Low-Flicker Variable Refresh Rate Display

Patent metadata

Field	Value
Publication number	US-2016196802-A1
Application number	US-201514591354-A
Country	US
Kind code	A1
Filing date	Jan 7, 2015
Priority date	Jan 7, 2015
Publication date	Jul 7, 2016
Grant date	—

Abstract

An electronic device may have a variable refresh rate display. Static content may be displayed on the display at a lower refresh rate than moving content to conserve power. The display may include an array of pixels. Display driver circuitry in the display may load image data into rows of the pixels. The display driver circuitry may have digital-to-analog converter circuitry that supplies data signals to the array. The display driver circuitry may respond to a variable refresh rate control signal that is asserted and deasserted depending on whether static or moving image content is to be displayed. The display driver circuitry may use the digital-to-analog converter circuitry to apply a time-varying scaling factor to the image data. The magnitude of the scaling factor may be adjusted during transitions between refresh rates to help suppress luminance variations that might otherwise result in flickering on the display.

First claim

What is claimed is:

1 . A variable refresh rate display, comprising:
display driver circuitry that receives image data; and an array of pixels for displaying images at multiple refresh rates, wherein the display driver circuitry comprises digital-to-analog circuitry that applies a time-varying scaling factor to the image data while loading the image data into the array of pixels to prevent visual artifacts due to refresh rate transitions.

2 . The variable refresh rate display defined in claim 1 wherein the multiple refresh rates include a first refresh rate and a second refresh rate that is lower than the first refresh rate and wherein the display driver circuitry is configured to apply a first scaling factor to the image data during use of the first refresh rate to refresh the image data on the array of pixels and is configured to apply a second scaling factor to the image data during use of the second refresh rate to refresh the image data on the array of pixels.

3 . The variable refresh rate display defined in claim 2 wherein second scaling factor is smaller than the first scaling factor.

4 . The variable refresh rate display defined in claim 3 wherein the display driver circuitry is configured to apply at least a third scaling factor to the image data when transitioning between the second refresh rate and the first refresh rate.

5 . The variable refresh rate display defined in claim 4 wherein the third scaling factor is greater than the first scaling factor.

6 . The variable refresh rate display defined in claim 5 wherein the display driver circuitry is configured to apply the first scaling factor to the image data after applying the third scaling factor to the image data when transitioning between the second refresh rate and the first refresh rate.

7 . A method of operating an electronic device with a variable refresh rate display, comprising:
receiving image data with display driver circuitry in the variable refresh rate display; displaying images at multiple refresh rates on an array of pixels in the variable refresh rate display using the display driver circuitry; and applying a time-varying scaling factor to the image data using digital-to-analog circuitry in the display driver circuitry while loading the image data into the array of pixels to prevent visual artifacts due to refresh rate transitions.

8 . The method defined in claim 7 wherein the multiple refresh rates include a first refresh rate and a second refresh rate that is lower than the first refresh rate and wherein applying the time-varying scaling factor comprises:
applying a first scaling factor to the image data during use of the first refresh rate to refresh the image data on the array of pixels; and
applying a second scaling factor to the image data during use of the second refresh rate to refresh the image data on the array of pixels.

9 . The method defined in claim 8 wherein the second scaling factor is smaller than the first scaling factor and wherein applying the second scaling factor comprises applying the second scaling factor that smaller than the first scaling factor.

10 . The method defined in claim 9 further comprising:
analyzing the image data with control circuitry in the electronic device to determine how to adjust the refresh rate.

11 . The method defined in claim 10 further comprising providing the image data from the control circuitry to the display driver circuitry, wherein analyzing the image data comprises processing the image data in a frame buffer in the control circuitry.

12 . The method defined in claim 11 further comprising:
asserting a variable refresh rate control signal with the control circuitry in response to detection of static image content when processing the image data in the frame buffer.

13 . The method defined in claim 12 wherein the second refresh rate is smaller than the first refresh rate, the method further comprising:
adjusting the refresh rate from the first refresh rate to the second refresh rate with the display driver circuitry in response to receipt of the asserted variable refresh rate control signal with the display driver circuitry.

14 . The method defined in claim 13 further comprising:
adjusting the refresh rate from the second refresh rate to the first refresh rate with the display driver circuitry in response to deassertion of the variable refresh rate control signal.

15 . The method defined in claim 14 further comprising:
applying at least a third scaling factor to the image data when transitioning between the second refresh rate and the first refresh rate.

16 . The method defined in claim 15 wherein the third scaling factor is greater than the first scaling factor, the method further comprising:
when transitioning between the second refresh rate and the first refresh rate, applying the first scaling factor to the image data with the display driver circuitry after applying the third scaling factor to the image data.

17 . The method defined in claim 16 further comprising:
deasserting the variable refresh rate control signal in response to identifying moving image content in the frame buffer with the control circuitry.

18 . An electronic device, comprising:
control circuitry that analyzes image data to identify static image content and moving image content in the image data, wherein the control circuitry asserts a variable refresh rate control signal in response to identifying the static image content and deasserts the variable refresh rate control signal in response to identifying the moving image content; and a variable refresh rate display having display driver circuitry and having an array of pixels on which the display driver circuitry displays images corresponding to the image data, wherein the display driver circuitry includes a digital-to-analog converter that scales the image data by different amounts at different times to minimize visible display artifacts when transitioning between multiple refresh rates for the variable refresh rate display.

19 . The electronic device defined in claim 18 wherein the control circuitry includes a frame buffer and wherein the control circuitry analyzes the image data by processing image data in the frame buffer.

20 . The electronic device defined in claim 18 wherein the digital-to-analog converter is configured to scale the image data by applying a time-varying scaling factor to data signals being loaded into the array of pixels and wherein the digital-to-analog converter adjusts the scaling factor in response to transitions between the refresh rates.

Assignees

• Apple Inc

Inventors

• Nho Hyunwoo
• Chen Wei
• Yao Wei
• Bi Yafei

Classifications

• G09G2320/0247

  Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes · CPC title

• G09G2320/0673

  for control of gamma adjustment, e.g. selecting another gamma curve · CPC title

• G09G2320/103

  Detection of image changes, e.g. determination of an index representative of the image change · CPC title

• G09G3/20 Primary

  for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix {no fixed position being assigned to or needed to be assigned to the individual characters or partial characters} · CPC title

• G09G2310/08

  Details of timing specific for flat panels, other than clock recovery · CPC title