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SOFTWARE TECHNIQUES FOR COMPENSATING ST7 ADC ERRORS

3. Even when you connect a multimeter to the analog input signal, it may introduce noise if the

probes of the multimeter are not shielded. Hence, they act like antennae. The results vary

by several (6 to 7) LSBs. The average value is always near to the center of the variations.

Figure 4. Illustration of Averaging technique

Comments

1. Averaging is the most popular technique because it requires only a little extra RAM space.

2. The disadvantage is, values affected by noise and the least occurring values (outliers) af-

fect the average.

2.2 AVERAGING BY QUEUE

This technique is Averaging of a LIFO queue (Last-in, first-out). The queue is maintained by

using an array to fill the ADC results. To do this:

– Maintain a variable which contains an index for array.

– After every new conversion, overwrite the converted value at the index and then take the

average and increment the index.

– Once the index reaches the end of array, reset the index to the start of array.

Thus, for every conversion you fill the queue and overwrite the old values with the new values.

This technique is useful when the application cannot wait for the required number of conver-

sions because the conversion time is too long. The time required to calculate the average

should be less than the time required to make the total number of conversions.

This technique can be used for slowly varying ADC signals. for example, battery monitoring.

Maximum

Converted

Value

Minimum

Converted

Value

Average

Value

Difference

(Max - Min)

AN1711 데이터시트(PDF) 11 Page - STMicroelectronics