14 비트 분해능을 갖는 2차 Sigma-Delta 변조기 설계를 위한 구성요소의 최대에러 허용 범위 조사

조병욱,최평,손병기,Cho, Byung-Woog,Choi, Pyung,Sohn, Byung-Ki 한국통신학회 1998 韓國通信學會論文誌 Vol.23 No.5

저주파의 아날로그 신호를 디지털 신호로 변환하기 위해 sigma-delta 아날로그-디지털 변환기의 이용이 용이하다. 이 변환기는 변조기와 디지털 필터로 구성되는데 여기에서는 변조기에 대해 언급한다. 14비트 분해능을 갖는 2차 sigma-delta 변조기를 설계하기 위한 변조기의 구성요소 즉 연산 증폭기, 적분기, 내부 ADC 및 DAC의 최대 허용 에러 범위를 규정하였다. 이를 위하여 먼저 이상적인 변조기를 모델링하고 다음으로 변조기의 성능을 저하시키는 여러 가지 에러 요인 즉 연산증폭기의 최대 출력 제한, DC 이득, slew rate, 축전기의 불일치에 의한 적분기 이득 에러와 내부 ADC 및 DAC의 에러 등을 이상적인 모델에 적용하여 성능을 검증하였다. 이러한 에러 허용 범위에 대한 조사를 바탕으로 sigma-delta 변조기 설계 시 요구되는 구성 요소의 사양을 결정 할 수 있으며, 제조과정에서 나타나는 에러 성분에 대한 한계를 규정하여 최종 제작될 변조기의 성능을 확신 할 수 있다. Sigma-delta converter is frequently used for conyerting low-frequency anglog to digital signal. The converter consists of a modulator and a digital filer, but our work is concentrated on the modulator. In this works, to design second-order sigma-dalta modulator with 14bit resolution, we define maximumerror limits of each components (operational smplifier, integrator, internal ADC, and DAC) of modulator. It is first performed modeling of an ideal second-order sigma-delta modulator. This is then modified by adding the non-ideal factors such as limit of op-amp output swing, the finit DC gain of op-amp slew rate, the integrator gian error by the capacitor mismatch, the ADC error by the cmparator offset and the mismatch of resistor string, and the non-linear of DAC. From this modeling, as it is determined the specification of each devices requeired in design and the fabrication error limits, we can see the final performance of modulator.

14 비트 분해능을 갖는 2차 Sigma-Delta 변조기 설계 및 검증

조병욱,최평,손병기,Cho, Byung-Woog,Choi, Pyung,Sohn, Byung-Ki 대한전자공학회 1999 電子工學會論文誌, S Vol.s36 No.5

저주파의 아날로그 신호를 디지털 신호로 변환하기 위해 sigma-delta 아날로그-디지털 변환기의 이용이 용이하다. 이 변환기는 변조기와 디지털 필터로 구성되는데 본 논문에서는 변조기에 대해서만 언급한다. 모델링을 통해 14비트 분해능을 갖는 2차 sigma-delta 변조기를 설계하기 위한 변조기의 구성요소 즉 연산 증폭기, 적분기, 내부 ADC 및 DAC의 최대 허용 에러 범위를 규정하였으며, 이를 토대로 연산증폭기, 2비트 ADC 및 DAC 등을 설계·검증하고, 이들을 서로 연결하여 2차 sigma-delta 변조기를 구성하였다. 3비트 ADC의 기준전압을 조절하여 변조기 성능 향상을 도모하였으며, 내부 DAC를 축전기 및 간단한 제어회로로 구성하여 비선형성 에러를 최소화하였다. 설계된 각각의 구성요소들은 모델링에서 정의된 에러 범위를 모두 만족하였으며, 전체 변조기는87㏈의 입력범위와 87㏈의 최대 신호 대 잡음 비를 가졌다.

