Evaluating Internal RC Oscillator Drift during Deep Power Down
Evaluating internal RC drift requires mapping temperature and voltage sags to expanded radio receive windows that drain battery reserves.
RC Relaxation Oscillator
Meaning
Electronic circuits that generate a periodic signal by repeatedly charging and discharging a capacitor through a resistor provide a simple clock source for timing non-critical system tasks. The integration of an RC relaxation oscillator on a silicon die offers a low-cost, low-power timing solution that does not require external components. The frequency of the generated signal is determined by the values of the internal resistor and capacitor.
Circuit Architecture
The oscillator consists of a comparator, a capacitor, a resistor, and a switch that discharges the capacitor when it reaches a reference voltage. This simple design consumes very little silicon area, which makes it highly cost-effective for microcontrollers.
Frequency Tolerance
The accuracy of the output frequency is lower than that of crystal-based oscillators and is highly sensitive to temperature and voltage changes. These variations limit the use of the circuit to functions that do not require precise timing, such as watchdog timers and low-power sleep state transitions.
Power Efficiency
The low current consumption of the circuit is its primary advantage for battery-powered applications. When the microcontroller enters a deep sleep state, this oscillator can remain active to keep track of time while the rest of the chip is powered down. This capability allows the system to wake up at regular intervals with minimal impact on the total energy budget.
Designers can optimize this sleep-wake cycle to extend the operating life of the device.