| 1. |
- Albertsson, Dagur Ingi, 1993-, et al.
(författare)
-
Compact Macrospin-Based Model of Three-Terminal Spin-Hall Nano Oscillators
- 2019
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Ingår i: IEEE transactions on magnetics. - : IEEE Press. - 0018-9464 .- 1941-0069. ; 55:10
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Tidskriftsartikel (refereegranskat)abstract
- Emerging spin-torque nano oscillators (STNOs) and spin-Hall nano oscillators (SHNOs) are potential candidates for microwave applications. Recent advances in three-terminal magnetic tunnel junction (MTJ)-based SHNOs opened the possibility to develop more reliable and well-controlled oscillators, thanks to individual spin Hall-driven precession excitation and read-out paths. To develop hybrid systems by integrating three-terminal SHNOs and CMOS circuits, an electrical model able to capture the analog characteristics of three-terminal SHNOs is needed. This model needs to be compatible with current electric design automation (EDA) tools. This work presents a comprehensive macrospin-based model of three-terminal SHNOs able to describe the dc operating point, frequency modulation, phase noise, and output power. Moreover, the effect of voltage-controlled magnetic anisotropy (VCMA) is included. The model shows good agreement with experimental measurements and could be used in developing hybrid three-terminal SHNO/CMOS systems.
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| 2. |
- Albertsson, Dagur Ingi, et al.
(författare)
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Experimental Demonstration of Duffing Oscillator-Based Analog Ising Machines
- 2024
-
Ingår i: LASCAS 2024 - 15th IEEE Latin American Symposium on Circuits and Systems, Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a proof-of-concept analog Ising Machine, which can solve combinatorial optimization problems using bifurcations in networks of coupled Duffing oscillators. The proof-of-concept system consists of a network of four coupled Duffing oscillators implemented with low-cost components on a prototyping board. Experimental results demonstrate that the proposed prototype operates as an Ising Machine and it can solve various Max-Cut problems. This work provides the foundation towards realizing analog Ising Machines based on circuits that exhibit bifurcation properties, such as the Duffing oscillators, and that can be scaled to large networks.
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| 3. |
- Albertsson, Dagur Ingi, et al.
(författare)
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Highly reconfigurable oscillator-based Ising Machine through quasiperiodic modulation of coupling strength
- 2023
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- Ising Machines (IMs) have the potential to outperform conventional Von-Neuman architectures in notoriously difficult optimization problems. Various IM implementations have been proposed based on quantum, optical, digital and analog CMOS, as well as emerging technologies. Networks of coupled electronic oscillators have recently been shown to exhibit characteristics required for implementing IMs. However, for this approach to successfully solve complex optimization problems, a highly reconfigurable implementation is needed. In this work, the possibility of implementing highly reconfigurable oscillator-based IMs is explored. An implementation based on quasiperiodically modulated coupling strength through a common medium is proposed and its potential is demonstrated through numerical simulations. Moreover, a proof-of-concept implementation based on CMOS coupled ring oscillators is proposed and its functionality is demonstrated. Simulation results show that our proposed architecture can consistently find the Max-Cut solution and demonstrate the potential to greatly simplify the physical implementation of highly reconfigurable oscillator-based IMs.
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| 4. |
- Albertsson, Dagur Ingi, et al.
(författare)
-
Ising Machine Based on Bifurcations in a Network of Duffing Oscillators
- 2023
-
Ingår i: Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- Ising Machines have been extensively explored latelyfor developing new nonconventional computing architectures. Arecently proposed approach, based on simulating a dynamicalsystem exhibiting bifurcations, has shown promising performance. Inspired by this concept, we propose using bifurcationsin a network of coupled electrical Duffing oscillators to realize anIsing Machine. Numerical simulations of large Duffing oscillatornetworks, solving various Max-Cut problems, demonstrate thepotential of our proposed approach for realizing Ising Machinesbased on bifurcations. It also establishes a new direction towardsanalog Ising Machine architectures.
