CN-0134

Circuit Note

Rev. B | Page 4 of 5

Table 3. Single-Carrier W-CDMA Composite EVM Results Comparing Filter vs. No Filter on ADF4350 RF Outputs

(Measured As Per 3GPP Specification Test Model 4)

Frequency (MHz)

Composite EVM No LO

Filtering

Composite EVM with LO Filtering,

Filter C

Modulator Output Power

(dBm)

2140

3.50%

1.80%

−7

1800

3.40%

1.50%

−7

900

3.30%

0.90%

−7

Error vector magnitude (EVM) is a measure of the quality of

the performance of a digital transmitter or receiver and is a

measure of the deviation of the actual constellation points from

their ideal locations, due to both magnitude and phase errors.

This is shown in Figure 5.

EVM measurements are given in Table 3 comparing results with

and without the filter. In this case the baseband I/Q signals were

generated using 3GPP test model 4 using a Rhode and Schwarz

AMIQ I/Q Modulation Generator with differential I and Q

analog outputs. Filter b was also used. A block diagram of the

test setup for EVM is given in Figure 6.

Adjacent channel leakage ratio (ACLR) is a measure of the

power in adjacent channels relative to the main channel power

and is specified in dBc.

The LO phase noise and the linearity of the modulator are the

main contributors to ACLR. The ACLR test setup is the same

as for EVM with the exception that coaxial filters were placed

on the I/Q outputs of the signal generator to reduce aliasing

products.

R&S AMIQ GEN.

I+

I–

Q+

Q–

SPECTRUM ANALYZER

[R&S FSQ 8]

POWER SUPPLY

CN-0134

EVALUATION

BOARD

5.5V

RF OUT

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 improves modulator

OIP2 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

ADF4350 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 b).

10

–60

–50

–40

–30

–20

–10

0

0

500

1000

1500

2000

2500

3000

3500

FREQUENCY (MHz)

SSB #10 +5dBm

SSB #10 +2dBm

SSB #10 –1dBm

SSB #10 –4dBm

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

A complete design support package for this circuit note can be

found at http://www.analog.com/CN0134-DesignSupport.

COMMON VARIATIONS

It is possible to use the auxiliary outputs on the ADF4350 to

switch between two filter types where wideband operation

beyond that possible with one single filter is required. This

is shown in Figure 8. An RF double-pole, 4-throw switch

(DP4T) is used to select the differential outputs of either

Filter 1 or Filter 2.