압전박막을 이용한 감압전장효과 트랜지스터 ( PSFET ) 의 동작특성

남기홍 ( Ki Hong Nam ),손병기 ( Byung Ki Sohn ),조병욱 ( Byung Woog Cho ),양규석 ( Gyu Suk Yang ),군대혁 ( Dae hyuk Kwon ) 한국센서학회 1995 센서학회지 Vol.4 No.2

A new FET type semiconductor pressure sensor (FSFET : pressure sensitive field effect transistors was fabricated and its operational characteristics were investigated. A ZnO thin film as a piezoelectric layer, 5000Å thick, was deposited on a gate oxide of FET by RF magnetron sputtering. he deposition conditions to obtain a axis poling structure were substrate temperature of power of 140watt, and working pressure of 5mtorr in Ar ambience. The fabricated PSFET den-ice showed good linearity and stability in the applied pressure range(1x10^5 Pa∼4x10^5 Pa)

백금전극과 감광성 고분자를 이용한 ISFET 포도당 및 자당센서의 감지성능 개선

조병욱,장원덕,김창수,박이순,손병기 ( Byuhng Woog Cho,Won Duk Jang,Chang Soo Kom,Lee Soon Park,byung Ki Sohn ) 한국센서학회 1995 센서학회지 Vol.4 No.4

The ISFET glucose and sucrose sensors containing platinum electrode and photopolymeric enzyme membrane were fabricated. The platinum working electrode was used for the electrolysis of hydrogen peroxide, which was the other product of the enzyme reaction, to improve sensing characteristics of the sensors. In order to improve response time, photo-crosslinkable polymer(PVA-SbQ) was used to the matrix for the enzyme immobilized membrane. The characteristics of glucose and sucrose sensors were investigated according to the variation of platinum electrode area. The response time was about 3∼5 minutes and determinations of glucose and sucrose in the range of about 30∼300mg/dl could be possible.

사진식각기술을 이용한 FET 형 반도체 요소 및 포도당센서의 제조와 그 특성

조병욱,김창수,서화일,손병기 ( Byung Woog Cho,Chang Soo Kim,Hwa Il Seo,Byung Ki Sohn ) 한국센서학회 1992 센서학회지 Vol.1 No.1

pH-ISFETs, the semiconductor pH sensors, were combined with immobilized enzyme membranes to prepare FET type urea and glucose sensors and its operational characteristics were investigated. Photolithography techniques wore applied to immobilize enzymes on the H^+ sensing membrane of the pH-ISFET with photo-sensitive polymers, PVA-SbQ. Fabricated urea and glucose sensors could determine 0.5∼50 mg/dl urea concentrations and 10∼1000 mg/dl glitdbse concentrations, respectively.

다채널 ISFET 측정용 단일 바이어스 회로의 설계

조병욱,김영진,김창수,최평,손병기 ( Byung Woog Cho,Young Jin Kim,Chang Soo Kim,Pyung Choi,Byung Ki Sohn ) 한국센서학회 1998 센서학회지 Vol.7 No.1

Multi-channel sensors can be used to increase the reliability and remove the random noise in ion-sensitive field effect transistors(ISFETs). Multi-channel sensors is also an essential step toward potential fabrication of sensors for several ionic species in one device. However, when the multi-channel sensors are separately biased, the biasing problems become difficult, that is to say, the bias circuit is needed as many sensors. In this work, a circuit for biasing the four pH-ISFETs in null-balance method, where bias voltages are switched, was proposed. The proposed concept is need only one bias circuit for the four sensors. Therefore it has advantages of smaller size and lower power consumption than the case that all sensors are separately biased at a time. The proposed circuit was tested with discrete devices and its performance was investigated. In the recent trend, sensor systems are implemented as portable systems. So the verified measurement circuit was integrated by using the CMOS circuit. Fortunately, ISFET fabrication process can be compatible with CMOS process. Full circuit has a mask area of 660㎛ x 500㎛. In the future, this step will be used for developing the smart sensor system with ISFET.

