Voltage programmed pixels

Like the standard AMLCD pixel, the two TFT AMOLED pixel is voltage programmed. That is, voltages are used to represent the image data. In 1998 Samoff Corporation, Planar America, Kodak, and Princeton University reported the earliest... 

FIGURE 6.4.20 Samoff four TFT self-compensating voltage-programmed AMOLED pixel. 

FIGURE 6.4.21 16 x 16 poly-Si TFT AMOLED pixel arrays using (a) two TFT pixel and (b) four TFT self-compensating voltage-programmed pixel. The additional area occupied by the circuitry of the four TFT pixel reduces the pixel fill-factor. 

Current-programmed pixels have the following advantages over voltage-programmed pixels ... 

It does not require the large summing capacitor needed by the antozeroing voltage-programmed pixel. 

Fig. 7.1. Two architectures for display driving, (a) shows a single transistor architecture appropriate for latching and holding charge on the pixel for field driven display elements such as liquid crystal displays or e-Ink. (b) schematically shows the matrixed version of this element, (c) shows a two transistor voltage-programmed current driver appropriate for OLEDs. More advanced voltage and current programmed circuits are also possible, but require more transistors.

This results in a light pulse with a time profile that depends on the phase differences between its spectral components, which in turn can be controlled by the LCD, driven by a special computer program (Fig. 11.34) [11.81,11.82]. A self-learning algorithm can be incorporated into the closed loop, which compares the output pulse form with the wanted one and tries to vary the voltage at the different pixels in such a way that the wanted pulse form is approximated [11.83]. More details can be found in [11.84]... 

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