326 research outputs found
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
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
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
Development of advanced control strategies for Adaptive Optics systems
Atmospheric turbulence is a fast disturbance that requires high control frequency. At the same time, celestial objects are faint sources of light and thus WFSs often work in a low photon count regime. These two conditions require a trade-off between high closed-loop control frequency to improve the disturbance rejection performance, and large WFS exposure time to gather enough photons for the integrated signal to increase the Signal-to-Noise ratio (SNR), making the control a delicate yet fundamental aspect for AO systems. The AO plant and atmospheric turbulence were formalized as state-space linear time-invariant systems. The full AO system model is the ground upon which a model-based control can be designed. A Shack-Hartmann wavefront sensor was used to measure the horizontal atmospheric turbulence. The experimental measurements yielded to the Cn2 atmospheric structure parameter, which is key to describe the turbulence statistics, and the Zernike terms time-series. Experimental validation shows that the centroid extraction algorithm implemented on the Jetson GPU outperforms (i.e. is faster) than the CPU implementation on the same hardware. In fact, due to the construction of the Shack-Hartmann wavefront sensor, the intensity image captured from its camera is partitioned into several sub-images, each related to a point of the incoming wavefront. Such sub-images are independent each-other and can be computed concurrently. The AO model is exploited to automatically design an advanced linear-quadratic Gaussian controller with integral action. Experimental evidence shows that the system augmentation approach outperforms the simple integrator and the integrator filtered with the Kalman predictor, and that it requires less parameters to tune
Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications
The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well
- …