AN2834 datasheet(20/45 Pages) STMICROELECTRONICS

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How to get the best ADC accuracy

AN2834

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DocID15067 Rev 2

How to get the best ADC accuracy

3.1

Reduce the effects of ADC-related ADC errors

The TUE is not the sum of all the errors EO, EG, EL, ED. It is the maximum deviation that can

occur between the ideal and actual digital values. It can result from one or more errors

occurring simultaneously.

As the ILE is the integral of the DLE, it can be considered as the indicator of the maximum

error. Do not add the DLE and ILE together to calculate the maximum error that may occur

at any digital step.

The maximum error values specified in the datasheet are the worst error values measured

in laboratory test environment over the given voltage and temperature range (see device

datasheet).

The ILE and DLE are dependent on the ADC design. It is difficult to calibrate them. They

can be calibrated by the measured ADC curve stored in the microcontroller memory but this

needs calibration of each individual device in final application.

Offset and gain errors can be easily compensated using the STM32x ADC self-calibration

feature or by microcontroller firmware.

3.2

Minimize ADC errors related to external environment of ADC

3.2.1

Reference voltage / Power supply noise minimization

Power supply side

Linear regulators have a better output in terms of noise. The mains must be stepped down,

rectified and filtered, then fed to linear regulators. It is highly recommended to connect the

filter capacitors to the rectifier output. Please refer to the datasheet of the used linear

regulator.

If you are using a switching power supply, it is recommended to have a linear regulator to

supply the analog stage.

It is recommended to connect capacitors with good high-frequency characteristics between

the power and ground lines. That is, a 0.1 µF and a 1 to 10 µF capacitor should be placed

close to the power source.

The capacitors allow the AC signals to pass through them. The small-value capacitors filter

high-frequency noise and the high-value capacitors filter low-frequency noise. Ceramic

capacitors are generally available in small values (1 pF to 0.1 µF) and with small voltage

ratings (16 V to 50 V). It is recommended to place them close to the main supply (VDD and

VSS) and analog supply (VDDA and VSSA) pins. They filter the noise induced in the PCB

tracks. Small capacitors can react fast to current surges and discharge quickly for fast-

current requirements.

Tantalum capacitors can also be used along with ceramic capacitors. To filter low-frequency

noise, you can use high-value capacitors (10 µF to 100 µF), which are generally electrolytic.

It is recommended to put them near the power source.



To filter high-frequency noise, you can use a ferrite inductance in series with the power

supply. This solution leads to very low (negligible) DC loss unless the current is high

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