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Adaptive Carrier Recovery with Multi-Loop DPLL for Mobile Communication Applications
김범섭 대한전자공학회 1995 CAD 및 VLSI 설계연구회지 Vol.4 No.1
A salient adaptive carrier recovery with a multi-order Digital Phase-Locked Loop (DPLL) based on Kalman filtering is presented in this paper. Using optimal loop gain sequence, that is Kalman gain sequence, for various optimization criteria, the proposed DPLL achieves fast phase acquisition and low phase fitter. Especially, the loop gain sequence optimized under the Least Squares (LS) criterion shows enough phase tracking capability under severe fading and can be used for mobile communication applications. Finally, the multi-order DPLL allows robust stability and bandwidth control and achieves zero phase offset.
고분자 열분해 방법으로 제조된 TiN-Ti<sub>5</sub>Si<sub>3</sub> 세라믹 복합체의 고온 산화 거동
김범섭,김득중,이동복,Kim, Beom-Seob,Kim, Deug-Joong,Lee, Dong-Bok 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.8
A new $TiN-Ti_5Si_3$ bulk composite was synthesized from preceramic, inorganic polymer (methylpolysilsesquioxane) and $TiH_2$ filler powders via polymer pyrolysis. Using this process, ceramics with high melting points can be produced relatively easily to a near net shape. The $TiN-Ti_5Si_3$ composite oxidized slowly during heating to $1000^{\circ}C$. During heating at the temperatures of at 700 and $800^{\circ}C$, TiN oxidized to Rutile-$TiO_2$ whereas $Ti_5Si_3$ resisted to oxidation. The oxide scale formed consisted primarily of $TiO_2$ containing $Ti_5Si_3$.
고분자 열분해에 의한 $MoSi_2$/SiC 세라믹 복합체
김범섭,김득중,김동표 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.8
The formation, microstructure and properties of MoSi2/SiC ceramic composites by polymer pyrolysis were investigated for the application of heating element material. Polymethylsiloxanes were mixed with Si, SiC, MoSi2 as filler and ceramic composites prepared by pyrolysis in N2 atmosphere at 1320~145$0^{\circ}C$ were studied. Dimensional change, density variation and phases were analyzed and correlated to the resulting material properties. Microstructures of ceramic composite prepared by polymer pyrolysis were composed of MoSi2, SiC and silicon oxycarbide glass matrix. Depending on the pyrolysis conditions, ceramic composites with a density of 86~90 TD%, a fracture strength of 213~284 MPa, a thermal expansion coefficient of 4~7$\times$10-6 were obtained. The electrical resistivity of the specimen decreased with increasing of temperature up to 50$0^{\circ}C$.
CDMA 무선 휴대폰 시스템을 위한 3.0V CMOS 연속 시간 저 대역 필터의 설계
김범섭,박찬홍 에스케이텔레콤 (주) 1996 Telecommunications Review Vol.6 No.1
0.8μm 의 CMOS 공정을 이용하여 6차의 Elliptic 저 대역 통과 필터를 설계하였다. 이 필터의 주파수 특성은 CDMA 방식의 무선 휴대폰에 사용되는 아날로그 프로세서에 장착할 수 있도록 사양에 맞추어 설계되었으며 SFG(signal flow graph) 방식으로 필터를 합성하여 소자 값에 대한 필터 특성의 민감도를 최소화 하였다. 또한 외부 조건 등에 의한 필터 특성 변화를 막기 위해 직접 샘플 방식을 이용한 자동 튜닝 회로를 첨가하여 안정된 외부 클럭에 의해 필터 특성이 조절될 수있도록 하였다. 이 필터는 시뮬레이션 결과 0.5dB 의 pass band ripple 과 50dB의 stop band attenuation을 가지며 약9mW의 전력소모를 나타냈다.
Formation of High-Density TiN/Ti5Si3 Ceramic Composites Using Preceramic Polymer
김범섭,홍성진,김득중 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.4
The formation, microstructure and properties of high-density TiN/Ti5Si3 ceramic composites created by the pyrolysis of preceramic polymer with filler were investigated. Methylpolysiloxane was mixed with TiH2 as filler and ceramic composites prepared by pyrolysis at 1200 °C to 1600 °C under N2, Ar and vacuum were studied. When a specimen with 70 vol.% TiH2 was pyrolyzed up to 1600 °C in a vacuum after a preheat treatment at 850 °C in a N2 atmosphere and subsequently heat-treated at 1600 °C for 1 h under Ar at a pressure of 2 MPa, a ceramic composite with full density was obtained. The microstructure of the ceramic composite was composed of TiN and Ti5Si3 phases. Under specific pyrolysis conditions, a ceramic composite with a density of 99.2 TD%, a Vickers hardness of 18 GPa, a fracture toughness of 3.5 MPam1/2, a flexural strength of 270 MPa and a electrical conductivity of 6200 ohm−1·cm−1 was obtained.