high resolution systems, avoid crossing analog and digital
lines altogether. It is important to keep clock lines as short as
possible and isolated from ALL other lines, including other
digital lines. In addition, the clock line should also be treated
as a transmission line and be properly terminated.
2.0 Applications Information
(Continued)
close to the ADC output pin as practical. This will limit the
charge and discharge current of the output capacitance and
improve noise performance. Since the series resistor and
the load capacitance form a low frequency pole, verify signal
integrity once the series resistor has been added.
The analog input should be isolated from noisy signal traces
to avoid coupling of spurious signals into the input. Any
external component (e.g., a filter capacitor) connected be-
tween the converter’s input pins and ground or to the refer-
ence input pin and ground should be connected to a very
clean point in the ground plane.
2.3 LAYOUT AND GROUNDING
Capacitive coupling between the noisy digital circuitry and
the sensitive analog circuitry can lead to poor performance.
The solution is to keep the analog circuitry separated from
the digital circuitry and the clock line as short as possible.
We recommend the use of a single, uniform ground plane
and the use of split power planes. The power planes should
be located within the same board layer. All analog circuitry
(input amplifiers, filters, reference components, etc.) should
be placed over the analog power plane. All digital circuitry
and I/O lines should be placed over the digital power plane.
Furthermore, all components in the reference circuitry and
the input signal chain that are connected to ground should
be connected together with short traces and enter the analog
ground plane at a single, quiet point.
Digital circuits create substantial supply and ground current
transients. The logic noise generated could have significant
impact upon system noise performance. To avoid perfor-
mance degradation of the ADC128S102 due to supply noise,
do not use the same supply for the ADC128S102 that is used
for digital logic.
Generally, analog and digital lines should cross each other at
90˚ to avoid crosstalk. However, to maximize accuracy in
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