Browsing by Author "Namgoong, Won"
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Item A Digitally-Assisted Blocker Resilient RF Receiver for Wideband SAW-less Applications(2018-08) Babakrpur Nalousi, Esmail; 0000-0002-3462-3180 (Babakrpur Malousi, E); Namgoong, WonThe demand for integrated wideband surface acoustic wave (SAW)-less receivers that support various wireless communication bands stipulate stringent linearity requirements. Local oscillator (LO) harmonic interferers and out-of-band interferers are two significant sources of signal distortion in wideband SAW-less receivers. Harmonic mixing products and intermodulation products of these interferers, which can be orders of magnitude stronger than the desired signal, fold on the desired signal band, resulting in significant distortion. To improve resilience of such receivers to LO harmonic interferers, a digitally-assisted dual-path receiver with nonuniform LO phases is proposed which employs an adaptive digital equalizer to suppress distortion products. An adaptive minimum mean-squared error (MMSE) harmonic rejection equalizer is developed that minimizes the desired signal distortion in the mean-squared error sense in the presence of harmonic interferers and the correlated noise between the two paths. The proposed receiver performs robust harmonic rejection of any LO harmonic including 7th and 9th using only four uniformly spaced clocks with 25% duty cycle. Although intermodulation products are inherently different in nature from harmonic mixing products, it has been shown that concurrent suppression of both distortions using one MMSE equalizer is feasible in the presence of distinct nonlinear receive chains. A mathematical framework is derived for analyzing signal distortion in the presence of harmonic and out-of-band interferers. This framework models a K-path SAW-less M-phase receiver, which provides sufficient front-end observations to cancel the distortion products. The proposed receiver jointly accounts for distortion products as well as correlated noise of the two paths. Furthermore, the use of passive mixer-first receiver topology to sense signals at higher LO harmonics is proposed. The advantages of such a receiver include sensing of multiple bands concurrently and reduced tuning range requirements in the frequency synthesizer. The single and joint harmonic matching performance of a zero-IF M-phase mixer-first receiver is analyzed. It is shown that minimum possible return loss for joint matching occurs when the geometric mean of input impedances at the highest and lowest sensing bands equals the antenna impedance. The noise figure when sensing higher order LO harmonics is shown to result in only modest degradation, with the loss becoming even less with increasing number of LO phases.Item Efficient and Quality Assured Techniques for Analog Circuit Design Automation(2017-12) Bi, Zhaori; 0000-0002-7315-3150 (Bi, Z); Zhou, Dian; Nourani, Mehrdad; Namgoong, Won; Lee, HoiAutomating the designs of analog and mixed signal circuits is challenging because circuit designs are heuristics intensive and the performance evaluations are expensive. This dissertation addresses multiple strategies to enhance the quality and efficiency of the circuit design automation. With comparing various global optimization solvers such as Evolutionary Algorithm (EA), Simulated Annealing (SA) and Genetic Algorithms (GA), we introduce Random Region Covering (RRC) method as our global optimizer. RRC explores the landscape by initiating local optimization solvers with multiple random starting points. The optimization quality improves as the number of starting points increases. We propose Random Region Covering Theory (RRCT) theory to explain why this technique is efficient at searching for the global optimum. In addition to analyzing the efficiency of the RRC, the theory gives a probability-based estimation of the goodness of the optimization result. Quantifying the goodness of the current design has two advantages. First, we can estimate the improvement margin of the candidate design. In this case, we can avoid extra costs associated with over-optimizing a qualified design. Second, we can estimate the cost of achieving the design goal which provides a sound termination condition to the optimization flow. To enhance the efficiency, an optimization scheme should either speed up the circuit simulation or invoke the high-cost circuit simulator as little as possible. A common technique to improve circuit simulation efficiency is to replace the transistor level model with a behavior level model. However, the accuracy of equation-based or knowledge-based behavioral models is problem dependent. For new circuit topologies, these methods have to develop fitted mathematical models which are time consuming and difficult, particularly with respect to Process, Voltage and Temperature (PVT) variations. Instead of directly applying a numerical optimization algorithm to full transistor-level response surface, it is more efficient to apply the optimization to a surrogate model trained by an iteratively updated, high-fidelity simulation database. The accuracy of the surrogate model becomes the key to achieving high quality optimization results. This dissertation proposes a novel optimization scheme with combining the advantages of Gaussian process (GP) model with RRC optimizer. We perform experiments to compare the proposed technique with well-known Bayesian Optimization (BO) methods. The results proved the effectiveness of the proposed method. The DesignEasy software was developed to implement the above functions and to provide a general User Interface (UI) for circuit design automation.Item Timing Jitter Distribution and Power Spectral Density of a Second-Order Bang-Bang Digital PLL with Transport Delay Using Fokker-Planck Equations(IEEE-Inst Electrical Electronics Engineers Inc, 2018-12-18) Bondalapati, Pratheep; Namgoong, Won; 0000-0002-8864-8324 (Bondalapati, P); 0000-0003-3047-2888 (Namgoong, W); Bondalapati, Pratheep; Namgoong, WonIn this paper, a second-order bang-bang digital phase-locked loop (BBPLL) with dominant random walk phase noise and transport delay is analyzed using Fokker-Plank equations. Explicit closed-form expressions are derived for the timing error probability distribution function, jitter variance, and power spectral density (psd). For the type-II BBPLL considered in this paper, the timing error distribution is shown to be Laplacian and not Gaussian distributed as previously assumed, while the derived psd is Lorentzian, which is consistent with earlier works. The analytical solutions are valid as long as the continuous-time approximation of the BBPLL dynamics is accurate as is the case for typical operating loop bandwidths. The accuracy of the derived expressions is validated via simulation.