In a recent question I (rightly or wrongly) said in a comment that calling a mid-rail generator (two resistors and a smoothing capacitor) a "virtual ground" was wrong and that the term "virtual ground" is reserved for when using negative feedback on an op-amp; if the non-inverting input is at 0V (ground) then the inverting input is regarded as a virtual ground due to negative feedback and the op-amp's very high open-loop gain.
I looked on wiki to find that their construction definition is: –
A voltage divider, using two resistors, can be used to create a
virtual ground node. If two voltage sources are connected in series
with two resistors, it can be shown that the midpoint becomes a
virtual ground if
Wiki then goes on to show this diagram: –
And they have some describing words thus: –
An active virtual ground circuit is sometimes called a rail splitter.
Such a circuit uses an op-amp or some other circuit element that has
gain. Since an operational amplifier has very high open-loop gain, the
potential difference between its inputs tend to zero when a feedback
network is implemented. To achieve a reasonable voltage at the output
(and thus equilibrium in the system), the output supplies the
inverting input (via the feedback network) with enough voltage to
reduce the potential difference between the inputs to microvolts. The
non-inverting (+) input of the operational amplifier is grounded;
therefore, its inverting (-) input, although not connected to ground,
will assume a similar potential, becoming a virtual ground if the
opamp is working in its linear region (i.e., outputs have not
saturated).
In the first sentence they mention a "rail splitter" then they go on to describe pretty much what I (currently) understand as a virtual ground. I have problems with Wiki's explanation because they started with the words "rail splitter" and, from my viewpoint, a "rail splitter" means "mid-rail generator".
I've provided the wiki explanation (before asking my question) just to show I've done some research on this.
My question is this: –
Is a mid-rail generator (formed by passive components and sometimes an
active buffer) a "virtual ground"?
Best Answer
Yes. I've used the term "virtual ground" for a node used as reference for signals and that was generated by making roughly a mid point between two supplies. I think that's pretty common usage.
I also agree that "virtual ground" can be used to describe the negative input of a opamp in inverting amplifier configuration, but only when the positive input is tied to ground.
This is a loose enough term that it should be defined before use, unless it is clear from context. Talking to someone about virtual ground without context or a definition is wrong.