사진식각기술을 이용한 FET형 반도체 요소 및 포도당센서의 제조와 그 특성

조병욱,김창수,서화일,손병기,Cho, Byung-Woog,Kim, Chang-Soo,Seo, Hwa-Il,Sohn, Byung-Ki 한국센서학회 1992 센서학회지 Vol.29 No.3

pH-ISFETs, the semiconductor pH sensors, were combined with immobilized enzyme membranes to prepare FET type urea and glucose sensors and its operational characteristics were investigated. Photolithography techniques were applied to immobilize enzymes on the $H^{+}$ sensing membrane of the pH-ISFET with photo-sensitive polymers, PVA-SbQ. Fabricated urea and glucose sensors could determine $0.5{\sim}50{\;}mg/dl$ urea concentrations and $10{\sim}1000{\;}mg/dl$ glucose concentrations, respectively. 반도체 pH 센서인 pH-ISFET와 효소 고정화막을 기술적으로 결합한 FET형 반도체 요소 및 포도당센서를 제조하고 그 동작특성을 조사하였다. 사진식각기술을 이용하여 pH-ISFET의 수소이온 감지막 위에 urease와 glucose oxidase를 감광성 고분자 물질인 PVA(polyvinyl alcohol)-SbQ(stilbazolium group)로 고정화(immobilization)시켰다. 제조된 요소센서와 포도당센서는 각각 $0.5{\sim}50{\;}mg/dl$ 범위의 요소농도와 $10{\sim}1000{\;}mg/dl$의 포도당 농도를 정량 할 수 있었다.

Sol - Gel 법으로 형성한 Ta2O5 게이트 ISFET 의 pH 드리프트 특성

권대혁,조병욱,김창수,손병기 ( Dae Hyuk Kwon,Byung Woog Cho,Chang Soo Kim,Byung Ki Sohn ) 한국센서학회 1996 센서학회지 Vol.5 No.2

The diffusion of hydrogen ions into a sensing membrane causes the output voltage of pH-ISFEI to van- with time, which might be considered to be drift in this sensor. We tried to deposit ultra-thin film for minimizing the drift that has been considered to be main obstacle for putting pH-ISFET to practical use. In this paper, tantalum pentoxide, known as a good pH sensing membrane, was formed to about 70Å thick by sol-gel method on Si₂N₄/SiO₂-gate of pH-ISFET. The fabricated Ta₂O_5-gate pH-ISFET showed good sensitivity(about 59mV/ pH) and good lineality in the range of pH 3-11, and had relatively small average pH drift of about 0.06 pH/day.

노즐의 원리를 도입한 ISFET 소형 카트리지 제작

이영철,손병기,조병욱,김영진,김현수 한국센서학회 1999 센서학회지 Vol.8 No.4

A small cartridge, with a nozzle system for washing off the dirt from the surfaces of sensing gates, was fabricated. The proposed nozzle structure was designed for cartridge by using the simulation tool of fluid (CFD-ACE). Whole size of the fabricated cartridge by using micromachining techniques is about 2.6 cm X 1.5 cm, the size of the washing nozzle is 0.2 mm X 0.6 mm and its dead volume is only about 20 ㎕. A micro-reference electrode was achieved by employing a differential system with ISFETs/QRE (quasi-reference electrode)/REFET (reference field-effect transistor). Metal electrodes was deposited at both ends of blowing channel were used to check the presence of bubble in the microchannel. The pH-ISFET was inserted into the fabricated cartridge and the washing effect of the nozzle system in cartridge was invested.

FET 센서 어레이를 이용한 이온 측정 시스템의 신뢰도 개선

김영진,이영철,손병기,조병욱,최정태,이승협 한국센서학회 1999 센서학회지 Vol.8 No.4

In general cases, compared with glass electrode, FET type electrolyte sensors have many advantages. But the drift, memory effect and the poor reproducibility of the FET type electrolyte sensor cause the decrease of the reliability in the measurement system. To improve the reliability, an ion-measuring system using FET type electrolyte sensor array with 8 sensors has been developed. Developed system employed the electronic switchs to connect a signal detecting circuit with 8 sensor array and the system can measure ion concentration of 4 different type electrolyte(H^+, Na^+, K^+, Ca^(2+)). The signal processing algorithm with insertion sorting method was adopted to enhance the reliability. We measured 3 different ion(H^+, Na^+, K^+) to evaluate the performance of developed system. The results show that the designed signal processing algorithm can reduce the error range in comparison with a simple arithmetic mean and the developed system has a good reliability over the previous single channel sensor system.