Label and CABC-MTK Platform

Label and CABC-MTK Platform

Author: cjok

Contact: cjok. Liao # gmail.com

Date: 2013.4.12

1. Introduction

As mobile devices become more intelligent and the hardware leaps forward, the power consumption is getting bigger and bigger. The result is a one-day stop. However, the current battery technology is still in progress, so we can only respond to the national call to start from "Energy Conservation and emission reduction. The display screen has always been a large power-consuming device in mobile devices. The backlight of the display screen is obviously a battery killer, so we take the backlight and open the knife to introduce the two practical applications and more feasible power-saving methods.

Lightadaptive brightness control-labc: controls the brightness of a backlight based on changes in ambient light.

Contentadaptive brightness control-CABC: adjusts the backlight and gamma values based on the display content.

 

2. labc

Labc technology needs to be implemented with an optical sensor. The host processor reads the optical value, and then the processor processes the value to directly control the PMIC (mt6329) output PWM to control the brightness of the backlight. In relatively dark lines, the backlight is reduced to save power. The following figure shows the functional modules of labc:

 

3. CABC

The CABC function requires a new imagecontent analyzer circuit in the LCD Driver IC. When the mobile phone processor transmits an image to the driver IC, after the Content Analyzer calculates and counts the image data, it automatically increases the gray-scale brightness by 30% based on the settings and algorithms (the image turns on at this time), and then reduces the backlight brightness by 30% (the image is dimmed at this time ). Because we have already compensated the brightness of the image through the analyzer circuit, the user can get a display effect that is similar to the original circuit, but reduces the backlight power consumption by 30%.

Simply put, the CABC function is to reduce the backlight Based on the display content, and then compensate the display brightness by adjusting the gamma (the higher the Gamma, the lower the gray level, the darker the image. The following figure shows the PMIC direct backlight control solution Module Based on the MTK platform:

 

 

The workflow is as follows:

1. Enable the PMIC (mt6329) CABC function;

2. Configure the LCD Driver IC (enable CABC and configure gamma parameters. Fae is required );

3. the CABC module analyzes and displays the output of the led_pwm signal to the PMIC. The PMIC controls the output waveform of the bl_drv signal of the driver module through a certain algorithm;

4. The expected result is that the brightness of the backlight is reduced, and the LCD Driver IC reduces the GAMMA value to compensate the screen brightness.

 

 

The analysis of the CABC module shows that the content outputs the PWM waveform. The larger the duty cycle, the larger the current to be output. The following two waveforms show the PWM waveforms output by CABC when the white and black pictures are displayed:

White Image

 

Black Image

It can be learned that the duty cycle of a black image is smaller than that of a white image. Using the CABC function, it is more cost-effective to display images in deep colors than those in light colors.

 

The following table shows how to enable or disable the CABC function to display the backlight current data measured by pure white and pure black pictures:

	Open CABC	Disable CABC
Pure White Image	8mA	12mA
Pure black image	7mA	12mA

From the data, we can see that after the CABC function is enabled, the power is reduced by about 30%, and the black image is more energy-saving than the white image. However, the actual display effect is slightly darker when the CABC function is enabled than when the CABC function is not enabled, and the display effect not boasted by an IC manufacturer will not be affected.

 

4. Comparison between labc and CABC

The basic backlight power-saving principle of labc and CABC is the same, but the judgment mechanism is slightly different: labc adjusts the brightness of the backlight according to the change of ambient light; CABC adjusts the backlight and Gamma by judging the content currently displayed. Relatively speaking, CABC is more practical than labc, and the power saving effect is more obvious.

5. Open both CABC and labc

Labc sets the brightnesslevel for PMIC by sending the I2C command. CABC sends the PWM signal to PMIC and uses an algorithm (only the persons who do the IC know how to process the PMIC --) after calculation, the PWM is output to the backlight.

6. Summary

At present, labc has been widely used on mobile devices. Almost every mobile phone is equipped with this function, but mobile devices equipped with the CABC function are rare. From the author's practical application, the power saving effect of the CABC function is quite obvious, but there are still some incomplete aspects, which have a great relationship with the CABC module, the CABC modules of LCD Driver IC vary from manufacturer to manufacturer, so the effects are also uneven.

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