# Patent

## Title
Display device that switches light emission states multiple times during one field period

## Abstract

A scan driving circuit includes a shift register unit and a logic circuit unit. The start of a start pulse of an output signal STp+1 of a p+1'th shift register is situated between the start and end of a start pulse of the output signal STp of a p'th shift register, and one each of a first enable signal through a Q'th enable signal exist in sequence between the start of the start pulse of the output signal STp and the start of the start pulse of the output signal STp+1. The operations of a (p′, q)'th NAND circuit are restricted based on period identifying signals, such that the NAND circuit generates scanning signals based only on a portion of the output signal STp corresponding to the first start pulse, the signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq.

## Background
CROSS REFERENCES TO RELATED APPLICATIONS
This present application is a Continuation Application of patent application Ser. No. 12/457,756, filed Jun. 19, 2009, with an issue date of Apr. 23, 2013 as U.S. Pat. No. 8,427,458, which claims priority from Japanese Patent Application No.: 2008-182369 filed in the Japanese Patent Office on Jul. 14, 2008, the entire contents of which being incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scan driving circuit and to a display device including the scan driving circuit. More particularly, the present invention relates to a scan driving circuit and to a display device including the scan driving circuit, in which signals can be supplied to scanning lines, initialization control lines, and display control lines, and a lit/unlit state of display elements can be switched multiple times during one field period by supplying multiple pulse signals to the display control lines during the field period, without affecting the signals being supplied to the scanning lines and initialization control lines.
2. Description of the Related Art
Examples of widely used display devices having display elements arranged in the form of a two-dimensional matrix include liquid crystal display devices made up of liquid crystal cells driven by voltage, and also display devices including light emitting units which emit light under application of electric current (e.g., organic electroluminescence light emitting units) and driving circuits for driving the light emitting units.
The luminance of display elements including light emitting units which emit light under application of electric current is controlled by the value of the current flowing through the light emitting units. In the same way as with liquid crystal display devices, such display devices having these display elements (e.g., organic electroluminescence display devices) can be driven by the simple matrix method and the active matrix method. While the active matrix method has shortcomings such as greater complexity in structure as compared with the simple matrix method, there are also various advantages, such as being capable of higher luminance.
Various types of driving circuits configured from transistors and capacitance units are in widespread use as circuits for driving a light emitting unit by the active matrix method. For example, Japanese Unexamined Patent Application Publication No. 2005-31630 discloses a display element configured of an organic electroluminescence light emitting unit and a driving circuit, and a driving method thereof. This driving circuit is a driving circuit configured of six transistors and one capacitance unit (hereinafter referred to as “6Tr/1C driving circuit”). FIG. 26 illustrates an equivalent circuit to a driving circuit (6Tr/1C driving circuit) of a display element of the m'th row and n'th column in a display device configured of display elements arrayed in the form of a two-dimensional matrix. Note that in the description, the display elements are assumed to be scanned in line sequence.
The 6Tr/1C driving circuit has a write transistor TRW, a driving transistor TRD, a capacitance unit C1, and also a first transistor TR1, a second transistor TR2, a third transistor TR2, and a fourth transistor TR4.
At the write transistor TRW, one source/drain region is connected to a data line DTLn, and the gate electrode is connected to a scanning line SCLm. At the driving transistor TRD, one source/drain region is connected to the other source/drain region of the write transistor TRW, thereby configuring a first node ND1. One end of the capacitance unit C1 is connected to a power supply line PS1. At the capacitance unit C1, a predetermined reference voltage (later-described voltage VCC in the example shown in FIG. 26) is applied to one end, and the other end is connected to the gate electrode of the driving transistor TRD, thereby configuring a second node ND2. The scanning line SCLm is connected to an unshown scanning circuit, and the data line DTLn is connected to a signal output circuit 100.
At the first transistor TR1, one source/drain region is connected to the second node ND2, and the other source/drain region is connected to the other source/drain region of the driving transistor TRD. The first transistor TR1 makes up a switch circuit portion connected between the second node ND2 and the other source/drain region of the driving transistor TRD.
At the second transistor TR2, one source/drain region is connected to a power supply line PS3 to which is applied a predetermined initializing voltage VIni (e.g., −4 volts) for initialization of the potential of the second node ND2, and the other source/drain region is connected to the second node ND2. The second transistor TR2 makes TR1 makes up a switch circuit portion connected between the second node ND2 and the power supply line PS3 to which is applied the predetermined initializing voltage VIni.
At the third transistor TR3, one source/drain region is connected to a power supply line PS1 to which is applied a predetermined driving voltage VCC (e.g., 10 volts), and the other source/drain region is connected to the first node ND1. The third transistor TR3 makes up a switch circuit portion connected between the first node ND1 and the power supply line PS1 to which is applied the predetermined driving voltage VCC.
At the fourth transistor TR4, one source/drain region is connected to the other source/drain region of the driving transistor TRD, and the other source/drain region is connected to one end of a light emitting unit ELP (more specifically, the anode electrode of the light emitting unit ELP). The fourth transistor TR4 makes up a switch circuit portion connected between the other source/drain region of the driving transistor TRD and one end of the light emitting unit ELP.
The gate electrode of the write transistor TRW and the gate electrode of the first transistor TR1 are connected to the scanning line SCLm. The gate electrode of the second transistor TR2 is connected to an initialization control line AZm. Scanning signal supplied to an unshown scanning line SCLm−1 scanned immediately prior to the scanning line SCLm is also supplied to the initialization control line AZm. The gate electrodes of the third transistor TR3 and the fourth transistor TR4 are connected to a display control line CLm for controlling the lit/unlit state of the display element.
For example, each transistor is formed as a p-channel thin-film transistor (TFT), with the light emitting unit ELP provided on an interlayer-insulating later or the like, formed so as to cover the driving circuit. At the light emitting unit ELP, the anode electrode is connected to the other source/drain region of the fourth transistor TR4, and the cathode electrode is connected to a power supply line PS2. Voltage VCat (e.g., −10 volts) is applied to the cathode electrode of the light emitting unit ELP. Symbol CEL represents the capacitance of the light emitting unit ELP.
Now, when configuring transistors of TFTs, irregularity in threshold voltage is unavoidable to a certain extent. In the event that there is irregularity in the amount of current flowing through the light emitting unit ELP due to irregularity in the threshold value of the driving transistor TRD, the uniformity of luminance of the display device suffers. Accordingly, an arrangement has to be made where the amount of current flowing through the light emitting unit ELP is not affected by irregularity in the threshold value of the driving transistor TRD. As described later, the light emitting unit ELP is driven so as to be unaffected by irregularity in the threshold value of the driving transistor TRD.
A driving method of a display element at the m'th row and n'th column of a display device configured as a two-dimensional array of N×M display elements will be described with reference to FIGS. 27A and 27B. FIG. 27A illustrates a schematic timing chart of signals on the initialization control line AZm, scanning line SCLm, and display control line CLm. FIGS. 27B through 28B schematically illustrate the on/off states and the likes of the transistors of a 6Tr/1C driving circuit. To facilitate description, we will refer the period during which the initialization control line AZm is scanned as the “m−1'th horizontal scan period”, and the period during which the scanning line SCLm is scanned as the “m'th horizontal scan period”.
As shown in FIG. 27A, in the m−1'th horizontal scan period, an initialization process is carried out, which will be described in detail with reference to FIG. 27B. In the m−1'th horizontal scan period, the initialization control line AZm goes from a high level to a low level, and the display control line CLm goes from a low level to a high level. Note that the scanning line SCLm remains at the high level. Accordingly, during the m−1'th horizontal scan period, the write transistor TRW, first transistor TR1, third transistor TR3, and fourth transistor TR4 are in an off state, while the second transistor TR2 is in an on state.
A predetermined initialization voltage VIni for initializing the potential of the second node ND2 is applied to the second node ND2 via the second transistor TR2 which is in the on state. Accordingly, the potential of the second node ND2 is initialized.
Next, as shown in FIG. 27A, a video signal VSig is written in the m'th horizontal scanning period. At this time, threshold voltage canceling processing of the driving transistor TRD is performed in conjunction. Specifically, the second node ND2 and the other source/drain region of the driving transistor TRD are electrically connected, the video signal VSig is applied from the data line DTLn to the first node ND1 via the write transistor TRW which has been placed in an on state due to the signal from the scanning line SCLm, thereby changing the potential of the second node ND2 toward a potential which can be calculated by subtracting the threshold voltage Vth of the driving transistor TRD from the video signal VSig.
More detailed description will be made with reference to FIGS. 27A and 28A. In the m'th horizontal scanning period, the initialization control line AZm goes from a low level to a high level, and the scanning line SCLm goes from a high level to a low level. Note that the display control line CLm remains at the high level. Accordingly, at the m'th horizontal scanning period, the write transistor TRW and first transistor TR1 are in an on state, while the second transistor TR2, third transistor TR3, and fourth transistor TR4 are in an off state.
The second node ND2 and the other source/drain region of the driving transistor TRD are electrically connected via the first transistor TR1 which is in an on state, and the video signal VSig from the data line DTn is applied to the first node NDD via the write transistor TRW which is in an on state due to the signal from the scanning line SCLm. Accordingly, the potential of the second node ND2 changes toward a voltage which can be calculated by subtracting the threshold voltage Vth of the driving transistor TRD from the video signal VSig.
According to the above-described initialization process, if the potential of the second node ND2 has been initialized such that the driving transistor TRD is in an on state at the start of the m'th horizontal scanning period, the potential of the second node ND2 changes toward the potential of the video signal VSig which is applied to the first node ND1. However, once the potential difference between the gate electrode of the driving transistor TRD and one source/drain region thereof reaches Vth, the driving transistor TRD goes to an off state. In this state, the potential of the second node ND2 is approximately (VSig−Vth).
Next, the light emitting unit ELP is driven by applying current to the light emitting unit ELP via the driving transistor TRD.
More detailed description will be made with reference to FIGS. 27A and 28B. At the end of the m'th horizontal scanning period, the scanning line SCLm goes from a low level to a high level. Also, the display control line CLm goes from a high level to a low level. Note that the initialization control line AZm remains at the high level. The third transistor TR3 and fourth transistor TR4 are in an on state, while the write transistor TRW, first transistor TR1, and second transistor TR2 are in an off state.
Driving voltage VCC is applied to one source/drain region of the driving transistor TRD via the third transistor TR3 which is in an on state. Also, the other source/drain region of the driving transistor TRD and one end of the light emitting unit ELP are connected via the fourth transistor TR4 which is in an on state.
The current flowing through the light emitting unit ELP is a drain current Ids which flows from the source region of the driving transistor TRD to the drain region thereof, so this can be expressed with the following expression (A) assuming that the driving transistor TRD operates ideally at the saturation region. As shown in FIG. 28B, the drain current Ids is applied to the light emitting unit ELP, and the light emitting unit ELP emits light at a luminance corresponding to the value of the drain current Ids.

Ids=k·μ·(Vgs−Vth)2  (A)

where μ represents effective mobility, L represents channel length, W represents channel width, Vgs represents voltage between the source region and gate region of the driving transistor TRD, and COX represents

(relative permittivity of gate insulation layer)×(permittivity of vacuum)/(thickness of gate insulation layer)

in

k=(1⁄2)·(W/L)·COX.

Further, since

Vgs≈VCC−(VSig−Vth)  (B)

holds, the above Expression (A) can be rewritten as follows.





