Current Regulated LED Driver with Fast Switch-Off Behavior for Integrated Optoelectronic Implants

This paper presents a power, speed and area optimized mini-LED driver integrated in 180 nm CMOS HV process and capable of sinking up to 4mA current. It aims to cover various applications of optoelectronic implants with a single design. The current driver consists of a drain-regulated self-cascode current mirror. An additional carrier sweep-out circuit reduces the mini-LED voltage fall time down to 4.7 ns. The current can be digitally adjusted from 0.5 mA to 4 mA, depending on its use-case. The temperature-compensated current reference provides 0.01 mA with a temperature coefficient (TC) of 210 ppm/°C between -10 °C and 110 °C leading to a TC of 357 ppm/°C for the output current. The successfully performed measurements for circuit under pad constructs revealed a possible size reduction only limited by the dimensions of the on-die processed mini-LEDs of 0.1 mm x 0.2 mm.