1,281 research outputs found
Time Encoding via Unlimited Sampling: Theory, Algorithms and Hardware Validation
An alternative to conventional uniform sampling is that of time encoding,
which converts continuous-time signals into streams of trigger times. This
gives rise to Event-Driven Sampling (EDS) models. The data-driven nature of EDS
acquisition is advantageous in terms of power consumption and time resolution
and is inspired by the information representation in biological nervous
systems. If an analog signal is outside a predefined dynamic range, then EDS
generates a low density of trigger times, which in turn leads to recovery
distortion due to aliasing. In this paper, inspired by the Unlimited Sensing
Framework (USF), we propose a new EDS architecture that incorporates a modulo
nonlinearity prior to acquisition that we refer to as the modulo EDS or MEDS.
In MEDS, the modulo nonlinearity folds high dynamic range inputs into low
dynamic range amplitudes, thus avoiding recovery distortion. In particular, we
consider the asynchronous sigma-delta modulator (ASDM), previously used for low
power analog-to-digital conversion. This novel MEDS based acquisition is
enabled by a recent generalization of the modulo nonlinearity called
modulo-hysteresis. We design a mathematically guaranteed recovery algorithm for
bandlimited inputs based on a sampling rate criterion and provide
reconstruction error bounds. We go beyond numerical experiments and also
provide a first hardware validation of our approach, thus bridging the gap
between theory and practice, while corroborating the conceptual underpinnings
of our work.Comment: 27 pgs, 11 figures, IEEE Trans. Sig. Proc., accepted with minor
revision
Asynchronous Signal Processing for Compressive Data Transmission
In this thesis we propose a power-efficient procedure useful in the acquisition of biological data in digital form without using high frequency samplers. The data is compressed so that transmission is limited to parts of the signal that are significant. Our procedure uses an asynchronous sigma delta modulator (ASDM) together with a time-to-digital converter (TDC) to obtain binary data that is transmitted via orthogonal frequency division multiplexing (OFDM). The asynchronous sigma delta modulator is a nonlinear feedback system that allows the representation of bounded signals by zero-crossing times of a binary signal. Using duty-cycle modulation, the ASDM is shown to be equivalent to an optimal level-crossing sampler. The zero-crossing times are measured with a time-to-digital converter that applies pulse-shrinking delay lines and requires no high-frequency clock. Reconstruction of the original signal is possible from the zero-crossing times of the ASDM output binary signal. ASDM time-domain compression is compared with discrete wavelet transform based data compression. For wireless data transmission, the orthogonal frequency division multiplexing (OFDM) reduces the bit error-rate in multipath fading channels. The performance of the proposed algorithm is illustrated using an electrocardiogram signal, which fits the bursty characteristic appropriate for our procedure
Network device interface for digitally interfacing data channels to a controller via a network
A communications system and method are provided for digitally connecting a plurality of data channels, such as sensors, actuators, and subsystems, to a controller using a network bus. The network device interface interprets commands and data received from the controller and polls the data channels in accordance with these commands. Specifically, the network device interface receives digital commands and data from the controller, and based on these commands and data, communicates with the data channels to either retrieve data in the case of a sensor or send data to activate an actuator. Data retrieved from the sensor is converted into digital signals and transmitted to the controller. Network device interfaces associated with different data channels can coordinate communications with the other interfaces based on either a transition in a command message sent by the bus controller or a synchronous clock signal
Digital pulse processing
