JP2007506145A - Circuit and method for driving an array of light emitting pixels - Google Patents

Abstract

Techniques for driving a column of pixels including light emitting elements are provided. The technology includes pixel drive circuitry with feedback data provided from the array data lines and feedback data sources connected to the feedback lines, and a feedback path. The technique can also include a block of reference elements for correction of the input signal.
[Selection] Figure 1

Description

  The present invention relates generally to light emitting device display technology, and more particularly to driving a light emitting element that includes a feedback architecture during programming to compensate for pixel instability and non-uniformity. It relates to the technology used.

  In recent years, active matrix organic light emitting diode (OLED) displays have become more attractive due to advantages over conventional liquid crystal flat displays. These advantages include the ability to produce OLED displays relatively inexpensively and with high efficiency. Furthermore, such a display does not require backlight illumination and provides a wide viewing angle.

An active matrix organic light emitting diode (AMOLED) display has an array of rows and columns of pixels, each pixel having an OLED and several active devices such as thin film transistors. OLED is current driven
driven) devices, the AMOLED pixel circuit must be able to supply an accurate and constant drive current to achieve consistent and uniform brightness.

  As disclosed in Patent Document 1, a simple pixel circuit has two thin film transistors (TFTs) and an OLED. In this circuit, the OLED is connected to the drain terminal of the driving TFT, and the gate terminal of the driving TFT is connected to the column line via the switching TFT. When the pixel circuit is disconnected from the column line, a storage capacitor connected between the gate terminal of the driving TFT and the ground is used to maintain the voltage at the gate terminal of the driving TFT. In this circuit, the current passing through the OLED strongly depends on the characteristic parameter of the driving TFT. The characteristic parameters of the TFT, especially the threshold voltage under bias stress, change with time, and since such changes differ from pixel to pixel, the induced image distortion is unacceptably high.

One method that has been adopted to make current driver circuits more insensitive to threshold voltage shifts is to program the pixel with current instead of voltage. In this method, the OLED current is less dependent on the voltage / current characteristics of the drive transistor. The configuration of a current-programmed pixel circuit for OLED is described in, for example, Yi in IEEE Electronics Device Literature, December 2000, Vol. 21, No. 12, pages 590-592.
“Current source a-Si: H thin film transistor circuit for active matrix organic light emitting display” by HE et al. A disadvantage of the current programming method is that it is slow, especially for low programming current levels, due to the large line capacitance. As a result, voltage programming methods are desirable considering speed. This is especially true for large area TVs and displays.

  Another way to make the drive current less sensitive to transistor parameters is to use current feedback. Patent Document 2 shows a drive system including current feedback. An external current comparator compares the pixel current with a reference current and generates an appropriate signal for controlling the pixel current. One drawback of the disclosed method is that the control signal is a current, which can limit the programming speed. Another drawback of the method is that the anode and cathode electrodes of each OLED must be patterned, which creates reliability problems in currently used OLED manufacturing processes.

Luminance feedback is another method that has been used to stabilize the brightness of OLEDs. As described in U.S. Pat. No. 6,053,047, a feedback readout circuit that responds to a feedback signal representing the light output of an OLED can be used to perform brightness control. The disadvantage of the disclosed method is that each pixel requires a photosensor optically coupled to the OLED. This results in an integration problem. Another drawback is that the low level of the feedback signal generated by the photosensor can lead to a poor signal-to-noise ratio, thereby narrowing the dynamic range of the system.
U.S. Pat.No. 5,748,160 US Patent Application Publication No. 2002/0101172 US Patent Application Publication No. 2003/0151569

  The present invention provides several drive circuits with a feedback control system architecture that can be used to drive columns of light emitting devices and are suitable for use in AMOLED displays. In the present invention, the feedback voltage is generated by an on-pixel feedback circuit or element. This voltage is used to adjust the program voltage of the pixel.

  According to one aspect of the present invention, each pixel in the column is connected to the feedback control unit via the signal line and the feedback line, and receives the scanning clock signal via the selection line connection terminal. A program voltage applied to the pixel via the signal line sets a drive current through the light emitting element. The program voltage can be accurately adjusted by an external control unit through the use of the feedback voltage generated by the on-pixel feedback circuit. The feedback voltage is proportional to the drive current of the light emitting element, and the program voltage to achieve the desired drive current in the presence of any instability (deviation of transistor and light emitting element characteristics) and non-uniformity across pixels. Used to set

  The column control unit can also be connected to a block of reference elements formed on the display substrate to correct output current level errors due to pixel component inaccuracies or temperature drifts. . The block of reference elements can also include a photosensor optically coupled to the light emitting element to provide brightness feedback compensation for brightness changes induced by organic material instabilities or temperature changes.

