AD9375BBCZ datasheet(59/61 Pages) AD

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Data Sheet

AD9375

Rev. 0 | Page 59 of 61

DIGITAL PREDISTORTION (DPD)

This device provides a fully integrated DPD function that

linearizes the output of the power amplifier (PA) of the transmit

system by altering the digital waveform to compensate for

nonlinearities in the PA response. Both the DPD actuator and

coefficient calculation engine are integrated. This functionality

uses the ORx channel to monitor the output of the PA and

calculates the appropriate predistortion to linearize the output.

The integrated DPD capability allows the system to drive the PA

closer to saturation, enabling a higher efficiency PA while

maintaining linearity. The DPD is optimized for small cell PAs

with rms output powers in the 250 mW to 10 W range and for a

maximum occupied signal bandwidth of 40 MHz. The

additional power consumed by the DPD block when enabled is

less than 100 mW.

Performance enhancement is shown in Figure 232 for a 20 MHz

LTE signal and in Figure 233 for a 40 MHz LTE output. In both

cases, a Band 7 Skyworks SKY66297 high efficiency PA is used

to demonstrate the adjacent channel level reduction (ACLR)

improvement for a particular device. Table 9 and Table 10 show

the details of ACLR improvement that are achieved for these two

scenarios when DPD is activated. Note that the magnitude of

improvement in ACLR is heavily PA dependent and generally

degrades as signal bandwidth increases.

–60

–50

–40

–30

–20

–10

2540

2560

2580

2600

2620

2640

2660

FREQUENCY (MHz)

DPD

NO DPD

Figure 232. Output Spectrum for Normal Operation (Red) and with DPD

Activated (Blue) for a 20 MHz LTE Signal

–60

–50

–40

–30

–20

–10

2500

2525

2550

2575

2600

2625

2650

2675

2700

FREQUENCY (MHz)

DPD

NO DPD

Figure 233. Output Spectrum for Normal Operation (Red) and with DPD

Activated (Blue) for a 40 MHz LTE Output

Table 9. ACLR Comparison With and Without DPD for a 20 MHz LTE Waveform

Mode1

20 MHz Offset (dBc)

40 MHz Offset (dBc)

60 MHz Offset (dBc)

Lower

Upper

Lower

Upper

Lower

Upper

Normal Operation

−32.15

−34.18

−51.71

−51.16

−59.29

−58.99

DPD Activated

−50.89

−51.90

−52.63

−56.57

−57.23

−59.49

1 Waveform is 10 ms (full-frame) LTE evolved universal terrestrial radio access (E-UTRA) Test Model 1.1 (E-TM 1.1) at 7.5 dB peak to average ratio (PAR), with crest factor

reduction (CFR), 28 dBm output, and 18.02 MHz occupied bandwidth.

Table 10. ACLR Comparison With and Without DPD for a 40 MHz LTE Waveform

Mode1

20 MHz Offset (dBc)

40 MHz Offset (dBc)

60 MHz Offset (dBc)

Lower

Upper

Lower

Upper

Lower

Upper

Normal Operation

−29.74

−33.69

−37.45

−41.65

−48.31

−47.95

DPD Activated

−47.42

−48.22

−49.84

−49.62

−52.06

−54.38

1 Waveform is 10 ms (full frame) LTE E-UTRA Test Model 1.1 (E-TM 1.1) at 7.5 dB PAR (with CFR), 27 dBm output, and 36.04 MHz occupied bandwidth.

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