A low noise, sub-1ppm/oC piecewise second-order curvature compensated bandgap reference for high resolution ADC

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 김수환.본 논문에서는 고해상도 analog to digital converter를 위한 저 잡음, 고 정밀 bandgap voltage reference를 제안한다. reference 회로의 성능 중 가장 중요한 것들은 바로 낮은 온도 계수(temperature coefficient)와 저주파 대역의 전기적 잡음이다. 제안된 Bandgap reference 회로는 위 두가지 요소를 개선 하였다. 먼저 낮은 온도 계수를 성취하기 위해서는 BJT Emitter-Base전압의 비선형적 온도의존성을 보상해주어야 하고, bandgap core을 이루는 Error amplifier의 DC offset을 제거해야 하며, 마지막으로 process variation에의한 추가적인 온도 의존성을 상쇄시켜야 한다. 제안된 bandgap reference는 여러가지 회로 기술들을 활용해 위 요소들을 보상하였다. BJT Emitter-Base전압의 비선형적 온도 의존성을 온도에 대해 2차 의존성을 갖는 compensation 전류를 생성하고 bandgap core에 흘려주어 제거하였다. Compensation 전류는 크게 current subtraction 동작과 current squaring 동작을 통해 생성되는데, 위 동작은 모두 process variation에 둔감하다. 두 번 째로 process variation에 의한 온도 특성의 변화를 보상해 주기 위해 trimming resistor를 사용하였다. 마지막으로 error amplifier에 chopping을 적용하여 Error amplifier DC offset을 약화시켰다. Bandgap reference의 저 주파수 전기적 잡음의 근원은 대부분 Error amplifier이므로 chopping 동작을 통해 저주파대역의 전기적 잡음 또한 제거된다. Chopping 동작을 통해 생겨난 리플 과, 고주파 대역으로 변조된 저주파 대역의 전기적 잡음은 RC filter를 통해 제거하였다. 제안된 bandgap reference는 스탠다드 0.13um CMOS 공정의 3.3V 전원 소자로 설계하였으며 레이아웃 사이즈는 0.0534mm2이다. Post layout simulation 결과 제안된 bandgap reference의 -40°C부터 125°C 사이의 온도 계수는 약 0.64ppm/°C이다. 0.1Hz부터 10Hz사이의 integrated noise는 약 2.7uVrms이다. 제안된 bandgap reference는 상온에서 약 44uA의 전류를 소모한다.In this thesis a low noise and high precision bandgap reference is presented. One of the most important characteristics of reference circuit for analog to digital converter with high resolution is low temperature drift and low noise. The proposed bandgap reference improves these two characteristics. To achieve low temperature coefficient(TC), non-linear temperature dependence of emitter-base voltage of bipolar transistor should be compensated. Also, degradation of TC due to dc offset of the error amplifier and process variation is another concern. The proposed bandgap reference compensates these factors by utilizing various circuit technique. Because non-linear temperature dependence of bipolar transistor has a concave shape with temperature, second order curvature compensation current is generated by using current subtraction circuit and current squaring circuit and injected into bandgap core. The current subtraction and squaring operation is tolerant to process variation. To achieve low temperature coefficient regardless of process variation, PTAT trimming is utilized to compensate added linear temperature dependence. At last, to remove dc offset of the error amplifier, chopping technique is applied to the error amplifier. Ripple and up-modulated low frequency caused by chopping operation is removed through RC-filter. The proposed bandgap reference is designed in 0.13um standard CMOS process. Layout size of the bandgap reference is 0.0534mm2. Post layout simulation shows that TC of the bandgap reference from -40°C to 125 °C is 0.64ppm/°C. In addition, integrated noise from 0.1Hz to 10Hz is about 2.7uVrms. The proposed bandgap reference consumes 44uA at room temperature제 1 장 서론 1 제 1 절 연구의 배경 1 제 2 절 기본적인 bandgap reference의 동작 원리. 4 1. bipolar 트랜지스터의 온도 특성 4 2. 기본적인 bandgap voltage reference의 동작 원리 7 3. 기본적인 bandgap current reference의 동작 원리 9 제 2 장 기본적인 bandgap reference의 성능적 한계 12 제 1 절 비선형적 온도 의존성 12 1. error amplifier dc offset 14 2. emitter-base 전압의 비선형적 온도 의존성 16 3. bipolar 트랜지스터 전류 이득에 의한 비선형적 온도 의존성 17 4. bipolar 트랜지스터의 베이스 저항에 의한 비선형적 온도 의존성 19 제 2 절 Bandgap reference의 전기적 잡음. 20 제 3 장 제안하는 저 잡음 고 정밀 bandgap voltage reference 22 제 1절 제안된 bandgap reference의 전체 구조 22 1. PTAT전류 생성 회로 23 2. reference 전류 생성 회로 24 3. bandgap core 25 제 2절 Curvature compensation technique 25 제 3절 Noise reduction technique 30 제 4절 Resistor trimming 32 제 5절 주요 성분 파라 미터 테이블 33 제 4 장 Layout 및 모의 실험 결과 34 제 1 절 Layout 34 제 2 절 모의 실험 결과 35 제 5 장 결론 40 제 6 장 부록 current squaring 회로의 동작 원리. 41 참고문헌 43 Abstract 43Maste

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