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Recently, in the field of medical ultrasound systems, the wireless smart probe is attracting attention mainly due to its benefits such as improved mobility, ease of use, and effective infection control. This probe has a constraint that all or part of the system beamformer should be integrated inside the probe handle to reduce the data transmission rate of the echo signals that should be transmitted from the probe to the main system. In this case, we should minimize the space of the integrated beamformer, as well as the power dissipation of the hardware in order not to violate the safety regulation, degrade the performance, or make the user uncomfortable due to the generated heat, while maintaining its proper performance. In this paper, we propose a novel beamforming method for wireless smart probe which combines sub-aperture beamforming with phase rotation, digital beamforming, and synthetic aperture sequential beamforming altogether in order to design a probe that meets these constraints effectively and is affordably implementable. The proposed method is verified by the Field II simulation, and the results show that the overall performance of the proposed method is comparable to that of the conventional delay-and-sum beamformer.

A synthetic aperture imaging method which uses a steered plane wave is advantageous in that the resolution can be improved by covering a wide area with a small number of transmissions, and that the calculation of focusing delay for transmit focus synthesis is relatively simple. Through simulation studies, we found, however, that the clutter level of this method is higher than that of SAI using virtual sources positioned in the imaging plane, and the main reason is considered to be that the area covered by plane wave (PW) is wider than that of the virtual source case so that the scattering occurs over a large area, and the received signal basically has higher clutter levels than the virtual source case. A straightforward solution to this problem would be to use narrower PWs. In this case, however, the number of transmissions needs to be increased to cover the same area, resulting in a lowered frame rate. In order to maintain the same frame rate while reducing the clutter level, we divide the aperture into several sub-apertures, and simultaneously transmit two PWs in spatially separated sub-apertures, and furthermore, we use an up-chirp signal for one PW and a down-chirp signal for the other PW to minimize the crosstalk between the two PWs. In addition, transmit apodization is employed to reduce the fringing effect of the transmit aperture, and a further reduction of clutter level is achieved.

Recently, short-lag spatial coherence (SLSC) imaging has drawn much attention from researchers due to benefits such as improved speckle signal-to-noise ratio and contrast-to-noise ratio compared to conventional B-mode imaging based on delay-and-sum beamforming. However, SLSC imaging has good performance just around the transmit focal point, which is quite a drawback. In this paper, we propose a new method that combines SLSC imaging and synthetic aperture imaging to address such a shortcoming. The efficacy of the proposed method is verified through simulations and experiments using Field II echo data and phantom data acquired with an actual ultrasound system.

Recent studies have reported the advantageous aspects of minimum variance beamforming (MVBF) such as an improvement in main lobe resolution and clutter level reduction. Unlike a conventional delay-and-sum beamformer (DASBF) that suffers from a degradation in resolution when the aperture size is limited, MVDF can cope with it. However, the covariance matrix dimension is also reduced resulting in low performance of MVBF. Moreover, spatial smoothing processing in MVBF also reduces the covariance matrix dimension. To overcome this problem, we herein propose a fine pitch array whose number of elements is increased using the same aperture size. Although this method requires more computation, it maximizes the performance of MVBF. The efficacy of the proposed method is verified by constructing and comparing images from pulse echo data using Field II simulation as well as from experimental data on a real tissue mimicking phantom.

In the diagnostic ultrasound system, a precise estimation of blood velocity requires a better removal of the clutter's influence. Adaptive clutter filtering has been researched for this purpose and recently, eigen-based clutter filtering methods are mainly researched. However, these methods have a drawback of a large amount of computational requirement to be applied to mid-to-low cost systems. In consideration of this point, a new adaptive clutter filtering method is presented in this paper. This new method is based on clutter down-mixing and the down-mixing frequency is determined by 2nd order AR (autoregressive) model so that performance is improved from conventional down-mixing method. The performance of the proposed method is verified through computer simulations. Two sorts of input signals are used for simulation, one from generated RF data using Field II and another is RF acquisition data obtained from actual system. Resultant images show that performance of the proposed method is not far behind eigen-based clutter filtering.

This paper describes recently held research about combining two methods of autocorrelation based normal tissue Doppler imaging (TDI) and synthetic aperture imaging (SAI). Doppler shift estimator based on autocorrelation has been widely used to various commercial TDI system because of its simple structure, robustness, and low computation power requirements. And through application of SAI, spatial resolution, contrast resolution and SNR can be improved without a drop of frame rate so itpsilas been researched until recent and the system utilizing this method will be shown to the market sooner or later. Since both methods are based on quite different approaches, direct combination of two methods has various problems. To solve these problems, source position staggering method is proposed in this paper. As a result, frame rate can be maintained as a normal B mode with stable TDI. Proposed method is verified by field II computer simulation and off-line processing of the actual echo signal obtained from the human body.