  According to another aspect of the invention, a pixel circuit for use in a display is provided. The display has a plurality of pixels, each pixel having a selection line, a signal line and a feedback line. The pixel circuit includes a light emitting element; and a driving unit that supplies a driving current to the light emitting element, the driving unit including a storage capacitor and a switching transistor, and the switching transistor is connected to the selection line. A driving unit having a gate terminal, a first terminal and a second terminal connected to the signal line; and a feedback element on the pixel for generating a feedback voltage representing a driving current supplied to the light emitting element. And a feedback element for supplying the feedback signal to the feedback line.

  According to another aspect of the invention, a pixel circuit for use in a display is provided. The display has a plurality of pixels, and each pixel has a first selection line, a second selection line, a signal line, and a feedback line. The pixel circuit includes a light emitting element; a driving unit that supplies a driving current to the light emitting element, a storage capacitor, a gate terminal connected to the first selection line, and a first terminal connected to the signal line And a switching transistor having a second terminal, and a driving transistor having a gate terminal connected to the second terminal of the switching transistor, a first terminal, and a second terminal connected to the light emitting element. A driving unit; and a feedback circuit on the pixel for generating a feedback voltage representing a driving current supplied to the light emitting element. The feedback circuit is connected to a resistor connected between the second terminal of the driving transistor and a certain potential, a gate connected to the second selection line, and a first terminal of the driving transistor. A feedback transistor having a first terminal and a second terminal connected to the feedback line.

  According to another aspect of the invention, a pixel circuit for use in a display is provided. The display has a plurality of pixels, each pixel having a selection line, a signal line and a feedback line. The pixel circuit includes a light emitting element; a driving unit that supplies a driving current to the light emitting element, and includes a storage capacitor, a gate terminal connected to the selection line, a first terminal connected to the signal line, and a first terminal A driving unit having a switching transistor having two terminals, and a driving transistor having a gate terminal connected to the second terminal of the switching transistor, a first terminal, and a second terminal connected to the light emitting element And a feedback circuit on the pixel for generating a feedback voltage representing a driving current supplied to the light emitting element. The feedback circuit includes a resistor connected between the second terminal of the driving transistor and a certain potential, a gate connected to the selection line, and a first connected to the first terminal of the driving transistor. A feedback transistor having a terminal and a second terminal connected to the feedback line.

  According to another aspect of the present invention, a display device is provided. The display device forms an array of pixels; a selection line; a signal line supplied with a voltage signal based on both luminance and feedback information; a feedback line supplied with a feedback voltage signal based on the current level of the drive current; A plurality of pixels, wherein each pixel in the plurality of pixels is formed at an intersection of the scan line, the signal line, and the feedback line on the substrate, and each pixel is for a light emitting element, a storage capacitor, and a switch A plurality of pixels having a current drive circuit having transistors and a feedback circuit for supplying a feedback signal representative of the current output of the current drive circuit; receiving the input signal and passing the input signal to each column on the substrate And adjusting the input signal in response to the feedback signal from the pixels in the column. And a selection-line driving circuit for sequentially driving a select line; and a display column control circuit in order to generate the desired brightness level of the light emitting element in a selected pixel.

  According to another aspect of the present invention, a method for driving a plurality of light emitting elements arranged in a row with a desired luminance is provided. The method includes selecting one of a plurality of pixels in the column and optically coupling a desired luminance of a reference light emitting element with a reference current flowing through the light emitting element to the reference light emitting element. Establishing by adjusting in response to a photocurrent from a selected photosensor; converting the reference current to a corresponding voltage level; and transmitting the voltage level to the selected pixel; Converting the voltage level into a drive current and generating a feedback signal representative of the drive current level; and adjusting the voltage level in response to the feedback signal from the selected pixel; Establishing a drive current substantially equal to the reference current; and storing the adjusted voltage level. And-up, the light emitting element is driven by a driving current based on the voltage level the adjusted, and a step of generating a desired luminance level in the pixel.

