MOS Oscillators with MultiDecade Tuning Range and Gigahertz Maximum Speed

This paper studies the realization of fully integrated MOS oscillators with multi-decade tuning range and top speed exceeding 1 GHz. This fast operation requires the use of submicrometer fabrication technology. In order to overcome the analog circuit limitations of the latter, the design of the oscillator is simplified and, in tum, highly redundant digital and analog control capability is provided. This strategy allows the implementation of certain oscillator features at the system level. A brief review of possible oscillator stnlctures is given and it is found that the best approach for highhyphen;speed, widehyphen;range specifications is the relaxation network of the constant current charge type. Circuit techniques are presented to increase the speed of the latter, based on active use of parasitics and simplified feedback networks. NMOS and CMOS implementations are discussed and compared. The design and perfonnance of an experimental submicrometer NMOS oscillator is presented. This device covers the 100hyphen;kHz to 1hyphen;GHz frequency range and has a robust structure.