  
    
      
        
          
            
              
                I
                ds
              
              =
              
                k
                ·
                μ
                ·
                
                  
                    (
                    
                      
                        V
                        CC
                      
                      -
                      
                        (
                        
                          
                            V
                            sig
                          
                          -
                          
                            V
                            th
                          
                        
                        )
                      
                      -
                      
                        V
                        th
                      
                    
                    )
                  
                  2
                
              
            
          
        
        
          
            
              =
              
                k
                ·
                μ
                ·
                
                  
                    (
                    
                      
                        V
                        CC
                      
                      -
                      
                        V
                        sig
                      
                    
                    )
                  
                  2
                
              
            
          
        
      
    
    
      
        (
        C
        )
      
    
  




As can be clearly understood from the above Expression (C), the threshold voltage Vth of the driving transistor TRD has no bearing on the value of the drain current Ids. In other words, a drain current Ids corresponding to the video signal VSig can be applied to the light emitting unit ELP unaffected by the value of the threshold voltage Vth of the driving transistor TRD. With the above-described driving method, irregularities in the threshold voltage Vth of the driving transistor TRD do not affect the luminance of the display element.
SUMMARY OF THE INVENTION
For a display device having the above-described display elements to operate, circuits have to be provided which supply signals to the scanning lines, initialization control lines, and display control lines. The circuits for supplying these signals are preferably circuits of an integrated structure, from the perspective of reduction in layout area of the circuits, and reduction of circuit costs. Also, enabling multiple pulse signals to be supplied to the display control lines within one field circuit without affecting the signals supplied to the scanning lines and initialization control lines is preferable from the perspective of reducing flickering of the image displayed on the display device.
It has been found desirable to provide a scan driving circuit capable of supplying signals to the scanning lines, initialization control lines, and display control lines, and capable of supplying multiple pulse signals to the display control lines within one field circuit without affecting the signals supplied to the scanning lines and initialization control lines.
A display device according to an embodiment of the present invention includes:
(1) display elements arrayed in the form of a two-dimensional matrix;
(2) scanning lines, initialization control lines configured to initialize the display elements, and display control lines configured to control lit/unlit states of the display elements, the scanning lines, initialization control lines, and display control lines extending in a first direction;
(3) data lines extending in a second direction different from the first direction; and
(4) a scan driving circuit.
A scan driving circuit according to the present invention, and also configuring the display device according to the present invention, includes:
(A) a shift register unit configured of P (wherein P is a natural number of 3 or greater) stages of shift registers, to sequentially shift input start pulses and output output signals from each stage, and
(B) a logic circuit unit configured to operate based on output signals from the shift register unit, and enable signals,
(C) where, with the output signals of a p'th (where p=1, 2, . . . P−1) stage shift register represented as STp, the start of a start pulse of an output signal STp+1 of a p+1'th shift register is situated between the start and end of a start pulse of the output signal STp,
(D) and where one each of a first enable signal through a Q'th enable signal (where Q is a natural number of 2 or greater) exist in sequence between the start of the start pulse of the output signal STp and the start of the start pulse of the output signal STp+1,
(E) and wherein the logic circuit unit includes (P−2)×Q NAND circuits;
wherein a first start pulse through a U'th (where U is a natural number of 2 or greater) start pulse are input to a first stage shift register during a period equivalent to one field period;
and wherein period identifying signals are input to the logic circuit unit to identify each period from a u'th (where u=1, 2, . . . U−1) start pulse in an output signal ST1 to a u+1'th start pulse, and a period from the start of the U'th start pulse to the start of the first start pulse in the next frame;
and wherein, with a q'th enable signal (where q=1, 2, . . . Q−1) represented as ENq, a signal based on a period identifying signal, the output signal STp, a signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq, are input to a (p′, q)'th NAND circuit;
and wherein the operations of the NAND circuit are restricted based on period identifying signals, such that the NAND circuit generates scanning signals based only on a portion of the output signal STp corresponding to the first start pulse, the signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq.
With the display device according to an embodiment of the present invention, with regard to a display element receiving supply of signals based on scanning signals from the (p′, q)'th NAND circuit (except for a case wherein (p′=1, q=1) via a scanning line,
a signal based on a scanning signal from a (p′−1, q′)'th NAND circuit in the event that q=1 holds, and a signal based on a scanning signal from a (p′, q′′)'th (wherein q′′ is a natural number from 1 through (q−1)) NAND circuit in the event that q>1 holds, are supplied from an initialization control line connected to the display element, and
a signal based on the output signal STp+1 from a p′+1'th shift register in the event that q=1 holds, and a signal based on an output signal STp+2 from a p′+2'th shift register in the event that q>1 holds, are supplied from a display control line connected to the display element.
Now, from the perspective of shortening the length of wiring from the initialization control line to a predetermined NAND circuit, with a display element where signals based on scanning signals from the (p′, q)'th NAND circuit are supplied via a scanning line, a configuration is preferable wherein a signal based on a scanning signal from a (p′−1, q′)'th NAND circuit in the event that q=1 holds, and signals based on scanning signals from a (p′, q−1)'th NAND circuit in the event that q>1 holds, are supplied from an initialization control line connected to the display element.
With a configuration wherein a first start pulse and a second start pulse are input to a first stage shift register within a period equivalent to one field period, an arrangement may be made wherein a period identifying signals is a signal which is at a low level or a high level in a period from the start of the first start pulse to the start of the second start pulse, and is at a high level or a low level in a period from the start of the second start pulse to the start of the first start pulse in the next frame. Thus, two periods can be identified using a single period identifying signal. Also, with a configuration wherein a first start pulse through a fourth start pulse are input to a first stage shift register within a period equivalent to one field period, an arrangement may be made wherein the period identifying signal is configured of a first period identifying signal and a second period identifying signal, thereby enabling identifying of four periods with the combination of high/low level of the first period identifying signal and second period identifying signal.
An arrangement may be made wherein, in a period including a period where the portion of the output signal ST1, corresponding to the first start pulse is applied, a signal based on the period identifying signal is applied to the input side of the (p′, q)'th NAND circuit, such that a signal based on the period identifying signal goes to a high level, but otherwise is at a low level. Note that in the event that the period identifying signal is configured of a first period identifying signal and a second period identifying signal, a signal based on the period identifying signal may be applied to the input side of the (p′, q)'th NAND circuit such that a signal based on the first period identifying signal and a signal based on the second period identifying signal both go to a high level only in the period including a period where the portion of the output signal STp′ corresponding to the first start pulse is applied. More specifically, it is sufficient for the period identifying signal to be input to the input side of the NAND circuit, either directly or via a NOR circuit, such that the above-described conditions are satisfied. Accordingly, the operations of the (p′, q)'th NAND circuit are restricted, and the NAND circuit only generates scanning signals based on the portion of the output signal STP corresponding to the first start pulse, the signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq.
With the display device according to an embodiment of the present invention having the scan driving circuit according to an embodiment of the present invention, signals for the scanning lines, initialization control lines, and display control lines, are supplied based on signals from the scan driving circuit. Accordingly, reduction in layout area of the circuits and reduction of circuit costs can be realized. Values of P and Q, and/or the value of U, should be set as appropriate for the specifications and so forth of the scan driving circuit and display device.
Also, with the display device according to an embodiment of the present invention, the display control lines are supplied with signals based on output signals from shift registers making up the scan driving circuit. With the scan driving circuit according to an embodiment of the present invention, a first start pulse through a U'th start pulse are input to the first stage shift register in a period equivalent to one field period. However, scanning signals output from the NAND circuit are not affected by the number of start pulses input to the first stage shift register. Accordingly, multiple pulse signals can be supplied to a display control line within one field period without affecting signals supplied to scanning lines and initialization control lines, by a simple arrangement of changing the number of start pulses input to the first stage shift register.
Note that the scanning signals from the NAND circuit and the output signals from the shift register should be inverted as appropriate and then supplied, depending on the polarity and the like of the transistors making up the display element. The term “a signal based on a scanning signal” may refer to the scanning signal itself, or may refer to a signal where the polarity of the scanning signal has been inverted. In the same way, the term “a signal based on an output signal from the shift register” may refer to the output signal from the shift register itself, or may refer to a signal where the polarity of the output signal from the shift register has been inverted.
The scan driving circuit according to an embodiment of the present invention can be manufactured by widely-employed semiconductor manufacturing techniques. The shift registers making up the shift register unit, the NAND circuits and NOR circuits configuring the logic circuit unit may be configurations and structures which are widely employed. The scan driving circuit may be configured as an independent circuit, or may be configured integrally with the display device. For example, in the event that the display elements configuring the display device have transistors, the scan driving circuit can be manufactured at the same time with the process for manufacturing the display elements.
With the display device according to an embodiment including various preferred configurations, display elements of a configuration so as to be scanned by signals from scanning lines and subjected to an initialization process based on signals from initialization control lines, and further display elements of a configuration wherein display periods and non-display periods are switched by signals from display control lines, can be widely used.
The display elements configuring the display device according to an embodiment of the present invention may include:
(1-1) a driving circuit including a write transistor, a driving transistor, and a capacitance unit; and
(1-2) a light emitting unit to which current is applied via the driving transistor. The light-emitting unit may be configured of a light emitting unit which emits light under application of electric current, examples of which include an organic electroluminescence unit, an inorganic electroluminescence unit, an LED light emitting unit, a semiconductor laser light emitting unit, and so forth. Of these, a configuration of light emitting units which are organic electroluminescence units is preferable from the perspective of configuring a flat display device for color display.
With the driving circuit configuring the display element as described above (hereinafter, may be referred to as “driving circuit configuring the display element according to an embodiment of the present invention”), an arrangement may be made wherein,
with regard to the write transistor,

    
    
        (a-1) one source/drain region is connected to the data line, and
        (a-2) the gate electrode is connected to the scanning line;
    
    


and wherein, with regard to the driving transistor,

    
    
        (b-1) one source/drain region is connected to the other source/drain region of the write transistor, thereby configuring a first node;
    
    


and wherein, with regard to the capacitance unit,

    
    
        (c-1) a predetermined reference voltage is applied to one end thereof, and
        (c-2) the other end is connected with the gate electrode of the driving transistor, thereby configuring a second node;
    
    


