Thinking In Terms of Current– Photodiode Circuit Example

From the last post (http://electroniccircuitdesignsharing.blogspot.com/2013/03/thinking-in-terms-of-current.html) that talk about the importance of being able to think in term of current, now let’s look at particular example of circuit that basically manipulate current to get the desired result.

Shown below is a circuit that convert infrared light level into a voltage. Now, the photodiode convert infrared light density into current. This circuit is to provide a 0V bias across the diode (operate the diode in Photovoltaic mode) and convert the current into a low impedance voltage level for further operation.


In this circuit, the diode being used in Photovoltaic mode, and details about the diode operation can be found from http://en.wikipedia.org/wiki/Photodiode as shown below:


This is just one of many examples of the advantage being to think comfortably in term of current. Try to make sense of this circuit only thinking in voltage term will be a nightmare, since the inverting input of the op-amp supposed to be a “virtual ground”, and 0V across the diode does not make much sense.