• Journal of electromagnetic engineering and science
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• 제7권2호
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• pp.64-68
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• 2007

An InGaP/GaAs HBT based differential Colpitts voltage control oscillator(VCO) is presented in this paper. In the VCO core, two switching transistors are introduced to steer the core bias current to save power. An LC tank with an inductor quality factor(Q) of 11.4 is used to generate oscillation frequency. It has a superior phase noise characteristics of -130.12 dBc/Hz and -105.3 at 1 MHz and 100 kHz frequency offsets respectively from the carrier frequency(1.566 GHz) when supplied with a control voltage of 0 volt. It dissipates output power of -5.3 dBm. Two pairs of on-chip base collector (BC) diodes are used in the tank circuit to increase the VCO tuning range(168 MHz). This VCO occupies the area of $1.070{\times}0.90mm^2$ including buffer and pads.

• Journal of Power Electronics
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• 제13권1호
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• pp.86-93
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• 2013

A half-cycle-waveform inversion based three reference modulations seven-level SPWM (TRM-SPWM) scheme with one carrier is proposed in this paper. To keep the same comparison logics for the modulations and carrier during the negative half cycle and the positive one for the modulations, in the negative half cycle of the modulations, the DC offsets related to the amplitude of the carrier are set on the three modulations, respectively. The seven-level SPWM waveform with dead time thereby is implemented with only one Digital Signal Processor (DSP) without any other attached logic circuit. The basis principle of the proposed TRM-SPWM is analyzed in detail, and the frequency spectrums of the conventional and the proposed schemes are derived and compared with each other through simulation. The DSP based implementation is presented and detailed experimental waveforms verify the accuracy and feasibility of the proposed TRM-SPWM scheme.

• ETRI Journal
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• 제38권1호
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• pp.30-40
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• 2016

Co-channel interference between macro-femtocell networks is an unresolved problem, due to the frequency reuse phenomenon. To mitigate such interference, a secondary femtocell must acquire channel-state knowledge about a co-channel macrocell user and accordingly condition the maximum transmit power of femtocell user. This paper proposes a pilot-based spectrum sensing (PSS) algorithm for overlaid femtocell networks to sense the presence of a macrocell user over a channel of interest. The PSS algorithm senses the pilot tones in the received signal through the power level and the correlation metric comparisons between the received signal and the local reference pilots. On ensuring the existence of a co-channel macrocell user, the maximum transmit power of the corresponding femtocell user is optimized so as to avoid interference. Time and frequency offsets are carefully handled in our proposal. Simulation results show that the PSS algorithm outperforms existing sensing techniques, even at poor received signal quality. It requires less sensing time and provides better detection probability over existing techniques.

• Journal of electromagnetic engineering and science
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• 제5권1호
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• pp.26-30
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• 2005

It is important to know phase offsets of PN(Pseudo Noise) sequences in spread spectrum communications since the acquisition is equivalent to making a phase offset between a receiving PN sequence and a PN sequence of local PN generator be identical. In this paper, a phase offset enumeration method for PN sequences with error detection, and its application to the synchronization are proposed. The phase offset enumeration for an n-tuple PN sequence and its error detection are performed when one period of the sequence is received. Once the phase offset of the receiving sequence is calculated, we can easily accomplish the synchronization by initializing shift registers of a local PN generator according to the phase offset value. The mean acquisition time performance of the proposed scheme was derived analytically. Since this synchronization scheme can be realized by using simple circuit and acquires very rapid acquisition in high SNR but shows performance degradation in low SNR, it can be especially useful in indoor and office environments.

• International Journal of CAD/CAM
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• 제8권1호
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• pp.45-53
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• 2009

As the point sampling technology evolves rapidly, there has been increasing need in generating tool path from dense point set without creating intermediate models such as triangular meshes or surfaces. In this paper, we present a new tool path generation method from point set using Euclidean distance fields based on Algebraic Point Set Surfaces (APSS). Once an Euclidean distance field from the target shape is obtained, it is fairly easy to generate tool paths. In order to compute the distance from a point in the 3D space to the point set, we locally fit an algebraic sphere using moving least square method (MLS) for accurate and simple calculation. This process is repeated until it converges. The main advantages of our approach are : (1) tool paths are computed directly from point set without making triangular mesh or surfaces and their offsets, and (2) we do not have to worry about no local interference at concave region compared to the other methods using triangular mesh or surface model. Experimental results show that our approach can generate accurate enough tool paths from a point set in a robust manner and efficiently.