and wherein the write transistor is controlled by signals from the scanning line.
The driving circuit configuring the display element according to an embodiment of the present invention may further include
(d) a first switch circuit unit connected between the second node and the other source/drain region of the driving transistor;
wherein the first switch circuit unit is controlled by signals from the scanning line.
The driving circuit configuring the display element including the above-described preferred configuration of an embodiment of the present invention may further include
(e) a second switch circuit unit connected between the second node and a power supply line to which a predetermined initialization voltage is applied;
wherein the second switch circuit unit is controlled by signals from the initialization control line.
The driving circuit configuring the display element including the above-described preferred configuration of an embodiment of the present invention may further include
(f) a third switch circuit unit connected between the first node and a power supply line to which a driving voltage is applied;
wherein the third switch circuit unit is controlled by signals from the display control line.
The driving circuit configuring the display element including the above-described preferred configuration of an embodiment of the present invention may further include
(g) a fourth switch circuit unit connected between the other source/drain region of the driving transistor and one end of the light emitting unit;
wherein the fourth switch circuit unit is controlled by signals from the display control line.
With a display device having a driving circuit including the above-described first switch circuit unit through fourth switch circuit unit, the light emitting unit may be driven by
(a) performing an initialization process of applying a predetermined initial voltage from a power supply line to a second node via the second switch circuit unit in an on state, following which the second switch circuit unit is placed in an off state, thereby setting the potential of the second node to a predetermined reference potential;
(b) performing a writing process of maintaining the off state of the second switch circuit unit, third switch circuit unit, and fourth switch circuit unit, while placing the first switch circuit unit in an on state, and in a state where the second node and the other source/drain region of the driving transistor are electrically connected by the first switch circuit unit in the on state, a video signal is applied to the first node form the data line via the write transistor placed in an on state by a signal from the scanning line, thereby changing the potential of the second node toward a potential which can be calculated by subtracting the threshold voltage of the driving transistor from the video signal;
(c) subsequently placing the write transistor in an off state by a signal from the scanning line; and
(d) and subsequently maintaining the off state of the first switch circuit unit and second switch circuit unit while electrically connecting the other source/drain region of the driving transistor to one end of the light emitting unit via the fourth switch circuit unit in the on state, and applying a predetermined driving voltage to the first node from the power supply line via the third switch circuit unit in the on state, thereby applying current to the light emitting unit via the driving transistor, and thus driving the light emitting unit.
With the driving circuit configuring the display device according to an embodiment of the present invention, a predetermined reference voltage is applied to one end of the capacitance unit, whereby the potential at the one end of the capacitance unit is maintained when the display device is operating. The value of the predetermined reference voltage is not restricted in particular. For example, a configuration may be made wherein one end of the capacitance unit is connected to a power supply line for applying predetermined voltage to the other end of the light emitting unit, so that the predetermined voltage is applied as the reference voltage.
With the display device according to an embodiment of the present invention including the above-described various preferred configurations, the configurations and structures of various wiring such as the scanning lines, initialization control lines, display control lines data lines, power supply lines, and so forth, may be of configurations and structures widely in use. Also, the configuration and structure of the light emitting unit may be of configurations and structures widely in use. Specifically, in the case of forming the light emitting unit as an organic electroluminescence light emitting unit, the light emitting unit may be configured of an anode electrode, hole transporting layer, emissive layer, electron transporting layer, cathode electrode, and so forth. Also, the configuration and structure of the signal output circuit connected to the data line, and so forth, may be of configurations and structures widely in use.
The display device according to an embodiment of the present invention may be of a so-called black-and-white display configuration, or may be of a configuration wherein each pixel is configured of multiple sub-pixels, specifically, a configuration wherein a pixel is confirmed of the three sub pixels of a red light emitting sub-pixel, a green light emitting sub-pixel, and a blue light emitting sub-pixel. Further, a pixel may be configured of a set where one type of multiple types of sub-pixels are added to the above three types of sub pixels (e.g., a set wherein a sub-pixel emitting white light is added for improving luminance, set wherein a sub-pixel emitting a complementary color is added for expanding the range of color reproduction, a set wherein a sub-pixel emitting yellow light is added for expanding the range of color reproduction, a set wherein sub-pixels emitting yellow and cyan light are added for expanding the range of color reproduction).
Examples of image display resolution regarding the number of pixels of the display device include, but are not restricted to, VGA (640, 480), S-VGA (800, 600), XGA (1024, 768), APRC (1152, 900), S-XGA (1280, 1024), U-XGA (1600, 1200), HD-TV (1920, 1080), Q-XGA (2048, 1536) and so forth, and also (1920, 1035), (720, 480), (1280, 960) and so forth. In the case of a black-and-white display device, basically, display elements of the same number as the number of pixels are formed in matrix fashion. In the case of a color display device, basically, display elements threefold the number of pixels are formed in matrix fashion. The display elements may be formed in a striped array, or in a delta array, and should be arrayed as appropriate in accordance with the design of the display device.
With the driving circuit making up the display element according to an embodiment of the present invention, the write transistor and driving transistor may be configured of p-channel type thin-film transistors (TFT), for example. Note that the write transistor may be an n-channel type instead. The first switch circuit unit, second switch circuit unit, third switch circuit unit, and fourth switch circuit unit may be configured of widely-used switching devices such as TFTs, and may be p-channel type TFTs or re-channel type TFTs, for example.
With the driving circuit making up the display element according to an embodiment of the present invention, the capacitance unit making up the driving circuit may be configured of one electrode, another electrode, and a dielectric layer (insulating layer) between these electrodes. The transistors and capacitance unit making up the driving circuit may be formed within a certain plane, and formed on a supporting body, for example. In the event that the light emitting unit is to be an organic electroluminescence light emitting unit, the light emitting unit may be formed above the transistors and capacitance unit making up the driving circuit. Also, the other source/drain region of the driving transistor may be connected to one end of the light emitting unit (anode electrode provided to the light emitting unit, etc.) via another transistor, for example. Also note that a configuration may be employed wherein transistors are formed on a semiconductor substrate.
Note that in the Present Specification, the term “one source/drain region” may be used regarding the one of the two source/drain regions which a transistor has, which is connected to the power source side. Also, the term that a transistor is in an “on state” means that a channel is formed between the source/drain regions, regardless of whether or not current is flowing from one source/drain region to the other source/drain region. Conversely, the term that a transistor is in an “off state” means that no channel is formed between the source/drain regions. The expression that a source/drain region of a certain transistor is connected to a source/drain region of another transistor means that the source/drain region of the certain transistor and the source/drain region of the other transistor occupy the same region. Further, the source/drain regions are not restricted to being configured of impurity-doped polysilicon, amorphous silicon, and the like, and may also be configured of layered strictures thereof, or layers of organic material (electroconductive polymers). Moreover, in the timing charts used for description in the Present Specification, it should be noted that the length of the horizontal axis representing periods (length of time) is a schematic representation, not necessarily indicating the ratio of duration of the time periods.
With the display device according to an embodiment of the present invention having the scan driving circuit according to an embodiment of the present invention, signals for the scanning lines, initialization control lines, and display control lines, are supplied based on signals from the scan driving circuit. Accordingly, reduction in layout area of the circuits and reduction of circuit costs can be realized.
With the scan driving circuit according to an embodiment of the present invention, multiple pulse signals can be supplied to a display control line within one field period without affecting signals supplied to scanning lines and initialization control lines, by a simple arrangement of changing the number of start pulses input to the first stage shift register. Also, with the display device according to an embodiment of the present invention, flickering of the image displayed on the display device can be reduced by a simple arrangement of changing the number of start pulses input to the first stage shift register configuring the scan driving circuit.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of a scan driving circuit according to a first embodiment;
FIG. 2 is a conceptual diagram of a display device according to the first embodiment, including the scan driving circuit shown in FIG. 1;
FIG. 3 is a schematic timing chart of a shift register unit making up the scan driving circuit shown in FIG. 1;
FIG. 4 is a schematic timing chart of an upstream stage of a logic circuit unit making up the scan driving circuit shown in FIG. 1;
FIG. 5 is a schematic timing chart of a downstream stage of a logic circuit unit making up the scan driving circuit shown in FIG. 1;
FIG. 6 is an equivalent circuit diagram of a driving circuit making up a display element at the m'th row and n'th column of the display device shown in FIG. 2;
FIG. 7 is a partial cross-sectional diagram of a portion of a display element making up the display device shown in FIG. 2;
FIG. 8 is a schematic driving timing chart of a display element at the m'th row and n'th column;
FIGS. 9A and 9B are diagrams schematically illustrating the on/off states of the transistors in the driving circuit making up the display element at the m'th row and n'th column;
FIGS. 10A and 10B are diagrams continuing from FIGS. 9A and 9B, schematically illustrating the on/off states of the transistors in the driving circuit making up the display element at the m'th row and n'th column;
FIGS. 11A and 11B are diagrams continuing from FIGS. 10A and 10B, schematically illustrating the on/off states of the transistors in the driving circuit making up the display element at the m'th row and n'th column;
FIGS. 12A and 12B are diagrams continuing from FIGS. 11A and 11B, schematically illustrating the on/off states of the transistors in the driving circuit making up the display element at the m'th row and n'th column;
FIG. 13 is a circuit diagram of a scan driving circuit according to a comparative example;
FIG. 14 is a timing chart of the scan driving circuit shown in FIG. 13 regarding the leading edges of start pulses between the start and end of a period T1 and trailing edges of start pulses between the start and end of a period T5;
FIG. 15 is a timing chart illustrating a case at the scan driving circuit according to the comparative example wherein a first start pulse and a second start pulse have been input to a first stage shift register during a period equivalent to one field period;
FIG. 16 is a circuit diagram of a scan driving circuit according to a second embodiment;
FIG. 17 is a schematic timing chart of a shift register unit making up the scan driving circuit shown in FIG. 16;
FIG. 18 is a schematic timing chart of an upstream stage of a logic circuit unit making up the scan driving circuit shown in FIG. 16;
FIG. 19 is a schematic timing chart of a downstream stage of a logic circuit unit making up the scan driving circuit shown in FIG. 16;
FIG. 20 is a circuit diagram of a driving circuit making up a display element at the m'th row and n'th column;
FIG. 21 is a circuit diagram of a scan driving circuit according to a third embodiment;
FIG. 22 is a schematic timing chart of a shift register unit making up the scan driving circuit shown in FIG. 21;
FIG. 23 is a schematic timing chart of an upstream stage of a logic circuit unit making up the scan driving circuit shown in FIG. 21;
FIG. 24 is a schematic timing chart of a downstream stage of a logic circuit unit making up the scan driving circuit shown in FIG. 21;
FIG. 25 is a circuit diagram of a driving circuit making up a display element at the m'th row and n'th column;
FIG. 26 is an equivalent circuit diagram of a driving circuit making up a display element at the m'th row and n'th column in a display device where display elements are arrayed in two-dimensional matrix fashion;
FIG. 27A is a schematic timing chart of signals on an initialization control line, scanning line, and display control line;
FIG. 27B is a schematic diagram illustrating the on/off states of the transistors of the driving circuit; and
FIGS. 28A and 28B are diagrams continuing from FIG. 27B, schematically illustrating the on/off states of the transistors in the driving circuit.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be described with reference to the drawings.
First Embodiment
The first embodiment relates to a scan driving circuit and to a display device having the scan driving circuit. The display device according to the first embodiment is a display device which uses display elements having a light emitting unit and a driving circuit thereof.
FIG. 1 is a circuit diagram of a scan driving circuit 110 according to the first embodiment, FIG. 2 is a conceptual diagram of a display device 1 according to the first embodiment, including the scan driving circuit shown in FIG. 1, FIG. 3 is a schematic timing chart of a shift register unit 111 configuring the scan driving circuit 110 shown in FIG. 1, FIG. 4 is a schematic timing chart of an upstream stage of a logic circuit unit 112 configuring the scan driving circuit 110 shown in FIG. 1, FIG. 5 is a schematic timing chart of a downstream stage of the logic circuit unit 112 making up the scan driving circuit 110 shown in FIG. 1, and FIG. 6 is an equivalent circuit diagram of a driving circuit 11 making up a display element 10 at the m'th (where m=1, 2, 3 . . . M) row and n'th (where n=1, 2, 3 . . . N) column of the display device shown in FIG. 2.
First, the overview of the display device 1 will be described. As shown in FIG. 2, the display device 1 includes:
(1) display elements 10 arrayed in the form of a two-dimensional matrix;
(2) scanning lines SCL, initialization control lines AZ configured to initialize the display elements 10, and display control lines CL configured to control lit/unlit states of the display elements, extending in a first direction;
(3) data lines DTL extending in a second direction different from the first direction; and
(4) a scan driving circuit 110. The scanning lines SCL, initialization control lines AZ, and display control lines CL are connected to the scan driving circuit 110. The data lines DTL are connected to a signal output circuit 100. Note that in FIG. 2, 3×3 display elements 10 are shown centered on a display element 10 at the m'th row and n'th column, but this is only an exemplary illustration. Also, the power supply lines PS1, PS2, and PS3, shown in FIG. 6, have been omitted from FIG. 2.
N display elements 10 are arrayed in the first direction and M are arrayed in the second direction which is different from the first direction. The display device 1 is configured of N/3×M pixels arrayed on a two-dimensional matrix form. One pixel is configured of three sub-pixels (a red light emitting sub-pixel which emits red light, a green light emitting sub-pixel which emits green light, and a blue light emitting sub-pixel which emits blue light). The display elements 10 making up the pixels are driven in line sequence, at a display frame rate of FR (times/second). That is to say, the display elements 10 making up of each of the N/3 pixels arrayed at the m'th row (N sub-pixels) are driven at the same time. In other words, the lit/unlit timing of the display elements 10 making up one row are subjected to control in increments of the row to which they belong.
As shown in FIG. 6, a display element 10 is configured of a driving circuit 11 having a write transistor TRW, driving transistor TRD, and capacitance unit C1, and a light emitting unit ELP to which current is applied via the driving transistor TRD. The light emitting unit ELP is configured of an electroluminescence light emitting unit. The display element 10 has a structure wherein the driving circuit 11 and the light emitting unit ELP are layered. The driving circuit 11 further has a first transistor TR1, second transistor TR2, third transistor TR3, and fourth transistor TR4; these transistors will be described later.
With the display element 10 at the m'th row and n'th column, one source/drain region of the write transistor TRW us connected to the data line DTLn, and the gate electrode is connected to the scanning line SCLm. At the driving transistor TRD, one source/drain region is connected to the other source/drain region of the write transistor TRW, thereby configuring a first node ND1. One end of the capacitance unit C1 is connected to the power supply line PS1. At the capacitance unit C1, a predetermined reference voltage (a later-described predetermined driving voltage VCC in the first embodiment) is applied to one end thereof, and the other end thereof is connected to the gate electrode of the driving transistor TRD, thereby configuring a second node ND2. The write transistor TRW is controlled by signals from the scanning line SCLm.
Video signals (driving signals, luminance signals) VSig are applied to the data line DTLn from the signal output circuit 100 to control luminance a the light emitting unit ELP, a point which will be described later.
The driving circuit 11 further has a first switch circuit unit SW1 connected between the second node ND2 and the other source/drain region of the driving transistor TRD. The first switch circuit unit SW1 is configured of the first transistor TR1. At the first transistor TR1, one source/drain region is connected to the second node ND2, and the other source/drain region is connected to the other source/drain region of the driving transistor TRD. The gate electrode of the first transistor TR1 is connected to the scanning line SCLm, and the first transistor TR1 is controlled by signals from the scanning line SCLm.
The driving circuit 11 further has a second switch circuit unit SW2 connected between the second node ND2 and the power supply line PS3 to which the later-described predetermined initialization voltage VIni is applied. The second switch circuit unit SW2 is configured of the second transistor TR2. At the second transistor TR2, one source/drain region is connected to the power supply line PS3, and the other source/drain region is connected to the second node ND2. The gate electrode of the second transistor TR2 is connected to the initialization control line AZm, and the second transistor TR2 is controlled by signals from the initialization control line AZm.
The driving circuit 11 further has a third switch circuit unit SW3 connected between the first node ND1 and the power supply line PS1 to which the driving voltage VCC is applied. The third switch circuit unit SW3 is configured of the third transistor TR3. At the third transistor TR3, one source/drain region is connected to the power supply line PS1, and the other source/drain region is connected to the first node ND1. The gate electrode of the third transistor TR3 is connected to the display control line CLm, and the third transistor TR3 is controlled by signals from the display control line CLm.
The driving circuit 11 further has a fourth switch circuit unit SW4 connected between the other source/drain region of the driving transistor TRD and one end of the light emitting unit ELP. The fourth switch circuit unit SW4 is configured of the fourth transistor TR4. At the fourth transistor TR4, one source/drain region is connected to other source/drain region of the driving transistor TRD, and the other source/drain region is connected to one end of the light emitting unit ELP. The gate electrode of the fourth transistor TR4 is connected to the display control line CLm, and the fourth transistor TR4 is controlled by signals from the display control line CLm. The other end of the light emitting unit ELP (cathode electrode) is connected to the power supply line PS2, whereby a later-described voltage VCat is applied. The symbol CEL represents the capacitance of the light emitting unit ELP.
The driving transistor TRD is configured of a p-channel type TFT, and the write transistor TRW also is configured of a p-channel type TFT. Further, the first transistor TR1, second transistor TR2, third transistor TR3, and fourth transistor TR4 are also configured of a p-channel type TFTs. Note that the write transistor TRW may be configured of an n-channel type TFT instead. The transistors are described as being depression type transistors, but are not restricted to this.
