RHF310

Intermodulation distortion product

Doc ID 15577 Rev 3

15/22

5

Intermodulation distortion product

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

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 (

ω

●

Third-order intermodulation terms IM3 by the frequencies (2

ω

ω

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.

V

out

C

0

C

C

2

in

… C

+

n

in

++

+

=

V

in

A

ω

sin

A

ω

sin

+

=

V

out

C

0

C

ω

sin

A

ω

sin

+

() C

ω

sin

A

ω

sin

+

()

ω

sin

A

ω

sin

+

()

n

++

+

=