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We are developing robot controllers based on biomimetic design principles. The goal is to realise the adaptive capabilities of the animal models in natural environments. We report feasibility studies of a hybrid architecture that instantiates a command and coordinating level with computed discrete-time map-based (DTM) neuronal networks and the central pattern generators with analogue VLSI (Very Large Scale Integration) electronic neuron (aVLSI) networks. DTM networks are realised using neurons based on a 1-D or 2-D Map with two additional parameters that define silent, spiking and bursting regimes. Electronic neurons (ENs) based on Hindmarsh–Rose (HR) dynamics can be instantiated in analogue VLSI and exhibit similar behaviour to those based on discrete components. We have constructed locomotor central pattern generators (CPGs) with aVLSI networks that can be modulated to select different behaviours on the basis of selective command input. The two technologies can be fused by interfacing the signals from the DTM circuits directly to the aVLSI CPGs. Using DTMs, we have been able to simulate complex sensory fusion for rheotaxic behaviour based on both hydrodynamic and optical flow senses. We will illustrate aspects of controllers for ambulatory biomimetic robots. These studies indicate that it is feasible to fabricate an electronic nervous system controller integrating both aVLSI CPGs and layered DTM exteroceptive reflexes.

New two-dimensional (2D) position sensitive solid state pixel detectors with dedicated multi-channel mixed-signal front-end readout integrated circuits (ICs) have been developed for x-ray and gamma ray imaging. These pixel detectors were designed to be versatile and accommodate many types of position-sensitive solid-state sensors. These 2D pixel detectors are designed to address the needs of a wide range of photon counting applications with high energy resolution imaging, high spatial resolution and for fast photon counting with simultaneous multiple energy binning capability. The first family of these pixel detectors is intended for spectroscopy applications with sensors such as Si, Ge, GaAs, HgI2, PbI2, Se, CdTe and CdZnTe in a variety of configurations to detect and image x-rays and gamma-rays of energies up to 1.3 MeV. The second family is developed for fast photon counting with simultaneous energy binning. They can be used with similar solid state sensors. The third family is for high spatial resolution imaging with resolution down to 50 times 50 micron.

An electronic circuit intended to simulate the nonlinear dynamics of a simplified 3-cell model of the pyloric central pattern generator in California spiny lobster stomato gastric ganglion is presented. The model employs the synaptic phase locked loop (SPLL) concept where the frequency of oscillations of a postsynaptic cell is mainly controlled by the synaptic current which depends on the phase shift between the oscillations. The theoretical study showed that the system has a stable steady state with correct phase shifts between the oscillations and that this regime is stable when the frequency of the pacemaker cell is varied over a wide range. The main bifurcations in the system were studied analytically, in computer simulations, and in experiments with the electronic circuit. The experimental measurements are in good agreement with the expectations of the theoretical model.

Utilization of chaotic signals for covert communications remains a very promising practical application. Multiple studies indicate that the major shortcoming of recently proposed chaos-based communication schemes is their susceptibility to noise and distortions in communication channels. In this paper, we review a new approach to communication with chaotic signals, which demonstrates good performance in the presence of channel distortions. This communication scheme is based upon chaotic signals in the form of pulse trains where intervals between the pulses are determined by chaotic dynamics of a pulse generator. The pulse train with chaotic inter-pulse intervals is used as a carrier. Binary information is modulated onto this carrier by the pulse position modulation method, such that each pulse is either left unchanged or delayed by a certain time, depending on whether "0" or "1" is transmitted. By synchronizing the receiver to the chaotic-pulse train we can anticipate the timing of pulses corresponding to "0" and "1" and thus can decode the transmitted information. Based on the results of theoretical and experimental studies we discuss the basic design principles for the chaotic-pulse generator, its synchronization, and the performance of the chaotic-pulse communication scheme in the presence of channel noise and filtering. We also discuss the possibilities of multiuser communication using CPPM and its advantages over standard communication techniques.

In this paper, we discuss fundamentals for the design of a source of chaotic signals based on a blocking oscillator circuit. We study a modification of a well-known circuit of blocking oscillator which leads to the onset of chaotic oscillations. The output signal of such chaotic oscillator is a series of short term pulses characterized by chaotic fluctuations of time intervals between pulses. Such chaotic pulse signals possess a broad-band continuous power spectrum and short correlation length. We discuss the results of theoretical and experimental studies of nonlinear dynamics of the chaotic blocking oscillator.

