Display systems with compensation for line propagation delay

• US 8,922,544 B2
• Filed: 03/13/2013
• Issued: 12/30/2014
• Est. Priority Date: 05/23/2012
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza, Azizi, Yaser
• Primary Examiner(s): Edun, Muhammad N
• Application Number:
  US13/800,153
• Publication Number:
  US 20130314394A1
• Time in Patent Office: 657 Days
• Field of Search: None
• US Class Current: 345/212
• CPC Class Codes: G09G 1/002 Intensity circuits G09G1/06 - G09G1/28 take precedence
• CPC Class Codes: G09G 1/12 the deflection signals being produced by essentially analogue means
• 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2330/10 Dealing with defective pixels
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/18 using liquid crystals
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: G09G 3/3225 using an active matrix
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A method for characterizing and eliminating the effect of propagation delay on data and monitor lines of AMOLED panels is introduced. A similar technique may be utilized to cancel the effect of incomplete settling of select lines that control the write and read switches of pixels on a row.

Claims

1. A display system comprising:

a pixel circuit including a light emitting device and a driving transistor for driving current through the light emitting device according to a driving voltage across the driving transistor, the pixel circuit further including one or more switch transistors arranged to selectively connect the pixel circuit to a signal line and a monitoring line;

a driver for programming the pixel circuit with the driving voltage via the signal line;

a monitor for measuring a current through the driving transistor via the monitoring line; and

a controller for operating the driver and the monitor, the controller being configured to;

measure a first current through the drive transistor, via the monitor, for a duration sufficient for the current on the monitoring line to settle at a steady value and thereby avoid propagation delay effects of the monitoring line;

measure a second current through the drive transistor, via the monitor, for a duration provided for a monitoring timing budget of the display; and

compare the measured first and second currents to extract the propagation delay effects of the monitoring line for the pixel.

2. The display system according to claim 1, wherein the controller is further configured to:

determine a gain factor associated with current measured from the pixel circuit based on a ratio of the measured first and second current values; and

scale a subsequent current measurement according to the determined gain factor so as to account for the propagation delay effects of the monitoring line.

3. The display system according to claim 1, wherein the display system comprises an array of pixel circuits arranged in rows and columns, and wherein the controller is further configured to repeat the measurement and comparison for a representative subset of the pixels in the display so as to characterize the propagation delay effects of the monitoring line at a range of line distances from the monitor.

4. The display system according to claim 1, wherein the controller is further configured to:

program the pixel circuit, via the driver, for a duration sufficient for the applied voltage to settle at a steady value on the signal line and thereby avoid propagation delay effects of the signal line;

measure a third current through the drive transistor, via the monitor;

program the pixel circuit, via the driver, for a duration provided for a programming timing budget of the display;

measure a fourth current through the drive transistor, via the monitor;

compare the third and fourth current values to extract the propagation delay effects of the signal line for the pixel.

5. The display system according to claim 4, wherein the display system comprises an array of pixel circuits arranged in rows and columns, and wherein the controller is further configured to repeat the program operations, the measurement operations, and the comparison for a representative subset of the pixels in the display so as to characterize the propagation delay effects of the signal line at a range of line distances from the driver.

6. The display system according to claim 1, wherein the controller is further configured to:

determine a time-dependent parameter of the driving transistor by measuring current through the driving transistor, while accounting for the propagation delay effects of the monitoring line; and

adjust a subsequent programming value according to the determined time-dependent parameter.

7. A method of characterizing propagation delay effects in a display system including a pixel circuit having a light emitting device driven by a driving transistor, the pixel circuit connected to a signal line for providing programming voltages to the pixel circuit for influencing the current through the driving transistor and a monitor line for measuring current levels through the driving transistor, the method comprising:

measuring a first current through the drive transistor, via the monitor, for a duration sufficient for the current to settle at a steady value and thereby avoid propagation delay effects of the monitoring line;

measuring a second current through the drive transistor, via the monitor, for a duration provided for a monitoring timing budget of the display; and

comparing the first and second current to extract the propagation delay effect of the monitor line for the pixel circuit.

8. The method according to claim 7, further comprising:

receiving a data input indicative of an amount of luminance to be emitted from the light emitting device; and

determining an adjustment to at least one of programming the display via the driver or the measuring based on the determined propagation delay effect such that the display system is operated substantially independent of line propagation delay effects.

9. The method according to claim 7, wherein the display system further includes a plurality of pixel circuits arranged in rows and columns, the method further comprising:

repeating the measuring and comparing for a subset of the pixel circuits in the display system so as to characterize the propagation delay effects of the monitor line at a range of line distances from the monitor.

10. A method of characterizing propagation delay effects in a display system including a pixel circuit having a light emitting device driven by a driving transistor, the pixel circuit connected to a signal line for providing programming voltages to the pixel circuit for influencing the current through the driving transistor and a monitor line for measuring current levels through the driving transistor, the method comprising:

programming the pixel circuit, via the driver, for a duration sufficient for an applied voltage to settle at a steady value on the signal line and thereby avoid propagation delay effects of the signal line;

measuring a first current through the driving transistor, via the monitor, responsive to the programming with the duration sufficient to avoid propagation delay effects;

programming the pixel circuit, via the driver, for a duration provided for a programming timing budget of the display;

measuring a second current through the driving transistor, via the monitor, responsive to the programming with the programming timing budget;

comparing the first and second current to extract the propagation delay effect of the signal line for the pixel circuit.

11. The method according to claim 10, further comprising:

receiving a data input indicative of an amount of luminance to be emitted from the light emitting device; and

determining an adjustment to at least one of the programming or measuring based on the determined propagation delay effect such that the display system is operated substantially independent of line propagation delay effects.

12. The method according to claim 10, wherein the display system further includes a plurality of pixel circuits arranged in rows and columns, the method further comprising:

repeating the programming, measuring, and comparing for a subset of the pixel circuits in the display system so as to characterize the propagation delay effects of the signal line at a range of line distances from the driver.