attiny167-esxz ATMEL Corporation, attiny167-esxz Datasheet - Page 190

• Manufacturer Part Number: attiny167-esxz
• Description: 8-bit Avr 8-bit Microcontroller Microcontroller With 16k Bytes In-system Programmable Flash And Lin Controller
• Manufacturer: ATMEL Corporation

17.7.1
17.7.2
17.7.3
190
ATtiny167
Analog Input Circuitry
Analog Noise Canceling Techniques
ADC Accuracy Definitions
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle
mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before enter-
ing such sleep modes to avoid excessive power consumption.
The analog input circuitry for single ended channels is illustrated in Figure 17-8. 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 impedant 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
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 17-8. 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:
An n-bit single-ended ADC converts a voltage linearly between GND and V
(LSBs). The lowest code is read as 0, and the highest code is read as 2
Several parameters describe the deviation from the ideal behavior:
a. Keep analog signal paths as short as possible. Make sure analog tracks run over the
b. Use the ADC noise canceler function to reduce induced noise from the CPU.
c. If any port pins are used as digital outputs, it is essential that these do not switch
generated when the ADC conversion completes. The CPU will remain in active mode
until a new sleep command is executed.
analog ground plane, and keep them well away from high-speed switching digital
tracks.
while a conversion is in progress.
ADCn
I
IH
I
IL
1..100 kO
ADC
C
/2) should not be present to avoid
S/H
= 14 pF
V
CC
n
/2
-1.
REF
7728A–AUTO–07/08
in 2
n
steps