TWI233587B - Method and circuit for improving a quality of display on an LCD screen - Google Patents

Abstract

A method and circuit for improving a quality of display on an LCD screen are disclosed. The method is to synchronize a vertical synchronization signal of a video signal supplied to an LCD system with an oscillation signal produced by a burst mode DC-to-AC inverter driving the lamps of the system in order to suppress interference noise appearing on an LCD screen. The circuit suggested includes mainly two semiconductor switches, impedance elements, and a diode to realize the synchronization function.

Description

1233587 V. Description of the invention (1) [Technical field to which the invention belongs] The present invention relates to a method and a circuit for improving the display quality of a liquid crystal display (Liquid Crystal Display, LCD) screen, and particularly to a video signal supplied to the liquid crystal display system. (Vide 〇) the vertical synchronization signal (ver 7 丨 ca 1 synchronization signal) and burst mode DC-to-AC inverter generated vibration signal synchronization to reduce the appearance on the LCD screen Method and circuit of interference noise. [Prior art] Applying liquid crystal display to generate images is a conventional technique. Liquid crystal displays are widely used in different applications, such as monitors, computers, televisions, and so on. Liquid crystal displays usually have a large number of liquid crystal display pixel elements. These pixel elements are effectively organized into a matrix (or array). This matrix includes pixel rows and pixel columns. Basically, a video signal is applied to a pixel unit in pixel-by-pixel units. A periodic vertical synchronization signal of a video signal is provided to scan all pixel lines repeatedly, and all pixel lines are scanned one after the other in each cycle of the vertical synchronization signal. The number of times each pixel cell in a pixel column is scanned in one second is the vertical synchronization signal rate. " '^ LCD systems use backlights to illuminate the LCD panel to produce images. The backlight includes a light tube, such as a cold cathode fluorescent lamp (CCFL), to generate light. The power of these lamps is generally provided by a DC-AC converter, and

Ϊ233587 V. Description of the invention (2) 5¾ / / device power supply), the second power supply is from another electric power source (such as a high LCD display, six, !!) for 'This DC AC converter will convert the DC voltage into a The voltage of 2 units is required, but this higher AC voltage is used to drive the fluorescent lamp to convert AC to AC. In addition, there is a DC-AC converter called burst mode, which generates step by step. The vibration surplus signal is transmitted with a further pulse, t pulse signal (burst pulsating signal). This burst is in the square two = Feng square wave signal and is suitable for adjusting the brightness of the light emitted by the lamp. For example, the voltage cover signal 乂 -h (unit: volts V) of the first wave, the explosive wave i Γ ^ Γ, ΓΛ, and the current signal Iiamp flowing through the lamp tube change over time. m, Sheng ^ 号 \ ㈣ ... th is obtained by the burst-mode direct-current converter; :: f is obtained according to the vibration signal v ~ and-: Ji :: 2. When the oscillation signal ¥ —High voltage > When muscle voltage Vr, burst pulse signal " ^ Seven is a high voltage. No = Burst voltage of burst pulse signal is close to zero. Then the current passes through la: f Burst pulse signal Burst is applied during the pulse and flows through the lamp ^ ^ 11 All, t? Drive and synchronize with each other to sound the display product f. Into the liquid, it is said that the display circuit is inconsistent, and the traditional circuit is affected: the display system, especially the multi-lamp liquid crystal display system, still has the problem of interference noise. When the DC converter generates = the frequency of the pulse signal is equal to or close to ^ ^ (har.onics) e,, „Λ„ ^ Λ ^ ^ ^ ^ ^ ^ Noise will appear on the display screen & s ° Λ Sexually produced. This dude lost again and produced the so-called I,