  Advantages of the present invention include the ability to supply a stable current to the light emitting element over time, thereby maintaining image quality. Furthermore, the combination of the external current feedback for pixel programming and the luminance feedback for data signal preprocessing provides luminance control and compensation regardless of pixel instability and non-uniformity. The circuit occupies only a small area and is programmed with voltage by voltage feedback. The use of voltages for programming and feedback improves the programming speed required for large area displays and TVs.

  This disclosure of the invention does not necessarily describe all features of the invention.

  These and other features of the present invention will become more apparent from the following description with reference to the accompanying drawings.

  The present invention includes a method for driving a column of pixels, wherein each pixel has a light emitting element, in particular an organic light emitting diode (OLED).

  FIG. 1 shows a display device having a feedback control system architecture 10 and an array of addressable pixels 11. The pixel 11 is controlled by the selection line driver 12 and the data driver 13. As shown in FIG. 1, a separate feedback control unit 14 is provided on each column line of the array. The feedback control unit 14 of a given column is connected to each pixel in the column via a signal line 15 and a feedback line 16. A block of reference elements 17 arranged on the display substrate can also be provided. The block of reference element 17 includes several elements for correcting the input signal of the pixel circuit, and can also include a photosensor optically coupled to the light emitting element to perform luminance feedback.

  The configuration of a given pixel 11 according to one embodiment of the invention is shown in FIG. As shown in FIG. 2, the pixel includes an OLED 21, a current driving circuit 22 controlled by a voltage level stored using a storage capacitor 23, a feedback circuit 24, and switches S1 and S2. The switches S1 and S2 can be any suitable switching device, but are preferably insulated gate field effect transistors. Pixel 11 operates in write and hold modes. In a write mode in which the select line (or multiple select lines) is driven, the switches S1 and S2 are turned on and the current driver circuit 22 receives the signal voltage from the control unit 14 while on-pixel feedback. Circuit 24 provides a voltage feedback signal. Thereby, the drive current passing through the OLED 21 can be accurately controlled by using negative feedback. In the holding mode, the switches S1 and S2 are turned off, and the drive circuit 22 supplies a drive current having a current level according to the voltage level for the storage capacitor 23.

  FIG. 3A shows a circuit diagram of a pixel driving circuit and the control circuit 14 according to another embodiment. The signals to control are shown in FIG. 3B.

  The pixel driving circuit includes three transistors 34, 36 and 38, a resistor 32, a storage capacitor Cs, and an OLED 31. The pixel driving circuit is connected to a selection line, a feedback line, and a signal line. A power supply node having a positive potential Vdd and a common ground are also shown.

  Transistors 34, 36, and 38 can be fabricated using amorphous silicon, polysilicon, suitable organic semiconductors, and NMOS or CMOS technology. The on-pixel feedback circuit consists of a thin film resistor 32 that can be fabricated from any suitable material and technology, which provides sufficient stability. For example, in amorphous silicon technology, resistor 32 can be fabricated using N + amorphous silicon or N + microcrystalline silicon.

  The drain terminal of the drive transistor 36 is connected to the cathode of the OLED 31. The source terminal of the transistor 36 is connected to the resistor 32, and the gate terminal is connected to the signal line via the transistor 34. The resistor 32 is connected between the source terminal of the transistor 36 and the common ground point.

  Transistors 34 and 38 are a drive switch transistor and a feedback switch transistor, respectively. The gate terminals of the transistors 34 and 38 are connected to the selection line. The source terminal of the transistor 34 is connected to the signal line, and the drain terminal is connected to the gate terminal of the transistor 36. The source terminal of the transistor 38 is connected to the feedback line, and the drain terminal is connected to the resistor 32. All OLEDs of different pixels have a common anode electrode and are connected to a power supply node (Vdd). The storage capacitor Cs is connected between the gate terminal of the transistor 36 and the common ground point. The storage capacitor can be connected between the gate terminal and the source terminal of transistor 36. In the latter case, the capacitor Cs can be formed by the gate / source capacitance of the transistor 36.

  In its simplest form, the external control unit 33 is a high gain, low offset differential amplifier with a negative feedback connection.