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| 5. |
- Albertsson, Dagur Ingi
(författare)
-
Spintronic and Electronic Oscillators for Magnetic Field Sensing and Ising Machines
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Oscillators can exhibit a range of complex dynamics which are often encountered in nature. These characteristics include synchronization, injection locking, chaos, bifurcations, etc. To date, the applications of electronic oscillators has mostly been limited to communication systems. However, in recent years, the possibility of using the rich dynamics of oscillators in unconventional applications, including time-based information processing and computational applications, has been also explored. In this thesis, this potential is investigated using emerging spintronic oscillators and established electronic oscillators. The first part of this thesis targets emerging spintronic oscillators, which exhibit a range of attractive features, including GHz operating frequency, wide tunability and nanoscale size. To explore the potential of these devices, an electrical behavioural model was developed for the promising three-terminal spin-Hall nano-oscillator. The behavioural model is based on the macrospin approximation, which is commonly used to describe the operation principles of spintronic oscillators, and it was implemented in Verilog-A. Moreover, the behavioural model was verified against experimental measurements from literature, demonstrating that the most important characteristics of three-terminal spin-Hall nano-oscillators are accurately captured. Subsequently, two potential applications that could benefit from the unique characteristics of spintronic oscillators were identified and explored. First, a magnetic field sensing system, which takes advantage of the wide frequency tunability of spintronic oscillators as a function of externally applied magnetic field, was proposed and demonstrated. This sensing system, inspired by voltage-controlled oscillator analog-to-digital converters, shows performance similar to the state-of-the-art magnetic field sensors, making it a promising application for spintronic oscillators. Next, the possibility of utilizing spintronic oscillators to realize Ising machines (IMs) was explored and demonstrated with numerical simulations. This was the first-time demonstration of spintronic oscillator-based Ising machines. The numerical simulation results show that spintronic oscillators are a promising device to realize ultra-fast Ising Machines able to solve complex combinatorial optimization problems on nano-second time scale.The second part of the thesis extends on the idea of oscillator-based IMs, but using electronic oscillators. The potential of realizing highly reconfigurable oscillator-based IMs based on quasiperiodically modulated coupling was explored. The advantages and potential challenges associated with this approach were highlighted, and a proof-of-concept IM using CMOS ring oscillators was proposed and simulated. Finally, a completely new type of IMs based on bifurcations in a network of coupled Duffing oscillators was proposed and developed. This work highlights a new research direction based on using dynamical systems implemented with analog circuits to realize IMs.
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| 6. |
- Albertsson, Dagur Ingi, et al.
(författare)
-
Ultrafast Ising Machines using spin torque nano-oscillators
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:11
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Tidskriftsartikel (refereegranskat)abstract
- Combinatorial optimization problems are known for being particularly hard to solve on traditional von Neumann architectures. This has led to the development of Ising Machines (IMs) based on quantum annealers and optical and electronic oscillators, demonstrating speed-ups compared to central processing unit (CPU) and graphics processing unit (GPU) algorithms. Spin torque nano-oscillators (STNOs) have shown GHz operating frequency, nanoscale size, and nanosecond turn-on time, which would allow their use in ultrafast oscillator-based IMs. Here, we show using numerical simulations based on STNO auto-oscillator theory that STNOs exhibit fundamental characteristics needed to realize IMs, including in-phase/out-of-phase synchronization and second harmonic injection locking phase binarization. Furthermore, we demonstrate numerically that large STNO network IMs can solve Max-Cut problems on nanosecond timescales.
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| 7. |
- Chaourani, Panagiotis, 1989-, et al.
(författare)
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A Study on Monolithic 3-D RF/AMS ICs: Placing Digital Blocks Under Inductors
- 2018
-
Ingår i: IEEE SOI-3D-Subthreshold Microelectronics Technology Unified Conference (S3S). - : IEEE conference proceedings.
-
Konferensbidrag (refereegranskat)abstract
- The placement of bottom tier blocks under top-tierinductors could significantly improve the area-efficiency of M3DRF/AMS circuits, paving the way for new applications of thisintegration technology. This work investigates the potential ofplacing digital blocks in the bottom tier, underneath top tierinductors. A design-technology co-optimization flow is appliedand a number of design guidelines are suggested. These guidelinesensure high electromagnetic isolation between the two tiers, withminimum penalties on the loading of bottom tier wires, as wellas on the inductor’s performance.
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| 8. |
- Chaourani, Panagiotis, et al.
