JP3256062B2 - Signal processing circuit of liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for a liquid crystal display, and more particularly to a brightness control.

[0002]

2. Description of the Related Art A liquid crystal panel of a liquid crystal display device comprises a display section comprising a large number of liquid crystal elements arranged in a matrix and a driver for driving the liquid crystal elements of the display section.
The signal processing circuit of the liquid crystal display device, based on the video signal,
It functions to send a display signal to the driver and a drive signal to the common electrode of the liquid crystal element.

As shown in FIG. 10, the signal processing circuit includes a brightness control circuit 101 for adjusting the brightness of the display unit, and a gamma correction circuit 102 for correcting the drive characteristics of the display unit. I have.

[0004] Brightness control circuit 101
Clamps the pedestal level of the video signal to the voltage V1 according to the clamp pulse.

The above-mentioned clamp pulse is applied for a predetermined period of the back porch (the period after the horizontal synchronizing signal in the horizontal blanking period) of the video signal (FIG. 11A).
As shown in (b), the level becomes high. Therefore, the pedestal level of the video signal can be clamped at the voltage V1 every horizontal scanning period. Therefore, the voltage V
By adjusting 1, the brightness of the display unit can be set to a desired brightness.

[0006] The gamma correction circuit 102 performs gamma correction of the signal obtained by the brightness control circuit 101. Then, a video signal 102a (FIG. 11D) obtained by gamma correction is output, and a video signal 102b (FIG. 11
(C)) is output.

The video signal 1 from the gamma correction circuit 102
02a and 102b are input to the switch circuit 103. The switch circuit 103 outputs the video signal 102b when the frame pulse is at a high level, and outputs the video signal 102a when the frame pulse is at a low level.

[0008] The above-mentioned frame pulse is shown in FIG.
As shown in (1), a high level and a low level are alternately taken every horizontal scanning period. Therefore, as shown in FIG. 11E, the output of the switch circuit 103 is a signal in which the video signal 102a and the video signal 102b are alternately switched every horizontal scanning period.

The output of the switch circuit 103 is
After being amplified at 04 and subjected to impedance conversion at the buffer 105, it is sent as a display signal to a driver for driving the above-described liquid crystal element.

[0010] The frame pulse is supplied to the amplifying circuit 10.
After being amplified at 6 and subjected to impedance conversion at the buffer 107, it is applied as a drive signal to the common electrode of the liquid crystal element.

[0011]

However, in the above-mentioned conventional configuration, since the pedestal level is clamped by the brightness control circuit 101, it is necessary to make all the electric couplings after the brightness control circuit 101 DC coupling. There is. For this reason, there is a problem that an offset voltage which causes a deterioration in image quality is easily generated.

Further, the amplitude of the display signal from the buffer 105 reaches 10 V peak-to-peak.
For this reason, there is a problem in that it is difficult to align the high-frequency components of the waveform that switches every horizontal scanning period. In addition, it is necessary to increase the withstand voltage of the driver for driving the liquid crystal element, which causes a problem that the cost is increased.

[0013]

According to a first aspect of the present invention, there is provided a signal processing circuit for a liquid crystal display device, comprising: a variable voltage generator for generating a pedestal level of a video signal; A first clamp circuit that clamps to an output voltage of the device, a first switch circuit that inserts a beacon pulse of a predetermined first voltage into a back porch of the signal pedestal-clamped by the first clamp circuit, A gamma correction circuit for gamma correcting the signal into which the marker pulse is inserted by the switch circuit, a first inverting amplifier for inverting the signal gamma corrected by the gamma correction circuit, and a pedestal of the signal gamma corrected by the gamma correction circuit A second clamp circuit for clamping the level to a predetermined second voltage, and a pedestal level of an inverted signal from the first inverting amplifier Pede of the gamma corrected signal
A third clamping circuit for clamping the third voltage to the difference between Stal-level constant, a second, a second switch circuit for selecting and outputting an output signal of the third clamp circuits alternately, a Amplifying the output signal from the second switch circuit.
Width circuit and liquid crystal element by performing impedance conversion after amplification
A first buffer for outputting a signal to a driver for driving a child
§ and, amplified voltage labeled pulse from the output of the amplifier circuit
Was a voltage signal corresponding to the output voltage of the variable voltage generator
A detection circuit for detecting Te, a second inverting amplifier and a third switch for the inverted signal selects alternately output from the output signal and a second inverting amplifier of the detection circuit for inverting the output signal of the detection circuit Circuit and the next stage of the third switch circuit.
Performs impedance conversion and outputs a signal to the common electrode of the liquid crystal element.
And a second buffer to be provided.

