GCN-RL Circuit Designer: Transferable Transistor Sizing with Graph Neural Networks and Reinforcement Learning

Automatic transistor sizing is a challenging problem in circuit design due to the large design space, complex performance trade-offs, and fast technological advancements. Although there has been plenty of work on transistor sizing targeting on one circuit, limited research has been done on transferring the knowledge from one circuit to another to reduce the re-design overhead. In this paper, we present GCN-RL Circuit Designer, leveraging reinforcement learning (RL) to transfer the knowledge between different technology nodes and topologies. Moreover, inspired by the simple fact that circuit is a graph, we learn on the circuit topology representation with graph convolutional neural networks (GCN). The GCN-RL agent extracts features of the topology graph whose vertices are transistors, edges are wires. Our learning-based optimization consistently achieves the highest Figures of Merit (FoM) on four different circuits compared with conventional black-box optimization methods (Bayesian Optimization, Evolutionary Algorithms), random search, and human expert designs. Experiments on transfer learning between five technology nodes and two circuit topologies demonstrate that RL with transfer learning can achieve much higher FoMs than methods without knowledge transfer. Our transferable optimization method makes transistor sizing and design porting more effective and efficient.Comment: Accepted to the 57th Design Automation Conference (DAC 2020); 6 pages, 8 figure

Post-Layout Simulation Driven Analog Circuit Sizing

Post-layout simulation provides accurate guidance for analog circuit design, but post-layout performance is hard to be directly optimized at early design stages. Prior work on analog circuit sizing often utilizes pre-layout simulation results as the optimization objective. In this work, we propose a post-layout-simulation-driven (post-simulation-driven for short) analog circuit sizing framework that directly optimizes the post-layout simulation performance. The framework integrates automated layout generation into the optimization loop of transistor sizing and leverages a coupled Bayesian optimization algorithm to search for the best post-simulation performance. Experimental results demonstrate that our framework can achieve over 20% better post-layout performance in competitive time than manual design and the method that only considers pre-layout optimization

A modelling tool for engine and exhaust aftertreatment performance analysis in altitude operation