Widely-used configurations and structures may be used for the configurations and structures of the signal output circuit 100, scanning lines SCL, initialization control lines AZ, display control lines CL, and data lines DTL. The power supply lines PS1, PS2, and PS3 extending in the same first direction as the scanning lines SCL are connected to an unshown power source unit. The driving voltage VCC is applied to the power supply line PS1, the voltage Vcat is applied to the power supply line PS2, and the initialization voltage VIni is applied to the power supply line PS3. Widely-used configurations and structures may be used for the configurations and structures of the power supply lines PS1, PS2, and PS3 as well.
FIG. 7 is a partial cross-sectional diagram of a portion of a display element 10 making up the display device 1 shown in FIG. 2. Each transistor and the capacitance unit C1 making up the driving circuit 11 of the display element 10 are formed on a supporting body 20, and the light emitting unit ELP is formed above the transistors and the capacitance unit C1 making up the driving circuit 11, with an inter-layer insulating layer 40 introduced therebetween, an arrangement which will be described later. The light emitting unit ELP has a widely-used configuration and structure of an anode electrode, hole transporting layer, emissive layer, electron transporting layer, cathode electrode, and so forth, for example. Note that in FIG. 7, only the driving transistor TRD is shown, and other transistors are hidden and are not visible. The other source/drain region of the driving transistor TRD is electrically connected to an anode electrode provided to the light emitting unit ELP via the unshown fourth transistor TR4, the connection between the fourth transistor TR4 and the anode electrode of the light emitting unit ELP also not being visible.
The driving transistor TRD is configured of a gate electrode 31, gate insulating layer 32, and semiconductor layer 33. More specifically, the driving transistor TRD has a channel formation region 34 corresponding to the semiconductor layer 33 between the one source/drain region 35 and the other source/drain region 36 provided to the semiconductor layer 33. The other unshown transistors are also of similar configuration.
The capacitance unit C1 is configured of an electrode 37, a dielectric layer configured of an extended portion of the gate insulating layer 32, and an electrode 38. Note that the connection between the electrode 37 and the gate electrode 31 of the driving transistor TRD, and the connection between the electrode 38 and the power supply line PS1, are not visible.
The gate electrode 31, part of the gate insulating layer 32, and the electrode 37 making up the capacitance unit C1, are formed on the supporting body 20. The driving transistor TRD and capacitance unit C1 and so forth are covered with the inter-layer insulating layer 40, with the light emitting unit ELP configured of an anode electrode 51, hole transporting layer, emissive layer, electron transporting layer, and cathode electrode 53 provided upon the inter-layer insulating layer 40. Note that in FIG. 7, the hole transporting layer, emissive layer, and electron transporting layer are represented with a single layer 52. A second inter-layer insulating layer 54 is provided on the inter-layer insulating layer 40 where the light emitting unit ELP is not provided, a transparent substrate 21 us disposed above the second inter-layer insulating layer 54 and cathode electrode 53, and the light emitted at the emissive layer is externally emitted through the substrate 21. Wiring 39 making up the cathode electrode 53 and power supply line PS2 is connected thereto via contact holes 56 and 55 provided in the second inter-layer insulating layer 54 and inter-layer insulating layer 40, respectively.
A manufacturing method of the display device shown in FIG. 7 will be described. First, the various types of wiring for the scanning lines and so forth, electrodes making up the capacitance units, transistors formed of semiconductor layers, inter-layer insulating layers, contact holes, and so forth, are formed on the supporting body 20 by techniques which are widely employed. Next, film formation and patterning is performed by techniques which are widely employed, thereby forming light emitting units ELP arrayed in matrix fashion. The supporting body 20 which has been subjected to the above processes is made to face a substrate 21 and the perimeter thereof is sealed. This is then connected with the signal output circuit 100 and scan driving circuit 110, whereby a display device can be completed.
Next, the scan driving circuit 110 will be described. Note that description of the scan driving circuit 110 will be made with reference to an arrangement wherein scanning signals for supply to scanning line SCL1 through scanning line SCL31 in line sequence, to facilitate description. Description will be made in this way in other embodiments as well.
As shown in FIG. 1, the scan driving circuit 110 includes:
(A) a shift register unit 111 configured of P (wherein P is a natural number of 3 or greater, hereinafter the same) stages of shift registers SR, to sequentially shift input start pulses STP and output output signals ST from each stage; and
(B) a logic circuit unit 112 configured to operate based on output signals ST from the shift register unit 111, and enable signals (with the first embodiment, later-described first enable signal EN1 and second enable signal EN2).
With the output signals of a p'th (where p=1, 2, . . . P−1) stage shift register SRp represented as STp, the start of a start pulse of an output signal STp+1 of a p+1'th shift register SRp+1 is situated between the start and end of a start pulse of the output signal STp, as shown in FIG. 3. The shift register unit 111 operates based on clock signals CK and start pulses STP, so as to satisfy the above conditions.
The first stage shift register SR1 receives input of a first start pulse through a U'th start pulse (wherein U is a natural number of 2 or greater, hereinafter the same) within a period equivalent to one field period (in FIG. 3, a period equivalent from the start of period T1 through the end of period T32. Note that in the first embodiment, U=2, and a first start pulse and a second start pulse are input.
Specifically, the first start pulse input to the first stage shift register SR1 has the leading edge thereof between the start and end of the period T1 shown in FIG. 3, and has the trailing edge thereof between the start and end of the period T13. Also, the second start pulse has the leading edge thereof between the start and end of the period T17 shown in FIG. 3 and has the trailing edge thereof between the start and end of the period T29. Each period such as T1 in FIG. 3 and other later-described drawings correspond to one horizontal scanning period (also represented by “1H”). The clock signal CK is a square wave signal which inverts polarity every two horizontal scanning periods (2H).
The first start pulse in the output signal ST1 of the shift register SR1 has the leading edge thereof at the start of the period T3, and has the trailing edge at the end of period T14. The first pulse in the output signals ST2, ST3, and so on, for the shift register SR2 and subsequent shift registers is a pulse which has been sequentially shifted by two horizontal scanning periods. Also, second start pulse in the output signal ST1 of the shift register SR1 has the leading edge thereof at the start of the period T19, and has the trailing edge at the end of period T30. The first pulse in the output signals ST2, ST3, and so on, for the shift register SR2 and subsequent shift registers is also a pulse which has been sequentially shifted by two horizontal scanning periods.
Also, one each of a first enable signal through a Q'th enable signal (where Q is a natural number of 2 or greater, hereinafter the same) exist in sequence between the start of the first start pulse of the output signal STp and the start of the first start pulse of the output signal STp+1. In the first embodiment Q=2, and there are one each of the first enable signal EN1 and the second enable signal EN2, in sequence. In other words, the first enable signal EN1 and the second enable signal EN2 are signals generated so as to satisfy the above conditions, which basically are square wave signals of the same cycle but with different phases. Note that one each of a first enable signal through a Q'th enable signal also exist in sequence between the start of the second start pulse of the output signal STp and the start of the second start pulse of the output signal STp+1.
Specifically, the first enable signal EN1 and the second enable signal EN2 are square wave signals having two horizontal scanning periods as one cycle. In the first embodiment, these signals invert polarity every horizontal scanning period, and the first enable signal EN1 and the second enable signal EN2 are in inverse phase relation. While FIGS. 3 through 5 show the high level of the enable signals EN1 and EN2 as lasting for one horizontal scanning period, the present invention is not restricted to this arrangement, and the high level may be a square wave signal with a period shorter than one horizontal scanning period, a point which holds true with the other embodiments as well.
For example, there sequentially exist one each of the first enable signal EN1 in the period T3 and the second enable signal EN2 in the period T4, between the start of the start pulse in output signal ST1 (i.e., the start of period T3) and the start of the start pulse in output signal ST2 (i.e., the start of period T3). In the same way, there sequentially exist one each of the first enable signal EN1 and the second enable signal EN2, between the start of the start pulse in output signal ST2 and the start of the start pulse in output signal ST3. This is the same for output signal ST4 and on.
As shown in FIG. 1, the logic circuit unit 112 has (P−2)×Q NAND circuits 113. Specifically, the logic circuit unit 112 has (1, 1)'th through (P−2, 2)'th NAND circuits 113. Period identifying signals SP for identifying each period from the start of the u'th start pulse (where u=1, 2, . . . U−1, hereinafter the same) start pulse in an output signal ST1 to the start of a (u+1)'th start pulse, and a period from the start of the U'th start pulse to the start of the first start pulse in the next frame, are input to the logic circuit unit 112.
In the first embodiment, U=2, and the period identifying signal SP is a signal for identifying the period from the start of the first start pulse in the output signal ST1 to the start of the second start pulse, and the period from the start of the second start pulse in output signal ST1 to the start of the first start pulse in the next frame. In FIGS. 3 through 5, the period from the start of the first start pulse in the output signal ST1 to the start of the second start pulse is a period from the start of period T3 to the end of period T18. Also, the period from the start of the second start pulse in output signal ST1 to the start of the first start pulse in the next frame is a period from the start of period T19 to the end of period T2 in the next frame. In the first embodiment, the period identifying signal SP is a signal which is at high level during the period from the start of period T3 to the end of period T18, and at low level during the period from the start of period T19 to the end of period T2 of the next frame.
With a q'th enable signal (where q is an arbitrary number from 1 to Q, hereinafter the same) represented as ENq, a signal based on the period identifying signal SP, the output signal STp, a signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq, are input to a (p′, q)'th NAND circuit 113 (where p is an arbitrary natural number from 1 to (P−2), hereinafter the same). As described later, the operations of the NAND circuit 113 are restricted based on the period identifying signal SP, such that the NAND circuit 113 generates scanning signals based only on a portion of the output signal STp′ corresponding to the first start pulse, the signal obtained by inverting the output signal STp′+1 and the q'th enable signal ENq.
More specifically, the output signal STp′+1 is inverted by the NOR circuit 114 shown in FIG. 1, and input to the input side of the (p′, q)'th NAND circuit 113. The output signal STp′ and the q'th enable signal ENq are directly input to the input side of the (p′, q)'th NAND circuit 113. Also, the period identifying signal SP is directly input to the input side of the (1, 1)'th through (8, 2)'th NAND circuits 113, as a signal based on the period identifying signal SP. the period identifying signal SP inverted by a NOR circuit 116 shown in FIG. 1 is input to the input side of the (9, 1)'th and subsequent NAND circuits 113, as a signal based on the period identifying signal SP.
As described above, the first start pulse and second start pulse are input to the first stage shift register SR1 within a period equivalent to one field period. If the (p′, q)'th NAND circuit 113 were to operate only by the output signal STp′, a signal obtained by inverting the output signal STp′+1 and the q'th enable signal ENq, the NAND circuit 113 would generate two scanning signals in the one field period. This will be described in detail next.
Let us consider the (8, 1)'th NAND circuit 113. Signals based on the scanning signals from the (8, 1)'th NAND circuit 113 are supplied to the scanning line SCL14. As shown in FIG. 4, in the period T17 in which the scanning signal should be generated, the output signal ST8, the signal obtained by inverting the output signal ST9, and the first enable signal EN1, are at high level. However, the first stage shift register SR1 has also received input of the second start pulse in addition to the first start pulse, so the output signal ST8, the signal obtained by inverting the output signal ST9, and the first enable signal EN1, are at high level in period T1 as well.
Accordingly, if the (8, 1)'th NAND circuit 113 were to operate based only on the output signal ST8, a signal obtained by inverting the output signal ST9, and the first enable signal EN1, trouble would occur in that a scanning signal would be supplied to the scanning line SCL14 not only in the period T17 in which the scanning signal should be generated, but also in the period T1.
In the first embodiment, the operations of the NAND circuit 113 are restricted based on the period identifying signal SP, so trouble where a scanning signal is supplied in the period T1 does not occur. That is to say, the period identifying signal SP is directly input to the input side of the (8, 1)'th NAND circuit 113, as a signal based on the period identifying signal SP, as described above. In period T1, the period identifying signal SP is at a low level. Accordingly, in period T1 the operations of the NAND circuit 113 are restricted, and do not generate a scanning signal. On the other hand, in period T17, the period identifying signal SP is at a high level. Accordingly, the (8, 1)'th NAND circuit 113 generates a scanning signal based only on a portion of the output signal ST8 corresponding to the first start pulse, a signal obtained by inverting the output signal ST9, and the first enable signal EN1.
Let us also consider the (9, 1)'th NAND circuit 113. Signals based on the scanning signals from the (9, 1)'th NAND circuit 113 are supplied to the scanning line SCL16 shown in FIG. 1. A signal based on the period identifying signal SP, the output signal ST9, the signal obtained by inverting the output signal ST10, and the first enable signal EN1, are applied to the input side of the (9, 1)'th NAND circuit 113. Unlike the case of the (8, 1)'th NAND circuit 113, a period identifying signal SP inverted by the NOR circuit 116 is input to the input side of the (9, 1)'th NAND circuit 113 as a signal based on the period identifying signal SP.
As shown in FIG. 5, in the period T19 in which the scanning signal should be generated, the output signal ST9, the signal obtained by inverting the output signal ST10, and the first enable signal EN1, are at high level. However, the first stage shift register SR1 has also received input of the second start pulse in addition to the first start pulse, so the output signal ST9, the signal obtained by inverting the output signal ST19, and the first enable signal EN1, are at high level in period T3 as well. As described above, a period identifying signal SP inverted by the NOR circuit 116 is input to the input side of the (9, 1)'th NAND circuit 113. In period T3, the period identifying signal SP is at a high level, so in period T3 the (9, 1)'th NAND circuit 113 does not generate a scanning signal. On the other hand, in period T19, the period identifying signal SP is at a low level, so the (9, 1)'th NAND circuit 113 generates a scanning signal in period T19.
While description has been made regarding the operations of the (8, 1)'th NAND circuit 113 and the (9, 1)'th NAND circuit 113, the operations are the same for the other NAND circuits 113 as well. The (p′, q)'th NAND circuit 113 generates a scanning signal based only on a portion of the output signal STp′ corresponding to the first start pulse, the signal obtained by inverting the output signal STp′+1 and the q'th enable signal ENq.
Description of the display device 1 will continue. As shown in FIG. 1, signals of the (1, 2)'th NAND circuit 113 are supplied to the scanning line SCL1 connected to the first row of display elements 10, and signals of the (2, 1)'th NAND circuit 113 are supplied to the scanning line SCL2 connected to the second row of display elements 10. This is true for the other scanning line SCL as well. That is to say, signals of the (p′, q)'th NAND circuit 113 (excluding a case wherein p′=1 and q=1) are supplied to the scanning line SCLm connected to the m'th (where m=Q×(p′−1)+q−1) row of display elements 10.
The display elements 10 to which signals based on the scanning signals from the (p′, q)'th NAND circuit 113 are supplied via the scanning line SCLm are supplied with signals based on scanning signals from the (p′−1, q′)'th NAND circuit 113 (where q′ is a natural number from 1 through Q, hereinafter the same) in the event that q=1, and signals based on scanning signals from the (p′, q′′)'th NAND circuit 113 (where q′′ is a natural number from 1 through (q−1), hereinafter the same) in the event that q>1, via the initialization control line AZm connected to the display elements 10.
More specifically, in the first embodiment, the display elements 10 to which signals based on the scanning signals from the (p′, q)'th NAND circuit 113 are supplied via the scanning line SCLm, are supplied with signals based on scanning signals from the (p′−1, Q)'th NAND circuit 113 in the event that q=1, and signals based on scanning signals from the (p′, q−1)'th NAND circuit 113 in the event that q>1, via the initialization control line AZm connected to the display elements 10.
Also, the display control line CLm connected to the display elements 10 is supplied with signals based on the output signal STp′+1 from the (p′+1)'th stage shift register SRp′+1 in the case that q=1, and is supplied with signals based on the output signal STp′+2 from the (p′+2)'th stage shift register SRp′+2 in the case that q>1. Note that the third transistor TR3 and fourth transistor TR4 shown in FIG. 6 are p-channel type transistors, so signals are supplied to the display control line CLm via the NOR circuit 115.
Description will be made in further detail with reference to FIG. 1. For example, looking at the display elements 10 to which signals based on the scanning signals from the (8′, 1)'th NAND circuit 113 are supplied via the scanning line SCL14, the initialization control line AZ14 connected to the display element 10 is supplied with signals based on the scanning signals from the (7′, 2)'th NAND circuit 113. Signals based on the output signal ST9 from the ninth stage shift register SR9 are supplied to the display control line CL14 connected to the display element 10. Also, looking at the display elements 10 to which signals based on the scanning signals from the (8′, 2)'th NAND circuit 113 are supplied via the scanning line SCL15, the initialization control line AZ15 connected to the display element 10 is supplied with signals based on the scanning signals from the (8′, 1)'th NAND circuit 113. Signals based on the output signal ST10 from the tenth stage shift register SR10 are supplied to the display control line CL15 connected to the display element 10.
Next, operation of the display device 1 will be described regarding operations of a display element 10 at the m'th row and n'th column, to which signals of the (p′, q)'th NAND circuit 113 are supplied from the scanning line SCLm. This display element 10 will hereinafter be referred to as “(n, m)'th display element 10” or “(n, m)'th sub-pixel”. Also, the horizontal scanning period of the display elements 10 arrayed on the m'th row (more specifically, the m'th horizontal scanning period of the current display frame) will be referred to simply as “m'th horizontal scanning period”. This will be the same for the other embodiments described later, as well.
FIG. 8 is a schematic driving timing chart of the display element 10 at the m'th row and n'th column. Also, FIGS. 9A and 9B are diagrams schematically illustrating the on/off states of the transistors in the driving circuit 11 making up the display element 10 at the m'th row and n'th column. FIGS. 10A and 10B are diagrams continuing from FIGS. 9A and 9B, schematically illustrating the on/off states of the transistors in the driving circuit 11 making up the display element 10 at the m'th row and n'th column. FIGS. 11A and 11B are diagrams continuing from FIGS. 10A and 10B, schematically illustrating the on/off states of the transistors in the driving circuit 11 making up the display element 10 at the m'th row and n'th column. FIGS. 12A and 12B are diagrams continuing from FIGS. 11A and 11B, schematically illustrating the on/off states of the transistors in the driving circuit 11 making up the display element 10 at the m'th row and n'th column.
Note that, for the sake of facilitating description, p′=8 and q=1, and m=14, when comparing the timing chart in FIG. 8 with FIGS. 3 through 5. Specifically, the timing chart of initialization control line AZ14, scanning line SCL14, and display control line CL14 in FIG. 4 is to be referred to.
In the lit state of the display element 10, the driving transistor TRD is driven so as to apply drain current Ids in accordance with the following Expression (1). In the lit state of the display element 10, the one source/drain region of the driving transistor TRD acts as a source region, and the other source/drain region acts as a drain region. To facilitate description, in the following description, the one source/drain region of the driving transistor TRD may be referred to simply as “source region”, and the other source/drain region simply as “drain region”. We will also say that
μ effective mobility,
L channel length,
W channel width,
Vgs voltage difference between the source region and gate region, and
COX (relative permittivity of gate insulation layer)×(permittivity of vacuum)/(thickness of gate insulation layer).

