Wolfgang Eberle

An implantable 455-active-electrode 52-channel CMOS neural probe

Several studies have demonstrated that understanding certain brain functions can only be achieved by simultaneously monitoring the electrical activity of many individual neurons in multiple brain areas [1]. Therefore, the main tradeoff in neural probe design is between minimizing the probe dimensions and achieving high spatial resolution using large arrays of small recording sites. Current state-of-the-art solutions are limited in the amount of simultaneous readout channels [2], contain a small number of electrodes [2,3] or use hybrid implementations to increase the number of readout channels [3,4].

A performance and complexity comparison of auto-correlation and cross-correlation for OFDM burst synchronization

A symbol timing synchronization scheme is critical in the design of an OFDM receiver. Large timing errors can result in a loss of orthogonality between subcarriers, ISI and severe bit error degradation. To minimize this degradation, standards incorporate preambles suitable for two kinds of synchronization algorithms: auto-correlation and crosscorrelation. Unfortunately, the performance and complexity tradeoffs between these algorithms have not been well explored. To address this problem, we have built an FPGA implementation of a synchronization system using both autocorrelation and cross-correlation. Based on our results, in this paper we propose a novel cross-correlation synchronizer and hardware architecture. We then compare its performance and complexity to auto-correlation algorithms for HiperLAN/2 and IEEE 802.11a preambles.

Endothelial cell responses to micropillar substrates of varying dimensions and stiffness

In the vascular niche, the extracellular matrix (ECM) provides a structural scaffold with a rich ligand landscape of essential matrix proteins that supports the organization and stabilization of endothelial cells (ECs) into functional blood vessels. Many of the physical interactions between ECs and macromolecular components of the ECM occur at both the micron and submicron scale. In addition, the elasticity of the ECM has been shown to be a critical factor in the progress of the angiogenic cascade. Here, we sought to determine the effect of substrate topography and elasticity (stiffness) on EC behavior. Utilizing a unique SiO(2) substrate with an array of micropillars, we first demonstrate that micropillars with heights >3 μm significantly decrease EC adhesion and spreading. Fibronectin (Fn) patterning of 1 μm high micropillars enabled EC adhesion onto the micropillars and promoted alignment in a single-cell chain manner. We then developed a robust method to generate a soft micropillar substrate array made of polydimethylsiloxane (PDMS), similar to the SiO(2) substrate. Finally, we examined the kinetics of EC adhesion and spreading on the soft PDMS substrates compared to the stiff SiO(2) substrates. Culturing cells on the PDMS substrates demonstrated an enhanced EC elongation and alignment when compared to stiff SiO(2) with similar topographical features. We conclude that the elongation and alignment of ECs is coregulated by substrate topography and stiffness and can be harnessed to guide vascular organization.

80-Mb/s QPSK and 72-Mb/s 64-QAM flexible and scalable digital OFDM transceiver ASICs for wireless local area networks in the 5-GHz band

With the advent of mobile communications, voice telecommunications became wireless. Future applications, however, target multimedia, messaging, and high-speed Internet access, all expressing the need for a broadband high-speed wireless access technique. Both the domestic multimedia and the wireless local area network (WLANs) business markets are addressed. Established systems deliver 2-11 Mb/s based on spectrally inefficient spread-spectrum techniques, where scalability has reached a limit. The next generation of modems requires spectrally more efficient low-power and highly integrated solutions. We describe here the design of two digital baseband orthogonal frequency division multiplex (OFDM) signal processing ASICs, implementing respectively a quaternary phase-shift keying (QPSK)-based 80-Mb/s and a 64 quadrature amplitude modulation (QAM)-based 72-Mb/s digital inner transceiver. The latter partially matches the Hiperlan/2 and IEEE 802.11a standards. Joint development of signal processing algorithms and architectures along with on-chip data transfer, control, and partitioning leads to a low-power, yet flexible and scalable implementation. Both ASICs were designed in a unique object-oriented C++ design flow starting from algorithm level. The ASICs were successfully tested in a 5-GHz testbed both for file data transfer and web-cam multimedia transmission.

A Multichannel Integrated Circuit for Electrical Recording of Neural Activity, With Independent Channel Programmability

Since a few decades, micro-fabricated neural probes are being used, together with microelectronic interfaces, to get more insight in the activity of neuronal networks. The need for higher temporal and spatial recording resolutions imposes new challenges on the design of integrated neural interfaces with respect to power consumption, data handling and versatility. In this paper, we present an integrated acquisition system for in vitro and in vivo recording of neural activity. The ASIC consists of 16 low-noise, fully-differential input channels with independent programmability of its amplification (from 100 to 6000 V/V) and filtering (1-6000 Hz range) capabilities. Each channel is AC-coupled and implements a fourth-order band-pass filter in order to steeply attenuate out-of-band noise and DC input offsets. The system achieves an input-referred noise density of 37 nV/√Hz, a NEF of 5.1, a CMRR >; 60 dB, a THD <; 1% and a sampling rate of 30 kS/s per channel, while consuming a maximum of 70 μA per channel from a single 3.3 V. The ASIC was implemented in a 0.35 μm CMOS technology and has a total area of 5.6 × 4.5 mm2. The recording system was successfully validated in in vitro and in vivo experiments, achieving simultaneous multichannel recordings of cell activity with satisfactory signal-to-noise ratios.

