EVAL-AD7934-6CB AD [Analog Devices], EVAL-AD7934-6CB Datasheet - Page 27

• Manufacturer Part Number: EVAL-AD7934-6CB
• Description: 4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer
• Manufacturer: AD [Analog Devices]

APPLICATION HINTS
GROUNDING AND LAYOUT
The printed circuit board that houses the AD7934-6 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 that can be easily separated. Generally, a
minimum etch technique is best for ground planes since it gives
the best shielding. Digital and analog ground planes should be
joined in only one place, and the connection should be a star
ground point established as close to the ground pins on the
AD7934-6 as possible. Avoid running digital lines under the
device as this couples noise onto the die. The analog ground
plane should be allowed to run under the AD7934-6 to avoid
noise coupling. The power supply lines to the AD7934-6 should
use as large a trace as possible to provide low impedance paths
and reduce the effects of glitches on the power supply line.
Fast switching signals, such as clocks, should be shielded with
digital ground to avoid radiating noise to other sections of the
board, and clock signals should never run near the analog
inputs. Avoid crossover of digital and analog signals. Traces on
opposite sides of the board should run at right angles to each
other. This reduces the effects 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 solder side.
Rev. A | Page 27 of 28
Good decoupling is also important. All analog supplies should
be decoupled with 10 µF tantalum capacitors in parallel with
0.1 µF capacitors to GND. To achieve the best 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 low effective series resistance
(ESR) and effective series inductance (ESI), such as the
common ceramic types or surface-mount types, which provide
a low impedance path to ground at high frequencies to handle
transient currents due to internal logic switching.
EVALUATING THE AD7934-6 PERFORMANCE
The recommended layout for the AD7934-6 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 AD7934-6
evaluation board, as well as with many other ADI evaluation
boards ending in the CB designator, to demonstrate/evaluate
the ac and dc performance of the AD7934-6.
The software allows the user to perform ac (fast Fourier
transform) and dc (histogram of codes) tests on the AD7934-6.
The software and documentation are on the CD that ships with
the evaluation board.
AD7934-6