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Load-Dependent Power Transfer Efficiency forOn-Chip Coils
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.ORCID iD: 0000-0002-8216-832x
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.ORCID iD: 0000-0003-4958-146x
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper presents a theory for the power transfer efficiency to on-chip coils, with focus on load-dependence for low-power single-chip systems. The theory is verified with electromagnetic simulations modelled on a 350~nm process which in turn are verified by measurements on manufactured integrated circuits. The power transfer efficiency is evaluated by on-chip rectification of a 225~MHz signal transmitted by a spiral coil printed on a ceramic substrate at 10 mm of separation. Such an approach avoids the influence of off-chip parasitic elements such as bond-wires which would reduce the accuracy of the evaluation.It is found that there exists a lower limit for the load below which reducing the power consumption of on-chip circuits yield no increase in power consumption. The paper is focused on the analysis and verification of the theory behind this limit.We relate the results presented in this work to the application of wireless single-chip temperature monitoring of power semiconductors.

Keywords [en]
condition monitoring, low power, near-field, on-chip coil, RFID, power semiconductor, wireless
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-73349OAI: oai:DiVA.org:ltu-73349DiVA, id: diva2:1300231
Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-08-27
In thesis
1. Wireless High-Temperature Monitoring of Power Semiconductors: A Single-Chip Approach
Open this publication in new window or tab >>Wireless High-Temperature Monitoring of Power Semiconductors: A Single-Chip Approach
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Trådlöshögtemperatursövervakning av krafthalvledare : En monolitisk ansats
Abstract [en]

Because failures in power electronic equipment can cause production stops and unnecessary damage to interconnected equipment, monitoring schemes that are able to predict such failures provide various economic and safety benefits. The primary motivation for this thesis is that such monitoring schemes can increase the reliability of energy production plants. Power semiconductors are crucial components in power electronic equipment, and monitoring their temperatures yields information that can be used to predict emerging failures.This thesis presents a system concept for wireless, single-chip, high-temperature monitoring of power semiconductors. A wireless single-chip solution is both cost effective and easy to integrate with existing power semiconductor modules. However, the concept presents two major challenges: the implementation of wireless power and communication, and the low-power design of the temperature sensors. To address these challenges, the feasibility of using on-chip coils to provide communication with and to obtain power from an external reader coil is demonstrated, and a low-power, high-temperature bandgap temperature sensor is developed.For the challenge of generating geometries of on-chip coils with high power transfer efficiencies, a gradient ascent algorithm is used to generate geometries that provide high power transfer efficiency at the frequency of interest. A theory is developed, focused on the relation between optimised coil geometries and the load requirements of an application. A cutoff-point is discovered, beyond which power delivered to the load does not increase even if the load is made lighter. Electromagnetic simulations for an on-chip coil model are presented, which show that this load-limit lies around 10 kΩ for one 350 nM process. The model is verified with measurements on manufactured devices.To generate coils which operate within a desired frequency band in which sufficient radiated energy is permitted, a methodology for tuning on-chip coils with on-chip fuses is presented. The decision to use fuses for tuning instead of transistors for this application is due a transistor's requirement of a DC supply for bias. For wireless single-chip systems, no such DC supply is available at system start-up. The methodology presented addresses the challenge of achieving high Q~factors for capacitor-fuse series connections despite the fact the fuse resistance of on-chip fuses is finite in their blown state and non-zero in their active state.A single-chip, on-chip coil solution comes with advantages such as galvanic isolation from the power device and simplicity of integration in existing modules. However, because a wireless design with a small on-chip coil will limit the amount of available power, it incurs the disadvantage of requiring a low-power design for the temperature sensor. Therefore, a design is presented of a temperature sensor consuming power in the microwatt range in the high-temperature region where it is useful for detecting incipient faults, particularly solder faults. This is achieved by compensating for leakage currents that arise in hot reverse-biased p-n junctions, which become significant at these temperatures.At high temperatures, these leakage currents can approach or even surpass the level of a circuit's quiescent current. Earlier work on leakage current compensation techniques is examined, compared to and combined with a compensation technique designed to compensate for collector-base leakage in the main bipolar pair of a Brokaw bandgap reference. Experiments show that fully analogue sensors operating at up to at least 230 °C for a sensitivity of 2 mV/°C are feasible at a power consumption around 10 µW. Such sensors would yield a resolution of 2 °C if an 8-bit analogue-to-digital converter is employed. However, the transmission of data to the transmitter coil remains future work. Furthermore, a discussion is held to address design of unimplemented system components which are needed in order to implement a complete single-chip temperature measurement system. Points discussed include high-temperature analogue-to-digital conversion, clock generation and wireless communication.

Place, publisher, year, edition, pages
Luleå University of Technology, 2019. p. 90
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-73350 (URN)978-91-7790-352-9 (ISBN)978-91-7790-353-6 (ISBN)
Public defence
2019-05-23, A1547, Laboratorievägen, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-04-04 Created: 2019-03-28 Last updated: 2019-05-14Bibliographically approved

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Nilsson, JoakimBorg, JohanJohansson, Jonny

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