P‐53: A Novel Pixel Circuit Providing Expanded Input Voltage Range for OLEDoS Microdisplays

Abstract

A novel pixel circuit providing expanded data voltage range is proposed for high resolution and high image quality organic lightemitting diode-on-silicon (OLEDoS) microdisplay applications. The proposed pixel circuit adopts a structure of four series connected NMOSFETs (4-SCN) to expand the input data voltage range, within which the circuit operates in the subthreshold region. In addition, the pixel circuit has improved image quality by introducing a compensation scheme. The proposed circuit is verified by the simulation based on a 0.18 μm BCDlite Isolation process. The proposed circuit can be integrated into a unit subpixel area of 2.9 × 8.7 μm 2 . The simulation results show that the input data voltage range of the proposed pixel circuit is 6.26 times wider than that of the traditional 2T1C pixel circuit [1], which is 4.42V. And the emission current deviation ranges from -4.7% to +4.2% under the threshold voltage variation of 5 mV, which is 31.01% for a traditional 2T1C pixel circuit [1].

P‐31: Pixel Circuit with Backgate Feedback for Deep and Rich Black Expressions on Light‐Emitting Display

“…In this paper, we propose a pixel circuit with a feedback network of backgate which utilizes active source loads on a source of a drive transistor for detecting output current. A combination of the active load and backgates has already been reported [5], but the proposed circuit is new with two points. Firstly, the effect of backgate can be arbitrarily adjusted by a balance of capacitances of upper and lower gate insulating films.…”

P‐47: An OLEDoS Pixel Circuit with Extended Data Voltage Range for High Resolution Micro‐Displays

“…Therefore, the data voltage rang could be extended to precisely control the emission current of OLED, especially small current of low gray levels. Moreover, equation (5) shows that due to the compensation scheme of "source-follower" structure, the proposed pixel circuit could also decrease the sensitivity of the driving transistor to the threshold voltage variation, simultaneously [2], [3], [5].…”

“…For high resolution applications, the pixel circuit area of OLEDoS micro-displays is limited to tens of μm 2 . The luminance of OLED is proportional to its current density [3]. To realize the same luminance, the OLED emission current decreases as the pixel circuit area becomes smaller.…”

“…Therefore, due to the restrictions of small pixel circuit area and requirements of low power consumption, the OLED emission current generally ranges from tens of pico-amperes (pA) to a few nano-amperes (nA) [2]- [5]. In order to precisely control the emission current of circuits with high resolution, it is necessary to extend the data voltage range [3], [5]. Furthermore, the threshold voltage (Vth) variation [2]- [5] of driving transistors, which is caused by the process, should also be compensated to realize high image quality OLEDoS micro-displays.…”

“…Several pixel circuits with Vth variation compensation function were proposed, yet with narrow data voltage range [6], [8]. For a conventional design [3], several serially connected transistors were used to expand the data voltage range, which increased the layout area significantly. Furthermore, the luminance efficiency of OLED is prone to decrease gradually after long working time.…”