During the write mode, the select line goes high, turning on transistors 34 and 38. As a result, the driving transistor 36 forms a circuit with negative feedback together with the external differential amplifier 33 and the resistor 32. The difference in voltage level between the input signal voltage and the voltage drop across resistor 32 is amplified by differential amplifier 33 to adjust the potential on the gate of transistor 36. After the initial transient, the output current is stable and for a high gain feedback loop, the current through OLED 31 is:
I _OLED = V _inp / Rf (1)
It becomes. During the hold mode, the select line is low, so transistors 34 and 38 are turned off and the pixel is disconnected. Since the gate voltage of the drive transistor 36 is stored in the capacitor Cs, the drive current does not change during the holding mode.

In the configuration shown in FIG. 3A, the current of pixel 31 depends on the absolute resistance of resistor 32, which is desirable due to possible inherent inaccuracies and poor thermal stability of the integrated resistor. Absent. FIG. 4 illustrates an architecture that addresses the above problem by implementing a reference resistor 42 and an external data current source 41 according to another embodiment of the present invention. The reference resistor 42 is made of the same material as the integrated resistor, and is formed on the display substrate. This configuration improves the temperature stability of the circuit. The programmed level of drive current for this circuit is:
I _OLED = I _inp (Rr / Rf) (2)
Where Rr is the resistance value of the reference resistor 42, and Rf is the resistance value of the feedback resistor 32. The above equation shows a significant improvement in program current accuracy due to insensitivity of the resistance ratio to temperature changes.

A portion of a current pixel driver circuit and column driver circuit according to another embodiment of the present invention is shown in FIG. The circuit is similar to the circuit of FIG. 3A, but in the circuit of FIG. 5, the cathode of the OLED 51 is common and is connected to the negative power supply potential V _ss . As a result, the cathode of the OLED is not patterned.

  The anode of the OLED 51 is connected to the source terminal of the transistor 56. The feedback resistor 32 is connected between the drain terminal of the transistor 56 and the ground node. The voltage level on the select line during the write mode must be high enough to ensure that transistor 54 is “on” for the full output current range. The feedback line in this configuration is connected to the non-inverting input terminal of the differential amplifier 33 to provide negative feedback.

  6A, 7 and 8 show a pixel driving circuit according to another aspect of the invention, in which a p-channel MOS transistor is used.

  FIG. 6A shows a pixel circuit according to another embodiment of the present invention. The feedback switch transistor 68 is a p-channel transistor. The circuit is similar to that of FIG. 5, but the configuration of the PMOS transistor requires an additional select line. FIG. 6B shows the corresponding waveforms for selection line A and selection line B. The advantage of this circuit over that of FIG. 5 is that the required voltage swing for the select line is much smaller.

  FIG. 7 shows a pixel circuit according to another embodiment of the present invention. Transistors 76 and 74 are p-channel transistors, and transistor 78 is an n-channel transistor. As an example in FIG. 7, this circuit also has two select lines with reduced voltage swings, marked A and B.

In the pixel circuit shown in FIG. 8, all transistors are p-channel transistors. In this case, the anode of the OLED 51 is connected to the drain terminal of the transistor 86, and the common cathode electrode of the OLED 51 is connected to the negative power supply potential V _ss .

  9 and 10 show the configuration of a pixel circuit according to an alternative embodiment of the present invention. In these pixel circuits, the current drive circuit is based on a current mirror architecture, ie transistors 95 and 97 and 106 and 110. The current level of the signal current is proportional to the current level of the drive current. In the circuit of FIG. 9, all transistors are n-channel transistors, and in the circuit of FIG. 10, all transistors are p-channel transistors.

  In FIG. 10, the feedback resistor 32 is connected between the drain terminal of the transistor 106 and a common ground point. The gates of the transistors 106 and 110 are connected. In the circuit of FIG. 9, the cathode electrode of the OLED 31 is connected to the drain terminal of the transistor 97, and the anode is common. The transistor 97 is a driving transistor and is connected to the OLED 31. In the circuit of FIG. 10, the cathode of the OLED 51 is common and the anode is connected to the drain terminal of the transistor 110.

  During the write mode, transistors 104 and 108 are in an “on” state, thus transistor 106 forms a feedback loop with feedback resistor 32 and an external control unit (differential amplifier 33). Although transistor 110 is not directly involved in the feedback loop, transistors 110 and 106 have the same gate / source voltage, so the current in transistor 110 is proportional to the current in transistor 106. The current ratio of transistors 110 to 106 is determined by the aspect ratio of these transistors. In these circuits, the feedback resistor 32 and the OLED 31 in FIG. 9 and the OLED 51 in FIG. 10 are not in the same current path, so that a longer life is expected.

