current to voltage converter that does not invert the output voltage

[zamundito]

Hi everybody,

I would like to ask if anyone knows how to build a current to voltage converter with only one OPAM like the one in the pic but with non inverted output voltage

https://upload.wikimedia.org/wikipedia/en/e/e3/Classic_300.jpg

Thank you

 

[schmitt trigger]

I'm assuming is that your request is with a single device, as opposed to a single IC package. Because you can get a dual opamp package in the same footprint (8 pins) as a single opamp.

But let's assume you want a single device, then you would have to perform the following steps:

The simplest current to voltage converter is.......a resistor.
But, a resistor is not a precision converter, as its voltage drop will increase with increasing current. Depending of the current source, this increasing voltage may introduce significant measurement errors.

Having said that...if you make the resistor low enough, such that even at its highest current the voltage drop is still very low, you can always put a high gain non-inverting amp following it, to amplify that small voltage drop to your requirements.

It still won't be a precision converter, but it can be close enough.

An example;
Let's say you want to convert a 0 to 1 mA current into a 0 to 5 V out. Non-inverting.
Then.... you apply that current thru a 10 ohm resistor, and you'll end up with a voltage of 0 to 10 mV.
To increase that to 0 to 5 V, you need to amplify it with a non-inverting stage with a gain of 500.

Needless to say, this circuit would require an ultra-low offset opamp...chopper stabilized, most likely.

 

[crutschow]

What is the source of the current?

 

[zamundito]

Thank you for the answers. I am thinking first in an ideal case with a single device. I would have an ideal current source and I wonder if I could make a circuit using only one OPAMP and resistors to have a current-to-voltage converter with non inverting output voltage. Maybe based in a non-inverting OPAMP amplifier configuration instead of the one in the pic that is based in a non-inverting config.

The solution with the resistor + non-inverting stage is the only one possible?

thanks!

 

[crutschow]

If you want an ideal current-to-voltage converter than you need negative feedback, and to get negative feedback the output signal has to be inverted from the input. Don't see anyway around that. :wink:

 

[schmitt trigger]

As Crutschow mentions, there is no way around.

Books on opamp theory explain precisely why is that the case.