According to a second aspect of the present invention, there is provided a signal processing circuit of a liquid crystal display device according to the first aspect, wherein the first clamp circuit includes a pedestal. A slice circuit for clipping a signal smaller than the pedestal level from the clamped signal is provided.

[0015]

According to the first aspect of the present invention, a display signal required for a driver of the liquid crystal panel is obtained from the second switch circuit, and a voltage to be applied to the common electrode of the liquid crystal element of the liquid crystal panel is changed by the third switch circuit. Obtained from the circuit. Further, the brightness of the liquid crystal panel can be controlled by adjusting the output voltage of the variable voltage generator.
Moreover, since the marker pulse is inserted into the video signal, a voltage corresponding to the output voltage of the variable voltage generator can be obtained by the detection circuit from the level of the marker pulse and the pedestal level. Therefore, it becomes possible to make the electrical coupling after the first clamp circuit for clamping the pedestal level of the gamma-corrected signal video signal to the output voltage of the variable voltage generator an AC coupling. This makes it difficult for an offset voltage to be generated, thereby improving image quality. Further, since the voltage to be applied to the common electrode is obtained from the video signal after the gamma correction, the adverse effect due to the variation between the transistors constituting the signal processing circuit is reduced.

According to the configuration of claim 2, in addition to the function of claim 1, the horizontal synchronizing signal is removed from the signal pedestal clamped by the first clamp circuit. For this reason, the peak-to-peak amplitude of the display signal sent to the driver of the liquid crystal panel can be reduced by the amplitude of the horizontal synchronizing signal as compared with the related art.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the signal processing circuit of the liquid crystal display device according to the present embodiment includes a variable voltage generator 1 for performing brightness control and a variable voltage generator 1 for controlling the pedestal level of a video signal. A clamp circuit 2 (first clamp circuit) for clamping to an output voltage V1, and a voltage V from a signal pedestal-clamped by the clamp circuit 2.
A slice circuit 3 for removing a signal smaller than 1 and a switch circuit 4 (first switch circuit) for inserting a marker pulse of a voltage V2 (first voltage) into a signal obtained by the slice circuit 3 are provided. .

Further, the signal processing circuit of the present embodiment includes a gamma correction circuit 5 for performing gamma correction on the signal into which the beacon is inserted by the switch circuit 4, and a signal from the gamma correction circuit 5 which is supplied with a voltage V3 (second voltage). ) And an inverting amplifier 7 having an amplification factor of -1 for inverting the signal from the gamma correction circuit 5.
(First inverting amplifier), a clamp circuit 8 (third clamp circuit) for clamping a signal from the inverting amplifier 7 to a voltage V4 (third voltage), a signal from the clamp circuit 6 and a signal from the clamp circuit 8 A switch circuit 9 (second switch circuit) for alternately switching and outputting a signal, an amplifier circuit 10 for amplifying a signal from the switch circuit 9, and an amplifier circuit 1
And a buffer 11 for converting a signal from 0 into an impedance and outputting the converted signal.

Further, the signal processing circuit of the present embodiment includes a detection circuit 12 for detecting a marker pulse from the signal from the amplifier circuit 10 and outputting a signal of a voltage corresponding to the output voltage V1 of the variable voltage generator 1. An inverting amplifier 13 (second inverting amplifier) having an amplification factor of -1 for inverting the detection signal;
Analog multiplexer 14 (third switch circuit) for alternately selecting and outputting a detection signal and an inverted detection signal
And a buffer 15.

Hereinafter, the operation of the signal processing circuit will be described mainly with reference to the waveform diagram of FIG.

The video signal (FIG. 2A) is input to the slice circuit 3 via the capacitor C1. Here, the capacitor C1 functions as a clamp capacitance of the clamp circuit 2.

The clamp circuit 2 includes a clamp pulse 2c
, The pedestal level of the video signal (FIG. 2A) is clamped to the output voltage V1 of the variable voltage generator 1.

