應用於生醫感測系統之電壓控制振盪器的連續時間三角積分類比前端電路設計

Design of Voltage-Controlled Oscillator Based Continuous-Time Delta-Sigma Analog Front-End Circuits for Biomedical Applications

王鈺凱(Yu-Kai Wang)

指導教授 ： 林宗賢

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201700283

摘要

及時的生理訊號感測在醫學臨床診斷上具有重要價值。隨著半導體工業的進步，使我們能將龐大的電路系統實現在單一晶片中。本論文著重探討應用於此系統之類比前端電路設計，此電路的主要任務為將振幅極小且低頻的生理信號直接轉換為數位訊號，同時維持訊號的完整度。但由於電路的直流偏移、閃爍雜訊與生醫訊號都落在低頻帶的範圍，因此訊號的品質容易受影響，故在本篇論文中使用截波器解決上述的問題。此外，傳統的類比訊號擷取電路由一個低雜訊放大器和一個類比數位轉換器組成，不論是在功率及面積方面都較沒效率，也增加了電路設計的複雜度。為了解決此問題，本篇採用電壓控制振盪器作為積分器的連續時間三角積分轉換器。
本論文實作並量測了兩個晶片，兩電路皆實作於台積電40奈米製程。第一個晶片實現了一個開路的電壓控制振盪器之類比前端電路，同時利用截波的技巧大幅降低來自電路的閃爍雜訊，核心晶片面積僅0.0145 mm2，為與目前相關文獻相比的最小晶片面積，同時維持50 dB的信號與雜訊比(頻寬為5 kHz)。然而此電路為開路的操作，最大的輸入信號會受到電壓控制振盪器的非線性所限制。在第二個晶片裡，我們延續使用電壓控制振盪器作為積分器及截波的技巧，並利用電容式的數位類比轉換器作回授，降低電壓控制振盪器的輸入振幅，大幅擴大電路的動態範圍到74.9 dB(頻寬為2 kHz)，在品質因素方面達到FoMs = 150 dB及FoMw = 1.16 pJ/conv，皆達到與相關文獻相比下的最好的品質因素。以上兩個晶片皆能符合生醫前端電路的需求，並且在能量效率及晶片面積上皆有很突出的表現。

關鍵字

生醫感測器 ； 電壓控制振盪器 ； 三角積分轉換器

並列摘要

Real-time biomedical signal acquisition is very crucial in modern diagnostics. Thanks to the development of microelectronics, it is possible to integrate the bulky system into a single chip. In this thesis, we will discuss the design of an analog front-end (AFE) which converts the weak analog signal into digital signal for biomedical applications while maintains signal integrity. Since the target signal, offset and flicker noise are all in the low-frequency range, the signal is susceptible to these non-idealities. To solve this problem, we apply chopping technique in this thesis. Additionally, conventional AFE system is composed of a low-noise amplifier and an ADC, which makes it not power/area efficient and also increases the circuit complexity. Our solution to this problem is applying a voltage-controlled oscillator (VCO) -based continuous-time delta-sigma modulator (CTDSM).
Two circuits are implemented and verified, both of them are fabricated in TSMC 40 nm process. The first one realizes a chopped open-loop VCO-based AFE that only takes the area of 0.0145 mm2 which is the smallest chip compared to the relative AFE references while maintains SNR of 50 dB (with the bandwidth of 5 kHz). However, due to the open-loop behavior, the dynamic range is limited by VCO non-linearity. In the second circuit, we apply a VCO-based integrator, chopper, and a capacitive-feedback DAC. With the capacitive-feedback DAC the amplitude of VCO input is decreased and the dynamic range is increased to 74.9 dB (with the bandwidth of 2 kHz). The figure of merits (FoM) FoMs = 150 dB and FoMw = 1.16 pJ/conv are shown respectively. Both of them reach the best FoM compared to the state-of-the-art of relative applications. These chips are not only suitable for biomedical applications but also reach great performances in power efficiency and chip area.

並列關鍵字

bio-potential sensor ； voltage-controlled oscillator ； delta-sigma modulator

參考文獻

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