運用在人工耳蝸的雙向雙極性電壓刺激器設計

Abstract

近年來，由於生醫科學與半導體的快速發展，許多植入到人體內的生醫相關的系統單晶片被提出。其中人工耳蝸也是一種植入式生醫相關的系統單晶片，它是用來幫助耳聾的人恢復失去的聽力。而在我們的人工耳蝸計畫中負責生醫相關研究的團隊研發出了一種新型的電極，這種電極必須要使用定電壓的刺激方法才能夠幫助耳聾的人恢復聽覺，所以根據這樣的需求，一個能夠輸出定電壓的刺激器設計被提出。 根據人工耳蝸計畫中的生醫團隊的研究，此電刺激器必須要能夠輸出雙極性的刺激電壓，並且此刺激電壓的大小與刺激時間都必須要能夠根據需求來做調整。發展已久的互補式金屬氧化物半導體製程非常適合用來實現植入式生醫元件，所以我們的植入式耳蝸會實現在0.18微米的互補式金屬氧化物半導體製程，此製程提供了一點八伏特與三點三伏特的元件。但刺激器的最高輸出電壓會高達七伏特，為了避免遭遇到閘極可靠度與電性過壓的問題，在這裡採用了堆疊電晶體與動態偏壓的技巧來避免上述的問題。根據本人工耳蝸計畫中的生醫團隊的研究，為了要使耳聾的病人有足夠的語音理解度，刺激器要能夠同時在耳蝸上刺激四個不同的位置，所以我們的刺激器有四通道的輸出。 植入式人工耳蝸只能透過外部無線傳輸電力到內部，而外部無線傳輸給內部的電壓為一點八伏特。而刺激器的最高輸出電壓為七伏特，所以此刺激器還包含了一個高電壓產生器，它可以將一點八伏特的電壓轉成八點四伏特的電壓給刺激器作使用。

Nowadays, due to the rapidly development of biomedical science and electronics, many System-on-Chips for biomedical application had been proposed to implant into human body. Cochlear implant is also one kind of medical application for the profound deafness. New type electrodes for cochlear implant had been proposed by our biomedical group, and these electrodes have to be driven by voltage. Thus, a stimulator can deliver voltage pulses to stimulate the auditory nerve in the cochlea is proposed. According the research of our biomedical group, the stimulator should be capable of providing biphasic voltage pulses with adjustable amplitudes and adjustable pulse widths. The well-developed CMOS processes had been attractive to realize implantable device for biomedical application, so the cochlear implant is implemented in the 0.18-um 1.8-V/3.3-V CMOS process. For the purpose of integration with other circuit blocks into a system-on-chip (SoC), the stimulator should also be implemented in the 0.18-um 1.8-V/3.3-V CMOS process. But the maximum output voltage of the stimulator can be as high as 7 V, so the dynamic bias technique and stacked MOS configuration are used to implement this stimulator in the low-voltage CMOS process, without causing the issues of electrical overstress and gate-oxide reliability during circuit operation. According the research of our biomedical group, to help deafness to have sufficient speech intelligibility, the stimulator should be able to deliver stimulus voltage to four different positions on the cochlea, so our stimulator has four output channels. The cochlear implant can only be powered by wirelessly power transmission, and the power supplied by wirelessly power transmission is VDD of 1.8 V. The maximum output voltage of the stimulator is 7 V, so the proposed stimulator also includes a positive high voltage generator, which can pumped VDD (1.8 V) to VDDH (8.4 V). Thus, the stimulator only needs one supply voltage of 1.8 V