# Op Amp virtual ground

• posted

Hi, This is mahak. can anybody tell me what is virtual ground concept.I refer to Micro electronics by Sedra & SMith. There it says Virtual Groung is because of infinite gain of amplifier. But if that is the case then it should be there for both inverting and non inverting amplifier. Please clarify.

• posted

An opamp with negative feedback connected between output and inverting input, tries to produce whatever output that will cause the inverting input voltage to match what is applied to the non inverting input. This is because the opamp has a very high differential voltage gain, so the only way the output will not be saturated either positive or negative is if the two inputs have an almost perfect match (the imperfection in that match providing the signal that is amplified by the high differential voltage gain to produce the finite output).

So, when you connect the non inverting voltage to ground, the feedback forces the inverting input to be an almost perfect copy of that ground voltage. From the viewpoint of any signal connected to an input network to the inverting input, that signal acts as if the input network were connected to ground, even though it is just balanced there by gain and feedback. Pretending that the inverting node is grounded (virtually grounded) makes it a lot simpler than doing the math that includes the tiny voltages at that node because the amplifier gain is not actually infinite. It is a useful approximation.

Of course, if you connect the non inverting input to some other voltage reference than zero, the inverting input is a virtual copy of whatever reference voltage you use, instead of ground.

• posted

Whew. I feel dizzy. I think it's best that the OP stick with Popelish' explanation.

Bob

• posted

"mahak"

** Virtual ground refers to the situation where the " + " input of an op-amp is connected to circuit ground and the circuit is an inverting amplifier stage.

Then the " - " input becomes a "virtual ground" since ( in all normal operation ) there is only the *tiniest* of AC or DC voltages on that pin.

So, it is "virtually grounded" during operation.

Calculations and analysis can use that simplifying assumption quite safely.

...... Phil

• posted

You do talk the most appalling tripe.

Graham

• posted

Ignore Jamie's 'explanation'. He's an utter f****it.

Phil Allison has explained it in a nutshell.

Graham

• posted

thanks. its convincing.

• posted

Hmm. I can't find that reference on the NET that you speak of.

In my eyes. A virtual ground is no more than a voltage divider where the divided network is the ground and the outer of the network are connected to the + & - of the single source of energy. In this system, the common would be derived from the center divide of the network. I don't see where the gain of an amp comes into play here unless, they are referring to the open-loop gain? That would be the (+) input connected to the common/virtual ground tap point, and the (-) being the input for example.

Taking measurements on this type of output with no input on (-) should yield 0 volts. This is assuming an ideal amp. biasing the (-) would result in very high gain but not infinite since in theory, only ideal op-amps have that and there is no such thing as an ideal op-amp or amp for that matter.

This seems to be a general theory question at best. Maybe you read it incorrectly ?

```--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.```
• posted

Assuming Jamie had ever used an opamp then he would know what "virtual ground" is and how to (simply) explain it.

It's amazing how people like Jamie will spew the limited knowledge that they have in an attempt to impress people. It always has the opposite effect, in the long run.

Jamie just needs to go to school. If he's been to school then he needs to go back.

Bob

• posted

Not understanding is the first sign of interest :)

```--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.```
• posted

Jamie wrote in news:e79Xi.120\$ snipped-for-privacy@newsfe05.lga:

He could have said it "nicer", but you're way off. Your entire post is:

The original question is in reference to an actual book often studied by EE's, not the NET.

No measurements are involved.

This is a very specific (and basic) question about the operation of opamps. His reading skills are fine...

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• posted

Love how you left out the rest of my post as it did go on with the op-amp discussion.

But that's typical of you any ways you lifeless turd.

Want to smell my shorts? I haven't changed them in a while! it should turn you on! I heard that turns you on!

```--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.```
• posted

I think it's time to play -- SPOT THE LOONEY!