A 7T2C Pixel Circuit Compensating for TFT Threshold Voltage Shift in Active-Matrix Simultaneous Neurostimulation

Implantable neuroprostheses require stimulators with a high number of channels and mechanical flexibility. Organic thin-film transistors (OTFTs) are potential for flexible circuits and large-area bioelectronic systems. However, inconsistent stimulating current levels across different pixels caused by non-uniform threshold voltages remains a challenge, due to fabrication process variations. This paper introduces a 7T2C pixel circuit utilizing OTFTs designed in neurostimulation system. The main function of the pixel circuit is to compensate for threshold voltage variations in the TFTs and provide stable and uniform currents to current-driving devices of the neurostimulation system. Measurement results confirm the relationship between the output stimulation currents and shifts in threshold voltage.