JP2003216112A - Liquid crystal driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent disturbance in the screen of an LCD (liquid crystal display) which is generated at the time of changing over a liquid crystal display device from a standby mode to a normal display mode. <P>SOLUTION: This liquid crystal driving circuit is provided with an analog part 4 outputting analog video signals, a counter 2 for setting a blanking period blanking the analog video signals at the time of changing over the liquid crystal display device from the standby mode to the normal display mode and a D/A converter 3 for adjusting luminance supplying analog signals for adjusting luminance for adjusting luminance of the analog video signals and the driving circuit sets forcibly the analog signals for adjusting luminance to a level corresponding to black levels during the blanking period. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal drive circuit, and more particularly to a liquid crystal drive circuit capable of switching between a standby mode and a normal display mode (also called a normal mode) according to a switching signal.

[0002]

2. Description of the Related Art FIG. 5 shows a circuit diagram of an LCD drive circuit according to a conventional example. In the figure, an LCD drive circuit shows various timing signals for driving the LCD (for example, LCD based on an external serial control signal SCO).
A digital section 10 for generating a driving signal), a timing signal from the digital section, and a video signal VIDEO from an external device (for example, a digital video camera) to output analog video signals of R, G, and B. And an analog section that

In order to save power consumption, this LCD drive circuit has a normal display mode for performing a normal display on the LCD and an L display mode.
It has a standby mode switching function to turn off the CD. Then, in the standby mode, the analog unit 1
Each of the R, G, and B outputs from 1 is fixed to a low level, so that the operation of the analog unit 11 is stopped to save power, and the operation of the analog unit 11 is started when returning to the normal display mode. Is configured.

In the normal display mode, the R, G, and B video signal outputs are inversely driven every horizontal period as is well known. Here, DC feedback is applied in order to control the average DC voltage of each output of R, G, and B at a constant level, and R, G, and
Smoothing capacitors C1, C2 and C3 are connected to the respective outputs of B.

[0005]

However, R,
The smoothing capacitors C1 and C are provided for the respective outputs of G and B.
Since C2 and C3 are provided, it takes a certain time to charge the smoothing capacitors C1, C2, and C3 even when the standby mode is switched to the normal display mode and the analog unit 11 starts operating. Therefore, during this period, R,
The G and B outputs are not stable and the LCD screen is disturbed.

Therefore, an object of the present invention is to provide an LCD drive circuit which prevents the LCD screen from being disturbed at the time of switching from the standby mode to the normal display mode.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. In a liquid crystal drive circuit capable of switching between a standby mode and a normal display mode according to a mode switching signal, an analog circuit is provided. An analog section for outputting a video signal, a counter for setting a blanking period for blanking the analog video signal when switching from the standby mode to the normal display mode, and an output for the analog section during the blanking time. And a blanking control circuit for setting the analog video signal to a black level.

According to the present invention, during switching from the standby mode to the normal display mode, during the blanking period,
If the analog video signal is set to the black level and the blanking period necessary for stabilizing the analog video signal is set, the analog video signal will be stably output after the blanking period ends. This can prevent the LCD screen from being disturbed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. (First Embodiment) FIG. 1 is a circuit diagram showing an LCD drive circuit according to a first embodiment of the present invention. See also FIG.
FIG. 3 is a waveform diagram for explaining the operation of the LCD drive circuit of FIG. 1. In FIG. 1, the same components as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

The serial control circuit 1 uses a serial control signal SCO to switch between a normal display mode (normal mode) and a standby mode, a mode switching signal MC, and a video signal brightness adjusting digital signal (for example, 8 bits). DB0 to DB7 are output. Here, it is assumed that the LCD drive circuit is switched to the standby mode when the mode switching signal MC is low and to the normal display mode when it is high level.

The counter 2 has the above-mentioned mode switching signal.
When MC is switched to the high level, the counting operation of the vertical synchronizing pulse Vsync of the video signal is started, and when the preset number of pulses is counted, its output is converted from the high level to the low level. Then, when the mode control signal MC is switched to the low level, the counter 2 is reset to the high level. Hereinafter, the same operation as this is repeated. As a result, the blanking control signal BC having the blanking period tB of 0.5 to 1.0 second with respect to the time t0 when the mode switching signal MC changes to high is generated.

On the other hand, the above-mentioned brightness adjustment digital signal DB0
~ DB7 is input to the brightness adjusting DA converter 3. Then, the brightness adjusting digital signals DB0 to DB7 convert the brightness adjusting digital signals DB0 to DB7 into brightness adjusting analog signals and supply them to the analog section 4. The analog unit 4 adjusts the DC level and the amplitude of the video signal VIDEO input from the outside based on the brightness adjustment analog signal, and RG
The B video signal is output.

