[sdiy] Non-inverting summing amplifier

[Tom Wiltshire]

On 28 Jan 2009, at 20:25, Ingo Debus wrote:

>
> Am 28.01.2009 um 20:38 schrieb 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.
>
> Now I'm really confused.

Yeah, sorry. I think it was me got confused, not you.

T.