Will a CMOS inverter work as an Amplifier?

[vlsi_whiz]

unbuffered inverter linear

Can anyone provide me some insights on this topic?

Will a CMOS inverter act as an amplifier under normal bias conditions? Will it amplify signals if it is biased at Vdd/2? If so, can any one give me a small explanation?

Thx

 

[Davood Amerion]

cmos gmcell

I think it is possible, because input impedance is very high and it has voltage gain.
but it is unusual and will draw more current from VDD.
It is better to use another IC for this purpose!!!!

regards
Davood Amerion

 

[sunking]

of course you can.
1. such as two stage opa, the last stage can be an inveter
2. use self-biased, you can use the inverter as an opa

 

[cherrytart]

the older simpler stuff for sure, like an unbuffered inverter from the old 4000 series. other than input protection, one of these inverters is just 2 totempole transistors.

 

[Fom]

Connect input to output through 1M resistor and you will get amplifier. This amplifier is often used in quartz oscillator circuit.

 

[suria3]

I agree with Davood, it is possible to use it as an amplifier with the gain,
A=Vout/Vin= 2*(gm1||gm2)*(ro1||ro2) but at the tradeoff with current from VDD.

For better amplification, u can use common source amplifer which will give you high gain with lesser current and more realistic.

 

[skal81]

Yes it is possible and called a Nauta's gmCell.
You can refer to "A CMOS Transconductance-C Filter Technique for Very High Frequencies" published in IEEE Journal of Solid-State Circuits, vol. 27, no.2 February 1992, pp 142-153. (sorry I don't have the PDF of the file)

It describe a transconductor (base for an amp) using an inverter. Actually 2 because it's a fully differential structure. The CMFB is also realized with inverters.

 

[mady79]

Inverter behaves as an amplifer if input signal does not saturate any of the
p/nmos transistors .pmos amplifies lower half of the input signal and nmos amplifies higher half of input small signal .singal swing has to be around the trip point of the inverter for good gains and make sure input swing does not saturate to rails .

It has the same problem as any other single ended designs ,trip point variations
due to supply ,one can notice this having more gain for positive cycle and less gain for negative cycle .

 

[zorro]

the older simpler stuff for sure, like an unbuffered inverter from the old 4000 series. other than input protection, one of these inverters is just 2 totempole transistors.

Exact. Use UB (unbuffered) series instead of B (buffered) series, inthe way Fom described. With buffered devices, the several (odd number of) inverter stages can be working in bad operating points.
There is an Application Note (I guess that fron National) on linear application with CMOS logical gates.
Attention: the static current can be excessive in some devices when polarized in this way.
Regards

Z

 

[muralikrishnap]

yes

when used in satyuraton region of opearetion

Added after 1 minutes:

yes

 

[tandr]

Yes , and just think about the transfer curve,
you will find the gain is high

 

[shaikhsarfraz]

Hi,
In saturation region invertor works as Amplifier with the gain given as
Gain = -gm*Rds.

In saturation region the gain is also given as
(Vout/Vin) = (Vdd + Vtn + Vtp√(Bn/Bp))/(1+√(Bn/Bp)).

thanks
sarfraz

 

[tandr]

Yes , in fact I just design a circuit use inverter
amp as the amplifier unit

 

[rajkumaru]

When trx work in linear region then it is inverter and when trx of inverter work in saturation region then it work as amplifier

 

[shaikhsarfraz]

Hi,
I have a doubt regarding this statement.

When trx work in linear region then it is inverter and when trx of inverter work in saturation region then it work as amplifier

The inverter operation of the transistor is digital operation, which is because of the switching operation of transistor. For switching the transistor switches between linear/saturation and Cutoff region. So for inverter operation it is not required that the transistor should only be in linear.

For using it as an amplifier we use it in saturation region because the gain of the transistor is highest at that point.

thanks
sarfraz

 

[vbhupendra]

yes CMOS acts an amplifier if both nmos & pmos are in saturation.

 

[wonbef]

hello, if inverter can't work as an Amplifier, many questions will appear!

 

[roykyn]

see 74hct14 datasheet........

 

[CMOS]

See Page 21 of this App. Note https://ww1.microchip.com/downloads/en/AppNotes/00236a.pdf

It uses CMOS inverter (4069) as demodulator as well as amplifier.

 

[Humungus]

Of course it can. Actually most crystals oscillators in micro controllers use an single inverter as crystal driver. The gain is roughly linearized by a feedback resistor.

Actually the inverter is a no very good amplifier in the sense of its analog characteristics: offset, linearity, rejection, etc.

But, anyway it is an inverting amplifier