[Show abstract][Hide abstract] ABSTRACT: In this study we implemented six mathematical models to describe the electric performance of 96 neural electrodes coated with a single film of conductive polymer. The experiments were performed in-vitro, reproducing the environment of the implanted electrodes, and impedance was measured using the electrochemical impedance spectroscopy (EIS) method. We found that the double-layer capacitance at the polymer/solution interface is the most representative parameter affecting charge transfer, and observed that this capacitance increases linearly with the polymer thickness.
[Show abstract][Hide abstract] ABSTRACT: The goal of functional electrical stimulation is to restore lost movements by excitation of motor axons innervating the target muscle. For optimal electrode placement and geometry the distribution and spatial orientation of the desired motor axons has to be known. In this study, the response of motor axons with different orientations to electrical stimulation was simulated. Three electrode geometries with the same area were used. The simulated axon activation was compared to experimental force measurements and showed good agreements. It is now assumed that optimal electrode geometry does strongly depend on motor axon orientation, which can vary from one subject to the other. Lack of knowledge about the dominant motor axon orientation makes the use of square, round or multipad electrodes favorable.
[Show abstract][Hide abstract] ABSTRACT: Memristive devices are promising candidates for future non-volatile memory applications and mixed-signal circuits. In the field of neuromorphic engineering these devices are especially interesting to emulate neuronal functionality. Therefore, new materials and material combinations are currently investigated, which are often not compatible with Si-technology processes. The underlying mechanisms of the device often remain unclear and are paired with low device endurance and yield. These facts define the current most challenging development tasks towards a reliable memristive device technology. In this respect, the MemFlash concept is of particular interest. A MemFlash device results from a diode configuration wiring scheme of a floating gate transistor, which enables the persistent device resistance to be varied according to the history of the charge flow through the device. In this study, we investigate the scaling conditions of the floating gate oxide thickness with respect to possible applications in the field of neuromorphic engineering. We show that MemFlash cells exhibit essential features with respect to neuromorphic applications. In particular, cells with thin floating gate oxides show a limited synaptic weight growth together with low energy dissipation. MemFlash cells present an attractive alternative for state-of-art memresitive devices. The emulation of associative learning is discussed by implementing a single MemFlash cell in an analogue circuit.
[Show abstract][Hide abstract] ABSTRACT: Diodes in forward direction exhibit excellent ESD ruggedness and are thus widely used in both discrete and on-chip electro-static discharge (ESD) protection devices. Due to the conductivity modulation under an ESD stress, a transient voltage overshoot is observed at the beginning of a fast discharge event. Since the voltage overshoot can be harmful, understanding the origin of the overshoot is crucial to design optimized protection diodes. In this paper, it will be shown that existing models can result in much underestimated overshoot voltage, especially for diodes with a large lowly doped region. This can be attributed to the negligence of transient charge distribution in the lowly doped region. A new model that takes this effect into account as well as impact-ionization is presented.
IEEE Transactions on Electron Devices 08/2014; 61(8):2682-2689. DOI:10.1109/TED.2014.2330365 · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work a 130 nm CMOS 64 channel neural stimulator is presented, which is scalable by connecting it in a daisy chain configuration, for applications requiring larger number of stimulation sites, as it is of interest for retinal implants with improved resolution. Each channel is composed of a hybrid architecture current steering 8 bit DAC, enabling the low power consumption and high channel integration on a small chip area. Besides, the DAC allows stimulating with several waveforms in order to save stimulation energy. An on-chip module was implemented to control galvanostatic deposition of PEDOT on the electrodes. A schema is presented to avoid the residual charge due to cross electrode stimulation and process mismatch.
[Show abstract][Hide abstract] ABSTRACT: Electrical Neurostimulation has been effective for treating and reducing symptoms of neurological diseases, for alleviating some types of chronic pain and for restoring sensory or neuromuscular deficits. Because of the energy and size limitation on fully implantable devices, it is important to keep devices small and at low power. It was already demonstrated that non-rectangular waveforms provide a more energy-efficient neural stimulation. In this article is shown how a hybrid architecture of current steering DAC is suitable to this application, because of its specifications: the ability to convert several waveforms directly from digital to analog current signals, low power consumption, small chip area requirement, the capability of sharing common stages and also for its simplicity. An ASIC has been developed composed of four stimulator channels, capable of driving several current waveforms. The design is implemented in 130 nm CMOS technology.
[Show abstract][Hide abstract] ABSTRACT: This paper presents intramuscular electromyogram (EMG) signals obtained with a fully implantable measurement system that were recorded during goal directed arm movements. In a first implantation thin film electrodes were epimysially implanted on the deltoideus of a rhesus macaque and the encapsulation process was monitored by impedance measurements. Increase of impedance reached a constant level after four weeks indicating a complete encapsulation of electrodes. EMG recorded with these electrodes yielded a signal-to-noise ratio of about 80 dB at 200 Hz. The EMG recorded during goal-directed arm movements showed a high similarity to movements in the same direction and at the same time presented clear differences between different movement directions in time domain. Six classifiers and seven time and frequency domain features were investigated with the aim of discriminating the direction of arm movement from EMG signals. Reliable recognition of arm movements was achieved for a subset of the movements under investigation only. A second implantation of the whole measurement system for nine weeks demonstrated simple handling during surgery and good biotolerance in the animals.
