Energy Efficient Startup of Crystal Oscillators Using Stepwise Charging

Crystal oscillators can be started up quickly by using energy injection techniques. However, the generation of the injection waveform, as well as driving the large capacitive load formed by the crystal, costs a large amount of energy. This article applies the concept of stepwise charging to reduce the energy required to drive the crystal. The energy required to generate the injection waveform by self-timed injection is reduced by using a discrete-time dynamic-bias comparator which uses a simple offset calibration method. Furthermore, the bridge switch resistance is varied dynamically through self-timed control logic to alleviate the accuracy-speed tradeoff. A prototype was manufactured in a 65-nm (triple-well) CMOS technology, which was tested with various crystals ranging from 24 to 50 MHz, improving upon the state of the art in energy consumption.