• 대한전자공학회논문지
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• 제27권5호
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• pp.656-665
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• 1990

In this paper, some new results on minimum-bandwidth system are presented. First, we state sufficient condition for the existance of a existance of a power spectral null at the zero frequency and Nyquist frequency. Second, eye boundary functions and eyewidth are obtained for minimum-bandwidth systems of arbitrary numbers of transmitted symbol levels. Third, for linear minimum-bandwidth systems usually known as PR systems, we derived formulars for evaluating DSVs and ASVs in terms of the coefficients of the system polynomials and using formulars, we obtain DSVs and ASVs of various PR systems. Last, the relations among DSV, ASV, power spectral nulls, system polynomial nulls, and the minimum-bandwidth property are summarized.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.197-206
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• 2003

It is intended to retrieve the time history of displacement from measured acceleration signal. In this study, the word retrieving means reconstructing the time history of original displacement signal from already measured acceleration signal not just extracting various information using relevant signal processing techniques. Unlike extracting required information from the signal, there are not many options to apply to retrieve the time history of displacement signal, once the acceleration signal is measured and recorded with given sampling rate. There are two methods, in general, to convert measured acceleration signal into displacement signal. One is directly integrating the acceleration signal in time domain. The other is dividing the Fourier transformed acceleration signal by the scale factor of - $\omega$$^2$and taking the inverse Fourier transform of it. It turned out both the methods produced a significant amount of errors depending on the sampling resolution in time and frequency domain when digitizing the acceleration signals. A simple and effective way to convert the time history of acceleration signal into the time history of displacement signal without significant errors is studied here with the analysis on the errors involved in the conversion process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 하계학술대회 논문집
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• pp.529-531
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• 1990

Because Filters do both the sampling or Sampled-and-Hold(S/H) operations, it result in the replication of the spectrum of input signal and (unless Nyquist's criterion is satisfied) induce aliasing distortion. In this paper, therefore, we designed AAF(Analog Anti-aliasing Filers) so as to remove high-frequency components from input signal for aliasing distortion prevention before input signal had been processed frequency seletion by filters. and then, researched characteristics of it.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3349-3354
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• 2012

Understanding exoelectrogenic reactions of the bioanode is limited due to its complexity and the absence of analytics. Impedance and thermodynamics of bioanode, abiotic anode, and riboflavin-amended anode were evaluated. Activation overpotential of the bioanode was negligible compared with that of the abiotic anode. Impedance spectroscopy shows that the bioanode had much lower charge transfer resistance and higher capacitance than the abiotic anode in low frequency reaction. In high frequency reaction, the impedance parameters, however, were relatively similar between the bioanode and the abiotic anode. At open-circuit impedance spectroscopy, a high frequency arc was not detected in the abiotic anode in Nyquist plot. Addition of riboflavin induced a phase angle shift and created curvature in high-frequency arc of the abiotic anode, and it also drastically changed impedance spectra of the bioanode.

• Journal of Power Electronics
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• 제18권5호
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• pp.1555-1566
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• 2018

Proportional capacitor-current-feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor-current-feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency ($f_s/6$). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor-inductor-capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system's robustness against grid impedance variation are demonstrated.

• JSTS:Journal of Semiconductor Technology and Science
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• 제17권3호
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• pp.378-386
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• 2017

A return-to-zero (RZ) digital-to-analog converter (DAC) with a tri-state switching scheme is proposed in this paper. The proposed scheme provides a triple weight output for RZ operation by using a conventional differential current switch and simple pseudo-differential F/Fs. The RZ function is realized with only two additional transistors in each F/F cell, which results in a power dissipation increase of less than 5%. To verify the performance of the proposed method, a 10-bit RZ DAC is fabricated using standard 180-nm CMOS technology. Measured results show that the worst SFDR performances are 60 dBc and 55 dBc in the 1st and 2nd Nyquist bands, respectively, when operating at 650 MHz clock frequency. The total power consumption is 64 mW, and the active area occupies $0.25mm^2$.

• 대한전자공학회논문지SD
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• 제42권6호
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• pp.1-8
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• 2005

본 논문에서는, 1.8V 6bit 2GSPS Nyquist CMOS A/D 변환기를 제안한다. 6bit의 해상도와 초고속의 샘플링과 입력 주파수를 만족시키면서 저 전력을 구현하기 위하여 Interpolation Flash type으로 설계되었다. 같은 해상도의 Flash A/D 변환기에 비해 프리앰프의 수가 반으로 줄기 때문에 작은 입력 커패시턴스를 가지며 면적과 전력소모 작게 할 수 있다. 또한 본 연구에서는 고속 동작의 문제점들을 해결하기 위하여 새로운 구조의 One-zero Detecting Encoder, Reference Fluctuation을 보정하기 위한 회로, 비교기 자체의 Offset과 Feedthrough에 의한 오차를 최소화하기 위하여 Averaging Resistor와 SNDR을 향상시키기 위한 Track & Hold, 제안하는 Buffered Reference를 설계하여 최종적으로 2GSPS Nyquist 입력의 A/D converter 출력 결과를 얻을 수가 있었다. 본 연구에서는 1.8V의 공급전압을 가지는 0.18$\mu$m 1-poly 3-metal N-well CMOS 공정을 사용하였고, 소비전력은 145mW로 Full Flash 변환기에 비해 낮음을 확인 할 수 있었다. 실제 제작된 칩은 측정결과 2GSPS에서 SNDR은 약 36.25dB로 측정되었고, Static 상태에서 INL과 DNL은 각각 $\pm$0.5LSB 로 나타났다. 유효 칩 면적은 977um $\times$ 1040um의 면적을 갖는다.

