IMSE Publications

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Author: Rubén Gómez Merchán
Year: Since 2002

Journal Papers

A Low-Latency, Low-Power CMOS Sun Sensor for Attitude Calculation Using Photovoltaic Regime and On-Chip Centroid Computation
R. Gomez-Merchan, J. A. Leñero-Bardallo, M. López-Carmona and Á. Rodríguez-Vázquez
Journal Paper · IEEE Transactions on Instrumentation and Measurement, 2023
abstract      doi      

The demand for sun sensors has skyrocketed in the last years due to the huge expected deployment of satellites associated with the New Space concept. Sun sensors compute the position of the sun relative to the observer and play a crucial role in navigation systems. However, the sensor itself and the associated electronics must be able to operate in harsh environments. Thus, reducing hardware and post-processing resources improves the robustness of the system. Furthermore, reducing power consumption increases the lifetime of microsatellites with a limited power budget. This work describes the design, implementation, and characterization of a proof-of-concept prototype of a low-power, high-speed sun sensor architecture. The proposed sensor uses photodiodes working in the photovoltaic regime and event-driven vision concepts to overcome the limitations of conventional digital sun sensors in terms of latency, data throughput, and power consumption. The temporal resolution of the prototype is in the microsecond range with an average power consumption lower than 100μW . Experimental results are discussed and compared with the state-of-the-art.

TEMAS: A Flexible non-AI Algorithm for Metrology of Single-core and Core-shell Nanoparticles from TEM images
Jorge J. Saenz Noval, Ruben Gomez-Merchan, Juan A. Leñero-Bardallo and Lionel C. Gontard
Journal Paper · Particle and Particle Systems Characterization, vol. 40, issue: 2, 2023
abstract      doi      

An essential application of electron microscopy is to provide feedback to tune the fabrication of nanoparticles (NPs). Real samples tend to follow a size distribution commonly linked to the synthesis process used and in turn to their functional properties. This study presents an algorithm for measuring particle size distributions in electron microscopy images. State-of-the-art methods based on Artificial Intelligence (e.g., Deep Learning) require extensive datasets of labeled images similar to those expected to be analyzed, and extensive supervised re-training is often required for cross-domain application. In contrast, the non-AI algorithm described in this study is accurate and can be quickly set up for measuring new experimental images in different domains. The accuracy of the method is validated quantitatively and comparing graphical and descriptive statistics. Different size distributions are measured on images of platinum and gold nanocatalysts supported on carbon black, amorphous carbon, and titanium dioxide crystals. Also, images of platinum-iron core-shell NPs supported on thin amorphous carbon film are successfully analyzed. The limitation of evaluating different algorithms for NPs metrology is the lack of standards that different researchers can use as ground truth. In order to overcome this limitation, the images and the ground truth measurements presented here are shared as an open dataset.

The Influence of MPPT Algorithms in the Lifespan of the Capacitor Across the PV Array
A. Alcaide, R. Gomez-Merchan, E. Zafra, E.P. Martin, J.M. López-Rodriguez, J.I. Leon, S. Vazquez and L.G. Franquelo
Journal Paper · IEEE Access, vol. 10, pp 40945 - 40952, 2022
abstract      doi      

PV systems efficiency highly depends on the MPPT strategy to be implemented in the PV converter. Many MPPT methods on the literature are focused on improving the steady state and transient system performance extracting the maximum energy from the sun. In this paper, the impact of the MPPT methods in the PV converter is analyzed focusing the study on the capacitor across the PV array lifespan. The obtained results demonstrate that the low frequency PV voltage oscillations that are present in many MPPT methods have a large negative impact on this capacitor lifespan. Experimental and simulation results are presented in order to show that advanced MPPT methods, which avoid these low frequency oscillations, achieve higher capacitor lifespan values compared with the values obtained by applying well-known MPPT methods such as the perturb and observe or incremental conductance strategies.

