Low-voltage, Crystal Controlled Comb Spectrum Oscillator for Injection Locked STW Based Clocks with Improved Stability

Abstract

This work presents the design and performance of a 100 MHz crystal controlled comb spectrum oscillator (CCCSO) which operates on 1.25V supply voltage according to the "step-up" converter principle and generates strong harmonics in the lower GHz range. The CCCSO is intended for improving the frequency stability and close-in phase noise of surface acoustic wave (SAW) and surface transverse wave (STW) oscillators by using an injection locking technique, thus making them as stable as a bulk acoustic wave (BAW) crystal oscillator. With -6 dBm of power at its 10-th harmonic, the CCCSO provides safe lock over a (-40 to +85) deg. C temperature range in a low-voltage 1 GHz STW oscillator with a loop power of 14 dBm, also operating according to the "step-up" converter principle. After injection locking, the short-term stability of the STW oscillator and its thermal stability improve by an order of magnitude as a result of BAW crystal stabilization in the CCCSO. The entire injection locked system is operated on 1.25V supply voltage, consumes 90 mA of DC current, generates 4 dBm of output power at 1 GHz and is expected to provide a thermal noise floor of -170 dBc/Hz