### Author Topic: Standart Inverter Problem  (Read 3452 times)

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#### igorbog

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##### Standart Inverter Problem
« on: October 30, 2011, 10:34:45 pm »
I have created simple inverter, but when I make trans. Simulation, It shows me Low output voltage. Do you have any idea?

#### amspire

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##### Re: Standart Inverter Problem
« Reply #1 on: October 30, 2011, 10:49:42 pm »
That inverter circuit is a logic inverter - it is not intended for analog.

One of two things could be happening.

1. Your FET models may be for a very small geometry FET and that is the best the Pchannel FET can do into 1K, or

2. The N-Channel FET is dominating and at that bias voltage, it is heavily on.  A check of the drain currents would show if this is occuring.

Richard

#### igorbog

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##### Re: Standart Inverter Problem
« Reply #2 on: October 30, 2011, 10:58:27 pm »
Thanks.
Tell me please where I can in Orcad change Pmos Channel width in order to make it simitery

#### amspire

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##### Re: Standart Inverter Problem
« Reply #3 on: October 30, 2011, 11:02:43 pm »
Can you plot the n-channel drain current first?

It may be very high.

#### igorbog

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##### Re: Standart Inverter Problem
« Reply #4 on: October 30, 2011, 11:19:44 pm »
attached

#### amspire

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##### Re: Standart Inverter Problem
« Reply #5 on: October 31, 2011, 12:22:00 am »
Wow! that is low.

I suspect the mosfet models you have used are designed for internal mosfets on a LSI chip. They are probably designed for a few uA of drain current in normal operation.

You should have other mosfet models.

But why are you trying to use a logic circuit for inverting a sinewave?

A n-channel mosfet with a 1K resistor and the gate DC biased for about half the supply volts on the drain would do a much better job as a sinewave inverter/amplifier.

Richard

#### igorbog

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##### Re: Standart Inverter Problem
« Reply #6 on: October 31, 2011, 05:20:02 am »
you are right, but I only wanted to try this circuit. tell me please what transistors to choose and hoow do you choose them?

#### amspire

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##### Re: Standart Inverter Problem
« Reply #7 on: October 31, 2011, 05:41:03 am »
Just get libraries from the manufacturers.

For example you could get the libraries for BSS84 (P Channel) and BSS123 (N channel).

These are both rated at about 0.13 A drain current and about 10 ohms resistance at 5V gate-drain voltage.

http://www.fairchildsemi.com/models/PSPICE/Discrete/MOSFET.html

Richard

Smf