RHF310 datasheet(15/22 Pages) STMICROELECTRONICS

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RHF310

Intermodulation distortion product

Doc ID 15577 Rev 3

15/22

Intermodulation distortion product

The non-ideal output of the amplifier can be described by the following series of equations.

where the input is Vin = Asinωt, C0 is the DC component, C1(Vin) is the fundamental and Cn

is the amplitude of the harmonics of the output signal Vout.

A one-frequency (one-tone) input signal contributes to harmonic distortion. A two-tone input

signal contributes to harmonic distortion and to the intermodulation product.

The study of the intermodulation and distortion for a two-tone input signal is the first step in

characterizing the driving capability of multi-tone input signals.

In this case:

therefore:

From this expression, we can extract the distortion terms and the intermodulation terms

from a single sine wave.

●

Second-order intermodulation terms IM2 by the frequencies (

1-ω2) and (ω1+ω2) with

an amplitude of C2A2.

●

Third-order intermodulation terms IM3 by the frequencies (2

1-ω2), (2ω1+ω2), (−

1+2ω2) and (ω1+2ω2) with an amplitude of (3/4)C3A

The intermodulation product of the driver is measured by using the driver as a mixer in a

summing amplifier configuration (Figure 25). In this way, the non-linearity problem of an

external mixing device is avoided.

out

1Vin

… C

sin

out

1 A

sin

() C

2 A

sin

()

2… C

n A

sin

()

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