ADL5374ACPZ-WP データシートの表示（PDF） - Analog Devices

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ADL5374ACPZ-WP

3000 MHz to 4000 MHz Quadrature Modulator

Analog Devices 

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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