Active-matrix-driven display device

• US 20060022305A1
• Filed: 07/29/2005
• Published: 02/02/2006
• Est. Priority Date: 07/30/2004
• Status: Abandoned Application

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamashita, Atsuhiro
• Application Number:
  US11/192,428
• Publication Number:
  US 20060022305A1
• Time in Patent Office: Days
• US Class Current: 257/565
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• CPC Class Codes: G09G 2310/066 Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

In a display panel, each pixel has a display element that emits light when fed with electric power, a writing transistor, a driving transistor that drives the display element, a first capacitive element that is provided in series with a line connecting the second electrode of the writing transistor and the control electrode of the driving transistor, and an adjustment transistor that, during a reset period, is turned on to feed a voltage commensurate with the electrode-to-electrode voltage of the display element to the writing-transistor-side electrode of the first capacitive element. A control signal generation circuit is provided that, during the reset period, lets a voltage commensurate with the light emission start electrode-to-electrode voltage of the display element be held in the first capacitive element.

Claims

1. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, the display panel being so driven that each frame period contains at least a reset period and a light emission period, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that is turned on when a scan voltage having a predetermined level is applied thereto from the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element during the light emission period;

a first capacitive element that is provided in series with a line connecting a second electrode of the writing transistor to the control electrode of the driving transistor; and

an adjustment transistor that is turned on during the reset period to feed to a writing-transistor-side electrode of the first capacitive element a voltage commensurate with an electrode-to-electrode voltage of the display element,

wherein the active-matrix-driven display device further includes a control signal generation circuit that, during the reset period, for each pixel circuit, lets a voltage commensurate with a light emission start electrode-to-electrode voltage of the display element be held in the first capacitive element.

2. The active-matrix-driven display device of claim 1,

wherein, after an end of the reset period, for each pixel circuit, the scan driver turns the writing transistor on so that a voltage commensurate with the data voltage and the light emission start electrode-to-electrode voltage is applied to the control electrode of the driving transistor.

3. The active-matrix-driven display device of claim 1,

wherein, during the reset period, for each pixel circuit, the control signal generation circuit, while turning the adjustment transistor on, turns a driving-transistor-side electrode of the first capacitive element to a predetermined potential to let the voltage commensurate with the light emission start electrode-to-electrode voltage of the display element be held in the first capacitive element, and then turns the adjustment transistor off.

4. The active-matrix-driven display device of claim 1,

wherein, in each pixel circuit, the driving transistor has a first electrode, a second electrode, and the control electrode and so operates as to control a current flowing between the first electrode and the second electrode according to a voltage between the control electrode and the first electrode, and

wherein the pixel circuit of each pixel further includes:

an on/off transistor that is provided in series with a power supply line extending from a power source from which to feed electric power to the display element and that turns on and off feeding of electric power to the display element; and

a threshold value compensation transistor that has a first electrode thereof connected to the control electrode of the driving transistor and that has a second electrode thereof connected to the second electrode of the driving transistor.

5. The active-matrix-driven display device of claim 4,

wherein, during the reset period, for each pixel circuit, the control signal generation circuit turns the on/off transistor on and thereby turns the driving transistor on, then turns the on/off transistor off and turns the adjustment transistor and the threshold value compensation transistor on to let a voltage commensurate with the light emission start electrode-to-electrode voltage of the display element and an operation threshold voltage of the driving transistor be held in the first capacitive element, and then turns the adjustment transistor and the threshold value compensation transistor off, and

wherein, after an end of the reset period, for each pixel circuit, the scan driver turns the writing transistor on so that a voltage commensurate with the data voltage, the light emission start electrode-to-electrode voltage, and the operation threshold voltage is applied to the control electrode of the driving transistor.

6. The active-matrix-driven display device of claim 4,

wherein, during the reset period, for each pixel circuit, the control signal generation circuit temporarily feeds from outside the pixel a predetermined reset voltage to the control electrode of the driving transistor to temporarily turn the driving transistor on without turning the on/off transistor on, then turns the adjustment transistor and the threshold value compensation transistor on to let a voltage commensurate with the light emission start electrode-to-electrode voltage of the display element and an operation threshold voltage of the driving transistor be held in the first capacitive element, and then turns the adjustment transistor and the threshold value compensation transistor off, and

wherein, after an end of the reset period, for each pixel circuit, the scan driver turns the writing transistor on so that a voltage commensurate with the data voltage, the light emission start electrode-to-electrode voltage, and the operation threshold voltage is applied to the control electrode of the driving transistor.

