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Open Access Publications from the University of California

Design Techniques in CMOS LC Quadrature Oscillators for Broadband Applications

  • Author(s): Bagheri, Mahdi
  • Advisor(s): Larson, Lawrence E
  • Buckwalter, Jim F
  • et al.

New standards are emerging every few months as wireless bands and services are proliferating across the world. End users of mobile headsets, wireless speakers, appliances controlled by internet, and many other devices want as many as possible new services and manufacturers have a hard time to keep up. Therefore, wireless radio solutions which can cover more bands and standards are in high demand. Multi-band multi mode radios by stacking up of multiple modules can be a choice to cover more bands in one system at a higher cost and larger area. Newer multi-band multi-mode radios integrate multiple radios into one chip and by reducing the packaging cost, sharing the peripheral components, and lowering the size, cover larger frequency range at lower cost. Software defined radios (SDRs) and cognitive radios (CRs) can address the increasing demand of users to have seamless connection at low service cost and support wide range of applications [24]. Ultra-wideband (UWB) radios also cover a wide spectrum supporting universal applications in different countries. The WiMedia UWB radio technology requires the frequency synthesizers to cover the 3.1 GHz to 10.6 GHz spectrum. Different communication systems take advantage of millimeter-wave phased arrays such as 60 GHz short-range communication and point-to-point communication at the E-band (71-76 and 81-86 GHz) and the W-band (75-110 GHz). All the mentioned radios need carrier frequency generators which are able to cover all the frequency bands of interest which is several GHz. Also, these frequency generators must be able to generate quadrature local oscillator signal (LO).

Quadrature signals are essential in modern transceivers which can be generated in different ways. Among different ways, quadrature oscillators show better performance. The LC-QOSCs show a superior phase noise performance with excellent quadrature accuracy. To practically use CMOS LC quadrature oscillators, the randomness of the quadrature phase of the QOSCs should be fixed. The random phase sequence in LC-QOSCs results in limited tuning range which might be even zero. The series coupled QOSCs proposed in here address the quadrature phase sequence ambiguity by guaranteeing oscillation in one mode. Furthermore we have proposed a novel idea where the S-QOSC quadrature mode can be selected, and since each mode has a different frequency, in this way a wider tuning range can be achieved from the QOSC which is essential in wide tuning range frequency synthesizers and is useful in multi-band radios, SDR, CR, and UWB radios.

Replacing the crystal oscillators (XTALs) which are the main reference frequency generators in transceivers has a high priority to reduce the overall cost and power consumption of different wireless systems. CMOS frequency generators mostly cannot compete with the accuracy and phase noise performance of XTALs and even with the aid of calibration cannot achieve descent frequency stability due to temperature variation as they are very sensitive to temperature.

The focus of this work is on wide tuning range oscillators applicable in broadband radios. This work presents a wide tuning range series coupled quadrature S-QOSCs which is able to oscillate in desired quadrature mode of oscillation and eliminate the randomness in the quadrature sequence. By selecting the mode, the proposed S-QOSC (Chapter 4) has a very wide tuning range which is the combination of tuning range of different modes. It has also been shown (Chapter 5) that the proposed S-QOSC can be designed to show two orders of magnitude less temperature sensitivity compared to other LC oscillators and can be implemented in a system to be calibrated to achieve the required frequency accuracy of various applications. In this work an LO-phase shifting approach based on ILO at frequency range of 71 to 86 GHz will be presented.

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