I'm developing two similar circuits that will enable me to differentiate the X and Y coordinates from a segmented photo-diode (Four segments). These coordinates will be dependent upon the position of a laser spot falling onto the surface of the segmented photo-diode. I hope to obtain a value between (0-5V) for X and (0-5V) for Y.
The circuit I based my design upon used a dual supply (+5/-5V). In my application I am using a micro-controller with a 5V rail. The design would also benefit from a single supply if the output was a value between 0 and 5V as it would be compatible with micro-controller's ADC input range. I would therefore like to run the circuit from a single supply and use a rail-to-rail op-amp to to remove the need for extra circuitry.
I've tried a few different simulations where I've attempted to offset the output by 2.5V using a simple voltage divider, but the results are not what I expected.
Can somebody explain to me why the result is this way and what I can do to obtain a 2.5V output when inputs (A, B, C and D) are 0V.