7. The active-matrix-driven display device of claim 6,

wherein the pixel circuit of each pixel further includes a resetting transistor that, when turned on, short-circuits between both electrodes of the first capacitive element,

wherein the reset voltage is fed from the data driver during the reset period, and

wherein, during the reset period, for each pixel circuit, the scan driver turns the writing transistor on and the control signal generation circuit turns the resetting transistor on so that the reset voltage is temporarily fed to the control electrode of the driving transistor.

8. The active-matrix-driven display device of claim 1,

wherein the active-matrix-driven display device further includes a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate, and

wherein the pixel circuit of each pixel includes a second capacitive element that feeds a variation in the ramp voltage to the writing-transistor-side electrode of the first capacitive element.

9. The active-matrix-driven display device of claim 8,

wherein the active-matrix-driven display device receives a gradation signal for image display to display an image,

wherein the data driver feeds a data voltage corresponding to the gradation signal to each pixel circuit, and

wherein the variation rate of the ramp voltage is so set that, for each pixel circuit,

let D represent a data voltage fed as corresponding to the received gradation signal,

let D_B represent a data voltage fed when the gradation signal represents a black level of gradation,

let L represent brightness obtained as a result of the display element emitting light according to the fed data voltage D,

let L_B represent brightness obtained when the gradation signal represents a black level of gradation,

let x represent D−

D_B, and

let y represent L−

L_B+1,

the formula y=a^x (where a is a constant fulfilling a>

1) is fulfilled.

40. The active-matrix-driven display device of claim 1,

wherein, in each pixel circuit, when a magnitude of the light emission start electrode-to-electrode voltage of the display element varies from a first voltage value to a second voltage value higher than the first voltage value, an effective value of a current that flows through the display element as corresponding to a given gradation signal increases.

10. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, the display panel being so driven that each frame period contains at least a reset period and a light emission period, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that is turned on when a scan voltage having a predetermined level is applied thereto from the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element during the light emission period;

a pulse width modulation circuit that outputs, during the light emission period, a predetermined light emission level voltage for making the display element emit light during a period commensurate with a data voltage fed from the data driver while the writing transistor is on;

a first capacitive element that is provided in series with a line connecting an output end of the pulse width modulation circuit to the control electrode of the driving transistor; and

an adjustment transistor that is turned on during the reset period to feed to a pulse-width-modulation-circuit-side electrode of the first capacitive element a voltage commensurate with an electrode-to-electrode voltage of the display element,

wherein the active-matrix-driven display device further includes a control signal generation circuit that, during the reset period, for each pixel circuit, lets a voltage commensurate with a light emission start electrode-to-electrode voltage of the display element be held in the first capacitive element.

11. The active-matrix-driven display device of claim 10,

wherein, before the light emission period, for each pixel circuit, the scan driver turns the writing transistor on so that a voltage commensurate with the light emission level voltage and the light emission start electrode-to-electrode voltage is applied to the control electrode of the driving transistor for the period commensurate with the data voltage.

12. The active-matrix-driven display device of claim 10,

wherein, during the reset period, for each pixel circuit, the control signal generation circuit, while turning the adjustment transistor on, turns a driving-transistor-side electrode of the first capacitive element to a predetermined potential to let the voltage commensurate with the light emission start electrode-to-electrode voltage of the display element be held in the first capacitive element, and then turns the adjustment transistor off.

13. The active-matrix-driven display device of claim 10,

wherein, in each pixel circuit, the driving transistor has a first electrode, a second electrode, and the control electrode and so operates as to control a current flowing between the first electrode and the second electrode according to a voltage between the control electrode and the first electrode, and

wherein the pixel circuit of each pixel further includes:

an on/off transistor that is provided in series with a power supply line extending from a power source from which to feed electric power to the display element and that turns on and off feeding of electric power to the display element; and

a threshold value compensation transistor that has a first electrode thereof connected to the control electrode of the driving transistor and that has a second electrode thereof connected to the second electrode of the driving transistor.

