A High 6318-PPI Pixel Circuit That Realizes 10-bit Gray Levels for Analog-PWM Driven Micro-LED Displays

• Published in: IEEE transactions on electron devices 2024-02, Vol.71 (2), p.1-9
• Main Authors: Cheng, Shih-Song, Chao, Paul C.-P.
• Format: Article
• Language: English
• Subjects: 10-bit grayscale; Analog circuits; analog pulsewidth modulation (A-PWM); data voltage range (<inline-formula xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> <tex-math notation="LaTeX"> textit{V}_{\text{data}}</tex-math> </inline-formula> range); Displays; Field effect transistors; high PPI; Hyperspectral imaging; Indexes; Inverters; Layout; LEDOS; Light emitting diodes; micro-LED; microdisplays; pixel circuit; Pixels; Pulse duration; Random access memory; Semiconductor devices; Switches; Voltage
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2023.3347183

A new pixel circuit is proposed to realize 10-bit gray levels for high 6318 pixel-per-inch (PPI) micro-light-emitting-diode (micro-LED) displays, with a ramping voltage varied from high to low, outputting a pulse-form pixel current ( \textit{I}_{\text{pixel}}\text{)} , while the pulsewidth of this \textit{I}_{\text{pixel}} can be modulated with two data voltages ( \textit{V}_{\text{data}} 's). The first \textit{V}_{\text{data}} is inputted and varies along the main 7-bit emitted grays, and the extra 3-bit gray levels are expanded as the second \textit{V}_{\text{data}} joins on the basis of the original 7-bit. Therefore, these 10-bit grays with the maximum 7-bit \textit{V}_{\text{data}} are realized in a smaller \textit{V}_{\text{data}} range ( \textit{R}_{\text{DATA}}\text{)} as opposed to a conventional 10 bit obtained with a 10-bit \textit{V}_{\text{data}} . The proposed circuit was fabricated in the pixel array of 6318PPI via the 55-nm CMOS process. The actual \textit{R}_{\text{DATA}} of 0.635 V allows this circuit to be able to majorly constructed by the 1.2-V low-voltage field-effect transistor (LVFET), differing from the conventional 10-bit that is realized in \textit{R}_{\text{DATA}} of above 5 V by all high-voltage FET (HVFET)-made pixel circuits, that is, the circuit composition of LVFET substituting for HVFET is in favor of the layout shrinking of a pixel, offered the advantage of this technique on high PPI. Based on the experiments, the gamma-corrected 8-bit trimmed from the outputted 10-bit grays shows a favorable result that the obtained gamma distributes within 1.99 and 2.26 with standard deviation \sigma