• Journal of the Institute of Convergence Signal Processing
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• v.8 no.2
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• pp.113-118
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• 2007

In this paper, a novel approach to using Subcircuit of Pspice in designing feedback for DC-DC converter systems is proposed. Proposed new approach, the feedback design procedures which are based on small signal modeling are programmed as a subcircuit in Pspice. For this purpose, Analog Behavioral Modeling (ABM) is used. By using the subcircuit, the component values of the error compensation amplifier can be easily obtained by means of Pspice DC analysis. The methodology of development is presented in detail and application examples demonstrated the effectiveness of the proposed approach in designing feedbacks for DC-DC converters. The converter with PWM method used continuous current mode and calculated buck converter control signal with average and linear current technique. To decide pole and zero K-method was adapted and this kind of design procedure took stable function.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6C
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• pp.637-644
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• 2006

This paper presents performance and implementation comparisons of standard and fast DCT algorithms that are commonly used for subband filter bank in MPEG audio coders. The comparison is made according to the architectural difference of the implementation hardware. Fast DCT algorithms are known to have much less computational complexity than the standard method that involves computing a vector dot product of cosine coefficient. But, due to structural irregularity, fast DCT algorithms require extra cycles to generate the addresses for operands and to realign interim data. When algorithms are implemented using DSP processors that provide special operations such as single-cycle MAC (multiply-accumulate), zero-overhead nested loop, the standard algorithm is more advantageous than the fast algorithms. Also, in case of the finite-precision processing, the error performance of the standard method is far superior to that of the fast algorithms. In this paper, truncation errors and algorithmic suitability are analyzed and implementation results are provided to support the analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12C
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• pp.764-773
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• 2011

Despite enormous performance gain with multi-antenna transmission in the single cell environment, its gain diminishes out in the multi-cell environment due to interference. It is also very hard to solve the efficient downlink beamforming with low complexity in multi-cell environment. First, this paper shows that the asymptotically sum rate optimal downlink beamformings at low and high SNR are maximum ratio transmit (MRT) and zero forcing (ZF) beamforming in the multi-cell system, respectively. Secondly, exploiting the asymptotically optimal downlink beamforming, we develop simple two types of near optimal downlink beamforming schemes having the form of minimum mean squared error (MMSE) beamforming obtained from the dual uplink problem. For each type, three different subclasses are also considered depending on the computational complexity. The simulation results show that the proposed near optimum algorithms provide the trade-off between the complexity and the performance.

• The Transactions of the Korea Information Processing Society
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• v.1 no.4
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• pp.479-489
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• 1994

At the present time, it is an important problem that we are to select a transmission line code for the very-high speed optical transmission system which can confidentially transfer the original information signal sequence efficiently, as it is to be the large capacity and the economization for the optical digital transmission system to transfer the information signal sequence at the very-high speed. Therefore, this paper is to select first the proper transmission line codes for the high speed(more than Mb/s) optical transmission system of the proposed two-level unipolar transmission line codes up to date, and to decide a mBIZ (m Binary with One Zero insertion) code as an optimal transmission line code for the very-high speed optical transmission system, resulting from analyzing the performance at the requirements of the transmission line code, such as the maximum consecutive identical digits, the transmission delay time, the increasing rate of clock, the mark rate, the circuit complexity, the supervision of transmission line error, and power spectrum among the selected transmission line codes.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.89-93
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• 2008

Ferrimagnetic Copper-Iron-Chromium Oxide $CuFe_{0.9}Cr_{1.1}O_4$ has been investigated over a temperature range from liquid nitrogen temperature upto $N{\acute{e}}el$ temperature using the Mossbauer technique. Its $N{\acute{e}}el$ temperature is found to be 355 K. Above the $N{\acute{e}}el$ temperature the quadrupole splitting is found to be 0.50 mm/s. On the other hand, all the electric quadrupole shift values are zero below the $N{\acute{e}}el$ temperature within experimental error. These seemingly contradictory phenomena have been explained by the model that the magnetic hyperfine field is randomly oriented with respect to the principal axes of the electric-field-gradient tensor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.12
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• pp.1274-1285
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• 1991

