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.

Supply voltage dependent on linearity

Status
Not open for further replies.

simplsoft

Full Member level 2
Joined
Nov 24, 2014
Messages
127
Helped
0
Reputation
0
Reaction score
0
Trophy points
16
Activity points
1,045
Hello

Can anyone tell me what is the relation between linearity and supply voltage. I have read some where that if we have low supply voltage in an op-amp then the linearity will be low compare to high supply voltage. How can I justify this.
 

I think you mean the opposite - linearity dependent on supply voltage.

I agree with Crutschow but bear in mind that the supply has to be at least as much as the voltage you want out of the amplifier. There will obviously be clipping if you try to get more out than you put in but on most op-amps there is also a non-linear zone as your signal approaches the supply rails. In that sense, more supply voltage may give you the safety margin you need to maintain linearity.

Brian.
 

yes linearity depends on supply voltage. If let say I have a supply voltage of +/-1 V then linearity (Gm vs vid) the vid linear range is les lets say +/- 0.2V vid only.
If I have 3 voltas supply then vid would be +/-0.8 for example. why so?
 

It is simply due to the voltage required to bias devices into linear conduction and their saturation voltages. Taking a BJT for example, it requires somewhere around 0.5 - 0.6V between base and emitter to pass enough bias current to work as an amplifier. If your supply was only 1V, more than half would be used just to make the transistor conduct and any negative (assuming NPN) input voltage would stop it conducting at all. If you wired the stage in darlington configuration, as is common in op-amps, you would need more bias voltage than the supply could provide. Add to the equation that you want the output pin to be able to swing over sufficient voltage range to be useful (VCEsat typically 0.2V and in reality you wouldn't want to reach saturation), it becomes clear that you simply run out of headroom to handle the signal as well.

So basically, although there are some op-amps for low supply voltage, most need enough supply to cater for the individual voltage dropped across each internal element while keeping those elements working in their linear region of conduction. If the supply is too low, the devices either cease to function or enter a non-linear region of their characteristics and distortion results.

Brian.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top