Circuit design for a subretinal stimulator
In this project we develop CMOS circuits optimized for the usage in medical implants. The emphasis is on low-power, optimized silicon area, and optimized performance.
As a first example we focus on an active pixel array chip for subretinal implants. In Germany, every year 17,000 people become blind, and about 4000 of those suffer from degenerative retinal diseases, which are called Retinitis pigmentosa (RP) and age-related macular degeneration (AMD). From the different nerve layers in the retinal tissue, only the photoreceptors (rods and cones) of the retina perish.
As a first step, to characterize the ciliary muscle potentials, a miniaturized implant was designed. It is composed of commercially available components and does not contain any custom chips. This design digitizes the recorded potentials with a 24 bit resolution at a rate of 250 Hz and transmits the data via Bluetooth Low Energy to an external PC. It is optimized for low power consumption to enable runtime of multiple weeks without the need to replace or recharge the battery.
The next step is to analyze the recorded signals to create a custom analog front end which is tailored to the characteristics of ciliary muscle potentials. To enable a long runtime for potential implants the power consumption should be reduced as far as possible without compromising the measurements. The acquired bio signals are quite slow (from 0.1 to 10 Hz) and low in amplitude (<10mV) which requires high amplification, high resolution and a robust protection against dc offsets and supply noise without attenuating the signal.