Datasheet

Data Sheet AD9119/AD9129
Rev. A | Page 53 of 68
For applications that operate the AD9119/AD9129 in Mix-Mode
with output frequencies extending beyond 2.2 GHz, the user may
want to consider the circuit shown in Figure 154. This circuit
uses a wideband balun (for example, −3 dB at 4.0 GHz), with a
configuration that is similar to the example shown in Figure 152,
to provide a dc bias path for the DAC outputs. This circuit was
implemented on an evaluation board, and the frequency response
was measured to compare it with the ideal curve in Figure 146.
The result is shown in Figure 155.
50Ω
50Ω
L
L
MINI-CIRCUITS
TCI-1-13M+
TCI-1-33M+
IOUTP
IOUTN
C
C
VDDA
11149-158
Figure 154. Recommended Mix-Mode Configuration Offering Extended RF
Bandwidth Using TC1-1-13M+ Balun
–36
–33
–30
–27
–24
–21
–18
–15
–12
–9
–6
–3
0
3
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
POWER (dBc)
FREQUENCY (MHz)
NORMAL MODE
MIX-MODE
MEASURED NORMAL
MEASURED MIX-MODE
11149-257
Figure 155. Measured vs. Ideal DAC Output Response; f
DAC
= 2.6 GSPS
To assist in matching the AD9119/AD9129 output, a Smith chart
is provided in Figure 156. The plot was taken using the circuit
in Figure 154, with the balun and the coupling capacitors
removed, and L = 270 nH. For the measured vs. ideal response of
the DAC output, see Figure 155, which illustrates that a nonideal
response occurs in the second half of the second Nyquist zone.
This area corresponds to the low impedance area between 2 GHz
and 3 GHz, as shown in the Smith chart in Figure 156. Output
matching can be used to compensate for this nonideal response;
the possible reduction in signal bandwidth must be considered if
such matching is used.
1. 300kHz 3.1341Ω 710.55mΩ 376.96nH
2. 1GHz 54.333Ω –44.210Ω 3.5999pF
3. 2GHz 13.113Ω –11.207Ω 7.1006pH
4. 3GHz 13.022Ω –14.259Ω 756.48pF
1
2
3
4
11149-256
Figure 156. Measured Smith Chart Showing the DAC Output Impedance;
f
DAC
= 2.6 GSPS