The Voltage Programming Pixel Circuit

From (11.2) we can find that the OLED current in independent on the threshold voltage Vp2, and at the same time it is increasing as the increases over time. 

The OLED current is also dependent on the programming voltage, so the current range of the OLED is determined by taking a proper value for Vp, thus this circuit i 

From Equation (11.5) the value of the trans-conductance (K) could be calculated and then the aspect-ratio (W/L) of the driver transistor M2 could be obtained. 

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