(författare)
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Inductors in a Monolithic 3-D Process : Performance Analysis and Design Guidelines
- 2019
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Ingår i: IEEE Transactions on Very Large Scale Integration (vlsi) Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-8210 .- 1557-9999. ; 27:2, s. 468-480
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Tidskriftsartikel (refereegranskat)abstract
- Monolithic 3-D (M3D) integration technology has demonstrated significant area reduction in digital systems. Recently, its applications to other fields have been considered as well. To fully investigate the potential of M3D for radio-frequency/analog-mixed signal (RF/AMS) circuits and systems, the behavior of inductors in this technology needs to be evaluated. Toward this, in this paper, the effect of M3D integration on their inductance densities and quality factors has been analyzed. The impact of shields on M3D inductors has been investigated, as well as the shunting of multiple metal layers to form multimetal inductors. In an attempt to improve the area efficiency of M3D RF/AMS circuits, the potential of placing bottom-tier blocks underneath top-tier inductors has been identified, and a set of guidelines has been proposed to maximize the inter-tier electromagnetic isolation. These guidelines deal with the suitable position of both low- and high-frequency blocks, their wiring, as well as the type of shield that is needed between them and the inductors. To prove the efficiency of these guidelines, an array of bottom-tier resistors has been placed underneath a top-tier inductor, resulting in more than 50 dB of inter-tier isolation for frequencies up to 20 GHz.
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| 9. |
- Fernández Schrunder, Alejandro, 1993-, et al.
(författare)
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A Bioimpedance Spectroscopy Interface for EIM Based on IF-Sampling and Pseudo 2-Path SC Bandpass ΔΣ ADC
- 2024
-
Ingår i: IEEE Transactions on Biomedical Circuits and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4545 .- 1940-9990. ; , s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a low-noise bioimpedance (bio-Z) spectroscopy interface for electrical impedance myography (EIM) over the 1 kHz to 2 MHz frequency range. The proposed interface employs a sinusoidal signal generator based on direct-digital-synthesis (DDS) to improve the accuracy of the bio-Z reading, and a quadrature low-intermediate frequency (IF) readout to achieve a good noise-to-power efficiency and the required data throughput to detect muscle contractions. The readout is able to measure baseline and time-varying bio-Z by employing robust and power-efficient low-gain IAs and sixth-order single-bit bandpass (BP) ΔΣ ADCs. The proposed bio-Z spectroscopy interface is implemented in a 180 nm CMOS process, consumes 344.3 - 479.3 μ W, and occupies 5.4 mm 2 area. Measurement results show 0.7 mΩ/√Hz sensitivity at 15.625 kHz, 105.8 dB SNR within 4 Hz bandwidth, and a 146.5 dB figure-of-merit. Additionally, recording of EIM in time and frequency domain during contractions of the bicep brachii muscle demonstrates the potential of the proposed bio-Z interface for wearable EIM systems.
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| 10. |
- Fernández Schrunder, Alejandro, 1993-, et al.
(författare)
-
A Finite Element Analysis and Circuit Modelling Methodology for Studying Electrical Impedance Myography of Human Limbs
- 2022
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Ingår i: IEEE Transactions on Biomedical Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9294 .- 1558-2531. ; 69:1, s. 244-255
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Electrical impedance myography (EIM) measures bioimpedance over muscles. This paper proposes a circuit-based modelling methodology originated from finite element analysis (FEA), to emulate tissues and effects from anthropometric variations, and electrode placements, on EIM measurements. The proposed methodology is demonstrated on the upper arms and lower legs. Methods: FEA evaluates impedance spectra (Z-parameters), sensitivity, and volume impedance density for variations of subcutaneous fat thickness (tf), muscle thickness (tm), and inter-electrode distance (IED), on limb models over 1Hz-1MHz frequency range. The limbs models are based on simplified anatomical data and dielectric properties from published sources. Contributions of tissues to the total impedance are computed from impedance sensitivity and density. FEA Z-parameters are imported into a circuit design environment, and used to develop a three Cole dispersion circuit-based model. FEA and circuit model simulation results are compared with measurements on ten human subjects. Results: Muscle contributions are maximized at 31.25kHz and 62.5kHz for the upper arm and lower leg, respectively, at 4cm IED. The circuit model emulates variations in tf and tm, and simulates up to 89 times faster than FEA. The circuit model matches subjects measurements with RMS errors < 36.43 and < 17.28, while FEA does with < 36.59 and < 4.36. Conclusions: We demonstrate that FEA is able to estimate the optimal frequencies and electrode placements, and circuit-based modelling can accurately emulate the limbs bioimpedance. Significance: The proposed methodology facilitates studying the impact of biophysical principles on EIM, enabling the development of future EIM acquisition systems.
