Low voltage surface transverse wave oscillators for the next generation CMOS technology

The design and performance of surface transverse wave (STW) based VCOs (VCSO) in the lower GHz frequency range, operating on supply and tuning voltages in the 1.2 to 3.3 V range, are presented. The VCSO outputs are switched between 0 V and the positive supply voltage U_S to provide safe CMOS-circuit switching while keeping the RF/DC efficiency to a maximum for low DC power consumption. This is achieved by operating the active oscillator circuit in one of the switched nonlinear classes that are known for their high power and efficiency, and low phase noise. The investigated 1.0 and 2.5 GHz VCSOs are varactor tuned feedback-loop oscillators stabilized with two-port STW resonators. Each VCSO has a DC coupled high-impedance switched output to drive the CMOS circuit directly, and an additional sinusoidal 50 Ω high-power output available for other low-noise system applications. Phase noise levels in the -103 to -115 dBc/Hz at 1 kHz carrier offset are achieved with a 1 GHz VCSO at an RF/DC efficiency in the 21 to 29% range. The 2.5 GHz prototypes demonstrate phase noise levels in the -97 to -102 dBc/Hz at 1 kHz carrier offset and efficiencies range between 8 and 15%.