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AN3137

Methods for precision improvement

Doc ID 16983 Rev 3

21/42

Methods for precision improvement

4.1

Introduction

ADC converter precision is fixed by its principle, design and implementation but it can also

be improved by several hardware and/or software methods. Hardware methods improve

ADC results by changing the environment around the ADC (PCB design, RC filters...) to

obtain more accurate ADC output. Software methods try to improve the raw ADC results by

post-processing methods. Some CPU computation power and time are required to perform

these methods, which can be implemented in the microcontroller firmware.

4.2

Hardware methods

●

Analog zooming (use appropriate VREF voltage):

–

select reference voltage between input signal ranges

–

gives full ADC range - minimum voltage per bit

●

White noise added to measured signal:

–

wobbling of input signal over several bits gives the opportunity to use averaging (if

input signal is very stable)

–

white noise gives independence from sampling frequency

●

Good hardware design:

–

grounding

–

reference voltage filtering

–

supply filtering

–

preamplifier usage

–

frequency independence

–…

4.2.1

Analog zooming

Analog zooming is a method which improves precision by properly selecting the reference

voltage. The reference voltage is selected in the expected range of the signal to be

measured.

If the measured signal has an offset, then the reference voltage should also have a similar

offset. If the measured signal has defined maximum amplitude, then the reference voltage

should also have a similar maximum value. By matching this reference voltage to the

measurement signal range, we obtain the maximum possible resolution using the full A/D

converter output range.

An analog zooming can be performed between VSS and VREF+ if VDDA > VREF+ ≥ 2.4 V.

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