How can one anticipate a problem? Most modern datasheets have a plot that shows the allowed common mode voltage versus output voltage. In this slide one of the plots from the AD8231 datasheet is used. The red ‘X’ on the plot illustrates the operation point desired from the previous example. Unfortunately this is outside the allowable region of operation. In order for the IC to operate correctly, it has to be inside the triable. This plot illustrates a few different points. One is that the allowed area varies dramatically with supply voltage. Notice the triangle for a 3V supply voltage is considerably smaller than tat for the 5V voltage. This explains why changing the power supply can be one solution to this problem. Another thing to notice is lowering gain and therefor lowing the desired output voltage, would help out. This explains why changing the gain also works. Typically the engineer would like to take as much gain as possible – since this helps noise, common mode rejection ratio, offset, etc. So the gain is a tradeoff.