AD9830

REV. A

–13–

Grounding and Layout

The printed circuit board that houses the AD9830 should be

designed so that the analog and digital sections are separated

and confined to certain areas of the board. This facilitates the

use of ground planes which can be separated easily. A mini-

mum etch technique is generally best for ground planes as it

gives the best shielding. Digital and analog ground planes

should only be joined in one place. If the AD9830 is the only

device requiring an AGND to DGND connection, then the

ground planes should be connected at the AGND and DGND

pins of the AD9830. If the AD9830 is in a system where mul-

tiple devices require AGND to DGND connections, the con-

nection should be made at one point only, a star ground point

that should be established as close as possible to the AD9830.

Avoid running digital lines under the device as these will couple

noise onto the die. The analog ground plane should be allowed

to run under the AD9830 to avoid noise coupling. The power

supply lines to the AD9830 should use as large a track as is pos-

sible to provide low impedance paths and reduce the effects of

glitches on the power supply line. Fast switching signals like

clocks should be shielded with digital ground to avoid radiating

noise to other sections of the board. Avoid crossover of digital

and analog signals. Traces on opposite sides of the board

should run at right angles to each other. This will reduce the ef-

fects of feedthrough through the board. A microstrip technique

is by far the best but is not always possible with a double-sided

board. In this technique, the component side of the board is

dedicated to ground planes while signals are placed on the other

side.

Good decoupling is important. The analog and digital supplies

to the AD9830 are independent and separately pinned out to

minimize coupling between analog and digital sections of the

device. All analog and digital supplies should be decoupled to

AGND and DGND respectively with 0.1

µF ceramic capacitors

in parallel with 10

µF tantalum capacitors. To achieve the best

from the decoupling capacitors, they should be placed as close

as possible to the device, ideally right up against the device. In

systems where a common supply is used to drive both the AVDD

and DVDD of the AD9830, it is recommended that the system’s

AVDD supply be used. This supply should have the recom-

mended analog supply decoupling between the AVDD pins of

the AD9830 and AGND and the recommended digital supply

decoupling capacitors between the DVDD pins and DGND.

AD9830 Evaluation Board

The AD9830 Evaluation Board allows designers to evaluate the

high performance AD9830 DDS Modulator with a minimum of

effort.

To prove that this device will meet the user’s waveform synthesis

requirements, the user only requires a +5 V power supply, an

IBM-compatible PC and a spectrum analyzer along with the

evaluation board. The evaluation setup is shown below.

The DDS Evaluation kit includes a populated, tested AD9830

printed circuit board along with software which controls the

AD9830 in a Windows environment.

AD9830.EXE

IBM COMPATIBLE PC

PARALLEL PORT

CENTRONICS

PRINTER CABLE

AD9830 EVALUATION

BOARD

Figure 25. AD9830 Evaluation Board Setup

Using the AD9830 Evaluation Board

The AD9830 Evaluation kit is a test system designed to simplify

the evaluation of the AD9830. Provisions to control the AD9830

from the printer port of an IBM-compatible PC are included

along with the necessary software. An application note is also

available with the evaluation board which gives information on

operating the evaluation board.

Prototyping Area

An area is available on the evaluation board where the user can

add additional circuits to the evaluation test set. Users may

want to build custom analog filters for the outputs or add buf-

fers and operational amplifiers which are to be used in the final

application.

XO vs. External Clock

The AD9830 can operate with master clocks up to 50 MHz. A

50 MHz oscillator is included on the evaluation board. How-

ever, this oscillator can be removed and an external CMOS

clock connected to the part, if required.

Power Supply

Power to the AD9830 evaluation board must be provided exter-

nally through the pin connections. The power leads should be

twisted to reduce ground loops.