AD9739 Analog Devices, AD9739 Datasheet - Page 42

• 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

AD9739
Output Stage Configuration
The
that require wide signal reconstruction bandwidth (that is,
DOCSIS CMTS) and/or high IF/RF signal generation. Optimum ac
performance can only be realized if the DAC output is configured
for differential (that is, balanced) operation with its output
common-mode voltage biased to analog ground. The output
network used to interface to the DAC should provide a near 0 Ω
dc bias path to analog ground. Any imbalance in the output
impedance between the IOUTP and IOUTN pins results in
asymmetrical signal swings that degrade the distortion
performance (mostly even order) and noise performance.
Component selection and layout are critical in realizing the
performance potential of the AD9739.
Most applications requiring balanced-to-unbalanced conversion can
take advantage of the Ruthroff 1:1 balun configuration shown in
Figure 66. This configuration provides excellent amplitude/phase
balance over a wide frequency range while providing a 0 Ω dc bias
path to each DAC output. Also, its design provides exceptional
bandwidth and can be considered for applications requiring
signal reconstruction of up to 2.2 GHz. The characterization plots
shown in this data sheet are based on the
board, which uses this configuration. Figure 67 compares the
measured frequency response for normal and mix mode using
the
and Mix Mode Operation Using a TC1-33-75G Transformer on the
Figure 67. Measured vs. Ideal Frequency Response for Normal (Baseband)
Figure 66. Recommended Balun for Wideband Applications with Upper
AD9739
AD9739
–12
–15
–18
–21
–24
–27
–30
–33
–36
–3
–6
–9
0
IOUTN
IOUTP
0
BASEBAND
TC1-33-75G
70Ω
evaluation board vs. the ideal frequency response.
is intended to serve high dynamic range applications
500
IDEAL MIX MODE
Bandwidths of up to 2.2 GHz
1000
90Ω
90Ω
Evaluation Board
IDEAL BASEBAND MODE
FREQUENCY (MHz)
1500
2000
MINI-CIRCUITS
2500
TC1-33-75G+
TC1-33-75G
MIX MODE
AD9739
3000
®
evaluation
3500
AD9739
Rev. B | Page 42 of 48
Figure 68 shows an interface that can be considered when
interfacing the DAC output to a self-biased differential gain
block. The inductors shown serve as RF chokes (L) that provide
the dc bias path to analog ground. The value of the inductor,
along with the dc blocking capacitors (C), determines the lower
cutoff frequency of the composite pass-band response. An RF
balun should also be considered before the RF differential gain
stage and any filtering to ensure symmetrical common-mode
impedance seen by the DAC output while suppressing any
common-mode noise, harmonics, and clock spurs prior to
amplification.
For applications operating the
frequencies extending beyond 2.2 GHz, the circuits shown in
Figure 69 should be considered. The circuit in Figure 69 uses a
wideband balun with a configuration similar to the one shown
in Figure 68 to provide a dc bias path for the DAC outputs. The
circuit in Figure 70 takes advantage of ceramic chip baluns to
provide a dc bias path for the DAC outputs while providing
excellent amplitude/phase balance over a narrower RF band.
These low cost, low insertion loss baluns are available for
different popular RF bands and provide excellent amplitude/
phase balance over their specified frequency range.
Figure 70. Lowest Cost and Size Configuration for Narrow RF Band Operation
Figure 68. Interfacing the DAC Output to the Self-Biased Differential Gain Stage
Figure 69. Recommended Mix Mode Configuration Offering Extended RF
IOUTN
IOUTP
IOUTN
IOUTP
IOUTP
IOUTN
70Ω
70Ω
70Ω
Bandwidth Using a TC1-1-43A+ Balun
90Ω
90Ω
90Ω
90Ω
180Ω
L
L
L
L
JOHANSON TECHNOLOGY
OPTIONAL BALUN AND FILTER
AD9739
C
C
CHIP BALUNS
MURATA
MINI-CIRCUITS
TC1-1-462M
in mix mode with output
LPF
Data Sheet
C
C
RF DIFF
AMP