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US-12626645-B2 - Baseline and shaped pulse driving for micro-light emitting diode display

US12626645B2US 12626645 B2US12626645 B2US 12626645B2US-12626645-B2

Abstract

A micro-LED driver applies a low baseline power (i.e., a baseline voltage or current) to pre-charge a micro-LED in a nominally-off (i.e., non-light-emitting) state in addition to applying an operating driving power to drive the micro-LED in a light-emitting state. By pre-charging the micro-LED prior to applying the operating driving power, the micro-LED driver significantly decreases the time between application of the operating driving power and onset of emission of light from the micro-LED. In some embodiments, the micro-LED driver applies an operating driving power having multiple phases of current density to reduce the time between application of the operating driving power and onset of emission of light from the micro-LED.

Inventors

  • Aurelien Jean Francois David
  • Patrick F. Brinkley
  • Carlin Vieri

Assignees

  • GOOGLE LLC

Dates

Publication Date
20260512
Application Date
20240930

Claims (20)

  1. 1 . An apparatus, comprising: a micro-LED display having: a micro-LED with a lateral dimension that is smaller than 20 μm, and a driver driving the micro-LED with a current pulse to emit a light pulse having a turn-on time, the current pulse having a pulse profile having different amplitudes at different times, the pulse profile being configured to cause the turn-on time to be less than 500 ns.
  2. 2 . The apparatus of claim 1 , wherein the pulse profile has a first phase having a relatively high current density and a second phase having a relatively low current density.
  3. 3 . The apparatus of claim 1 , wherein the pulse profile has a first phase having a current density higher than a current density of a second phase of the pulse profile.
  4. 4 . The apparatus of claim 1 , wherein the light pulse has a light output within +/−10% of a predetermined value.
  5. 5 . The apparatus of claim 1 , wherein the driver includes a plurality of power paths that generate the pulse profile.
  6. 6 . The apparatus of claim 1 , wherein the current pulse has a pulse profile including a discharge pulse.
  7. 7 . The apparatus of claim 1 , wherein the pulse profile is configured to match the turn-on time and a turn-off time of the light pulse.
  8. 8 . An apparatus, comprising: a micro-LED display having a micro-LED with a lateral dimension smaller than 20 μm; and a driver driving the micro-LED with a current pulse configured to emit a light pulse having a turn-on time and a turn-off time, the current pulse having a pulse profile with different amplitudes at different times, the pulse profile being configured to match the turn-on time and the turn-off time.
  9. 9 . The apparatus of claim 8 , wherein the pulse profile has a first phase having a relatively high current density and a second phase having a relatively low current density.
  10. 10 . The apparatus of claim 8 , wherein the pulse profile has a first phase having a current density higher than a current density of a second phase of the pulse profile.
  11. 11 . The apparatus of claim 8 , wherein the light pulse has a light output within +/−10% of a predetermined value.
  12. 12 . The apparatus of claim 8 , wherein the pulse profile includes a discharge pulse.
  13. 13 . An apparatus comprising: a micro-LED display having a micro-LED with a lateral dimension smaller than 20 μm, and a driver driving the micro-LED with a power pulse configured to emit a light pulse having a turn-off time, the power pulse has a pulse profile having different amplitudes at different times, the pulse profile including a discharge step configured to cause the turn-off time to be short.
  14. 14 . The apparatus of claim 13 , wherein the discharge step removes charge from the micro-LED.
  15. 15 . The apparatus of claim 13 , wherein the discharge step includes a discharge pulse.
  16. 16 . The apparatus of claim 13 , wherein the pulse profile has a first phase having a current density higher than a current density of a second phase of the pulse profile.
  17. 17 . The apparatus of claim 13 , wherein the light pulse has a light output within +/−10% of a predetermined value.
  18. 18 . The apparatus of claim 13 , wherein the power pulse is configured to emit the light pulse such that the light pulse has a turn-on time.
  19. 19 . The apparatus of claim 13 , wherein the power pulse is configured to emit the light pulse such that the light pulse has a turn-on time shorter than the turn-off time.