Based on experiments with the locust olfactory system, we demonstrate that model sensory neural networks with lateral inhibition can generate stimulus specific identity-temporal patterns in the form of stimulus-dependent switching among small and dynamically changing neural ensembles (each ensemble being a group of synchronized projection neurons). Networks produce this switching mode of dynamical activity when lateral inhibitory connections are strongly non-symmetric. Such coding uses ‘winner-less competitive’ (WLC) dynamics. In contrast to the well known winner-take-all competitive (WTA) networks and Hopfield nets, winner-less competition represents sensory information dynamically. Such dynamics are reproducible, robust against intrinsic noise and sensitive to changes in the sensory input. We demonstrate the validity of sensory coding with WLC networks using two different formulations of the dynamics, namely the average and spiking dynamics of projection neurons (PN).

We report on experimental studies of synchronization phenomena in a pair of analog electronic neurons (ENs). The ENs were designed to reproduce the observed membrane voltage oscillations of isolated biological neurons from the stomatogastric ganglion of the California spiny lobster Panulirus interruptus. The ENs are simple analog circuits which integrate four-dimensional differential equations representing fast and slow subcellular mechanisms that produce the characteristic regular/chaotic spiking–bursting behavior of these cells. In this paper we study their dynamical behavior as we couple them in the same configurations as we have done for their counterpart biological neurons. The interconnections we use for these neural oscillators are both direct electrical connections and excitatory and inhibitory chemical connections: each realized by analog circuitry and suggested by biological examples. We provide here quantitative evidence that the ENs and the biological neurons behave similarly when coupled in the same manner. They each display well defined bifurcations in their mutual synchronization and regularization. We report briefly on an experiment on coupled biological neurons and four-dimensional ENs, which provides further ground for testing the validity of our numerical and electronic models of individual neural behavior. Our experiments as a whole present interesting new examples of regularization and synchronization in coupled nonlinear oscillators., R.D. Pinto was supported by the Brazilian Agency Fundaçao de Amparo a Pesquisa do Estado de Sao Paulo - FAPESP. P.V. acknowledges support from MEC. Partial support for this work came from the U.S. Department of Energy, Office of Science, under Grants Nos. DE-FG03-90ER14138 and DE-FG03-96ER14592.

Small assemblies of neurons such as central pattern generators (CPG) are known to express regular oscillatory firing patterns comprising bursts of action potentials. In contrast, individual CPG neurons isolated from the remainder of the network can generate irregular firing patterns. In our study of cooperative behavior in CPGs we developed an analog electronic neuron (EN) that reproduces firing patterns observed in lobster pyloric CPG neurons. Using a tuneable artificial synapse we connected the EN bidirectionally to neurons of this CPG. We found that the periodic bursting oscillation of this mixed assembly depends on the strength and sign of the electrical coupling. Working with identified, isolated pyloric CPG neurons whose network rhythms were impaired, the EN/biological network restored the characteristic CPG rhythm both when the EN oscillations are regular and when they are irregular.

Using chaotic signals in spread-spectrum communications has a few clear advantages over traditional approaches. Chaotic signals are nonperiodic, wideband, and more difficult to predict, reconstruct, and characterize than periodic carriers. These properties of chaotic signals make it more difficult to intercept and decode the information modulated upon them. However, many suggested chaos-based communication schemes do not provide processing gain, a feature highly desirable in spread-spectrum communication schemes. In this paper, we suggest two communication schemes that provide a processing gain. The performance of these and of the earlier proposed differential chaos shift keying is studied analytically and numerically for discrete time implementations. It is shown that, when performance is characterized by the dependence of bit error rate on E/sub b//N/sub 0/, the increase of the spreading sequence length beyond a certain point degrades the performance. For a given E/sub b//N/sub 0/, there is a length of the spreading sequence that minimizes the bit error rate.

Synchronization of chaotic systems by control using a phase feedback loop is investigated. Suggested algorithm of synchronization can be used both for discrete time and for continuous time systems. Due to similarity to the usual phase lock loop, this method allows generalization of the majority of applications of phase lock-in for chaotic systems.

We have developed a new readout ASIC for multienergy CT applications, which can be flip-chip bonded directly to a two-dimensional solid-state pixel detector. Its initial intended use is in CT breast imaging. This chip has an array of 80 × 96 readout channels with a pitch of 0.2 mm × 0.2 mm. The design uses through-silicon vias for the ASIC's power, bias and digital 1/0 connections to allow for a fully abuttable layout with a die size of 19.1 mm × 16.3 mm. Each channel has a charge-sensitive amplifier with individually adjustable parameters such as gain and baseline offset. The amplifiers are designed for count rates up to 1.25 × 108 photons per second per square millimeter (5 × 106 photons per second per pixel). The amplifier signals are discriminated by four comparators and counted in 12-bit pulse counters. The readout dead time is kept at negligible levels by copying each counter's data to its own dedicated readout register at the end of each count period, for readout during the following period. Reading the more than 30,000 registers can be accomplished in less than 0.5 ms, allowing for a frame rate of 2000 frames per second.

