Biography
Enrollment Date: 2012
Graduation Date：2015
Degree：M.S.
Defense Date：2015.06.03
Advisors：Baoyong Chi
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research on Key Techniques of CMOS Mm-Wave VCO / DCO
Abstract:
As the demands for wireless communication becoming higher and higher, circuits working in millimeter wave have caused great attention in the world of wireless technology. Compared with the low-frequency band, millimeter wave has the advantage of offering broad bandwidth capable of supporting Multi-Gb/s data rate and small area. Monolithic microwave integrated circuit can help meet the unprecedented growth of broadband communication system (59-64 GHz ISM band broadband wireless local area network) and the need for 76-77 GHz automatic cruise control system as well as the 77-79 GHz millimeter automatic collision avoidance system. Among various mm-wave circuit blocks, the oscillator draws special attention since mm-wave signal sources are demanded in almost all mm-wave electrical systems. The heavy lossy silicon-substrate and metal layers in CMOS result in low quality-factor (Q) passive components which limits the mm-wave circuit performance. However, with the scaling CMOS technology and innovative circuit techniques proposed in the literatures, it becomes practical to implement competitive mm-wave circuits in advanced deep-submicron CMOS process. All the circuits implemented in this thesis are fabricated in 65 nm CMOS process. Two different kinds of frequency oscillators are researched in this thesis, A 40 GHz cross-coupled differential voltage controlled oscillator (VCO) is presented for a 60 GHz wireless transceiver. To shorten the gap between the simulated and measured results in millimeter wave circuits, the inductor and its extension metal line are simulated with 3D electromagnetic simulator. Thick gate varactor is utilized to widen the frequency tuning range. The VCO chip has been implemented in 65nm CMOS, and the measured results show that the chip achieves a tuning range of 12.2%, from 38.4 GHz to 43.4 GHz, which satisfies the frequency requirements of the 60GHz wireless transceiver with two stage down-conversion supporting IEEE 802.11ad. Digital control artificial dielectric (DiCAD) structure is proposed to realize the fine frequency tuning in the digitally-controlled oscillator (DCO). The DiCAD digitally controls the permittivity by placing the periodic metal strips and CMOS switches underneath the differential transmission lines or inductors and enables high quality factor, fine frequency resolution, compact layout and robustness over process variations compared with the traditional analog frequency tuning approach. With the proposed approach, an 80~83 GHz DCO has been implemented in 65nm CMOS and the measured results show that the DCO has achieved a tuning range of 3 GHz. In the third part, to the problems of L-DCO designed in the second part, we redesign a DCO based a transformer. The fine tuning part of this T-DCO is formed by a weakly coupled transformer with a secondary coil with tunable capacitor array. It achieved a frequency resolution of 3.5MHz. Better frequency resolution can be achieved by changing the structure of the capacitor array. Besides, CLASS-C T-DCO can achieve a comparable phase noise with smaller power consumption.