Edge Modulation Research Articles

Multiple converter performance and active filtering

The application of active power filtering to power systems in limited by the low switching rate of available high power inverter switches. In this paper, parallel and series connection of multiple voltage source inverter bridges are examined to increase their effective switching rate. The analysis of the inverter voltage spectrum for double edge modulation shows the modulation desired for the separate bridges in open loop. Intuitively i bridges in series or parallel increases the effective switch rate by a factor i. However the modulation process for each power converter maintains its pattern for its switching period T which gives a roll off at high frequencies and reduces effective bandwidth. The experimental system of two 10 kVA voltage source inverters demonstrated how the closed loop control strategies for the active filter can be applied for multiple bridges implementing periodic optimized error sawtooth feedback control. The double bridge closed loop system showed that the lowest switch frequency terms were double that of the separate bridges. The higher frequency switching lines that should have been cancelled in theory were still discernible due to the finite precision of the edge timing. >

Using coherent pulse width and edge modulations in artificial neural systems.

This paper describes an existing silicon implementation of an artificial neural system based on coherent pulse width and edge modulation techniques. A chip set with different neural functions has been conceived, manufactured and tested. Neural circuits have been optimized for lowest computation energy and highest reconfigurability. The main device is a 32 x 32 synaptic array consuming 10 mW of power at 140 MCPS. Synapsis size is about 7.200 microns 2 using a standard 1.5 microns CMOS technology. The problem of interfacing robotic sensors and actuators is addressed: voltage, current and resistance-based sensors are considered for the measurement of physical quantities such as temperature, pressure, strain, etc. Low resolution imaging sensors for robotic vision are also considered.

Excitonic electroabsorption in type II superlattices

Electric field dependence of the exciton absorption in the ZnSe0.35Te0.65-ZnTe type II superlattice has been studied theoretically. Large effective blue shift of the absorption edge and strong modulation of the absorption prove that type II structures can be used in visible spatial light modulators and switches.

Theoretical study of subband transitions in strain-induced quantum well wires

We have modeled the lateral quantum confinement in a GaAs quantum well due to partial strain release on the side walls of an InGaAs stressor located on the top of the well. We used the finite element method to solve both the continuum elasticity equation and the Luttinger four-band Hamiltonian with strain. This model was used to systematically study the wire width dependence of lateral band edge modulation, subband splitting, and relative transition strength in the strain-induced quantum well wire structures.

Observation of quantum dot levels produced by strain modulation of GaAs–AlGaAs quantum wells

We present the first observation of resolved quantum dot levels produced by strain modulation of a semiconductor. Excitons are confined in lateral potential wells of up to 60 meV, the largest yet reported for strain-induced quantum wire or dot structures. The dependence of the quantum dot level separation on dot size is in agreement with calculations of the strain-induced band edge modulation. For 200 nm wide carbon dot stressors the level separations are approximately 2 meV. Frustration of acceptor recombination by three-dimensional localization of carriers in the strain-induced potential wells is clearly observed. Finally, we detect luminescence from a single quantum dot at low excitation intensity, a result of the frustration of nonradiative recombination by localization.

Use of leading-edge modulation to transform boost and flyback converters into minimum-phase-zero systems

In leading edge modulation, the pulse width modulated (PWM) signal is turned off at the clock signal and turned on when the error signal crosses the ramp waveform. It is shown that the positive zero in the power stage transfer function of boost and flyback regulators can be shifted into the left-half-plane under suitable conditions. These conditions are as follows: (1) leading edge modulation must be used in the pulse width modulator; (2) the feedback compensation must not average the capacitor EST-generated output voltage switching ripple; and (3) appropriate power stage parameter values are necessary. The design procedure for shifting the positive zero into the left-half-plane is presented. Experimental verification is provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Observation of electronic subbands in PbTe nipi structures

PbTe doping superlattices with band edge modulations up to 30meV were investigated by far infrared magnetotransmission. Due to nonparabolicity several cyclotron resonance transitions originating from different electric subbands are observed. The subbands for the two types of valleys associated with the [111] growth directions are calculated self consistently.

Compositional and doping superlattices in III-V semiconductors

Abstract The unusual electrical and optical properties of three important types of semiconductor superlattices are reviewed. The artificial structures which were grown by molecular beam epitaxy (MBE) consist of a periodic sequence of ultrathin crystalline layers of alternating composition (Al x Ga1-x As/GaAs or Ga x In1-x As/GaAs y Sb1-y ) or of alternating doping (n-GaAs/p-GaAs). The electronic energy bands in these superlattives are split into quasi-two-dimensional subbands whose spacing and width can be tailored by appropriate choice of the design parameters of the structure. After a brief outline of the electronic properties of compositional superlattices, we discuss the unique properties of GaAs doping superlattices in detail. The space charge induced band edge modulation in doping superlattices leads to an indirect energy gap in real space. As a consequence, the electrons and holes are spatially separated and their recombination lifetimes are strongly enhanced, i.e. non-equilibrium free-carrier dist...

Computer assisted MTF determination in CT

A series of computer programs have been written to analyze a scan of the AAPM CT performance phantom resolution insert with little operator assistance. A representative analysis is done on a scan from an AS&E scanner as an example. Its point spread function, edge response function and modulation transfer function are presented.