JPH06222329A - Back light driving device for liquid crystal - Google Patents

Abstract

PURPOSE:To prevent a video signal processing circuit from being affected by a noise component radiated from a back light driving circuit. CONSTITUTION:A horizontal synchronizing signal is obtained by being counted down from VCO 3 with a frequency divider 4. The horizontal synchronizing signal is compared with the horizontal synchronizing signal obtained by synchronizing separating an input video signal by a phase comparator 2, and the VCO 3 is controlled through a low-pass filter, and the horizontal synchronizing signal (2fH) of gradual multiplication locked to the synchronism of the input video signal is obtained. The horizontal synchronizing signal (fH) is 2-frequency divided by a 2-frequency divider 5, and the fH and whose inversion polarity 2fH are switched as the gate signal of an AND/OR gate 6, and the inverted fH signal of gradual multiplication becomes the driving signal of a fluorescent lamp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal backlight drive device, and more particularly, to a multiplying sync signal which is synchronized with a horizontal / vertical sync signal of a projected video image.
Moreover, by using a signal whose polarity is inverted for each line as a driving signal for the fluorescent lamp, even if the noise radiated from the lamp that is lit at high frequency affects the image, the liquid crystal is less disturbed on the screen. Backlight drive device for vehicle.

[0002]

2. Description of the Related Art Pocketable televisions and video monitor devices using liquid crystals are expected to become more and more popular in the future due to their thinness and light weight, but transmissive liquid crystal type devices have a backlight as a light source. is necessary. However, because of its compactness, the circuit blocks such as the liquid crystal drive section, the video signal processing section (tuner / detection section if there is a TV function), and the backlight drive section inside the device are integrated, and therefore, in the vicinity. The issue is how to prevent each other's interference.

For example, since a fluorescent lamp used as a backlight often has a scan rate of a video signal of 60 Hz, it is necessary to light it at a sufficiently high frequency. If the drive frequency of the fluorescent lamp is 60 (Hz)
_X525 (book) = 31.5 (KHz) = f _HSync , NTSC (National Television System Committee)
In the period in which the image of the Color System) system constitutes one picture, the period during which the fluorescent lamp is turned off is for one line, and in this case, the screen is not partially darkened.

For this reason, the drive frequency of the backlight of a liquid crystal display device displaying an image is 30 KHz.
Often selected around -50 KHz. However, due to the above-described reason, even though the high-frequency lighting system is used, a line enters the fluorescent lamp extinguishing period every 30 Hz from the video cycle, in other words, the difference beat component is 3
Since it comes every 0 Hz, if the energy component of the drive circuit of the fluorescent lamp is large, it will be on the screen because it is asynchronous with the video signal. In order to prevent this in the conventional device, the fluorescent lamp drive circuit itself is covered with a shield case, and it is prevented by devising the pattern of the board and the layout of parts so as not to interfere with the ground of the signal processing system. I had no hand.

FIG. 4 is a block diagram (conventional example) of a DC-AC inverter circuit as a drive circuit for a conventional fluorescent lamp.
It is composed of a Royer circuit. First, when the input voltage is applied, one of the transistors Q1 and Q2 is turned on first. Now, assuming that the transistor Q1 is turned on first, the collector current Ic1 is → N1 winding → Q1 →
When flowing to GND, an induced voltage that further drives Q1 is generated in the N3 winding, and the ON state of the transistor Q1 is established. However, when the bias of the transistor Q1 disappears, Q1 is turned off, the primary voltage of the transformer is inverted, and the transistor Q2 is turned on this time. After that, oscillation is continued by repeating this ON / OFF state. The oscillating frequency at this time is determined by the L1 and the N1 (or N2) windings, and is naturally a free running frequency for the video signal.

FIG. 5 and FIG. 6 are synchronization processing circuits in a television receiver, which are circuit configuration diagrams (conventional examples 2 and 3) in which the free run in FIG. 4 is improved and synchronized with the horizontal frequency of the image. In the figure, 21 is a sync separation circuit, 22 is a horizontal AFC (Automatic Frequency Control) circuit, 23 is a pulse shaping circuit, 24 is a transistor, 25 is a drive transformer, 26 is a capacitor, 27
Is a fluorescent lamp, 31 is a synchronous separation circuit, 32 is a phase comparison circuit, and 33 is an electrically controlled oscillator (VCO).
ed oscillator), 34 is a 1/32 frequency divider, 35 is a pulse shaping circuit, 36a and 36b are transistors, 37 is a drive transformer, 38 is a capacitor, and 39 is a fluorescent lamp.