Experimental evidence is provided for the synchronization of chaotic self-excited oscillators and chaotic synchronous response. With unidirectional coupling between two chaotic nonlinear circuits, synchronous chaotic oscillations can result from either forced synchronization or the response phenomenon. With mutual coupling, two originally chaotic oscillators can become time periodic, a result that we have shown to persist for values of the coupling down to noise level.

Synchronization of chaotic self-excited oscillations and chaotic synchronous response are studied using chaotic electronic oscillators with unidirectional coupling.

We have developed a new readout ASIC for high-resolution gamma-ray spectroscopy, which can be flip-chip bonded directly to a two-dimensional solid-state pixel array. This chip, called DANA-3 (Detector Array for Nuclear Applications), has a 16 × x16 array of anode readout channels with a pitch of 0.5 mm × 0.5 mm, plus an extra channel optimized for the cathode signals. To minimize power consumption, the ASIC was designed in a 0.18 µm process. To further reduce power dissipation, we incorporated automatic switching between different modes of operation (Watchdog, Counting, and Spectroscopy) depending on user-selectable radiation level thresholds, an ability to power down unused channels, and a low-power, low-noise differential I/O interface. Power dissipation ranges from 7 mW in watchdog mode to 50 mW with all channels enabled in spectroscopy mode. In the latter mode, the circuit features low-noise, high-energy resolution performance and allows for depth-of-interaction optimization using the cathode signal. The ASIC layout is three-side abuttable, so individual circuits can be combined into larger arrays. For optimal performance of the ASIC in different applications the main parameters of the analog channels can be programmed (globally or individually) over a wide range. In this paper we describe the ASIC design details and preliminary results of lab testing and characterization, including noise measurements and testing with pulser signals.

A new type of synchronized chaos conditioned by the threshold synchronization of relaxation oscillators with chaotic behaviour is studied experimentally. It is shown that for a certain parameter ratio the pulses generated by the chaotic oscillator may be synchronized by periodic and chaotic pulse sequences generated by the drive oscillator. It is found that the threshold synchronization regime enables one to detect modulation of chaotic signals.

We have developed a prototype of a scalable high-resolution direction and energy sensitive gamma-ray detection system that operates in both coded aperture (CA) and Compton scatter (CS) modes to obtain optimal efficiency and angular resolution over a wide energy range. The design consists of an active coded aperture constructed from 52 individual CZT planar detectors each measuring 3×3×6 mm3 arranged in a MURA pattern on a 10×10 grid, with a monolithic 20×20×5 mm3 pixelated (8×8) CZT array serving as the focal plane. The combined mode is achieved by using the aperture plane array for both Compton scattering of high-energy photons and as a coded mask for low-energy radiation. The prototype instrument was built using two RENA-3 test systems, one each for the aperture and the focal plane, stacked on top of each other at a distance of 130 mm. The test systems were modified to coordinate (synchronize) readout and provide coincidence information of events within a user-adjustable 40-1,280 ns window. The measured angular resolution of the device is

We have developed a pixel detector hybrid called DANA-2 (Detector Array for Nuclear Applications). DANA-2 consists of a two-dimensional, monolithic Cadmium Zinc Telluride (CZT) detector array flip-chip bonded directly to a readout IC designed for high energy resolution. Both the detector and the IC have 16 × 16 pixels with a pitch of 0.5 mm × 0.5 mm; the detector thickness is 3 mm. Each readout channel features a low-noise, charge-sensitive input amplifier with continuous-reset feedback and two selectable energy ranges; a gain amplifier with a five-bit gain adjustment and eight-bit offset DAC; a shaper with eight selectable shaping times ranging from 0.5 μs to 4 μs; a peak detector; and a trigger comparator. The data readout is controlled by a programmable token logic, which affords the user a high degree of flexibility in the selection of nearest-neighbor channels to be read out to account for charge sharing between pixels. To process the signals from the detector cathode, one of the readout channels, which is normally connected to a corner pixel, can instead be connected to the cathode through a dedicated I/O pad. The different characteristics of these cathode signals are accommodated through user configuration options for the signal polarity and input FET size. Other features of DANA-2 include the ability to disable the trigger on any channel and thus turn off “hot” pixels, and several test features such as an AC-coupled test signal input and the option to operate any peak detector in follower mode and connect it to the analog output to continuously monitor the shaper signal. We present below details of the DANA-2 design and first results from its performance characterization.