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 71-74).This thesis develops an exact approach for processing pulse signals from an integrate-and-fire system directly in the time-domain. Processing is deterministic and built from simple asynchronous finite-state machines that can perform general piecewise-linear operations. The pulses can then be converted back into an analog or fixed-point digital representation through a filter-based reconstruction. Integrate-and-fire is shown to be equivalent to the first-order sigma-delta modulation used in oversampled noise-shaping converters. The encoder circuits are well known and have simple construction using both current and next-generation technologies. Processing in the pulse-domain provides many benefits including: lower area and power consumption, error tolerance, signal serialization and simple conversion for mixed-signal applications. To study these systems, discrete-event simulation software and an FPGA hardware platform are developed. Many applications of pulse-processing are explored including filtering and signal processing, solving differential equations, optimization, the minsum / Viterbi algorithm, and the decoding of low-density parity-check codes (LDPC). These applications often match the performance of ideal continuous-time analog systems but only require simple digital hardware. Keywords: time-encoding, spike processing, neuromorphic engineering, bit-stream, delta-sigma, sigma-delta converters, binary-valued continuous-time, relaxation-oscillators.by Martin McCormick.S.M
Operation and reconstruction of signals based on integrate-and-fire conversion using FPGA
Neurons are diverse in terms of functionality and behaviour; however a family of them can be modeled as an electrical circuit aggregating input currents from neighboring neurons. Integration-and-Fire Neuron (IFN) is a simplified view of a neuron operation that reduces the model to a first order fire-and-reset system. IFN can be used as a modulation technique to transmit data in a very efficient way. It is also possible to perform some signal operations in the IFN space, just looking into the time space in-between IFN spikes, and there are several approaches to reconstruct back the analog signal, at the receiver side, either in time-domain or frequency-domain. After the analysis of the different methods for signal reconstruction based on IFN modulation technique, and also after surveying different methods of doing mathematical operations in the IFN space, the main goal of the thesis is then to synthesize, on an FPGA, the fundamental mathematical operations over the spike based signals, together with a reconstruction method that will convert the IFN signal back to a magnitude/time signal, with a reasonable bit resolution
Front-ends para LiDAR baseados em ADC e TDC
Autonomous vehicles are a promising technology to save over a million lives each
year that are lost in road accidents. However, bringing safe autonomous vehicles
to market requires massive development, starting with vision sensors. LiDAR is a
fundamental vision sensor for autonomous vehicles, as it enables high resolution
3D vision. However, automotive LiDAR is not yet a mature technology, and, also
requires massive development in many aspects.
This thesis aims to contribute to the maturity of LiDAR, focusing on sampling
architectures for LiDAR front-ends. Two architectures were developed.
The first is based on a pipelined ADC, available from an AD-FMCDAQ2-EBZ
board. The ADC is synchronized with the emitted pulse and able to sample
at 1 Gsample/s. The second architecture is based on a TDC that is directly
implemented in an FPGA. It relies on a tapped delay line topology comprising 45
delay elements and on a mux-based decoder, resulting in a resolution of 50 ps.
Preliminary test results show that both implementations operate correctly,
and are both suitable for sampling short pulses typically used by LiDARs. When
comparing both architectures, we conclude that an ADC consumes a significant
amount of power, and uses many FPGA resources. However, it samples the LiDAR
waveform without any loss of information, therefore enabling maximum range and
precision. The TDC is just the opposite: it consumes little power, and uses less
FPGA resources. However, it only captures one sample per pulse.Os veículos autónomos são uma tecnologia promissora para salvar mais de um
milhão de vidas por ano, colhidas por acidentes rodoviários. Contudo, colocar
veículos autónomos seguros no mercado requer inúmeros desenvolvimentos, a
começar por sensores de visão. O LiDAR é um sensor de visão fundamental para
veículos autónomos, pois permite uma visão 3D de alta resolução. Contudo, o
LiDAR automotivo não é uma tecnologia madura, e portanto requer também
desenvolvimento em vários aspectos.
Esta dissertação visa contribuir para a maturidade do LiDAR, com foco em
arquiteturas de amostragem para front-ends de LiDAR. Foram desenvolvidas duas
arquiteturas. A primeira assenta numa ADC pipelined, por sua vez implementada
numa placa de teste AD-FMCDAQ2-EBZ. A ADC opera em sincronismo com
o pulso emitido, e permite capturar amostras a 1 Gsample/s. A segunda
arquitetura assenta num TDC implementado diretamente numa FPGA. O
TDC baseia-se numa topologia tapped delay line com 45 linhas de atraso, e num
descodificador à base de multiplexers, permitindo uma resolução temporal de 50 ps.