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| 11. |
- Fernández Schrunder, Alejandro, 1993-, et al.
(författare)
-
A Low-Distortion Current-Mode Signal Generator for Wide-Range Bioimpedance Spectroscopy
- 2023
-
Ingår i: ISCAS 2023. - : IEEE.
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a low-distortion current-mode sinusoidal signal generator for bioimpedance spectroscopy measurements. The proposed full current-mode operation enables linearity enhancement and potential savings in silicon area and power consumption. Programmability in the low-pass filter and current driver enables impedance measurements from 0.2 Ω to10 kΩ over a wide frequency range from 1 kHz to 1 MHz.The current generator, designed in a 0.18 μm CMOS process, consumes between 736 μW at the lowest frequency and gain, and 1.70 mW at the highest frequency and gain, and occupies 1.76 mm2 silicon area. Post-layout simulation results show a spurious-free dynamic range larger than 40 dBc over the entire frequency range, which enables bioimpedance measurements with errors below 1%, as it is required for wearable devices evaluating neuromuscular disorders.
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| 12. |
- Fernández Schrunder, Alejandro, 1993-, et al.
(författare)
-
A Mixer-First Analog Front-End or Dry-electrode Bioimpedance Spectroscopy
- 2023
-
Ingår i: BioCAS 2023 - 2023 IEEE Biomedical Circuits and Systems Conference, Conference Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a high input impedance,low-noise, and low-distortion analog front-end (AFE) forbioimpedance (bio-Z) spectroscopy measurements targeting neu-romuscular health assessments. The proposed 8-phase quadra-ture mixer-first architecture achieves a high input impedancethrough passive mixers driven by non-overlapping clocks. The 8-phase signals are recombined to extract the real and imaginaryparts of the bio-Z, while rejecting unwanted harmonics toimprove linearity. Programmability of the AFE enables accuratebio-Z measurements up to 10 kΩ for 11 logarithmically spacedfrequencies, in the 1 kHz to 1 MHz frequency range. The AFE,designed in a 0.18 μm CMOS process, consumes 245.99 μW atthe lowest gain and 300.56 μW at the highest gain, and occupies2.4 mm2 silicon area. Post-layout simulation results show that theinput impedance is always higher than the electrode impedanceby more than 10x. The AFE achieves a sensitivity of 7.7 mΩrms,and a maximum SNDR of 103.87 dBFS over a 61 Hz bandwidth.These results demonstrate that the proposed AFE enables bio-Zmeasurements, using dry electrodes, with errors below 1%.
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| 13. |
- Fernández Schrunder, Alejandro, 1993-, et al.
(författare)
-
A Real-Time Muscle Fatigue Detection System Based on Multi-Frequency EIM and sEMG for Effective NMES
- 2024
-
Ingår i: IEEE Sensors Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-437X .- 1558-1748. ; , s. 1-1
-
Tidskriftsartikel (refereegranskat)abstract
- Neuromuscular electrical stimulation (NMES) is a self-directed home based therapeutic tool in early rehabilitation for musculoskeletal (MSK) conditions. However, the effectiveness of traditional NMES is fundamentally constrained by muscle fatigue. To address this limitation, this work proposes a detection system, which simultaneously records multifrequency electrical impedance myography (EIM) and surface electromyography(sEMG) in real time for time-frequency analysis of muscle activation, contraction, and fatigue. To demonstrate the ability to monitor these muscle physiological states, two experiments involving weightless and weighted dynamic contractions of the biceps brachii muscle were performed. Results from these experiments show synchronous changes in sEMG and EIM spectra during contractions, and clear trends in sEMG’s mean power frequency (MPF) and EIM spectra with fatigue progression. Additionally, the configurable 4-channel NMES has been electrically evaluated for clinical use, demonstrating the feasibility of the proposed system for closed-loop stimulation. This work showcases the potential of sEMG and multi-frequency EIM to enhance the effectiveness of NMES for MSK conditions by capturing the behavior of distinct mechanisms of muscle fatigue.
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| 14. |
- Huang, Yu-Kai, et al.
(författare)
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A 4-Channel NMES IC for Wearable Applications
- 2021
-
Ingår i: BioCAS 2021 - IEEE Biomedical Circuits and Systems Conference, Proceedings. - : Institute of Electrical and Electronics Engineers Inc..
