Intermodulation Distortion Product

TS615

17/36

5 Intermodulation Distortion Product

The non-ideal output of the amplifier can be described by the following series, due to a non-linearity in the

input-output amplitude transfer:

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

contributes to a harmonic distortion and an intermodulation product.

This intermodulation product, or rather, the study of the intermodulation distortion of a two-tone input

signal is the first step in characterizing the amplifiers capability for driving multi-tone signals.

The two-tone input is equal to:

giving:

In this expression, we can extract distortion terms and intermodulations terms from a single sine wave:

second-order intermodulation terms IM2 by the frequencies (

(

We can measure the intermodulation product of the driver by using the driver as a mixer via a summing

amplifier configuration. In doing this, the non-linearity problem of an external mixing device is avoided.

Figure 46. Non-inverting summing amplifier

V

out

C

o

C

C

n

++

+

=

V

in

A

ω

1

t

sin

B

ω

2

t

sin

+

=

V

out

C

0

C

1

A

ω

1

t

sin

B

ω

2

t

sin

+

() C

2

A

ω

1

t

sin

B

ω

2

t

sin

+

()

n

A

ω

1

t

sin

B

ω

2

t

sin

+

()

n

++

+

=

Rg1

Rfb1

Vout diff.

11

10

13

+Vcc

100

Ω

50

Ω

49.9

Ω

49.9

Ω

1/2

TS615

-Vcc

√2:1

1/2

TS615

Rfb2

Rg2

33

Ω

33

Ω

1k

Ω

1k

Ω

1k

Ω

1k

Ω

49.9

Ω

49.9

Ω

49.9

Ω

49.9

Ω

50

Ω

400

Ω

1:

√2

50

Ω

400

Ω

1:

√2

Vin1

Vin2

_

+

_

+

North Hills

0315PB

North Hills

0315PB

North Hills

0315PB

Rg1

Rfb1

Vout diff.

11

10

13

+Vcc

100

Ω

50

Ω

49.9

Ω

49.9

Ω

1/2

TS615

-Vcc

√2:1

1/2

TS615

Rfb2

Rg2

33

Ω

33

Ω

1k

Ω

1k

Ω

1k

Ω

1k

Ω

49.9

Ω

49.9

Ω

49.9

Ω

49.9

Ω

50

Ω

400

Ω

1:

√2

50

Ω

400

Ω

1:

√2

Vin1

Vin2

_

+

_

+

North Hills

0315PB

North Hills

0315PB

North Hills

0315PB