A digital driving method using pulse‐density modulation with a random dither matrix for higher motion image quality

Abstract

We propose a new digital driving technique using pulse‐density modulation (PDM) with a random dither matrix for evenness of luminance uniformity and higher motion image quality. As a digital driving technique, pulse‐width modulation (PWM) is conventionally used for active‐matrix organic light‐emitting diode (AMOLED) displays in order to improve luminance uniformity. However, in PWM driving, it is difficult to realize high‐frame‐rate driving for improving motion image quality. On the other hand, it is considered that PDM driving method is effective to obtain high motion image quality because of non‐frame‐refreshing property. In the present paper, we proposed a PDM driving technique using a random dither matrix and evaluated the relationship between the display image quality and the driving frequency in the proposed method through simulations. As a result, it is confirmed that good image quality can be obtained by using a blue‐noise mask as a random dither matrix at a practical driving frequency. Moreover, we demonstrated the proposed technique using an actual AMOLED panel.

[Paper] Mechanism of Degradation of Moving Image Quality with Pulse Width Modulation Grayscale Expression Methods

“…Also addressing may limits the pulse frequency. But dithering technique will solve these problems 9) . Another solution is reduction of duty ratio.…”

A High 5292-PPI Pixel Circuit for Micro Displays With 10-Bit Gray Levels Realized via the Technique of Analog Sub-Frame Integral

“…These solutions directly add extra burden to the whole driving system. Based on the PWM, the technique of pulse density modulation (PDM) was developed to run dimming the discontinuity of luminance intensity between frames for improving false contour without a speedy refresh rate [14]- [16], but this optical artifact is not perfectly eliminated on such digitally driven schemes of impulse illuminating. The technique of analog PWM (A-PWM), a PWM-behaved scheme that outputs its I pixel by hold type illuminating and functions by inputting analog data voltages (V data 's) into the pixel circuit to modulate illuminating time [17]- [19], could rule out false contours completely since the variations of the illuminating time between adjacent gray levels are continuously consistent, performed the same effectiveness to the other hold illuminating schemes of pulse amplitude modulation (PAM) that runs with V data 's to obtain different I pixel 's in a fixed illuminating time [20]- [22].…”

“…2 shows the four phases of the proposed circuit running with its corresponding timing depicting in Fig. 3, the first two are for generating initial current of I pixel (I P-I ) at the 1st Possible FET Configuration to build the 10-bit Pixel Circuit [7] 2 HV-and 1 LV-FETs [8] 1 HV-and 1 LV-FETs [9] 1 HV-and 1 LV-FETs [14] 1 HV-and 1 LV-FETs [15] 1 HV-and 1 LV-FETs [16] 1 HV-and 1 LV-FETs [17] sub-frame and the last two happened at the 2nd or beyond sub-frame would switch the output current to an updated I pixel (I P-U ), where the number of sub-frames is 8 (3-bit). In phase-1, V data1 and V data2 are respectively delivered to the nodes of na and nc, the logic 1 of V sel biases node ne, node nd receives logic 0 via INV1; then these logics would be maintained with the latch made of INV1 and INV2, making T4 turned on and delivering V ref to node nb.…”