Timing Distortion Research Articles

Virtual Space-Time DiversityTurbo Equalization Using Cluster Sparse Proportional Recursive Least Squares Algorithm for Underwater Acoustic Communications

The oceanic positioning, navigation and timing (PNT) network requires high-quality underwater acoustic message transmission. Turbo equalization technology has exhibited superior performance for underwater acoustic (UWA) communications compared with conventional channel equalizers. To overcome the performance reduction caused by severe doubly selective UWA channels, the virtual space-time diversity soft direct-adaptation turbo equalization is proposed for UWA communications. The proposed scheme improves the ability of the typical turbo equalizer to deal with both Doppler and multipath effects for time varying channels. We utilize a fractionally spaced soft interference cancellation equalizer (FS-SE) instead of a hard decision to constitute the soft-input soft-output (SISO) equalizer. Combined with another virtual time-reversal mirror equalizer component, we can obtain virtual space and time diversity with only a single receiving transducer and mitigate the error propagation phenomenon of the feedback filter. To satisfy the sparse UWA channel, the ℓp,q-PRLS algorithm is applied to adaptive updates for FS-SE. In the proposed scheme, an adjustable interpolator and digital phase-locked loop are embedded into the equalizer to overcome the residual Doppler frequency shift and recover the timing distortion. Results of simulations and field lake trial show that the proposed scheme achieves better performance than existing ones under the same equalizer order.

Effects of ketamine optical isomers, fluoxetine and naloxone on timing in differential reinforcement of low-rate response (DRL) 72-s task in rats

(S)-ketamine-induced rapid-acting antidepressant effects have revolutionized the pharmacotherapy of major depression; however, this medication also produces psychotomimetic effects such as timing distortion. While (R)-ketamine produces fewer dissociative effects, its antidepressant actions are less studied. Depression is associated with time overestimation (i.e., subjectively, time passes slowly). Our recent report suggests that while (S)-ketamine induces an opposite effect, i.e., time underestimation, the (R)-isomer does not affect timing. It has been suggested that opioid receptors are involved in the antidepressant effect of ketamine. In the present study we tested (R)- and (S)-ketamine, and fluoxetine as a positive control in the differential-reinforcement-of-low-rate (DRL) 72-s schedule of reinforcement in male rats following naloxone pretreatment. DRL classic metrics as well as peak deviation analyses served to determine antidepressant-like actions and those associated with timing. We report antidepressant-like effects of (S)-ketamine (30-60 mg/kg) that resemble fluoxetine's (2.5-10 mg/kg), as both compounds increased reinforcement rate and peak location (suggesting increased performance), reduced premature responses (suggesting time underestimation) and decreased Weber's fraction (suggesting increased timing precision). (R)-ketamine (30, but not 60 mg/kg) increased only the reinforcement rate and peak location but did not affect timing. Only fluoxetine decreased burst responses, suggesting decreased impulsivity. Naloxone pretreatment did not block ketamine enantiomers’ actions, but unexpectedly, increased fluoxetine’ performance. Thus, while all three medications produced antidepressant-like effects in DRL 72-s, fluoxetine- and (S)- but not (R)- ketamine-induced time underestimation (the subject experiences the time as passing quickly). The potentiation of DRL performance of fluoxetine by naloxone was unexpected and warrants clinical studies.

Effects of ketamine optical isomers, psilocybin, psilocin and norpsilocin on time estimation and cognition in rats

RationaleKetamine and psilocybin belong to the rapid-acting antidepressants but they also produce psychotomimetic effects including timing distortion. It is currently debatable whether these are essential for their therapeutic actions. As depressed patients report that the “time is dragging,” we hypothesized that ketamine and psilocybin-like compounds may produce an opposite effect, i.e., time underestimation, purportedly contributing to their therapeutic properties.ObjectivesTiming was tested following administration of (R)- and (S)-ketamine, and psilocybin, psilocin, and norpsilocin in the discrete-trial temporal discrimination task (TDT) in male rats. Timing related to premature responses, and cognitive and unspecific effects of compounds were tested in the 5-choice serial reaction time task (5-CSRTT) in the standard 1-s, and “easier” 2-s stimulus duration conditions, as well as in the vITI variant promoting impulsive responses.Results(S)-ketamine (15 but not 3.75 or 7.5 mg/kg) shifted psychometric curve to the right in TDT and reduced premature responses in 5-CSRTT, suggesting expected time underestimation, but it also decreased the accuracy of temporal discrimination and increased response and reward latencies, decreased correct responses, and increased incorrect responses. While (R)-ketamine did not affect timing and produced no unspecific actions, it reduced incorrect responses in TDT and increased accuracy in 5-CSRTT, suggesting pro-cognitive effects. Psilocin and psilocybin produced mainly unspecific effects in both tasks, while norpsilocin showed no effects.ConclusionsTime underestimation produced by (S)-ketamine could be associated with its antidepressant effects; however, it was accompanied with severe behavioral disruption. We also hypothesize that behavioral disruption produced by psychedelics objectively reflects their psychotomimetic-like actions.

