Synchronous backlight device and operation method thereof

Patent metadata

Field	Value
Publication number	US-10692443-B2
Application number	US-201715828396-A
Country	US
Kind code	B2
Filing date	Nov 30, 2017
Priority date	Nov 30, 2017
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

Abstract

A synchronous backlight device and an operation method thereof are provided. The synchronous backlight device includes a pulse width modulation (PWM) control circuit and a backlight driving circuit. The PWM control circuit receives the video sync information from a video processing circuit and generates a PWM control signal. Wherein, the video sync information defines a plurality of video frame periods, the PWM control circuit at least divides each of the video frame periods into a first period and a second period, the lengths of the first periods of the video frame periods are equal to one another. The frequency of the PWM control signal in the first periods is different from the frequency of the PWM control signal in the second periods. The backlight driving circuit drives the backlight source of a display panel in accordance with the PWM control signal.

First claim

What is claimed is:

1. A synchronous backlight device, comprising:
a pulse width modulation (PWM) control circuit, configured to receive video sync information from a video processing circuit and generate a PWM control signal, wherein the video sync information defines a plurality of video frame periods, and the PWM control circuit at least divides each of the video frame periods into different sub-frame periods including a first period and a second period, wherein lengths of the first periods of at least two of the video frame periods are substantially equal, and lengths of the second periods of the at least two of the video frame periods are different, and the PWM control signal in each of the second periods of the video frame periods has substantially a same frequency; and
a backlight driving circuit, coupled to the PWM control circuit to receive the PWM control signal, and configured to drive a backlight source of a display panel according to the PWM control signal,
wherein a flicker effect of the backlight source is reduced by performing a PWM setting operation in each of the sub-frame periods,
wherein the PWM setting operation represents that a first frequency of the PWM control signal in each of the first periods is different from a second frequency of the PWM control signal in each of the second periods, and a first duty ratio of the PWM control signal in each of the first periods is equal to a second duty ratio of the PWM control signal in each of the second periods.

2. The synchronous backlight device according to claim 1 , wherein the video processing circuit comprises a scalar circuit, and the video sync information comprises a vertical sync signal.

3. The synchronous backlight device according to claim 1 , wherein the PWM control circuit at least divides each of the video frame periods into the first period and the second period according to the video sync information, the first period comprises part or all of a data period of one of the video frame periods, and the second period comprises part or all of a blanking period of the one of the video frame periods.

4. The synchronous backlight device according to claim 1 , wherein the first frequency of the PWM control signal in each of the first periods is less than the second frequency of the PWM control signal in each of the second periods.

5. The synchronous backlight device according to claim 1 , wherein the PWM control circuit comprises:
a period defining circuit, configured to receive the video sync information from the video processing circuit and generate a first enablement signal and a second enablement signal according to a timing of the video sync information, wherein the first enablement signal defines the first periods, and the second enablement signal defines the second periods;
a first PWM signal generating circuit, coupled to the period defining circuit to receive the first enablement signal, and configured to generate a first PWM signal according to the first enablement signal in the first periods and determine a duty ratio of the first PWM signal in the first periods according to a duty ratio parameter;
a second PWM signal generating circuit, coupled to the period defining circuit to receive the second enablement signal, and configured to generate a second PWM signal according to the second enablement signal in the second periods and determine a duty ratio of the second PWM signal in the second periods according to the duty ratio parameter, wherein a frequency of the second PWM signal is different from a frequency of the first PWM signal; and
a superimposing circuit, coupled to the first PWM signal generating circuit to receive the first PWM signal, coupled to the second PWM signal generating circuit to receive the second PWM signal, and configured to superimpose the first PWM signal and the second PWM signal to obtain the PWM control signal.

6. The synchronous backlight device according to claim 5 , wherein the first PWM signal generating circuit further determines a phase of the first PWM signal in the first periods according to a delay parameter.

7. The synchronous backlight device according to claim 1 , wherein the PWM control circuit comprises:
a low pass filter, configured to receive the video sync information from the video processing circuit and output a smoothed signal;
a period defining circuit, coupled to the low pass filter to receive the smoothed signal and generate a first enablement signal and a second enablement signal according to a timing of the smoothed signal, wherein the first enablement signal defines the first periods, and the second enablement signal defines the second periods;
a first PWM signal generating circuit, coupled to the period defining circuit to receive the first enablement signal, and configured to generate a first PWM signal in the first periods according to the first enablement signal and determine a duty ratio of the first PWM signal in the first periods according to a duty ratio parameter;
a second PWM signal generating circuit, coupled to the period defining circuit to receive the second enablement signal, and configured to generate a second PWM signal in the second periods according to the second enablement signal and determine a duty ratio of the second PWM signal in the second periods according to the duty ratio parameter, wherein the frequency of the second PWM signal is different from the frequency of the first PWM signal; and
a superimposing circuit, coupled to the first PWM signal generating circuit to receive the first PWM signal, coupled to the second PWM signal generating circuit to receive the second PWM signal, configured to superimpose the first PWM signal and the second PWM signal to obtain the PWM control signal.

8. An operation method of a synchronous backlight device, comprising:
receiving video sync information from a video processing circuit, wherein the video sync information defines a plurality of video frame periods;
at least dividing each of the video frame periods into different sub-frame periods including a first period and a second period by a PWM control circuit, wherein lengths of the first periods of at least two of the video frame periods are substantially equal, and lengths of the second periods of the at least two of the video frame periods are different;
generating a PWM control signal by the PWM control circuit, wherein the PWM control signal in each of the second periods has substantially a same frequency; and
driving a backlight source of a display panel by a backlight driving circuit according to the PWM control signal,
wherein a flicker effect of the backlight source is reduced by performing a PWM setting operation in each of the sub-frame periods,
wherein the PWM setting operation represents that a first frequency of the PWM control signal in each of the first periods is different from a second frequency of the PWM control signal in each of the second periods, and a first duty ratio of the PWM control signal in each of the first periods is equal to a second duty ratio of the PWM control signal in each of the second periods.

9. The operation method according to claim 8 , wherein the video processing circuit comprises a scalar circuit, and the video sync information comprises a vertical sync signal.

10. The operation method according to claim 8 , wherein the PWM control circuit at least divides each of the video frame periods into the first period and the second period according to the video sync information, the first period comprises part or all of a data period of one of the video frame periods, and the second period comprises part or all of a blanking period of the one of the video frame periods.

11. The operation method according

Assignees

• Novatek Microelectronics Corp

Inventors

• Wu Chung-Wen
• Lin Wen-Chi
• Wang Sih-Ting

Classifications

• H03K7/08 Primary

  Duration or width modulation {; Duty cycle modulation} · CPC title

• G09G2320/064

  by time modulation of the brightness of the illumination source · CPC title

• G09G2320/0247

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

• G09G3/3406 Primary

  Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336) · CPC title

• G02F1/133602

  Direct backlight · CPC title