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Lee J. Johnson, Eyal Margalit, Costa Colbert; High Speed Wireless Retinal Prosthesis System. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4958.
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© ARVO (1962-2015); The Authors (2016-present)
Many wireless transceivers for use with retinal prostheses use individual wireless channels for each electrode or use digital multiplexers to distribute the wirelessly transmitted data. One problem is that digital multiplexers may require a digital address for each pixel, which reduces the image framerate. An alternative method is to use an analog multiplexer to reduce pixel address overhead. A significant problem is that the speed of the analog multiplexer clock is often greater than 1MHz. The 1MHz clock allows the chip to load the image data into all the pixels in less than 5ms. A 1 MHz analog multiplexer clock would require a wireless transceiver data clock of at least 8MHz and its resultant power requirements.
We present a demonstration system for high speed wireless data transmission for a retinal prosthesis. A microprocessor controlled buffering method is used to accumulate asynchronous data at low wireless transmission data rates and release the buffered data synchronously at faster rates. The system uses low powered Bluetooth wireless (CSR, Inc) and 8051 microcontroller chips (Silicon Labs, Inc). The chips control and drive the Naval Research Laboratory designed retinal stimulation array with 3200 electrodes. To obtain the highest data rates the Bluetooth data is asynchronous; meaning arbitrary blank periods occur between actual data signals. The retinal stimulator chip requires synchronous data; it must have predictable data input signals without blank periods.
The demonstration system transmitted image data simulated by sine waves. The effective wireless data rate was 230K bits per second. We transferred that data synchronously to the stimulator chip at an effective digital data rate of 11 Mbits per second. The total throughput in the demonstration system is 7 images per second with each image consisting of 3200 pixels with 64 gray levels.
Our wireless retinal prosthesis demonstration system shows that high resolution image data can be transmitted using current low power Bluetooth wireless technology. Software improvements will yield faster data rates allowing for 30 images per second. The wireless chip is 3.2mm x 3.5mm and the microcontroller is 4mm x 4mm, making both of them small enough for implantation.
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