14. The active-matrix-driven display device of claim 13,

wherein, during the reset period, for each pixel circuit, the control signal generation circuit turns the on/off transistor on and thereby turns the driving transistor on, then turns the on/off transistor off and turns the adjustment transistor and the threshold value compensation transistor on to let a voltage commensurate with the light emission start electrode-to-electrode voltage of the display element and an operation threshold voltage of the driving transistor be held in the first capacitive element, and then turns the adjustment transistor and the threshold value compensation transistor off, and

wherein, before the light emission period, for each pixel circuit, the scan driver turns the writing transistor on so that a voltage commensurate with the light emission level voltage, the light emission start electrode-to-electrode voltage, and the operation threshold voltage is applied to the control electrode of the driving transistor for the period commensurate with the data voltage.

15. The active-matrix-driven display device of claim 13,

wherein the pixel circuit of each pixel further includes a clipping circuit that prevents a potential at the control electrode of the driving transistor from becoming higher than a predetermined clip potential, or lower than a predetermined clip potential,

wherein the clip potential is set at a potential that permits, during the reset period, for each pixel circuit, the control signal generation circuit to turn the adjustment transistor on and thereby temporarily turn the driving transistor on,

wherein, during the reset period, for each pixel circuit, the control signal generation circuit turns the adjustment transistor and the threshold value compensation transistor on, without turning the on/off transistor on, to let a voltage commensurate with the light emission start electrode-to-electrode voltage of the display element and an operation threshold voltage of the driving transistor be held in the first capacitive element, and then turns the adjustment transistor and the threshold value compensation transistor off, and

wherein, before the light emission period, for each pixel circuit, the scan driver turns the writing transistor on so that a voltage commensurate with the light emission level voltage, the light emission start electrode-to-electrode voltage, and the operation threshold voltage is applied to the control electrode of the driving transistor for the period commensurate with the data voltage.

16. The active-matrix-driven display device of claim 10,

wherein the active-matrix-driven display device further includes a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate, and

wherein, in each pixel circuit, the pulse width modulation circuit performs pulse width modulation on the data voltage by using the ramp voltage, and outputs, during the light emission period, the light emission level voltage for a period corresponding to a width of a pulse resulting from the pulse width modulation.

17. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, the display panel being so driven that each frame period contains a first field and a second field of which each consists of a light emission preparation period and a light emission period, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that is turned on when a scan voltage having a predetermined level is applied thereto from the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element;

a first capacitive element that, at one end thereof, is connected to the control electrode of the driving transistor; and

an adjustment transistor that is so connected to the display element as to receive, at a first electrode thereof, a voltage commensurate with an electrode-to-electrode voltage of the display element and that can transmit a feedback voltage commensurate with a light emission start electrode-to-electrode voltage of the display element to the first capacitive element,

wherein the active-matrix-driven display device further includes a feedback controller that, during the light emission preparation period of, of the first and second fields, only the first field, for each pixel circuit, transmits the feedback voltage to the first capacitive element so that a held voltage reflecting the feedback voltage is held in the first capacitive element.

18. The active-matrix-driven display device of claim 17,

wherein the active-matrix-driven display device receives a gradation signal for image display to display an image,

wherein the active-matrix-driven display device further includes a gamma conversion circuit that, on receiving a gradation signal representing a middle level of gradation, converts the gradation signal into a first converted gradation signal corresponding to the first field and a second converted gradation signal corresponding to the second field and then feeds the first and second converted gradation signals to the data driver so that an effective value of a current that flows through the display element during the light emission period of the first field is smaller than an effective value of a current that flows through the display element during the light emission period of the second field, and

wherein the data driver feeds each pixel circuit with a data voltage corresponding to the first converted gradation signal in the first field and with a data voltage corresponding to the second converted gradation signal in the second field.

19. The active-matrix-driven display device of claim 17,

wherein the active-matrix-driven display device receives a gradation signal for image display to display an image,

wherein the active-matrix-driven display device further includes a gamma conversion circuit that converts the gradation signal into a first converted gradation signal corresponding to the first field and a second converted gradation signal corresponding to the second field and then feeds the first and second converted gradation signals to the data driver so that, assuming that an effective value of a current to be passed through the display element of each pixel circuit to correspond to a gradation signal representing a middle level of gradation is a reference current value, an effective value of a current that flows through the display element during the light emission period of the first field is smaller than the reference current value and an effective value of a current that flows through the display element during the light emission period of the second field is larger than the reference current value,

wherein the data driver feeds each pixel circuit with a data voltage corresponding to the first converted gradation signal in the first field and with a data voltage corresponding to the second converted gradation signal in the second field.

