adl5373 Analog Devices, Inc., adl5373 Datasheet - Page 15

• Manufacturer Part Number: adl5373
• Description: 2300 Mhz To 3000 Mhz Quadrature Modulator
• Manufacturer: Analog Devices, Inc.

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.
USING THE AD9779 AUXILIARY DAC FOR CARRIER
FEEDTHROUGH NULLING
The
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. This adds four resistors to the
interface.
AD9779
OUT1_N
OUT2_N
OUT1_P
OUT2_P
AD9779
–10
–20
–30
–40
–50
–60
0
Figure 33. Frequency Response for DAC Modulator Interface
1
93
92
84
83
features an auxiliary DAC that can be used to
RBQN
RBQP
RBIP
RBIN
Figure 32. DAC Modulator Interface with
50Ω
50Ω
50Ω
50Ω
with 10 MHz Third-Order Bessel Filter
10 MHz Third-Order Bessel Filter
53.62nF
53.62nF
GROUP DELAY
C1Q
C1I
FREQUENCY (MHz)
771.1nH
771.1nH
771.1nH
771.1nH
350.1pF
350.1pF
LNQ
LPQ
LPI
10
LNI
C2Q
C2I
MAGNITUDE
RSLQ
100Ω
100Ω
RSLI
23
24
19
20
IBBP
IBBN
QBBN
QBBP
F-MOD
100
36
30
24
18
12
6
0
Rev. 0 | Page 15 of 20
WiMAX OPERATION
Figure 35 shows the first and second adjacent 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 2600 MHz.
Figure 35 illustrates that optimal performance is achieved
when the output power from the modulator is −10 dBm or
greater. The noise floor rises with increasing output power,
but at less than half the rate at which ACPR degrades. Thus,
operating at powers greater than −10 dBm can improve the
signal-to-noise ratio.
Figure 35. Adjacent and Alternate Channel Power Ratios and 30 MHz Offset
AD9779
Noise Floor vs. Channel Power for a 10 MHz 1024-OFDMA Waveform at
OUT1_N
AUX1_N
AUX2_N
OUT2_N
AUX1_P
OUT1_P
OUT2_P
AUX2_P
–62
–64
–66
–68
–70
–72
–74
–76
Figure 34. DAC Modulator Interface with Auxiliary DAC Resistors
–21
ALTERNATE CHANNEL
–19
90
500Ω
93
92
500Ω
500Ω
89
500Ω
87
84
83
86
POWER RATIO
RBQN
RBQP
RBIN
RBIP
50Ω
50Ω
50Ω
50Ω
–17
53.62nF
250Ω
250Ω
250Ω
2600 MHz; LO Power = 0 dBm
250Ω
53.62nF
ADJACENT CHANNEL
–15
OUTPUT POWER (dBm)
C1Q
C1I
POWER RATIO
–13
771.1nH
771.1nH
771.1nH
771.1nH
350.1pF
350.1pF
LNQ
LPQ
LPI
LNI
C2Q
C2I
–11
RSLQ
–9
100Ω
100Ω
RSLI
30MHz OFFSET
NOISE FLOOR
–7
23
24
19
20
–5
ADL5373
IBBP
IBBN
QBBN
QBBP
F-MOD
–3
–150
–151
–152
–153
–154
–155
–156
–157