Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

How can a CMOS be used as an amplifier?

Status
Not open for further replies.

Amninder

Newbie level 6
Joined
Jul 12, 2009
Messages
14
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
California
Activity points
1,405
Hi,
I am new to the Analog field. I was reading the Book by Behzad razavi "Design of Analog CMOS ICs'. I understood how an nMOS and a pMOS can act like an amplifier individually . But then I came to know that the CMOS technology is used for designing RF chips.
Can anybody tell me how a CMOS ( an nMOS connected to pMOS ) can be used for amplification.
I am not sure if my understanding of CMOS is currect. For me a CMOS is a basic inverter circuit which can be used to make higher level digital circuits.

A reply would be of great help.
 

LvW

Advanced Member level 5
Joined
May 7, 2008
Messages
5,824
Helped
1,739
Reputation
3,480
Reaction score
1,338
Trophy points
1,393
Location
Germany
Activity points
39,133
cmos as amplifier

You are right. The CMOS inverter mostly is used in digital circuits.
However, it has a rather steep transition range between the on and the off state.
Always, such a region can be used for amplification (like in each "normal" amplification stage), when you can fix a bias point in the middle of this range.
And, luckily, this is possible with a CMOS stage. This is because an input voltage of Vdd/2 (at both gate nodes) will produce an output voltage at Vdd/2 (middle of the transition region). Therefore, connect a rather large resistor between output and input - and you have a fixed bias point due to negative feedback. If you then inject a signal via a coupling C you have an inverting amplifier. As an alternative, you can inject the input via another resistor (lower than the feedback resistor) - and you have an amplifier with signal feedback and lower gain. Try it.
Regards
 

Audioguru

Advanced Member level 5
Joined
Jan 19, 2008
Messages
9,113
Helped
2,115
Reputation
4,224
Reaction score
1,939
Trophy points
1,393
Location
Toronto area of Canada
Activity points
57,249
bias cmos inverter amplifier

A Cmos inverter like a CD4069 or a 74C04 can be used as an amplifier. They are symmetrical.
They cannot drive a low resistance and they have pretty bad distortion when the output level is high.

A negative feedback resistor from its output to its input self-biases it at close to half the supply voltage. Its gain and frequency response is affected by its supply voltage.

Here is an old graph from RCA:
 
  • Like
Reactions: malden

    malden

    points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top