CN-0243 Datasheet, PDF (7/8 Pages) Analog Devices – High Dynamic Range RF Transmitter Signal Chain Using Single External Frequency Reference for DAC Sample Clock and IQ Modulator LO Generation

Circuit Note
CN-0243
USB
DPG2
PC
DIGITAL PATTERN
GENERATOR
USB
USB ADAPTER
BOARD
IQ DATA
I
Q
DIGITAL
INTERFACE
EVAL-CN0243-EB1Z
EVALUATION BOARD
PLL REFERENCE
INPUT
REFERENCE
FREQUENCY
GENERATOR
10MHz – 200MHz +3dBm
+5V GND
POWER
SUPPLY
RF OUTPUT
SPECTRUM
ANALYZER
Figure 13. Test Setup Functional Block Diagram
data rate should be equal to the DAC sample rate
(614.4 MSPS) in Figure 13 divided by the programmed
interpolation rate of the AD9122.
5. Note that as the various devices are activated and
programmed, the current will increase. At the end of this
exercise, the current should be between 1.4 A and 1.5 A,
depending on DAC sample rate.
6. Use the DPG2 software to create a waveform (single,
multi tone, or comms standard signals are available).
A digital back-off of −8 dB should be used initially to
optimize linearity of the DAC/ADRF6702 combination.
Complex signal generation should also be selected in the
DPG2 GUI. When the waveform is created, use the "load"
and "play" buttons in the GUI to load the digital pattern
into the DPG memory itself.
7. Start the ADRF6702 GUI. To begin with, the only options
in the ADRF6702 GUI which need to be selected are the
input reference frequency and LO output frequency. To
program these values, click the reference input frequency
or the LO output values in the top center of the
ADRF6702 GUI. Another window will appear which will
allow you to enter these values. Important: After entering
these values, the user must finish with a carriage return to
make sure that the values are entered into the GUI.
8. Programming the ADRF6702 is the last step in setting up
the EVAL-CN0243-EB1Z evaluation board. As an
example, if the DPG2 generates a series of tones (20 MHz
to 25 MHz with 1 MHz spacing) @ −8 dB back-off, and
the LO of the ADRF6702 is programmed to 1940 MHz,
the spectrum should look very similar to that shown in
Figure 14.
REF –20dBm
–20
RBW 10kHz MARKER 1 [T1]
VBW 30kHz
–104.90dB
ATT 10dBm SWT 15ms
1.89005GHz
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
CENTER 1.94GHz
10MHz/DIV
SPAN 100MHz
Figure 14. Spectrum of Complex Multitone Signal at LO Frequency of
1940 MHz at ADRF6702 RF Output, Desired Sideband Offset: +20 MHz,
Undesired Sideband Offset: −20 MHz
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