Ids=k·μ·(Vgs−Vth)2  (1)

Also, while the following voltage and potential values will be used in the first embodiment and later-described other embodiments, these are only values for explanatory purposes, and the present invention is not restricted to these values.
VSig Video signal for controlling the luminance at the light emitting unit ELP
0 volts (maximum luminance) to 8 volts (minimum luminance)
VCC Driving voltage
10 volts
VIni Initialization voltage for initializing the potential of the second node ND2 
−4 volts
Vth Threshold voltage of driving transistor TRD 
2 volts
Vcat Voltage applied to power supply line PS2 
−10 volts
Period TP(1)−2 (See FIGS. 8A through 9A)
The Period TP(1)−2 is a period in which the (n, m)'th display element 10 is in a lit state, in accordance with the video signal V′Sig written thereto earlier. For example, in the case of m=14, the Period TP(1)−2 corresponds to the period from the start of the period T′3 (period corresponding to period T3 shown in FIG. 4 in the preceding frame) to the end of the period T14. The initialization control line AZ14 and scanning line SCL14 are at the high level, and the display control line CL14 is at the low level.
Accordingly, the write transistor TRW, first transistor TR1, and second transistor TR2 are in an off state. The third transistor TR3 and fourth transistor TR4 are in an on state. The light emitting unit ELP at the display element 10 making up the (n, m)'th display element 10 has applied thereto a drain current I′ds based on a later-described Expression (5), and the luminance of the display element 10 configuring the (n, m)'th sub-pixels is a value corresponding to this drain current I′ds.
Period TP(1)−1 (See FIGS. 8A, 8B, and 9B)
The (n, m)'th display element 10 is in an unlit state from this Period TP(1)−1 is to a later-described Period TP(1)2. For example, in the case of m=14, the Period TP(1)−1 corresponds to the period T′15 in FIG. 4. The initialization control line AZ14 and scanning line SCL14 maintain the high level, and the display control line CL14 goes to the high level.
Accordingly, the write transistor TRW, first transistor TR1, and second transistor TR2 maintain the off state. The third transistor TR3 and fourth transistor TR4 go from the on state to the off state. Thus, the first node ND1 is in a state of being cut off from the power supply line PS1, and further, the light emitting unit ELP and driving transistor TRD are in a state of being cut off. Accordingly, current does not flow to the light emitting unit ELP, which is accordingly in an off state.
Period TP(1)0 (See FIGS. 8A, 8B, and 10A)
The Period TP(1)0 is the (m−1)'th horizontal scanning period in the current display frame. For example, in the case of m=14, the Period TP(1)0 corresponds to the period T16 in FIG. 4. The scanning line SCL14 and the display control line CL14 maintain the high level. The initialization control line AZ14 goes to the low level, and then goes to the high level at the end of the period T16.
In this Period TP(1)0, the first switch circuit unit SW1, third switch circuit unit SW3, and fourth switch circuit unit SW4 maintain the off state, and following applying the predetermined initialization voltage VIni from the power supply line PS3 to the second node ND2 via the second switch circuit unit SW2 placed in the on state, the second switch circuit unit SW2 is set to an off state, thereby performing an initialization process for setting the potential of the second node ND2 to the predetermined reference potential.
That is to say, the write transistor TRW, first transistor TR1, third transistor TR3, and fourth transistor TR4 are in an off state. The second transistor TR2 goes from an off state to an on state, and the predetermined initialization voltage VIni is applied from the power supply line PS3 via the second transistor TR2 placed in the on state. At the end of the Period TP(1)0, the second transistor TR2 goes to the off state. The driving voltage VCC is applied to one end of the capacitance unit C1 such that the potential at the one end of the capacitance unit C1 is in a maintained state, so the potential of the second node ND2 is set to the predetermined reference voltage (−4 volts) by the initialization voltage VIni.
Period TP(1)1 (See FIGS. 8A, 8B, and 10B)
The Period TP(1)1 is the m'th horizontal scanning period in the current display frame. For example, in the case of m=14, the Period TP(1)1 corresponds to the period T17 in FIG. 4. The initialization control line AZ14 and the display control line CL14 are at the high level, and the scanning line SCL14 goes to the low level.
In this Period TP(1)1, the second switch circuit unit SW2, third switch circuit unit SW3, and fourth switch circuit unit SW4 maintain the off state, the first switch circuit unit SW1 is placed in an on state, and in a state wherein the second node ND2 and the other source/drain region of the driving transistor TRD are electrically connected by the first switch circuit unit SW1 in the on state, the video signal VSig is applied from the data line DTLn to the first node ND1 via the write transistor TRW placed in the on state by the signals from the scanning line SCLm, thereby performing a writing process for changing the potential of the second node ND2 toward a potential which can be calculated by subtracting the threshold voltage Vth of the driving transistor TRD from the video signal VSig.
That is to say, the off state of the second transistor TR2, third transistor TR3, and fourth transistor TR4 is maintained. The write transistor TRW and first transistor TR1 are placed in an one state by signals from the scanning line SCLm. The second node ND2 and the other source/drain region of the driving transistor TRD are placed in an electrically connected state via the first transistor TR1 in the on state. Also, the video signal VSig is applied from the data line DTLn to the first node ND1 via the write transistor TRW which has been placed in the on state by the signal from the scanning line SCLm. Accordingly, the potential of the second node ND2 changes toward a potential which can be calculated by subtracting the threshold voltage Vth of the driving transistor TRD from the video signal VSig.
That is to say, due to the above-described initialization process, the potential of the second node ND2 is initialized such that the driving transistor TRD is in an on state at the start of the Period TP(1)1, so the potential of the second node ND2 changes toward the potential of the video signal VSig applied to the first node ND1. However, upon the potential difference between the gate electrode of the driving transistor TRD and the one source/drain region reaching the threshold voltage Vth, the driving transistor TRD goes to an off state. In this state, the potential of the second node ND2 is approximately (VSig−Vth). The voltage VND2 of the second node ND2 is as expressed in the following Expression (2). Before the (m+1)'th horizontal scanning period starts, the write transistor TRW and first transistor TR1 are placed in an off state by signals from the scanning line SCLm.

