Inverter as amplifier

[karko]

Hi guys,

I am a complete noob in electronics. Just started to learn about CMOS transistors. I finally understood how cmos inverter is working! . The problem is I have find a graph showing that CMOS inverter can work as amplifier. I am not sure but is this the correct circut?

**broken link removed**

And now I learned that pMOS is diode connected so it acts like diode. Still I dont get why it works as amplifier. As I understand when there is logic '1' on nMOS it is 'open'. Where is the gain? And what is the gain?

Sorry if I am unclear. I am really beginner. So please give me an easy explanation. Thanks!

 

[crutschow]

Forget logic when you are talking about using CMOS as a amplifier. In this case Vin is biased at some point between logic one and logic zero to give operation in the linear region as an amplifier.

In the circuit you show, the PMOS is acting like a drain load resistor for the NMOS. The PMOS is connected so it acts like a diode, but it is a diode with significant resistance. It is that resistance that acts as a load.

If you substituted a resistor for the PMOS, then you would better see how it works.

 

[karko]

Thanks for quick response. Ok I understand now that PMOS acts like a resistor for the NMOS. But still I dont get how Vout will be increased? What is amplified?

 

[audioguru]

A CD4069 or 74C04 has six Cmos logic inverters inside. If they are biased properly then they will be a high gain amplifier but the distortion will be fairly high.

 

[Roff]

The circuit Audioguru posted is self-biased by the 10Meg feedback resistor. The input needs to be AC coupled to use it, and the 1k resistor can be increased to decrease the gain.

 

[crutschow]

Thanks for quick response. Ok I understand now that PMOS acts like a resistor for the NMOS. But still I dont get how Vout will be increased? What is amplified?

It amplifies a small-signal AC signal. Do you understand the operation of AC transistor amplifiers?