Basic virtual ground
Above we have a Aol of 100K, a feedback of 10%, so overall G = 10. But notice the Vir Gnd V,
its 99 uV. In other words at the diff input the two inputs are essentiually same V due to the
feedback.
Now lets reduce the Aol (Slider Gain) to 100 -
Here we see large error in Vout, and we are losing the Vir Gnd, its jumped to 90 mV, almost
100X what it was when we had large Aol.
The importance of Vir Gound, one example, is the classic summer -
Basically when Virtual Ground is solid then the current thru each input is unaffected by
the other input currents, eg I = V1/R = V2/R = V3/R in this case.
So lots of Slider G (forward path gain) here makes the simple summer work well. Or higher
Feedback Factor (which applies more error correction when closed loop G
is lowered).
Regards, Dana.