Microcontroller Solutions TechZone Magazine, April 2011 - Digikey

Analog interference
Mixing analog and digital circuits on the same board has its own
challenges. Board layout and routing become important in order
to keep the analog noise levels at a low level in order to ensure
accurate sampling of low-level analog signals. Doing a good
mixed-signal design requires careful hardware considerations and
skills. Software design can also affect the quality of the analog
measurements. Performing a lot of I/O activity at the same time
as sampling analog signals will cause many digital lines to toggle
state at the same time – a candidate for introducing extra noise
into the A/D converter.
Power debugging will help to identify interference from digital and
power supply lines affecting the analog parts. Interrupt activity
can easily be displayed in the Timeline window together with
power data. Be sure to study the power graph right before the A/D
converter interrupts. Power spikes in the vicinity of A/D conversions
could be the source of noise and must be investigated. All data
presented in the timeline window is correlated to the executed
code; simply double-clicking on a suspicious power sample will
bring up the corresponding C source code.
Conclusion
Power debugging techniques provide embedded developers the
ability to understand the effect of source code on their application’s
power consumption. By careful analysis of power “hot spots” and
the review of programming methods used, engineers can make
signifi cant battery lifetime savings even during the early stages of
project development.
Figure 4: Power spike due to stepper motor interfering with A/D-sampling.
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Cortex-M0: a simple choice
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