Hybrid on-chip clocking for sensor nodes

On-chip clock generation is an attractive alternative to external quartz oscillators for low-power sensing systems. LC and ring oscillators typically use less power, and can start and stop much faster than traditional quartz oscillators, allowing systems to spend more time in low-power sleep states. A hybrid on-chip clocking scheme is evaluated in which a ring oscillator is used as the reference clock for digital processing, and an LC oscillator is used when a more stable, accurate reference is needed for digital communication. Simulations show that the fast wakeup capabilities of the hybrid clock system lead to as much as 80% reduced power in interrupt-driven applications compared to a system using a crystal reference clock source. The on-chip clock generators of the WIMS series of microsystems are described to demonstrate the concept of the hybrid clock scheme.