# Inverting amplifier

1. Nov 8, 2005

### Midas_Touch

I have attached an image of an inverting circuit.

If I set R1 = 10 k ohms and R2 = 100 k ohms, I need to verify if this circuit works or not. Therefore, would the voltage between points A and B be equal to 0.1 V since B is connected to ground? The voltage input is 0.1 volts.

Thank you

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2. Nov 8, 2005

### dlgoff

Why don't you just measure the output?

3. Nov 8, 2005

### Midas_Touch

Yeah, I did that too. But one of the questions asks us to determine what the voltage will be between those two points.

Also, is it possible to create a circuit with a -0.1 v gain? I would think so, if I varied the resistors.

Last edited by a moderator: Nov 8, 2005
4. Nov 8, 2005

### dlgoff

Look at the the node equation for the currents entering the (-) terminal.

i.e. (Vin-0)/10k + (Vout-0)/100k = 0
so Vout = -(100k/10k)Vin
note that the gain is 100/10=10 and the output is inverted from the input.

edit:changed sign

5. Nov 8, 2005

### Staff: Mentor

Nope. Vab would not be 0.1V. Look for the concept of the "virtual ground" node in your opamp text, and think about what the large open loop gain of the opamp does for you when you close the loop in the inverting (gain = -10X as shown) configuration.

And yes, you can make a gain of -0.1X if you want with this configuration and a different resistor ratio.