VND2≈(VSig−Vth)  (2)

Period TP(1)2 (See FIGS. 8A, 8B, 11A)

The Period TP(1)2 is a period up to the emitting period starting following the writing process, and the (n, m)'th display element 10 is in an unlit state. For example, in the case of m=14, the Period TP(1)2 corresponds to the period T18 in FIG. 4. The scanning line SCL14 goes to the high level, and the initialization control line AZ14 and display control line CL14 maintain the high level.
Accordingly, the write transistor TRW and first transistor TR1 go to an off state, and the second transistor TR2, third transistor TR3, and fourth transistor TR4 maintain the off state. The first node ND1 maintains the state of being cut off from the power supply line PS1, and the light emitting unit ELP and driving transistor TRD maintain the state of being cut off. The potential VND2 of the second node ND2 maintains the above Expression (2) due to the capacitance unit C1.
Period TP(1)3 (See FIGS. 8A, 8B, 11B)
In this Period TP(1)3, the first switch circuit unit SW1 and second switch circuit unit SW2 maintain the off state, the other source/drain region of the driving transistor TRD and the one end of the light emitting unit ELP are electrically connected via the fourth switch circuit unit SW4 placed in an on state, the predetermined driving voltage VCC is applied to the first node ND1 from the power supply line PS1 via the third switch circuit unit SW3 placed on the on state, thereby performing an emitting process for driving the light emitting unit ELP by applying current to the light emitting unit ELP via the driving transistor TRD.
For example, in the case of m=14, the Period TP(1)3 corresponds to the period from the start of period T19 to the end of period T30 in FIG. 4. The initialization control line AZ14 and scanning line SCL14 maintain the high level and the display control line CL14 goes to the low level.
That is to say, the first transistor TR1 and second transistor TR2 maintain the off state, and the third transistor TR3 and fourth transistor TR4 go from the off state to the on state due to signals from the display control line CLm. The predetermined driving voltage VCC is applied to the first node ND1 via the third transistor TR3 placed in the on state. Also, the other source/drain region of the driving transistor TRD and the one end of the light emitting unit ELP are electrically connected via the fourth transistor TR4 which has been placed in the on state. Thus, the light emitting unit ELP is driven by current being applied to the light emitting unit ELP via the driving transistor TRD.
Based on Expression (2),

Vgs≈VCC(VSig−Vth)

holds, so Expression (1) can be rewritten as follows.





  
    
      
        
          
            
              
                I
                ds
              
              =
              
                k
                ·
                μ
                ·
                
                  
                    (
                    
                      
                        V
                        gs
                      
                      -
                      
                        V
                        th
                      
                    
                    )
                  
                  2
                
              
            
          
        
        
          
            
              =
              
                k
                ·
                μ
                ·
                
                  
                    (
                    
                      
                        V
                        CC
                      
                      -
                      
                        V
                        sig
                      
                    
                    )
                  
                  2
                
              
            
          
        
      
    
    
      
        (
        4
        )
      
    
  




