TSH310

Intermodulation Distortion Product

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6 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 form a single

sine wave: second-order intermodulation terms IM2 by the frequencies (

The measurement of the intermodulation product of the driver is achieved by using the driver as a mixer

by a summing amplifier configuration (see Figure 29). In this way, the non-linearity problem of an external

mixing device is avoided.

Figure 29: Inverting summing amplifier (using evaluation board SO8_S_MULTI)

Vout

C

0

C

1

V

in

C

2

V

2

in

…C

n

V

n

in

++

+

=

V

in

A

ω

1

t

sin

A

ω

2

t

sin

+

=

V

out

C

0

C

1

A

ω

1

t

sin

A

ω

2

t

sin

+

() C

2

A

ω

1

t

sin

A

ω

2

t

sin

+

()

n

A

ω

1

t

sin

A

ω

2

t

sin

+

()

n

++

+

=

+

_

R

1k

Ω

+

_

R

1k

Ω