[EN] New regulation standards on engine pollutant emissions are widening the engine operating conditions subjected to type approval tests as a way to prevent from the gap between regulated and real-driving emissions. In this regard, ambient temperature and driving altitude are new boundaries to be considered. Although the basis of the impact of these variables has been studied concerning the engine performance, new challenges appear to meet the emission limits and the aftertreatment conversion efficiency. In this work, a gas dynamic modelling tool is approached to explore the maximisation of the engine torque when operating at high altitude in a wide range of ambient temperatures. Particular focus is put on the modelling of the combustion, the turbocharger and the exhaust aftertreatment system. Starting from a sea-level calibration, the proposed methodology accounts for mechanical criteria as well as the impact on the engine raw emissions and exhaust flow properties to define new combustion settings for altitude operation. Next, these boundaries are applied to the exhaust aftertreatment system to analyse the impact on the catalyst conversion efficiency and the particulate filter performance concerning pressure drop and filtration efficiency.This research has been partially supported by FEDER and the Government of Spain through project TRA2016-79185-R. Additionally, the Ph.D. student Bárbara Diesel has been funded by a grant from the Government of Generalitat Valenciana with reference ACIF/2018/109.Serrano, J.; Piqueras, P.; Sanchis-Pacheco, EJ.; Barbara-Diesel, C. (2019). A modelling tool for engine and exhaust aftertreatment performance analysis in altitude operation. Results in Engineering. 4:1-11. https://doi.org/10.1016/j.rineng.2019.100054S1114Dardiotis, C., Martini, G., Marotta, A., & Manfredi, U. (2013). Low-temperature cold-start gaseous emissions of late technology passenger cars. Applied Energy, 111, 468-478. doi:10.1016/j.apenergy.2013.04.093Ko, J., Jin, D., Jang, W., Myung, C.-L., Kwon, S., & Park, S. (2017). Comparative investigation of NOx emission characteristics from a Euro 6-compliant diesel passenger car over the NEDC and WLTC at various ambient temperatures. Applied Energy, 187, 652-662. doi:10.1016/j.apenergy.2016.11.105Cédric, L., Goriaux, M., Tassel, P., Perret, P., André, M., & Liu, Y. (2016). Impact of Aftertreatment Device and Driving Conditions on Black Carbon, Ultrafine Particle and NOx Emissions for Euro 5 Diesel and Gasoline Vehicles. Transportation Research Procedia, 14, 3079-3088. doi:10.1016/j.trpro.2016.05.454Hooftman, N., Messagie, M., Van Mierlo, J., & Coosemans, T. (2018). A review of the European passenger car regulations – Real driving emissions vs local air quality. Renewable and Sustainable Energy Reviews, 86, 1-21. doi:10.1016/j.rser.2018.01.012Serrano, J., Piqueras, P., Abbad, A., Tabet, R., Bender, S., & Gómez, J. (2019). Impact on Reduction of Pollutant Emissions from Passenger Cars when Replacing Euro 4 with Euro 6d Diesel Engines Considering the Altitude Influence. Energies, 12(7), 1278. doi:10.3390/en12071278Luján, J. M., Climent, H., García-Cuevas, L. M., & Moratal, A. (2018). Pollutant emissions and diesel oxidation catalyst performance at low ambient temperatures in transient load conditions. Applied Thermal Engineering, 129, 1527-1537. doi:10.1016/j.applthermaleng.2017.10.138Piqueras, P., García, A., Monsalve-Serrano, J., & Ruiz, M. J. (2019). Performance of a diesel oxidation catalyst under diesel-gasoline reactivity controlled compression ignition combustion conditions. Energy Conversion and Management, 196, 18-31. doi:10.1016/j.enconman.2019.05.111Faria, M. V., Varella, R. A., Duarte, G. O., Farias, T. L., & Baptista, P. C. (2018). Engine cold start analysis using naturalistic driving data: City level impacts on local pollutants emissions and energy consumption. Science of The Total Environment, 630, 544-559. doi:10.1016/j.scitotenv.2018.02.232Weber, C., Sundvor, I., & Figenbaum, E. (2019). Comparison of regulated emission factors of Euro 6 LDV in Nordic temperatures and cold start conditions: Diesel- and gasoline direct-injection. Atmospheric Environment, 206, 208-217. doi:10.1016/j.atmosenv.2019.02.031Ko, J., Myung, C.-L., & Park, S. (2019). Impacts of ambient temperature, DPF regeneration, and traffic congestion on NOx emissions from a Euro 6-compliant diesel vehicle equipped with an LNT under real-world driving conditions. Atmospheric Environment, 200, 1-14. doi:10.1016/j.atmosenv.2018.11.029Bermúdez, V., Serrano, J. R., Piqueras, P., Gómez, J., & Bender, S. (2017). Analysis of the role of altitude on diesel engine performance and emissions using an atmosphere simulator. International Journal of Engine Research, 18(1-2), 105-117. doi:10.1177/1468087416679569Ramos, Á., García-Contreras, R., & Armas, O. (2016). Performance, combustion timing and emissions from a light duty vehicle at different altitudes fueled with animal fat biodiesel, GTL and diesel fuels. Applied Energy, 182, 507-517. doi:10.1016/j.apenergy.2016.08.159Yu, L., Ge, Y., Tan, J., He, C., Wang, X., Liu, H., … Wang, X. (2014). Experimental investigation of the impact of biodiesel on the combustion and emission characteristics of a heavy duty diesel engine at various altitudes. Fuel, 115, 220-226. doi:10.1016/j.fuel.2013.06.056Wang, H., Ge, Y., Hao, L., Xu, X., Tan, J., Li, J., … Yang, R. (2018). The real driving emission characteristics of light-duty diesel vehicle at various altitudes. Atmospheric Environment, 191, 126-131. doi:10.1016/j.atmosenv.2018.07.060Hamedi, M. R., Doustdar, O., Tsolakis, A., & Hartland, J. (2019). Thermal energy storage system for efficient diesel exhaust aftertreatment at low temperatures. Applied Energy, 235, 874-887. doi:10.1016/j.apenergy.2018.11.008Luján, J. M., Serrano, J. R., Piqueras, P., & Diesel, B. (2019). Turbine and exhaust ports thermal insulation impact on the engine efficiency and aftertreatment inlet temperature. Applied Energy, 240, 409-423. doi:10.1016/j.apenergy.2019.02.043Sujesh, G., & Ramesh, S. (2018). Modeling and control of diesel engines: A systematic review. Alexandria Engineering Journal, 57(4), 4033-4048. doi:10.1016/j.aej.2018.02.011Galindo, J., Serrano, J. R., Arnau, F. J., & Piqueras, P. (2009). Description of a Semi-Independent Time Discretization Methodology for a One-Dimensional Gas Dynamics Model. Journal of Engineering for Gas Turbines and Power, 131(3). doi:10.1115/1.2983015Serrano, J. R., Olmeda, P., Arnau, F. J., Dombrovsky, A., & Smith, L. (2014). Analysis and Methodology to Characterize Heat Transfer Phenomena in Automotive Turbochargers. Journal of Engineering for Gas Turbines and Power, 137(2). doi:10.1115/1.4028261Serrano, J. R., Olmeda, P., Arnau, F. J., Dombrovsky, A., & Smith, L. (2015). Turbocharger heat transfer and mechanical losses influence in predicting engines performance by using one-dimensional simulation codes. Energy, 86, 204-218. doi:10.1016/j.energy.2015.03.130Serrano, J. R., Olmeda, P., Páez, A., & Vidal, F. (2010). An experimental procedure to determine heat transfer properties of turbochargers. Measurement Science and Technology, 21(3), 035109. doi:10.1088/0957-0233/21/3/035109Torregrosa, A. J., Serrano, J. R., Arnau, F. J., & Piqueras, P. (2011). A fluid dynamic model for unsteady compressible flow in wall-flow diesel particulate filters. Energy, 36(1), 671-684. doi:10.1016/j.energy.2010.09.047Galindo, J., Serrano, J. R., Piqueras, P., & García-Afonso, Ó. (2012). Heat transfer modelling in honeycomb wall-flow diesel particulate filters. Energy, 43(1), 201-213. doi:10.1016/j.energy.2012.04.044Macián, V., Serrano, J. R., Piqueras, P., & Sanchis, E. J. (2019). Internal pore diffusion and adsorption impact on the soot oxidation in wall-flow particulate filters. Energy, 179, 407-421. doi:10.1016/j.energy.2019.04.200Serrano, J. R., Climent, H., Piqueras, P., & Angiolini, E. (2016). Filtration modelling in wall-flow particulate filters of low soot penetration thickness. Energy, 112, 883-898. doi:10.1016/j.energy.2016.06.121Lee, K. W., & Gieseke, J. A. (1979). Collection of aerosol particles by packed beds. Environmental Science & Technology, 13(4), 466-470. doi:10.1021/es60152a013Logan, B. E., Jewett, D. G., Arnold, R. G., Bouwer, E. J., & O’Melia, C. R. (1995). Clarification of Clean-Bed Filtration Models. 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Design techniques for ultra-low-power sensor interface circuits and systems in nano-scale CMOS technologies