The above-mentioned clamp pulse 2c is at a high level as shown in FIG. 2B for a predetermined period in the back porch of the video signal. Therefore, every horizontal scanning period,
The pedestal can be clamped so that the pedestal level of the video signal becomes the voltage V1. Therefore,
By adjusting the output voltage V1 of the variable voltage generator 1, the brightness of the display unit can be set to a desired brightness.

The slice circuit 3 clips a signal smaller than the voltage V1 from the signal pedestal clamped by the clamp circuit 2. As a result, a signal (FIG. 2C) in which the pedestal level is clamped at the voltage V1 and the horizontal synchronization signal is removed is obtained.

The switch circuit 4 receives a control pulse (FIG. 2).
(D)) outputs a predetermined voltage V2 during the high level period, and outputs a signal from the slice circuit 3 during the control pulse low level period.

The control pulse is set to a high level for a predetermined period in the back porch of the video signal. For this reason,
Voltage V2 is selected only during this period.

Thus, according to the magnitude of the voltage V2,
As shown in FIG. 2E, a beacon is inserted above or below the pedestal level. The height of the beacon from the pedestal level is | V2-V1 |.

The gamma correction circuit 5 performs gamma correction on the signal obtained by the switch circuit 4. This gamma correction circuit 5 has input / output characteristics as shown in FIG. 7B. For example, when the signal of FIG.
(B) A signal having a value indicated by the lower curve is output.

The clamp circuit 6 includes a clamp pulse 6c
According to (FIG. 2 (f)), the pedestal level of the signal obtained by gamma correction by the gamma correction circuit 5 is changed to the voltage V
3 (FIG. 2 (g)).

The clamp pulse 6c goes high during the horizontal blanking period and excluding the period of the beacon pulse. Therefore, the pedestal level of the signal obtained by gamma correction by the gamma correction circuit 5 can be clamped to the voltage V3 every horizontal scanning period.

The inverting amplifier 7 inverts the signal obtained by the gamma correction by the gamma correction circuit 5.

The clamp circuit 8 has a clamp pulse 6c
, The pedestal level of the signal obtained by inverting by the inverting amplifier 7 is clamped to the voltage V4 (FIG. 2).
(H)).

The switch circuit 9 has a frame pulse 9f
(FIG. 2 (i)) outputs a signal from the clamp circuit 8 during the high level period, and outputs a signal from the clamp circuit 6 during the frame pulse 9f is low level (FIG. 2).
(J)).

The above-mentioned frame pulse 9f is at a high level every horizontal scanning period (or every vertical scanning period).
Take low level alternately. Therefore, the output of the switch circuit 9 is a signal obtained by alternately switching the signals from the clamp circuits 6 and 8 every horizontal scanning period (or every vertical scanning period). Thus, the level difference between the black level of the signal obtained by inverting the video signal and the black level of the non-inverted signal can be made constant.

The amplifier circuit 10 amplifies the signal from the switch circuit 9. The signal amplified by the amplifier circuit 10 is subjected to impedance conversion in the buffer 11 and then sent as a display signal to a driver (not shown) for driving a liquid crystal element.

The signal amplified by the amplifier circuit 10 is
It is also input to the detection circuit 12. The detection circuit 12 detects the marker pulse by the clamp pulse 12c (FIG. 2 (k)). That is, the voltage Vb of the signal amplified by the amplifier circuit 10 during the period when the clamp pulse 12c is at the high level is held and output (see FIG. 2 (l)).

The difference between the voltage Vb and the pedestal level is
(V2-V1) K. Here, K is the amplifying circuit 10
Is the amplification factor. Therefore, the voltage Vb of the detection signal obtained by the detection circuit 12 is equal to the output voltage V1 of the variable voltage generator 1.
It is a signal according to.

Therefore, brightness control can be performed based on the detection signal.

The detection signal is inverted by the inverting amplifier 13. The analog multiplexer 14 outputs the signal from the detection circuit 12 while the frame pulse 14f (FIG. 2 (m)) is at a high level, and outputs the signal from the inverting amplifier 13 while the frame pulse 14f is at a low level. Is output.

The frame pulse 14f alternately takes a high level and a low level every horizontal scanning period (or every vertical scanning period). Therefore, the output of the analog multiplexer 14 is a signal that alternately switches between the detection signal and the signal obtained by inverting the detection signal for each horizontal scanning period (or for each vertical scanning period).