$ 7 pages 1233587 V. Description of the invention (3) Ripple phenomenon. For example, if the frequency of the vertical synchronization signal is 60 Hertz (Hz), when the frequency of the burst pulse signal generated by the DC-AC converter is equal to 120, 180, 240 Hertz or higher (60 Hertz spectral wave frequency), Obvious interference noise can occur. The frequency of the burst pulse signal is often preferably set to about 50 Hz or higher to avoid frequencies close to harmonic frequencies or flicker noise that can be felt by the human eye. However, due to the temperature-affected components, especially the capacitors of the DC-AC converters, the tethered amplifiers, or the operational amplifiers, there is a certain tolerance for the changes. The tolerance of the burst pulses and frequencies may be very large. Therefore, the frequency of the burst pulse signal is not very stable, and the noise problem "ripple phenomenon" is still very important. From the foregoing reasons, it is known that it is necessary to add to the problem of the ripple phenomenon caused by interference noise. [Summary of the Invention] According to the above, there is a need for a system that includes a direct capture, * phantom crystal ... It is to provide a solution to the problem: the vertical synchronization signal of the frequency signal of the present invention is synchronized with the burst signal: ... to the liquid crystal display system to synchronize the apparent signal to reduce interference noise. : When the vibration step signal produced by the DC-AC converter changes state, the oscillation signal 轳 = step is the result that when the vertical synchronism · signal later changes back to the original shape g, crosses to a low value, and when the vertical complex oscillation fluctuates . The i-oscillation signal of another embodiment of the present invention rises again and recovers. It is to provide a message to implement the above method, including the following elements. A first semiconductor switch and a circuit according to the principles of the present invention, for example, is the first impedance element connected to a power supply.

1233587

An impedance element is connected to a filling, and the handle is Φ2, and the first semiconductor switch is ^ :: 2. The first semiconductor switch has a vertical synchronizing signal generated by a controller from the first control terminal to the first control terminal and receiving a video image (=). First: Connected to the other end. A second adapter, two semiconductors, a second control electrode body connected to the second control switch using a non-inverter converter, for example, a wall body and a reference low voltage, and there are two The control terminal is connected to the above-mentioned nodes. The oscillating signal of the above two-machine converter. This diode is optional. That is, the second semiconductor switch can be directly connected to the orthogonal diode ^. If the voltage value of the above supply voltage is applied, the conductor switch will be opened. The above-mentioned semiconductor two can be a field effect transistor, and the above-mentioned impedance element is an example of a resistor. ^ s, the present invention provides a solution and the implementation of this solution to reduce the "including the phenomenon of ripples appearing on the LCD screen" fl other features and advantages will be explained in the following narrative or It is obvious from the following summary, and can be obtained from the implementation of the present invention. [Embodiment] The first embodiment ^ summarizes one embodiment of the method of the present invention. In this embodiment, a liquid crystal display device includes a video graphics array (Video Graphics AFFay 'VGA) type liquid crystal display. The front panel and the tube used to generate light are in a burst mode DC converter. The liquid crystal display panel includes a liquid crystal display 7 ^ pixel array, and light generated by the lamp tube irradiates the liquid crystal display panel. This burst mode DC converter drives these lamps.

