Figure 41-5. ADC Timing for One Conversion with Offset Compensation, 12-bit
CLK_ADC
STATE
START
SAMPLING
MSB
10
9
8
7
6
5
4
3
2
1
LSB
INT
Offset Compensation
The impact of resolution on the sampling rate is seen in the next two figures, where free-running sampling
in 12-bit and 8-bit resolution are compared.
Figure 41-6. ADC Timing for Free Running in 12-bit Resolution
CLK_ADC
STATE
CONVERT
SAMPLING
MSB
10
9
8
7
6
5
4
3
2
1
LSB
INT
SAMPLING
MSB
9
8
10
7
6
LSB
Figure 41-7. ADC Timing for Free Running in 8-bit Resolution
CLK_ADC
STATE
CONVERT
SAMPLING
6
5
4
3
2
1
LSB
INT
LSB
MSB
SAMPLING
6
5
4
3
2
1
LSB
MSB
SAMPLING
MSB
The propagation delay of an ADC measurement is given by:
PropagationDelay = 1 + Resolution
�
ADC
Example.
In order to obtain 1MSPS in 12-bit resolution with a sampling time length of
four CLK_ADC cycles, f
CLK_ADC
must be 1MSPS * (4 + 12) = 16MHz. As the minimal
division factor of the prescaler is 2, GCLK_ADC must be 32MHz.
41.6.2.9. Accumulation
The result from multiple consecutive conversions can be accumulated. The number of samples to be
accumulated is specified by the Sample Number field in the Average Control register
(AVGCTRL.SAMPLENUM). When accumulating more than 16 samples, the result will be too large to
match the 16-bit RESULT register size. To avoid overflow, the result is right shifted automatically to fit
within the available register size. The number of automatic right shifts is specified in the table below.
Note:
To perform the accumulation of two or more samples, the Conversion Result Resolution field in
the Control C register (CTRLC.RESSEL) must be set.
Table 41-1. Accumulation
Number of
Accumulated
Samples
AVGCTRL.
SAMPLENUM
Number of
Automatic Right
Shifts
Final Result
Precision
Automatic
Division Factor
1
0x0
0
12 bits
0
2
0x1
0
13 bits
0
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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