ATTINY24 Datasheet, PDF (140/238 Pages) ATMEL Corporation – 8-bit AVR Microcontroller with 2/4/8K Bytes In-System Programmable Flash

Figure 16-8. Analog Input Circuitry
ADCn
I_IH
I_IL
1..100 kohm
C_S/H = 14 pF
V_CC/2
Note: The capacitor in the figure depicts the total capacitance, including the sample/hold capacitor and
any stray or parasitic capacitance inside the device. The value given is worst case.
16.9
Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. When conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
• Keep analog signal paths as short as possible.
• Make sure analog tracks run over the analog ground plane.
• Keep analog tracks well away from high-speed switching digital tracks.
• If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress.
• Place bypass capacitors as close to V_CC and GND pins as possible.
Where high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode, as
described in Section 16.7 on page 139. This is especially the case when system clock frequency
is above 1 MHz, or when the ADC is used for reading the internal temperature sensor, as
described in Section 16.12 on page 144. A good system design with properly placed, external
bypass capacitors does reduce the need for using ADC Noise Reduction Mode
16.10 ADC Accuracy Definitions
An n-bit single-ended ADC converts a voltage linearly between GND and V_REF in 2ⁿ steps
(LSBs). The lowest code is read as 0, and the highest code is read as 2ⁿ-1.
Several parameters describe the deviation from the ideal behavior, as follows:
140 ATtiny24/44/84
8006J–AVR–08/10