This paper describes a clock skew variation compensating technique for maintaining the skew amount between local clock meshes which have relative skew between them due to PVT variations and unbalanced load distribution. A skew detector that senses skew amount between clock meshes and converts it to effective logic values with a digitally controlled delay set which corrects the clock skew of the meshes enables 72% reduction in skew variation, from 160 ps to 45.2 ps.

This paper presents a research for enhancing B-mode image quality using both of synthetic aperture imaging and tissue harmonic imaging in the medical ultrasound imaging. Synthetic aperture imaging has been actively researched until recently for improving spatial resolution and contrast resolution of the ultrasound image. Tissue harmonic imaging also has been actively researched with a similar purpose however way of approach is quite different. Thus it can be predicted that if both methods are appropriately combined, improved image quality is obtained and it has been proven by experiment. Experimental data is acquired from Medison's Accuvix system and acquired RF echo data from the human body and the phantom are processed off-line.

This paper presents novel nonoverlapping cuspid-pulsed flip-flop, which consists of a cuspid-pulse generator and a domino-like latch. The cuspid-pulse generator supplies the domino-like latch with nonoverlapping negative and positive cuspid-shape pulses. The flip-flop allows the elimination of the second stage in the conventional semi-dynamic pulse-based flip-flops, leading to a significant reduction of data-to-output latency. The simulation results using a 65 nm CMOS process technology indicate that the data-to-output delay of the proposed flip-flop was decreased by up to 63%. They also indicate that the improvement on energy-delay product was up to 75% as compared to the conventional flip-flops.

This paper proposes a power-aware cache block allocation algorithm for the way-selective set-associative cache on embedded systems to reduce energy consumption without additional delay or performance degradation. For this goal, way selection logic and specialized replacement policy are designed to enable only one way of set-associative cache as in the direct-mapped cache. Overall cache access time becomes almost the same as that of a conventional set associative cache with accessing additional way selection logic. Because data array can be accessed without waiting for tag comparison, multiplexer delay can be removed totally. The simulation result shows that the proposed architecture can reduce a per access power consumption by 59% over conventional set-associative caches with average 0.06% of negligible performance loss.

In this study, learning spillovers in the production of TFT-LCD are investigated with the quarterly market data on TFT-LCD panel prices and the plant-level data on panel outputs and glass inputs. Learning curves of TFT-LCD are estimated with a multi-output model, which is developed and modified from a traditional single output model. It turns out that spillovers are significant and external learning from rival companies' production experience is much bigger than internal learning from a company's own production experience. It means that newcomers can easily enter into the TFT-LCD industry to acquire manufacturing technical skills and know-how. The difference between internal and external learning is smaller in the 3rd generation process than in the 2nd generation process when Korean enterprises went into market in full scale. Moreover, Korean firms' experience from DRAM production enables them to lower their learning curves of TFT-LCD easily, which is another factor of their success. This study explains industrial dynamics of TFT-LCD, entry barrier, leadership change, etc, using learning curves. It also delivers implications for the persistence of leadership.

More and faster transistors with less power and lower voltage create many opportunities. As a microprocessor technology advances beyond sub-quarter micron, the performance benefits from scaling down tapers off. The combination of short-channel effects, difficulty in producing gate oxides thinner than 3 nm, and some fundamental problems narrow down the improvements for each new process generation. Silicon-on-insulator (SOI) transistors along with copper interconnections offer a breakthrough for the 21st century microprocessor technology for performance, power, and cost. Microprocessor technology has been waiting for more and faster transistors with less power and lower operating voltage and more and faster interconnections with less electrical and physical shortcomings. A 0.25/spl mu/m FD-SOI4-Metal CMOS 64b Alpha microprocessor is fabricated containing 9.66 million transistors and measures 14.4x14.5mm2 at 60OMHz operating frequency under typical operating conditions with 1.5V power supply along 2.0V interface.

High performance microprocessors with high stabilities are fabricated on Si and SiGe inserted (SGI) SOI wafers. The operation margins of voltages and frequency are characterized. For body floating devices, the operation margins at high Vdd and low frequency are narrow due to the floating body effect (FBE). These operation limits are drastically improved by applying a body contact for only NMOS at the critical circuits sensitive to the FBE. The maximum operation voltage increases from 1.8 V up to 2.5 V. The minimum operation frequency is lowered from 370 MHz to 220 MHz. The functionality of the NMOS body contact SOI microprocessor is comparable to that of the bulk. To maximize the SOI performance gain, body contacted and floating SOI devices should be optimized, and the smaller portion of body contacted devices are conclusive. For body floating SOI devices, the SGI SOI technology is very effective in suppressing SOI FBE and provides stable circuit operation.