Effect of Insertion Speed on Tissue Response and Insertion Mechanics of a Chronically Implanted Silicon-Based Neural Probe

In this study, the effect of insertion speed on long-term tissue response and insertion mechanics was investigated. A dummy silicon parylene-coated probe was used in this context and implanted in the rat brain at 10 μm/s (n = 6) or 100 μm/s ( n = 6) to a depth of 9 mm. The insertion mechanics were assessed by the dimpling distance, and the force at the point of penetration, at the end of the insertion phase, and after a 3-min rest period in the brain. After 6 weeks, the tissue response was evaluated by estimating the amount of gliosis, inflammation, and neuronal cell loss with immunohistochemistry. No difference in dimpling, penetration force, or the force after a 3-min rest period in the brain was observed. However, the force at the end of the insertion phase was significantly higher when inserting the probes at 100 μm/s compared to 10 μm/s. Furthermore, an expected tissue response was seen with an increase of glial and microglial reactivity around the probe. This reaction was similar along the entire length of the probe. However, evidence for a neuronal kill zone was observed only in the most superficial part of the implant. In this region, the lesion size was also greatest. Comparison of the tissue response between insertion speeds showed no differences.

From myth to methodology: cross-layer design for energy-efficient wireless communication

During the last decade, wireless communication has seen a trend towards application diversification leading to a significant growth in users. With the availability of - however energy-limited - nomadic devices and real-time multimedia applications, user demand is shifting from simply asking for higher data rates to more complex requirements in terms of quality of service (QoS) and energy-efficiency. In this new context energy management is becoming a key success factor. Optimized energy-efficiency requires an energy management that continuously trades off QoS and energy adapting to varying user expectations and environment dynamics. But, QoS can only be evaluated on top of the whole protocol stack while energy consumption largely appears at the lower layers. To minimize overhead during the transitions between layers, we need to address the problem from a cross-layer perspective. We present a methodology that, based on systematic exploration, effective problem partitioning and minimal cross-layer interface, allows energy management in a cross-layer way, while maintaining efficient layered semantics. Different case studies in the context of wireless LAN (WLAN) for multimedia and data traffic transport are discussed, to show how cross-layer energy management can easily be included in systems running state-of-the-art protocols.

Synaptic dysfunction in hippocampus of transgenic mouse models of Alzheimer's disease: A multi-electrode array study

APP.V717I and Tau.P301L transgenic mice develop Alzheimers disease pathology comprising important aspects of human disease including increased levels of amyloid peptides, cognitive and motor impairment, amyloid plaques and neurofibrillary tangles. The combined model, APP.V717I×Tau.P301L bigenic mice (biAT mice) exhibit aggravated amyloid and tau pathology with severe cognitive and behavioral defects. In the present study, we investigated early changes in synaptic function in the CA1 and CA3 regions of acute hippocampal slices of young APP.V717I, Tau.P301L and biAT transgenic animals. We have used planar multi-electrode arrays (MEA) and improved methods for simultaneous multi-site recordings from two hippocampal sub-regions. In the CA1 region, long-term potentiation (LTP) was severely impaired in all transgenic animals when compared with age-matched wild-type controls, while basal synaptic transmission and paired-pulse facilitation were minimally affected. In the CA3 region, LTP was normal in Tau.P301L and APP.V717I but clearly impaired in biAT mice. Surprisingly, frequency facilitation in CA3 was significantly enhanced in Tau.P301L mice, while not affected in APP.V717I mice and depressed in biAT mice. The findings demonstrate important synaptic changes that differ considerably in the hippocampal sub-regions already at young age, well before the typical amyloid or tau pathology is evident.

Single-cell recording and stimulation with a 16k micro-nail electrode array integrated on a 0.18 μm CMOS chip

To cope with the growing needs in research towards the understanding of cellular function and network dynamics, advanced micro-electrode arrays (MEAs) based on integrated complementary metal oxide semiconductor (CMOS) circuits have been increasingly reported. Although such arrays contain a large number of sensors for recording and/or stimulation, the size of the electrodes on these chips are often larger than a typical mammalian cell. Therefore, true single-cell recording and stimulation remains challenging. Single-cell resolution can be obtained by decreasing the size of the electrodes, which inherently increases the characteristic impedance and noise. Here, we present an array of 16,384 active sensors monolithically integrated on chip, realized in 0.18 μm CMOS technology for recording and stimulation of individual cells. Successful recording of electrical activity of cardiac cells with the chip, validated with intracellular whole-cell patch clamp recordings are presented, illustrating single-cell readout capability. Further, by applying a single-electrode stimulation protocol, we could pace individual cardiac cells, demonstrating single-cell addressability. This novel electrode array could help pave the way towards solving complex interactions of mammalian cellular networks.

Synchronization and AGC proposal for IEEE 802.11 a burst OFDM systems

Synchronization is critical in the design of an OFDM receiver. Large timing offsets result in a loss of orthogonality between subcarriers, ISI, and severe bit error degradation. To minimize this degradation, standards incorporate preambles intended for all OFDM acquisition functions including automatic gain control (AGC) and synchronization. Several synchronization algorithms have been proposed. Unfortunately, these proposals do not take into account AGC effects which degrade results in practice. To address this problem, we have built an FPGA implementation of both an AGC and synchronization system. Based on these results, in this paper we propose a novel standard compliant auto-correlation synchronization algorithm and AGC interface, then measure the total system performance.