When to Use a Double Transformer Configuration.” Rob
Reeder and Ramya Ramachandran.
Analog Dialogue,
40-07.)
Because sideband suppression performance is dependent on the
modulator quadrature accuracy, better sideband suppression is
achievable when driving the LO input ports differentially vs.
single-ended. The
ADF4350
has differential RF outputs
compared to a single-ended output available on most
competitor PLL devices with integrated VCO.
SIDEBAND SUPPRESSION (dBc)
–20
–30
–40
–50
–60
–70
0
500
1000
1500
2000
2500
FREQUENCY (MHz)
Figure 2. Sideband Suppression, RFOUT Swept from 68.75 MHz to 2200 MHz
This circuit achieves comparable or improved sideband
suppression performance when compared to driving the
ADL5385
with a low noise RF signal generator, as used in the
data sheet measurement. Using the differential RF outputs of
the
ADF4350
provides even-order harmonic cancellation and
improves modulator quadrature accuracy. This impacts sideband
suppression performance and EVM (error vector magnitude).
A single carrier W-CDMA composite EVM of better than 2%
was measured with the circuit shown in Figure 1. The solution
thus provides a low EVM broadband solution for frequencies
from 68.75 MHz to 2.2 GHz. For frequencies above 2.2 GHz,
a divide-by-1 modulator block should be used, as described in
CN-0134.
A complete design support package for this circuit note can be
found at
http://www.analog.com/CN0144-DesignSupport.
Rev. C | Page 2 of 4
08835-002
Circuit Note
R&S AMIQ
CN-0144
IP
RF
OUT
A+
ADF4350
EVALUATION BOARD
RF
OUT
A–
LOIN
LOIP
IN
QP
QN
AD5385 EVALUATION BOARD
ADAPTED TO ACCEPT
RFOUT
DIFFERENTIAL LO INPUTS
SPECTRUM
ANALYZER
5V
08835-003
POWER SUPPLY
Figure 3. Sideband Suppression Measurement Test Setup (Simplified Diagram)
COMMON VARIATIONS
The PLL-to-modulator interface described in this circuit note is
applicable to all I/Q modulators that contain a 2XLO-based
phase splitter. It is also applicable to 2XLO-based I/Q
demodulators such as the
ADL5387.
Functional Block Diagram
The
CN-0144
contains the function block diagram of the described
test setup in Figure 3.
Setup and Test
After setting up the equipment, use standard RF test methods to
measure the sideband suppression of the circuit.
CIRCUIT EVALUATION AND TEST
The
CN-0144
uses the
EVAL-ADF4350EB1Z
and the
ADL5385-EVALZ
boards for evaluation of the described circuit,
allowing for quick setup and evaluation. The
EVAL-ADF4350EB1Z
board uses the standard
ADF4350
programming software,
contained on the CD that accompanies the evaluation board.
FURTHER IMPROVEMENTS WITH FILTERING
The sideband suppression of this circuit can be further improved
by filtering the LO signal before the LOIP and LOIN pins of the
ADL5385.
Filtering attenuates harmonic levels so as to minimize
errors in the quadrature generation block of the
ADL5385.
At
some frequencies, this can result in improvements over 10 dB.
However, using a filter will limit the bandwidth of the circuit.
See Figure 4 for narrowband results.
0
–10
Equipment Needed
Windows® XP, Windows Vista (32-bit), or Windows 7 (32-bit) PC
with USB Port, the
EVAL-ADF4350EB1Z,
and the
ADL5385-
EVALZ
circuit evaluation boards, the
ADF4350
programming
software, power supplies, I-Q signal source, such as a Rhode &
Schwarz AMIQ, and a spectrum analyzer. See the
CN-0144
and the
UG-109
user guide for evaluation board
EVAL-ADF4350EB1Z
and the
ADF4350
and
ADL5385
data sheets.
SIDEBAND SUPPRESSION (dBc)
–20
–30
–40
–50
–60
–70
–80
700
Getting Started
This circuit note contains a description of the circuit, the schematic,
and a block diagram of the test setup. The user guide
UG-109
details the installation and use of the
EVAL-ADF4350
evaluation
software. The
UG-109
also contains board setup instructions
and the board schematic, layout, and bill of materials. The
ADL5385-EVALZ
board schematic, block diagram, bill of
materials, layout, and assembly information is included in the
ADL5385
data sheet. See the
ADF4350
and
ADL5385
data sheet
for device information.
NO FILTER
WITH FILTER
800
900
1000
1100
RF
OUT
(MHz)
1200
1300
08835-004
Figure 4. Sideband Suppression Comparison With and Without a Harmonic Filter
The LO signal was passed through a low-pass filter with a 3 dB
point at approximately 2600 MHz. This results in a usable
output frequency up to approximately 1300 MHz.
Rev. C | Page 3 of 4
CN-0144
LEARN MORE
CN0144 Design Support Package:
http://www.analog.com/CN0144-DesignSupport
ADIsimPLL Design Tool
ADIsimPower Design Tool
ADIsimRF Design Tool
Brandon, David, David Crook, and Ken Gentile. AN-0996
Application Note,
The Advantages of Using a Quadrature
Digital Upconverter (QDUC) in Point-to-Point Microwave
Transmit Systems.
Analog Devices.
CN-0134,
Broadband Low EVM Direct Conversion Transmitter.
Analog Devices.
CN-0147,
Using the ADP150 LDO Regulators to Power the
ADF4350 PLL and VCO.
Analog Devices.
Nash, Eamon. AN-1039 Application Note,
Correcting
Imperfections in IQ Modulators to Improve RF Signal
Fidelity.
Analog Devices.
Reeder, Rob, and Ramya Ramachandran. “Wideband
A/D Converter Front-End Design Considerations:
When to Use a Double Transformer Configuration.”
Analog Dialogue,
40-07.
Circuit Note
Data Sheets and Evaluation Boards
ADF4350 Data Sheet
ADF4350 Evaluation Board
ADL5385 Data Sheet
ADL5385 Evaluation Board
ADP150 Data Sheet
ADP3334 Data Sheet
REVISION HISTORY
10/12—Rev.
B to Rev. C
Added Further Improvements with Filtering Section ..................3
11/10—Rev. A to Rev. B
Changes to Circuit Note Title ..........................................................1
Added Evaluation and Design Support Section ............................1
Changes to Figure 3 ...........................................................................3
Added Circuit Evaluation and Test Section ...................................3
8/10—Rev. 0 to Rev. A
Changes to Circuit Function and Benefits Section .......................1
Changes to Circuit Description Section .........................................2
Added Common Variations Section ...............................................3
3/10—Revision 0: Initial Version
(Continued from first page) Circuits from the Lab circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you
may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by
application or use of the Circuits from the Lab circuits. Information furnished by Analog Devices is believed to be accurate and reliable. However, Circuits from the Lab circuits are supplied
"as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability, noninfringement or fitness for a particular
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