AD8398A
Rev. D | 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
07760-010
FREQUENCY (MHz)
OUTPUT POWER (dB)
042861210 1614 2018
Figure 13. MTPR of a Typical VDSL2 Profile 17a DMT Test Signal,
V
S
= ±6 V, Output Power = 14.5 dBm
07760-020
–120
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
012345678910
OUTPUT POWER (dBm/Hz)
FREQUENCY (MHz)
Figure 14. MTPR of a Typical VDSL2 Profile 8b DMT Test Signal,
V
S
= ±6 V, Output Power = 20.4 dBm
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
07760-012
FREQUENCY (MHz)
OUTPUT POWER (dB)
0 0.5 1.0 1.5 2.0 2.5 3.0
Figure 15. MTPR of a Typical ADSL2+ DMT Test Signal,
V
S
= ±6 V, Output Power = 20.4 dBm
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.
