AD7934 datasheet(29/32 Pages) AD

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AD7933/AD7934

Rev. B | Page 29 of 32

APPLICATION HINTS

GROUNDING AND LAYOUT

Design the printed circuit board that houses the AD7933/AD7934

so that the analog and digital sections are separated and con-

fined to certain areas of the board. This facilitates the use of

ground planes that can be easily separated. Generally, a minimum

etch technique is best for ground planes because it offers

optimum shielding. Join digital and analog ground planes in

only one place, establishing a star ground point connection as

close as possible to the ground pins on the AD7933/AD7934.

Avoid running digital lines under the device because this

couples noise onto the die. However, the analog ground plane

should be allowed to run under the AD7933/AD7934 to avoid

noise coupling. To provide low impedance paths and reduce the

effects of glitches on the power supply line, use as large a trace

as possible on the power supply lines to the AD7933/AD7934.

Shield fast switching signals, such as clocks, with digital ground

to avoid radiating noise to other sections of the board, and

never run clock signals near the analog inputs. Avoid crossover

of digital and analog signals. To reduce the effects of feedthrough

through the board, run traces on opposite sides of the board at

right angles to each other. A microstrip technique is by far the

best, but it 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 solder side.

Good decoupling is also important. Decouple all analog

supplies with 10 μF tantalum capacitors in parallel with 0.1 μF

capacitors to GND. To achieve the best performance from these

decoupling components, they must be placed as close as

possible to the device, ideally right up against the device. The

0.1 μF capacitors should have a low effective series resistance

(ESR) and effective series inductance (ESI), such as the

common ceramic types or surface-mount types. These types of

capacitors provide a low impedance path to ground at high

frequencies to handle transient currents due to internal logic

switching.

EVALUATING THE AD7933/AD7934

PERFORMANCE

The recommended layout for the AD7933/AD7934 is outlined

in the evaluation board documentation. The evaluation board

package includes a fully assembled and tested evaluation board,

documentation, and software for controlling the board from the

PC via the evaluation board controller. The evaluation board

controller can be used in conjunction with the AD7933/AD7934

evaluation board, as well as many other Analog Devices evalua-

tion boards ending in the CB designator, to demonstrate and

evaluate the ac and dc performance of the AD7933/AD7934.

The software allows the user to perform ac (fast Fourier transform)

and dc (histogram of codes) tests on the AD7933/AD7934. The

software and documentation are on the CD that ships with the

evaluation board.

AD7934 Datasheet(PDF) 29 Page - Analog Devices

AD7934 Datasheet(HTML) 29 Page - Analog Devices

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