Operational Amplifier

Thread Starter


Joined Sep 20, 2011
I was going through op-amp.... I have certain doubts.....
1) Concept of virtual ground
2) Output swing
can anybody please answer this..... thanks a lot in advance


Joined Mar 24, 2008
Welcome to AAC Anasha.

Virtual ground is based on the concept of negative feedback, and the fact the op amp tries to make both inputs the same voltage. If the positive input on a inverting amplifier is grounded, and the negative input is made to look the same on this amplifier, then the negative is virtually a ground, it will measure the same, it will act the same, unless you know the schematic it will be hard to tell the difference.

Take this circuit for example, I have left off the input resistor. The output will swing to what ever voltage needed to make the minus input the same as the positive input. To the outside world, the negative input appears to be a ground, while the output of the op amp will have a voltage that accurately reflects the input current.

Output swing is pretty generic, it is such loose statement it doesn't really have a good definition.

Op amps in general can go the range of their power supply, with exceptions. The exceptions is they are not rail to rail, they generally can not quite reach the power supply voltage on either side. There are huge numbers of op amp part numbers out there, so there are going to be parts made that will be exceptions to this rule.

There are other factors that affect output swing, frequency response is pretty basic. Another variable is slew rate, which is the rate of change an output voltage can move. If you run up against slew rate it can appear to be a frequency response problem, but when you look at it closer it isn't.

Not too many girls choose to enter this profession, so I suspect while you have your picture up you will find more help than most. Guys can't help themselves, it is like +3 on beauty points. :D Did I mention a fair percentage of the guys qualify to be called nerds (not excepting myself either)?