[sdiy] Non-inverting summing amplifier

[Tom Wiltshire]

On 28 Jan 2009, at 18:40, Ingo Debus wrote:

>
> 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.

I thought he meant that the inv amp arrangement makes it look like  
the *output* impedance of the thing you feed into it is infinite. So  
you get all the voltage that you sent out, without any losses.

T.