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

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 (
${I}_{\text {pixel}}{)}$
, while the pulsewidth of this
${I}_{\text {pixel}}$
can be modulated with two data voltages (
${V}_{\text {data}}$
’s). The first
${V}_{\text {data}}$
is inputted and varies along the main 7-bit emitted grays, and the extra 3-bit gray levels are expanded as the second
${V}_{\text {data}}$
joins on the basis of the original 7-bit. Therefore, these 10-bit grays with the maximum 7-bit
${V}_{\text {data}}$
are realized in a smaller
${V}_{\text {data}}$
range (
${R}_{\text {DATA}}{)}$
as opposed to a conventional 10 bit obtained with a 10-bit
${V}_{\text {data}}$
. The proposed circuit was fabricated in the pixel array of 6318PPI via the 55-nm CMOS process. The actual
${R}_{\text {DATA}}$
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
${R}_{\text {DATA}}$
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 $
of 0.03, successfully validating the proposed high PPI pixel circuit for realizing 10-bit gray levels.