• Journal of IKEEE
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• v.27 no.4
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• pp.573-578
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• 2023

This paper introduces a new locking technique applicable to high-performance digital Phase-Locked Loops (DPLL). The study employs additional thermometer codes to reduce quantization errors in LC-based Digital Controlled Oscillators (DCO). Despite not implementing the entire DCO codes in thermometer mode, this method effectively reduces quantization errors through enhanced linearity. In the initial locking phase, binary codes are used, and upon completion of locking, the system transitions to thermometer codes, achieving high frequency linearity and reduced jitter characteristics. This approach significantly reduces the number of switches required and minimizes the oscillator's area, especially in applications requiring low DCO gain (Kdco), compared to the traditional method that uses only thermometer codes. Furthermore, the jitter performance is maintained at a level equivalent to that of the thermometer-only approach. The efficacy of this technique has been validated through modeling and design at the RTL level using SystemVerilog and Verilog HDL.

• Journal of IKEEE
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• v.27 no.4
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• pp.425-429
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• 2023

In this paper, the scheme to activate the active elements of reconfigurable intelligent surface(RIS) is proposed. Recently, RIS has been studied as a technology that improves communication coverage and spectral efficiency in wireless communication system. RIS can adjust the phase and amplitude of the received signal, and can ensure better communication performance in areas with many obstacles, such as urban areas. However, due to RIS, the signal undergoes fading twice and performance decrease in communication. Recently, RIS using active reflection elements has been studied to solve these problems. However, if the entire RIS is used as an active reflection element, energy consumption increases. Accordingly, in this paper, we propose a system that utilizes some of the RIS reflective elements as active reflective elements and a scheme for selecting active reflective elements to be activated.

• Journal of Advanced Navigation Technology
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• v.26 no.6
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• pp.487-495
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• 2022

This paper describes the design and development of a high-power transmit receive module(TRM) for mounting on X-band synthetic aperture radar(SAR) of the NEXTSat-2. The TRM generates a high-power pulse signal with a bandwidth of 100 MHz in the target frequency range of X-band and amplifies a low-noise on the received signal. Tx. path of the TRM has output signal level of more than 200 watts (53.01 dB), pulse droop of 0.35 dB, signal strength change of 0.04 dB during transmission signal output, and phase change of 1.7 ˚. Rx. path has noise figure of 3.99 dB and gain of 37.38 ~ 37.46 dB. It was confirmed the TRM satisfies all requirements. The TRM mounted on the NEXTSat-2 flight model(FM) which will be launched using the KSLV-II (Nuri).

• Geophysics and Geophysical Exploration
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• v.8 no.2
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• pp.145-155
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• 2005

A two-dimensional (2-D) interpretation of MT data has been performed for the purpose of fracture detection for geothermal development. Remote stations have been operated in Kyushu, Japan (480 km apart) as well as in Korea (60 km and 165 km apart in 2002 and 2003 data set, respectively). Apparent resistivity and phase curves calculated by remote processing with the Japan remote data showed enough quality for 2-D inversion for the whole frequency range. Remote reference processing with Korea remote reference data also showed quite good continuity in apparent resistivity and phase curves except some noisy frequency bands; around the power frequency, 60 Hz, and around the dead band $10^{-1}Hz\;Hz\;\~1\;Hz$, where the natural EM signal is known to be very weak. Even though the subsurface showed severe three-dimensional (3-D) characteristics in the survey area so that 2-D inversion by itself could not give enough information for deep geological structures, the 2-D inversion for the 5 survey lines showed several common features. The conductive semi-consolidate mudstone layer is dipping from north to south (about 500 m depth on the south and 200 m on the north most part of the survey area). The boundary between the low (L-2) and high (H-2) resistivity anomalies can be thought as a major fault with strike $N15^{\circ}E$, passing through the sites 206, 112 and 414. The shallow (< 1 km) conductive anomalies (L-4) seem to be fracture zones having strike E-W (at site 105) and $N60^{\circ}W$ (at site 434). And there exists a conductive layer in the western and west-southern part of the survey area in the depth below $2\~3\;km$, for which further investigation is to be needed.