Page 9 1233587, Description of the invention (5) Behind the array, “This straight AC converter often shows eight”, “Moonlight straight parent flow converter”. For a video image array type liquid crystal panel, there are 48 pixel rows in the pixel array, which means that there are 480 pixel units in the column. A video signal is supplied to the display system. In addition, the burst mode direct AC converter oscillates the signal V-Earth Day] five sawtooth (unit is Xiawang: f tine waveform signal 'and this vibrating signal V pays ... As shown in Figure 2 (8) and its frequency is 210 Hz, Gai L said that the period of Vsawt〇Qth is about 4.76 milliseconds (1/210 seconds). ^ All lamps should be driven simultaneously and synchronized with each other Therefore, all the oscillating signals of the external amplifier must also be the same and synchronized with each other. In addition, the periodic vertical synchronization signal of the video signal ^ ... is displayed at 2 (b) ^ i and its frequency is 60 Hz. In other words, Each image field of each pixel column: 被 is scanned 60 times in one second. The cycle of this vertical synchronization signal Sync is approximately 16 67 milliseconds (1/60 seconds). T = square f It is the oscillating signal VsawtQ ° th and the vertical synchronization signal Sync, and the reference signal shown in Figure 2 (C) * is the exhaustion signal after synchronization (the unit will be V). When the vertical synchronization signal changes state (from 2〇) 〇) When it becomes a low value, the original oscillating signal v in Figure 2 (a) changes state simultaneously (shown by 202) It is a low value. The tip is straight, and the step signal Sync changes state again (shown by 204) and returns; when the value is up, the vibration signal in Figure 2 (c) is also β ′ and starts again. Oscillation fluctuation (shown by 2006). The burst pulse signal is obtained by comparing the synchronized exhaustion signal with a reference DC Y voltage Vr, and it is shown in Figure 2 (d). When the oscillation signal is synchronized

1233587 V. Description of the invention (6) The voltage is higher than the reference DC voltage. The burst pulse signal should be “,” or the same voltage, otherwise the burst pulse signal Burst voltage will be close to zero. On the frf surface, the current signal flowing through the tube It is applied during the burst pulse Burst. In another case, the waveform of the vertical synchronization signal ^ "is the opposite of the waveform 俨 in Figure 2 (b), that is, the period of the high voltage state becomes low voltage ^ ", And the period of the low power state becomes the period of the high voltage state. ^ At 2f, when the vertical synchronization signal Sync transitions to a high value, the original oscillation signal Vsawt in the figure A t (a) in the figure At the same time, the state is changed; ',, and a low value. Later, when the vertical synchronization signal Sync changes state again = the first low value, the vibration | signal VsawtQ ° th also rises again at the same time and starts to oscillate. There is no soup step between the signal ¥ _Can and the vertical synchronization signal Sync. The frequency of the burst pulse ^ bBurst will be the same as the frequency of the original vibration _ ° th and equal to 21 Hz, so the burst pulse = sign BUrst The period is about 4.76 milliseconds (1/210 seconds); on the contrary, after the same I ^ L, as shown in Figure 2 (d), the width of the third rabbit pulse of the burst pulse letter is more than the width of other pulses Narrow, and the second to fourth pulses are: 24 times less than twice the original period (4. 76 milliseconds multiplied by 2 equals 9. i day η. At -60 Hz vertical sync signal Sync every-week The gas period, l, the total average current of the lamp remains the same. What you have difficulty with is that every time the vertical synchronization signal Sync changes state to become one, the chip at ', the oscillation signal is pulled to a low value, and this low value is No need to go; Volts. If the lowest voltage of the original oscillating signal Vsa_〇th is greater than 1233587 V. Description of the invention (7) Zero volts, a low value close to zero volts will affect the burst pulse signal Burst can reach the maximum Therefore, this duty value is more suitable to be set slightly lower than the original oscillation signal v __ _a sawtooth

The lowest voltage. According to the specifications of this liquid crystal display system, the maximum operating time ratio should exceed 95 percent to maintain sufficient image display brightness at a specific root-mean-SqUared value of the lamp current. U. Second Embodiment In order to implement the above method, the present invention further provides a consistent embodiment of a related circuit. Refer to the circuit in Figure 3. In this circuit, two semiconductor switches, such as two N-type metal-oxide-semiconductor field-effect transistors (NMOSFETs) 300 and 302, are used as switches. The first transistor 300 and a resistor 304 are connected to the node A, and are connected to the ground as a reference potential. The value of the resistor 304 is 10 ohms (kil0-〇hm, κ), and the resistor 304 is connected to a DC voltage of 5 volts (V). This DC voltage can come from a power source and when applied to a second When the control terminal of the transistor 3 〇 2, this DC voltage must be able to turn on the second transistor 302. The control terminal of the first transistor 300 receives the vertical synchronization signal having a waveform as shown in FIG. 2 (b) via the resistor 3 08, and the value of the resistor 308 is 1 ohm. The second power Crystal 3 〇2 is connected to a monopole 3 1 0 ′ and is connected to the ground as a reference potential. Diode 3 丨 0 is connected to the original vibration signal Vsawt00th (the waveform is shown in Figure 2 (a)) 3 2. The oscillating signal VsawtQQth is provided by a backlight DC converter. The control terminal of the second transistor 302 is connected to the node a.

