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Achieving high sensing in 0.5 nA for the driving pixel currents in AMOLEDs with settling time of 7 µs by a new external current sensing circuit

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Abstract

A new external current sensing circuit with baseline compensation for the active matrix organic light emitting diode (AMOLED) display is developed herein to achieve the sensing precision of 0.5 nA in pixel with 7 µs of settling time. Current sensing circuit incorporates a new push–pull transient current feedforward whereas the current analog to digital converter (CADC) based digital baseline current compensation incorporates an 11-bit current digital-to-analog converter, a current comparator and a digital control circuit with an 11-bit successive approximation register. The proposed integrated mixed signal IC drives a 6T1C pixel-based AMOLED panel with one horizontal time of 7.7 µs at a scan frequency of 60 Hz. The design readout chip can simultaneously sense and compensate TFT baseline current variation. The readout circuit and the baseline compensation circuit are implemented in the integrated chip with chip area of 125 μm × 46 μm and fabricated via TSMC T18 process. With the standard 3.3 V supply, experimental result shows that the overall power consumption of the chip is 988 µW watt. The minimum LSB current for the CADC is 10 nA and the maximum achievable sampling rate is 500 KS/s. The measured INL and DNL of CADC is 0.84 and 0.98 respectively. Despite of heavy data line parasitic capacitances (2.6 KΩ/20 pF) of the AMOLED display, experimental results show that the proposed circuit can sense 0.5 nA current within 7 µs of settling time. The sensing precision of 0.5 nA within 7 µs are the best among all reported literature to date whereas the current sense range (0.5–500 nA), system sampling rate (142 KS/s), INL (0.84) and DNL (0.98) of the CADC is approximately comparable among all reported.

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Acknowledgements

The authors appreciate the supports from National Chip Implementation Center Taiwan. This study is supported by Ministry of Science and Technology, Taiwan Grant No. MOST 107-2221-E-009-166-MY2, MOST 107-2218-E-009-006, MOST 107-3017-F-009-003, MOST 107-2622-E-009-025-CC2, MOST 108-2823-8-009-002,109-2622-8-009 -018 -TE1, and MOST 108-2623-E-009-004-D. It was also supported in part by the Novel Bioengineering and Technological Approaches to Solve Two Major Health Problems in Taiwan sponsored by the Taiwan Ministry of Science and Technology Academic Excellence Program under Grant Number: MOST 108-2633-B-009-001. This work was financially supported by the “Center for Intelligent Drug Systems and Smart Bio-devices (IDS2B)” from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan. It was also supported in part by Hsinchu Science Park Bureau, MOST Grant No. 108A31B. A part of this work was funded by AU Optronics Corp (AUO), Taiwan.

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  1. Department of Electrical Engineering, National Chiao Tung University, Hsinchu, 300, Taiwan

    Rajeev Kumar Pandey, Tzu Hao Huang, Wei-Hsuan Ho, Eka Fitrah Pribadi & Paul C.-P. Chao

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  1. Rajeev Kumar Pandey
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  2. Tzu Hao Huang
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  3. Wei-Hsuan Ho
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  4. Eka Fitrah Pribadi
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  5. Paul C.-P. Chao
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Pandey, R.K., Huang, T.H., Ho, WH. et al. Achieving high sensing in 0.5 nA for the driving pixel currents in AMOLEDs with settling time of 7 µs by a new external current sensing circuit. Microsyst Technol 26, 3349–3369 (2020). https://doi.org/10.1007/s00542-020-04859-w

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