20. The active-matrix-driven display device of claim 18,

wherein, in each pixel circuit, the driving transistor,

during the light emission period of the second field, receives at the control electrode thereof a voltage commensurate with the data voltage corresponding to the second converted gradation signal and drives the display element according to that voltage, and,

during the light emission period of the first field, receives at the control electrode thereof a voltage commensurate not only with the data voltage corresponding to the first converted gradation signal but also with the held voltage and drives the display element according to those voltages.

21. The active-matrix-driven display device of claim 17,

wherein, in each pixel circuit, the adjustment transistor has a second electrode thereof connected to the first capacitive element, and

wherein, during the light emission preparation period of the first field, for each pixel circuit, the feedback controller extracts, via the adjustment transistor and the display element, a positive electric charge at the second electrode of the adjustment transistor which is temporarily given a potential higher than a potential equal to a sum of a potential at a cathode of the display element and the light emission start electrode-to-electrode voltage to thereby transmit the feedback voltage to the first capacitive element, and then turns the adjustment transistor off to thereby let the held voltage be held in the first capacitive element.

22. The active-matrix-driven display device of claim 17,

wherein the feedback controller includes a control signal generation circuit that controls turning on and off of the adjustment transistor in each pixel circuit,

wherein, in each pixel circuit, the first capacitive element is provided in series with a line connecting a second electrode of the writing transistor to the control electrode of the driving transistor, and a second electrode of the adjustment transistor is connected to the writing-transistor-side electrode of the first capacitive element, and

wherein, during the light emission preparation period of the first field, for each pixel circuit, the control signal generation circuit turns the adjustment transistor on to transmit the feedback voltage to the first capacitive element, and then turns the adjustment transistor off to let the held voltage be held in the first capacitive element.

23. The active-matrix-driven display device of claim 22,

wherein the active-matrix-driven display device further includes a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate, and

wherein the pixel circuit of each pixel includes a second capacitive element that feeds a variation in the ramp voltage to the writing-transistor-side electrode of the first capacitive element.

24. The active-matrix-driven display device of claim 22,

wherein, in each pixel circuit, the driving transistor has a first electrode, a second electrode, and the control electrode and so operates as to control a current flowing between the first electrode and the second electrode according to a voltage between the control electrode and the first electrode, and

wherein the pixel circuit of each pixel further includes:

an on/off transistor that is provided in series with a power supply line extending from a power source from which to feed electric power to the display element and that turns on and off feeding of electric power to the display element; and

a threshold value compensation transistor that has a first electrode thereof connected to the control electrode of the driving transistor and that has a second electrode thereof connected to the second electrode of the driving transistor.

25. The active-matrix-driven display device of claim 17,

wherein the feedback controller includes a ramp voltage generation circuit that, during the light emission period of each field, for each pixel circuit, feeds a first ramp voltage to the first electrode of the writing transistor and that outputs a second ramp voltage for controlling turning on and off of the adjustment transistor,

wherein, in each pixel circuit, the first capacitive element is provided in series with a line connecting a second electrode of the writing transistor to the control electrode of the driving transistor, and a second electrode of the adjustment transistor is connected to the driving-transistor-side electrode of the first capacitive element, and

wherein, during the light emission preparation period of the first field, for each pixel circuit, the ramp voltage generation circuit turns the adjustment transistor on to transmit the feedback voltage to the first capacitive element, and then turns the adjustment transistor off to let the held voltage be held in the first capacitive element.

26. The active-matrix-driven display device of claim 17,

wherein the active-matrix-driven display device further includes a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate and that, during each light emission period, for each pixel circuit, feeds a variation in the ramp voltage via the first capacitive element to the control electrode of the driving transistor,

wherein, in each pixel circuit, the one end of the first capacitive element is connected to a second electrode of the writing transistor, and another end of the first capacitive element is connected to a second electrode of the adjustment transistor, and

wherein, during the light emission preparation period of the first field, for each pixel circuit, the feedback controller turns the adjustment transistor on to transmit the feedback voltage to the first capacitive element, and then turns the adjustment transistor off to let the held voltage be held in the first capacitive element.

37. The active-matrix-driven display device of claim 17,

wherein the pixels constituting the display panel are divided into a first pixel group and a second pixel group with periodicity in a vertical and/or a horizontal direction of the display panel, and

wherein, during each frame period, the first and second fields are made to occur in different orders between in the first and second pixel groups.