Neural-Network Based Modeling of I/O Buffer Predriver under Power/Ground Supply Voltage Variations.

This paper presents a neural-network based nonlinear behavioral modelling of I/O buffer that accounts for timing distortion introduced by nonlinear switching behavior of the predriver electrical circuit under power and ground supply voltage (PGSV) variations. Model structure and I/O device characterization along with extraction procedure were described. The last stage of the I/O buffer is modelled as nonlinear current-voltage (I-V) and capacitance voltage (C-V) functions capturing the nonlinear dynamic impedances of the pull-up and pull-down transistors. The mathematical model structure of the predriver was derived from the analysis of the large-signal electrical circuit switching behavior. Accordingly, a generic and surrogate multilayer neural network (NN) structure was considered in this work. Timing series data which reflects the nonlinear switching behavior of the multistage predriver’s circuit PGSV variations, were used to train the NN model. The proposed model was implemented in the time-domain solver and validated against the reference transistor level (TL) model and the state-of-the-art input-output buffer information specification (IBIS) behavioral model under different scenarios. The analysis of jitter was performed using the eye diagrams plotted at different metrics values.

Design and development of radio frequency system for pulse positron low energy beam and its electron beam trials

Details of the design and development of radio frequency (RF) system at 37.5 MHz and 150 MHz and initial test results of electron beam trials of a pulsed positron beam line being developed at BARC, Mumbai are presented in this paper. The RF part of the beam line is based on the conventional positron pulsing technique of chopper-pre buncher-buncher arrangement. Picosecond (ps) pulsing is achieved by a 150 MHz quarter wave resonator, which times focuses the chopped positron beam onto the sample. The chopper and pre buncher, preceding the buncher, are designed to operate at one-fourth of the frequency of the buncher. The reflection type grid chopper uses sinusoidal waves riding on a DC offset to chop the incoming beam into less than 2 ns pulses. These various structures were excited by the RF power coupled from an overall two frequency RF system. This RF system comprises of amplifiers at 37.5 MHz and 150 MHz that derive a single common input from an arbitrary frequency generator (AFG) to reduce the timing distortion, their respective impedance matching units and RF coupling lines made of RF components used for amplitude and phase adjustments and then, feeds the RF power to these structures. The RF system was initially tested on a prototype setup before incorporating in the main pulsed positron beam line. RF interference suppression techniques like filtering and shielding were used to ensure minimum interference between RF signals and the various detector electronics. Before positron beam trials, electron beam trials were performed in the positron beam line. A final pulse width 280 ps was measured with an electron beam.

Distortion Distribution of Neural Spike Train Sequence Matching With Optogenetics.

This paper uses a simple optogenetic model to compare the timing distortion between a randomly-generated target spike sequence and an externally-stimulated neuron spike sequence. Optogenetics is an emerging field of neuroscience where neurons are genetically modified to express light-sensitive receptors that enable external control when the neurons fire. Two different measures are studied to determine the timing distortion. The first measure is the delay in externally-stimulated spikes. The second measure is the root-mean-square-error between the filtered outputs of the target and stimulated spike sequences. The mean and the distribution of the distortion are derived in closed form when the target sequence generation rate is sufficiently low. The derived results are verified with simulations. The proposed model and distortion measures can be used to measure the deviation between neuron spike sequences that are prescribed and what can be achieved via external stimulation. Given the prominence of neuronal signaling within the brain and throughout the body, optogenetics has significant potential to improve the understanding of the nervous system and to develop treatments for neurological diseases. This work is a step towards an analytical model to predict whether different spike trains were observed from the same external stimulus, and the broader goal of understanding the quantity and reliability of information that can be carried by neurons.