1233587 V. Invention I㈣⑻ '" " " "-The operation principle of this circuit is as follows. Please refer to Fig. 2 (c), which is the intentional rise y of the original oscillating signal vsawtQQth 312 after the influence of the circuit operation (that is, after synchronization). When the vertical synchronizing signal Sync changes state (not shown by 200) and becomes a low value, the first transistor 300 is turned off, so the voltage at the node A is about 5 volts, resulting in a second transistor 302 is opened. Therefore, the original oscillating signal 312 is pulled down (shown by 202) to a low value because the second transistor 302 is turned on. Since the voltage of the output terminal of the second transistor 3 2 used to connect to the diode 31 0 at this time is close to zero volts (ground potential), this low value is fixed at the forward bias voltage of the diode 31 0

Joltage), which is about 0.7 volts. Diode 310 is used to prevent the original oscillating signal vsawtQQth 312 from being pulled down to an excessively low value close to zero, causing the burst pulse signal to be poor-31 W, that is, the second transistor 302 is directly connected to the original Vibration signal v 312. Therefore, the diode 31 can be added according to actual needs.

On the other hand, when the vertical synchronization #lack Q%%-, 1 slogan Sync changes state again (from 204 households: 1 :: back to the original high value, the voltage of the first transistor into a point A is at zero The volts (ground potential) '/ ta is said to be turned off. The resulting result is that the oscillator can be used to achieve the purpose of synchronizing the vertical synchronization signal with the oscillator. = 〇Vsawt〇〇th 口 J 艾 第Three embodiments

Page 13 1233587 V. Description of the invention (9) ^ This is another example of the circuit provided by the present invention in order to implement the above method. As mentioned earlier, when the waveform of the vertical sync signal Sync 疋 in Figure 2 (b) is opposite (the original oscillation signal v and 〆 are unchanged, the waveform is as shown in Figure 2 (a) (Shown), then the electricity in Figure 3: : = Feng replaced the first transistor 300 (which is an N-type metal oxide semiconductor transistor) with a P-type metal oxide semiconductor transistor (PMOSFET), as shown in the figure * =. In the fourth figure, the first transistor 40 ° is a p-type metal oxide semiconductor transistor: while the second transistor 402 is still an N-type metal oxide semiconductor transistor, the other το components and connection methods are the same as those in the circuit in FIG. 3. The operation principle of the circuit As described below. When the vertical synchronization signal Sync transitions to a high value, the first transistor 400 is turned off, so the voltage at node A is about 5 volts, causing the second transistor 402 to be turned on. So The original oscillating signal v s_〇th 412 originally provided by the backlight DC converter was pulled down to a low value * due to the second transistor 40 being turned on. This low value is fixed at the diode The forward bias voltage of the body 41o, that is, approximately 0.7 volts 2 L. Similarly, the diode 41o is optional but not necessary. The vertical sync signal sync again changes state and returns to the original Low value 0, the first transistor 400 is turned on, resulting in The voltage of A is at zero volts (ground potential), so the second transistor 4O2 is turned off. The result is that the oscillation signal vsawt00th rises again at the same time and starts to oscillate. This circuit has also reached vertical The purpose of the synchronization signal Sync and the oscillating signal I. The fourth embodiment