• 한국해양학회지
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• v.30 no.6
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• pp.550-564
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• 1995

The temporal and spatial characteristics of wind fields over the neighbouring seas of the Korean peninsula are investigated using 10-years daily wind data during 1978${\sim}$1987 which have been spatially smoothed and low-pass filtered. Long term annual and monthly means are examined for synoptic patterns and spectral analyses are made for temporal variability and spatial coherence. Spatial patterns of the annual mean wind stress and curl have a strong resemblance with those of monthly means during the winter season. Two outstanding periodicities are observed at 1 and 2 cycles per year. The synoptic winds over the study area are highly coherent at both the annual and semi-annual periodicities. However, each basin has its own characteristic spatial pattern. For instance, the prevailing wind during the winter season is northerIy over the northern East Sea (ES), Yellow Sea (YS), and northern East China Sea (ECS), while it is northwesterly over the southern ES and northesterly over the northern ES and southern ECS. At the same time, the wind stress curl is positive over the northern ES and southern ECS, while it is negative over the southern ES, YS and northern ECS. On the other hand, the wind field during the summer season, with its strength being much reduced, is completely different from that during the winter season, and frequent passage of tropical storms provokes large temporal variability over ECS. One remarkable point is that the annual cycle, dominated by the Siberian High, tends to propagate from northeast to southwest, i.e., from northern 25 toward southern ES, YS and ECS, while the semi-annual cycle propagates in the opposite direction, from southwest to northeast. The semi-annual periodicity may reflect development of extratropical cyclones in spring and fall which frequently cross the Korean peninsula. In higher frequencies, there are no dominant periodicities, but local winds over YS and ES are highly correlated for frequencies larger than 0.1 cycles per day and phase difference increases linearly with frequency. This linear increase of phase corresponds to phase speed of 550 and 730 km/d at 0.1 and 0.3 cpd, respectively, The phase speed is apparently coincident with moving speed of extratropical cyclones across the Korean peninsula in the west-east direction.

• Investigative Magnetic Resonance Imaging
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• v.8 no.1
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• pp.42-49
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• 2004

Purpose : The quantization noise in magnetic resonance imaging (MRI) systems is analyzed. The signal-to-quantization noise ratio (SQNR) in the reconstructed image is derived from the level of quantization in the signal in spatial frequency domain. Based on the derived formula, the SQNRs in various main magnetic fields with different receiver systems are evaluated. From the evaluation, the quantization noise could be a major noise source determining overall system signal-to-noise ratio (SNR) in high field MRI system. A few methods to reduce the quantization noise are suggested. Materials and methods : In Fourier imaging methods, spin density distribution is encoded by phase and frequency encoding gradients in such a way that it becomes a distribution in the spatial frequency domain. Thus the quantization noise in the spatial frequency domain is expressed in terms of the SQNR in the reconstructed image. The validity of the derived formula is confirmed by experiments and computer simulation. Results : Using the derived formula, the SQNRs in various main magnetic fields with various receiver systems are evaluated. Since the quantization noise is proportional to the signal amplitude, yet it cannot be reduced by simple signal averaging, it could be a serious problem in high field imaging. In many receiver systems employing analog-to-digital converters (ADC) of 16 bits/sample, the quantization noise could be a major noise source limiting overall system SNR, especially in a high field imaging. Conclusion : The field strength of MRI system keeps going higher for functional imaging and spectroscopy. In high field MRI system, signal amplitude becomes larger with more susceptibility effect and wider spectral separation. Since the quantization noise is proportional to the signal amplitude, if the conversion bits of the ADCs in the receiver system are not large enough, the increase of signal amplitude may not be fully utilized for the SNR enhancement due to the increase of the quantization noise. Evaluation of the SQNR for various systems using the formula shows that the quantization noise could be a major noise source limiting overall system SNR, especially in three dimensional imaging in a high field imaging. Oversampling and off-center sampling would be an alternative solution to reduce the quantization noise without replacement of the receiver system.

• Investigative Magnetic Resonance Imaging
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• v.18 no.4
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• pp.303-313
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• 2014

Purpose : In-vivo conductivity reconstruction using transmit field ($B_1{^+}$) information of MRI was proposed. We assessed the accuracy of conductivity reconstruction in the presence of statistical noise in complex $B_1{^+}$ map and provided a parametric model of the conductivity-to-noise ratio value. Materials and Methods: The $B_1{^+}$ distribution was simulated for a cylindrical phantom model. By adding complex Gaussian noise to the simulated $B_1{^+}$ map, quantitative conductivity estimation error was evaluated. The quantitative evaluation process was repeated over several different parameters such as Larmor frequency, object radius and SNR of $B_1{^+}$ map. A parametric model for the conductivity-to-noise ratio was developed according to these various parameters. Results: According to the simulation results, conductivity estimation is more sensitive to statistical noise in $B_1{^+}$ phase than to noise in $B_1{^+}$ magnitude. The conductivity estimate of the object of interest does not depend on the external object surrounding it. The conductivity-to-noise ratio is proportional to the signal-to-noise ratio of the $B_1{^+}$ map, Larmor frequency, the conductivity value itself and the number of averaged pixels. To estimate accurate conductivity value of the targeted tissue, SNR of $B_1{^+}$ map and adequate filtering size have to be taken into account for conductivity reconstruction process. In addition, the simulation result was verified at 3T conventional MRI scanner. Conclusion: Through all these relationships, quantitative conductivity estimation error due to statistical noise in $B_1{^+}$ map is modeled. By using this model, further issues regarding filtering and reconstruction algorithms can be investigated for MREPT.

