Patent Application
20090096742
Embodiments of the present disclosure relate to systems of backlight modulation circuits that are typically used in liquid crystal displays (LCDs), and more particularly to a backlight modulation circuit with rough and fine modulation functions.
Because LCDs have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, etc.
A conventional LCD typically includes a liquid crystal (LC) panel, a backlight module with a plurality of light sources for illuminating the LC panel, and a backlight modulation circuit for modulating illumination provided by the backlight module.
Referring to
In a digital method for modulating illumination provided by a backlight module, pulse width modulation (PWM) and pulse frequency modulation (PFM) may be used.
One drawback of the above-described analog and digital PWM methods is that they can only modulate the illumination provided by the backlight module little by little. However, if an LCD needs to be modulated in both a large range and a precise range, then many modulation commands and signals may need to be analyzed. In such case, modulating the many commands and signals wastes valuable processor cycles and consumes additional energy.
It is desired to provide a backlight modulation circuit which can overcome the above-described deficiencies.
In one embodiment, a backlight modulation circuit includes a backlight source, a backlight driving circuit, a rough modulation key, a fine modulation key, a scaler, and an illumination modulation signal processing circuit. The backlight driving circuit is configured for driving the backlight source. The rough modulation key and the fine modulation key are configured for generating a rough triggering signal and a fine triggering signal. The scaler is configured for receiving the rough triggering signal and the fine triggering signal, and generating an illumination modulation signal. The illumination modulation signal processing circuit is configured for receiving the illumination modulation signal, and processing the illumination modulation signal to generate one of a rough modulation controlling signal to modulate illumination of the backlight source in a large range and a fine modulation controlling signal to modulate the illumination of the backlight source in a small range.
Other novel features and advantages of the backlight modulation circuit will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
Reference will now be made to the drawings to describe various inventive embodiments of the present disclosure in detail, wherein like numerals refer to like elements throughout.
The scaler 23 includes a rough signal processing circuit 231, a rough controlling signal generating circuit 232, a fine signal processing circuit 233, a fine controlling signal generating circuit 234, and a modulating circuit 235. The rough signal processing circuit 231 is electrically connected to the rough controlling signal generating circuit 232. The fine signal processing circuit 233 is electrically connected to the fine controlling signal generating circuit 234. The fine controlling signal generating circuit 234 and the rough controlling signal generating circuit 232 are connected to the modulation circuit 235. The modulating circuit 235 includes a controlling variable resistor (not shown). When the rough signal processing circuit 231 receives a rough triggering signal, the rough controlling signal generating circuit 232 generates a rough controlling signal. The rough controlling signal controls the controlling variable resistor of the modulation circuit 235 to generate a desired direct current voltage. When the fine signal processing circuit 233 receives a fine triggering signal, the fine controlling signal generating circuit 234 generates a fine controlling signal. The fine controlling signal may be a PWM signal. A pulse width of the PWM signal increases each time the fine modulation key 22 is triggered. In a typical application, the number of output terminals of the scaler 23 as well as the number of input terminals of the illumination modulation signal processing circuit 24 is limited. Accordingly, the fine controlling signal and the rough controlling signal are combined into the illumination modulation signal.
The illumination modulation signal processing circuit 24 includes a first integrating and smoothing circuit 241, a reversing circuit 242, a PWM filter circuit 243, a second integrating and smoothing circuit 244, a summing circuit 245, an amplifying circuit 246, a selecting circuit 247, and a counting and comparing circuit 248. The first integrating and smoothing circuit 241 and the PWM filter circuit 243 receive the illumination modulation signal from the scaler 23. The illumination modulation signal is integrated and smoothed into a first direct current voltage by the first integrating and smoothing circuit 241, and then is reversed into a negative direct current voltage by the reversing circuit 242. The negative direct current voltage is transmitted to the summing circuit 245. At the same time, the illumination modulation signal is filtered into a PWM signal by the PWM filter circuit 243, and then is integrated into a second direct current voltage by the second integrating and smoothing circuit 244. The second direct current voltage is sent to a second selecting terminal 2472 of the selecting circuit 247 to function as a fine modulation signal. Simultaneously, the second direct current voltage is transmitted to the summing circuit 245. The second direct current voltage and the negative direct current voltage are added by the summing circuit 245, and the summed voltage is amplified by the amplifying circuit 246 to function as a rough modulation signal. The rough modulation signal provided from the amplifying circuit 246 is sent to a first selecting terminal 2471 of the selecting circuit 247.
The counting and comparing circuit 248 includes a counter and comparator 2481, a memory 2482, and a clock signal generator 2483. The memory 2482 stores a pulse width of a predetermined reference PWM signal. The counter and comparator 2481 receives the PWM signal from the PWM filter circuit 243. The clock signal generator 2483 generates clock signals to enable the counter and comparator 2481 to calculate a pulse width of the PWM signal received from the PWM filter circuit 243. The counter and comparator 2481 compares the reference pulse width stored in the memory 2481 with the pulse width of the received PWM signal. When the two compared pulse widths are different, the counter and comparator 2481 outputs a high level voltage to the selecting circuit 247. The pulse width of the received PWM signal is stored in the memory 2482 as the reference PWM signal for a next comparison. In response to the high level voltage, the selecting circuit 247 outputs the fine modulation controlling signal to the backlight driving circuit 25. The backlight driving circuit 25 adjusts illumination of the backlight module 26 in a small and precise range according to the fine modulation controlling signal. When the two compared pulse widths are the same, the counter and comparator 2481 outputs a low level voltage to the selecting circuit 247. In response to the low level voltage, the selecting circuit 247 outputs the rough modulation controlling signal to the backlight driving circuit 25. The backlight driving circuit 25 adjusts illumination of the backlight module 26 in a large and relatively imprecise range according to the rough modulation controlling signal.
The backlight modulation circuit 20 can modulate illumination of the backlight module 26 in both a large and relatively imprecise range and a small and precise range. This provides convenience and reduces operation times.
The first integrating and smoothing circuit 341 and the PWM filter circuit 343 receive an illumination modulation signal from a scaler (not labeled). The illumination modulation signal is integrated and smoothed into a first direct current voltage by the first integrating and smoothing circuit 341. The first direct current voltage is transmitted to the summing circuit 345. At the same time, the illumination modulation signal is filtered into a PWM signal by the PWM filter circuit 343, and then is integrated into a second direct current voltage by the second integrating and smoothing circuit 344. The second direct current voltage is sent to a second selecting terminal (not labeled) of the selecting circuit 347 to function as a fine modulation signal. Simultaneously, the second direct current voltage is reversed into a negative direct current voltage by the reversing circuit 342. The negative direct current voltage is transmitted to the summing circuit 345. The first direct current voltage and the negative direct current voltage are added by the summing circuit 345, and the summed voltage is amplified by the amplifying circuit 346 to function as a rough modulation signal. The rough modulation signal provided from the amplifying circuit 346 is sent to a first selecting terminal (not labeled) of the selecting circuit 247. The backlight modulation circuit 30 can achieve advantages similar to those of the backlight modulation circuit 20.
It is to be understood, however, that even though numerous characteristics and advantages of certain inventive embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only; and that changes may be made in detail, especially in matters of arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200710123810.6 | Oct 2007 | CN | national |