Page 14 1233587 V. Description of the invention αο) The invention is described here. The liquid noise of this system is reduced and the wave signal is supplied to this panel, lamp, and circuit. The light generated by this liquid crystal display is irradiated to the surplus signal to drive this in synchronization with the oscillating signal. Although the present invention has been described in detail, anyone familiar with the present invention can make various appended patent application embodiments. In this embodiment, the image display quality of a liquid crystal display screen is good, that is, the dry streak phenomenon has been greatly improved. The video signal is synchronized with the vertical. This system mainly includes a liquid crystal display parent w converter, and a plurality of pixel units organized in an array in the same electrical panel as described above. Lamp This LCD panel. This DC-AC converter produces some lamps. The purpose of this circuit is to expose the vertical synchronization signal as above, but it is not intended for the artist ′ without departing from the spirit and changes of the present invention. Therefore, the scope of the present invention ’s guarantee: Bawei shall prevail. The rail view is 1233587. The diagram is simple. [The diagram is simple.] The first diagram is the waveform of the oscillation signal Vsawt〇Qth, the burst pulse signal Burst, and the current signal Ilamp with time. The second diagram (a) is the vibration surplus. 5 Tiger VsawtQQth Pic Wave chart of day-to-day variation. Figure 2 (b) is the waveform of vertical synchronization signal Sync over time. Figure 2 (c) is the oscillating signal v after drawing after synchronization; sawtc ^ th k is a waveform diagram of a time-varying wave; FIG. 2 (d) is a graph showing the change of burst burst signal Burst with time; FIG. 3 is a circuit diagram of a method for implementing the present invention; and FIG. Another circuit diagram. [A brief description of the symbol of the component] 200 The vertical sync signal Sync transition state 202 The original oscillation signal VsawtQ () th transition state 2 04 The vertical sync signal Sync transition state 2 0 6 The oscillation signal VsawtQQth rises again and starts to fluctuate 3 0 0, 3 0 2 N-type metal oxide semiconductor field effect transistor 304, 308 resistor 3 1 0 Diode 312 original oscillation signal VsawtQQth 400 P-type metal oxide semiconductor transistor 402 N-type metal oxide semiconductor transistor 4 1 0 Diode The original vibration signal v_t_h of the body 412

Claims (1)

