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We know that the nmos below is an enhancement mode mosfet. I am just wondering if there is some method that i can change the enhancement one into depletion mode one, but still the circuit acts like an inverter. Note that i do not mean that use a depletion mode load mosfet to replace the resistor.
Really thanks!!

 

Welcome to AAC!

We know that the nmos below is an enhancement mode mosfet.

No we don't. The symbol used in your schematic is for a depletion mode MOSFET.

This is the symbol for an enhancement mode MOSFET (note the dashed line by the polarity arrow):

 

The problem with a depletion mode MOSFET is that it requires a negative gate-source voltage to turn it off.
Is that available?

 

Welcome to AAC!
No we don't. The symbol used in your schematic is for a depletion mode MOSFET.

I mean if we just consider it to be an enhancement mode, but now try to change it into a depletion mode and can i make it the similar characteristics of an inverter as enhancement mode nmos does?
Best wishes!

 

The problem with a depletion mode MOSFET is that it requires a negative gate-source voltage to turn it off.
Is that available?

I have thought of this before and i have one way is to add negative dc component into the input voltage, more like an offset voltage. Can it work?
Best wishes!

 

I mean if we just consider it to be an enhancement mode, but now try to change it into a depletion mode and can i make it the similar characteristics of an inverter as enhancement mode nmos does?

You can make an inverter with either enhancement or depletion mode MOSFETs. The devil is in the details.

Which depletion mode MOSFET do you have in mind (they are uncommon), what supply voltages are available, and what will be driving the gate (voltage levels)?

 

Can it work?

If you can generate a negative voltage sufficient to turn off the particular depletion-mode MOSFET you will use.

But why do you want to?

 

If you can generate a negative voltage sufficient to turn off the particular depletion-mode MOSFET you will use.

But why do you want to?

Thanks for your guidance.
For example, if i want to use this inverter to act like a buffer which can change the sin wave into square wave to drive the gate of mosfet in buck circuit. I can achieve this inverter with normal enhancement mode nmos and a resistor. I just curious if i can replace the enhancement into depletion mode nmos (not for load) to achieve the same function of buffer.
Really thanks!