Datasheet

943
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181C–SAM-D21_Datasheet–07/2014
(GAINCORR). The offset and gain correction value is subtracted from the converted data before writing the Result
register (RESULT).
Table 36-24. Offset and Gain correction feature
36.9.4.3 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 36-3 shows the ADC input channel equivalent circuit.
Figure 36-3. ADC Input
To achieve n bits of accuracy, the capacitor must be charged at least to a voltage of
The minimum sampling time for a given can be found using this formula:
for a 12 bits accuracy:
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
R
SOURCE
R
SAMPLE
Analog Input
AINx
C
SAMPLE
V
IN
VDDANA/2
C
SAMPLE
V
CSAMPLE
V≥
IN
12
n 1+()–
–()×
t
SAMPLEHOLD
R
SOURCE
t
SAMPLEHOLD
R
SAMPLE
R+
SOURCE
()C
SAMPLE
()× n 1+() 2()ln××≥
t
SAMPLEHOLD
R
SAMPLE
R+
SOURCE
()C
SAMPLE
()× 9.02×≥