# Art of Electronics Exercise 4.3 Operational inverter

1. Mar 20, 2013

### CSOleson

1. The problem statement, all variables and given/known data
The circuits in Figure 4.14 let you invert or amplify without inversion, by flipping a switch. The voltage gain is either +1 or -1, depending on the switch position.
http://tinypic.com/r/2hnql2c/6
http://tinypic.com/r/2hnql2c/6

2. Relevant equations
Gain for the first image with the switch set to ground is equal to -R2/R1, because it is an inverting amplifier, struggling to identify how to consider the circuit as a follower, because it doesn't look like a typical follower circuit. Unsure how to consider the circuit when the positive and negative terminals are connected.

3. The attempt at a solution

Last edited: Mar 20, 2013
2. Mar 20, 2013

### Staff: Mentor

What is the difference in voltage between the + and - inputs for an opamp in the follower configuration? So what is the feedback current in this configuration?

3. Mar 20, 2013

### CSOleson

are the + and - inputs equal, because of the negative feedback loop?

4. Mar 20, 2013

### CSOleson

so the voltage across the 1st resistor would be 0V because it is V+ - V-

5. Mar 20, 2013

### Staff: Mentor

Correct-a-mundo

Kind of a wierd follower, but that's one of the ways that H&H teaches us how to be comfortable thinking about circuits. Have you seen this thread?