142 research outputs found
Very Low Cost Entropy Source Based on Chaotic Dynamics Retrofittable on Networked Devices to Prevent RNG Attacks
Good quality entropy sources are indispensable in most modern cryptographic
protocols. Unfortunately, many currently deployed networked devices do not
include them and may be vulnerable to Random Number Generator (RNG) attacks.
Since most of these systems allow firmware upgrades and have serial
communication facilities, the potential for retrofitting them with secure
hardware-based entropy sources exists. To this aim, very low-cost, robust, easy
to deploy solutions are required. Here, a retrofittable, sub 10$ entropy source
based on chaotic dynamics is illustrated, capable of a 32 kbit/s rate or more
and offering multiple serial communication options including USB, I2C, SPI or
USART. Operation is based on a loop built around the Analog to Digital
Converter (ADC) hosted on a standard microcontroller.Comment: 4 pages, 6 figures. Pre-print from conference proceedings; IEEE 21th
International Conference on Electronics, Circuits, and Systems (ICECS 2014),
pp. 175-178, Dec. 201
Noise Weighting in the Design of {\Delta}{\Sigma} Modulators (with a Psychoacoustic Coder as an Example)
A design flow for {\Delta}{\Sigma} modulators is illustrated, allowing
quantization noise to be shaped according to an arbitrary weighting profile.
Being based on FIR NTFs, possibly with high order, the flow is best suited for
digital architectures. The work builds on a recent proposal where the modulator
is matched to the reconstruction filter, showing that this type of optimization
can benefit a wide range of applications where noise (including in-band noise)
is known to have a different impact at different frequencies. The design of a
multiband modulator, a modulator avoiding DC noise, and an audio modulator
capable of distributing quantization artifacts according to a psychoacoustic
model are discussed as examples. A software toolbox is provided as a general
design aid and to replicate the proposed results.Comment: 5 pages, 18 figures, journal. Code accompanying the paper is
available at http://pydsm.googlecode.co
Output Filter Aware Optimization of the Noise Shaping Properties of {\Delta}{\Sigma} Modulators via Semi-Definite Programming
The Noise Transfer Function (NTF) of {\Delta}{\Sigma} modulators is typically
designed after the features of the input signal. We suggest that in many
applications, and notably those involving D/D and D/A conversion or actuation,
the NTF should instead be shaped after the properties of the
output/reconstruction filter. To this aim, we propose a framework for optimal
design based on the Kalman-Yakubovich-Popov (KYP) lemma and semi-definite
programming. Some examples illustrate how in practical cases the proposed
strategy can outperform more standard approaches.Comment: 14 pages, 18 figures, journal. Code accompanying the paper is
available at http://pydsm.googlecode.co
Should {\Delta}{\Sigma} Modulators Used in AC Motor Drives be Adapted to the Mechanical Load of the Motor?
We consider the use of {\Delta}{\Sigma} modulators in ac motor drives,
focusing on the many additional degrees of freedom that this option offers over
Pulse Width Modulation (PWM). Following some recent results, we show that it is
possible to fully adapt the {\Delta}{\Sigma} modulator Noise Transfer Function
(NTF) to the rest of the drive chain and that the approach can be pushed even
to a fine adaptation of the NTF to the specific motor loading condition. We
investigate whether and to what extent the adaptation should be pursued. Using
a representative test case and extensive simulation, we conclude that a mild
adaptation can be beneficial, leading to Signal to Noise Ratio (SNR)
improvements in the order a few dB, while the advantage pushing the adaptation
to the load tracking is likely to be minimal.Comment: Sample code available at http://pydsm.googlecode.co
Coding of Stereo Signals by a Single Digital {\Delta}{\Sigma} Modulator
The possibility of using a single digital {\Delta}{\Sigma} modulator to
simultaneously encode the two channels of a stereo signal is illustrated. From
the modulated stream, the two channels can be recovered with minimal processing
and no cross-talk. Notably, demultiplexing does not affect the sample-depth so
that, after it, one still has a data stream suitable for directly driving a
power bridge and convertible into analog by mere low-pass filtering.
Furthermore, the approach is very flexible and if one channel is unused, it
lets the other get improved dynamic range and SNR. The approach can take
advantage of recent techniques for the design of {\Delta}{\Sigma} modulators,
including methods for psychoacoustically optimal distribution of quantization
noise. Code is available to replicate the proposed examples and as a general
computer aided design tool.Comment: 4 pages, 5 figures. Pre-print from conference proceeding
From Chirps to Random-FM Excitations in Pulse Compression Ultrasound Systems
Pulse compression is often practiced in ultrasound Non Destructive Testing
(NDT) systems using chirps. However, chirps are inadequate for setups where
multiple probes need to operate concurrently in Multiple Input Multiple Output
(MIMO) arrangements. Conversely, many coded excitation systems designed for
MIMO miss some chirp advantages (constant envelope excitation, easiness of
bandwidth control, etc.) and may not be easily implemented on hardware
originally conceived for chirp excitations. Here, we propose a system based on
random-FM excitations, capable of enabling MIMO with minimal changes with
respect to a chirp-based setup. Following recent results, we show that
random-FM excitations retain many advantages of chirps and provide the ability
to frequency-shape the excitations matching the transducers features.Comment: 4 pages, 4 figures. Post-print from conference proceedings. Note that
paper in conference proceedings at http://dx.doi.org/10.1109/ULTSYM.2012.0117
has some rendering issue
Can a single low-intensity premature stimulus induce ventricular arrhythmias in the normal heart?
Previously, we observed that a single low-intensity premature ventricular stimulation could occasionally induce spontaneous ectopic beats in normal rat hearts. Possible hypothesis for the arrhythmia is that a premature beat can encounter a zone of conduction block to initiate reentry. However, enhanced dispersion of repolarization, a necessary condition for initiation of reentry, is unlikely to be present in normal myocardium. Thus, the main objective of the present study was to perform detailed pace mapping measurements in normal ventricular myocardium with a view to identify pacing sites and critical coupling intervals which could induce spontaneous ectopic beats and to characterize the reentrant circuits
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