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Why do some analog circuits use a FET with shorted drain and source? Depending of the type of FET, it may either act as a capacitor or a diode? It each case, why not just use a cap or a diode? Below is one example.

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Slimane
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1 Answers1

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That circuit uses a JFET as a very low leakage diode, presumably, but there's no clear requirement for such a function as a similar diode is built into the CMOS gate, and 100K is not a particularly high resistance.

For example this application note shows a diode-connected JFET used where fA matter.

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Spehro Pefhany
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