AD8349 Datasheet, PDF (21/28 Pages) Analog Devices – 700 MHz to 2700 MHz Quadrature Modulator

APPLICATIONS
3GPP WCDMA SINGLE-CARRIER APPLICATION
The interpolation filter used for the measurement of WCDMA
performance is shown in Figure 57. This third order Bessel filter
has a 3 dB bandwidth of 12 MHz. While the 3GPP single
channel bandwidth is only 3.84 MHz, this wide 3 dB bandwidth
of 12 MHz was driven by the need for a flat group delay out to
at least half the bandwidth of the baseband signal. Figure 58
shows a plot of a WCDMA spectrum at 2140 MHz using the
3 GPP Test Model 1 (64 channels active). At an output power of
–17.3 dBm, an adjacent channel power ratio (ACPR) just shy of
–69 dBc was measured.
Figure 59 shows the variation in ACPR with output power at
1960 MHz and 2140 MHz. It also shows the noise floor
measured at an offset of 30 MHz from the center of the
modulated WCDMA signal. From the graphs, it can be seen that
there is an optimal output power at which to operate that
delivers the best ACPR. If the output power is increased beyond
that point, the ACPR degrades as the result of increased
distortion. Below that optimum, the ACPR degrades due to a
reduction in the signal-to-noise ratio of the signal.
AD9777
I_OUTA1
73
40.2Ω
I_OUTB1
72 ^40.2Ω
680nH
100pF
270pF
680nH
I_OUTA2
69
40.2Ω
I_OUTB2
68 ^40.2Ω
680nH
100pF
270pF
680nH
AD8349
1
IBBP
240Ω
2
IBBN
16
QBBP
240Ω
15
QBBN
Figure 57. Single-Carrier WCDMA Application Circuit
(DAC-Modulator Interconnect)
AD8349
–33
–40
–50
–60
–70
–80
–90
–100
–110
–120
ALT
–130
LO
ADJ
LO
CENTER 2.14GHz
CH PWR = –17.3dBm
ADJ CPR = –68.7dB
ALT CPR = –72.7dB
CH
ADJ
ALT
UP
UP
SPAN 24.6848MHz
Figure 58. Single-Carrier WCDMA Spectral Plot at 2140 MHz,
including ACPR and Alternate Channel Power Ratio
–62
–147
–63
1960 ACPR
–64
–148
–149
–65
–150
–66
2140 ACPR
–67
–151
–152
–68
–153
–69
1960 NOISE
–70
–154
–155
–71
2140 NOISE
–72
–26 –24 –22 –20 –18 –16 –14 –12 –10
–156
–157
–8
CHANNEL POWER (dBm)
Figure 59. Single-Carrier WCDMA ACPR and Noise Floor (dBm/Hz) at 30 MHz
Carrier Offset vs. Channel Power at 1960 MHz and 2140 MHz
(Test Model 1 with 64 Active Channels)
WCDMA MULTICARRIER APPLICATION
The high dynamic range of the AD8349 also permits use in
multicarrier WCDMA applications.
Figure 60 shows a 4-carrier WCDMA spectrum at 1960 MHz.
At a per-carrier power of –23 dBm, an ACPR of –60.7 dB is
achieved. Figure 61 shows the variation in ACP and noise floor
(dBc/Hz) with output power.
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