An example is probably the best way to illustrate this. The AD8231 is shown, which uses internal op amps that have rail to rail inputs and rail to rail outputs. n this example, the AD8231 is configured with a gain of four and driven with a 1V differential voltage. This 1V differential input multiplied by a gain of four should result in 4V at the output. In order to illustrate the effect of common mode voltage near the rails, this example has used a common mode voltage of 4V. This results in a positive input voltage of 4.5V – pretty near the rail. However, the inputs and outputs are still well within the range of the AD8231’s internal rail to rail op amps.