This paper presents a statistical convergence analysis of the normalized least mean square(NLMS)algorithm that employs a single-pole lowpass filter, In this algorithm the lowpass filter is used to adjust its output towards the estimated value of the input signal power recursively. The estimated input signal power so obtained at each time is then used to normalize the convergence parameter. Under the assumption that the primary and reference inputs to the adaptive filter are zero mean wide sense stationary, and Gaussian random processes, and further making use of the independence assumption. we derive expressions that characterize the mean and maen squared behavior of the filter coefficients as well as the mean squared estimation error. Conditions for the mean and mean squared convergence are explored. Comparisons are also made between the performance of the NLMS algorithm and that of the popular least mean square(LMS) algorithm Finally, experimental results that show very good agreement between the analytical and emprincal results are presented.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.11
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• pp.924-927
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• 2017

This paper presents a 6~18 GHz 8-bit true time delay (TTD) circuit. The unit delay circuit is based on m-derived filter with relatively constant group delay. The designed 8-bit TTD is implemented with two single-pole double-throw (SPDT) switches and seven double- pole double-throw (DPDT) switches. The reflection characteristics are improved by using inductors. The designed 8-bit TTD was fabricated using $0.18{\mu}m$ CMOS. The measured delay control range was 250 ps with 1 ps of delay resolution. The measured RMS group delay error was less than 11 ps at 6~18 GHz. The measured input/output return losses are better than 10 dB. The chip consumes zero power at 1.8 V supply. The chip size is $2.36{\times}1.04mm^2$.

• Journal of Power Electronics
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• v.16 no.1
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• pp.297-309
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• 2016

Grid-connected inverters (GCIs) with an LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion is amplified significantly under highly distorted grid conditions. This paper proposes a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in the αβ stationary frame using the parallel virtual resistance-based active damping (PVR-AD) strategy for grid-interfaced distributed generation (DG) systems to suppress LCL resonance. Although both a proportional-resonant (PR) controller in the αβ stationary frame and a PI controller in the dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at the fundamental frequency. Therefore, an accurate SRF-EPI controller in the αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, the harmonic rejection capability, and the influence of the control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, grid voltage feed-forward and multiple PR controllers are integrated into the current loop to mitigate the current distortion introduced by the grid background distortion. In addition, the parameters design guidelines are presented to show the effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.10
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• pp.2197-2204
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• 2009

In this paper, we analyze the performance of the sphere decoding algorithm at MIMO system. The BER performance of this algorithm is the same as that of ML receiver, but computational complexity of SD algorithm is much less than that of ML receiver. The independent signals from each transmit antennas are modulated by using the QPSK and 16QAM modulation in the richly scattered Rayleigh flat-fading channel. The received signals from each receivers is independently detected by the receiver using Fincke & Pohst SD algorithm, and the BER output of the algorithm is compared with those of ZF, MMSE, SIC, and ML receivers. We also investigate the Viterbo & Boutros SD algorithm which is the modified SD algorithm, and the BER performance and the floting point operations of the algorithms are comparatively studied.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.551-554
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• 2005

The method of the reduction of the automotive induction noise can be classified by the method of passive control and the method of active control. However, the passive control method has a demerit to reduce the effect of noise reduction at low frequency (below 500Hz) range and to be limited by a space of the engine room. Whereas, the active control method can overcome the demerit of passive control method. The algorithm of active control is mostly used the LMS (Least-Mean-Square) algorithm because the LMS algorithm can easily obtain the complex transfer function in real-time. Especially, When the Filtered-X LMS (FXLMS) algorithm is applied to an ANC system. However, the convergence performance of LMS algorithm goes bad when the FXLMS algorithm is applied to an active control of the induction noise under rapidly accelerated driving conditions. Thus Normalized FXLMS algorithm was developed to improve the control performance under the rapid acceleration. The advantage of Normalized FXLMS algorithm is that the step size is no longer constant. Instead, it varies with time. But there is one additional practical difficulty that can arise when a nonstationary input is used. If the input is zero for consecutive samples, then the step size becomes unbounded. So, in order to solve this problem. the Correlation FXLMS algorithm was developed. The Correlation FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. In this paper, the performance of the Correlation FXLMS Is presented in comparison with that of the other FXLMS algorithms based on computer simulations.