In FIG. 5, from the video horizontal sync signal,
In this example, a horizontal drive signal is generated and used as a drive signal for a high voltage generating transformer. In this example, the vertical frequency of the image is free, so horizontal 1 /
The deviation of 2H becomes a beat of 30Hz cycle and interferes with the image. Furthermore, when driving in the horizontal cycle, unless the slope of the signal waveform is included within the horizontal blanking period, the lamp is displayed on the screen. The influence of the high voltage waveform of.

In FIG. 6, the point is similar, but the point that it is locked to the vertical synchronizing signal is improved. In FIG. 6, the drive frequency may be horizontal double. In addition, the method shown in FIGS.
It is called horizontal synchronous lighting method.

[0009]

However, in Conventional Example 1, the difference between the horizontal synchronization and the oscillation frequency of the lamp interferes with the image as a beat component, and in Conventional Examples 2 and 3, no difference beat is produced. The peak portion or slope portion of the high-voltage waveform interferes with the image in a static manner. That is, there is a problem that noise does not flow on the screen but appears as a stationary "vertical streak".

The present invention has been made in view of the above circumstances, and is a signal in which a multiplied sync signal is generated in synchronization with the horizontal / vertical sync signal of a video image to be projected, and the polarity of each line is inverted. It is an object of the present invention to provide a backlight drive device for a liquid crystal in which the interference on the screen is reduced even if noise radiated from a lamp that is turned on at a high frequency affects the image by using as a driving signal for the fluorescent lamp. I am trying.

[0011]

To achieve the above object, the present invention provides a sync separation circuit for synchronously separating an input video signal, a horizontal / vertical sync signal and a voltage controlled oscillator separated by the sync separation circuit. A phase-locked loop circuit for phase-comparing the frequency-divided horizontal sync signal and controlling the voltage-controlled oscillator by its output to obtain a multiplied horizontal sync signal, and a multiplied horizontal sync signal obtained by the phase-locked loop circuit. A signal and a switching circuit for switching a 1/2 horizontal synchronization signal obtained by dividing the horizontal synchronization signal by two, and are obtained by switching between the multiplied horizontal synchronization signal and the multiplied horizontal synchronization signal of the inverted polarity of the horizontal synchronization signal. The control signal to be used is a lamp lighting drive signal, and lighting is performed in synchronization with a synchronizing signal of the input video signal.

[0012]

In order to reduce the static vertical stripe phenomenon which is a problem in the conventional horizontal synchronous lighting system, the drive signal waveform is inverted every other line to apparently reduce the interference fringe. That is, a means for obtaining a multiplied horizontal synchronizing signal by a phase locked loop (PLL) circuit for controlling the VCO and a 1/2 horizontal synchronizing signal obtained by dividing the horizontal synchronizing signal by two are switched to obtain the multiplied horizontal synchronizing signal. A control signal obtained by switching between the horizontal synchronizing signal which is a multiplication of the inverted polarity is used as the lamp lighting drive signal. In the backlight driving device having such a configuration, the interference fringes do not flow as beats, and the stationary vertical stripes are reduced as dotted lines instead of lines.

[0013]

Embodiments will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining an embodiment of a liquid crystal backlight drive device according to the present invention, in which 1 is a sync separation circuit, 2 is a phase comparison circuit, and 3 is a voltage controlled oscillator (VCO: Voltage). Controlled Oscillator), 4 is a frequency divider, 5 is a frequency divider by 2, 6 is an AND or gate, 7 is a transistor, 8 is a drive transformer, 9 is a capacitor, 1
0 is a fluorescent lamp. 2A to 2H are diagrams showing signal waveforms of respective parts in FIG. 1. FIG. 2A shows a signal A,
(B) is signal B, (c) is signal C, (d) is signal H, (e) is signal D, (f) is signal F, (g) is signal G, (g) is h) corresponds to the signal E, respectively.

