IMD3

IMD3 refers to the intermodulation distortion from the third order of a circuit. It is of particular importance in narrow band signals because its distortion is often in the signal band. This can be seen by looking at a signal that is made up of two sine waves, one at f 1 and one at f 2 . When you cube the sum of these sine waves you will get sine waves at various frequencies including 2 × f 2 − f 1 and 2 × f 1 − f 2 . If f 1 and f 2 are large but very close together then 2 × f 2 − f 1 and 2 × f 1 − f 2 will be very close to f 1 and f 2 .