# Explanation on why there is no feedback in the circuit for higher voltages of input signal

simulate this circuit – Schematic created using CircuitLab

I don't understand the reasoning behind the analysis of this circuit. The professor started by saying that if diodes D2 and D5 are ON and D4 and D3 are OFF than there is no global feedback in the circuit and V+ and V- of the first ideal op amp are not the same because the I1 is independent and Vo=R2*IO. Same goes for the other two diodes with the output being Vo=-R2*I0. When all 4 diodes are working then there is feedback and Vo=V2 because V+=V-.

He than proceeded to draw a diagram that is confirmed by the simulation. He also added that if there were a resistor in parallel with the I1 there would be feedback in all cases but the feedback would be weak and not much would change.

How do I know that there is no feedback in the case where 2 diodes are working and the other 2 are off and how does that change when the resistor in parallel with I1 is added. Also how do all 4 working diodes introduce the feedback here?

Isn't feedback a connection between the input and the output, and adding diodes doesn't seem to do anything with the input signal as far as i can see.

• For a start: remove R1, V2 and opamps OA1 and OA2, from your circuit, and connect the wire where the output of opamp OA1 originally was, to ground. (So, cathode D4 = anode D2 = GND). That should give insight what happens when 1) enabling D2/D5 and disabling D3/D4, 2) enabling D3/D4 and disabling D2/D5 and 3) enabling all diodes. – Huisman Mar 26 at 22:17
• Next, insert a voltage source between cathode D4 and ground and check what happens for different voltages for step 1), 2) and 3) ... Step 4) Place a resistor parallel with I1 and determine what happens in that situation. – Huisman Mar 26 at 22:52