Energy-efficient CMOS RC frequency reference

국문 초록 (Abstract)

이 논문에서는 씨모스 온도 센서와 저항-커패시터 기준 주파수 생성기의 에너지 효율에 대한 분석을 바탕으로, 사물 인터넷 애플리케이션을 위한 온도 정밀도와 에너지 효율이 높은 씨모스 기준 주파수 생성기를 제안합니다.
첫 번째 연구는 저항-커패시터 다위상 필터와 디지털 구조의 FLL 을 활용한 소형 씨모스 온도 센서를 제안합니다. 다위상 필터의 온도에 따른 위상 변화를 ZC detector 를 이용하여 검출하고, 이는 FLL 이 효율적인 면적으로 구현되도록 합니다. 이 온도 센서는 7000 μm2 의 면적만을 사용하고 0.85 V 의 낮은 전압으로부터 동작할 수 있으며 68μW 의 전력을 소모합니다. 그리고 -40 °C 에서 85 °C 의 온도 범위에서 ±0.12 °C (3σ)의 정밀도를 갖고, 2.5 mK 의 온도 해상도를 갖습니다. 이 결과는 0.43 pJ·K2 의 에너지 효율 FoM 에 해당됩니다.
두번째 연구는 무선 센서를 위한 씨모스 저항-커패시터 기준 주파수 생성기를 제안합니다. DCO 가 반대 온도 계수를 갖는 두 다위상필터를 구동하고, 그들의 출력 위상 변화를 디지털 위상 영역의 ΔΣ 모듈레이터로 읽어냅니다. 이 모듈레이터 출력은 디지털 영역에서 보상되고, 이는 DCO 의 주파수를 온도 변화에 독립적으로 만들어줍니다. 이 주파수 생성기는 28 MHz 의 주파수 출력에서 -40 °C 에서 85 °C 의 온도 범위에서±200 ppm 의 정밀도를 달성합니다. 그리고 오직 5 pJ/cycle 의 에너지 효율과 0.06 mm2 의 면적을 가지면서 0.85 V 의 전원 전압으로부터 동작할 수 있습니다.

다국어 초록 (Multilingual Abstract)

In this thesis, based on the analysis of the efficiency of CMOS temperature sensors and RC frequency references, it discusses high-temperature stability, high-efficiency CMOS RC frequency reference for internet of-things (IoT) applications.
The first study proposes a compact resistor-based CMOS temperature sensor based on an RC poly-phase filter (PPF) made from silicided p-poly resistors and metal–insulator–metal (MIM) capacitors and a highly digital frequency-locked loop (FLL). The PPF’s temperature-dependent phase shift is determined by a zero crossing (ZC) detector, allowing the rest of the FLL to be realized in an area-efficient manner. The sensor occupies only 7000 μm2. It can operate from supply voltages as low as 0.85 V and consumes 68 μW, and achieves an inaccuracy of ±0.12 °C (3σ) from −40 °C to 85 °C and a resolution of 2.5 mK in a 1-ms conversion time. This corresponds to a resolution figure-of-merit (FoM) of 0.43 pJ·K2.
The second study proposes a CMOS RC frequency reference for wireless sensor nodes. A digital controlled oscillator (DCO) drives two PPFs with opposite temperature coefficients. Their temperature-dependent phase shifts are read out by the digital phase-domain ΔΣ modulators, whose outputs are compensated in the digital domain to force the DCO’s frequency to be temperature-independent. The reference achieves an inaccuracy of ±200 ppm from -40 °C to 85 °C at 28 MHz. It can operate from 0.85 V supplies with an energy-efficiency of 5 pJ/cycle, while occupying only 0.06 mm2.

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