Systematic Optimization of Phase Noise of Voltage-Controlled Oscillators for Millimeter-Wave Radar. (2017)

WANG, WEIHU. Systematic Optimization of Phase Noise of Voltage-Controlled Oscillators forMillimeter-Wave Radar.(Under the direction of Brian Floyd.)Silicon technology has advanced to the point that millimeter-wave transceiver systems operating up to 100 GHz can be integrated to realize sophisticated functionality at reduced consumer cost.These millimeter-wave radar and radio systems require a high-performance local oscillator (LO) solution to generate reference signals used within the receiver and transmitter.As a consequence, novel design techniques for voltage-controlled oscillators (VCOs) in the millimeter-wave frequency range are needed to achieve low phase noise, wide tuning range, and low energy consumption.Although integrated VCOs have been studied for decades, challenges also emerge as the operating frequency goes up, with the passive device quality (Q) factor and the transistor speed becoming two limiting factors that degrade performance.First, VCOs used in frequency-modulated continuous-wave (FMCW) radar applications require wide continuous tuning range and low phase noise simultaneously.These high-gain VCOs will typically have high phase noise, due to a high conversion from amplitude-modulated noise to phasemodulated noise arising in the VCO's tuning path and the bias circuitry.A transformer-coupled inductor-capacitor (LC) tank is introduced which can enable wide tuning-range and low phase noise simultaneously, suitable for both long-range and short-range FMCW radar sensors.To demonstrate the technique, a 20GHz VCO with wide continuous tuning range is incorporated in a W-band FMCW radar transceiver (TRX).The VCO satisfies both the phase noise requirement of long-range radar (LRR) and the tuning range requirement of short-range radar (SRR), effectively reducing the area and cost of an otherwise two VCO solution.Second, the active circuit affects phase noise through the additional noise being injected into the tank as well as the signal power of oscillation, whereas power efficiency of the active device is also crucial for certain applications.In this study, these problems are addressed using a newly proposed ring-type LC quadrature VCO (QVCO), which, when compared to a conventional Colpitts structure, has a smaller loading capacitance to the LC tank.To demonstrate the usefulness of this topology, a 20 GHz QVCO is fabricated in conjunction with a frequency quadrupler as a solution to obtain an LO signal at 80 GHz, suitable for W-band automotive radar systems or licensed E-band communication systems.Third, as suggested by Leeson's equation, the passive Q has a significant impact on phase noise.To handle the passive device Q factor, the loss mechanism and accurate modeling of monolithic inductors have been studied thoroughly in the literature; however, despite the accurate modeling, designers still often approach the optimization problem on a trial-and-error basis.Hence, it is of interest to study the impact of operating frequency on passive Q, thus clarifying the choice of the VCO operating frequency.In this work, a systematic study will be presented on the optimization and frequency response of resonator Q.Based on the result, it is made possible to predict the phase noise before actually designing the circuit, given the operating frequency, tuning range, and power requirement of the VCO.This then provides a method which system designers can use for deciding the best VCO frequency.To demonstrate the validity of this approach, VCOs are simulated and measured at 10 GHz, 20 GHz, and 40 GHz for comparison.As will be shown in this dissertation, the systematic optimization of millimeter-wave VCO