The video signal is synchronously separated to obtain a horizontal sync signal and a vertical sync signal. The case where the oscillation frequency of the VCO 3 is 14.4 MHz will be described below.
The frequency is counted down by the frequency divider 4 from 3, and a horizontal synchronizing signal is obtained internally. Since the frequency divider 4 is reset by the vertical synchronizing signal, the frequency divider 4 is counted with respect to the vertical period of the input video. And the phase comparator 2
The internal horizontal synchronizing signal and the horizontal synchronizing signal obtained by synchronously separating the input video signal are compared with each other, and the VCO 3 is controlled through a low pass filter.
By the LL (Phase Locked Loop) operation, it is possible to obtain the multiplied horizontal synchronizing signal (2f _H ) locked to the synchronization of the input video signal.

2f _H is obtained by the frequency divider 4 by outputting from the frequency division counter before f _H. Further, the horizontal synchronizing signal is divided into two by T-FF (flip-flop),
Is switched to f _H and 2f _H of the inverse polarity that set output and reset output as the gate signal of the AND-OR gate. As a result, the multiplied f that is inverted every other line
_{The H} signal becomes the driving signal for the fluorescent lamp. Even if the video signal does not arrive, the VCO is not externally locked and the multiplied horizontal pulse is output, so that there is no problem in driving the backlight.

FIGS. 3 (a) to 3 (d) are diagrams comparing the high-voltage pulse waveform of a fluorescent lamp with the horizontal synchronous lighting system of the prior art example 3. FIG. 3 (a) shows signal A and FIG. 3 (b) shows. The signal B corresponds to the signal I, the diagram (c) corresponds to the signal I, and the diagram (d) corresponds to the signal J. Here, the drive waveform J of Conventional Example 3 is synchronized with the video signal, so that the waveform always has its peak height at a certain point of the video signal. Therefore, if the radiation of drive energy is large, one field of the video signal The peak point does not move at any point and therefore appears vertically as vertical stripes. On the other hand, in the waveform I, the peak heights of the peaks are deviated between the lines adjacent to each other, and the waveforms are inverted in the next field. Therefore, the peaks have a diagonal positional relationship with respect to the video signal. They are arranged and do not appear as vertical stripes compared to the conventional example. In other words, the conventional example has a solid line vertical stripe, and the improved example has a dotted line vertical stripe, but the peak points coincide with each other in every frame, and almost no noise fringes should be confirmed. You will not be able to do so.

[0017]

As is apparent from the above description, the present invention has the following effects. That is, in the liquid crystal display device, since the video signal processing circuit is less likely to be affected by the noise component radiated from the backlight drive circuit, the layout on the circuit is facilitated and the EMI countermeasures such as the shield case are minimized. There is.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a backlight driving device for liquid crystal according to the present invention.

FIG. 2 is a diagram showing a signal waveform of each part in FIG.

FIG. 3 is a diagram showing a state of a high-voltage pulse waveform of a fluorescent lamp of a backlight driving device for liquid crystal according to the present invention.

FIG. 4 is a diagram showing a conventional drive circuit for a fluorescent lamp.

FIG. 5 is a diagram showing a synchronization processing circuit in a conventional television receiver.

FIG. 6 is a diagram showing another synchronization processing circuit in the conventional television receiver.

[Explanation of symbols]

1 ... Sync separation circuit, 2 ... Phase comparison circuit, 3 ... Voltage controlled oscillator (VCO), 4 ...
Frequency divider, 5 ... 2 frequency divider, 6 ... And or gate, 7 ... Transistor, 8 ... Drive transformer, 9 ... Capacitor.

Claims (1)

[Claims] 1. A sync separation circuit for synchronously separating an input video signal, a phase comparison between a horizontal / vertical sync signal separated by the sync separation circuit and a horizontal sync signal divided by a voltage controlled oscillator, and an output thereof. A phase-locked loop circuit for controlling a voltage-controlled oscillator to obtain a multiplied horizontal synchronizing signal, and a multiplied horizontal synchronizing signal obtained by the phase-locked loop circuit and 1/2 horizontal synchronizing obtained by dividing the horizontal synchronizing signal by two. A switching circuit for switching signals, and a control signal obtained by switching between the multiplied horizontal synchronizing signal and the multiplied horizontal synchronizing signal of the inverted polarity of the horizontal synchronizing signal is used as a lamp lighting drive signal, and the input video signal is synchronized. A backlight drive device for a liquid crystal, which is turned on in synchronization with a signal.