ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 200

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

ADC Noise Canceler
Analog Input Circuitry
200
ATmega169/V
external voltage. If no external voltage is applied to the AREF pin, the user may switch
between AVCC and 1.1V as reference selection. The first ADC conversion result after
switching reference voltage source may be inaccurate, and the user is advised to dis-
card this result.
The ADC features a noise canceler that enables conversion during sleep mode to
reduce noise induced from the CPU core and other I/O peripherals. The noise canceler
can be used with ADC Noise Reduction and Idle mode. To make use of this feature, the
following procedure should be used:
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 entering such sleep modes to avoid excessive power consumption.
The analog input circuitry for single ended channels is illustrated in Figure 90. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that
pin, regardless of whether that channel is selected as input for the ADC. When the chan-
nel 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 impedance 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 recom-
mended 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
either 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 90. Analog Input Circuitry
1. Make sure that the ADC is enabled and is not busy converting. Single Con-
2. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a con-
3. If no other interrupts occur before the ADC conversion completes, the ADC
version mode must be selected and the ADC conversion complete interrupt
must be enabled.
version once the CPU has been halted.
interrupt will wake up the CPU and execute the ADC Conversion Complete
interrupt routine. If another interrupt wakes up the CPU before the ADC con-
version is complete, that interrupt will be executed, and an ADC Conversion
Complete interrupt request will be generated when the ADC conversion
completes. The CPU will remain in active mode until a new sleep command
is executed.
ADCn
I
IH
I
IL
1..100 kW
ADC
C
S/H
/2) should not be present for
= 14 pF
V
CC
/2
2514P–AVR–07/06