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안정철,최석우,윤창훈 대한전자공학회 1998 電子工學會論文誌, C Vol.c35 No.5
In this paper, a design of current-mode continuous-time filters for low voltage and low frequency applications using complementary bipolar current mirrors is presented. The proposed current-mode filters consist of simple bipolar current mirrors and capacitors and are quite suitable for monolithic integration. Since the design method of the proposed current-mode filters are based on the integrator type of realization, it can be used for a wide range of applications. Since the input impedance of simple bipolar current mirror is small, in this paper, negative feedback amplifier is used to realize is designed by cascade method. The cutoff frequency of the designed filter can be easily tunable by the DC controlling current from 60kHz to 120kHz. The characteristics of the designed current-mode filters are simulated and examined by SPICE using standard bipolar transistor parameters.
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안정철,최석우,윤창훈 대한전자공학회 1997 電子工學會論文誌, C Vol.c34 No.11
In this paper, a design of current-mode continuous-time filters for low voltage and high frequency applictions using complementary bipolar current mirror paris is presented. The proposed current-mode filters consist of simple bipolar current mirrors and capacitors and are quite suitable for monolithic integrtion. Since the design method of the proposed curent-mode filters is based on the integrator type of realization, it can be used for a wide range of applications. And the cutoff frequency of th efilters can be easily changed by the DC cntrolling current. As design examples, the 5th order butterworth filters are designed by cascade and leapfrog methods with tunable cutoff frequencies from 30MHz to 100MHz. The characteristics of the designed current mode filters are simulated and examined by SPICE using standard bipolar transistor parameters.
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안정철,이은정,홍익표 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.47 No.-
Artificially spheroidized natural graphite (SNG) was processed to obtain expanded graphite and graphenenanoplatelets using GIC (graphite intercalation compound)-assisted exfoliation process. Sulfuric acid andhydrogen peroxide were used as the intercalant and oxidant for the GIC formation, respectively. SNG wassuccessfully converted into both expanded graphite and graphene nanoplatelets. Degree of exfoliation ofthe produced graphene nanoplatelets was found to be proportional to the average diameter of startingmaterials. Graphene nanoplatelets prepared from SNG with average diameter of 50 mm were analyzed tohave the averaged lateral size of 45.4 mm at the thickness of ca. 5 nm.
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안정철,김헤정,홍익표 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.26 No.-
Several-micrometer-wide at a few-nanometer-thick graphene platelets were successfully prepared from Kish graphite by simple GIC (graphite intercalation compound) via exfoliation process. High crystalline Kish graphite flakes were recovered from the steelmaking by-product using the modified beneficiation process. Sulfuric acid was served as the functional intercalating agent in the GIC formation step. XRD results revealed the stable and clear first-stage state formed in the acid-intercalated GIC. Carbon content in the recovered Kish graphite was found to influence the average thickness of prepared graphene nanoplatelets. Larger Kish graphite flakes were also beneficial to produce thin graphene platelets with the average thickness of 5 nm.
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전류 적분기를 이용한 2V CMOS 연속시간 필터 설계
안정철,유영규,최석우,윤창헌,김동용 대한전자공학회 1998 電子工學會論文誌, C Vol.c35 No.9
본 논문에서는 상보형 high swing cascode 전류미러를 이용하여 저전압, 저전력 구동이 가능하고 고주파수 응용이 가능한 전류 적분기를 설계하였다. 간단한 전류미러로 구성된 적분기는 적분기의 비 이상적인 입력, 출력 저항 때문에 출력 전류 오차가 발생하는데 제안된 전류 적분기는 출력 저항이 증가하여 출력 전류의 오차가 감소하였다. 설계된 무손실, 유손실 전류 적분기를 이용한 설계 예로 3차 버터워스 저역통과 필터를 개구리도약형으로 구현하였다. 필터 구현시 무손실 전류 적분기의 위상 추이 때문에 발생하는 차단주파수 부근에서의 크기 특성 왜곡을 predistortion 설계법을 이용하여 감소시켰다. 설계된 전류모드 필터를 0.8㎛ CMOS n-well 공정 파라미터를 이용하여 SPICE 시뮬레이션한 결과 단일 2V 공급 전압에서 차단주파수는 20MHz, 전력소모는 615㎼를 갖는다. 또한 필터의 차단주파수는 DC 바이어스 전류에 의해 동조 할 수 있다. In this paper, the design of a current integrator for low-voltage, low-power, and high frequency applications using complementary high swing cascode current-mirror is presented. The proposed integrator decreases output current errors due to non-zero input resistance and non-infinite output resistance of the simple current integrator. As a design example, the 3rd order Butterworth lowpass filter is designed by a leapfrog method. Also, we apply the predistortion design method to reduce the magnitude distortion which occurs at a cutoff frequency by the undesirable phase shift of a lossless current integrator. The designed current-mode filter is simulated and examined by SPICE using 0.8$\mu\textrm{m}$ CMOS n-well process parameters. The simulation results show 20MHz cutoff frequency and 615㎼ power dissipation with a 2V power supply. And the cutoff frequency of the filters can be easily changed by the DC bias current.
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