Datasheet

38.6.3.1 Performance with the Averaging Digital Feature
Averaging is a feature which increases the sample accuracy. ADC automatically computes an average
value of multiple consecutive conversions. The numbers of samples to be averaged is specified by the
Number-of-Samples-to-be-collected bit group in the Average Control register
(AVGCTRL.SAMPLENUM[3:0]) and the averaged output is available in the Result register (RESULT).
Table 38-13. Averaging Feature
Average
Number
Condition SNR(dB) SINAD(dB) SFDR(dB) ENOB(bits)
1 In differential mode, 1x gain,
VDDANA=3.0V, VREF=1.0V, 350kSps
at 25°C
66 65 72.8 10.5
8 67.6 65.8 75.1 10.62
32 69.7 67.1 75.3 10.85
128 70.4 67.5 75.5 10.91
38.6.3.2 Performance with the hardware offset and gain correction
Inherent gain and offset errors affect the absolute accuracy of the ADC. The offset error cancellation is
handled by the Offset Correction register (OFFSETCORR) and the gain error cancellation, by the Gain
Correction register (GAINCORR). The offset and gain correction value is subtracted from the converted
data before writing the Result register (RESULT).
Table 38-14. Offset and Gain Correction Feature
Gain Factor Conditions Offset Error
(mV)
Gain Error
(mV)
Total Unadjusted
Error (LSB)
0.5x In differential mode, 1x gain,
VDDANA=3.0V, VREF=1.0V,
350kSps at 25°C
0.25 1 2.4
1x 0.2 0.1 1.5
2x 0.15 -0.15 2.7
8x -0.05 0.05 3.2
16x 0.1 -0.05 6.1
38.6.3.3 Inputs and Sample and Hold Acquisition Times
The analog voltage source must be able to charge the sample and hold (S/H) capacitor in the ADC in
order to achieve maximum accuracy. Seen externally the ADC input consists of a resistor (
SAMPLE
) and a
capacitor (
SAMPLE
). In addition, the source resistance (
SOURCE
) must be taken into account when
calculating the required sample and hold time. The figure below shows the ADC input channel equivalent
circuit.
SAM D21 Family
Electrical Characteristics at 105°C
© 2018 Microchip Technology Inc.
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