A comparative study of stacked-diode configurations operating in the photovoltaic region
R. Gómez-Merchán, D. Palomeque-Mangut, J.A. Leñero-Bardallo, M. Delgado-Restituto and A. Rodríguez-Vázquez
Journal Paper · IEEE Sensors Journal, vol. 20, no. 16, pp 9105-9113, 2020
abstract      doi      

This article presents a detailed comparative analysis of two possible stacked-diode configurations operating as solar cells. The performance of a single p-well - deep n-well diode is compared with the combination of such diode with a n-diff - pwell diode in parallel. Both configurations occupy the same area but offer different performance and, accordingly, they can have different application scopes. A test circuit to gauge the diodes performance and their spectral sensitivity has been integrated along with the two diode configurations in a 0.18 μm CMOS standard fabrication technology. The measured experimental results for the two diode configurations under study are validated with an analytical diode physical model.


A self-powered asynchronous image sensor with independent in-pixel harvesting and sensing operations
R. Gomez-Merchan, J.A. Leñero-Bardallo and A. Rodríguez-Vázquez
Conference · IS&T International Symposium on Electronic Imaging 2023

A self-powered asynchronous sensor with a novel pixel architecture is presented. Pixels are autonomous and can harvest or sense energy independently. During the image acquisition, pixels toggle to a harvesting operation mode once they have sensed their local illumination level. With the proposed pixel architecture, most illuminated pixels provide an early contribution to power the sensor, while low-illuminated ones spend more time sensing their local illumination. Thus, the equivalent frame rate is higher than the one offered by conventional self-powered sensors that harvest and sense illumination in independent phases. The proposed sensor uses a Time-to-First-Spike readout that allows trading between image quality and data and bandwidth consumption. The device has HDR operation with a dynamic range of 80 dB. Pixel power consumption is only 70 pW. The article describes the sensors and pixel’s architectures in detail. Experimental results are provided and discussed. Sensor specifications are benchmarked against the art.

PixiStamp: A tool to acquire, process, and sequence AER data from event-driven systems
R. de la Rosa-Vidal, R. Gomez-Merchan, J.A. Leñero-Bardallo and A. Rodríguez-Vázquez
Conference · Conference on Ph.D Research in Microelectronics and Electronics PRIME 2022

We present a new tool, PixiStamp, to readout, process, and sequence data of event-driven systems that exchange data using the Address Event Representation (AER) protocol. PixiStamp is a compact acquisition board that can be easily attached to other devices. Over other existing solutions, it has enhanced hardware processing capabilities to process AER data and generate control signals after data processing, making possible a closed-loop device control. The article describes in detail the system architecture, its mechanical design, and its main features.

On the implementation of in-pixel controlled diodes with sensing and energy harvesting capabilities
R. Gomez-Merchan, R. de la Rosa-Vidal, J.A. Leñero-Bardallo and A. Rodríguez-Vázquez
Conference · Conference on Ph.D Research in Microelectronics and Electronics PRIME 2022

Energy harvesting plays a crucial role in low-power systems and Internet-of-Things (IoT) sensing nodes. Measuring the illumination level of the scene is desired in such applications. Few studies have explored the possibility of designing image sensors that use photodiodes to harvest energy from the scene to reduce consumption or even achieve a self-powered operation using frame-based approaches. This work aims to validate the switching capabilities of photodiodes independently within a photodiode array. While most studies focus on alternating the harvesting and sensing operation in two different phases, in this approach a fraction of the photodiodes are connected to a global node to harvest energy, while the rest are sensing. This configuration qualifies to design asynchronous imagers and optimize the harvesting operation. The preliminary experimental results reported in this publication emphasize the validity of this asynchronous switching in photodiode arrays.

A high-speed low-power sun sensor with solar cells and continuous operation
R. Gomez-Merchan, M. López-Carmona, J.A. Leñero-Bardallo and A. Rodríguez-Vázquez
Conference · European Solid-State Circuits Conference ESSCIRC 2021

A novel sun sensor concept is presented. Photodiodes operating as solar cells with continuous operation and dedicated logic to calculate the centroid position are integrated to achieve lower latency and energy consumption. The output data flow is remarkably reduced because the centroid of the illuminated pixels is the only sensor output data. It overcomes conventional digital sun sensors based on Active Pixel Sensor (APS) pixels and Address Event Representation (AER) in terms of latency and power consumption. Its latency is in the order of microseconds with an average power consumption lower than 100 uW. Experimental results are provided and benchmarked.


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