Circuit Note

CN-0205

Rev. 0 | Page 7 of 9

20mA TO 0mA

AD9122

0mA TO 20mA

50Ω

SPECTRUM

ANALYZER

DPG

DATA

PATTERN

GENERATOR

SIGNAL

GENERATOR

ADL5375-05

SIGNAL

GENERATOR

FOR LO

LO

100Ω

100Ω

BB

FILTER

AD9122-M5375-EBZ

POWER SUPPLY

5V

J9

J1

J6

PC

DPG

DOWNLOADER

SOFTWARE

AD9122

SOFTWARE

USB

USB

50Ω

50Ω

50Ω

BB

FILTER

20mA TO 0mA

0mA TO 20mA

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.

and the signal generator for LO to 2140 MHz @ 0 dBm.

4. Turn on the power supply and signal generators. Set the

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

•

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

frequency.