I know that op-amp can provide virtual ground for the circuit, and can have benefits in eliminating crosstalk. But the latter part confuses me.
Suppose that voltage sources are modeled as independent voltage source plus resistor. In such a case, resistor can be added to existing resistors to provide total resistance value, and voltage laws to calculate voltage works, so crosstalk does not affect the sum value, as long as resistance value of each source is quite different.
Is the whole concern regarding crosstalk related to different sources having different output impedance? Or am I understanding something completely wrong?
To summarize, I do understand that adding voltage makes the output voltage higher than input voltages, and current flows from high voltage to low voltage. But Kirchoff's voltage laws are still there unless we are talking about distributed circuits, and the calculation using same output impedance for different voltage sources results in an accurate-enough sum. So why active summer over passive summer?