AN672 Datasheet, PDF (1/3 Pages) Silicon Laboratories – PRECISION32™ SI32LIBRARY OVERVIEW

AN672
APPLICATION NOTE
OPTIMIZING THE ST6 A/D CONVERTER ACCURACY
INTRODUCTION
When using the internal Analog to Digital Converter of the ST62 family and maximum A/D con-
verter accuracy is required, it is desirable to filter out any noise present on the analog input,
but also noise present on the ground and V_CC supply lines of the MCU as V_CC is also the
voltage reference of the A/D converter. Good decoupling must be made with capacitors on the
analog input and between V_CC and ground. It is also recommended to put the MCU in wait
state while the conversion is in progress, so as to minimize noise injected into V_CC by the op-
eration of the micro-controller itself.
Finally, when enough time is available, it is highly recommended to make several successive
A/D conversions and take an average of the results. This is the most effective way to get the
most accuracy out of the ST6 family A/D converter.
The following code fragment demonstrates a burst of 256 successive measurements, after
which the average is put into the accumulator. The whole routine takes approximately 30 milli-
seconds with an 8 MHz clock. When less time is available, it is of course possible to reduce the
number of conversions: 8, 16 or 32 conversions also give good results, although the most con-
versions give the best results.
AN672/1104
Rev. 2.0
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