A prototype 64-electrode stimulator in 65 nm CMOS process towards a high density epi-retinal prosthesis

This paper presents a highly flexible 64-electrode stimulator using 65 nm CMOS process fabricated as a stage towards a 1024-electrode epi-retinal prosthesis, which aims to restore partial vision in patients suffering from eye diseases such as retinitis pigmentosa (RP) and age-related macular degradation (AMD). The stimulator drives 64 electrodes with many flexible features, which are necessary before making a complete 1024-electrode implant chip. Each electrode driver can provide a bi-phasic stimulus current with fully programmable parameters such as amplitude, pulse duration, inter-phase gap, and stimulation rate. The electrode driver operates in an alternately pull-push manner with only one current source working at a time, which helps reduce headroom voltage while controlling charge balance at the active electrode. The stimulator varies both stimulus current amplitude and stimulation rate to represent phosphene brightness. The stimulus current amplitude starts from the tissue depolarization threshold with 64 different levels. The selection of active and return electrodes is arbitrary, any electrodes and any number of them can be selected at any time. The power consumption of the stimulator is 400 μW excluding the stimulus power. Measurement results verify correct operation. The stimulator is easily scaled up to drive 1024 electrodes.