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.

This paper presents a 16-channel analog frontend (AFE) for wearable multi-channel surface electromyography recording. The proposed architecture adopts frequency-division multiplexing (FDM), enabling extensive sharing of signal conditioning circuitry and requiring only three cables for transmission to an external back-end for digital signal processing. Benefiting from the up-conversion process, the FDM signal exhibits robustness against cable motion artifacts and mains interference, allowing short-distance communication without compromising signal quality. This work achieves a channel-to-cable ratio of 16:3, dramatically reducing system complexity. Implemented in a 180 nm CMOS technology, the proposed 16-channel AFE occupies only 6.42 mm2 and consumes 40.1 µW per channel from a 1.5 V supply. Measurements on a forearm demonstrate the capability to simultaneously detect muscle activation from various muscle groups, showcasing its potential for gesture recognition applications.

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.

This thesis presents an innovative approach to the development of a fully integrated multi-channel neuromuscular electrical stimulator (NMES) system and a multi-channel surface electromyography (sEMG) acquisition system for musculoskeletal (MSK) healthcare applications. The main objective is to integrate therapeutic and diagnostic tools into a compact wearable device, enabling closed-loop electrical therapy. By leveraging advancements in semiconductor technology, this thesis explores the implementation of application-specific integrated circuits (ASIC) to combine high-voltage (HV) NMES and low-voltage sEMG signal acquisition circuits on a single chip using a 180 nm bipolar-CMOS-DMOS technology.  

The research addresses several key challenges in existing NMES and sEMG systems: the need for a compact, multi-channel NMES device; the need for safe electrical muscular stimulation; the need for spatiotemporal information through multi-channel acquisition; and the need for high channel counts and efficient chip area utilization. To overcome these challenges and advance the NMES technology, this thesis proposes several innovative circuit solutions, including a configurable HV-tolerant multi-channel stimulator, an integrated fail-safe protection circuit, and an inductorless on-chip HV generator. Additionally, channel-sharing techniques for multi-channel biopotential acquisition are comprehensively explored, and a novel frequency-division multiplexed architecture is proposed, featuring low noise, low power consumption, and minimized system complexity. 

A significant contribution of this thesis work is the integration of multi-channel NMES and sEMG systems in an ASIC, leading to the development of a real-time embedded system for wearable medical applications. This embedded system incorporates the proposed ASIC for bidirectional interfacing with muscles and an off-the-shelf microcontroller for data acquisition, signal processing, and stimulation pattern control. The proposed system facilitates the continuous collection of vital physiological conditions (e.g., motion intention, contraction force, and fatigue level) of the human muscular system, enabling timely adjustments and interventions via electrical stimulation. In-vivo experimental results showcase its potential to enhance electrical therapy outcomes through closed-loop control and pave the way for improved patient care.

Denna avhandling presenterar ett innovativt tillvägagångssätt för utveckling av ett fullt integrerat flerkanals neuromuskulärt elektriskt stimulator (NMES) system och ett flerkanals ytelektromyografi (sEMG) insamlingssystem för applikationer inom muskuloskeletal hälsovård. Huvudmålet är att integrera terapeutiska och diagnostiska verktyg i en kompakt bärbar enhet, vilket möjliggör sluten elektrisk terapi. Genom att utnyttja framsteg inom halvledarteknologi undersöker denna avhandling implementeringen av applikationsspecifika integrerade kretsar (ASIC) för att kombinera högspännings (HV) NMES och lågspännings sEMG-signalupptagningskretsar på ett enda chip med hjälp av en 180 nm bipolär-CMOS-DMOS-teknologi.

Forskningen adresserar flera centrala utmaningar i befintliga NMES- och sEMG-system: behovet av en kompakt flerkanals NMES-enhet; behovet av säker elektrisk muskelstimulering; behovet av spatiotemporal information genom flerkanals signalupptagning; samt behovet av hög kanalantal och effektiv chipytanvändning. För att övervinna dessa utmaningar och främja NMES-teknologin, föreslår denna avhandling flera innovativa kretsslösningar, inklusive en konfigurerbar HV-tolerant flerkanals stimulator, en integrerad failsafe skyddskrets och en induktorlös on-chip HV-generator. Dessutom utforskas kanaldelningstekniker omfattande, och ett nytt frekvensdelningsmultiplexat flerkanals biopotential-insamlingssystem utvecklas, som kännetecknas av låg brusnivå, låg strömförbrukning och minimerad systemkomplexitet.

En betydande insats i denna avhandling är integrationen av flerkanals NMES- och sEMG-system i en ASIC, vilket leder till utvecklingen av ett realtids inbäddat system för bärbara medicinska applikationer. Detta inbäddade system inkorporerar den föreslagna ASIC för tvåvägsgränssnitt med muskler och en standard mikrokontroller för datainsamling, signalbehandling och styrning av stimulansmönster. Det föreslagna systemet underlättar kontinuerlig insamling av vitala fysiologiska förhållanden (t.ex. rörelseavsikt, kontraktionskraft och trötthetsnivå) i människans muskelsystem, vilket möjliggör snabba justeringar och interventioner via elektrisk stimulering. In-vivo experimentella resultat visar dess potential att förbättra resultaten av elektrisk terapi genom sluten styrning och banar väg för förbättrad patientvård.

Biopotential acquisition chopper instrumentation amplifiers require a dc-servo loop (DSL) in order to filter electrode dc offsets. However, the noise performance degradation due to the addition of the DSL is often overlooked despite that it can be very detrimental at the frequencies of interest. This article presents an in-depth noise analysis of biopotential acquisition chopper instrumentation amplifiers with analog DSLs. Analytical expressions that predict the noise of different DSL implementations are found and a design flow to minimize their noise contribution is proposed. The design methodology is demonstrated with example circuits targeting biopotential recording systems. These circuits are implemented using a standard 180 nm CMOS technology, and their performance is verified through postlayout simulations. The findings of this work provide a comprehensive understanding of the noise characteristics of a DSL, its impact on noise performance, and design strategies for noise optimization.

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.

Neuromuscular electrical stimulation (NMES) requires voltages exceeding several tens of volts which are typically obtained by using DC-DC boost converters. However, these converters incorporate a large external inductor, which hinders integration and severely restricts the minimum size of the stimulator. This paper presents a charge pump (CP) high-voltage generator particularly designed for NMES applications. The proposed hybrid CP comprises a low-voltage latched CP followed by a high-voltage Dickson CP with boosted pumping clocks. This architecture generates an output voltage of 40.5 V from a 3.3 V supply, enabling the delivery of up to 30 mA stimulation pulses at a maximum frequency of 50 Hz. The circuit is designed in a 180 nm HV CMOS process and occupies a silicon area of 2.7 mm 2 . By eliminating the inductor and requiring only one external storage capacitor, this design has the potential of being used in compact stimulators for wearable medical applications.

Chopper amplifiers for biopotential acquisition commonly suppress differential electrode DC offsets by using a DC-servo loop (DSL). However, the noise contribution of the DSL is always neglected in noise analysis. The noise introduced by the DSL, in particular at low frequencies, is of great importance in biosensor applications. This work presents the noise modeling of a current-balancing chopper amplifier with DSL and describes the effect of the DSL on the noise performance. Two different DSL implementations are analyzed. It is found that the exact placement of the chopper in the DSL has a strong impact in the noise performance; therefore, its placement can not be arbitrarily selected. A circuit topology to minimize its noise contribution is then proposed and verified by simulation.

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.