31 research outputs found
유전알고리즘 및 강화학습을 사용한 고속 회로 설계 자동화 프레임워크
Get PDF학위논문(석사) -- 서울대학교대학원 : 융합과학기술대학원 지능정보융합학과, 2022.2. 전동석.Although design automation is a key enabler of modern large-scale digital systems, automating the transistor-level circuit design process still remains a challenge. Some recent works suggest that deep learning algorithms could be adopted to find optimal transistor dimensions in relatively small circuitry such as analog amplifiers. However, those approaches are not capable of exploring different circuit structures to meet the given design constraints. In this work, we propose an automatic circuit design framework that can generate practical circuit structures from scratch as well as optimize the size of each transistor, considering performance and reliability. We employ the framework to design level shifter circuits, and the experimental results show that the framework produces novel level shifter circuit topologies and the automatically optimized designs achieve 2.8-5.3× lower PDP than prior arts designed by human experts.설계 자동화는 대규모 디지털 시스템을 가능하게 하는 핵심 요소이지만 트랜지스터 수준에서 회로 설계 프로세스를 자동화하는 것은 여전히 어려운 과제로 남아 있습니다. 최근 연구에서는 아날로그 앰프와 같은 비교적 작은 회로에서 최적의 성능을 보이는 트랜지스터 크기를 찾기 위해 deep learning 알고리즘을 활용할 수 있다고 말합니다. 그러나 이러한 접근 방식은 주어진 설계 constraint를 충족하는 다른 회로 구조 탐색에 적용하기 어렵습니다. 본 연구에서는 성능과 신뢰성을 고려하여 각 트랜지스터의 크기를 최적화할 뿐만 아니라 처음부터 실용적인 회로 구조를 생성할 수 있는 자동 회로 설계 framework를 제안합니다. 우리는 framework를 사용하여 level shifter 회로를 설계했으며 실험 결과는 프레임워크가 새로운 level shifter 회로 토폴로지를 생성하고 자동으로 최적화된 설계가 인간 전문가가 설계한 선행 기술보다 2.8-5.3배 더 낮은 PDP를 달성한다는 것을 보여줍니다.Abstract i
Contents ii
List of Tables iv
List of Figures v
List of Algorithms vi
1 Introduction 1
2 Related work 6
2.1 Genetic Algorithm 6
2.2 NeuroEvolution of Augmenting Topologies (NEAT) 7
2.3 Reinforcement Learning (RL) 10
2.4 DDPG, D4PG, and PPO 12
2.5 Level Shifter 14
3 Proposed circuit design framework 17
3.1 Topology Generator 17
3.2 Circuit Optimizer 25
4 Experiment Result 32
4.1 Level Shifter Design 32
4.2 Topology Generation 34
4.3 Circuit Optimization 36
4.4 Test Chip Fabrication 42
4.5 Applicability of Topology Generator 47
5 Conclusion 50
Abstract (In Korean) 57석
Dynamics of electrowetting: spreading dynamics and oscillation-induced droplet transport
No full textDoctorElectrowetting (EW) controls wettability of a drop on an insulator-coated electrode surface by applying DC or AC electrical voltages externally. EW has many advantages, such as fast and precise control of contact angle with a low driving voltage. Thus, EW has attracted considerable attention in both industry and academia, and many practical applications have been developed, including digital microfluidics, liquid lenses, micro switches, optical valves and mirrors, and reflective displays. These practical applications should require accurate, quick, and stable positioning of the contact line (CL), which has been one of the main challenges in EW research. In this study, the effects of drop size and viscosity on the DC EW-driven spreading characteristics of drops (e.g., response time, spreading pattern transition, and maximum velocity) in air are investigated both experimentally and theoretically. Both switching time (i.e., time to reach maximum wetted radius) and settling time (i.e., time to reach equilibrium radius) are found to be proportional to 1.5th power of the effective base radius. The effect of drop viscosity on drop spreading is investigated by observing spreading patterns with respect to applied voltage, and the critical viscosity where a spreading pattern changes from under- to over-damped response is obtained. By fitting the theoretical models to the experimental results, the friction coefficient is found to be strongly correlated to drop viscosity and be rarely influenced by applied voltage and drop size. In addition, EW-based devices have been frequently used in water/oil systems, because oil medium reduces contact angle hysteresis (CAH, i.e., difference between advancing and receding contact angles) and prevents drop evaporation. However, the viscosity of oil medium acts as a resistance force, thereby limiting the speed of transporting drops. The entrapment of the oil film between a drop and a solid surface also degrades the performance of EW-based devices in a water/oil system. To resolve these problems practically as well as to extend the aforementioned research academically, the effects of oil viscosity and drop size on the spreading behavior of a drop submerged in oil under various DC EW actuations are investigated. Settling time is found to be linearly proportional to the radius of the spherical drop and oil viscosity. The oil entrapment process and the instability of the entrapped oil film are also investigated by observing the bottom part of the spreading drops submerged in oil. The size of the oil drops generated by oil-film instability decreases as the applied voltage increases. However, it is rarely affected by oil viscosity. AC EW-driven drop oscillation method (or resonance oscillation) has been used in many practical applications, such as manipulation of cells and particles inside drops, measurement of surface degradation, and transporting (or detachment) of drops without any complicated electrical control. The resonance frequency of an oscillating drop is determined by its mass and surface tension, whereas drop viscosity damps its oscillation. However, most previous studies focused on exploring the oscillation of levitated drops. Here, the effects of drop viscosity on the oscillation dynamics of a sessile drop, such as resonance frequency and oscillation amplitude, are investigated based on both experiments and theoretical modeling. Drop viscosity rarely affects resonance frequency, but has strong influence on the oscillation amplitude and peak width of the resonance frequency. In addition, drop oscillation in the resonance mode is no longer observed, when drop viscosity is larger than the critical value, which increases with applied AC voltage. AC EW-induced drop oscillation method can be used to overcome CAH and mobilize small drops sticking on a solid surface. It enables drops to slide down a patterned electrode substrate with a small angle of inclination by applying low-frequency AC EW. The effects of AC frequency on the sliding velocity of drops are investigated. As a result, the sliding velocity is found to be maximized at resonance frequency. By using the unique dependence of drop motion on its volume and the applied AC frequency, a drop of a specific size is selectively slid on the inclined substrate. Similarly, a drop constrained between two non-parallel electrodes moves into a narrow gap via AC EW-driven drop oscillation. When AC frequency is below 100 Hz, drops move toward the narrow gap by repeated wetting and de-wetting. At frequencies higher than 10 kHz, however, drops move slowly in the same direction with weak oscillation and then suddenly penetrate the narrow gap. Both of the drop sliding on an inclined plate and the drop transporting between two non-parallel plates result from a combination effects of initially asymmetric contact angle of a drop, CAH, and interfacial oscillation driven by AC EW
Effect of size and viscosity of a droplet on spreading dynamics in electrowetting (전기습윤 시 액적의 크기와 점도가 퍼짐 거동에 미치는 영향)
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