-
Konferensbidrag (refereegranskat)abstract
- This paper presents an integrated circuit solution for multi-channel neuromuscular electrical stimulation (NMES). The stimulation waveform is digitally controlled and supports monophasic pulses, and both symmetric and asymmetric biphasic pulses. In addition, the current intensity is programmable, ranging from 0 mA to 31 mA with 5-bit resolution. The integrated circuit occupies an area of 1 mm2and it is designed and simulated in a 180 nm high-voltage CMOS technology. The circuits are powered using standard 1.8 V and 3.3 V power supplies for the digital control and digital-to-analog converter, and a single 40 V power supply for the output drivers. The simulation results show that the design achieves a voltage compliance of up to 35 V, meeting the requirements for NMES applications while offering a very compact and scalable solution.
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| 15. |
- Huang, Yu-Kai, et al.
(författare)
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A Current Monitoring and Over-Current Detection Circuit for Safe Electrical Stimulation
- 2023
-
Ingår i: IEEE Transactions on Circuits and Systems - II - Express Briefs. - : Institute of Electrical and Electronics Engineers (IEEE). - 1549-7747 .- 1558-3791. ; 70:5, s. 1684-1688
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Tidskriftsartikel (refereegranskat)abstract
- This brief presents an integrated solution to over-current protection in neuromuscular stimulators. The proposed approach provides fast detection of a single-fault condition, i.e., unintentional electrode short circuit or malfunction of the stimulator, thereby preventing prolonged high-intensity currents from flowing into tissues. In addition, a programmable current threshold enables the system to be also used for monitoring the stimulation intensity. The proposed solution was designed in a 180 nm high-voltage CMOS technology, and its functionality was verified by post-layout simulations in which the safety mechanisms were tested under fault conditions. The implementation only occupies an area of 0.286 mm2, making it feasible to be embedded in fully integrated NMES stimulators while providing the required patient safety.
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| 16. |
- Hussain, Muhammad Waqar, 1985-, et al.
(författare)
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A 500 °C Active Down-Conversion Mixer in Silicon Carbide Bipolar Technology
- 2018
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Ingår i: IEEE Electron Device Letters. - : IEEE Press. - 0741-3106 .- 1558-0563. ; 39:6, s. 855-858
-
Tidskriftsartikel (refereegranskat)abstract
- This letter presents an active down-conversion mixer for high-temperature communication receivers. The mixer is based on an in-house developed 4H-SiC BJT and down-converts a narrow-band RF input signal centered around 59 MHz to an intermediate frequency of 500 kHz. Measurements show that the mixer operates from room temperature up to 500 °C. The conversion gain is 15 dB at 25 °C, which decreases to 4.7 dB at 500 °C. The input 1-dB compression point is 1 dBm at 25 °C and −2.5 dBm at 500 °C. The mixer is biased with a collector current of 10 mA from a 20 V supply and has a maximum DC power consumption of 204 mW. High-temperature reliability evaluation of the mixer shows a conversion gain degradation of 1.4 dB after 3-hours of continuous operation at 500 °C.
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| 17. |
- Hussain, Muhammad Waqar, 1985-, et al.
(författare)
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A SiC BJT-Based Negative Resistance Oscillator for High-Temperature Applications
- 2019
-
Ingår i: IEEE Journal of the Electron Devices Society. - : Institute of Electrical and Electronics Engineers (IEEE). - 2168-6734. ; 7:1, s. 191-195
-
Tidskriftsartikel (refereegranskat)abstract
- This brief presents a 59.5 MHz negative resistanceoscillator for high-temperature operation. The oscillator employs an in-house 4H-SiC BJT, integrated with the requiredcircuit passives on a low-temperature co-fired ceramic substrate. Measurements show that the oscillator operates from room-temperature up to 400 C. The oscillator delivers an output◦power of 11.2 dBm into a 50 Ω load at 25 C, which decreases to 8.4 dBm at 400 C. The oscillation frequency varies by 3.3% in the entire temperature range. The oscillator is biased witha collector current of 35 mA from a 12 V supply and has amaximum DC power consumption of 431 mW.
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| 18. |
- Hussain, Muhammad Waqar, 1985-, et al.
