Fast startup crystal oscillator design

Generating the clock that is reliable, accurate and available as soon as the power is up is very essential for any application that requires the time base reference. For generating these clocks, crystal oscillator is a very good option. But usually the crystal oscillator circuit suffers from slow startup. Therefore, it is essential to improve the startup time with optimally controlled crystal drive such that crystal drive power rating is not compromised. We propose a method that discusses about increasing the negative resistance during startup using a startup circuit for fast start. Once the reliable startup is achieved, the startup circuit is disconnected for lower negative resistance in stable operation mode. In the 32768 Hz real time clock generating oscillator, the startup time can be improved from 330 ms to 220 ms using the conventional startup method. With the proposed method, lesser startup time of 160 ms is achieved.