5.9 A 24MHz crystal oscillator with robust fast start-up using dithered injection

Wireless nodes in Internet-of-Everything (IoE) applications achieve low power consumption by operating the radio at very low duty cycles. The wireless node spends most of its time in sleep, waking only occasionally to transmit or receive data. For some standards, such as Bluetooth Low Energy (BLE), the data or advertising packet length can be less than the time it takes the crystal oscillator, which is used as the reference clock for the radio's PLL, to turn on. Figure 5.9.1 shows a simplified power profile for a node with a typical BLE advertising packet length. A significant fraction of energy used for each RX/TX burst is used to turn on the oscillator. For applications where average power is not dominated by sleep power, the crystal oscillator start-up time can be a large contributor to average power consumption.