Patent ID: 7847763

Claim:
A method for driving a passive matrix organic light emitting diode (PMOLED) array, the method comprising: providing a pulse width modulation (PWM) constant current to an OLED pixel through a segment of the PMOLED array connected to the OLED pixel directly when a scan line of the PMOLED array connected to the OLED pixel is activated by a scan pulse, wherein the segment is not pre-charged before the PWM constant current is provided to the OLED pixel, and wherein the OLED pixel displays a plurality of gray scales in response to the PWM constant current; determining an offset value Y corresponding to missing gray scales X in the plurality of gray scales of the OLED pixel, the missing gray scales being caused by not pre-charging the segment, and the missing gray scales being not caused by aging of organic materials of the OLED pixel; setting a zero point of the plurality of gray scales to the offset value, and rescaling the gray scales starting from the offset value to obtain a compensated PWM constant current; and driving the OLED pixel by the compensated PWM constant current corresponding to the rescaled gray scales during each of a plurality of horizontal line periods, wherein Y=Z*X/(Z−X), where Z is the number of the plurality of gray scales of the OLED pixel.