38. The active-matrix-driven display device of claim 17,

wherein, during each frame period, the first and second fields occur simultaneously,

wherein each pixel has two of the pixel circuit, and

wherein, during each frame period, for each pixel, the feedback controller makes one pixel circuit operate in the first field and simultaneously makes the other pixel circuit operate in the second field, and in addition switches, every predetermined number of frames, between the two pixel circuits the pixel circuits that are made to operate in the first and second fields.

39. The active-matrix-driven display device of claim 17,

wherein the active-matrix-driven display device further includes a supply voltage controller that controls a magnitude of a supply voltage for feeding electric power, in each pixel circuit, via the driving transistor to the display element, and

wherein the supply voltage controller makes the magnitude of the supply voltage lower in the second field than in the first field.

27. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, the display panel being so driven that each frame period contains a first field and a second field of which each consists of a light emission preparation period and a light emission period, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that is turned on when a scan voltage having a predetermined level is applied thereto from the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element;

a first capacitive element that, at one end thereof, is connected to the control electrode of the driving transistor; and

an adjustment transistor that is so connected to the display element as to receive, at a first electrode thereof, a voltage commensurate with an electrode-to-electrode voltage of the display element and that can transmit a feedback voltage commensurate with a light emission start electrode-to-electrode voltage of the display element to the first capacitive element,

wherein the active-matrix-driven display device receives a gradation signal for image display to display an image, and further includes;

a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate and that, during each light emission period, for each pixel circuit, feeds a variation in the ramp voltage via the first capacitive element to the control electrode of the driving transistor;

a feedback controller that, during the light emission preparation periods of both the first and second fields, for each pixel circuit, transmits the feedback voltage to the first capacitive element so that a held voltage reflecting the feedback voltage is held in the first capacitive element; and

a gamma conversion circuit that converts the gradation signal into a first converted gradation signal corresponding to the first field and a second converted gradation signal corresponding to the second field and then feeds the first and second converted gradation signals to the data driver so that, for each pixel circuit, a first data voltage that represents as a data voltage a high-gradation side of the gradation signal is fed to the pixel circuit in the first field and a second data voltage that represents as a data voltage a low-gradation side of the gradation signal is fed to the pixel circuit in the second field,

wherein the variation rate of the ramp voltage in the second field is higher than the variation rate of the ramp voltage in the first field.

28. The active-matrix-driven display device of claim 27,

wherein, in each pixel circuit, the adjustment transistor has a second electrode thereof connected to the first capacitive element, and

wherein, during the light emission preparation period of each of the first and second fields, for each pixel circuit, the feedback controller extracts, via the adjustment transistor and the display element, a positive electric charge at the second electrode of the adjustment transistor which is temporarily given a potential higher than a potential equal to a sum of a potential at a cathode of the display element and the light emission start electrode-to-electrode voltage to thereby transmit the feedback voltage to the first capacitive element, and then turns the adjustment transistor off to thereby let the held voltage be held in the first capacitive element.

29. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, the display panel being so driven that each frame period contains at least a reset period and a light emission period, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that is turned on when a scan voltage having a predetermined level is applied thereto from the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element during the light emission period;

a switching transistor that, when turned on, feeds a voltage for turning the driving transistor on to the control electrode of the driving transistor;

a first capacitive element that is provided in series with a line connecting a second electrode of the writing transistor to a control electrode of the switching transistor; and

an adjustment transistor that is turned on during the reset period to feed to a writing-transistor-side electrode of the first capacitive element a voltage commensurate with an electrode-to-electrode voltage of the display element,

wherein the active-matrix-driven display device further includes a control signal generation circuit that, during the reset period, for each pixel circuit, lets a voltage commensurate with a light emission start electrode-to-electrode voltage of the pixel be held in the first capacitive element.

30. The active-matrix-driven display device of claim 29,

wherein the active-matrix-driven display device further includes a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate, and

wherein the pixel circuit of each pixel includes a second capacitive element that feeds a variation in the ramp voltage to the writing-transistor-side electrode of the first capacitive element.

