A typical instrumentation amplifier has two stages. The first stage amplifies the differential signal while the second stage removes the common mode voltage. Because this architecture amplifies the differential signal as soon as possible, errors introduced in later stages have little effect. This is great for performance. However, this means that internal nodes have a combination of both amplified differential voltage as well as common mode voltage causing signals on the internal nodes that can be larger than signals on either the inputs or the output. If the signals on these internal nodes are too large, the internal nodes can rail and make it appear as if the instrumentation amplifier has lost gain.