Data Sheet
959
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
z VCM_IN > VREF/4 – 0.3*VDDANA - 0.1V
3. The ADC channels on pins PA08, PA09, PA10, PA11 are powered from the VDDIO power supply. The ADC perfor-
mance of these pins will not be the same as all the other ADC channels on pins powered from the VDDANA power
supply.
4. The gain accuracy represents the gain error expressed in percent. Gain accuracy (%) = (Gain Error in V x 100) /
(Vref/GAIN)
36.9.4.1 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).
36.9.4.2 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 36-28. Offset and Gain correction feature
Table 36-26. Averaging Feature, Device Variant A
Average
Number
Conditions SNR (dB) SINAD (dB) SFDR (dB)
ENOB
(bits)
1
In differential mode, 1x gain,
V
DDANA
=3.0V, V
REF
=1.0V, 350kSps at
25°C
66.0 65.0 72.8 9.75
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
Table 36-27. Averaging Feature, Device Variant B
Average
Number
Conditions SNR (dB) SINAD (dB) SFDR (dB)
ENOB
(bits)
1
In differential mode, 1x gain,
V
DDANA
=3.0V, V
REF
=1.0V, 350kSps at
25°C
66.0 65.0 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
Gain Factor Conditions
Offset Error
(mV)
Gain Error
(mV)
Total Unadjusted Error
(LSB)
0.5x
In differential mode, 1x gain,
V
DDANA
=3.0V, V
REF
=1.0V, 350kSps
at 25°C
0.25 1.0 2.4
1x 0.20 0.10 1.5
2x 0.15 -0.15 2.7
8x -0.05 0.05 3.2
16x 0.10 -0.05 6.1