Op amps - assignment

[darko31]

Hi guys,

we've been given an extra points assignment in my electronics class, and I've been having some trouble with it. The assignment is in the attachment. Basically, the OP1 and OP2 are configured as non-inverting, but the OP0 and OP3 are giving me headaches. I'm stuck at b) point, to find out V0 in function to V1, V2 and V3.

The OP3 is configured as buffer and it's just transferring input from pot, but the OP0 looks like it's configured as differential amp although R3 should be connected to ground. My way of seeing it is like the OP3 and pot are shifting the ground for the R3 but the problem is that I'm not sure how to write it down in equations.

So far, I've got this V1=Va+R1(Va-Vb)/xP and V2=Vb-R1(Va-Vb)xP

and for the OP0, V0=R3/R2(V2-V1) + something with V3

I'll be reaching my teaching assistant, but I'd like to hear what eevbloggers have to say.

Thanks in advance.

[XFDDesign]

It's an instrumentation amplifier configuration. The amplifiers are not labeled, and I can't read the assignment. Can you redraw with labels?

[darko31]

Yeah, sorry about that

[jimmc]

Might be worth taking a look at this ti.com article www.ti.com/lit/an/slyt226/slyt226.pdf

Jim

[XFDDesign]

You've then got the basics, but you're relying too much on patterns and not analysis.

If you know V2 and V3, you can solve the voltage at the non-inverting node by superposition.

[free_electron]

solve it for R3 tied to 0 v . this is a classic diff amp.

then replace 0v with the voltage coming from the other opamp.

tis is basically a diff amp with offset control for its output. last stage acts as summing amplifier

[darko31]

@jimmc

Will do.

You've then got the basics, but you're relying too much on patterns and not analysis.

If you know V2 and V3, you can solve the voltage at the non-inverting node by superposition.

Yeah, I'm still grasping the methods of solving opamp circuits. Will try that out.

solve it for R3 tied to 0 v . this is a classic diff amp.

then replace 0v with the voltage coming from the other opamp.

tis is basically a diff amp with offset control for its output. last stage acts as summing amplifier

Yup, got similar idea, thanks for confirmation.