• Journal of IKEEE
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• v.12 no.3
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• pp.176-183
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• 2008

The high efficiency power management IC(PMIC) with DTMOS(Dynamic Threshold voltage MOSFET) switching device is proposed in this paper. PMIC is controlled with PWM control method in order to have high power efficiency at high current level. DTMOS with low on-resistance is designed to decrease conduction loss. The control parts in Buck converter, that is, PWM control circuits consist of a saw-tooth generator, a band-gap reference circuit, an error amplifier and a comparator circuit as a block. The Saw-tooth generator is made to have 1.2 MHz oscillation frequency and full range of output swing from ground to supply voltage(VDD:3.3V). The comparator is designed with two stage OP amplifier. And the error amplifier has 70dB DC gain and $64^{\circ}$ phase margin. DC-DC converter, based on Voltage-mode PWM control circuits and low on-resistance switching device, achieved the high efficiency near 95% at 100mA output current. And DC-DC converter is designed with LDO in stand-by mode which fewer than 1mA for high efficiency.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.3
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• pp.699-706
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• 2010

We have studied to obtain the slanted finger interdigital(SFIT) type filter was formed on the Langasite substrate and was evaporated two IDT electrode by Aluminum-Copper alloy respectively. We can fabricate that the block weighted type IDT as an input transducer of the filter and the withdrawal weighted type IDT as an output transducer of the filter from the results of our computer-simulation. Also, we have performed to obtain the properly design conditions about phase shift conditions of the SPIT type filter. We have employed that the number of pairs of the input and output IDT are 50 pairs and the thickness and the width of reflectors are $5000\;{\AA}$ and $3.6{\mu}m$ respectively. At the first sample, we have employed that the distance from the hot electrode to the reflectors is $2.4{\mu}m$ distance from the ground electrode to the reflectors is $1.8{\mu}m$ and the distance from the hot electrode to the ground is $1.5{\mu}m$ respectively. At the other sample, we have also employed that the distance from the hot electrode to the reflectors and the distance from the ground electrode to the reflectors are $2.4{\mu}m$. Frequency response of the fabricated SAW filter has the property that the center frequency is about 190MHz and bandwidth at the 3dB is probably 7.3 MHz. And we could obtain that return is less than -20dB, ripple characteristics is probably 3dB and triple transit echo(TTE) is less than -22dB after when we have matched impedance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.8 s.338
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• pp.33-40
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• 2005

This paper presents a structure of the searcher using a diversity in array antenna systems operating in the cdma2000 1x signal environments. The new technique exploits the fact that the In-phase and quadrature components of interferers can respectively be viewed as an independent gaussian noise at each antnna element in most practical cdma signal environments. The proposed PN acquisition scheme is a singles-dwell PN acquisition system consisting of two stages, that is, the searching stage and the verification stage. The searching stage independently correlates the receiver multiple signals with PN generator of each antenna element for obtaining the synchronous energy at the entire region. Then, the searching results of each antenna element are non-coherently combinind. The verification stage compares the searching energy with the optimal threshold, which is predesigned in the lock detector, and decides whether the acquisition is successful or fail. In this paper, we analyzed the effect of tile diversity order to determine the mean acquisition time. In general, it is known that the mean acquisition time significantly decrease as the number of antenna elements increases. But, as the diversity order goes up, the enhancement of the performance is saturated. Therefore, to decrease the mean acquisition time of the searcher, we must design the optimal array antenna systems by considering the operating SNR range of the receiver, the probability of detection $P_D$ and that of false alarm $P_{FA}$ . The Performance of the proposed PN acquisition scheme is analyzed in frequency selective Rayleigh fading channels. In this paper, the effect of the number of antenna elements on PN acquisition scheme is shown according to the probability of detection $P_D$ and that of false alarm $P_{FA}$.