CN-0285 Datasheet, PDF (4/5 Pages) Analog Devices – Broadband Low Error Vector Magnitude (EVM) Direct Conversion Transmitter

CN-0285
Circuit Note
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%
R&S AMIQ GEN.
I+ I– Q+ Q–
CN-0285
EVALUATION
BOARD
5.5V
SPECTRUM ANALYZER
[R&S FSQ 8]
RF OUT
POWER SUPPLY
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).
–20
–30
–40
–50
–60
–4dBm
–70
–1dBm
+2dBm
+5dBm
–80
–90
800
1000 1200 1400 1600 1800 2000 2200 2400
CARRIER FREQUENCY (MHz)
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.
RF_OUTA+ 12
RF_OUTA– 13
FILTER 1
RF_OUTB+ 14
RF_OUTB– 15
FILTER 2
DP4T
SWITCH
1nF
3 LOIP
1nF
4 LOIN
ADF4351
ADL5375
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.
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