User Manual

252
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
8271E–AVR–07/2012
Figure 24-13. 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.
24.7 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 V
REF
the selected voltage reference (see Table 24-3 on page
254 and Table 24-4 on page 255). 0x000 represents analog ground, and 0x3FF represents the selected reference
voltage minus one LSB.
24.8 Temperature Measurement
The temperature measurement is based on an on-chip temperature sensor that is coupled to a single ended ADC8
channel. Selecting the ADC8 channel by writing the MUX3...0 bits in ADMUX register to "1000" enables the tem-
perature sensor. The internal 1.1V voltage reference must also be selected for the ADC voltage reference source
in the temperature sensor measurement. When the temperature sensor is enabled, the ADC converter can be
used in single conversion mode to measure the voltage over the temperature sensor.
The measured voltage has a linear relationship to the temperature as described in Table 24-2. The voltage sensi-
tivity is approximately 1 mV/°C and the accuracy of the temperature measurement is +/- 10°C.
The values described in Table 24-2 are typical values. However, due to the process variation the temperature sen-
sor output voltage varies from one chip to another. To be capable of achieving more accurate results the
Output Code
0x3FF
0x000
0
V
REF
Input Voltage
DNL
1 LSB
ADC
V
IN
1024
V
REF
--------------------------=
Table 24-2. Temperature vs. Sensor Output Voltage (Typical Case)
Temperature / C-45C+25C+85C
Voltage / mV 242mV 314mV 380mV