Current to Voltage Converter

Can you provide some details of this circuit? A functional block diagram is a good start and a schematic is even better.

Some questions for you: What are the voltage measurements being used for? What is the range of current that is being measured? How do you know that you are not already measuring the voltage accurately?

What makes you think that adding resistance would increase the measurements???

As you provide more details, we can provide more answers. Otherwise, its a shot in the dark.

the current range being measured is very low form -10pA to 10 pA;

the voltage range is something around -2048 mV to 2048 mV.

hope this may help you a little.

so the schematic below is a potentiostat for an electrochemical array.

Broad question.

• In industrial control loops using 4-20mA signals, a precision resistor of 250Ω wired in series in the loop will give a 1-5V signal of similar accuracy to the resistor accuracy.

Does that help?

You do have a good generic idea here. An ideal current source driving its current into a higher resistance will produce a higher voltage. However, there are many hidden assumptions and complications in that statement that people forget.

First, there will always be a limit to how high of a resistance one can place in a circuit for multiple reasons. One of these reasons is that parasitic resistances of insulators and capacitor leakage can easily become alternate paths for your current that you are trying to measure. Next, the input impedance and biasing currents of your measuring instrument can induce significant errors when resistance values get too high. Let's not forget that your current source will not be ideal, too. Your current source must operate in a region to be linear while also itself having some finite output impedance. Then there's the aspect that baffles many novices, thermal noise. The noise produced by heat can produce a larger error component with large resistors trying to measure tiny currents.