[sdiy] Non-inverting summing amplifier

[Ingo Debus]

Am 28.01.2009 um 08:23 schrieb David G. Dixon:

> In an inverting summer, on the other hand, the inputs act as  
> current sources
> into the negative input terminal, which in turn acts as a summed  
> current
> source through the feedback resistor.  Hence, the opamp makes the  
> voltage
> inputs look like current sources with infinite impedance.

You mean, the input impedance of an inverting amplifier is infinite?  
Sure aout this?
As I understand it, the input impedance is just the value of the  
input resistor, since its other end is tied to virtual ground.

Ingo