Electronics: Notes on Op-amps - 1

Single versus dual supply: An Opamp can be powered by a single supply or a dual supply. Dual supply is the natural selection. However, when designing portable devices usually we have to use a single supply (a battery) which gives for example a 10V (Vcc). The important problem is that the output should be bias to swing around half the supply rails, which here is Vcc/2. That is if we have a 10V supply, the input should be biased so that the ouput swings with a DC of 5V and the maximum swing would be [10-Vx, 0+Vx] where Vx (called headroom) is usually 1.5 to 3V.

A work-around for creating negative voltage in the circuit with a single supply is to create "phantom ground" (reference)

Great Readings:
Single-Supply AC Inverting Opamp
Stability of single supply opamp:

Instrumentation op-amp applications: In sensors like medical applications, the input is sort of different. In normal application one of the - or + are actually the ground (or the phantom ground). While in the sensing applications, we are amplifying the sensed voltage which is differential and non or the - or + are actually the ground. In these ones, to find the actual output (in regards to the ground) we have to know what is a value of Vin + or Vin-. For example see the formula at figure 2 of this analog devices document. Or a better circuit is the two-amplifier approach of figure 3 of the same reference (read on for even better and more complex circuits).