(författare)
-
An Intermediate Frequency Amplifier for High-Temperature Applications
- 2018
-
Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 65:4, s. 1411-1418
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a two-stage small signal intermediate frequency amplifier for high-temperature communication systems. The proposed amplifier is implemented using in-house silicon carbide bipolar technology. Measurements show that the proposed amplifier can operate from room temperature up to 251 °C. At a center frequency of 54.6 MHz, the amplifier has a gain of 22 dB at room temperature, which decreases gradually to 16 dB at 251 °C. Throughout the measured temperature range, it achieves an input and output return loss of less than-7 and-11 dB, respectively. The amplifier has a 1-dB output compression point of about 1.4 dBm, which remains fairly constant with temperature. Each amplifier stage is biased with a collector current of 10 mA and a base-collector voltage of 3 V. Under the aforementioned biasing, the maximum power dissipation of the amplifier is 221 mW.
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| 19. |
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| 20. |
- Hussain, Muhammad Waqar, 1985-, et al.
(författare)
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Silicon Carbide BJT Oscillator Design Using S-Parameters
- 2018
-
Ingår i: European Conference on Silicon Carbide and Related Materials (ECSCRM), Birmingham September 2-6, 2018..
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Konferensbidrag (refereegranskat)abstract
- Radio frequency (RF) oscillator design typically requires large-signal, high-frequency simulation models for the transistors. The development of such models is generally difficult and time consuming due to a large number of measurements needed for parameter extraction. The situation isfurther aggravated as the parameter extraction process has to be repeated at multiple temperature points in order to design a wide-temperature range oscillator. To circumvent this modelling effort, analternative small-signal, S-parameter based design method can be employed directly without goinginto complex parameter extraction and model fitting process. This method is demonstrated through design and prototyping a 58 MHz, high-temperature (HT) oscillator, based on an in-house 4H-SiC BJT. The BJT at elevated temperature (up to 300 0C) was accessed by on-wafer probing and connectedby RF-cables to the rest of circuit passives, which were kept at room temperature (RT).
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| 21. |
- Hussain, Muhammad Waqar, 1985-, et al.
(författare)
-
Silicon carbide BJT oscillator design using S-parameters
- 2019
-
Ingår i: Silicon Carbide and Related Materials 2018. - : Trans Tech Publications Ltd. ; , s. 674-678
-
Konferensbidrag (refereegranskat)abstract
- Radio frequency (RF) oscillator design typically requires large-signal, high-frequency simulation models for the transistors. The development of such models is generally difficult and time consuming due to a large number of measurements needed for parameter extraction. The situation is further aggravated as the parameter extraction process has to be repeated at multiple temperature points in order to design a wide-temperature range oscillator. To circumvent this modelling effort, an alternative small-signal, S-parameter based design method can be employed directly without going into complex parameter extraction and model fitting process. This method is demonstrated through design and prototyping a 58 MHz, high-temperature (HT) oscillator, based on an in-house 4H-SiC BJT. The BJT at elevated temperature (up to 300 °C) was accessed by on-wafer probing and connected by RF-cables to the rest of circuit passives, which were kept at room temperature (RT).
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| 22. |
- Ivanisevic, Nikola, et al.
(författare)
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A 14-ENOB Delta-Sigma-Based Readout Architecture for ECoG Recording Systems
- 2018
-
Ingår i: IEEE Transactions on Circuits and Systems Part 1. - 1549-8328 .- 1558-0806. ; 05
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a delta-sigma based readout architecture targeting electrocortical recording in brain stimulation applications. The proposed architecture can accurately record a peak input signal up to 240 mV in a power-efficient manner without saturating or employing offset rejection techniques. The readout architecture consists of a delta-sigma modulator with an embedded analog front-end. The proposed architecture achieves a total harmonic distortion of -95 dB by employing a current-steering DAC and a multi-bit quantizer implemented as a tracking ADC. A system prototype is implemented in a 0.18 μm CMOS triple-well process and has a total power consumption of 54 μW. Measurement results, across 10 packaged samples, show approximately 14-ENOB over a 300Hz bandwidth with an input referred noise of 5.23 μVrms, power-supply/common-mode rejection ratio of 100 dB/98 dB and an input impedance larger than 94 MΩ.
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| 23. |
- Ivanisevic, Nikola, et al.
