開發新式骨導式人工耳蝸-子計畫三：骨導式人工耳蝸之可程式化低能耗數位訊號處理器設計( I )

Abstract

傳統的人工電子耳藉由分頻之訊號強度對植入耳蝸的電極陣列施以適當電流刺激以重建聽覺訊號，其基本假設為耳蝸基底部之聽覺神經負責高頻訊號與耳蝸項部負責低頻訊號。然而不同聽覺神經所接受之頻率成份事實上是由耳蝸的物理結構決定，聲音的機械震動通過外耳和中耳之後，在耳蝸的各處與基底膜發生共振，其外窄內寬的結構使得不同頻率成份在基底膜的不同部位產生共振。經實驗結果證實，不同電極長度與植入位置，對語言學習能力並無差別。同時傳統的植入方式容易經由外淋巴液造成感染、造成耳蝸骨化、與傷及顏面神經。本計畫提出一個透過骨頭傳導之人工耳蝸系統，透過電壓所建立之電場對耳蝸進行刺激以傳遞聲音訊號，去除了傳統手術可能造成的傷害。 此子計畫的目標在於開發應用於骨導式人工耳蝸之數位訊號處理與數位傳輸晶片設計，對接收之聲音訊號進行處理並在植入式裝置將傳遞訊號與控制訊號進行回復以控制電壓刺激器。晶片設計重點為高度可程式化，以供動物實驗進行參數調整決定最佳操作模式，同時又必須減少能量消耗以延長外在裝置電池使用壽命與降低傳輸電力至內部植入裝置的電路設計複雜度。外部裝置的主要功能包括聲音聚束以提供適當音源指向性、增益控制提供適當輸入音量強度、濾波器以抑制雜訊與擷取重要與語音訊號，最後將訊號經由適當混波傳入內部植入裝置。內部裝置進行錯誤偵測以確保傳遞資料之正確性，並且傳遞訊號與指令轉換以控制刺激電極電壓時序與強度。未來將與其他子計畫整合形成一套前瞻且完整的骨導式人工耳蝸系統以應用於聽力受損之重建。

Conventionally, a cochlear implant system converts sound to electric impulses delivered to the auditory nerve. A filterbank strategy maps the frequency components of the received sound onto electrodes in place within the cochlear. The electrodes are thus driven by currents with proper amplitude and duration according to the strength of the frequency components. It is assumed that the auditory nerve fibers near base and near apex of the basilar membrane are sensitive to high-pitched and low-pitched, respectively. However, the wave propagation along the membrane is actually dependent on the physical structure of the cochlear. It has been confirmed that the length and the location of the electrodes have negligible effect on the language learning. In addition, conventional cochlear implants may cause meningitis, cochlear ossificans, facial nerve injury, and loss of residual hearing. In this project, we propose a novel bone-guided cochlear prosthesis by using voltage, rather than current, to stimulate auditory nerve. The proposed scheme eliminates the potential risks due to the surgery of the conventional implantation. The target of this sub-project is to develop a DSP processor for auditory signal processing and wireless transmission for the bone-guided cochlear prosthesis. The DSP processor has two parts: external unit and internal unit. The function of the external unit is to analyze and extract the important auditory signals. The internal unit is responsible for decoding the received signals and to control the stimulator. The DSP processor is highly reconfigurable such that all the key parameters can be adjusted for animal test. It is also energy efficient to extend the battery life and to simplify the design complexity of the power delivery circuits. The key building blocks of the external unit include beamforming, gain control, filter bank, channel selection, and amplitude mapping. A proper packet format with dedicated error detection scheme is used to improve the transmission reliability. The key building blocks of the internal unit include error detection and error control, converting the data and command information into proper stimulation signals. The ultimate goal is this project is to integrate the research outcomes of other sub-groups for hearing-loss recovery.