Data Sheet
AD9737A/AD9739A
Rev. | Page 59 of 64
OUTPUT STAGE CONFIGURATION
range applications that require wide signal reconstruction
bandwidth (that is, DOCSIS CMTS) and/or high IF/RF signal
generation. Optimum ac performance can be realized only 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
MINI-CIRCUITS
TC1-33-75G+
90
IOUTP
IOUTN
70
09616-
100
Figure 181. Recommended Balun for Wideband Applications with Upper
Bandwidths of up to 2.2 GHz
Most applications requiring balanced-to-unbalanced conversion
can take advantage of the Ruthroff 1:1 balun configuration
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
evaluation board vs. the ideal frequency response.
–36
–33
–30
–27
–24
–21
–18
–15
P
O
W
E
R
(
d
Bc)
–12
–9
–6
–3
0
500
1000
1500
2000
2500
3000
3500
FREQUENCY (MHz)
IDEAL BASEBAND MODE
MIX MODE
TC1-33-75G
BASEBAND
TC1-33-75G
IDEAL MIX MODE
09616-
101
Figure 182. Measured vs. Ideal Frequency Response for Normal (Baseband)
and Mix-Mode Operation Using a TC1-33-75G Transformer on
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.
90
IOUTP
IOUTN
70
L
RF DIFF
AMP
C
OPTIONAL BALUN AND FILTER
90
LPF
09616-
102
Figure 183. Interfacing the DAC Output to the Self-Biased Differential
Gain Stage
with output frequencies extending beyond 2.2 GHz, the circuits
shown in
Figure 184 should be considered. The circuit in
Figure 184 uses a wideband balun with a configuration similar
to the one shown in
Figure 183 to provide a dc bias path for the
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.
C
MINI-CIRCUITS
TC1-1-462M
90
IOUTP
IOUTN
70
L
90
09616-
103
Figure 184. Recommended Mix-Mode Configuration Offering Extended RF
Bandwidth Using a TC1-1-43A+ Balun
MURATA
JOHANSON TECHNOLOGY
CHIP BALUNS
180
IOUTP
IOUTN
70
09616-
104
Figure 185. Lowest Cost and Size Configuration for Narrow RF Band
Operation
C