Re: virtual ground
Hi,
"virtual ground" is concern to an op. With the feedback of an output terminal of an op to the negative input terminal of the op, the voltage on the negative input terminal of the op is equal to the voltage of positive input terminal of the op. This effect is call "virtual ground".
The voltage of the negative input terminal is not really equal to ground. But, if the positive input terminal is connected to ground, the voltage of the negative input terminal is equal to ground.