  Several methods have been used to reduce charge injection and clock feed-through effects in integrated circuits. As the simplest method, a dummy transistor driven by an inversion signal of a selection line connected to the gate of the driving transistor can reduce both charge injection and clock feedthrough error caused by the driving switch. The drain and source terminals of the dummy transistor are connected to the gate of the driving transistor. FIG. 11 shows an example of such a modification to the embodiment of FIG. The width of the dummy transistor 118 is half the width of the drive transistor 116. It will be apparent to those skilled in the art that the width of the dummy transistor 118 can be any suitable size.

  FIG. 12 is a schematic circuit diagram of a pixel circuit, a column control unit, and a reference cell according to another embodiment of the present invention. In this case, the implemented luminance feedback improves the linearity of the light output characteristics of the video signal and also compensates for luminance instability due to organic material instability, aging, temperature changes or other environmental stresses. . The compensation circuit with luminance feedback includes a resistor R1, a differential amplifier 121 and an NMOS transistor 122 which are part of the control unit, and elements of a reference cell 123 including an OLED 124 and a photodiode 125. The photodiode 125 is optically coupled to the reference OLED 124 to form a feedback current signal that is responsive to the emitted light. The circuit is in equilibrium when the input current through resistor R1 is equal to the feedback current generated by photodiode 125. A current flowing through the OLED 124 via the transistor 122 and the resistor 42 is an input signal to the next stage of the device, and the next stage is the same as the embodiment of FIG.

  FIG. 13 is a schematic diagram of an alternative embodiment of the embodiment of FIG. In this embodiment, the diodes D1 and D2 are used in place of the feedback resistor R1 and the reference resistor R2 of FIG. Since circuit functions with reasonably low programming current level errors require a good match between the reference diode and the pixel diode, the manufacturing technique allows for diodes with reproducible forward current / voltage characteristics. It must be efficient for the manufacture of the array.

  A schematic diagram of a circuit according to another embodiment of the invention is shown in FIG. This circuit implements a common cathode OLED array configuration. In the write mode, the input current from the external current data source 41 generates a voltage drop across the reference OLED 141. The differential amplifier 33 in the negative feedback connection is designed to maintain the same voltage level on the pixel OLED 142. During the hold mode, a voltage stored in capacitor Cs causes a current with a programmed current level to flow through both transistor 146 and OLED 142.

  Although embodiments of the present invention have been described in connection with OLEDs, it is contemplated that other similar display elements such as light emitting diodes (LEDs) may be used in other embodiments.

  The present invention has been described with reference to one or more embodiments. However, it will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as set forth in the claims.

FIG. 1 is a block diagram showing an example of the configuration of a display device having a feedback control system architecture according to an embodiment of the present invention. FIG. 2 is a block diagram of a pixel architecture according to one embodiment of the present invention. FIG. 3A is a circuit diagram of a pixel circuit and column control unit according to an embodiment of the present invention. FIG. 3B shows the corresponding waveforms of the circuit of FIG. 3A according to one embodiment of the present invention. FIG. 4 is a circuit diagram of a modification of the embodiment of FIG. 3A. FIG. 5 is a schematic diagram of a pixel circuit for a common cathode OLED configuration according to one embodiment of the present invention. FIG. 6A is a circuit diagram of a pixel circuit having a p-channel transistor and a column control unit according to an embodiment of the present invention. FIG. 6B shows the corresponding waveforms of the circuit of FIG. 6A according to one embodiment of the present invention. FIG. 7 is a circuit diagram of a pixel circuit and a column control unit including a p-channel transistor switch according to an embodiment of the present invention. FIG. 8 is a circuit diagram of a pixel circuit and a column control unit having p-channel and n-channel transistors according to an embodiment of the present invention. FIG. 9 is a circuit diagram of a pixel circuit and a column control unit including a current mirror as a current driving circuit according to an embodiment of the present invention. FIG. 10 is a circuit diagram of a modification of the embodiment of FIG. FIG. 11 is a circuit diagram of a modification of the embodiment of FIG. FIG. 12 is a circuit diagram of a pixel circuit, column control unit and reference cell with implemented luminance feedback according to one embodiment of the present invention. FIG. 13 is a circuit diagram of a column control unit and a pixel circuit including a reference diode according to an embodiment of the present invention. FIG. 14 is a circuit diagram of a column control unit and a pixel circuit including a reference OLED according to an embodiment of the present invention. FIG. 15 is a circuit diagram of a modification of the embodiment of FIG.

