The Design Of Cochlear Implant's Speech Processing Circuit And Its Experimental Test

Cochlear Implant (CI) is a kind of electrical nerve stimulative device, which uses microelectronics technology to restore hearing in deaf patients. Many scholars of clinical medicine, neural engineering and rehabilitation engineering attach great importance to it. As a key component in CI, the speech signal processing circuit's function is to convert speech signals into electrical signals which is used to stimulate the person ear auditory nerves. Since the research of CI started late in our country, the CI's key technologies including the design of speech processing electronic circuit are needed to be further improved. The research of CI's speech signals processing circuit in this project is helpful to improve the CI's progress in our country, which will benefit more than 20 million profoundly deaf patients, and will bring tremendous social and economic benefits.On the basis of analysing the physiological structure of human auditory organ, CI's speech signals processing strategies and some related key technologies, a CI's speech signals processing scheme had been designed in this project.This project constructed the signal processing circuit by using digital signal processor TMS320VC5402, designed the speech signal acquisition circuit by emploing audio chip TLV320AIC23, set up the signal transmission circuit based on wireless digital transmission chip nRF2401A and designed the other peripheral circuits. In the proposed scheme, as a core, the digital signal processor not only carried on the signal processing, but also managed the peripheral circuits so as to control their initialization and set their estates of tasks via some interfaces such as the multichannel buffered serial port and the host port. On the basic of hardware design, this research proposed a new kind of speech signals processing strategy, which is based on the combination of continuous interleaved sampling strategy and continuously variable slope delta algorithm. The new strategy filtered the signals and implemented the speech-electricity transform, additionly attained high compression ratio when losing little signal quality in order to transmit data wireless conveniently. Finally, the corresponding speech signals processing strategy had been actualized in the DSP's development environment----code composer studio software, so that the processed signals become the signals which could provide the speech information for the stimulator. Considering the small volume requirement of the CI circuit, the entire layout of the PCB design optimization had been carried on and the circuit eventually achieved the target of portability. Synchronously, according to the requirements of CI's functional modules, some corresponding testing experimental schemes had been designed. In these schemes, main points had been analysed, questions encountered in these experiments had been solved. Finally, these schemes discussed test results. The results indicated that: this circuit can accomplish the acquisition of speech Signals, the signals filtering, compression and quantification for the speech-electricity mapping, frames packing and wireless transmission. The CI circuit achieved the basic function which the CI's speech signals processing circuit requested.