Meaning
Electronic circuit blocks that generate a periodic clock signal using a combination of resistors and capacitors provide a low-cost, low-power timing reference for integrated circuits. An rc oscillator is typically integrated directly onto the silicon of microcontrollers and wireless system-on-chips to eliminate the need for external timing components. This integration reduces both the physical size and the bill of materials of the completed board assembly.
Accuracy and Drift
On-chip timing circuits are highly sensitive to variations in operating temperature and supply voltage. Unlike quartz crystals, an rc oscillator can experience significant frequency drift over time, often deviating by several percentage points from its nominal frequency. This drift can cause communication failures in time-sensitive wireless protocols if the oscillator is not calibrated periodically.
To address this issue, modern wireless chips include auto-calibration circuits that align the oscillator to a high-precision reference during active states.
Power Advantage
The primary benefit of this clock source is its exceptionally low power consumption and rapid start-up time. An rc oscillator can start oscillating in a fraction of a microsecond, whereas crystal oscillators often require several milliseconds to stabilize. This fast start-up allows the microcontroller to wake up, perform a quick task and return to sleep almost instantly, maximizing the energy savings in battery-powered devices.
This rapid transition is a key factor in achieving multi-year lifetimes.
System Limit
Because of their low frequency stability, these oscillators cannot be used as the primary carrier reference for RF synthesizers. They are instead restricted to sleep timing and watchdog functions.
