AT90PWM2 datasheet(245/365 Pages) ATMEL

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4317K–AVR–03/2013

AT90PWM2/3/2B/3B

Figure 21-13. Differential Non-linearity (DNL)

•

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.

21.7

ADC Conversion Result

After the conversion is complete (ADIF is high), the conversion result can be found in the ADC

Result Registers (ADCL, ADCH).

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

Table 21-3 on page 247 and Table 21-4 on page 248). 0x000 represents analog ground, and

0x3FF represents the selected reference voltage.

If differential channels are used, the result is:

where V

POS is the voltage on the positive input pin, VNEG the voltage on the negative input pin,

GAIN the selected gain factor and V

REF the selected voltage reference. The result is presented

in two’s complement form, from 0x200 (-512d) through 0x1FF (+511d). Note that if the user

wants to perform a quick polarity check of the result, it is sufficient to read the MSB of the result

(ADC9 in ADCH). If the bit is one, the result is negative, and if this bit is zero, the result is posi-

tive. Figure 21-14 shows the decoding of the differential input range.

Table 82 shows the resulting output codes if the differential input channel pair (ADCn - ADCm) is

selected with a reference voltage of V

REF.

Output Code

0x3FF

0x000

VREF Input Voltage

DNL

1 LSB

ADC

1023



REF

--------------------------

ADC

POS

NEG

–

 GAIN 512



REF

------------------------------------------------------------------------

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