[sdiy] Using Opamps as INV or NON-INV amplifiers

[Aaron Lanterman]

On Wed, 21 Jun 2006, Ian Fritz wrote:

>> If you want to sum multiple signals together you need to use inverting 
>> configuration.

> As a general statement, that simply isn't true.  If you have several inputs 
...
> various inputs from interacting.  So in that case the inverting summer is 
> adventageous.  But if you are summing signals from fixed-impedance sources, 
> or if the variable impedance is just a trimmer that is set once, then you can 
> use the generalized differential summer.  This saves an opamp, at the cost of 
> some calculations.

For a good example of what Ian describes, you can take a look at the way 
the input and feedback signals are summed in a typical SSM2040 style four 
pole OTA-C type cascade.

- Aaron