Hi All,

I have been reading about differential amplifiers and I am unsure about something...

When using negative feedback, a voltage divider is used between ground and the output with the centre of the divider going to the inverting input of the op-amp... which will amplify the input on the noninverting input according to the ratio of the divider.. thats fair enough...

the bit I don't understand is that when you want a differential amp, you have to add another divider on the noninverting input too... why cant you connect one input to what would be the ground of the divider and the other to the noninverting input?

I'm probably being really stupid here!

Cheers
Shaun

 

Fundamentally, you can, but the output will not be purely differential. It will have the input that is connected to what would be the ground of the divider added to the differential result. Get it?

When you connect it the other way, it cancels out this effect.

 

Fundamentally, you can, but the output will not be purely differential. It will have the input that is connected to what would be the ground of the divider added to the differential result. Get it?

When you connect it the other way, it cancels out this effect.

I think I'm starting to see what you are saying... I think I'll go and sleep on it

Thanks for your reply.

Cheers
Shaun