AD8349 datasheet(21/28 Pages) AD

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AD8349

Rev. 0 | Page 21 of 28

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.

680nH

100pF

40.2

Ω

40.2

Ω

240

Ω

IOUTB1

IOUTA1

IBBN

IBBP

AD9777

AD8349

270pF

680nH

100pF

40.2

Ω

40.2

Ω

240

Ω

IOUTB2

IOUTA2

QBBN

QBBP

270pF

Figure 57. Single-Carrier WCDMA Application Circuit

(DAC-Modulator Interconnect)

–130

–120

–110

–100

–90

–80

–70

–60

–50

–40

–33

CENTER 2.14GHz

SPAN 24.6848MHz

CH PWR = –17.3dBm

ADJ CPR = –68.7dB

ALT CPR = –72.7dB

ALT

ADJ

ALT

Figure 58. Single-Carrier WCDMA Spectral Plot at 2140 MHz,

including ACPR and Alternate Channel Power Ratio

–72

–70

–68

–69

–71

–66

–67

–64

–65

–63

–62

–157

–151

–149

–150

–147

–148

–156

–154

–155

–152

–153

–26

–24

–22

–20

–18

–14

–16

–12

–10

–8

1960 ACPR

CHANNEL POWER (dBm)

2140 ACPR

1960 NOISE

2140 NOISE

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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