1233587 6. Scope of patent application 1 · A circuit used in a liquid crystal display system, which is used to combine a vertical synchronization signal of a video signal supplied to the liquid crystal display system with an oscillating signal generated by a burst mode direct current converter Synchronization, the burst mode orthogonal L " L converter is used to drive the lamp of the liquid crystal display system, and the circuit includes as small as: a first one first connected to the off has a second and receives a second signal, Semiconductor. Dot. 2. Rushen 1 Diode Switch 3. Rushen has been open the 4th. Rushen Switch is 5. Russ impedance element, the first impedance element is connected to a high voltage line; Semiconductor switch, the first semiconductor The switch has a node with the first impedance element and is connected to a reference low voltage, the first semiconductor opens a first control terminal; an impedance element, the second impedance element is connected to the first control terminal, and the vertical synchronization signal; And a semiconductor switch, one end of the second semiconductor switch receives the oscillation and the second semiconductor switch is connected to a reference low voltage, the second switch has a second control terminal, and the second control terminal is connected to the patentable scope of this section The circuit according to item 1, wherein the circuit further includes a body, and the diode receives the oscillating signal and is connected to the second end of the second body. = The circuit described in item 1 of the patent scope, wherein the high-voltage line is connected to /; IL voltage 'and the DC voltage is applied to the second control terminal to act as a semiconductor switch. Please refer to the circuit described in item 1 above, wherein the first semiconductor field effect transistor. ° The circuit of item 1 of the monthly patent scope, wherein the second semiconductor 1233587 6. Scope of patent application The switch is a field effect transistor. 6. The circuit according to item 1 of the scope of patent application, wherein the impedance of the first impedance element is equal to about 10 ohms. 7. The circuit according to item 1 of the scope of patent application, wherein the impedance of the second impedance element is equal to about 1 ohm. 8. —A method for reducing noise to improve the display quality of a liquid crystal display screen in a liquid crystal display system, the liquid crystal display system includes a liquid crystal display panel, at least one lamp tube, and an AC converter, the at least one lamp tube It is used to generate light, and the light is introduced into the liquid crystal display panel. A video signal and a vertical synchronization signal are supplied to the liquid crystal display system. The vertical synchronization signal has a first state and a second state. The method includes at least: Synchronizing the vertical synchronization signal with an oscillating signal generated by the DC-AC converter, the oscillating signal is used to drive the at least one lamp tube, so that when the vertical synchronization signal is switched from the first state to the second state At this time, the oscillation signal is switched to a low state, and when the vertical synchronization signal is later switched back to the first state, the oscillation signal rises again and starts to oscillate. 9. The method according to item 8 of the scope of patent application, wherein a phenomenon of noise is a ripple phenomenon generated when the liquid crystal display screen is displayed. 10. The method according to item 8 of the scope of patent application, wherein the first state of the vertical synchronization signal is a high state and the second state is a low state. 11. The method according to item 8 of the scope of patent application, wherein the first state of the vertical synchronization signal is a low state and the second state is a high state. 1 2. A liquid crystal display system in which a video signal and a vertical synchronization signal are supplied to the liquid crystal display system, and the vertical synchronization signal has a first state Page 18 1233587 " 2 ------------ 6. Scope of patent application and a second state, the liquid crystal display system includes at least: a liquid crystal display panel, the liquid crystal display panel has a plurality of pixel units The pixel units are organized into an array; at least one lamp tube is used to generate light, and the light is introduced into the liquid crystal display panel; an AC converter, the DC converter generates an oscillating signal, and the oscillation A signal is used to drive the at least one lamp; and a circuit is used to synchronize the vertical synchronization signal with the oscillating signal, so that when the vertical synchronization signal transitions from the first state to the second state, the The oscillating signal is converted to a low state, and when the vertical synchronization signal is switched back to the first state, the vibratory signal rises again and starts to oscillate. The circuit at least includes: a first impedance element, the first impedance element is connected To a high voltage line; a first semiconductor switch 'the first semiconductor switch and the first impedance element are connected to a node and connected to a reference low voltage The first semiconductor switch has a first control terminal; a first impedance element, the second impedance element is connected to the first control terminal, and receives the vertical synchronization signal; and a first semiconductor switch, the second semiconductor switch One terminal receives the oscillating signal, and the second semiconductor switch is connected to a reference low voltage. The second semiconductor switch has a second control terminal. The second control terminal is connected to the node. 1 3 · The liquid crystal display system according to item 2 of the patent application range, wherein the circuit further includes a diode, and the diode receives the oscillating signal and is connected to Page 19 1233587 6. Scope of patent application This end of the second semiconductor switch. 14. The liquid crystal display system according to item 12 of the scope of patent application, wherein the first state of the vertical synchronization signal is a high state, and the second state is a low state. 15. The liquid crystal display system according to item 12 of the scope of patent application, wherein the first state of the vertical synchronization signal is a low state and the second state is a high state. 16. The liquid crystal display system according to item 12 of the patent application scope, wherein the high voltage line receives a DC voltage, and if the DC voltage is applied to the second control terminal, the second semiconductor switch is turned on. 1 7. The liquid crystal display system according to item 12 of the scope of patent application, wherein the first semiconductor switch is a field effect transistor. 1 8. The liquid crystal display system according to item 12 of the scope of patent application, wherein the second semiconductor switch is a field effect transistor. 19. The liquid crystal display system according to item 12 of the scope of patent application, wherein the impedance of the first impedance element is equal to about 10 ohms. 20. The liquid crystal display system according to item 12 of the scope of patent application, wherein the impedance of the second impedance element is equal to about 1 ohm. Page 20