ADL5375ACPZ-R7 datasheet(23/36 Pages) AD

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Data Sheet

ADL5375

Rev. C | Page 23 of 36

Sideband suppression is discussed further in AN-1100, Wireless

Transmitter IQ Balance and Sideband Suppression, as well as in

AN-1039, Correcting Imperfections in IQ Modulators to Improve

RF Signal Fidelity.

INTERFACING THE ADF4350 PLL TO THE ADL5375

With an output frequency range of 137.5 to 4.4 GHz, a high

performance integrated VCO and an LO output power level

that can be programmed from −4 dBm to +5 dBm, the

ADF4350 wideband synthesizer is ideally suited to drive the

ADL5375 LO port.

Care must be taken to adequately suppress the harmonics of the

LO signal from the PLL. VCOs typically have a third harmonic

power of approximately −10 dBc. A large third harmonic on the

LO degrades the quality of the quadrature generation inside the

IQ Modulator. The third harmonic should be suppressed to a

level of –30 dBc or lower to prevent quadrature degradation. So

approximately 20 dB of attenuation is required to get the third

harmonic below −30 dBc. Figure 57 shows PLL modulator

interfaces schematic that for this operation at four different

frequencies, and Table 4 shows the optimized components value

of Figure 57. Because filtering of the third harmonic is most

critical, and to ensure wide frequency range coverage, the 3 dB

corner of the filters have been set to approximately 1.2~1.5

times the maximum desired LO frequency. A Chebyshev filter

topology at 100 Ω differential source impedance and 50 Ω

differential load impedance was used for optimal performance.

ADF4350

RFOUTA+

RFOUTA–

ADL5375

LOIP

LOIN

1nF

C1a

C1c

C2a

C2c

C3a

C3c

ZBIAS

120pF

0.1µF

3.3V

Figure 57. PLL-Modulator Interface Schematic

Table 4. PLL Modulator Interface Components Values (DNI = Do Not Insert)

Frequency Range (MHz)

Zbias (nH)

R1 (Ω)

L1 (nH)

L2 (nH)

C1a (pF)

C1c (pF)

C2a

C2c (pF)

C3a (pF)

C3c (pF)

500 to 1300

100

3.9

DNI

4.7

DNI

5.6

DNI

3.3

850 to 2450

100

2.7

3.3

DNI

4.7

DNI

3.3

DNI

1250 to 2800

7.5

100

0 Ω

3.6

DNI

2.2

DNI

1.5

DNI

2800 to 4400

3.9

100

0 Ω

DNI

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