Accordingly, the current Ids of the light emitting unit ELP is proportionate to the value of the potential difference between VCC and VSig squared. In other words, the current Ids flowing through the light emitting unit ELP is not dependent on the threshold voltage Vth of the driving transistor TRD, meaning that the amount of emission (luminance) of the light emitting unit ELP is not affected by the threshold voltage Vth of the driving transistor TRD. The luminance of the (n, m)'th display element 10 is a value corresponding to this Ids.
Period TP(1)4 (See FIGS. 8A, 8B, 12A)
In the case of m=14 for example, this Period TP(1)4 is the period between the end of the second start pulse in the output signal ST9 (the end of the period T30 in FIG. 4) and immediately before the leading edge of the first start pulse in the next frame (the end of the period T2 in the next frame in FIG. 4). At the start of this period, the output signal ST9 goes from the high level to the low level. The display control line CL8 goes from the low level to the high level. The initialization control line AZ8 and scanning line SCL8 maintain the high level.
Accordingly, the third transistor TR3 and fourth transistor TR4 go from the on state to the off state. The write transistor TRW, first transistor TR1, and second transistor TR2 maintain the off state. Accordingly, the first node ND1 is cut off from the power supply line PS1, and further, the light emitting unit ELP and driving transistor TRD are in a cut off state. Thus, no current flows to the light emitting unit ELP, which is accordingly in an unlit state.
Period TP(1)5 (See FIGS. 8A, 8B, 12B)
In the case of m=14 for example, this Period TP(1)5 is the period after the start of the first start pulse in the next frame (the start of the period T3 in the next frame in FIG. 4). In this period, the output signal ST9 goes from the low level to the high level. The display control line CL8 goes from the high level to the low level. The initialization control line AZ8 and scanning line SCL8 maintain the high level.
Accordingly, the third transistor TR3 and fourth transistor TR4 go from the off state to the on state. The write transistor TRW, first transistor TR1, and second transistor TR2 maintain the off state. Accordingly, the first node ND1 and the power supply line PS1 are reconnected, and the light emitting unit ELP and driving transistor TRD are also reconnected. Thus, current flows to the light emitting unit ELP, which is accordingly in lit state again.
The lit state of the light emitting unit ELP continues to a period equivalent to the end of the Period TP(1)−2 of the next frame. Thus, the operations of emission of the display element 10 configuring the (n, m)'th sub-pixels are completed.
The length of the until period is the same, regardless of the value of m. However, the ratio of the Period TP(1)−1 and Period TP(1)2 making up the unlit periods change depending on the value of m. This holds true in the later-described other embodiments as well. For example, in the timing chart for scanning line SCL15 in FIG. 4, there is no Period TP(1)−1. Note that the absence of the Period TP(1)−1 does not pose any problem in particular to operations of the display device.
The scan driving circuit 110 according to the first example is an integrated circuit of a structure where signals are supplied to the scanning lines SCL, initialization control line AZ, and display control line CL. Accordingly, reduction in layout area of the circuits, and reduction of circuit costs can be realized. Also, with the display device 1 according to the first embodiment, the lit/unlit state of the display elements 10 can be switched multiple times in one field period by a simple arrangement of changing the number of start pulses input to the first stage shift register making up the scan driving circuit 110, thereby reducing flickering of the image displayed on the display device.
Description will further be made with comparison to a comparative example. FIG. 13 is a circuit diagram of a scan driving circuit 120 according to a comparative example. In the scan driving circuit 120, the configuration of a logic circuit unit 122 differs from the logic circuit unit 112 of the scan driving circuit 110 according to the first embodiment. The configuration of the shift register unit 121 of the scan driving circuit 120 is the same as the shift register unit 111 of the scan driving circuit 110.
More specifically, with the scan driving circuit 120, the period identifying signal SP has been omitted, and further, the NOR circuits 114 and 115 shown in FIG. 1 have been omitted. Also, at the display element 10 to which signals based on scanning signals from a (p′, q)'th NAND circuit 123 are supplied via the scanning line SCL, signals based on the output signal STp′ from the (p′)'th shift register SRp′ are supplied in the case of q=1, and signals based on the output signal STp′+1 from the p′+1'th shift register SRp′+1 are supplied in the case of q>1, from the display control line CL connected to the display element 10.
With the scan driving circuit 120 of the configuration described above, the (p′, q)'th NAND circuit 123 generates scanning signals based on the output signal STp, output signal STp′+1 and the q'th enable signal ENq. Accordingly, in the event that there are multiple q'th enable signals ENq in the overlapping period of the start pulse of output signal STp′ and the start pulse of output signal STp′+1 multiple scan signals will be generated in the overlapping period. Accordingly, if the start pulse STP is to have a leading edge between the start of the period T1 and the end thereof, settings have to be made such that the trailing edge of the start pulse SRP is between the start and end of the period T5. The scan driving circuit 110 according to the first embodiment does not have such restrictions.
FIG. 14 is a timing chart of the scan driving circuit 120 shown in FIG. 13 where the start pulse STP has a leading edge between the start and end of the period T1, and a trailing edge between the start and end of the period T5. As can be clearly seen in comparison with the timing chart in FIG. 4, similar signals as with the case in FIG. 4 are supplied to the initialization control line AZ and scanning line SCL, albeit there be phase shifting.
FIG. 15 is a timing chart regarding the scan driving circuit 120 according to the comparative example, where the first start pulse and second start pulse are input to the first stage shift register SR1 within a period equivalent to one field period. In this case, multiple scanning signals are generated within one field period. Accordingly, with the scan driving circuit 120 according to the comparative example, there are restrictions that only one start pulse can be input to the first stage shift register SR1, and also there are restrictions regarding the end thereof, as well. The scan driving circuit 110 according to the first embodiment has no such restrictions.
Second Embodiment
The second embodiment also relates to a scan driving circuit and to a display device having the scan driving circuit. As shown in FIG. 2, the display device 2 is of the same configuration as the display device 1 according to the first embodiment, other than the scan driving circuit being different. Accordingly, description of the display device 2 according to the second embodiment will be omitted.
FIG. 16 is a circuit diagram of a scan driving circuit according to a second embodiment, FIG. 17 is a schematic timing chart of a shift register unit making up the scan driving circuit shown in FIG. 16, FIG. 18 is a schematic timing chart of an upstream stage of a logic circuit unit 212 making up the scan driving circuit 210 shown in FIG. 16, and FIG. 19 is a schematic timing chart of a downstream stage of a logic circuit unit 212 making up the scan driving circuit 210 shown in FIG. 16.
With the scan driving circuit 110 according to the first embodiment, the first start pulse and second start pulse are input to the first stage shift register SR1 in a period equivalent to one field period. With the scan driving circuit 210 according to the second embodiment, a third start pulse and fourth start pulse are also input in addition to these. Also, with the second embodiment, the period identifying signal is configured of a first period identifying signal SP1 and a second period identifying signal SP2. These are the primary points in which the second embodiment differs from the first embodiment. With the second embodiment, four periods are identified by combining the high/low level of the first period identifying signal SP1 and second period identifying signal SP2. Accordingly, with the second embodiment, the number of times of switching the display elements between lit/unlit states can be increased beyond that of the first embodiment.
As shown in FIG. 16, the scan driving circuit 210 also includes:
(A) a shift register unit 211 configured of P stages of shift registers SR, to sequentially shift input start pulses STP and output output signals ST from each stage; and
(B) a logic circuit unit 212 configured to operate based on output signals ST from the shift register unit 211, and enable signals (as with the first embodiment, first enable signal EN1 and second enable signal EN2).
With the scan driving circuit 210, the configuration of the logic circuit unit 212 differs from that of the logic circuit unit 112 of the scan driving circuit 110 according to the first embodiment. The configuration of the shift register unit 211 of the scan driving circuit 210 is the same as that of the shift register unit 111 of the scan driving circuit 110.
As mentioned above, the first start pulse through fourth start pulse are input to the first stage shift register SR1 within a period equivalent to one field period. Specifically, as shown in FIG. 17, the first start pulse input to the first stage shift register SR1 is a pulse having a leading edge between the start and of the period T1 and having a trailing edge between the start and of the period T5. The second start pulse is a pulse having a leading edge between the start and of the period T9 and having a trailing edge between the start and of the period T13. The third start pulse is a pulse having a leading edge between the start and of the period T17 and having a trailing edge between the start and of the period T21. The fourth start pulse is a pulse having a leading edge between the start and of the period T25 and having a trailing edge between the start and of the period T29.
As with the case of the first embodiment, the clock signal CK is a square wave signal which inverts polarity every two horizontal scanning periods (2H). The first start pulse in the output signal ST1 of the shift register SR1 has the leading edge thereof at the start of the period T3, and has the trailing edge at the end of period T6. The first start pulse in the output signals ST2, ST3, and so on, for the shift register SR2 and subsequent shift registers is a pulse which has been sequentially shifted by two horizontal scanning periods.
Also, the second start pulse in the output signal ST1 of the shift register SR1 has the leading edge thereof at the start of the period T11, and has the trailing edge at the end of period T14. The third start pulse in the output signal ST1 of the shift register SR1 has the leading edge thereof at the start of the period T19, and has the trailing edge at the end of period T22. The fourth start pulse in the output signal ST1 of the shift register SR1 has the leading edge thereof at the start of the period T27, and has the trailing edge at the end of period T30. The second through fourth pulses in the output signals ST2, ST3, and so on, for the shift register SR2 and subsequent shift registers, are also pulses which have been sequentially shifted by two horizontal scanning periods.
Also, one each of a first enable signal through a Q'th enable signal exist in sequence between the start of the first start pulse of the output signal STp and the start of the first start pulse of the output signal STp+1. In the second embodiment as well, Q=2, and there are one each of the first enable signal EN1 and the second enable signal EN2, in sequence. The first enable signal EN1 and the second enable signal EN2 have been described in the first embodiment, and accordingly description thereof will be omitted here.
As shown in FIG. 16, the logic circuit unit 212 has (P−2)×Q NAND circuits 213. Specifically, the logic circuit unit 212 has (1, 1)'th through (P−2, 2)'th NAND circuits 213. Period identifying signals SP for identifying each period from the start of the u'th start pulse start pulse in an output signal ST1 to the start of a (u+1)'th start pulse, and a period from the start of the U'th start pulse to the start of the first start pulse in the next frame, are input to the logic circuit unit 212.
In the second embodiment, U=4, and the period identifying signal SP is a signal for identifying the period from the start of the first start pulse in the output signal ST1 to the start of the second start pulse, the period from the start of the second start pulse to the start of the third start pulse, the period from the start of the third start pulse to the start of the fourth start pulse, and the period from the start of the fourth start pulse to the start of the first start pulse in the next frame. In the second embodiment, the period identifying signal SP is configured of the first period identifying signal SP1 and the second period identifying signal SP2.
The first period identifying signal SP1 is a signal which is at high level during the period from the start of period T3 to the end of period T18, and at low level during the period from the start of period T19 to the end of period T2 of the next frame. That is to say, the first period identifying signal SP1 is the same as the period identifying signal SP in the first embodiment. Conversely, the second period identifying signal SP2 is a signal which is at high level during the period from the start of period T3 to the end of period T10, at low level during the period from the start of period T11 to the end of period T18, at high level during the period from the start of period T19 to the end of period T26, and at low level during the period from the start of period T27 to the end of period T2 of the next frame.
With a q'th enable signal represented as ENq, as shown in FIG. 16 signals based on the period identifying signal SP (i.e., a signal based on the first period identifying signal SP1 and a signal based on the second period identifying signal SP2), the output signal STp, a signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq, are input to a (p′, q)'th NAND circuit 213, whereby the operations of the NAND circuit 213 are restricted based on the first period identifying signal SP1 and second period identifying signal SP2, such that the NAND circuit 213 generates scanning signals based only on a portion of the output signal STp′ corresponding to the first start pulse, the signal obtained by inverting the output signal STp′+1 and the q'th enable signal ENq.
The output signal STp′+1 is inverted by the NOR circuit 214 shown in FIG. 16, and input to the input side of the (p′, q)'th NAND circuit 213. The output signal STp′ and the q'th enable signal ENq are directly input to the input side of the (p′, q)'th NAND circuit 213.
With the second embodiment, the first period identifying signal SP1 is directly input to the input side of the (1, 1)'th through (4, 2)'th NAND circuits 213, and the second period identifying signal SP2 is also directly input. The first period identifying signal SP1 is directly input to the input side of the (5, 1)'th through (8, 2)'th NAND circuits 213, and the second period identifying signal SP2 inverted by a NOR circuit 216 shown in FIG. 16 is input.
Also, the first period identifying signal SP1 is inverted by a NOR circuit 217 shown in FIG. 16 and input to the input side of the (9, 1)'th through (12, 2)'th NAND circuits 213, and the second period identifying signal SP2 is directly input. The first period identifying signal SP1 is inverted by the NOR circuit 217 and input to the input side of the (13, 1)'th through (16, 2)'th NAND circuits 213, and the second period identifying signal SP2 is inverted by the NOR circuit 216 and is input.
Let us consider the (8, 1)'th NAND circuit 213. Signals based on the scanning signals from the (8, 1)'th NAND circuit 213 are supplied to the scanning line SCL14. As shown in FIG. 16, in the period T17 in which the scanning signal should be generated, the output signal ST8, the signal obtained by inverting the output signal ST9, and the first enable signal EN1, are at high level. However, the first stage shift register SR1 has also received input of the second start pulse through fourth start pulse in addition to the first start pulse, so the output signal ST8, the signal obtained by inverting the output signal ST9, and the first enable signal EN1, are at high level in periods T1, T9, and T25, as well.
Accordingly, if the (8, 1)'th NAND circuit 213 were to operate based only on the output signal ST8, a signal obtained by inverting the output signal ST9, and the first enable signal EN1, trouble would occur in that a scanning signal would be supplied to the scanning line SCL14 not only in the period T17 in which the scanning signal should be generated, but also in the periods T1, T9, and T25. However, as described above, the first period identifying signal SP1 is directly input to the input side of the (8, 1)'th NAND circuit 213, and the second period identifying signal SP2 is inverted and input. In periods T1, T9, T17, and T25, the only period where the first period identifying signal SP1 is at a high level and the second period identifying signal SP2 is at a low level is the period T17. Accordingly, the (8, 1)'th NAND circuit 213 generates a scanning signal based only on the output signal ST8, a signal obtained by inverting the output signal ST9, and the first enable signal EN1.
Let us also consider the (9, 1)'th NAND circuit 213. Signals based on the scanning signals from the (9, 1)'th NAND circuit 213 are supplied to the scanning line SCL16 shown in FIG. 1. As shown in FIG. 19, in the period T19 in which the scanning signal should be generated, the output signal ST9, the signal obtained by inverting the output signal ST10, and the first enable signal EN1, are at high level. However, the first stage shift register SR1 has also received input of the second start pulse through fourth start pulse in addition to the first start pulse, so the output signal ST9, the signal obtained by inverting the output signal ST10, and the first enable signal EN1, are at high level in periods T3, T11, and T27, as well.
Accordingly, if the (9, 1)'th NAND circuit 213 were to operate based only on the output signal ST9, a signal obtained by inverting the output signal ST10, and the first enable signal EN1, trouble would occur in that a scanning signal would be supplied to the scanning line SCL16 not only in the period T19 in which the scanning signal should be generated, but also in the periods T3, T11, and T27. However, as described above, the first period identifying signal SP1 is inverted and input to the (9, 1)'th NAND circuit 213, and the second period identifying signal SP2 is directly input. In periods T3, T11, T19, and T27, the only period where the first period identifying signal SP1 is at a low level and the second period identifying signal SP2 is at a high level is the period T19. Accordingly, the (9, 1)'th NAND circuit 213 generates a scanning signal based only on the output signal ST9, a signal obtained by inverting the output signal ST10, and the first enable signal EN1.
While description has been made regarding the operations of the (8, 1)'th NAND circuit 213 and the (9, 1)'th NAND circuit 213, the operations are the same for the other NAND circuits 213 as well. The (p′, q)'th NAND circuit 213 generates a scanning signal based only on a portion of the output signal STP′ corresponding to the first start pulse, the signal obtained by inverting the output signal STp′+1 and the q'th enable signal ENq.
FIG. 20 is a schematic driving timing chart of the display element 10 at the m'th row and n'th column, corresponding to FIG. 8 in the first embodiment. In the same way as with the first embodiment, p′=8 and q=1, and m=14, when comparing the timing chart in FIG. 20 with FIGS. 17 through 19. Specifically, the timing chart of initialization control line AZ14, scanning line SCL14, and display control line CL14 in FIG. 18 is to be referred to.
The operations of the Period TP(2)−2 through Period TP(2)2 shown in FIG. 20 are the same as the operations of the Period TP(1)−2 through Period TP(1)2 described with the first embodiment, so description thereof will be omitted. Also, Period TP(2)9 shown in FIG. 20 corresponds to the Period TP(1)9 described with the first embodiment, albeit there be different in the start thereof.
With the first embodiment, the lit period and unlit period switch once between the end of Period TP(1)2 and the start Period TP(1)5 in FIG. 8. On the other hand, with the second embodiment, the lit period and unlit period switch three times between the end of Period TP(2)2 and the start Period TP(2)9 in FIG. 20. Accordingly, flickering the image displayed on the display device is further reduced.
Third Embodiment
The third embodiment also relates to a scan driving circuit and to a display device having the scan driving circuit. As shown in FIG. 2, the display device 3 according to the third embodiment is of the same configuration as the display device 1 according to the first embodiment, other than the scan driving circuit being different. Accordingly, description of the display device 3 according to the third embodiment will be omitted.
FIG. 21 is a circuit diagram of a scan driving circuit 310 according to the third embodiment, FIG. 22 is a schematic timing chart of a shift register unit 311 making up the scan driving circuit 310 shown in FIG. 21, FIG. 23 is a schematic timing chart of an upstream stage of a logic circuit unit 312 making up the scan driving circuit 310 shown in FIG. 21, and FIG. 24 is a schematic timing chart of a downstream stage of the logic circuit unit 312 making up the scan driving circuit 310 shown in FIG. 21.
With the scan driving circuit 110 according to the first embodiment, a first enable signal EN1 and second enable signal EN2 are used. With the scan driving circuit 310 according to the third embodiment, a third enable signal EN3 and fourth enable signal EN4 are used in addition to these. Accordingly, the number of stages making up the shift register unit configuring the scan driving circuit can be reduced as compared with the case of the scan driving circuit 110 according to the first embodiment.
As shown in FIG. 21, the scan driving circuit 310 also includes:
(A) a shift register unit 311 configured of P stages of shift registers SR, to sequentially shift input start pulses STP and output output signals ST from each stage; and
(B) a logic circuit unit 312 configured to operate based on output signals ST from the shift register unit 311, and enable signals (in the case of the third embodiment, first enable signal EN1, second enable signal EN2, third enable signal EN3, and fourth enable signal EN4).
Representing the output signals of the p'th stage shift register SRp with STp, the start of the start pulse in the output signal STp+1 of the p+1'th stage shift register SRp+1 is situated between the start and end of the start pulse in the output signal STp, as shown in FIG. 22. The shift register unit 311 operates based on the clock signals CK and start pulse STP so as to satisfy the above conditions.
A first start pulse through a U'th start pulse are input to the first stage shift register SR1 in a period equivalent to one field period. Note that with the third embodiment, U=2 the same as with the first embodiment, and the first start pulse and second start pulse are input.
Specifically, the first start pulse input to the first stage shift register SR1 is a pulse which has a leading edge between the start and end of the period T1 shown in FIG. 22, and which has a trailing edge between the start and end of the period T9. Also, the second start pulse is a pulse which has a leading edge between the start and end of the period T17 shown in FIG. 22, and which has a trailing edge between the start and end of the period T25.
With the first and second embodiments, the clock signal CK is a square wave signal of which the polarity inverts every two horizontal scanning periods. Conversely, with the third embodiment, the clock signal CK is a square wave signal of which the polarity inverts every four horizontal scanning periods.
The first start pulse in the output signal ST1 of the shift register SR1 is a pulse which has the leading edge thereof at the start of the period T3, and has the trailing edge at the end of period T10. The first start pulses in the output signals ST2, ST3, and so on, for the shift register SR2 and subsequent shift registers, are pulses which have been sequentially shifted by four horizontal scanning periods. The second start pulse in the output signal ST1 of the shift register SR1 is a pulse which has the leading edge thereof at the start of the period T19, and has the trailing edge at the end of period T26. The second start pulses in the output signals ST2, ST3, and so on, for the shift register SR2 and subsequent shift registers, are pulses which have been sequentially shifted by four horizontal scanning periods.
Also, one each of a first enable signal through a Q'th enable signal exist in sequence between the start of the first start pulse of the output signal STp and the start of the first start pulse of the output signal STp+1. In the third embodiment, Q=4, and there are one each of the first enable signal EN1, second enable signal EN2, third enable signal EN3, and fourth enable signal EN4 in sequence. In other words, the first enable signal EN1, second enable signal EN2, third enable signal EN3, and fourth enable signal EN4 are signals generated so as to satisfy the above conditions, and basically are square wave signals of the same cycle but with different phases.
Specifically, the first enable signal EN1 is a square wave signal of which one cycle is four horizontal scanning periods. The second enable signal EN2 is a signal of which the phase is delayed as to the first enable signal EN1 by one horizontal scanning period. The third enable signal EN3 is a signal of which the phase is delayed as to the first enable signal EN1 by two horizontal scanning periods. The fourth enable signal EN4 is a signal of which the phase is delayed as to the first enable signal EN1 by three horizontal scanning periods.
For example, one each of the first enable signal EN1 in the period T3, the second enable signal EN2 in the period T4, the third enable signal EN3 in the period T5, and the fourth enable signal EN4 in the period T6, sequentially exist between the start of the start pulse in the output signal ST1 (i.e., start of period T3) and the start of the start pulse in the output signal ST2 (i.e., start of period T7). In the same way, one each of the first enable signal EN1, second enable signal EN2, third enable signal EN3, and fourth enable signal EN4, serially exist between the start of the start pulse in the output signal ST2 and the start of the start pulse in the output signal ST3.
As shown in FIG. 21, the logic circuit unit 312 has (P−2)×Q NAND circuits 313. Specifically, the logic circuit unit 312 has (1, 1)'th through (P−2, 4)'th NAND circuits 313. Period identifying signals SP for identifying each period from the start of the u'th start pulse start pulse in an output signal ST1 to the start of a (u+1)'th start pulse, and a period from the start of the U'th start pulse to the start of the first start pulse in the next frame, are input to the logic circuit unit 312.
In the third embodiment, U=2, and the period identifying signal SP is as described with the first embodiment. That is to say, the period identifying signal SP is a signal for identifying the period from the start of the first start pulse in the output signal ST1 to the start of the second start pulse, and the period from the start of the second start pulse to the start of the first start pulse in the next frame. In the third embodiment as well, the period identifying signal SP is a signal which is at high level during the period from the start of period T3 to the end of period T18, and at low level during the period from the start of period T19 to the end of period T2 of the next frame.
With a q'th enable signal represented as ENq, as shown in FIG. 21 signals based on the period identifying signal SP, the output signal STp, a signal obtained by inverting the output signal STp+1, and the q'th enable signal ENq, are input to a (p′, q)'th NAND circuit 313, whereby the operations of the NAND circuit 313 are restricted based on the period identifying signal SP, such that the NAND circuit 313 generates scanning signals based only on a portion of the output signal STp′ corresponding to the first start pulse, the signal obtained by inverting the output signal STp′+1 and the q'th enable signal ENq.
The output signal STp′+1 is inverted by the NOR circuit 314 shown in FIG. 21, and input to the input side of the (p′, q)'th NAND circuit 313. The output signal STp′ and the q'th enable signal ENq are directly input to the input side of the (p′, q)'th NAND circuit 313.
With the third embodiment, as with the first embodiment, the period identifying signal SP is directly input to the input side of the (1, 1)'th through (4, 4)'th NAND circuits 313. The period identifying signal SP is inverted by the NOR circuit 316 and input to the input side of the (5, 1)'th through (8, 4)'th NAND circuits 313.
Let us consider the (4, 3)'th NAND circuit 313, for example. Signals based on the scanning signals from the (4, 3)'th NAND circuit 313 are supplied to the scanning line SCL14 shown in FIG. 21. As shown in FIG. 23, in the period T17 in which the scanning signal should be generated, the output signal ST4, the signal obtained by inverting the output signal ST5, and the third enable signal EN3, are at high level. However, the first stage shift register SR1 has also received input of the second start pulse in addition to the first start pulse, so the output signal ST4, the signal obtained by inverting the output signal ST5, and the third enable signal EN3, are at high level in period T1 as well.
Accordingly, if the (4, 3)'th NAND circuit 313 were to operate based only on the output signal ST4, a signal obtained by inverting the output signal ST5, and the third enable signal EN3, trouble would occur in that a scanning signal would be supplied to the scanning line SCL14 not only in the period T17 in which the scanning signal should be generated, but also in the period T1. However, as described above, the period identifying signal SP is directly input to the input side of the (4, 3)'th NAND circuit 313. Of periods T1 and T17, the only period where the period identifying signal SP is at a high level is the period T17. Accordingly, the (4, 3)'th NAND circuit 313 generates a scanning signal based only on the output signal ST4, a signal obtained by inverting the output signal ST5, and the third enable signal EN3.
Let us also consider the (5, 1)'th NAND circuit 313. Signals based on the scanning signals from the (5, 1)'th NAND circuit 313 are supplied to the scanning line SCL16 shown in FIG. 21. As shown in FIG. 24, in the period T19 in which the scanning signal should be generated, the output signal ST5, the signal obtained by inverting the output signal ST6, and the first enable signal EN1, are at high level. However, the first stage shift register SR1 has also received input of the second start pulse in addition to the first start pulse, so the output signal ST5, the signal obtained by inverting the output signal ST6, and the first enable signal EN1, are at high level in period T3 as well.
Accordingly, if the (5, 1)'th NAND circuit 313 were to operate based only on the output signal ST5, a signal obtained by inverting the output signal ST6, and the first enable signal EN1, trouble would occur in that a scanning signal would be supplied to the scanning line SCL16 not only in the period T19 in which the scanning signal should be generated, but also in the period T3. However, as described above, the period identifying signal SP is inverted and input to the (5, 1)'th NAND circuit 313. Of periods T3 and T19, the only period where the period identifying signal SP is at a low level is the period T19. Accordingly, the (5, 1)'th NAND circuit 313 generates a scanning signal based only on the output signal ST5, a signal obtained by inverting the output signal ST6, and the first enable signal EN1.
While description has been made regarding the operations of the (4, 3)'th NAND circuit 313 and the (5, 1)'th NAND circuit 313, the operations are the same for the other NAND circuits 313 as well. The (p′, q)'th NAND circuit 313 generates a scanning signal based only on a portion of the output signal STp′ corresponding to the first start pulse in the output signal STp′, the signal obtained by inverting the output signal STp′+1, and the q'th enable signal ENq.
FIG. 25 is a schematic driving timing chart of the display element 10 at the m'th row and n'th column, corresponding to FIG. 8 in the first embodiment. Here, p′=4 and q=3, and in the same way as with the first embodiment, m=14, when comparing the timing chart in FIG. 25 with FIGS. 22 through 24. Specifically, the timing chart of initialization control line AZ14, scanning line SCL14, and display control line CL14 in FIG. 23 is to be referred to.
The operations of the Period TP(3)−2 through Period TP(3)2 shown in FIG. 25 are the same as the operations of the Period TP(1)−2 through Period TP(1)2 described with the first embodiment, so description thereof will be omitted. Also, the operations of Period TP(3)3 through Period TP(3)5 shown in FIG. 25 are the same as the operations of Period TP(1)3 through Period TP(1)5 described with the first embodiment, albeit there be different in the length of periods thereof, so description thereof will be omitted.
While the present invention has been described so far with reference to preferred embodiments, the present invention is not restricted by these embodiments. The configuration and structure of the various components configuring the scan driving circuit, display device, and display elements, and the processes in the operations of the display device, described in the embodiments, may be modified as appropriate.
For example, with the driving circuit 11 configuring the display element 10 shown in FIG. 6, in the event that the third transistor TR3 and fourth transistor TR4 are re-channel type transistors, the NOR circuit 115 shown in FIG. 1, the NOR circuit 215 shown in FIG. 16, and the NOR circuit 315 shown in FIG. 21, can be omitted. In this way, the polarity of signals from the scan driving circuit can be suitably set in accordance with the configuration of the display elements, and supplied to the scanning lines, initialization control lines, and display control lines.
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-182369 filed in the Japan Patent Office on Jul. 14, 2008, the entire content of which is hereby incorporated by reference.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.

