링 오실레이터를 이용한 CMOS 온도 감지 센서 설계에 관한 연구 = A study on the design of CMOS temperature sensor using ring oscillators

다국어 초록 (Multilingual Abstract)

Currently, the explosive demand of mobile devices requires a very large number of CMOS on a chip. The degree of integration on a chip increases the heat generated per unit chip area. Device performance is temperature-dependent with higher temperatures accelerating performance degradation. So, mobile devices must need an on-chip temperature sensor to monitor the temperature variation of devices.
In the case of DRAM, the charge amount of the capacitor is discharged and loses the stored information. In order to prevent this, DRAM needs systems for providing a data retention current. Besides, as recent semiconductor process evolves, channel length has been reduced and leakage current has increased significantly. This is required to higher self-refresh frequency of operation. Conventional DRAM determines the frequency of self-refresh on the basis of the worst case at highest operating temperature. This makes the data retention current be wasted at low temperature due to increasing the frequency of self-refresh and it causes an increase of unnecessary power consumption. Therefore, the on-chip temperature sensor is required in order to measure the temperature variation and adjust the proper self-refresh period. Additionally, the high performance temperature sensors are usually required in the following applications.

(1) Low power consumption by adjusting the data retention current period in memory devices.
(2) Temperature monitoring for semiconductor manufacturing systems.
(3) Thermal compensation for flat panel displays.
(4) Controlling temperature in portable consumer electronics products such as mobile phone, personal computer.
(5) Thermal sensing for fire detection systems.

Conventional band-gap temperature sensors, which consist of substrate bipolar transistors and Analog-to-Digital Converter (ADC), have been used widely as on-chip temperature sensors in CMOS VLSI systems. However, it increases the complexity of the circuit design, the poor reliability and the power consumption for stand-by current. Since then, digital CMOS temperature sensors using inverter delay lines have been proposed because they occupy a small area , have a simple design, and provide high resolution. The digital CMOS temperature sensors typically have reference sources, such as reference delay lines or external clocks. The delay differences between an inverter delay line and a reference delay line are compared using a delay sensing scheme. Analog bias circuits are used to maintain the delay of the reference lines, which generate bias currents or voltages regardless of temperature, voltage and process variations. However, the bias circuits have a complex design and consume stand-by currents. In addition, the use of external clocks as the reference source cannot be applied to some applications having various operating frequencies.
In this paper, low cost all digital on-chip temperature sensor using dual ring oscillators is proposed for maintaining the performance benefit of CMOS digital circuit. This novel temperature sensor does not require any bias circuits or reference external clocks. The novel temperature sensor measures the delay variations between the temperature-sensitive ring oscillator and the temperature-insensitive ring oscillator according to temperature. The sensitivity of the delay variations is adjusted according to only CMOS channel length. The difference between two clocks can be amplified using counters. Each counter doubles the signal period and using 5 counters for each ring-oscillators lead to 32 times multiplication. Finally, it is possible to sense the temperature variation by using TDC(Time to Digital Converter). The circuit was designed by the 0.11μm 1P6M process, and its effective resolution was 1.43℃ from 0℃ to 100℃ and the chip area was only 0.035mm^2

목차 (Table of Contents)

• 1. 서 론 1
• 1.1 온도 감지 센서
• 1.2 온도 감지 센서의 기술 동향 및 기존 기술의 문제점
• 2. 온도 감지 센서의 이론적 고찰 및 검증
• 2.1 캐리어 이동도의 산란 현상 및 온도 의존성
• 2.2 게이트 채널 길이에 따른 이동도 산란의 온도 의존성 변화
• 2.3 CMOS 동적 특성 및 수식적 해석
• 2.4 게이트 채널 길이에 따른 CMOS 동적 특성의 온도 의존성 변화
• 2.5 시뮬레이션에 의한 이론 검증
• 3. 링 오실레이터를 이용한 온도 감지 센서 제안 및 설계
• 3.1 온도 감지 메커니즘 제안
• 3.2 온도에 의존하는 클록 발생기 제안
• 3.3 온도에 의존하는 클록 감지 회로 제안
• 3.4 온도 감지 센서 설계
• 4. 제안한 온도 감지 센서 특성 측정 및 고찰
• 4.1 제안한 온도 감지 센서의 시뮬레이션 결과 및 고찰
• 4.1.1 클록 발생기의 시뮬레이션 결과 및 고찰
• 4.1.2 클록 감지 회로의 시뮬레이션 결과 및 고찰
• 4.1.3 제안한 온도 감지 센서의 시뮬레이션 결과 및 평가
• 4.2 제안한 온도 감지 센서의 특성 측정 및 고찰
• 4.2.1 클록 발생기의 설계 측정 결과 및 고찰
• 4.2.2 제안한 온도 감지 센서의 실제 측정 결과 및 고찰
• 5. 결 론