IEEE Transactions on Instrumentation and Measurement 07/2013; 62(7). DOI:10.1109/TIM.2013.2253992 · 1.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper describes a single stage fully differential folded cascode operational transconductance amplifier (OTA) with fully differential gain boosting amplifiers designed in 1.2 VDC 130nm CMOS process technology. The amplifier is the driver for the analog to digital converter (ADC) of a blood pressure sensing medical implant  which uses wireless power transmission as its energy source . The medical implant’s design specifications require an amplifier with wide output swing, high accuracy, and the bandwidth to drive a differential 5 pF load at 4 ksps with minimum power consumption. The gain boosting amplifiers are telescopic cascoded amplifiers, which, by their design, have an input and output common mode voltage relationship which is opposite to what is needed for a gain boosted cascode configuration. To correct for this, a method for DC shifting the amplifier’s input voltage using a switched capacitor network is presented.
[Show abstract][Hide abstract] ABSTRACT: A memristive operation mode of a single floating gate transistor is presented. The device resistance varied accordingly to the charge flow through the device. Hysteretic current-voltages including a resistance storage capability were observed. These experimental findings are theoretically supported by a capacitive based model. The presented two-terminal MemFlash-cell can be considered as a potential substitute for any memristive device (especially for reconfigurable logic, cross-bar arrays, and neuromorphic circuits) and is basically compatible with current Si-fabrication technology. The obvious trade-off between a memristive device based on a state-of-the-art silicon process technology and power consumption concerns will be discussed.
[Show abstract][Hide abstract] ABSTRACT: Neuromuscular electrical stimulation is useful for restoring the movement of extremities in the treatment of some neurological disorders. A portable neuromuscular stimulator was developed for rehabilitation, Functional Electrical Stimulation (FNS) and for experimentation. The device is battery powered and can be controlled wirelessly. The adjustable current output is one of the advantages of this stimulator, because it can deliver several waveforms and it is possible to change every parameter on the stimulation signal. Power consumption, high selectivity, patient comfort and portability are important terms for medical electronic devices. Several setups were developed for the neuromuscular stimulator in order to perform different experiments.
[Show abstract][Hide abstract] ABSTRACT: Electrical Neurostimulation is useful in several medical therapies, for the treatment of neuromuscular deficits and for restoring physiological and sensory functions. Fully implantable devices are preferable in order to reach high selectivity and to give comfort to the patient. However, smaller devices bring more challenges regarding fabrication techniques and technology compliances, and power consumption is an important issue. In this study we analyze the use of different waveforms for performing neuromuscular stimulation, and we show how different waveforms require less energy to produce the same muscle reaction.
[Show abstract][Hide abstract] ABSTRACT: This paper will describe a wireless power transmission system which has been used during in vivo testing to power a blood pressure sensing implant  located inside the abdominal aorta of a 100 kg swine. Wireless power transmission is accomplished using an external power sender which is magnetically coupled to an RF energy harvester block which has been integrated into the medical implant's system package. The power sender is a class E amplifier which drives a wire loop antenna at 4 MHz, and the power receiver uses a ferro-magnetic core in an LC resonant circuit coupled to a Schottky diode charge pump rectifier followed by a DC voltage regulator.
[Show abstract][Hide abstract] ABSTRACT: An array test structure for highly parallelized stressing and measurements of ultrathin MOS gate dielectrics is presented. The array test structure consisting of thousands of NMOS devices under test (DUTs) provides a large and significant statistical base for analysis of dielectric breakdown and the stress induced degradation of transistor parameters. The test array has been fabricated in a standard mixed-mode 130 nm CMOS technology. As such technologies offer both thin and thick gate dielectrics for MOS transistors, different gate dielectric thicknesses have been chosen for DUTs and digital control logic which gives the possibility to stress the DUTs with high gate voltages and prevent the control logic from degradation.
[Show abstract][Hide abstract] ABSTRACT: Electrical Neurostimulation has been effective in several medical therapies and also for restoring physiological, sensory and neuromuscular deficits. The rectangular pulse waveform has been used as a standard shape for neural stimulation. However, it has been shown that non-rectangular waveforms provide a more energy-efficient neural stimulation. An ASIC has been developed composed of a stimulator, capable of driving several current waveforms, and an analog channel for biosignal acquisition. The design is implemented in 130 nm / 1.2 V CMOS technology, requiring a silicon area of 0.696 mm2. Experimental results show that the stimulator can generate analog signals from a digital input of 8 bits. The output stage can drive up to ±9.8 μA, with a DNL and INL of 0.47 and 1.05 LSB, respectively. Its SFDR is 50.2 dB. And it consumes a maximum of 128.12 μW. The analog input channel presents a power consumption of 140 μW, a gain of 52.2 dB, a bandwidth of 0.5 – 1130 Hz and 10 μVrms of noise.
[Show abstract][Hide abstract] ABSTRACT: A capacitive sensor system is integrated into an active capacitive ECG electrode. This system provides a signal, which is correlated with movement artifacts during ECG signal acquisition, and can be used as reference signal in an adaptive filter.
Biomedical Engineering International Conference (BMEiCON), 2012; 01/2012