Real-Time Simulation of Passage-of-Time Encoding in Cerebellum Using a Scalable FPGA-Based System.

The cerebellum plays a critical role for sensorimotor control and learning. However, dysmetria or delays in movements' onsets consequent to damages in cerebellum cannot be cured completely at the moment. Neuroprosthesis is an emerging technology that can potentially substitute such motor control module in the brain. A pre-requisite for this to become practical is the capability to simulate the cerebellum model in real-time, with low timing distortion for proper interfacing with the biological system. In this paper, we present a frame-based network-on-chip (NoC) hardware architecture for implementing a bio-realistic cerebellum model with ∼100 000 neurons, which has been used for studying timing control or passage-of-time (POT) encoding mediated by the cerebellum. The simulation results verify that our implementation reproduces the POT representation by the cerebellum properly. Furthermore, our field-programmable gate array (FPGA)-based system demonstrates excellent computational speed that it can complete 1sec real world activities within 25.6 ms. It is also highly scalable such that it can maintain approximately the same computational speed even if the neuron number increases by one order of magnitude. Our design is shown to outperform three alternative approaches previously used for implementing spiking neural network model. Finally, we show a hardware electronic setup and illustrate how the silicon cerebellum can be adapted as a potential neuroprosthetic platform for future biological or clinical application.

A 120 dB Dynamic Range 400 mW Class-D Speaker Driver With Fourth-Order PWM Modulator

High efficiency Class-D speaker drivers have become ubiquitous in battery driven mobile audio applications. Analog switching errors and timing jitter are known limitations to the dynamic range in these types of switching audio drivers. To overcome these limitations the Class-D architecture chosen in this paper provides a low 667 kHz pulse rate. This architecture is based on a 4th-order digital modulator with pulse-width modulation (PWM) feedback. The modulator loop processes the PWM signals at a high 24 MHz clock rate, and provides pulse edge timing resolution within a single clock period of the high-rate clock. Timing distortion errors due to uniform sampling of the low-rate PWM signals are reduced with the high forward loop gain of the digital modulator feedback loop. The driver receives a 22-bit digital audio input and combines the functionality of a high-fidelity digital-to-analog converter (DAC) with a speaker driver. It achieves 120 dB dynamic range over a 20 kHz bandwidth, provides 88% power efficiency while driving an 8 Ω speaker load, and consumes a total quiescent current of 2.4 mA.

Phase spectrum algorithm for correction of time distortion in a wavelength demultiplexing analog-to-digital converter

An algorithm based on phase spectrum analysis is proposed that can be used to correct the timing distortion between the multiple parallel demultiplexed post-sampling pulse trains in wavelength demultiplexing analog-to-digital converters. The algorithm is theoretically presented and its operational principle is explained. The algorithm is then applied to two parallel demultiplexed post-sampling signals from a proof-of-principle system and fairly good results are obtained. This algorithm is potentially applicable in other opto-electronic hybrid systems where an interleaving and/or multiplexing mechanism is utilized, such as optical time-division multiplexing and optical clock division systems, photonic arbitrary waveform generators, and so on.

Adaptive Network-based Fuzzy Inference System for Assessment of Lower Limb Peripheral Vascular Occlusive Disease

Detecting lower limb peripheral vascular occlusive disease (PVOD) early is important for patients to prevent disabling claudication, ischaemic rest pain and gangrene. According to previous research, the pulse timing and shape distortion characteristics of photoplethysmography (PPG) signals tend to increase with disease severity and calibrated amplitude decreases with vascular diseases. However, this is not a reliable method of evaluating the condition of PVOD because of noise effect. In this paper, an adaptive network-based fuzzy inference system (ANFIS) is proposed to assess lower limb PVOD based on PPG signals. PPG signals are non-invasively recorded from the right and left sides at the big toe sites from twenty subjects, including normal condition (Nor), lower-grade disease (LG), and higher-grade disease (HG) groups. The number of each group is 10, 8 and 2 respectively, and the ages ranged from 24 to 65years. With the time-domain technique, the parameters for the absolute bilateral differences (right-to-left side of foot) in pulse delay and amplitude were extracted for analyzing ANFIS. The results indicated that ANFIS based on three timing parameters base bilateral differences, including ΔPTTf and ΔPTTp, and ΔRT has a high rate and noise tolerance of PVOD assessment.

