BACKGROUND:  Because of nonlinear effects, it is virtually impossible to generate useable submillimeter waves of a frequency greater than 190GHz using CMOS oscillators. In conventional oscillator circuits, which are nonlinear systems, increases in frequency are accompanied by a corresponding loss in gain or efficiency and an increase in noise.

INNOVATION:  The invention is the first submillimemter-wave source fabricated solely in CMOS technology. Four voltage-controlled oscillators (VCOs), each with a fundamental frequency of 81GHz, were fabricated in conventional CMOS technology. The output signal was linearly generated by superimposing the rectified phase-shifted outputs of the VCOs to generate an output waveform with an oscillation frequency that was four-times the fundamental frequency, or 324GHz.

POTENTIAL APPLICATIONS:  Submillimeter waves generated by CMOS oscillators could pave the way for a new generation of imaging devices such as high-resolution sensors on spacecraft. Also, highly integrated and lightweight imagers to see through fog or clothing fabric will have tremendous implications in improving travel safety. Furthermore, increasing the frequency also increases the available bandwidth for communication systems, leading to faster communication speeds.

ADVANTAGES

• The first CMOS oscillator to generate submillimeter waves
• Compatible with conventional CMOS fabrication
• Higher frequencies are possible by superimposing additional phases of fundamental tones
• The generated sub-millimeter wave signal can be phase-locked
• A very small active device area would occupy a small footprint on circuit boards
• A high DC-to-RF conversion efficiency
• Low phase noise

DEVELOPMENT-TO-DATE:  A CMOS VCO chip was fabricated and independently verified to output an oscillation frequency of 324GHz.

Reference: UCLA Case No. 2007-487