In recent decades, the internet of things (IoT) has been sprout, resulting from the improvement of the circuit design and manufacturing techniques. Moreover, the emerging of 5G technologies further enhances its growth. Autonomous wireless sensors and their networks have been one of the most prevailing and important research topics for the past decades. Although researchers have been pushing the state-of-the-art of sensor readout to have higher and higher power and area efficiency, the results turn out to be insufficient to meet the modern requirements, especially considering the number of sensors is dramatically growing and a large portion of them are battery-less devices. Thus, maintaining a high resolution and low noise while achieving a high power and area efficiency has been one of the major challenges for sensor readout circuit designs in recent years. This thesis proposes several novel power- and area-saving techniques for the fundamental building blocks: 1) the inverter-stacking technique; and 2) the tail-less inverter-stacking technique for LNA; 3) the CT-SAR-assisted two-step SAR ADC with kT/C noise attenuated. The first work presents a highly power-efficient amplifier. By stacking inverters and splitting the capacitor feedback network, the proposed amplifier achieves 6-time current reuse, thereby significantly boosting the transconductance and lowering noise but without increasing the current consumption. A novel biasing scheme is devised to ensure robust operation under 1 V supply. A prototype in 180 nm CMOS has 5.5 μV [subscript rms] noise within 10 kHz BW while consuming only 0.25 μW power, leading to a noise efficiency factor (NEF) of 1.07, which is the best among reported amplifiers. The second work presents a low-noise capacitively-coupled instrumentation amplifier, featuring the better-than-bipolar power efficiency. The tail-less structure removes the tail current source, reducing the supply voltage to be 0.6 V, and thus significantly reducing the power consumption. Compared with other recently reported front-end amplifiers, it achieves the best trade-off between power consumption and input-referred noise (IRN). AC-coupling and current mode biased are employed to enhance its PVT robustness.f In addition, several other design techniques are used, including AC coupling with optimized gain allocation-based ripple reduction, CM-pre-filtering based CMRR enhancement. The prototype fabricated in 180-nm CMOS process achieved an integrated input-referred rms noise of 1.38 μV [subscript rms] within an 8-kHz bandwidth. With one global 0.6-V supply voltage, the prototype consumes 2.7-μW of total power, leading to a PEF of 0.96. The peak CMRR and PSRR are measured to be 84 dB and 78 dB, respectively, which validates the performance enhancement techniques with the pseudo-differential input stage. The third work presents a two-step analog-to-digital converter (ADC) that operates its 1st-stage successive approximation register (SAR) ADC in the continuous-time (CT) domain. It avoids the front-end sample-and-hold (S/H) circuit and its associated sampling noise. Hence, the proposed ADC allows the input capacitor size to be substantially reduced without incurring large sampling noise penalty. With input AC coupling, the 1st-stage CT SAR can simultaneously perform input tracking and SAR quantization. Its conversion error is minimized by accelerating the SAR speed and providing redundancy. A floating inverter-based (FIB) dynamic amplifier (DA) is used as the inter-stage amplifier and acts as a low-pass filter for the 1st-stage residue. To verify the proposed techniques, a 13-bit prototype ADC is built in 40nm CMOS process. Its input capacitor is only 120 fF, which is over 20 times smaller than what would be needed in a classic Nyquist ADC with the S/H circuit. Operating at 2 MS/s, it achieves 72-dB SNDR at the Nyquist rate while consuming only 25 μW of power and 0.01 mm² of area.Electrical and Computer Engineerin