The RENA-3 (Readout Electronics for Nuclear Applications) is a 36-channel self-resetting, charge sensitive amplifier/shaper IC with trigger output, wide energy range and sparse readout designed for use with position-sensitive, spectroscopy-grade radiation detectors. It has in recent years been favored to provide the front-end electronics in prototype instruments for various applications — from space physics research through medical imaging to homeland security — that employ CZT or CdTe in the form of planar sensor assemblies or monolithic pixel/strip arrays. We will present a summary of spectroscopic data drawn from the body of RENA-3-based results obtained in our laboratories and by other RENA-3 users. Spectroscopic performance metrics will be discussed relative to the requirements of the specific application targeted in each case as well as from the general standpoint of what may be achievable within this detector-array/RENA-3 approach. A method to automate the test and calibration of RENA-3 ICs will also be described.

We have developed a new version of the MARY (MAmmogRaphY) pixel detector with its custom readout integrated circuit (IC) optimized for electron collection in semiconductor detectors such as CdZnTe (CZT), CdTe, a-Se and GaAs. This new pixel detector and readout IC, the MARY-N50, is essentially comprised of a 192 x 384 array of channels at a 50 μm x 50 μm pitch, which can be flip-chip bump-bonded with a matching detector pixel array. A 100 μm pitch pixel detector, the MARY-N100, was also developed, with a 64 x 192 pixel array. Standard features of both versions of MARY-N include: TDI (Time Delay Integration) or “staring” CCD readout capability; low noise and wide dynamic range; internal clock drivers; fat zero input; overflow control; multiple independent readout stages (24 for MARY-N50, 8 for MARY-N100) to accommodate large charge collection due to direct conversion.

We have developed high energy and high spatial resolution two-dimensional (2D) solid-state imaging pixel detectors and their custom integrated circuits (ICs). Solid-state pixel detectors and their readout ICs are now regarded to be an integral part of position-sensitive semiconductor detectors such as Si, CdTe and CdZnTe for x-ray and gamma-ray imaging. These detectors have a 2D structure. We have also developed one-dimensional (1D) detectors, which are mostly used for scanning type imaging. The new 2D pixel detectors we have developed can be used for both scanning and staring mode imaging applications. Because the requirements of various detector applications tend to be diverse, a custom IC is typically designed for a specific detector array. This often lengthens the time and raises the cost of system development. To help close the readout technology gap and facilitate advances in this field, we have been formulating and implementing strategies for instrumenting different detectors of a given application category with highly versatile ICs that meet a range of requirements. The solid-state pixel detectors that have been developed within this effort are presented below.

The RENA-3 (R Readout E eadout Electronics for N lectronics Nuclear A uclear Applications) is a multi-channel mixed-signal integrated circuit (IC) developed for the readout of position-sensitive solid-state detectors with excellent energy resolution. We will present results of experiments characterizing its performance as used with a variety of spectroscopy-grade detectors currently available in the industry, notably CZT pixel arrays as well as other detector configurations. The merits of specific RENA-3 design features vis-a-vis different detector applications will also be discussed.

We review a new approach to communication with chaotic signals based upon chaotic signals in the form of pulse trains where intervals between the pulses are determined by chaotic dynamics of a pulse nary information is modulated onto this carrier by the pulse position modulation method, such that each pulse is either left unchanged or delayed by a certain time, depending on whether 0 or 1 is transmitted. By synchronizing the receiver to the chaotic-pulse train we can anticipate the timing of pulses corresponding to 0 and 1 and thus can decode the transmitted information. Based on the results of theoretical and experimental studies we discuss the basic design principles for the chaotic-pulse generator, its synchronization, and the performance of the chaotic-pulse communication scheme in the presence of channel noise and filtering.

This chapter provides a brief overview of some of the digital communications techniques that have been proposed recently employing nonlinear dynamics, along with a comparison to traditional approaches. Both wireless modulation techniques as well as optical communications approaches are be presented.

We have developed high energy and high spatial resolution 1D and 2D solid state imaging detectors and their custom integrated circuits (ICs). Readout ICs are now regarded to be an integral part of position-sensitive semiconductor detectors, especially for Si and CdZnTe for x-ray and gamma-ray imaging. These detectors have a 1D or 2D structure. The 1D structure types are mostly used for scanning purposes with some staring type imaging while 2D pixel detectors can be used for both scanning and staring mode imaging applications. Because the requirements of various detector applications tend to be diverse, a custom IC is typically designed for a specific detector array. This often lengthens the time and raises the cost of system development. To help close the readout technology gap and facilitate advances in this field, we have been formulating and implementing strategies for instrumenting different detectors of a given application category with highly versatile ICs that meet a range of requirements. The solid-state detectors and their ICs that have been developed within this effort are presented.