The signal from the analog multiplexer 14 is subjected to impedance conversion in the buffer 15 and then applied as a drive signal (FIG. 2 (n)) to a common electrode (not shown) of the liquid crystal element. . Usually, the amplitude of the drive signal is set to a voltage at which the transmittance of the liquid crystal element sharply decreases, as shown in FIG.

Although the above-mentioned frame pulses 9f and 14f are basically the same, the polarity of the switch
The polarity is set to the same polarity or the opposite polarity according to the circuit configuration of the analog multiplexer 14.

As described above, since the level difference between the black level of the inverted signal of the video signal and the black level of the non-inverted signal can be made constant by the clamp circuits 6 and 8, the withstand voltage of the driver for driving the liquid crystal element can be increased. You don't have to. Further, since the voltage to be applied to the common electrode is obtained from the video signal after the gamma correction, the adverse effect due to the variation between the transistors constituting the signal processing circuit can be reduced.

The circuit example of the above signal processing circuit is shown in FIG.
3 to 6 corresponding to the reference numerals attached to the locks . Note that this is an example of a signal processing circuit, and the present invention is not limited to this.

The gamma correction circuit 5 (FIG. 4) in this signal processing circuit includes a first clip circuit including NPN transistors 21 and 22, a PNP transistor 23,
24, an inverting circuit 25 for inverting a signal from the first clipping circuit, and an amplifying circuit 26
It consists of

Signal from switch circuit 4 (FIG. 9A)
Is clipped by the first and second clipping circuits at the voltage V _TH , respectively, and is a clip signal of the voltage V _TH or more (FIG. 9B)
And a clip signal (FIG. 9C) equal to or lower than the voltage V _TH . The clip signal having the voltage _VTH or more is supplied to the inversion circuit 25
Is inverted. The inverted signal, the clip signal of the voltage _VTH or less, and the original signal from the switch circuit 4 are added and synthesized to obtain a gamma-corrected signal (FIG. 9D).

In the above circuit, various input / output characteristics can be easily obtained by changing the number of clipping circuits and the combination ratio at the time of addition and combination.

The signal processing circuit of the liquid crystal display device according to the present invention comprises a variable voltage generator 1 and a clamp circuit 2 for clamping a pedestal level of a video signal to an output voltage V1 of the variable voltage generator 1. A switch circuit 4 for inserting a marker pulse of a predetermined voltage V2 into the back porch of the signal pedestal-clamped by the clamp circuit 2, a gamma correction circuit 5 for gamma-correcting the signal with the marker pulse inserted by the switch circuit 4. Amplifier 7 for inverting the signal gamma-corrected by the gamma correction circuit 5
A clamp circuit 6 for clamping the pedestal level of the signal gamma-corrected by the gamma correction circuit 5 to a predetermined voltage V3, and a clamp circuit for clamping the pedestal level of the inverted signal from the inverting amplifier 7 to a predetermined voltage V4. 8, a switch circuit 9 for alternately selecting and outputting the output signals of the clamp circuits 6 and 8, and detecting a beacon pulse from the output of the switch circuit 9 to generate a voltage corresponding to the output voltage of the variable voltage generator 1. A detection circuit 12 for outputting a signal, an inverting amplifier 13 for inverting the output signal of the detection circuit 12, and an analog multiplexer for alternately selecting and outputting the output signal of the detection circuit 12 and the inverted signal from the inverting amplifier 13 14 is provided.

According to this, a display signal required for the driver of the liquid crystal panel is obtained from the switch circuit 9, and a voltage to be applied to the common electrode of the liquid crystal element of the liquid crystal panel is obtained from the analog multiplexer 14. Further, the brightness control of the liquid crystal panel can be performed by adjusting the output voltage V1 of the variable voltage generator 1. Moreover, since a beacon was inserted into the video signal,
The detection circuit 12 can determine a voltage corresponding to the output voltage V1 of the variable voltage generator 1 from the level of the marker pulse and the pedestal level. Therefore, the pedestal level of the video signal is changed to the output voltage V of the variable voltage generator 1.
The electric coupling after the clamp circuit 2 to be clamped at 1 can be AC coupling. This makes it difficult for an offset voltage to be generated, thereby improving image quality.

