Browsing by Subject "Phased Array"
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Item Circuit Design Techniques For Wideband Phased Arrays(2015-06) Kalia, SachinThis dissertation focuses on beam steering in wideband phased arrays and phase noise modeling in injection locked oscillators. Two different solutions, one in frequency and one in time, have been proposed to minimize beam squinting in phased arrays. Additionally, a differential current reuse frequency doubler for area and power savings has been proposed. Silicon measurement results are provided for the frequency domain solution (IBM 65nm RF CMOS), injection locked oscillator model verification (IBM 130nm RF-CMOS) and frequency doubler (IBM 65nm RF CMOS), while post extraction simulation results are provided for the time domain phased array solution (the chip is currently under fabrication, TSMC 65nm RF CMOS). In the frequency domain solution, a 4-point passive analog FFT based frequency tunable filter is used to channelize an incoming wideband signal into multiple narrowband signals, which are then processed through independent phase shifters. A two channel prototype has been developed at 8GHz RF frequency. Three discrete phase shifts (0 & +/- 90 degrees) are implemented through differential I-Q swapping with appropriate polarity. A minimum null-depth of 19dB while a maximum null-depth of 27dB is measured. In the time domain solution, a discrete time approach is undertaken with signals getting sampled in order of their arrival times. A two-channel prototype for a 2GHz instantaneous RF bandwidth (7GHz-9GHz) has been designed. A QVCO generates quadrature LO signals at 8GHz which are phase shifted through a 5-bit (2 extra bits from differential I-Q swapping with appropriate polarity) cartesian combiner. Baseband sampling clocks are generated from phase shifted LOs through a CMOS divide by 4 with independent resets. The design achieves an average time delay of 4.53ps with 31.5mW of power consumption (per channel, buffers excluded). An injection locked oscillator has been analyzed in s-domain using Paciorek's time domain transient equations. The simplified analysis leads to a phase noise model identical to that of a type-I PLL. The model is equally applicable to injection locked dividers and multipliers and has been extended to cover all injection locking scenarios. The model has been verified against a discrete 57MHz Colpitt's ILO, a 6.5GHz ILFD and a 24GHz ILFM with excellent matching between the model and measurements. Additionally, a differential current reuse frequency doubler, for frequency outputs between 7GHz to 14GHz, design has been developed to reduce passive area and dc power dissipation. A 3-bit capacitive tuning along with a tail current source is used to better conversion efficiency. The doubler shows FOM$_{T}$ values between 191dBc/Hz to 209dBc/Hz when driven by a 0.7GHz to 5.8GHz wide tuning VCO with a phase noise that ranges from -114dBc/Hz to -112dBc/Hz over the same bandwidth.Item Refocusing of Dual-mode ultrasound arrays for optimal therapeutic gain.(2012-04) Ballard, John RobertDual mode ultrasound arrays (DMUA) have recently been introduced in the field of image-guided noninvasive surgery using high intensity focused ultrasound (HIFU). The goal of this dissertation is to investigate the use of DMUAs for transthoracic targeting of abdominal tumors. DMUAs are capable of operating in both imaging and therapy modes using the same array transducers. The inherent registration between these coordinate systems allows for the use of image feedback in refocusing the DMUA at target point(s) while avoiding critical structures in the path of the HIFU beam. In the #12;rst part of this dissertation, we propose an image-based refocusing algorithm which minimizes the power deposition over critical structures while maintaining or improving the power deposition at the focal location(s) by taking advantage of the available acoustical window. This is of particular importance when targeting abdominal tumors located in the liver or kidneys that are partially obstructed by the rib cage. An optimal weighted minimum-norm least-squares solution is shown to achieve the goal of maintaining desired power level(s) at the target point(s) while minimizing exposure to the ribs. Measurements and simulation results show that the optimal solution channels the ultrasound energy to the target through the intercostals, thus avoiding the ribs. One possible limitation of this approach is the creation of a virtual array in the rib plane, which could result in unacceptably high grating lobes in the target plane. The second part of this dissertation explores the use of a multiple-frequency optimal synthesis approach to mitigate the grating-lobe problem. In addition to the use of simulation and basic measurements in verification, the thesis research includes an extensive investigation of the basic characteristics of HIFU-induced lesions using both single-frequency and multiple-frequency synthesis approaches. Lesion formation experiments using these approaches were performed both in vitro and in vivo using small-animal models. In addition, the synergistic effects of the use of multiple frequency excitation, including enhancement of the thermal rate due to cavitation and increased harmonic generation are discussed.