Resultados preliminares mostram que ambas as implementações operam
corretamente, e são adequadas para amostrar pulsos curtos tipicamente associados
a LiDAR. Em termos comparativos, a arquitectura com base numa ADC tem
um consumo de potência considerável e requer uma quantidade significativa
de recursos da FPGA. Contudo, esta permite amostrar a forma de onda de
LiDAR sem nenhuma perda de informação, permitindo assim alcance e precisão
máximos. A arquitectura com base num TDC é exatamente o oposto: tem um
baixo consumo de potência e requer poucos recursos da FPGA. Contudo, permite
capturar apenas uma amostra por pulso.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
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Continuous-Time and Companding Digital Signal Processors Using Adaptivity and Asynchronous Techniques
The fully synchronous approach has been the norm for digital signal processors (DSPs) for many decades. Due to its simplicity, the classical DSP structure has been used in many applications. However, due to its rigid discrete-time operation, a classical DSP has limited efficiency or inadequate resolution for some emerging applications, such as processing of multimedia and biological signals. This thesis proposes fundamentally new approaches to designing DSPs, which are different from the classical scheme. The defining characteristic of all new DSPs examined in this thesis is the notion of "adaptivity" or "adaptability." Adaptive DSPs dynamically change their behavior to adjust to some property of their input stream, for example the rate of change of the input. This thesis presents both enhancements to existing adaptive DSPs, as well as new adaptive DSPs. The main class of DSPs that are examined throughout the thesis are continuous-time (CT) DSPs. CT DSPs are clock-less and event-driven; they naturally adapt their activity and power consumption to the rate of their inputs. The absence of a clock also provides a complete avoidance of aliasing in the frequency domain, hence improved signal fidelity. The core of this thesis deals with the complete and systematic design of a truly general-purpose CT DSP. A scalable design methodology for CT DSPs is presented. This leads to the main contribution of this thesis, namely a new CT DSP chip. This chip is the first general-purpose CT DSP chip, able to process many different classes of CT and synchronous signals. The chip has the property of handling various types of signals, i.e. various different digital modulations, both synchronous and asynchronous, without requiring any reconfiguration; such property is presented for the first time CT DSPs and is impossible for classical DSPs. As opposed to previous CT DSPs, which were limited to using only one type of digital format, and whose design was hard to scale for different bandwidths and bit-widths, this chip has a formal, robust and scalable design, due to the systematic usage of asynchronous design techniques. The second contribution of this thesis is a complete methodology to design adaptive delay lines. In particular, it is shown how to make the granularity, i.e. the number of stages, adaptive in a real-time delay line. Adaptive granularity brings about a significant improvement in the line's power consumption, up to 70% as reported by simulations on two design examples. This enhancement can have a direct large power impact on any CT DSP, since a delay line consumes the majority of a CT DSP's power. The robust methodology presented in this thesis allows safe dynamic reconfiguration of the line's granularity, on-the-fly and according to the input traffic. As a final contribution, the thesis also examines two additional DSPs: one operating the CT domain and one using the companding technique. The former operates only on level-crossing samples; the proposed methodology shows a potential for high-quality outputs by using a complex interpolation function. Finally, a companding DSP is presented for MPEG audio. Companding DSPs adapt their dynamic range to the amplitude of their input; the resulting can offer high-quality outputs even for small inputs. By applying companding to MPEG DSPs, it is shown how the DSP distortion can be made almost inaudible, without requiring complex arithmetic hardware
Efficient Computation in Adaptive Artificial Spiking Neural Networks
Artificial Neural Networks (ANNs) are bio-inspired models of neural
computation that have proven highly effective. Still, ANNs lack a natural
notion of time, and neural units in ANNs exchange analog values in a
frame-based manner, a computationally and energetically inefficient form of
communication. This contrasts sharply with biological neurons that communicate
sparingly and efficiently using binary spikes. While artificial Spiking Neural
Networks (SNNs) can be constructed by replacing the units of an ANN with
spiking neurons, the current performance is far from that of deep ANNs on hard
benchmarks and these SNNs use much higher firing rates compared to their
biological counterparts, limiting their efficiency. Here we show how spiking
neurons that employ an efficient form of neural coding can be used to construct
SNNs that match high-performance ANNs and exceed state-of-the-art in SNNs on
important benchmarks, while requiring much lower average firing rates. For
this, we use spike-time coding based on the firing rate limiting adaptation
phenomenon observed in biological spiking neurons. This phenomenon can be
captured in adapting spiking neuron models, for which we derive the effective
transfer function. Neural units in ANNs trained with this transfer function can
be substituted directly with adaptive spiking neurons, and the resulting
Adaptive SNNs (AdSNNs) can carry out inference in deep neural networks using up
to an order of magnitude fewer spikes compared to previous SNNs. Adaptive
spike-time coding additionally allows for the dynamic control of neural coding
precision: we show how a simple model of arousal in AdSNNs further halves the
average required firing rate and this notion naturally extends to other forms
of attention. AdSNNs thus hold promise as a novel and efficient model for
neural computation that naturally fits to temporally continuous and
asynchronous applications
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