Abstract
This paper presents a method of driving active-matrix organic
light-emitting diode (AMOLED) displays with amorphous silicon (a-Si)
thin-film transistors (TFTs). By using current feedback, the method
effectively compensates for the effect of shift in the threshold voltage $(V_{T})$ of a-Si TFTs on the OLED current. A CMOS transresistance
amplifier is used as the column driver to cancel the effect of large
parasitic capacitance of data lines. An accelerating pulse is used at the
start of the programming cycle to improve the settling at low currents. A
detailed analysis has been done to investigate the effect of circuit
components on the sensitivity of the OLED current to $V_{T}$ shift and the settling behavior of the circuit. Prototypes of
pixel circuits and the transresistance amplifier were fabricated in an a-Si
TFT process and a 0.8-$\mu{\hbox{m}}$ 20-V CMOS technology, respectively. Measurements show less than
5% change in the OLED current for 2.5-V shift in $V_{T}$ of TFTs. Settling times smaller than 50 $\mu{\hbox{s}}$ were achieved for parasitic capacitances of 50–200 pF
and programming currents as small as 200 nA.
© 2009 IEEE
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