  20. 20 . The apparatus of claim 13 , wherein the pulse profile is configured to match a turn-on time of the light pulse and the turn-off time.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 18/400,609, filed on Dec. 29, 2023, entitled “BASELINE AND SHAPED PULSE DRIVING FOR MICRO-LIGHT EMITTING DIODE DISPLAY”, which claims priority to U.S. patent application Ser. No. 17/687,020, filed on Mar. 4, 2022, entitled “BASELINE AND SHAPED PULSE DRIVING FOR MICRO-LIGHT EMITTING DIODE DISPLAY”, now U.S. Pat. No. 11,862,069, which claims priority to International Patent Application No. PCT/US2021/023601, filed on Mar. 23, 2021, entitled “BASELINE AND SHAPED PULSE DRIVING FOR MICRO-LIGHT EMITTING DIODE DISPLAY”, the disclosures of which are incorporated by reference herein in their entirety. BACKGROUND A display panel includes an array of pixels arranged in rows and columns, typically having on the order of thousands or even tens-of-thousands of rows and columns. Each pixel may be implemented as a matrix of sub-pixels, such as a particular arrangement of red, green, and blue (RGB) sub-pixels, each of which is controlled to emit light of the corresponding color at a corresponding luminance, and the combination of light colors and their luminance results in the intended brightness and color for the pixel as a whole. Light emitting diode (LED) displays include an array of LEDs forming the sub-pixels, with drivers that employ pulse width modulation (PWM) to modulate the LEDs between an off- and an on-state to display images, with a modulation frequency in the kHz range. The rise and fall times of the LEDs are commensurate with a kHz-range frequency, providing an adequate response time for displaying images at the frequency of the PWM. Future displays are expected to include micro-LEDs with pixels having a lateral dimension that is smaller than 50 μm. The micro-displays are expected to include light-emitting elements (i.e., micro-LEDs) and a driver to feed a current pulse to the light-emitting elements. It is an object of the present disclosure to provide an improved method and of driving micro-LEDs that obviates or mitigates one or more problems associated with known methods, whether identified herein or otherwise. SUMMARY According to a general aspect, a micro-LED driver applies a low baseline power (i.e., a baseline voltage or current) to pre-charge a micro-LED in a nominally-off (i.e., non-light-emitting) state in addition to applying an operating driving power to drive the micro-LED in a light-emitting state. By pre-charging the micro-LED prior to applying the operating driving power, the micro-LED driver significantly decreases the time between application of the operating driving power and onset of emission of light from the micro-LED. In some embodiments, the micro-LED driver applies an operating driving power having multiple phases of current density to reduce the time between application of the operating driving power and onset of emission of light from the micro-LED. According to a first aspect, there is provided a method comprising driving a first micro light emitting diode (micro-LED) having a lateral dimension that is smaller than 20 μm in a nominally-off state at a first baseline power greater than zero. The method further comprises driving the first micro-LED in a light-emitting state at a power greater than the first baseline power, wherein an amount of light emitted by the first micro-LED in the nominally-off state is negligible compared to a minimum amount of light emitted by the first micro-LED in the light-emitting state. Driving the first micro-LED at the first baseline power may comprise applying the first baseline power prior to driving the first micro-LED in the light-emitting state. Driving the first micro-LED in the nominally-off state may be performed immediately prior to driving the first micro-LED in the light-emitting state. The method may further comprise driving a second micro-LED in a nominally-off state at a second baseline power greater than zero. The second baseline power may be different from the first baseline power. The method may further comprise driving the second micro-LED in a light-emitting state at a power greater than the second baseline power. The first micro-LED and the second micro-LED may emit different color light from one another. Driving the first micro-LED in the light-emitting state may comprise driving the first micro-LED with a current pulse comprising a first phase having a relatively higher current density and a second phase having a relatively lower current density. The first phase may immediately precede the second phase. The first phase may have a current density at least twice the current density of the second phase. The method may further comprise driving a second micro-LED in a light-emitting state. Driving the second micro-LED in the light-emitting state may comprise driving the second micro-LED with a current pulse comprising a second micro-LED first phase having a relatively higher current density and a second micro-LED second phase h