/diy/ - Do It Yourself

>>1490017
an instrumentation amp is a block that's designed to reckon the difference between two voltages and multiply them by some relatively low gain factor, all with respect to some given zero point
an op amp is just a high-gain differential amplifier that multiplies the difference between its inputs by a very high but imprecise gain factor
a plain op amp with a low input bias current and a common-mode range slightly below 0V is good enough for a photodiode detector. an LM358A might do in a pinch, with a typical input bias current of -15nA (but max of -100nA), which may be adequate for your application if you don't need much dynamic range