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In this paper, we propose a pixel circuit immune to the electrical characteristic variation of organic light-emitting diodes (OLEDs) for organic light-emitting diode-on-silicon (OLEDoS) microdisplays with a 0.4 inch video graphics array (VGA) resolution and a 6-bit gray scale. The proposed pixel circuit is implemented using five p-channel metal oxide semiconductor field-effect transistors (MOSFETs) and one storage capacitor. The proposed pixel circuit has a source follower with a diode-connected transistor as an active load for improving the immunity against the electrical characteristic variation of OLEDs. The deviation in the measured emission current ranges from -0.165 to 0.212 least significant bit (LSB) among 11 samples while the anode voltage of OLED is 0 V. Also, the deviation in the measured emission current ranges from -0.262 to 0.272 LSB in pixel samples, while the anode voltage of OLED varies from 0 to 2.5 V owing to the electrical characteristic variation of OLEDs.

-Two simple pixel circuits are proposed for high resolution and high image quality organic light-emitting diode-on-silicon microdisplays. The proposed pixel circuits achieve high resolution due to simple pixel structure comprising three n-type MOSFETs and one storage capacitor, which are integrated into a unit subpixel area of 3 × 9 μm 2 using a 90 nm CMOS process. The proposed pixel circuits improve image quality by compensating for the threshold voltage variation of the driving transistors and extending the data voltage range. To verify the performance of the proposed pixel circuits, the emission currents of 24 pixel circuits are measured. The measured emission current deviation error of the proposed pixel circuits A and B ranges from À2.59% to +2.78%, and from À1.86% to +1.84%, respectively, which are improved from the emission current deviation error of the conventional current-source type pixel circuit when the threshold voltage variation is not compensated for, which ranges from À14.87% to +14.67%. In addition, the data voltage ranges of the proposed pixel circuits A and B are 1.193 V and 1.792 V, respectively, which are 2.38 and 3.57 times wider than the data voltage range of the conventional current-source type pixel circuit of 0.501 V.

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We study the relaxation properties of the voter model with i.i.d. random bias. We prove under mild conditions that the disorder-averaged relaxation of this biased random voter model is faster than a stretched exponential with exponent d/(d + α), where 0 < α 2 depends on the transition rates of the non-biased voter model. Under an additional assumption, we show that the above upper bound is optimal. The main ingredient of our proof is a result of Donsker and Varadhan. § Postdoctoraal onderzoeker FWO. Bursaal IWT. 0305-4470/99/447653+12$30.00