Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics 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

Biasing of pushpull amplifier

Status
Not open for further replies.
E

edinburghtech

Junior Member level 2
Joined
Jan 28, 2012
Messages
21
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,467
Hello

I am a wannabe Analog Designer....
Playing around with CMOS circuits.. But not sure how to bias them. I understand MOS current equation. But not sure how to put a transistor into linear or saturation mode in a circuit (how to size the device to achieve this) . Any basic guide to biasing (DC biasing) and transistor sizing required to achieve certain mode of operation will be helpful. Also I am trying to learn a push pull amplifier configuration (figure https://obrazki.elektroda.pl/6983232400_1353596119.png). I got this circuit from https://users.ece.gatech.edu/pallen/Academic/ECE_6412/Spring_2004/L060-Push-Pull(2UP).pdf but I am not sure how to size transistors and which transistros are in what mode (Linear/Saturation). My plan is to use this circuit to drive a low impedance load (5 Ohms). Please help

Regards
Edintech
 

Have you tried playing with a simulation?

Here is my screenshot using Falstad's animated simulator. It is great for showing immediate results when you adjust values.



I find that the biasing is tricky to get right (as is typical with a push-pull amplifier). There is a tradeoff between efficiency and amount of distortion.

For large input signals it appears to work simply to bias Vgg3 and Vgg4 nearly to the supply rails.

The gain is just over .5.
I don't know if it is intended to increase gain or not.
 

BradtheRad said:
Have you tried playing with a simulation?

Here is my screenshot using Falstad's animated simulator. It is great for showing immediate results when you adjust values.



I find that the biasing is tricky to get right (as is typical with a push-pull amplifier). There is a tradeoff between efficiency and amount of distortion.

For large input signals it appears to work simply to bias Vgg3 and Vgg4 nearly to the supply rails.

The gain is just over .5.
I don't know if it is intended to increase gain or not.
Click to expand...

Hello BradtheRad Thank you very much for the post. It was very useful.
Can you please suggest me from where I can learn CMOS biasing basics quickly..
 

Mosfets have been coming out in different varieties. It is an advantage on one hand, but OTOH it creates more details that we must pay attention to.

The gate needs to see a definite reference voltage on the other side of the emitter/source, to achieve reliable biasing.

The gate threshold voltage must be considered. Some devices have a lower threshold, others higher. The same with the full-On gate voltage.

The body diode must be considered.

Static charge must be guarded against.

There is no substitute for hands-on experience with real components.

Expect to burn up a few mosfets in the process.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top