Keong Kam

Detection of atypical texture features in early malignant melanoma

Background: The presence of an atypical (irregular) pigment network (APN) can indicate a diagnosis of melanoma. This study sought to analyze the APN with texture measures.

An Effective Method of Probe Calibration in Phase-Resolved Near-Field Scanning for EMI Application

Near-field scanning can be used to determine the far-field emissions of electronic devices. In general, this requires phase-resolved electric and magnetic near-field data. To capture a broad frequency range relatively quickly, a multichannel oscilloscope can be used for data capture. The phase relationship of the fields between different space points and between the electric and the magnetic field needs to be known. Consequently, it is required to determine the complex-valued probe factor (PF) of the probe, cable, and amplifier chain. This paper presents a fast and efficient calibration method which uses the same setup and instruments during calibration and measurement, and it allows for easy and economical integration of the calibration hardware and software into the scanning system. Known fields are created by a microstrip trace driven with a comb generator. By referencing measured data to this known field, the PF is obtained over a broad frequency range by capturing one time-domain waveform.

EMC guideline for synchronous buck converter design

Synchronous buck converters generate broadband noise typically in 50–300 MHz range. In this paper, the root cause of this broadband noise and possible coupling mechanisms are analysed. Then, a list of EMC design guideline for minimizing the broadband noise is presented. The guideline contains circuit level guideline which involves input filtering, component selection, and an effective snubber strategy using a parallel resistor and inductor. The guideline also contains layout level guideline, which involves decoupling capacitor placement, layer stackup, and minimizing exposed phase voltage area. For each suggested guideline item, an example illustrates the impact of the particular strategy through experimental results or SPICE simulations, leading to a strong reduction of broadband noise from the synchronous buck converter. Key words: Broadband EMI, Synchronous Buck Converter, SMPS, Snubber

DC-DC Buck Converter EMI Reduction Using PCB Layout Modification

The paper treats the effect of layout on the electromagnetic interference (EMI) of buck converters. An optimized layout design for dc-dc synchronous buck converter is proposed for EMI reduction. Six different layout versions are analyzed with respect to loop area, loop inductance, radiating dipole moments, and far-field radiation. Optimizations are done with respect to field-effect transistor (FET), decoupling capacitor and via placement. Passive full-wave simulations are used to estimate and verify the loop inductance and far-field emissions. Those are compared with measurements. A gigahertz transverse electromagnetic (GTEM) cell is used to quantify the dipole moments in the printed circuit board (PCB) for estimating the far field and comparing to measurement.

EMI prediction in switched power supplies by full-wave and non-linear circuit co-simulation

This paper treats the problem of electromagnetic interference in switched mode power supplies using co-simulation. Co-simulation combines full-wave EM solution with non linear SPICE circuit. Voltages, currents (at different nodes in the circuit) that drive the EMI can be simulated. Different co-simulation strategies are discussed along with their pros and cons. Also different commercial software tools have been evaluated for this simulation technique and promising results have been compared to measurements of voltages, TEM cell coupling and coupling to an antenna. The circuit investigated is a DC-DC buck converter.

Quantification of Self-Damping of Power MOSFET in a Synchronous Buck Converter

Ringing in the switching waveform of the switching power supply (e.g., synchronous buck converter) is known to cause broadband electromagnetic interference problems in the 30-300 MHz range. The measured switching waveform shows overshoot and, then, exponential decay of the ringing. It has been observed that this exponential decay rate varies significantly between using different low-side FETs; thus, the low-side FET dominates the attenuation of the ringing. This paper provides a novel method for quantifying the losses by using the measureable quantity “ Ross,” which is equivalent to the loss of the output capacitance Coss of the FET. This paper describes the method of measuring Ross and explains its relevance to the self-damping of the switch ringing. The method permits selection of a low-side FET to optimize the electromagnetic compatibility performances of the supply.

An evaluation of TVS devices for ESD protection

TVS components are widely used to protect electronic systems from ESD. However, there are various technologies of TVS components as well as numerous manufacturers for each technology. Choosing the right component is not easy, as a typical TVS data sheet does not always provide all the relevant information. This paper presents the pros and cons of different technologies as well as empirical data to facilitate the design of adequate and economical ESD protection.

Improvement of CAN BUS Performance by Using Error-Correction Codes

In this paper, two variants of the Hybrid Automatic Repeat Request (HARQ) scheme for CAN bus are presented. The basic HARQ uses error-correction code based on the Reed-Solomon (RS) technique and the Cyclic Redundancy Check (CRC) method to detect errors. The second scheme uses the cyclic error-correction method instead of the CRC error-detection method to further improve the throughput. Moreover, the second scheme uses no additional bit overhead when compared with the basic HARQ scheme. This paper presents the performance of the proposed schemes using MATLAB and NS2 simulations. Experimental data of error patterns were used for realistic evaluation. The basic HARQ method corrects 100% of error bursts shorter than 7 bits. When the burst length falls between 7 to 10 the scheme corrects between 86% and 56% of the corrupted frames. Network Simulator (NS2) simulations showed that the throughput increased by 92% when the user message size was increased from the standard 64 bits to 512 bits as a result of reduced overhead per user bit.

Microwave resonant out-of-plane fed elliptical slot antenna for imaging applications

Development of an effective microwave antenna is important issue for nondestructive sensing and imaging applications. Recently a one-shot, rapid and portable microwave imaging system with a PIN diode-loaded resonant elliptical slot has been developed. In this paper a new approach for feeding a resonant slot used in such a systems is considered. It includes coupling the transmitted and received signals into the slot using out-of-plane (perpendicular) microstrip feed. Three feeds are considered, namely; a 90°-bent microstrip-line feed, a microstrip line proximity feed and a direct microstrip line connection to the slot load. The simulation and measured results show that the antenna with the 90° bent microstrip-line feed demonstrates the best radiation and modulation efficiencies.

Microwave resonant switched-slot probe with perpendicular coaxial feed

Development of efficient microwave real-time imaging systems is of great interest for many applications. A cost-effective design of such systems utilizes a switched transmit-receive array composed of efficient antenna elements. The utilized imaging arrays are typically planner and consist of large number of closely-spaced elements. The performance of these systems depends largely on the efficiency of the array element and its feeding structure, isolation between the elements as well as the transmit-receive isolation. Implementing the required efficient feeding and high-isolation switching, in-plane with the elements of a compact array is rather challenging at high microwave frequencies, e.g., 24 GHz. In this paper, a resonant switched slot with an out-of-plane coaxial feed is introduced as an efficient element for microwave imaging arrays. The slot is loaded with a PIN Diode and hence it is switched directly. The proposed array element design involves coupling the transmitted/received signals into/from the slot using a coaxial feed perpendicular to the plane of the slot. Two design variations of this out-of-plane feeding structure are considered here, namely; electrical and magnetic coupling. Simulation and measurement results show that high radiation and switching isolation can be obtained with these feed designs.