Electronic – Negative resistance from MOSFET circuit


From the paper https://ir.nctu.edu.tw/bitstream/11536/5095/1/A1979JE36000027.pdf

I'm trying to understand this MOSFET circuit which creates negative resistance. Whilst the paper explores how it works, I'm not really understanding it.
I've tried simulating it in SPICE however I'm not really seeing the negative resistance effect, i.e negative current is proportional to voltage. A general overview of this circuit would be greatly appreciated as well as some indication of how to recreate it in LTSpice would be handy.

Equally any more examples of MOSFET based negative resistance would be helpful to understand it deeper.

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Best Answer

Say you increase the voltage at \$V_{DS}\$. This increases the voltage on Q2's gate, increasing the conductivity of its channel, lowering the voltage at \$V_{GS}\$. This decreases the current through Q3's channel. So by increasing the voltage \$V_{DS}\$ you've decreased the current that the \$V_{DS}\$ supply must provide, which is the definition of a negative resistance load.

Of course this all depends on Q1, Q2, and Q3 being in the appropriate operating modes, so there will be a limited range of voltages over which the negative resistance behavior can be observed.

negative current is not proportional to voltage.

If you apply a positive voltage to a circuit branch and it sends current back out towards you ("negative current") then that branch is delivering power to you, not absorbing power from you.

This circuit doesn't do that.

But it does have a region where \$\frac{dV_{DS}}{dI_{DS}}<0\$, which is what the authors are referring to as negative resistance (and also what we call negative resistance in the case of common negative-resistance elements like glow tubes and Esaki diodes).