Explanation of symbols

10 feedback control system architecture 11 pixel 12 selection line driver 13 data driver 14 feedback control unit

Claims (21)

A pixel circuit for use in a display, wherein the display has a plurality of pixels, each pixel having a select line, a signal line, and a feedback line.
A light emitting element;
A driving unit for supplying a driving current to the light emitting element, the driving unit including a storage capacitor and a switching transistor, the switching transistor being connected to the selection line; and the signal line A drive unit having a connected first terminal and a second terminal;
A feedback element on a pixel that adjusts a signal supplied to the signal line by generating a feedback signal representing a driving current supplied to the light emitting element, and the feedback signal is shared by two or more pixels. A feedback element as supplied to the feedback line,
A pixel circuit comprising:   2. The pixel circuit according to claim 1, wherein the feedback element is a feedback circuit.   The pixel circuit according to claim 1, wherein the driving unit further includes a driving transistor, and the driving transistor is connected to a gate terminal connected to a second terminal of the switching transistor and to the light emitting element. A pixel circuit having a first terminal and a second terminal. 4. The pixel circuit of claim 3, wherein the feedback circuit is
A resistor connected between the second terminal of the driving transistor and a certain potential to supply the feedback signal having a feedback voltage at a level proportional to the driving current;
A feedback transistor having a gate connected to the selection line, a first terminal connected to a second terminal of the driving transistor, and a second terminal connected to the feedback line;
A pixel circuit comprising:   2. The pixel circuit according to claim 1, wherein the driving unit includes a first transistor having a gate terminal, a first terminal, and a second terminal, and a second driving transistor having a gate terminal, the first terminal, and the second terminal. The first transistor and the second driving transistor are arranged to form a current mirror structure, and each gate terminal is connected to a second terminal of the switching transistor, and the first transistor A pixel circuit, wherein a first terminal and a first terminal of the second driving transistor are connected to a power supply node, and a second terminal of the second driving transistor is connected to the light emitting element.   6. The pixel circuit according to claim 5, wherein the feedback circuit is connected between the second terminal of the first transistor and a certain potential and is in the form of a voltage level proportional to the current level of the drive current. The pixel further comprising: a resistor for supplying a signal; and a feedback transistor connected between the second terminal of the first transistor and the feedback line and having a gate connected to the selection line. circuit.   2. The pixel circuit according to claim 1, wherein the driving unit includes a first transistor having a gate terminal, a first terminal, and a second terminal, and a second driving transistor having a gate terminal, the first terminal, and the second terminal. The first transistor and the second driving transistor are arranged to form a current mirror structure, and each gate terminal is connected to a second terminal of the switching transistor, and the first transistor A second terminal is connected to the feedback line, a first terminal of the second driving transistor is connected to the light emitting element, and a second terminal of the driving transistor is connected to a ground point. Pixel circuit.   6. The pixel circuit of claim 5, wherein the feedback element provides a feedback signal in the form of a current level proportional to the drive current, between the second terminal of the first transistor and the feedback line. And a feedback transistor having a gate terminal connected between the first terminal of the first transistor and the power supply node and connected to the selection line. Pixel circuit.   4. The pixel circuit according to claim 3, wherein the feedback element is a diode connected between the second terminal of the driving transistor and a predetermined potential to supply the feedback signal in the form of a voltage level or a current level. And the feedback switch is connected between the second terminal of the driving transistor and the feedback line and has a gate connected to the selection line. A pixel circuit which is a transistor.   4. The pixel circuit according to claim 3, further comprising a feedback transistor connected between the second terminal of the driving transistor and the feedback line and having a gate connected to the first selection line. The feedback circuit has a gate connected to a second selection line, a first terminal connected to a second terminal of the driving transistor, and a second terminal connected to a ground potential, A pixel circuit, further comprising a switch transistor for supplying a feedback signal in the form of a current level equal to the drive current.   2. The pixel circuit according to claim 1, wherein the light emitting element is an organic light emitting diode.   6. The pixel circuit according to claim 5, wherein the transistor is an insulated gate field effect transistor having an n-channel transistor and a p-channel transistor. A pixel circuit for use in a display, wherein the display has a plurality of pixels, each pixel having a first selection line, a second selection line, a signal line, and a feedback line. Circuit
