junction. The parasitic acts almosts like a normal diode in a MOSFET process.
    It is espeacially usefull in a bandgap circuit.

    Hope this is what you wanted to know.



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    MOSFET Parasitic Diode

    "Parasitic diode is because a MOSFET does not have a PN junction" Any detailed/further explaination on this?

    Thanks



    •   Alt30th July 2007, 08:58

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    Re: MOSFET Parasitic Diode

    the parasitic diode of MOSFET or the body diode is the due to the PN junction formed between the source and the gate.... this usually causes latchup when left open and is connected to the lowest supply to avoid latchup but due to its reverse capacitance and diode nature it causes trouble... so generally body and source are shorted to minimise its effect...



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    Re: MOSFET Parasitic Diode

    Quote Originally Posted by A.Anand Srinivasan
    the parasitic diode of MOSFET or the body diode is the due to the PN junction formed between the source and the gate.... this usually causes latchup when left open and is connected to the lowest supply to avoid latchup but due to its reverse capacitance and diode nature it causes trouble... so generally body and source are shorted to minimise its effect...
    I think u wrongly mentioned Gate instead of Body(Or bulk)..

    Parasitic diode occurs because the substrate is P substrate(in Nmos) and the source and drain r n+regions.. So both the bulk and source(and drain) regions forms a diode.. When it is forward biased,it becomes an alternate path for current to flow and most of the currents may pass to the bulk instead of through the channel.. When reverse biased,it wil develop capacitance due to the inherent nature of the diode..



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    Re: MOSFET Parasitic Diode

    Quote Originally Posted by dineshbabumm
    I think u wrongly mentioned Gate instead of Body(Or bulk)..

    Parasitic diode occurs because the substrate is P substrate(in Nmos) and the source and drain r n+regions.. So both the bulk and source(and drain) regions forms a diode.. When it is forward biased,it becomes an alternate path for current to flow and most of the currents may pass to the bulk instead of through the channel.. When reverse biased,it wil develop capacitance due to the inherent nature of the diode..
    ya, sorry i wrote gate instead of body in a hurry...



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    Re: MOSFET Parasitic Diode

    what is the best way to minimize this parasitic? tnx.



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    Re: MOSFET Parasitic Diode

    Quote Originally Posted by forkschgrad
    what is the best way to minimize this parasitic? tnx.
    Make it reverse biased so that no current flow through the diode.. For example,tie the bulk to source so that there is no forward bias for the diode as both the p and n+ region are in same potential..

    But then if we reverse bias the diode, it also increases the capacitance and may make the circuit work much slower!



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