Datasheet

152
8197C–AVR–05/11
ATtiny261A/461A/861A
• Quantization Error: Due to the quantization of the input voltage into a finite number of codes,
a range of input voltages (1 LSB wide) will code to the same value. Always ± 0.5 LSB.
• Absolute Accuracy: The maximum deviation of an actual (unadjusted) transition compared to
an ideal transition for any code. This is the compound effect of offset, gain error, differential
error, non-linearity, and quantization error. Ideal value: ± 0.5 LSB.
15.11 ADC Conversion Result
After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
Result Registers (ADCL, ADCH). The form of the conversion result depends on the type of the
conversio as there are three types of conversions: single ended conversion, unipolar differential
conversion and bipolar differential conversion.
15.11.1 Single Ended Conversion
For single ended conversion, the result is
where V
IN
is the voltage on the selected input pin and V
REF
the selected voltage reference (see
Table 15-4 on page 156 and Table 15-5 on page 157). 0x000 represents analog ground, and
0x3FF represents the selected voltage reference minus one LSB. The result is presented in one-
sided form, from 0x3FF to 0x000.
15.11.2 Unipolar Differential Conversion
If differential channels and an unipolar input mode are used, the result is
where V
POS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and V
REF the selected voltage reference (see Table 15-4 on page 156 and Table 15-5 on page
157). The voltage on the positive pin must always be larger than the voltage on the negative pin
or otherwise the voltage difference is saturated to zero. The result is presented in one-sided
form, from 0x000 (0d) to 0x3FF (+1023d). The GAIN is either 1x, 8x, 20x or 32x.
15.11.3 Bipolar Differential Conversion
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode
can be selected by writting the BIN bit in the ADCSRB to one. In the bipolar input mode two-
sided voltage differences are allowed and thus the voltage on the negative input pin can also be
larger than the voltage on the positive input pin. If differential channels and a bipolar input mode
are used, the result is
ADC
V
IN
1024⋅
V
REF
--------------------------=
ADC
V
POS
V
NEG
–()1024⋅
V
REF
--------------------------------------------------------
GAIN⋅=