• 한국음향학회지
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• 제23권1호
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• pp.54-60
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• 2004

44.1 kHz 샘플링 비율의 표준 CD음질의 오디오 신호를 인터넷 상에서 전송 및 분배하기 위해서 네트워크 대역폭과 저장 공간의 제한점을 고려해야 한다. 이러한 제한은 오디오 신호의 샘플링 비율을 낮추거나 MP3와 같은 오디오 데이터 압축 기법을 이용하여 해결할 수 있지만, 공통적으로 고 주파수 (High frequency) 대역의 정보가 손실 된다는 문제가 발생한다. 이러한 고 주파수 손실은 결국 저 샘플링 비율의 오디오 신호를 생성하게 되며 표준 CD음질을 가지는 오디오 신호보다 제한된 저 주파수 대역만을 재생할 수 있게 된다. 일반적으로 오디오 신호의 고주파 성분은 위치정보와 명료도, 재생 환경 등에 대한 음의 풍부한 정보를 제공한다. 본 논문의 목적은 LMS 적응 필터링과 DWT 분석/합성을 이용하여 저 샘플링 비율을 가지는 오디오 신호로부터 고 주파수 대역의 정보를 효과적으로 추정하는 것이다. 제안된 알고리즘은 DWT 영역에서 LMS 적응 알고리즘을 이용하여 고 주파수 정보를 추정하고 DWT 합성을 이용하여 고 주파수 정보가 강화된 고음질의 오디오 신호를 재생한다. 제안된 알고리즘의 성능 평가를 위해 실제 음성신호와 음악 신호를 이용하여 컴퓨터 모의 실험과 청취 평가를 수행하여 기존 알고리즘과 비교하였으며, 실험 결과 제안된 알고리즘의 우수성을 확인하였다.

• 한국해양공학회지
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• 제24권1호
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• pp.166-171
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• 2010

In this paper, the front-end of a digital receiver with a 25 kHz carrier frequency, 5 kHz symbol rate, and any excess-bandwidth is designed using two basic facts. The first is known as the uniform sampling theorem, which states that the sampled sequence might not suffer from aliasing even if its sampling rate is lower than the Nyquist sampling rate if the analog signal is a bandpass one. The other fact is that if the sampling rate is 4 times the center frequency of the sampled sequence, the front-end processing complexity can be dramatically reduced due to the half of the sampled sequence to be multiplied by zero in the demixing process. Furthermore, the designed front-end is simplified by introducing sub-filters and sub-sampling sequences. The designed front-end is composed of an A/D converter, which takes samples of a bandpass filtered signal at a 20 kHz rate; a serial-to-parallel converter, which converts a sampled bandpass sequence to 4 parallel sub-sample sequences; 4 sub-filter blocks, which act as a frequency shifter and lowpass filter for a complex sequence; 4 synchronized switches; and 2 adders. The designed front-end dramatically reduces the computational complexity by more than 50% for frequency shifting and lowpass filtering operations since a conventional front-end requires a frequency shifting and two lowpass filtering operations to get one lowpass complex sample, while the proposed front-end requires only four filtering operation to get four lowpass complex samples, which is equivalent to one filtering operation for one sample.

• Corrosion Science and Technology
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• 제6권5호
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• pp.227-232
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• 2007

The corrosion behavior of carbon steel (N80) in carbon dioxide saturated 1%NaCl solution with and without acetic acid or acetate was investigated by weight-loss test, electrochemical methods (polarization curve, Electrochemical impedance spectroscopy). The major objective is to make clear that the effect of acetic acid and acetate on the corrosion of carbon steel in $Co_2$ environments. The results indicate that either acetic acid or acetate accelerates cathodic reducing reaction, facilitates dissolution of corrosion products on carbon steel, and so promotes the corrosion rate of carbon steel in carbon dioxide saturated NaCl solution. All Nyquist Plots are consisting of a capacitive loop in high frequency region, an inductive loop in medial frequency region and a capacitive arc in low frequency region. The high frequency capacitive loop, medial frequency inductive loop and low frequency capacitive arc are corresponding to the electron transfer reaction, the formation/adsorption of intermediates and dissolution of corrosion products respectively. All arc of the measured impedance reduced with the increase of the concentration of Ac-, especially HAc. However, the same phenomenon is not notable after reducing pH value by adding HCl. HAc is a stronger proton donor and can be reduced directly by electrochemical reaction firstly. Ac- can't participate in electrochemistry reaction directly, but $Ac^-$ an hydrate easily to create HAc in carbon dioxide saturated environments. HAc is as catalyst in $Co_2$ corrosion. As a result, the corrosion rate was accelerated in the presence of acetate ion even pH value of solution increased.