CN-0205 Datasheet, PDF (7/9 Pages) Analog Devices – Interfacing the ADL5375 I/Q Modulator to the AD9122 Dual Channel, 1.2 GSPS High Speed DAC

Circuit Note
CN-0205
DPG
DATA
PATTERN
GENERATOR
F_DATA
DPG
USB DOWNLOADER
SOFTWARE
USB
PC
AD9122
SOFTWARE
I_OUT1
I_OUT1
AD9122
0mA TO 20mA
50Ω
BB
FILTER
100Ω
50Ω ^{20mA TO 0mA}
J6
ADL5375-05
I_OUT2
I_OUT2
0mA TO 20mA
50Ω
20mA TO 0mA
50Ω
BB _100Ω
FILTER
J1
F_DAC
SIGNAL
GENERATOR
FOR F_DAC
AD9122-M5375-EBZ
5V
POWER SUPPLY
J9
LO
SPECTRUM
ANALYZER
SIGNAL
GENERATOR
FOR LO
Figure 16. Test Setup Functional Block Diagram
Further insight to proper layout can be found by examining the
AD9122-M5375-EBZ layout files in the design support package
www.analog.com/CN0205-DesignSupport.
COMMON VARIATIONS
The interface described in this circuit note can be used between
any TxDAC digital-to-analog converter (AD9779A, AD9788,
AD9125, AD9148) that is set for 20 mA full-scale current and
the ADL5370, ADL5371/ADL5372, ADL5373, ADL5374,
ADL5385, ADL5386, etc., family of I/Q modulators that require
0.5 V baseband dc bias levels.
The interface can also be adapted to the AD8345/AD8349 low
current modulators, with some adjustment to the bias level by
properly selecting the DAC termination resistors.
CIRCUIT EVALUATION AND TEST
The following section describes details of performing the
common-mode test (results shown in Figure 10). The test setup
is flexible and allows other measurements shown in this circuit
note to be performed.
Equipment Needed (Equivalents Can be Substituted)
• DPG : ADI Digital Pattern Generator
• Signal Generator for clock: Agilent E4437B
• Signal generator for LO: Agilent 8665B
• Spectrum analyzer: Agilent E4440A
• Power supply: Agilent E3631A
Setup and Test
1. Connect the setup and measurement system shown in
Figure 16.
2. Set the power supply to +5 V.
3. Set the signal generator for FDAC to 368.64 MHz @ 5 dBm,
and the signal generator for LO to 2140 MHz @ 0 dBm.
4. Turn on the power supply and signal generators. Set the
spectrum analyzer at 2 × FDAC MHz, 1 MHz span.
5. Set up the AD9122 through USB at AD9122/AD9125
SPI control software as shown in Figure 17 and run.
Refer to the AD9122 Evaluation Board Quick Start
Guide in www.analog.com-CN0205-DesignSupport.
• Interpolation ("1" in Figure 17) : 1×
• Fine modulation ("2" in Figure 17) : ON
• Data rate ("3" in Figure 17) : same as FDAC
frequency
• NCO frequency ("4" in Figure 17) : 173.32 MHz
6. Set up DPG (refer to AD9122 Evaluation Board Quick
Start Guide)
• Make sure DCO frequency ("1" in Figure 18)
is close to FDAC frequency.
• Set sample rate ("2" in Figure 18) same as
FDAC frequency and 1 MHz at desired
frequency.
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