Using Evolutionary Algorithms for Signal Integrity Assessment of High-Speed Data Buses

Today's high performance computer systems must have fast, reliable access to memory and I/O devices. Unfortunately, inter-symbol interference, transmission line effects and other noise sources can distort data transfers. Engineers must therefore determine if bus designs have signal integrity--i.e., can transfer data with minimal amplitude or timing distortion. One method of determining signal integrity on buses is to conduct a set of data transfers and measure various signal parameters at the receiver end. But the tests must be conducted with stressful test patterns that maximize noise to help identify any potential problems. In this paper we describe how an evolutionary algorithm was used to evolve test patterns for use in intrinsic testing.

Exploring data rate limitations of channel front-ends for rigid disk drives

Each of the components of the channel front-end (i.e., medium, heads, interconnects, and read/write electronics), can limit the data rate. In the read path, the head-to-electronics suspension interconnect forms the major bottleneck. The skin-effect losses, multi-mode propagation effects and reflections limit the maximum achievable data rate. In the write path, the reflections along the suspension interconnect causing long settling times and also the relatively slow response of the ferromagnetics of the write-head limit the data rate. Modeling shows that the overall write path is data rate limited by settling times that are too long, leading to uncorrectable timing distortion in the location of the one but nearest neighbor transitions.

High‐speed bus circuit methodology

High-speed bus circuits are the key to high performance systems with built-in processors. However, conventional bus circuits with low power consumption suffer problems such as ringing and dips caused by reflection and, as a result, the bus transmission rate cannot reach 100 MHz. Lattice diagrams have been used to analyze bus circuits, but these only show the approximate reflection behavior and cannot graphically portray the relation between reflection timing and waveform distortion due to reflection. This paper introduces a bus circuit with non-power-consuming termination that can achieve data transmission speeds over 100 MHz, 2.5 to 3 times faster than conventional low-power bus circuits. The paper also proposes a newly devised lattice diagram that can graphically clarify the relation between reflection timing and waveform distortion due to reflection. A SPICE simulation was carried out to examine the data transmission rate for each bus circuit. It was experimentally confirmed that our bus circuit, with non-power-consuming termination, operates at a 167-MHz data transmission rate. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 49–59, 1998

High-speed bus circuit methodology

High-speed bus circuits are the key to high performance systems with built-in processors. However, conventional bus circuits with low power consumption suffer problems such as ringing and dips caused by reflection and, as a result, the bus transmission rate cannot reach 100 MHz. Lattice diagrams have been used to analyze bus circuits, but these only show the approximate reflection behavior and cannot graphically portray the relation between reflection timing and waveform distortion due to reflection. This paper introduces a bus circuit with non-power-consuming termination that can achieve data transmission speeds over 100 MHz, 2.5 to 3 times faster than conventional low-power bus circuits. The paper also proposes a newly devised lattice diagram that can graphically clarify the relation between reflection timing and waveform distortion due to reflection. A SPICE simulation was carried out to examine the data transmission rate for each bus circuit. It was experimentally confirmed that our bus circuit, with non-power-consuming termination, operates at a 167-MHz data transmission rate. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 49–59, 1998

高速バス回路方式

High-speed bus circuits are the key to high performance systems with built-in processors. However, conventional bus circuits with low power consumption suffer problems such as ringing and dips caused by reflection and, as a result, the bus transmission rate cannot reach 100 MHz. Lattice diagrams have been used to analyze bus circuits, but these only show the approximate reflection behavior and cannot graphically portray the relation between reflection timing and waveform distortion due to reflection. This paper introduces a bus circuit with non-power-consuming termination that can achieve data transmission speeds over 100 MHz, 2.5 to 3 times faster than conventional low-power bus circuits. The paper also proposes a newly devised lattice diagram that can graphically clarify the relation between reflection timing and waveform distortion due to reflection. A SPICE simulation was carried out to examine the data transmission rate for each bus circuit. It was experimentally confirmed that our bus circuit, with non-power-consuming termination, operates at a 167-MHz data transmission rate. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 49–59, 1998