EVAL-AD7934CB Analog Devices Inc, EVAL-AD7934CB Datasheet - Page 29

• Manufacturer Part Number: EVAL-AD7934CB
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7934CB

• Lead Free Status / Rohs Status: Not Compliant

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.
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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.
AD7933/AD7934