ADL5370-EVALZ Просмотр технического описания (PDF) - Analog Devices
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ADL5370-EVALZ Datasheet PDF : 20 Pages
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ADL5370
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
ADL5370
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 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 utilize the auxiliary DACs. This adds four resistors to the
interface.
AUX1_P
AD9779
90
500Ω
250Ω
OUT1_P
OUT1_N
93
RBIP
50Ω
RBIN
92 50Ω
1.1nF
C1I
AUX1_N
89
500Ω
250Ω
AUX2_N
OUT2_N
OUT2_P
87
500Ω
84
250Ω
RBQN
50Ω
RBQP
83 50Ω
1.1nF
C1Q
AUX2_P
86
500Ω
250Ω
LPI
2.7nH
1.1nF
C2I
LNI
2.7nH
LNQ
2.7nH
1.1nF
C2Q
LPQ
2.7nH
RSLI
100Ω
ADL5370
19
IBBP
20
IBBN
23
QBBN
RSLQ
100Ω
24
QBBP
Figure 33. DAC Modulator Interface with Auxiliary DAC Resistors
GSM OPERATION
Figure 34 shows the GSM EVM and spectral mask performance
vs. output power for the ADL5370 at 450 MHz. For a given LO
amplitude, the performance is independent of output power.
–35
2.0
250kHz
–42
EVMRMS (%)
–49
1.5
–56
EVMPK (%)
–63
1.0
–70
400kHz
–77
0.5
1200kHz
600kHz
–84
–91
0
0
1
2
3
4
5
6
7
OUTPUT POWER (dBm)
Figure 34. GSM EVM and Spectral Performance vs. Channel Power at
450 MHz vs. Output Power; LO Power = 0 dBm
Figure 35 shows the GSM EVM, spectral mask performance
and 6 MHz offset noise vs. LO amplitude at 450 MHz with an
output power of 6 dBm. Increasing the LO drive level improves
the noise performance but degrades EVM performance.
–35
3.1
–42
–49
250kHz
2.9
EVMPK (%)
2.7
–56
2.5
–63
2.3
400kHz
–70
2.1
–77
600kHz
1.9
–84
1.7
–91
1.5
–98
EVMRMS (%)
1200kHz
1.3
–105
1.1
–112 6 MHz OFFSET NOISE
0.9
–6
–4
–2
0
2
4
6
LO AMPLITUDE (dBm)
Figure 35. GSM EVM, Spectral Performance, and 6 MHz Noise Floor vs.
LO Power at 450 MHz; Output Power = 6 dBm
Figure 35 illustrates that an LO amplitude of 0 dBm provides
the ideal operating point for noise and EVM for a GSM signal
at 450 MHz.
Rev. 0 | Page 14 of 20
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