OLED display with control

• US 7,088,051 B1
• Filed: 04/08/2005
• Issued: 08/08/2006
• Est. Priority Date: 04/08/2005
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Cok, Ronald S.
• Primary Examiner(s): Tran, Thuy V.
• Assistant Examiner(s): VY, HUNG T
• Application Number:
  US11/102,354
• Time in Patent Office: 487 Days
• Field of Search: 3151691- 3, 345/204, 345/55, 345/76
• US Class Current: 315/169.1
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2360/147 the originated light output being determined for each pixel
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• 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

An OLED device and control circuit, comprising: a) an OLED responsive to a drive signal; b) a drive circuit connected to the OLED responsive to a charge signal for controlling the drive signal; c) one or more variable charge storage capacitors providing the charge signal; d) a deposition circuit for depositing variable charge in the one or more variable charge storage capacitors; and e) a modulation circuit responsive to an external modulation signal for removing charge from the one or more variable charge storage capacitors.

Claims

1. An OLED device and control circuit, comprising:

a) an OLED responsive to a drive signal;

b) a drive circuit connected to the OLED responsive to a charge signal for controlling the drive signal;

c) one or more variable charge storage capacitors providing the charge signal;

d) a deposition circuit for depositing variable charge in the one or more variable charge storage capacitors; and

e) a modulation circuit responsive to an external modulation signal for removing charge from the one or more variable charge storage capacitors.

2. The OLED device and control circuit claimed in claim 1, wherein the deposition circuit is responsive to a deposition signal that periodically refreshes the charge in the one or more variable charge storage capacitors, and wherein the modulation signal has a common frequency and period with the deposition signal, but differs in phase from the deposition signal.

3. The OLED device and control circuit claimed in claim 1, wherein the deposition circuit is responsive to a deposition signal that periodically refreshes the charge in the one or more variable charge storage capacitors, and wherein the modulation circuit responsive to the external modulation signal changes the charge in the one or more variable charge storage capacitors after the charge has been refreshed and each time the charge has been refreshed.

4. The OLED device and control circuit claimed in claim 3, wherein the variable capacitor charge is decreased.

5. The OLED device and control circuit claimed in claim 4, wherein the variable capacitor charge is removed.

6. The OLED device and control circuit claimed in claim 1, wherein the deposition circuit is responsive to a deposition signal that periodically refreshes the charge in the one or more variable charge storage capacitors, and wherein the OLED emits light at a first level for a first portion of each refresh period and emits light at a second level for a second portion of each refresh period.

7. The OLED device and control circuit claimed in claim 6, wherein the OLED does not emit any light for the second portion of each refresh period.

8. The OLED device and control circuit claimed in claim 6, wherein the drive circuit has a preferred operating range and wherein the drive circuit is operated inside the preferred operating range during the first portion and does not operate within the preferred range during the second portion.

9. The OLED device and control circuit claimed in claim 8, wherein the length of the first portion is chosen to cause the OLED to output the desired amount of light and to cause the display driver to operate in the preferred range.

10. The OLED device and control circuit claimed in claim 6, wherein the length of the first portion is chosen to compensate for the aging of the OLED.

11. The OLED device and control circuit claimed in claim 1, further comprising a plurality of OLEDs with associated modulation circuits connected to a common external modulation signal.

12. The OLED device and control circuit claimed in claim 11, wherein the device comprises OLEDs that emit light of different colors, and wherein the plurality of OLEDs connected to the common external modulation signal are OLEDs that emit light of the same color.

13. The OLED device and control circuit claimed in claim 1, wherein the drive circuit is a voltage-controlled drive circuit or a current-controlled drive circuit.

14. An OLED device and control circuit claimed in claim 1, wheren the OLED device is an OLED display comprising:

a plurality of OLEDs, each responsive to a drive circuit;

the drive circuit of each OLED responsive to a storage circuit;

the storage circuit of each OLED responsive to a control signal for storing a variable signal in the storage circuit, and the storage circuit responsive to a modulation signal for modifying the stored signal; and

a controller for providing control and modulation signals to each storage circuit;

wherein the periodic control signal to each storage circuit has a period P for refreshing a stored first value in the storage circuit;

the modulation signal has the same period P but a different phase for modifying the stored value in the storage circuit to a stored second value; and

the drive circuit drives the OLED at a first brightness V₁ corresponding to the stored first value and at a second brightness V₂ corresponding to the second stored value.

15. The control system of claim 14 wherein the perceived brightness of an OLED is determined by ((V₁*P₁)+(V₂*P₂))/P, where P₁ is the time between the beginning of the period P and the beginning of the modulation signal for modifying the stored signal and P₂ is the time between the beginning of the modulation signal and the end of the period P.

16. The control system of claim 15 wherein V₂ is zero.

17. The control system of claim 15 wherein P₁ is determined by the relative efficiency of the OLEDs.

18. The control system of claim 15 wherein R is the ratio of P₁ and P, R_initial is the initial value of R, E_T is the relative efficiency of the light emitting materials at time T, and the ratio of P1 and P is changed over time in accordance with R=R_initial/E_T.

19. The control system of claim 18 wherein the value V₁ of the control signal during the first portion P₁ is a predetermined maximum value V_Max corresponding to the desired brightness of the OLED elements divided by the ratio of P₁ and P.

20. The control system of claim 14 wherein the period P is equal to the period of a frame refresh of a video signal.