Data Sheet

AD8398A

Rev. E | Page 9 of 12

MULTITONE POWER RATIO

The discrete multitone (DMT) signal used in xDSL systems

carries data in discrete tones or bins that appear in the frequency

domain in evenly spaced 4.3125 kHz intervals. In applications

using this type of waveform, multitone power ratio (MTPR) is

a commonly used measure of linearity. Generally, designers are

concerned with two types of MTPR: in band and out of band.

In-band MTPR is defined as the measured difference from the

peak of one tone that is loaded with data to the peak of an adjacent

tone that is intentionally left empty. Out-of-band MTPR is defined

as the spurious emissions that occur in the receive bands. Transmit

band power and receive band MTPR are shown in Figure 13,

Figure 14, and Figure 15 for Profile 17a, Profile 8b, and ADSL2+,

respectively.

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

FREQUENCY (MHz)

04

28

612

10

16

14

20

18

Figure 13. MTPR of a Typical VDSL2 Profile 17a DMT Test Signal,

–120

–110

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

01

23

45

67

89

10

FREQUENCY (MHz)

Figure 14. MTPR of a Typical VDSL2 Profile 8b DMT Test Signal,

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0

FREQUENCY (MHz)

0

0.5

1.0

1.5

2.0

2.5

3.0

Figure 15. MTPR of a Typical ADSL2+ DMT Test Signal,

LIGHTNING AND AC POWER FAULT

DSL line drivers are transformer-coupled to the twisted pair

telephone line. In this environment, the AD8398A may be

subject to large line transients resulting from events such as

lightning strikes or downed power lines. Additional circuitry

is required to protect the AD8398A from possible damage due

to these events.