Intermodulation distortion product

TSH350

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Intermodulation distortion product

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

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:

then:

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 (

●

third order intermodulation terms IM3 by the frequencies (2

and (

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

summing amplifier configuration (see Figure 33). In this way, the non-linearity problem of an

external mixing device is avoided.

Figure 33.

Inverting summing amplifier (using evaluation board SO8_S_MULTI)

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

++

+

=

+

_

R

R

fb

100

V

out

V

in2

V

in1

+

_

R

R

fb

100

V

out

V

in2

V

in1