Remnant cholesterol and severity of nonalcoholic fatty liver disease

Abstract Background Serum remnant cholesterol levels are being increasingly acknowledged as a causal risk factor for atherosclerotic disease, regardless of conventional lipid parameters. The positive association between remnant cholesterol and nonalcoholic fatty liver disease (NAFLD) has been revealed in previous studies. However, whether remnant cholesterol is associated with the severity of NAFLD remains unknown. This study aimed to explore the association between serum remnant cholesterol and the risk of NAFLD severity. Methods This cross-sectional study included a total of 6,053 participants who attended health checkups. The severity of hepatic steatosis was evaluated by liver ultrasound transient elastography. Univariable and multivariable logistic regression analyses were performed to calculate the odds ratio (OR) and 95% confidence interval (95% CI) for the association between remnant cholesterol and the severity of hepatic steatosis. To explore whether the association between remnant cholesterol and NAFLD severity was independent of conventional lipid parameters, we further investigated this association in individuals with normal values of low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C) and triglycerides. Results In total, 36.9% of individuals had mild steatosis, and 5.9% had moderate-to-severe steatosis. The serum level of remnant cholesterol in nonsteatosis, mild steatosis and moderate-to-severe steatosis gradually increased (0.71 ± 0.33, 0.97 ± 0.52 and 1.07 ± 0.63 mmol/L, respectively). In the multivariable mode, remnant cholesterol was positively associated with mild hepatic steatosis (OR: 1.730, 95% CI: 1.541 − 1.941, P < 0.001) and moderate-to-severe steatosis (OR: 2.342, 95% CI: 1.765 − 3.109, P < 0.001). These associations were not significantly altered in individuals with normal triglycerides, HDL-C and LDL-C (OR: 1.664, 95% CI: 1.448 − 1.911, P < 0.001; OR: 2.269, 95% CI: 1.619 − 3.180, P < 0.001, respectively). Conclusions Higher levels of serum remnant cholesterol were associated with more severe hepatic steatosis, regardless of conventional lipid parameters. Individuals with higher remnant cholesterol may need more attention in regular surveillance of NAFLD

Determining plasmonic hot-carrier energy distributions via single-molecule transport measurements

Hot carriers in plasmonic nanostructures, generated via plasmon decay, play key roles in applications such as photocatalysis and in photodetectors that circumvent bandgap limitations. However, direct experimental quantification of steady-state energy distributions of hot carriers in nanostructures has so far been lacking. We present transport measurements from single-molecule junctions, created by trapping suitably chosen single molecules between an ultrathin gold film supporting surface plasmon polaritons and a scanning probe tip, that can provide quantification of plasmonic hot-carrier distributions. Our results show that Landau damping is the dominant physical mechanism of hot-carrier generation in nanoscale systems with strong confinement. The technique developed in this work will enable quantification of plasmonic hot-carrier distributions in nanophotonic and plasmonic devices