## Claims

1. A display apparatus comprising:
a plurality of pixel circuits having a light emitting device, a first transistor, a second transistor, a first switch circuit, a second switch circuit, and a capacitor,
wherein a initialization voltage is supplied from a first voltage line to a gate of said second transistor via said second switch circuit during a first period,
wherein a display voltage is supplied to a gate of said second transistor via a current path established between a signal line and the gate of the second transistor through said first transistor, said second transistor, and said first switch circuit while a data voltage is applied to the signal line and during a second period after the first period,
wherein a driving current is supplied to said light emitting device according to said display voltage during a third period after the second period,
wherein said light emitting device has an anode electrode, a light emitting layer, and a cathode electrode, and is provided on a first insulation layer covering said plurality of pixel circuits,
wherein said cathode electrode is provided on a second insulation layer which is arranged on said first insulation layer, and is connected to a second power-supply line via a first contact formed in said first insulation layer and a second contact formed in the second insulation layer, and
wherein said light emitting device is configured to emit multiple times in one field period.

2. The display apparatus according to claim 1, wherein the plurality of pixel circuits include a red-light emitting pixel, a green-light emitting pixel, a blue-light emitting pixel, and white-light emitting pixel.

3. The display apparatus according to claim 1, wherein the plurality of pixel circuits include a red-light emitting pixel, a green-light emitting pixel, a blue-light emitting pixel, and yellow-light emitting pixel.