(författare)
-
Area-Efficient Switched-Capacitor Integrator with Flicker Noise Cancellation
- 2018
-
Konferensbidrag (refereegranskat)abstract
- A fully differential switched-capacitor circuit that combines the functionality of a voltage buffer and an integrator is proposed. The employed switching scheme exhibits intrinsic flicker noise canceling properties, whereas conventional techniques require additional circuit components. The circuit has been designed in a 0.18 μm CMOS process for 1.8 V supply. The estimated power consumption is 13.5 μW, while the occupied area is 121×442 μm2. Area-efficient design is achieved by exploiting the correlation between the effective noise bandwidth and noise floor density in the proposed circuit. The sampled input referred noise floor is −133 dBV/√Hz, which is remarkably low when considering that the sampling capacitance is just 1.8 pF.
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| 24. |
- Ivanisevic, Nikola, 1988-
(författare)
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Circuit Design Techniques for Implantable Closed-Loop Neural Interfaces
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Implantable neural interfaces are microelectronic systems, which have the potential to enable a wide range of applications, such as diagnosis and treatment of neurological disorders. These applications depend on neural interfaces to accurately record electrical activity from the surface of the brain, referred to as electrocorticography (ECoG), and provide controlled electrical stimulation as feedback. Since the electrical activity in the brain is caused by ionic currents in neurons, the bridge between living tissue and inorganic electronics is achieved via microelectrode arrays. The conversion of the ionic charge into freely moving electrons creates a built-in electrode potential that is several orders of magnitude larger than the ECoG signal, which increases the dynamic range, resolution, and power consumption requirements of neural interfaces. Also, the small surface area of microelectrodes implies a high-impedance contact, which can attenuate the ECoG signal. Moreover, the applied electrical stimulation can also interfere with the recording and ultimately cause irreversible damages to the electrodes or change their impedance. This thesis is devoted to resolving the challenges of high-resolution recording and monitoring the electrode impedance in implantable neural interfaces.The first part of this thesis investigates the state-of-the-art neural interfaces for ECoG and identifies their limitations. As a result of the investigation, a high-resolution ADC is proposed and implemented based on a ΔΣ modulator. In order to enhance performance, dynamic biasing and area-efficient switched-capacitor circuits were proposed. The ΔΣ modulator is combined with the analog front-end to provide a complete readout solution for high-resolution ECoG recording. The corresponding chip prototype was fabricated in a 180 nm CMOS process, and the measurement results showed a 14-ENOB over a 300-Hz bandwidth while dissipating 54-μW.The second part of this thesis expands upon the well-known methods for impedance measurements and proposes an alternative digital method for monitoring the electrode-tissue interface impedance. The proposed method is based on the system identification technique from adaptive digital filtering, and it is compatible with existing circuitry for neural stimulation. The method is simple to implement and performs wide-band measurements. The system identification was first verified through behavioral simulations and then tested with a board-level prototype in order to validate the functionality under real conditions. The measurement results showed successful identification of the electrode-electrolyte and electrode-skin impedance magnitudes.
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| 25. |
- Ivanisevic, Nikola, et al.
(författare)
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Impedance Spectroscopy Based on Linear System Identification
- 2019
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Ingår i: IEEE Transactions on Biomedical Circuits and Systems. - : IEEE. - 1932-4545 .- 1940-9990. ; 13:2, s. 396-402
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Tidskriftsartikel (refereegranskat)abstract
- Impedance spectroscopy is a commonly used mea-surement technique for electrical characterization of a sample-under-test over a wide frequency range. Most measurementmethods employ a sine wave excitation generator, which implies apoint-by-point frequency sweep and a complex readout architec-ture. This paper presents a fast, wide-band, measurement methodfor impedance spectroscopy based on linear system identification.The main advantage of the proposed method is the low hardwarecomplexity, which consists of a 3-level pulse waveform, aninverting voltage amplifier and a general purpose ADC. A proof-of-concept prototype, which is implemented with off-the-shelfcomponents, achieves an estimation fit of approximately 96%.The prototype operation is validated electrically using knownRC component values and tested in real application conditions.
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| 26. |
- Ivanisevic, Nikola, et al.
(författare)
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Impedance spectroscopy systems : Review and an all-digital adaptive IIR filtering approach
- 2017
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Ingår i: 2017 IEEE Biomedical Circuits and Systems Conference, Turin, October 19-21, 2017. - Turin, Italy : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- Impedance spectroscopy is a low-cost sensing technique that is generating considerable interest in wearable and implantable biomedical applications since it can be efficiently integrated on a single microchip. In this paper, the fundamental characteristics of the most well-known system architectures are presented, and a more robust and hardware-efficient solution is proposed. An all-digital implementation based on adaptive filtering is used for identifying the impedance parameters of a sample-under-test. The coefficients of an infinite-impulse-response (IIR) filter are tuned by an adaptive algorithm based on pseudo-linear regression and output-error formulation. A three-level pseudorandom noise generator with a concave power spectral density is employed without deteriorating the nominal performance. Proof-of-concept has been verified with behavioral simulations.
