Sami Smaili

Accurate and efficient modeling of random demodulation based compressive sensing systems with a general filter

Random demodulation provides a hardware-compact architecture for realizing compressive sensing systems. A random demodulator is realized by a mixer, with a random signal as the oscillator, and a low pass filter. In order to recover the original signal from the compressive sensing measurements, accurate modeling of the hardware components is needed. Typically, the reconstruction model assumes the low pass filter to be an ideal integrator. While this assumption is valid at low frequencies, it poses tremendous challenges at frequencies higher than 50MHz. In this paper, we provide an accurate and efficient model for the random demodulator that takes into account the actual structure of the filter. Using our model at reconstruction allows random demodulation for bandwidths extending to the GHz range, while, as we demonstrate, assuming an ideal integrator at reconstruction severely limits the system bandwidth.

A sub-Nyquist reconfigurable receiver via random demodulation

In this paper we propose a reconfigurable receiver that utilizes random demodulation, a compressive sensing architecture for efficient signal projection on a sensing signal. In the proposed system, the sensing signal is designed to annihilate the contribution of undesired frequency components in the collected measurements, thus allowing for the recovery of selected signal bands. The acquisition rate is proportional to the desired signal bandwidth rather than the total bandwidth of the input signal.

Differential pair sense amplifier for a robust reading scheme for memristor-based memories

Memristors-based memories utilize the memristors resistance programmability and small structure to realize high density non-volatile memories. This programmability arises from the dependence of the memristors resistance on the magnetic flux and total charge, rather than the voltage and current passing through it. However, a critical requirement in memory applications is that the reading scheme should preserve the memristor state after the read. In this paper, we propose a robust reading scheme for memristor-based memories that uses a differential pair sensing amplifier.

Analytic modeling of memristor variability for robust memristor systems designs

In this paper we derive conditions for bounding the state change in a memristor due to an applied signal. The main memristor functionality is a programmable resistor, but its resistance changes due to the signal passing through it. Therefore, it is necessary to guarantee that any signal through the memristor causes a small resistance change as tolerable by the application. The derived conditions relate the desired bound on the resistance change to a bound on the signal flux through the memristor. We show examples for the case of a sinusoidal signal and demonstrate the impact of the derived conditions on the design of memristor-based systems.

On the design of RF-DACs for random acquisition based reconfigurable receivers

Meeting the pressing power and bandwidth requirements of modern communication systems requires the development of highly efficient reconfigurable transceivers. On the receiver side, we present a new class of reconfigurable receiver that utilizes random projections to balance the power-bandwidth tradeoff. Such random projection front-ends are ubiquitous and allow the use of sub-Nyquist ADCs. These systems utilize high speed DACs, typically found in transmitters, to generate high fidelity random signals. The emergence of RF-DACs, used for direct digital-to-RF synthesis, can be leveraged for random projection reconfigurable receivers. However, the need for high output power and linearity in both the transmitter and receiver DACs forces an evaluation of RF-DAC topologies with respect to drain efficiency. In this paper, the power efficiencies of several RF-DAC topologies are compared.

A Multi-Channel Random Demodulation Reconfigurable Receiver

In this letter, we propose a new approach to reconfigurable receivers using random acquisition techniques. Random projections have been widely used within the context of compressive sensing for sub-Nyquist signal acquisition. In the system we propose, we design the random sensing signals so as to filter undesired components in the signal and result in measurements equivalent to those obtained had the signal been filtered prior to acquisition. Because the random signals are digitally generated, the system is reconfigurable; the signals components to be filtered can be changed by changing the digitally generated random signals. The system digitizes the measurements at a rate proportional to the desired bandwidth only, not the total signal bandwidth.

Design considerations for a multi-integrator architecture for random demodulation compressive sensing

The random demodulator architecture is a compressive sensing based receiver that allows the reconstruction of frequency-sparse signals from measurements acquired at a rate below the signals Nyquist rate. This in turn results in tremendous power savings in receivers because of the direct correlation between the power consumption of analog-to-digital converters (ADCs) in communication receivers and the sampling rate at which these ADCs operate. In this thesis, we propose design techniques for a robust and efficient random demodulator. The resetting mechanism can pose challenges in practical settings that can degrade the performance of the random demodulator. We propose practical approaches to mitigate the effect of resetting and propose resetting schemes that provide robust performance.

Understanding the impact of particle separation in a plasmonic dimer on the resonance wavelength

Plasmonic dimers consist of two nanopar-ticles in near vicinity of each other, which give the dimer unique properties that the single constituents do not have. Given the increased interest in these types of particles, establishing efficient modeling techniques for dimers becomes essential to be able to design systems with optimal performance. Moreover, modeling dimers is a key first step into modeling more complex systems of interacting nanoparticles where traditional simulation methods are highly inefficient. In this paper, we present an efficient modeling technique for dimers based on the quasistatic approximation. Our modeling technique can capture the resonance properties of dimers and our formulation of the quasistatic approximation problem is efficient to implement.

Capturing the effect of the nanoshell aspect ratio on the resonance wavelength and quality factor in sensing applications using an impedance-based model

Nanoshells promise to be valuable in a wide range of applications ranging from chemical sensing to cancer treatment. Different applications require different performance from the nanoshell and pose different constraints on them, and thus the nanoshell sensor has to be designed according to the given application. In this regard, the resonance wavelength and the Q factor are the most important properties to consider. In this paper we provide analysis for the nanoshell resonance wavelength and Q factor based on an impedance model of the nanoshell.

An analytical impedance-based compact model for capturing the resonance wavelength of a nanoshell resonator under dipole approximation

Nanoshells have been utilized in a wide range of applications, from cancer treatment to sensing of chemicals and biological materials. Such applications are based on Surface Plasmon Polariton (SPP) oscillations that nanoshells support, where resonance peaks in the extinction of electromagnetic waves are observed at certain wavelengths that depend on the size of the nanoshell as well as its composite material. In this paper, we develop an impedance model that captures the resonance wavelength of nanoshells allowing for the design of nanoshells to meet specific requirements, depending on the application in which the nanoshell is used. The nanoshell is modeled as a resonator, and the model can accurately and efficiently predict the resonance wavelength of the nanoshell.