Mathematically, IP3 is the theoretical input power at the intersection of the fundamental wave and the third-order distortion output curve. Line A is the curve of output power of fundamental (useful) signal changing with input power, and line B is the curve of output power of third-order distortion changing with input power. The slope of line B is three times that of line A (in dB), and it theoretically intersects with line A. This intersection point is the third-order intercept point. At this time, it is assumed that the input power is input IP3 and the output power is output IP3.