Invented by Oh-Kyong Kwon, Samsung Display Co Ltd
The Samsung Display Co Ltd invention works as followsThe OELD circuit and pixel comprises: an organic EL for emitting light in response a selected signal on a scanline; a TFT to supply the current in response the data voltage to a gate via the TFT. A second TFT with a gate coupled to a gate connected to the TFT of the TFT of the TFT of the TFT of the TFT of the TFT of the TFT of the TFT of the a TFT of the TFT of the TFT of
Background for Organic Electroluminescent Display, Driving Method and Pixel Circuit Thereof
(a ) Field of the Invention
The present invention relates an organic electroluminescent display (EL), a driving technique of the EL Display, and a pixel-circuit of the EL Display. The present invention relates more specifically to an organic EL (OELD), driving methods, and a pixel-circuit that can compensate the deviation of threshold voltage when driving pixels of the OELD using the thin film transistor.
(b). Description of the Related Art”.
The methods for driving organic luminescent cell as described above can be classified as passive matrix and active matrix. The passive matrix method selects lines, drives them and forms the positive electrodes perpendicularly to the negative electrodes.
Referring to FIG. As to the operation of the pixel with the above-described configuration, FIG. When the transistor Ma is switched on by the Select[n] signal supplied to its gate, the data voltage VDATA via a dataline is applied to the gate (node B) of the transistor Ma. The transistor Mb emits light in response to the data voltage VDATA applied to its gate.
The current flowing to the OELD can be expressed in the following way:
where IOELD is the current flowing into the OELD; VGS is the voltage between source and gate of transistor Mb; VTH is the threshold voltage of transistor Mb; VDATA represents data voltage and? represents a constant.” “where? represents a constant.
As expressed in Equation 1 according to the pixel-circuit as shown in FIG. The OELD is fed a current corresponding to VDATA, the data voltage supplied. In response to this current, the OELD emits a light. The data voltage VDATA in this case has multiple values within a range of predetermined values so that the gray is shown.
The conventional pixel circuit is unable to achieve high grayscale because the threshold voltage of the TFT depends on the manufacturing process. In the case where the TFT pixels are driven with data voltages in the range 3V/256, two adjacent gray levels have to be separated by approximately 12 mV (=3V/256), in order to achieve 8-bit (256) grayscale. It is difficult to distinguish between data voltages if the threshold voltage deviation is less than 100mV. This results in a decreased grayscale.
The present invention aims to provide an OELD that compensates for deviations in the threshold voltage and displays high gray scale.
The OELD of one aspect of this invention includes: a plurality data lines for transmitting image signals, a number of scan lines to transmit select signals, and a number of pixel-circuits formed on a variety of pixels defined by these data lines and scan lines. Each pixel-circuit comprises: an organic EL for emitting light in response to a current supplied; a switch for switching the data voltage to a line in response a select signal to a line; a TFT first for supplying current via a
The method of driving an OELD according to an aspect of the invention consists of: supplying a voltage for displaying images to the data line; supplying a scan signal to select a pixel to the scan line; switching the voltage supplied to data lines in response the select signal; compensating the voltage supplied to data lines to reduce the threshold voltage deviation of TFT; transmitting the compensated voltage to a TFT gate and supplying current.
The method can also include the step of initializing data voltages supplied to the TFT gate in response to an input control signal.
The OELD pixel is based on a plurality pixels that are defined by a number of data lines and scanning lines. It comprises an organic electroluminescent element (EL), a TFT with a gate connected to a TFT of the previous TFT and a TFT with a gate coupled directly to a TFT of the former TFT. A second TFT has a gate coupled in parallel to a TFT of the prior TFT and a TFT’s gate and drain being coupled together.
In this detailed description, the preferred embodiment has only been described and shown, illustrating the best way that the inventors envisaged to carry out the invention. The invention can be modified in many obvious ways, without compromising the original invention. The drawings and descriptions are therefore to be considered as indicative and not restrictive.
As shown, an OELD panel 10, a data driver 30, and a scan driver 20 comprise the OELD.
The OELD panel 10 consists of a number of data lines (D1 through Dy) for transmitting voltages to display image signals, scan lines (S1 through Sz) for transmitting selected signals and pixel circuits 11 on each of a group of pixels surrounded with the data lines and scan lines.Click here to view the patent on Google Patents.