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AVR® ADC Noise Reduction Mode

Last modified by Microchip on 2023/11/09 09:02

AVR® devices have an Analog to Digital Converter (ADC) Noise Reduction mode, that stops the CPU and all I/O modules except asynchronous timer, PTC, and ADC, to minimize switching noise during ADC conversions. It's used when a high-resolution ADC measurement is required. ADC measurements are then implemented when the core is put to sleep.

Entering/Exiting ADC Noise Reduction

The SLEEP instruction makes the MCU enter ADC Noise Reduction mode, stopping the CPU but allowing the ADC, the external interrupts, the two-wire serial Interface address watch, Timer1, and the Watchdog to continue operating (if enabled). This sleep mode basically halts clkI/O, clkCPU, and clkFLASH, while allowing the other clocks to run. This improves the noise environment for the ADC, enabling higher-resolution measurements. If the ADC is enabled, a conversion starts automatically when this mode is entered.

ADC Noise Reduction

Apart from the ADC Conversion Complete interrupt, only these events can wake up the MCU from ADC Noise Reduction mode:

  • External Reset
  • Watchdog System Reset
  • Watchdog Interrupt
  • Brown-out Reset
  • Two-wire Serial Interface address match
  • Timer/Counter interrupt
  • SPM/EEPROM ready interrupt
  • External level interrupt on INT
  • Pin change interrupt

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Note: Timer/Counter only keeps running in Asynchronous mode.

Additional Information