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재구성가능 연산증폭기를 사용한 저전력 4차 델타-시그마 변조기 설계
성재현(Jae-Hyeon Sung),이동현(Dong-Hyun Lee),윤광섭(Kwang Sub Yoon) 대한전자공학회 2017 전자공학회논문지 Vol.54 No.5
본 논문에서는 생체 신호 처리를 위한 12비트 이상의 고 해상도를 갖는 저 전력 CMOS 4차 델타-시그마 변조기를 설계하였다. 제안하는 4차 델타-시그마 변조기는 시간 분할 기법을 이용하여 회로를 시간에 따라 재구성해 4개의 연산증폭기가 필요한 회로를 1개의 연산증폭기만으로 구동 시켰다. 이를 통하여 일반적인 구조보다 전력소모를 75% 감소시킬 수 있다. 또한 kT/C 잡음과 칩 면적을 고려하여 변조기의 입력단과 출력 단의 커패시터들을 안정적으로 구동하기 위하여 적분기내 가변되는 증폭기를 설계하였다. 첫 번째와 두 번째 클럭 위상에서는 2단 연산 증폭기가 동작하고, 세 번째와 네 번째 위상에서는 1단 연산 증폭기가 동작한다. 이로 인하여 두 가지 위상 조건에서 연산증폭기의 위상여유가 60~90도 이내에 존재하게 하므로서 변조기의 안정성을 크게 향상시켰다. 제안한 변조기는 0.18μm CMOS N-well 1 poly 6 metal 공정을 이용하여 제작되었으며, 1.8V의 공급전압에서 354μW의 전력소모가 측정되었다. 256kHz의 동작주파수, 128배의 오버샘플링 비율 조건에서 250Hz의 입력 신호를 인가하였을 때, 최대 SNDR은 72.8dB, ENOB은 11.8 비트로 측정되었다. 또한 종합 성능 평가지수인 FOM(Walden)은 49.6pJ/step, FOM(Schreier)는 154.5dB로 측정되었다. In this paper, a low power 4th order delta-sigma modulator was designed with a high resolution of 12 bits or more for the biological signal processing. Using time-interleaving technique, 4th order delta-sigma modulator was designed with one operational amplifier. So power consumption can be reduced to 1/4 than a conventional structure. To operate stably in the big difference between the two capacitor for kT/C noise and chip size, the variable-stage amplifier was designed. In the first phase and second phase, the operational amplifier is operating in a 2-stage. In the third and fourth phase, the operational amplifier is operating in a 1-stage. This was significantly improved the stability of the modulator because the phase margin exists within 60~90deg. The proposed delta-sigma modulator is designed in a standard 0.18μm CMOS n-well 1 poly 6 Metal technology and dissipates the power of 354μW with supply voltage of 1.8V. The ENOB of 11.8bit and SNDR of 72.8dB at 250Hz input frequency and 256kHz sampling frequency. From measurement results FOM1 is calculated to 49.6pJ/step and FOM2 is calculated to 154.5dB.
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정모두부방사선사진 촬영시 두부의 수직회전에 따른 투사오차
고은희,이기헌,황현식,성재현 전남대학교 치의학연구소 2002 구강과학 Vol.14 No.4
This study was performed to find out how much projection errors in the cephalometric measurements were made by vertical head rotation in taking posteroanterior cephalograms. 25 adults without any apparent facial asymmetry or severe sagittal skeletal discrepancy were selected and the posteroanterior cephalograms were taken with the head rotated 5˚, 10˚ superior and inferior each to the reference position(0˚), The 7 height. 5 width and 6 angular measurements were taken at each 5 positions. Through the statistical analysis of all measurements taken at each rotated position, following results were obtained. 1. The projection errors of height measurements were remarkably larger than those of width or angular measurements. 2. Among the height measurements, the farther to the rotation axis the measurements were. the larger the projection errors were. 3. Among the width measurements. mandibular width and intermolar width of mandibular first molars showed significant differences between the values taken at each rotated position. while nasal width, maxillary width and intermolar width of maxillary first molars did not. 4. Among the angular measurements. the angle between horizontal reference line and the line that is connected to crista galli and antegonion or maxillare showed significant differences between the values taken at each rotated position. The above results suggest that it is needed to the effort to keep constant head rotation for taking the useful posteroanterior cephalogram, because projection errors are caused by vertical head rotation.
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윤일선,황현식,이기헌,성재현 전남대학교 치의학연구소 2001 구강과학 Vol.13 No.4
The purpose of this study was to classify the facial asymmetry by cluster analysis using the variables of the posteroanterior cephalogram, and to find out the characteristics of each group. The posteroanterior cephalogram and frontal facial photograph of one hundred orthodontic patients were used. Cluster analysis was executed using the measurements which indicated the degree of facial asymmetry. The resultant groups were compared each other according to the measurements to find out the characteristics of each group. Through the statistical analysis, following results were obtained. 1. Facial asymmetry was classified into five groups, A, B, C, D, and E, on the basis of menton deviation, apical base midline discrepancy and vertical difference of distance between right and left antegonions. 2. The degree of Menton deviation was severe in the group A, moderate in the group C and D, and mild in the group B and E. 3. Apical base midline discrepancy showed high value in the group A and C. 4. Antegonion was superiorly positioned on the same side of menton deviation in the group A and D, whereas it was superiorly positioned on the opposite side of menton deviation in the group B. 5. All measurements except the curvature of mandibular inferior border showed high value in the group A whereas very low in the group E. 6. While the characteristics of the group D were similar with those of the group A, the degree of difference was less in the group D. The group B showed unique characteristics as many measurements showed negative value. The above results suggest that facial asymmetry can be simply classified by cluster analysis on the basis of menton deviation, apical base midiine discrepancy and the vertical positional difference of antegonion between right and left sides.
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