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Q&A

What is this fourth connection in NMOS device?

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I know that in transistors there is base, collector and emitter, and in FETs there is gate, drain and source, but what is the fourth grounded connection opposite the gate in this NMOS circuit?

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Cannot comment on Andy's answer so I comment here (1 comment)
Pass transistors (1 comment)

1 answer

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That fourth connection is the bulk/body/substrate connection: -

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Image from here. On a normal 3 terminal MOSFET the "body" is connected to the source. On your device, the 3 n-channel MOSFETs share a common bulk pin that should usually be connected to the most negative voltage of your circuit (quite often 0 volts or GND). $$$$ Internally, the body/bulk connection is shown in the picture below: -

Image alt text

As the gate voltage rises positively with respect to the source, the p type material between drain and source inverts to n type material and forms a conducting channel.

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1 comment thread

In what cases would you want to have the body connection exposed if it is usually shorted to source? ... (3 comments)

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