31. The active-matrix-driven display device of claim 30,

wherein the active-matrix-driven display device receives a gradation signal for image display to display an image,

wherein the data driver feeds a data voltage corresponding to the gradation signal to each pixel circuit, and

wherein the variation rate of the ramp voltage is so set that, for each pixel circuit,

let D represent a data voltage fed as corresponding to the received gradation signal,

let D_B represent a data voltage fed when the gradation signal represents a black level of gradation,

let I represent an effective value of a current that flows through the display element as corresponding to the fed data voltage D,

let I_B represent an effective value of a current that flows through the display element when the gradation signal represents a black level of gradation,

let x represent D−

D_B, and

let y_I represent I−

I_B+1,

the formula y_I=a^x (where a is a constant fulfilling a>

1) is fulfilled.

35. The active-matrix-driven display device of claim 29,

wherein, in each pixel circuit, the voltage fed to the control electrode of the driving transistor while the switching transistor is on is constant.

36. The active-matrix-driven display device of claim 29,

wherein, in each pixel circuit, an operating point at which the driving transistor operates while the switching transistor is on is set within a linear region.

32. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, the display panel being so driven that each frame period contains a first field and a second field of which each consists of a light emission preparation period and a light emission period, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that is turned on when a scan voltage having a predetermined level is applied thereto from the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element;

a switching transistor that, when turned on, feeds a voltage for turning the driving transistor on to the control electrode of the driving transistor;

a first capacitive element that is provided in series with a line connecting a second electrode of the writing transistor to a control electrode of the switching transistor; and

an adjustment transistor that is so connected to the display element as to receive, at a first electrode thereof, a voltage commensurate with an electrode-to-electrode voltage of the display element and that can transmit a feedback voltage commensurate with a light emission start electrode-to-electrode voltage of the display element to the first capacitive element,

wherein the active-matrix-driven display device further includes a feedback controller that, during the light emission preparation period of, of the first and second fields, only the first field, for each pixel circuit, transmits the feedback voltage to the first capacitive element so that a held voltage reflecting the feedback voltage is held in the first capacitive element.

33. The active-matrix-driven display device of claim 32,

wherein the active-matrix-driven display device further includes a ramp voltage generation circuit that generates a ramp voltage whose voltage value varies at a predetermined variation rate, and

wherein the pixel circuit of each pixel includes a second capacitive element that feeds a variation in the ramp voltage to the writing-transistor-side electrode of the first capacitive element.

34. The active-matrix-driven display device of claim 33,

wherein the active-matrix-driven display device receives a gradation signal for image display to display an image,

wherein the active-matrix-driven display device further includes a gamma conversion circuit that converts the gradation signal into a first converted gradation signal corresponding to the first field and a second converted gradation signal corresponding to the second field and then feeds the first and second converted gradation signals to the data driver,

wherein the data driver feeds each pixel circuit with a first data voltage corresponding to the first converted gradation signal in the first field and with a second data voltage corresponding to the second converted gradation signal in the second field, and

wherein the variation rate of the ramp voltage is so set that, for each pixel circuit,

let D represent a first data voltage fed as corresponding to the received gradation signal,

let D_B represent a first data voltage fed when the gradation signal represents a black level of gradation,

let I represent an effective value of a current that flows, in the first field, through the display element as corresponding to the fed first data voltage D,

let I_B represent an effective value of a current that flows, in the first field, through the display element when the gradation signal represents a black level of gradation,

let x represent D−

D_B, and

let y_I represent I−

I_B+1,

the formula y_I=a^x (where a is a constant fulfilling a>

1) is fulfilled.

41. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that has a control electrode thereof connected to the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element;

a first capacitive element that is provided in series with a line connecting a second electrode of the writing transistor to the control electrode of the driving transistor; and

an adjustment transistor that turns on and off conduction between a writing-transistors-side electrode of the first capacitive element and the display element.

42. An active-matrix-driven display device including a display panel composed of a plurality of pixels arrayed in a matrix, the display panel being connected to a scan driver for feeding a scan voltage to each pixel and a data driver for feeding a data voltage to each pixel, each pixel being built with a pixel circuit including:

a display element that emits light when fed with electric power;

a writing transistor that has a first electrode thereof connected to the data driver and that has a control electrode thereof connected to the scan driver;

a driving transistor that drives, according to a voltage applied to a control electrode thereof, the display element;

a switching transistor that has one conducting electrode thereof connected to the control electrode of the driving transistor;

a first capacitive element that is provided in series with a line connecting a second electrode of the writing transistor to a control electrode of the switching transistor; and

an adjustment transistor that turns on and off conduction between a writing-transistors-side electrode of the first capacitive element and the display element.