ADL5374ACPZ-WP 데이터 시트보기 (PDF) - Analog Devices
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ADL5374ACPZ-WP Datasheet PDF : 20 Pages
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An example is shown in Figure 32 with a third-order, Bessel
low-pass filter with a 3 dB frequency of 10 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. The frequency response of this filter is
shown in Figure 33.
AD9779
OUT1_P
OUT1_N
93
RBIP
50Ω
RBIN
92 50Ω
53.62nF
C1I
LPI
771.1nH
350.1pF
C2I
LNI
771.1nH
RSLI
100Ω
F-MOD
19
IBBP
20
IBBN
OUT2_N
OUT2_P
LNQ
84
771.1nH
23
RBQN
50Ω 53.62nF
RBQP
C1Q
350.1pF
C2Q
RSLQ
100Ω
83 50Ω
24
LPQ
771.1nH
Figure 32. DAC Modulator Interface with
10 MHz Third-Order, Bessel Filter
QBBN
QBBP
0
36
MAGNITUDE
–10
30
–20
24
GROUP DELAY
–30
18
–40
12
–50
6
–60
1
0
10
100
FREQUENCY (MHz)
Figure 33. Frequency Response for DAC Modulator Interface with
10 MHz Third-Order Bessel 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 34 shows the interface required to
use the auxiliary DACs, which adds four resistors to the interface.
ADL5374
AUX1_P
AD9779
90
500Ω
250Ω
OUT1_P
OUT1_N
93
RBIP
50Ω
RBIN
92 50Ω
53.62nF
C1I
AUX1_N
89
500Ω
250Ω
AUX2_N
OUT2_N
OUT2_P
87
500Ω
84
RBQN
50Ω
RBQP
83 50Ω
250Ω
53.62nF
C1Q
AUX2_P
86
500Ω
250Ω
LPI
771.1nH
350.1pF
C2I
LNI
771.1nH
LNQ
771.1nH
350.1pF
C2Q
LPQ
771.1nH
RSLI
100Ω
F-MOD
19
IBBP
20
IBBN
23
QBBN
RSLQ
100Ω
24
QBBP
Figure 34. DAC Modulator Interface with Auxiliary DAC Resistors
WiMAX OPERATION
Figure 35 shows the adjacent and alternate channel power ratios
(10 MHz offset and 20 MHz offset), and the 30 MHz offset
noise floor vs. output power for a 10 MHz 1024-OFDMA
waveform at 3500 MHz.
–62
–150
–64
–66
ADJACENT CHANNEL
POWER RATIO
–68
–70
–72
ALTERNATE CHANNEL
POWER RATIO
–74
30MHz OFFSET
NOISE FLOOR
–151
–152
–153
–154
–155
–156
–76
–157
–78
–22 –20 –18 –16 –14 –12 –10 –8
–158
–6
OUTPUT POWER (dBm)
Figure 35. Adjacent and Alternate Channel Power Ratios and
30 MHz Offset Noise Floor vs. Channel Power for a
10 MHz 1024-OFDMA Waveform at 3500 MHz; LO Power = 0 dBm
Figure 35 illustrates that optimal performance is achieved when
the output power from the modulator is −12 dBm or more. The
noise floor rises with increasing output power, but at less than half
the rate at which ACPR degrades. Therefore, operating at powers
greater than −12 dBm can improve the signal-to-noise ratio.
Rev. 0 | Page 15 of 20
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