ACHIEVING SENSING PRECISION OF 0.5nA IN PIXEL WITH 7 mu s SETTLING TIME BY A NEW EXTERNAL CURRENT SENSING CIRCUIT FOR AMOLED DISPLAYS

Abstract

This study proposes a new push-pull transient current feedforward (PPTCF) based pixel current sensing circuit for active matrix organic light emitting diode (AMOLED) displays with precision within 0.5nA. A finite state machine (FSM) based digital control circuit is designed and developed for the baseline compensation. In order to achieve high accuracy, the digital baseline compensation circuit also incorporates the current digital -to -analog converter (CDAC) and successive approximation current analog-to-digital converter (CADC). The minimum LSB current for the CADC is 10nA. The readout circuit is implemented in the integrated chip with chip area of 1251.1m x 46 m and fabricated via TSMC T18 process. With standard 3.3V supply, the experimental result shows that the overall power consumption of the chip is 990 W watt. Despite of all parasitic capacitances of the panel display, experimental results show that the proposed circuit can sense 0.5nA current within 7 s of settling time. The sensing precision of 0.5nA within 71 mu s are the best among all reported literature to date.