• ETRI Journal
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• 제46권3호
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• pp.421-431
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• 2024

In this study, a direct position tracking method for non-circular (NC) signals using distributed passive arrays is proposed. First, we calculate the initial positions of sources using a direct position determination (DPD) approach; next, we transform the tracking into a compensation problem. The offsets of the adjacent time positions are calculated using a first-order Taylor expansion. The fusion calculation of the noise subspace is performed according to the NC characteristics. Because the proposed method uses the signal information from the previous iteration, it can realize automatic data associations. Compared with traditional DPD and two-step localization methods, our novel process has lower computational complexity and provides higher accuracy. Moreover, its performance is better than that of the traditional tracking methods. Numerous simulation results support the superiority of our proposed method.

• Structural Engineering and Mechanics
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• 제71권6호
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• pp.603-625
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• 2019

Main cable configurations under final dead load and in the unloaded state and critical construction parameters (e.g. unstrained cable length, unstrained hanger lengths, and pre-offsets for tower saddles and splay saddles) are the core considerations in the design and construction control of a suspension bridge. For the purpose of accurate calculations, it is necessary to take into account the effects of cable strands over the anchor spans, arc-shaped saddle top, and tower top pre-uplift. In this paper, a method for calculating the cable configuration under final dead load over a main span, two side spans, and two anchor spans, coordinates of tangent points, and unstrained cable length are firstly developed using conditions for mechanical equilibrium and geometric relationships. Hanger tensile forces and unstrained hanger lengths are calculated by iteratively solving the equations governing hanger tensile forces and the cable configuration, which gives careful consideration to the effect of hanger weight. Next, equations for calculating the cable configuration in the unloaded state and pre-offsets of saddles are derived from the cable configuration under final dead load and the conditions for unstrained cable length to be conserved. The equations for the main span, two side spans and two anchor spans are then solved simultaneously. In the proposed methods, coupled nonlinear equations are solved by turning them into an unconstrained optimization problem, making the procedure simplified. The feasibility and validity of the proposed methods are demonstrated through a numerical example.

• 대한토목학회논문집
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• 제42권4호
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• pp.509-517
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• 2022

도시의 대형화로 인해 도심지 지하공간은 점점 고밀화되어 가고 있으며, 지하공간 활용에 대한 수요 또한 급격히 증가하고 있다. 도심지에서는 상부뿐만 아니라 지중에도 통신, 교통 등을 위한 지중 구조물 또한 존재하고 있다. 이러한 도심지의 지중에 신설 구조물을 시공할 경우, 상부 및 지중에 존재하는 인접 구조물과의 상호거동에 대한 이해가 필수적이다. 따라서 본 연구에서는 기존 군말뚝 및 운영중 터널에 인접하여 터널이 신설될 경우 침하와 지중의 전단변형을 유한요소해석을 통해 분석한다. 운영 중 터널-말뚝 간의 이격거리, 말뚝 개수, 말뚝 중심간격 등이 변수로 고려되었으며, 수치해석을 통해 말뚝 및 인접 지반 침하를 비교한 결과, 말뚝의 중심간격보다 군말뚝-신설 터널 수직이격거리 및 운영중 터널-신설 터널 간의 수평이격거리가 침하에 더 큰 영향을 미치는 것으로 나타났다. 또한, 구조물 간의 이격거리 증가에 따라 신설 터널 굴착에 따른 전단변형률이 미치는 영향이 감소되는 것으로 나타났다.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(A)
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• pp.170-172
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• 2012

실시간 시스템(real-time system)은 논리적 연산을 일정한 시간적 제약 하에서 수행하는 시스템이다. 시간적 제약을 충족하도록 주기적 태스크(periodic task)를 스케줄(schedule)할 때 일반적으로 태스크 오프셋(initial offset)이 0 이거나 고정된 것으로 가정한다. 그러나 오프셋에 약간의 유연성을 허용함으로써 태스크들의 평균 응답 시간을 줄일 수도 있다. 이 논문에서는 주기적 태스크의 오프셋을 주어진 허용 범위 안에서 선택하여 평균 응답 시간(response time)을 최적화할 수 있음을 보이고, 임의의 태스크 집합에 대하여 최적 오프셋이 존재하는 좁은 범위를 제시한다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제17권3호
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• pp.347-353
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• 2017

We present a STT-MRAM read-circuit which mitigates the performance degradation caused by offsets from device mismatches. In the circuit, a single current source supplies read-current to both the data and the reference cells sequentially eliminating potential mismatches. Furthermore, an offset-free pre-amplification using a capacitor storing the mismatch information is employed to lessen the effect of the comparator offset. The proposed circuit was implemented using a 130-nm CMOS technology and Monte Carlo simulations of the circuit demonstrate its effectiveness in suppressing the effect of device mismatch.