Datasheet

Data Sheet AD8016
Rev. C | Page 17 of 20
Once an optimum turns ratio is determined, the amplifier has
an MTPR performance for each setting of the power-down
pins. Table 8 demonstrates the effects of reducing the total
power dissipated by using the PWDN pins on MTPR perfor-
mance when driving 20.4 dBm downstream onto the line with
a transformer turns ratio of 1:1.4.
Table 8. Dynamic Power Dissipation of Downstream
Transmission
PWDN1 PWDN0 PD (W) MTPR
1 1 1.454 −78 dBc
1 0 1.262 −75.3 dBc
0 1 1.142 −57.2 dBc
0
1
0
0.120
N/A
1
This mode is quiescent power dissipation.
GENERATING DMT
At this time, DMT modulated waveforms are not typically
menu selectable items contained within arbitrary waveform
generators. Even using AWG software to generate DMT signals,
AWGs that are available today may not deliver DMT signals
sufficient in performance with regard to MTPR due to limita-
tions in the DAC and output drivers used by AWG manufacturers.
Similar to evaluating single-tone distortion performance of an
amplifier, MTPR evaluation requires a DMT signal generator
capable of delivering MTPR performance better than that of
the driver under evaluation.
POWER DISSIPATION
To properly size the heat sinking area for the user’s application,
it is important to consider the total power dissipation of the
AD8016. The dc power dissipation for V
IN
= 0 V is I
Q
(V
CC
−
V
EE
), or 2 × I
Q
× V
S
.
For the AD8016 powered on +12 V and −12 V supplies (±V
S
),
the number is 0.6 W. In a differential driver circuit (Figure 41),
one can use symmetry to simplify the computation for a dc
input signal.
L
OUT
OUT
SSQ
D
R
V
VVVIP )(42 −×+××=
where:
V
OUT
is the peak output voltage of an amplifier.
This formula is slightly pessimistic due to the fact that some of
the quiescent supply current is commutated during sourcing or
sinking current into the load. For a sine wave source, integra-
tion over a half cycle yields








−+××=
L
OUT
L
S
OUT
SQ
D
R
V
R
VV
VIP
2
4
22
π
The situation is more complicated with a complex modulated
signal. In the case of a DMT signal, taking the equivalent sine
wave power overestimates the power dissipation by ~23%. For
example:
P
OUT
= 23.4 dBm = 220 mW
V
OUT
@ 50 Ω = 3.31 V rms
V
OUT
= 2.354 V
at each amplifier output, which yields a P
D
of 1.81 W.
Through measurement, a DMT signal of 23.4 dBm requires
1.47 W of power to be dissipated by the AD8016. Figure 46
shows the results of calculation and actual measurements
detailing the relationship between the power dissipated by
the AD8016 vs. the total output power delivered to the back
termination resistors and the load combined. A 1:2 transformer
turns ratio was used in the calculations and measurements.
Figure 46. Power Dissipation vs. Output Power (Including Back
Terminations), See Figure 9 for Test Circuit
OUTPUT POWER (mW)
2.5
0
POWER DISSIPATION
2.0
1.5
100 200 300
1.0
0.5
0
MEASURED
SINE
MEASURED
DMT
CALCULATED
01019-046