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| 27. |
- Katic, Janko, 1986-, et al.
(författare)
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A High-Efficiency Energy Harvesting Interface for Implanted Biofuel Cell and Thermal Harvesters
- 2017
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Ingår i: IEEE transactions on power electronics. - : IEEE Press. - 0885-8993 .- 1941-0107. ; 33:5, s. 4125-4134
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Tidskriftsartikel (refereegranskat)abstract
- A dual-source energy harvesting interface that combines energy from implanted glucose biofuel cell and thermoelectric generator is presented. A single-inductor dual-input dual-output boost converter topology is employed to efficiently transfer the extracted power to the output. A dual-input feature enables the simultaneous maximum power extraction from two harvesters, while a dual-output allows a control circuit to perform complex digital functions at nW power levels. The control circuit reconfigures the converter to improve the efficiency and achieve zero-current and zero-voltage switching. The measurement results of the proposed boost converter, implemented in a 0.18 μm CMOS process, show a peak efficiency of 89.5% when both sources provide a combined input power of 66 μW. In the single-source mode, the converter achieves a peak efficiency of 85.2% at 23 μW for the thermoelectric source and 90.4% at 29 μW for the glucose biofuel cell. The converter can operate from minimum input voltages of 10 mV for the thermoelectric source and 30 mV for the glucose biofuel cell.
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| 28. |
- Ollmar, Stig, et al.
(författare)
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A battery-less implantable glucose sensor based on electrical impedance spectroscopy
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The ability to perform accurate continuous glucose monitoring without blood sampling has revolutionised the management of diabetes. Newer methods that can allow measurements during longer periods are necessary to substantially improve patients’ quality of life. This paper presents an alternative method for glucose monitoring which is based on electrical impedance spectroscopy. A battery-less implantable bioimpedance spectroscope was designed, built, and used in an in vivo study on pigs. After a recovery period of 14 days post surgery, a total of 236 subcutaneous bioimpedance measurements obtained from intravenous glucose tolerance tests, with glucose concentration ranges between 77.4 and 523.8 mg/dL, were analyzed. The results show that glucose concentrations estimated by subcutaneous bioimpedance measurements correlate very well to the blood glucose reference values. The pigs were clinically healthy throughout the study, and the postmortem examinations revealed no signs of adverse effects related to the sensor. The implantation of the sensor requires minor surgery. The implant, being externally powered, could in principle last indefinitely. These encouraging results demonstrate the potential of the bioimpedance method to be used in future continuous glucose monitoring systems.
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| 29. |
- Onet, Raul, et al.
(författare)
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High-Purity and Wide-Range Signal Generator for Bioimpedance Spectroscopy
- 2018
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Ingår i: IEEE Transactions on Circuits and Systems - II - Express Briefs. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1549-7747 .- 1558-3791. ; 65:12, s. 1884-1888
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Tidskriftsartikel (refereegranskat)abstract
- This brief presents an integrated high-purity current signal generator (SG), part of a bioimpedance spectroscopy system that performs measurements in the frequency range from 1 kHz to 2 MHz, and it is able to measure bioimpedance values from 100 Omega to 1 M Omega. The SG is implemented in a 0.18-mu m CMOS process, it is powered by a single 1.8 V voltage source, and occupies a total area of 1.62 mm(2). It is able to generate single-frequency signals from 1 kHz to 2 MHz in 12 steps logarithmically spaced. High signal purity is achieved by using a second-order low-pass filter, with a bandwidth that can be programmed from 4 kHz to 8 MHz, in 12 points logarithmically spaced. The SG's power consumption varies from 750 mu W, at the lowest frequencies and gain, to 2.06 mW at the highest frequencies and gain. The output current levels can be modified from 130 nA up to 10 mu A in five programmable steps (9.5 dB per step). The SG achieves a spurious-free dynamic range larger than 40 dB while covering almost three decades in frequency. Such performance enables measurements with errors below 1%, as it is required for accurate bioimpedance measurements in many medical applications.
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| 30. |
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| 31. |
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