生醫應用之解析度可調變ΣΔ類比數位轉換器

Abstract

本論文的研究提出一個可依選擇的模式而改變解析度的三角積分類比數位轉換器，總共分為二種模式可供選擇，此二種模式依不同的輸入訊號而有不同需求的解析度，一為生理電訊號，一為生理影像訊號。則在生理電訊號和生理影像訊號的擷取系統中，透過後端的控制來轉換不同解析度的模式，達到不同通道共用一顆ADC的設計以結省整體系統面積和功耗。ADC的架構選用Sigma-Delta的架構，主要分為二個部分：三角積分模組和後端的降頻數位濾波器。 此ADC電路操作在1.28MHz的操作頻率，訊號取樣頻率為640kHz，對生理電訊號而言，超取樣率為256；對生理影像訊號而言，超取樣率為32。整個ADC電路的輸出為SPI bus標準介面輸出，使此電路可直接和後端的運算電路(DSP)作溝通。且使用低電壓源1.5V的電壓供應，最後結果為在生理電訊號的模式時，SNDR為60dB，ENOB為10-bit；在生理影像訊號模式時，SNR為50dB，ENOB為8-bit。此電路實現使用TSMC 0.18-um 1P6M CMOS製程，整體電路功耗14.2mW，其中Sigma-Delta modulator的功耗為0.98 mW；數位降頻濾波器和其餘數位控制電路功耗為13.3 mW，其晶片大小為3.21mm2。

This paper presents a Sigma-Delta ADC which can change resolutions when the type of the input signal is different. This ADC provides two modes. One is designed for bio-electric signals; the other is designed for bio-image signals. This ADC can change its resolution by the control unit of a multi-channel design for bio-electric and bio-image signal through SPI. It includes two parts: Sigma-Delta modulator and decimation filter. The proposed ADC operates at 1.28 MHz. Sampling rate is 640 kHz. For bio-electric signals, oversampling rate (OSR) is 256; for bio-image signals, OSR is 32. The ADC communicates with DSP or other devices by SPI bus. In the bio-electric signal mode, SNR is 50dB, effective number of bits (ENOB) is 10-bit; in the bio-image signal mode SNR is 50dB, ENOB is 8-bit. It has been fabricated by TSMC 0.18 □m CMOS 1P6M standard process. The total power consumption of the chip is about 14.4 mW under 1.5V supply, and the power consumption of Sigma-Delta modulator is about 0.98 mW; the power consumption of digital part is 13.3 mW. The area of the chip is 3.21 mm2.