A digitally driven pixel circuit with current compensation for AMOLED microdisplays

Abstract

A novel digitally driven pixel circuit for active‐matrix organic light‐emitting diode (OLED) microdisplays is proposed and evaluated. This circuit supports both pulse width modulation and pulse density modulation digital drive approaches. Only three transistors and one capacitor are required per pixel for the proposed circuit. A current mirror is used to compensate for the pixel current changes that occur because of the degradation of the OLEDs over time. The compensation current depends on the potential of the common cathode, the properties of the current mirror, and the Width/Length (W/L) ratio of the drive transistor. The proposed digital pixel circuit also has advantages in circuit layout compared with analog pixel circuits.

Fully Differential Touch Screen Controller with Wide Input Dynamic Range for Thin Displays

“…This assumption is valid for most mobile OLED displays. The current density of pixels required to represent the maximum grayscale is approximately 0.1 nA/um 2 [15], and several hundred microamperes of current may flow through the common electrode in a 6-inch display with FHD resolution (1920 x 1080 pixels). Hence, R C is usually managed as less than 10 Ω to prevent non-uniform display images due to IR (current x resistance) drop in the common electrode.…”

HD OLED-on-silicon micro-display aided by high-efficient operator IP

“…Traditional pixel data transmitting sequence obeys the electron beam scanning strategy: from left to right and from top to bottom [12,13,14]. The obvious advantage of this operation is that this strategy is suitable for current systems.…”

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

“…Especially in the products of virtual reality (VR) or augmented reality (AR), micro displays were broadly developed for improving the flaw of screen door effect [1][2], featured their PPIs above 2000 [3]- [5]. Many driving schemes were considered for these displays, the technique of pulse width modulation (PWM) is implemented with a fixed pixel current (I pixel ) to digitally modulate the time passing the current for the corresponding gray level [6] [7], where the passing signals of "on" or "off" could be realized by the pixel circuit consisting of one or a few field-effect-transistors (FETs), which implies its benefit to high PPI [8] [9]. However, conventional PWMs suffer from their unique issue of false contour that is the unsmooth gradient possibly occurred between the edge of adjacent gray levels for static or dynamic displaying [10] [11].…”

“…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.…”