AD9739 Analog Devices, AD9739 Datasheet - Page 41

• Manufacturer Part Number: AD9739
• Description: 14-Bit, 2500 MSPS, RF Digital-to-Analog Converter
• Manufacturer: Analog Devices

Specifications of AD9739

• Resolution (bits): 14bit
• Dac Update Rate: 2.5GSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: LVDS,Par

Data Sheet
Figure 64 shows the IOUTP vs. DACCODE transfer function
when I
Peak DAC Output Power Capability
The maximum peak power capability of a differential current
output DAC is dependent on its peak differential ac current, I
and the equivalent load resistance it sees. Because the
includes a differential 70 Ω resistance, it is best to use a doubly
terminated external output network similar to what is shown in
Figure 65. In this case, the equivalent load seen by the ac current
source of the DAC is 25 Ω.
20
18
16
14
12
10
Figure 64. Gain Curve for FSC[9:0] = 512, DAC Offset = 1.228 mA
8
6
4
2
0
OUTFS
0
is set to 19.65 mA.
4096
DAC CODE
8192
15/32 × I
Figure 65. Equivalent Circuit for Determining Maximum Peak Power to a 50 Ω Load
I
PEAK
OUTFS
I
OUTFS
=
12,288
= 8.6 – 31.2mA
AC
AD9739
16,384
70Ω
PEAK
Rev. B | Page 41 of 48
,
180Ω
If the
current is 9.375 mA and its peak power delivered to the equivalent
load is 2.2 mW (that is, P = I
resistance seen by the 1:1 balun are equal, this power is shared
equally; therefore, the output load receives 1.1 mW or 0.4 dBm.
To calculate the rms power delivered to the load, the following
must be considered:
•
•
•
For example, a reconstructed sine wave with no digital backoff
ideally measures −2.6 dBm because it has a peak-to-rms ratio of
3 dB. If a typical balun loss of 0.4 dBm is included, −3 dBm of
actual power can be expected in the region where the sinc response
of the DAC has negligible influence. Increasing the output power is
best accomplished by increasing I
linearity performance must be considered acceptable for the
target application.
R
SOURCE
= 50Ω
Peak-to-rms of the digital waveform
Any digital backoff from digital full scale
The DAC’s sinc response and nonideal losses in external
network
AD9739
LOSSLESS
BALUN
1:1
is programmed for I
R
= 50Ω
LOAD
2
R). Because the source and load
OUTFS
OUTFS
, although any degradation in
= 20 mA, its peak ac
AD9739