A multi-channel front-end readout IC is developed for position sensitive solid-state detectors. It is called RENA-3. It has 36 low noise channels. Each channel has externally selectable input polarity. The channel inputs are optimized for 2 or 9 pF detector capacitance, which is externally selectable. It also has selectable dual energy range, 56K and 338K electrons (250 keV and 1.5 Mev for CZT, respectively). A fast trigger output is provided applications that require timing. A novel circuit produces arrival time difference measurement for each channel. It is developed to serve as front-end readout electronics for a variety of position-sensitive solid-state semiconductor detectors such as CdZnTe, Si, GaAs and HgI2. It also has flexibility for use with other types of solid-state detectors such as Ge, Se, PbI2 and CdTe in a multichannel strip or pixel geometry to detect and image x-rays and gamma-rays with energies up to 1.3 MeV. Also a novel register circuit and process allows nearest neighbor readout capability for pixel detectors. Combination of RENA-3 chips with a variety of semiconductor detectors would be suitable for numerous applications in astrophysics, nuclear physics, nuclear medicine, security and industrial imaging. Some possible applications include gamma camera, SPECT, small animal PET and SPECT, nuclear source detection and spectroscopy, space x-ray and gamma-ray astronomy missions, NDE and NDI.

Invertebrate central pattern generators (CPGs) can serve as the basis for building biomimetic controllers based on real biological principles. Here we describe a CPG made of electronic neurons and synapses for robotic applications and for possible use in a clinical neuroprosthetic device

Experimental results on the synchronization of chaotic oscillations and data transmission in the system “oscillator-response subsystem” are presented.

We discuss a VLSI electronic neuron circuit that implements the Hindmarsh and Rose neuron model. Magnitude and time scaling techniques are employed for a 2 V power supply operation. A subthreshold operation technique and a single MOS resistor are used to minimize area and power consumption. Output bursts of the electronic neuron can be modulated dynamically by varying the input voltage level. The circuit is designed using a 0.25 /spl mu/m CMOS standard process, and the total power dissipation is 163.4 /spl mu/watt.

The Ultra Wide Band (UWB) communicating systems draw a tremendous attention in the last few years because of many potential advantages the UWB technology can bring to the wireless industry. It can solve the RF spectrum availability problem, improve the security, can provide less expensive, less power consuming equipment for a variety of wireless applications. We study a communication device, in which the Chaotic (Rossler) Oscillator (CO) combined with a linear Voltage Controlled Oscillator (VCO) is used to generate the UWB carrier signal with Chaotic Frequency Modulation (CFM). The information signal can be transmitted via the Frequency Modulation (FM) in analog systems or the Binary Frequency Shift Key‐in (BFSK) modulation in digital applications. The receiver has the similar CO and VCO with closed parameters. A simple circuit based on the Phase locked Loop (PLL) is used for both synchronization of the chaotic oscillators and demodulation of the carrier signal. Using the dynamical systems approach we show that the suggested device has a broad parameter region in which the synchronization and demodulation take place. In computer simulations we demonstrate that the system is robust against the noise and parameters mismatch.

Using chaotic signals in spread spectrum communications (SSC) has advantages over traditional approaches. Chaotic signals are non-periodic, wideband, and more difficult to predict, reconstruct, and characterize than periodic carriers, which makes it more difficult to intercept and decode the information modulated upon them. However, many suggested chaos based-communication schemes do not provide processing gain (PG), a key feature of SSC schemes. Here we consider three communication schemes that provide PG. Their performance is studied for discrete time implementations. It is shown that the increase of the spreading factor beyond certain point degrades the performance.

▪ Abstract We examine early olfactory processing in the vertebrate and insect olfactory systems, using a computational perspective. What transformations occur between the first and second olfactory processing stages? What are the causes and consequences of these transformations? To answer these questions, we focus on the functions of olfactory circuit structure and on the role of time in odor-evoked integrative processes. We argue that early olfactory relays are active and dynamical networks, whose actions change the format of odor-related information in very specific ways, so as to refine stimulus identification. Finally, we introduce a new theoretical framework (“winnerless competition”) for the interpretation of these data.

A new spread spectrum communication system utilizing chaotic frequency modulation of sinusoidal signals is discussed. A single phase lock loop (PLL) system in the receiver is used both to synchronize the local chaotic oscillator and to recover the information signal. We study the dynamics of the synchronization process, stability of the PLL system, and evaluate the bit-error-rate performance of this chaos-based communication system.