Datasheet

33.6.5 Differential and Single-Ended Conversions
The ADC has two conversion options: differential and single-ended:
• If the positive input may go below the negative input, the differential mode should be used in order
to get correct results.
• If the positive input is always positive, the single-ended conversion should be used in order to
have full 12-bit resolution in the conversion.
The negative input must be connected to ground. This ground could be the internal GND, IOGND or an
external ground connected to a pin. Refer to the Control B (CTRLB) register for selection details.
If the positive input may go below the negative input, creating some negative results, the differential mode
should be used in order to get correct results. The differential mode is enabled by setting DIFFMODE bit
in the Control B register (CTRLB.DIFFMODE). Both conversion types could be run in single mode or in
free-running mode. When the free-running mode is selected, an ADC input will continuously sample the
input and performs a new conversion. The INTFLAG.RESRDY bit will be set at the end of each
conversion.
Related Links
33.8.5 CTRLB
33.6.5.1 Conversion Timing
The following figure shows the ADC timing for one single conversion. A conversion starts after the
software or event start are synchronized with the GCLK_ADC clock. The input channel is sampled in the
first half CLK_ADC period.
Figure 33-3. ADC Timing for One Conversion in Differential Mode without Gain
1 2 3 4 5 6 7 8
CLK_ADC
START
SAMPLE
INT
Converting Bit
MSB 10 9 8 7 6 5 4 3 2 1 LSB
The sampling time can be increased by using the Sampling Time Length bit group in the Sampling Time
Control register (SAMPCTRL.SAMPLEN). As example, the next figure is showing the timing conversion.
SAM D21 Family
ADC – Analog-to-Digital Converter
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 897