AD9739A Analog Devices, AD9739A Datasheet - Page 58

• Manufacturer Part Number: AD9739A
• Description: 14-Bit, 2.5 GSPS, RF D/A Converter
• Manufacturer: Analog Devices

Specifications of AD9739A

• Resolution (bits): 14bit
• Dac Update Rate: 2.5GSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): n/a
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: LVDS,Par

AD9737A/AD9739A
The code-dependent current measured at the IOUTP and
IOUTN outputs is as follows:
Figure 179 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 AD9737A/
AD9739A
a doubly terminated external output network similar to what is
shown in Figure 181. In this case, the equivalent load seen by
the ac current source of the DAC is 25 Ω.
Figure 179. Gain Curve for FSC[9:0] = 512, DAC OFFSET = 1.228 mA
IOUTP = 17/32 × I
IOUTN = 17/32 × I
20
18
16
14
12
10
8
6
4
2
0
OUTFS
0
include a differential 70 Ω resistance, it is best to use
is set to 19.65 mA.
4096
OUTFS
OUTFS
DAC CODE
+ 15/32 × I
− 15/32 × I
8192
15/32 × I
I
PEAK
OUTFS
OUTFS
I
Figure 180. Equivalent Circuit for Determining Maximum Peak Power
OUTFS
OUTFS
12,288
=
× F(Code)
× F(Code)
= 8.6 – 31.2mA
AC
16,384
70Ω
PEAK
Rev. | Page 58 of 64
(4)
(5)
,
to a 50 Ω Load
C
180Ω
If the
the peak ac current is 9.375 mA and the peak power delivered to
the equivalent load is 2.2 mW (that is, P = I
and load 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
degradation in 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
AD9737A/AD9739A
LOSSLESS
BALUN
1:1
R
= 50Ω
LOAD
are programmed for I
2
R). Because the source
OUTFS
Data Sheet
, although any
OUTFS
= 20 mA,