Inverter design but change the enhancement mode mosfet into depletion mode mosfet

Thread Starter

PuPuuuuu10

Joined Jun 30, 2021
23
1625665216230.png
This image is from internet.
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!!
 

dl324

Joined Mar 30, 2015
13,537
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):
1625668142305.png
 

crutschow

Joined Mar 14, 2008
28,206
The problem with a depletion mode MOSFET is that it requires a negative gate-source voltage to turn it off.
Is that available?
 

Thread Starter

PuPuuuuu10

Joined Jun 30, 2021
23
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!
 

Thread Starter

PuPuuuuu10

Joined Jun 30, 2021
23
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!
 

dl324

Joined Mar 30, 2015
13,537
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)?
 

Thread Starter

PuPuuuuu10

Joined Jun 30, 2021
23
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!
 
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