Datasheet

577
Atmel | SMART SAM D20 [DATASHEET]
Atmel-42129K–SAM-D20_datasheet–06/2014
32.8.4.1 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).
Table 32-20. Averaging feature
32.8.4.2 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 32-21. Offset and Gain correction feature
32.8.4.3 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 ( ) and a capacitor ( ). In
addition, the source resistance ( ) must be taken into account when calculating the required sample and hold
time. Figure 32-3 shows the ADC input channel equivalent circuit.
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
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
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
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
R
SAMPLE
C
SAMPLE
R
SOURCE