“IMD3”的意思、由来-开放百科全书

词条

IMD3

释义

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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 and one at . When you cube the sum of these sine waves you will get sine waves at various frequencies including and . If and are large but very close together then and will be very close to and .

In the animation above, the 3rd order intermodulation products (D3 and D4) are the result of nonlinear behavior of an amplifier. The input power level into the amplifier is increased by 1 dB in each successive frame. The output power of the two carriers (M1 and M2) increases by about 1 dB in each frame, while the 3rd order intermodulation products (D3 and D4) grow by 3 dB in each frame. Higher-order intermodulation products (5th order, 7th order, 9th order) are visible at very high input power levels as the amplifier is driven past saturation. Near saturation, each additional dB of input power results in proportionally less output power going into the amplified carriers and proportionally more output power going into the unwanted intermodulation products. At and above saturation, additional input power results in a decrease in output power, with most of that additional input power getting dissipated as heat and increasing the level of the non-linear intermodulation products with respect to the two carriers.

2 : Electrical circuits|Frequency mixers

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