143
8006K–AVR–10/10
ATtiny24/44/84
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.
16.11 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.
16.11.1
Single Ended Conversion
For single ended conversion, the result is
where V
IN is the voltage on the selected input pin and VREF the selected voltage reference (see
0x3FF represents the selected reference voltage minus one LSB. The result is presented in one-
sided form, from 0x3FF to 0x000.
16.11.2
Unipolar Differential Conversion
If differential channels and an unipolar input mode are used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference. The voltage of the positive pin must always be larger
than the voltage of the negative pin or otherwise the voltage difference is saturated to zero. The
result is presented in one-sided form, from 0x000 (0d) through 0x3FF (+1023d). The GAIN is
either 1x or 20x.
16.11.3
Bipolar Differential Conversion
If differential channels and a bipolar input mode are used, the result is
where VPOS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,
and VREF the selected voltage reference. The result is presented in two’s complement form, from
0x200 (-512d) through 0x1FF (+511d). The GAIN is either 1x or 20x. Note that if the user wants
ADC
VIN 1024
VREF
--------------------------
=
ADC
VPOS VNEG
–
() 1024
VREF
--------------------------------------------------------
GAIN
=
ADC
VPOS VNEG
–
() 512
VREF
-----------------------------------------------------
GAIN
=