Active matrix electroluminescent display device

• US 6,542,138 B1
• Filed: 09/11/2000
• Issued: 04/01/2003
• Est. Priority Date: 09/11/1999
• Status: Expired due to Term

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Knapp, Alan G., Shannon, John M.
• Primary Examiner(s): WU, XIAO MIN
• Application Number:
  US09/658,925
• Time in Patent Office: 932 Days
• Field of Search: 345/74.1, 345/75.1, 345/75.2, 345/76, 345/77, 345/78, 345/79, 345/80, 345/81, 345/82, 345/83, 315/169.1, 315/169.3
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• 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 2300/088 using a non-linear two-terminal element
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: H10K 59/13 comprising photosensors that control luminance

Abstract

An active matrix electroluminescent display device in which the drive current through an electroluminescent display element (20) in each pixel (10) in a drive period is controlled by a driving device (22) based on a drive signal applied during a preceding address period and stored as a voltage on an associated storage capacitor (36). In order to counteract the effects of display element ageing, through which the light output for a given drive signal level diminishes over time, the pixel includes electro-optic discharging means (40) coupled to the storage capacitor and responsive to the display element'"'"'s light output to leak stored charge and to control the integrated light output of the display element in the drive period. For improved control, the discharging means is arranged to rapidly discharge the capacitor at a controlled point in the drive period, upon the drive of the display element falling to a low level. A photoresponsive transistor can conveniently be utilised for this purpose.

Claims

1. A display pixel employed within an active matrix electroluminescent display device, said display pixel comprising:

an electroluminescent display device operable to emit light in response a current flowing through said electroluminescent display device;

a driving device operable to control a flow of the current through said electroluminescent display device in response to a reception of a drive signal during an address period and a drive period of said display panel, the drive period succeeding the address period;

an address device operable to provide the drive signal to said driving device during the address period of said display pixel;

a storage device operable to store the drive signal during the address period of said display pixel, said storage device further operable to discharge and provide the drive signal to said driving device during the drive period of said display pixel; and

an optical feedback device operable to be electro-optically coupled to said electroluminescent display device during the address period and the driver period of said display device, said optical feedback device operable to control a discharge rate of the drive signal by said storage device during the drive period of said display pixel, the discharge rate being dependent on the output level of the light emitted by said electroluminescent display device,

wherein an operation of said driving device during the address period of said display pixel is unaffected by an electro-optical coupling of said electroluminescent display device and said optical feedback device during the address period of said display pixel.

2. The display pixel of claim 1,

wherein the output light of the light emitted by said electroluminescent display device continually decreases during the drive period.

3. The display pixel of claim 1,

wherein a first mode of operation of said optical feedback device is defined by the output level of the light emitted by said electroluminescent display device (20) during the drive period being above a threshold;

wherein a second mode of operation of said optical feedback device is defined by the output level of the light emitted by said electroluminescent display device (20) during the drive period being below the threshold; and

wherein a first average of the discharge rate during the first mode of operation is less than a second average of the discharge rate during the second mode of operation.

4. A display pixel employed within an active matrix electroluminescent display device, said display pixel comprising:

an electroluminescent display device operable to emit light in response a current flowing through said electroluminescent display device;

a driving device operable to control a flow of the current through said electroluminescent display device in response to a reception of a drive signal during an address period and a drive period of said display panel, the drive period succeeding the address period;

an address device operable to provide the drive signal to said driving device during the address period of said display pixel;

a storage device operable to store the drive signal during the address period of said display pixel, said storage device further operable to discharge and provide the drive signal to said driving device during the drive period of said display pixel; and

an optical feedback device operable to be electro-optically coupled to said electroluminescent display device during the address period and the driver period of said display device, said optical feedback device operable to control a discharge rate of the drive signal by said storage device during the drive period of said display pixel, the discharge rate being dependent on the output level of the light emitted by said electroluminescent display device,

wherein the output light of the light emitted by said electroluminescent display device continually decreases during the drive period.

5. The display pixel of claim 4,

wherein a first mode of operation of said optical feedback device is defined by the output level of the light emitted by said electroluminescent display device (20) during the drive period being above a threshold;

wherein a second mode of operation of said optical feedback device is defined by the output level of the light emitted by said electroluminescent display device (20) during the drive period being below the threshold; and

wherein a first average of the discharge rate during the first mode of operation is less than a second average of the discharge rate during the second mode of operation.