Would someone be right in saying that a photodiode produces a current as output and that to be able to make use of this current, you ABSOLUTELY need to convert it into a voltage by using a current to voltage op-amp circuit? I've heard this from someone but to be honest doesn't make much sense to me. I mean if you get a current from the photodiode, surely it means you have a voltage present. In other words, if you have a current, it inherently implies you have a voltage and vice versa. So, I don't understand the need for a 'current to voltage' circuit unless what you want to do is amplify the signal from your photodiode. So if anyone has any understanding of this 'current to voltage' concept, please enlighten me!