Here, the brightness adjusting analog signal output from the brightness adjusting DA converter 4 is fixed to a level corresponding to the black level during the blanking period tB according to the blanking control signal BC. For example, a brightness adjustment digital signal DB
When 0 to DB7 are all "1" and white and all "0" are black, the luminance adjustment analog signal is assumed to be "0" in all bits of the luminance adjustment digital signals DB0 to DB7. Is converted into an analog signal corresponding to. This allows
The R, G, and B outputs are forcibly set to the black level.

The operation of the LCD driving circuit having the above structure will be described with reference to FIG. Now, assuming that the mode switching signal MC is at a low level, the LCD drive circuit is set to the standby mode. At this time, the outputs of R, G, and B are fixed at a low level, and the operation of the analog unit 4 is stopped to save power.

When the mode switching signal MC is switched to the high level, the LCD drive circuit is set to the normal display mode. Then, the counter 2 operates, and during the blanking period tB, each output of R, G, and B is forcibly set to the black level for inversion driving by the DA converter 4 for brightness adjustment. Then, after the blanking period tB has elapsed, the forcible setting of the black level by the brightness adjusting DA converter 4 is canceled, and a normal RGB video signal is output.

Therefore, if the blanking period tB is ensured to be a period sufficient for stabilizing the respective outputs of R, G and B, the blanking period tB will be LCD.
Since the screen display is not performed, it is possible to prevent the LCD screen from being disturbed when the standby mode is switched to the normal display mode.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
3 is a circuit diagram showing an LCD drive circuit according to the embodiment of FIG. The same components as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. A feature of this embodiment is that a switch circuit 5 for switching between an analog video signal from the analog section 4 and a black level is provided in accordance with a blanking control signal BC generated from the counter 2 and a blanking period tB is provided. The middle point is that the RGB analog video signals are forcibly set to the black level.

The operation timing of the LCD drive circuit of this embodiment is exactly the same as that shown in FIG. As shown in FIG. 4, the switch circuit 5 includes an analog switch AS1 that receives a video signal (for example, an R signal) from the analog section 4 and is controlled by a blanking control signal BC,
It can be configured with an analog switch AS1 to which the black level VB is input and which is controlled by the blanking control signal BC. The G and B video signal outputs from the analog section 4 can be similarly configured.

Thus, when the blanking control signal BC is at high level, the black level VB is output, and when the blanking control signal BC is at low level, normal R, G, B video signals are output. . Therefore, as in the first embodiment, it is possible to prevent the LCD screen from being disturbed when the standby mode is switched to the normal display mode.

[0020]

According to the present invention, when switching from the standby mode to the normal display mode, the analog video signal output from the analog section is set to a black level during a predetermined blanking period, and after the blanking period has elapsed. Tried to cancel this.

As a result, the video signal becomes unstable due to the smoothing capacitor connected to the analog section, and the LCD becomes unstable.
It is possible to prevent the problem that the screen is disturbed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an LCD drive circuit according to a first embodiment of the present invention.

FIG. 2 is a system diagram illustrating the operation of the LCD drive circuit according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of an LCD drive circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a switch circuit of an LCD drive circuit according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of an LCD drive circuit according to a conventional example.

[Explanation of symbols]

1 Serial control circuit 2 counter 3 DA converter for brightness adjustment 4 analog section 5 switch circuits

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 641 G09G 3/20 641C 670 670E F term (reference) 2H093 NC24 NC27 NC65 ND07 ND58 ND60 5C006 AA01 AA16 AA22 AC26 AF46 AF46 AF50 AF51 AF53 AF73 AF83 BC13 BC16 BF22 FA01 FA18 FA21 5C080 AA10 BB05 DD03 DD09 EE28 GG07 GG08 JJ02 JJ03 JJ04

Claims (3)

[Claims] 1. A liquid crystal drive circuit capable of switching between a standby mode and a normal display mode in response to a mode switching signal, and an analog section for outputting an analog video signal, and the analog unit when switching from the standby mode to the normal display mode. A counter for setting a blanking period for blanking the video signal, and a blanking control circuit for setting the analog video signal output from the analog unit to a black level during the blanking time. LCD drive circuit. 2. The blanking control circuit includes a brightness adjusting DA converter for supplying a brightness adjusting analog signal for adjusting the brightness of the analog video signal to the analog section, and the blanking control from the counter is performed. 2. The liquid crystal drive circuit according to claim 1, wherein the analog signal for brightness adjustment is forcibly set to a level corresponding to a black level according to a signal. 3. The blanking control circuit includes a switch circuit for switching between an analog video signal from the analog section and a black level according to a blanking control signal from the counter, and the analog circuit is provided during the blanking period. The liquid crystal drive circuit according to claim 1, wherein the video signal is forcibly set to a black level.