ATMEGA168-20PI Atmel, ATMEGA168-20PI Datasheet - Page 250
![IC AVR MCU 16K 20MHZ 28DIP](/photos/7/21/72189/453-28-dip_sml.jpg)
ATMEGA168-20PI
Manufacturer Part Number
ATMEGA168-20PI
Description
IC AVR MCU 16K 20MHZ 28DIP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA168-20PI
Core Processor
AVR
Core Size
8-Bit
Speed
20MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
23
Program Memory Size
16KB (8K x 16)
Program Memory Type
FLASH
Eeprom Size
512 x 8
Ram Size
1K x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 6x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
28-DIP (0.300", 7.62mm)
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
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23.6.1
23.6.2
250
ATmega48/88/168
Analog Input Circuitry
Analog Noise Canceling Techniques
The analog input circuitry for single ended channels is illustrated in Figure 23-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-
less of whether that channel is selected as input for the ADC. When the channel is selected, the
source must drive the S/H capacitor through the series resistance (combined resistance in the
input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher imped-
ance is used, the sampling time will depend on how long time the source needs to charge the
S/H capacitor, with can vary widely. The user is recommended to only use low impedance
sources with slowly varying signals, since this minimizes the required charge transfer to the S/H
capacitor.
Signal components higher than the Nyquist frequency (f
kind of channels, to avoid distortion from unpredictable signal convolution. The user is advised
to remove high frequency components with a low-pass filter before applying the signals as
inputs to the ADC.
Figure 23-8. Analog Input Circuitry
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. If conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
a. Keep analog signal paths as short as possible. Make sure analog tracks run over the
b. The AV
c. Use the ADC noise canceler function to reduce induced noise from the CPU.
d. If any ADC [3..0] port pins are used as digital outputs, it is essential that these do not
analog ground plane, and keep them well away from high-speed switching digital
tracks.
an LC network as shown in
switch while a conversion is in progress. However, using the 2-wire Interface (ADC4
ADCn
CC
pin on the device should be connected to the digital V
I
IH
I
Figure
IL
23-9.
1..100 kOhm
ADC
/2) should not be present for either
C
S/H
= 14 pF
CC
supply voltage via
V
CC
/2
2545S–AVR–07/10
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