Active matrix electroluminescent display device

• US 6,356,029 B1
• Filed: 10/02/2000
• Issued: 03/12/2002
• Est. Priority Date: 10/02/1999
• Status: Expired due to Term

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Hunter, Iain M.
• Primary Examiner(s): Philogene, Haissa
• Application Number:
  US09/677,803
• Time in Patent Office: 526 Days
• Field of Search: 315/169.3, 315/169.1, 315/169.2, 315/224, 315/291, 345/76, 345/36, 345/45, 345/92, 345/204, 345/214
• US Class Current: 315/169.1
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• 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 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• 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 an active matrix electroluminescent display device the drive current through an EL display element (20) in each pixel (10) in a drive period is controlled by a driving device (22) based on a drive signal applied to the pixel in 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 of an element for a given drive signal level diminishes over time, the pixel includes a feedback circuit (40, 45, 47, 48) which is responsive to the potential difference across the display element in an initial part of the drive period indicative of the extent of ageing and which is arranged to adjust the voltage stored on the storage capacitance accordingly.

Claims

1. An active matrix electroluminescent display device comprising an array of display pixels each comprising an electroluminescent display element and a driving device for controlling the current through the display element in a drive period based on a drive signal applied to the pixel during a preceding address period and stored as a voltage on a storage capacitance connected to the driving device, characterised in that each pixel includes feedback adjustment means responsive to the potential difference across the display element in the drive period and arranged to adjust the voltage stored on the storage capacitance in the address period in accordance therewith.

2. An active matrix electroluminescent display device according to claim 1, characterised in that the pixel includes a switching device operable to prevent electrical current flowing through the display element during the address period and allow drive current to flow through the display element in the drive period.

3. An active matrix electroluminescent display device according to claim 1, characterised in that the feedback adjustment means is responsive to the transient potential difference increase across the display element at the beginning of the drive period.

4. An active matrix electroluminescent display device according to claim 1, characterised in that said feedback adjustment means comprises a high pass filter circuit connected to the display element and responsive to the rise in voltage across the display element immediately following the address period to provide an output in accordance therewith which output controls the adjustment of the voltage stored on the storage capacitance.

5. An active matrix electroluminescent display device according to claim 4, characterised in that the output of the high pass filter controls a further switching device connected between the storage capacitance and a predetermined potential and operable by said output to provide supplemental charging of the storage capacitor.