A light emitting element;
A drive unit for supplying a drive current to the light emitting element,
A storage capacitor;
A switching transistor having a gate terminal connected to the first selection line, a first terminal connected to the signal line, and a second terminal;
A driving transistor having a gate terminal connected to the second terminal of the switching transistor, a first terminal, and a second terminal connected to the light emitting element;
A drive unit having
A feedback circuit on the pixel for generating a feedback voltage representing a drive current supplied to the light emitting element,
A resistor connected between the second terminal of the driving transistor and a certain potential;
A feedback transistor having a gate connected to the second selection line, a first terminal connected to a first terminal of the driving transistor, and a second terminal connected to the feedback line;
A feedback circuit having
A pixel circuit comprising:   14. The pixel circuit according to claim 13, wherein the switching and driving transistors are n-type and the feedback transistor is p-type.   14. The pixel circuit according to claim 13, wherein the switching and driving transistors are p-type and the feedback transistor is n-type. A pixel circuit for use in a display, wherein the display has a plurality of pixels, each pixel having a select line, a signal line, and a feedback line.
A light emitting element;
A drive unit for supplying a drive current to the light emitting element,
A storage capacitor;
A switching transistor having a gate terminal connected to the selection line, a first terminal connected to the signal line, and a second terminal;
A driving transistor having a gate terminal connected to the second terminal of the switching transistor, a first terminal, and a second terminal connected to the light emitting element;
A drive unit having
A feedback circuit on the pixel for generating a feedback voltage representing a drive current supplied to the light emitting element,
A resistor connected between the second terminal of the driving transistor and a certain potential;
A feedback transistor having a gate connected to the selection line, a first terminal connected to a first terminal of the driving transistor, and a second terminal connected to the feedback line;
A feedback circuit having
A pixel circuit comprising:   17. The pixel circuit according to claim 16, wherein the switching transistor, the driving transistor, and the feedback transistor are p-type. A selection line,
A signal line to which a voltage signal based on both luminance and feedback information is supplied;
A feedback line to which a feedback voltage signal based on the current level of the drive current is supplied;
A plurality of pixels forming an array of pixels and arranged in columns, wherein each pixel in the plurality of pixels is formed at an intersection of the selection line, the signal line and the feedback line on the substrate; But,
A light emitting element;
A current drive circuit having a storage capacitor and a switching transistor;
A feedback circuit for supplying a feedback signal representing a current output of the current driving circuit;
A plurality of pixels having
Provided for the column of pixels and receiving an input signal, adjusting the input signal using a reference circuit formed in each column on the substrate, and the input signal from the pixels in the column A display column control circuit that generates a desired brightness level of the light emitting element in a selected pixel by modifying in response to the feedback signal;
A selection line driving circuit for sequentially driving the selection lines;
A display device comprising:   19. The display device according to claim 18, wherein the feedback circuit includes a resistor for supplying the feedback signal in the form of a voltage level proportional to the drive current, and the reference circuit is formed of the same material as the resistor. A display device comprising a reference resistance.   19. The display device according to claim 18, wherein the reference circuit includes a photosensor optically coupled to a reference light emitting element for luminance control, and the display column control circuit uses the generated photocurrent as an input current level. A display device comprising a compensator for comparing and adjusting a current passing through the reference light emitting element to achieve a desired luminance level. In a method of driving a plurality of light emitting elements arranged in a row with a desired luminance,
Selecting one of a plurality of pixels in the column;
Establishing a desired brightness of a reference light emitting element by adjusting a reference current flowing through the light emitting element in response to a photocurrent from a photosensor optically coupled to the reference light emitting element;
Converting the reference current to a corresponding voltage level;
Communicating the voltage level to the selected pixel;
Converting the voltage level to a drive current and generating a feedback signal representative of the drive current level;
Establishing a drive current substantially equal to the reference current by adjusting the voltage level in response to the feedback signal from the selected pixel;
Storing the adjusted voltage level;
Driving the light emitting element with a drive current based on the adjusted voltage level to generate a desired luminance level in the pixel;
A method characterized by comprising:

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