ADL5372 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADL5372' PDF : 24 Pages View PDF
Data Sheet
An example is shown in Figure 32 with a third-order, elliptical,
low-pass filter with a 3 dB frequency of 3 MHz. Matching input
and output impedances makes the filter design easier, so the
shunt resistor chosen is 100 Ω, producing an ac swing of
1 V p-p differential.
AD9779
OUT1_P
OUT1_N
93
RBIP
50Ω
RBIN
92 50Ω
1.1nF
C1I
LPI
2.7nH
1.1nF
C2I
LNI
2.7nH
RSLI
100Ω
F-MOD
19
IBBP
20
IBBN
OUT2_N
OUT2_P
84
RBQN
50Ω
RBQP
83 50Ω
1.1nF
C1Q
LNQ
2.7nH
1.1nF
C2Q
LPQ
2.7nH
RSLQ
100Ω
23 QBBN
24 QBBP
Figure 32. DAC Modulator Interface with 3 MHz Third-Order, Elliptical
Low-Pass Filter
USING THE AD9779 AUXILIARY DAC FOR CARRIER
FEEDTHROUGH NULLING
The AD9779 features an auxiliary DAC that can be used to
inject small currents into the differential outputs for each main
DAC channel. This feature can be used to produce the small
offset voltages necessary to null out the carrier feedthrough
from the modulator. Figure 33 shows the interface required
to use the auxiliary DACs. This adds four resistors to the
interface.
AUX1_P
AD9779
OUT1_P
OUT1_N
AUX1_N
AUX2_N
OUT2_N
OUT2_P
AUX2_P
90
500Ω
93
RBIP
50Ω
RBIN
92 50Ω
89
500Ω
87
500Ω
84
RBQN
50Ω
RBQP
83 50Ω
86
500Ω
250Ω
1.1nF
C1I
250Ω
250Ω
1.1nF
C1Q
250Ω
LPI
2.7nH
1.1nF
C2I
LNI
2.7nH
LNQ
2.7nH
1.1nF
C2Q
LPQ
2.7nH
RSLI
100Ω
F-MOD
19
IBBP
20
IBBN
RSLQ
100Ω
23 QBBN
24
QBBP
Figure 33. DAC Modulator Interface with Auxiliary DAC Resistors
ADL5372
GSM OPERATION
Figure 34 shows the GSM EVM, spectral mask, and noise vs. the
output power for the ADL5372 at 1960 MHz. For a given LO
amplitude, the performance is independent of output power.
4.0
–30
250kHz
3.5
–40
3.0
–50
2.5
PEAK EVM
–60
2.0
400kHz
–70
1.5
600kHz
–80
1.0
1.2MHz
–90
RMS EVM
0.5
6 MHz NOISE FLOOR
–100
0
–6
–4
–2
0
2
4
OUTPUT POWER (dBm)
–110
6
Figure 34. GSM EVM and Spectral Performance vs. Channel Power at
1960 MHz vs. Output Power; LO Power = 0 dBm
Figure 35 shows the GSM EVM and noise performance vs. the
LO amplitude at 1960 MHz with an output power of 5 dBm.
Increasing the LO drive level improves the noise performance
but degrades EVM performance.
4.0
–80
3.5
–85
3.0
PEAK EVM
–90
2.5
–95
2.0
1.5
RMS EVM
1.0
6MHz NOISE FLOOR
–100
–105
–110
0.5
–115
0
–120
–6
–4
–2
0
2
4
6
LO DRIVE (dBm)
Figure 35. GSM EVM and 6 MHz Noise Floor vs. LO Power at 1960 MHz;
Output Power = 5 dBm
Figure 35 illustrates that an LO amplitude of 3 dBm provides
the ideal operating point for noise and EVM for a GSM signal
at 1960 MHz.
Rev. A | Page 15 of 24
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