Data telemetry with interference cancellation for retinal prosthesis

Age-related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP) are the leading causes of blindness in the United States, and there are currently no effective methods for curing the diseases. Although AMD and RP patients suffer from the loss of the photoreceptor layer in the retina, the succeeding neurons such as bipolar cells and ganglion cells usually survive despite the damage. Researchers have demonstrated that electrically stimulating the surviving neuron cells can generate visual perception in blind patients by bypassing the photoreceptor layer. The prosthetic work may generate useful vision perception such as recognizing objects and identifying the environment.; This thesis focuses on the design of an inductively-coupled data telemetry to support a 1000-electrode retinal prosthesis. The telemetry system uses separate power and data carrier frequencies to achieve both power transfer efficiency and a high data rate (1 or 2 Mbps). However, since the power and data coils are placed coaxially due to surgical constraints, the power signal at 1 MHz interferes with the 20 MHz data transmission. On the data receiver side, the demodulator employs a differential scheme to cancel the interference, thus avoiding high-order filters in the front-end.; Differential Phase Shift Keying (DPSK) is chosen as the data modulation scheme, because it is a convenient scheme for performing interference cancellation, and also because it has a higher power efficiency than Amplitude Shift Keying (ASK) and Frequency Shift Keying (FSK). The DPSK receiver uses bandpass sampling to reduce the implementation complexity, avoiding carrier synchronization. Furthermore, the receiver performs demodulation in the analog domain using switched-capacitor circuits, which saves power consumption by avoiding a high speed Analog to Digital Converters (ADC). The DPSK demodulator is fabricated in 0.35 mum CMOS process with an active area of 1.7 mm x 2.6 mm. A prototype system is built to test the demodulator in a real environment, which includes both the data telemetry and power telemetry. The testing results show that, when the interference from the power telemetry is 12 dB higher than the data signal, the demodulator chip can still recover the data with no additional filters.