CN-0285

Circuit Note

Rev. 0 | Page 4 of 5

Table 3. Single-Carrier W-CDMA Composite EVM Results Comparing Filter vs. No Filter on ADF4351 RF Outputs (Measured As

Per 3GPP Specification Test Model 4)

Frequency (MHz)

ADF4350 Composite

EVM No LO Filtering

ADF4350 Composite

EVM with LO Filtering, Filter B

ADF4351 Composite

EVM with LO Filtering, Filter B

2140

3.27%

1.31%

1.02%

1800

1.46%

1.13%

0.95%

900

10.01%

1.03%

0.96%

Figure 6. EVM Measurement Setup (Simplified Diagram)

In addition to the improvement in sideband suppression and EVM,

there is also a performance benefit to driving the ADL5375

LO inputs differentially. This benefit improves modulator output

IP2 performance by 2 dB to 5 dB, compared with single-ended

LO drive. Note that most external VCOs only come with a single-

ended output, so using the differential outputs on the ADF4351

provides a benefit over an external VCO in this case.

Figure 7 shows sideband suppression results using an 850 MHz

to 2450 MHz filter (Filter Type B).

Figure 7. Sideband Suppression Results for 850 MHz to 2450 MHz Filter Type B

A complete design support package for this circuit note can be

found at http://www.analog.com/CN0285-DesignSupport.

COMMON VARIATIONS

It is possible to use the auxiliary outputs on the ADF4351 to

switch between two filter types where wideband operation beyond

that possible with one single filter is required (see Figure 8).

An RF double-pole, 4-throw switch (DP4T) is used to select

the differential outputs of either Filter 1 or Filter 2.

Figure 8. Application Diagram Showing Possibility of Filter Switching Using

the ADF4351 Main and Auxiliary Outputs

CIRCUIT EVALUATION AND TEST

The EVAL-CN0285-EB1Z evaluation board contains the circuit

described in CN-0285, allowing for the quick setup and evaluation

of the performance of the circuit. The control software for the

EVAL-CN0285-EB1Z uses the standard ADF4351 programming

software located on the CD that accompanies the evaluation board.

Equipment Needed

The following equipment is needed:

•

A standard PC running Windows® XP, Windows Vista (32-

bit), or Windows 7 with a USB port

•

The EVAL-CN0285-EB1Z circuit evaluation board

•

The ADF435x programming software

•

5.5 V power supplies

•

An I-Q signal source, such as the Rohde & Schwarz AMIQ

•

A spectrum analyzer, such as the Rohde & Schwarz FSQ8

For additional details, see the UG-521 User Guide, the ADF4351

data sheet, and the ADL5375 data sheet.

R&S AMIQ GEN.

I+

I–

Q+

Q–

SPECTRUM ANALYZER

[R&S FSQ 8]

POWER SUPPLY

CN-0285

EVALUATION

BOARD

5.5V

RF OUT

–90

–80

–70

–60

–50

–40

–30

–20

800

1000

1200

1400

1600

1800

2000

2200

2400

CARRIER FREQUENCY (MHz)

–4dBm

–1dBm

+2dBm

+5dBm

ADF4351

12

13

14

15

ADL5375

3

LOIP

4

LOIN

1nF

1nF

FILTER 1

DP4T

SWITCH

FILTER 2