Performance-Optimized Terahertz Signal Sources in Silicon

Title:  Performance-Optimized Terahertz Signal Sources in Silicon

Speaker:  Pei-Yuan Chiang

Date/Time:  Monday, June 2, 2014, 10:00AM

Location: Engineering Hall 2111

Committee Members:
Payam Heydari (Chair)
Michael Green
Ozdal Boyraz

Abstract: Terahertz (THz) and sub-millimeter wave band are known to provide unique applications in spectroscopy, imaging and high-data-rate wireless communication. An imaging system operating in this frequency region exhibits non-invasive and high-resolution characteristics due to the non-ionized and short-wavelength radiation waves, which makes it attracting for security surveillance. On the other hand, the THz wireless transceiver operating in the license-free spectrum is capable of achieving tens of gigabits-per-second by utilizing a simple modulation scheme. All the benefits mentioned above make THz a promising research topic. Towards realization of a high-performance THz system, one of the most challenging steps is to design a frequency synthesizer.

A voltage-controlled oscillator (VCO) is one of the important building blocks within a synthesizer. Due to the server performance degradation of varactors and transistors at high frequencies, new ways of designing VCOs need to be investigated. Here, two different ideas are proposed. First, an inductive-tuning mechanism with high quality-factor and wide tuning-range is introduced. This tuning technique is based on a variable inductor seen at the emitter terminal of a base-degenerated transistor. By adding a series RL at the base terminal, the variable inductor, exhibiting low loss and high tunability, improves the VCO output power and phase noise while achieving a wide tuning range. The second idea, double-stacked cross-coupled VCO, is to design a strong negative resistance cell to compensate for the server loss of the varactor at THz frequencies. By implementing a source-degenerated negative resistor of a conventional cross-coupled pair, the overall negative resistance is enhanced. It also reduces the parasitic capacitance, making it an attracting approach for THz applications.

Finally, a novel THz frequency synthesizer is proposed. A 300GHz phase-locked-based synthesizer incorporating a triple-push VCO with Colpitts-based active varactor (CAV) and a three-phase injection locked divider is introduced. The CAV is used to tune the oscillation frequency, enhance output power, and buffer the VCO’s fundamental signal. The divider’s locking-range is vastly increased attribute to the three-phase injection. This work demonstrates the highest-frequency synthesizer in silicon.