Firmware techniques for improving the conversion accuracy

AN4073

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DocID022945 Rev 5

2.2

Additional recommendation

ADC conversion results are the ratio of the input voltage to the reference voltage. If there is

noise in the reference voltage, then the results may not be accurate. Both hardware and

firmware design are responsible for reducing the noise.

The execution of code generates some non-negligible noise on the internal power supply

supply pins are available on the microcontroller package; you can connect a capacitor filter

to these power supply pins to filter a high frequency noise.

Here are some general firmware design tips for reducing system noise in order to achieve a

better ADC conversion accuracy:

1.

Avoid starting transmission on any communication peripheral just before starting the

ADC conversion. The toggling of the I/Os may create some noise in the supply voltage.

2.

Avoid toggling high-sink I/Os which cause noise ripples in the power supply.

3.

Avoid toggling digital outputs on the same I/O port as the A/D input is being converted.

This can introduce switching noise into the analog inputs.

4.

It is recommended to configure the STM32F2/F4 ART with data cache + Instruction

cache enable and to disable the prefetch. This will avoid extra CPU accesses to the

Flash memory causing an additional noise which can significantly decrease the ADC

accuracy in some applications.