AN1711 datasheet(29/40 Pages) STMICROELECTRONICS

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SOFTWARE TECHNIQUES FOR COMPENSATING ST7 ADC ERRORS

ported as less than the expected result and negative offset error causes the reported result to

be more than the expected result.

For example: Offset error = 3 LSBs

Gain error = -1 LSB

So total error = 4 LSBs for 1023 steps.

To avoid using floating point arithmetic, we can take 1 LSB per 255 steps (approximately) to

be compensated.

Therefore, add 3 to digital results in the range 1-255.

256-510 add 2

511 - 765 add 1

765 - 1023 subtract 1

Caution: This technique is provided for theoretical understanding. The error distribution may

not be linear. Please refer to the Zone compensation as below.

4.2.5 Zone compensation

As explained in the linear compensation technique, the ADC errors may not be equally distrib-

uted over the entire analog input range.

There are analog ranges in which there are positive errors and other ranges with negative er-

rors. Figure 19 shows the approximate error distribution curve. The actual values on the Y axis

depend on the device.

Figure 19. Error distribution

Thus, we can divide the ADC converted values into zones which have positive and negative

errors. To simplify the calculations we can use following zones for error correction.

+2.5

-2.5

LSB

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AN1711 Datasheet(PDF) 29 Page - STMicroelectronics