Further, since the voltage to be applied to the common electrode is obtained from the video signal after the gamma correction, the adverse effect due to the variation between the transistors constituting the signal processing circuit can be reduced.

The signal processing circuit of the liquid crystal display device according to the second aspect of the present invention is the signal processing circuit of the liquid crystal display device of the first aspect, wherein a signal pedestal-clamped by the clamp circuit 2 is used to determine a pedestal level. This is a configuration in which a slice circuit 3 that clips a small signal is provided.

According to this, in addition to the effect of the first aspect, the horizontal synchronizing signal is removed from the signal pedestal-clamped by the clamp circuit 2. For this reason, the peak-to-peak amplitude of the display signal sent to the driver of the liquid crystal panel can be reduced by the amplitude of the horizontal synchronizing signal as compared with the related art.

[0054]

As described above, the signal processing circuit of the liquid crystal display device according to the first aspect of the present invention includes the variable voltage generator and the second embodiment for clamping the pedestal level of the video signal to the output voltage of the variable voltage generator. A first clamp circuit, a first switch circuit for inserting a marker pulse of a predetermined first voltage into the back porch of the signal pedestal clamped by the first clamp circuit, and a marker pulse inserted by the first switch circuit Gamma correction circuit for gamma-correcting the resulting signal, a first inversion amplifier for inverting the signal gamma-corrected by the gamma correction circuit, and a second predetermined pedestal level of the signal gamma-corrected by the gamma correction circuit.
Gamma and second clamp circuit for clamping a voltage, a pedestal level of the inverted signal from the first inverting amplifier
Keep the difference between the corrected signal and the pedestal level constant.
A third clamp circuit for clamping to a third voltage, a second switch circuit for alternately selecting and outputting output signals of the second and third clamp circuits, and a second switch circuit.
Circuit that amplifies the output signal of the
Signal to the driver that drives the liquid crystal element by
, A detection circuit for detecting the amplified voltage of the marker pulse from the output of the amplification circuit as a signal of a voltage corresponding to the output voltage of the variable voltage generator, and inverting the output signal of the detection circuit. A second inverting amplifier, a third switch circuit for alternately selecting and outputting an output signal of the detection circuit and an inverting signal from the second inverting amplifier, and a third switch .
Impedance conversion is performed at the next stage of the
Since a second buffer for outputting a signal to the common electrode of the liquid crystal panel is provided, a display signal necessary for the driver of the liquid crystal panel is obtained from the second switch circuit and applied to the common electrode of the liquid crystal element of the liquid crystal panel. Voltage from the third switch circuit. Furthermore, by adjusting the output voltage of the variable voltage generator, the brightness and
You can take control. Moreover, since the marker pulse is inserted into the video signal, a voltage corresponding to the output voltage of the variable voltage generator can be obtained by the detection circuit from the level of the marker pulse and the pedestal level. Therefore, the electrical coupling after the first clamp circuit that clamps the pedestal level of the video signal to the output voltage of the variable voltage generator can be AC coupled. As a result, an offset voltage is less likely to be generated, and an effect of improving image quality is achieved. Further, since the voltage to be applied to the common electrode is obtained from the video signal after the gamma correction, the effect of reducing the adverse effect due to the variation between the transistors constituting the signal processing circuit is also achieved.

The signal processing circuit of the liquid crystal display device according to the second aspect of the present invention is the signal processing circuit of the liquid crystal display device of the first aspect, wherein the signal processing circuit is pedestal-clamped by the first clamp circuit. Since the slice circuit for clipping a signal smaller than the pedestal level from the signal is provided, in addition to the effect of the first aspect, the horizontal synchronization signal is removed from the signal pedestal clamped by the first clamp circuit. For this reason, the peak-to-peak amplitude of the display signal sent to the driver of the liquid crystal panel can be reduced by the amplitude of the horizontal synchronizing signal as compared with the related art. As a result, the high frequency components of the inversion waveform and the non-inversion waveform of the display signal can be easily aligned with each other, and an inexpensive low withstand voltage driver can be used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a signal processing circuit of a liquid crystal display device according to the present invention.

FIG. 2 is a waveform chart showing an operation of the signal processing circuit of FIG.

FIG. 3 is a circuit diagram illustrating an example of a signal processing circuit of FIG. 1;

FIG. 4 is a circuit diagram of a signal processing circuit following FIG. 3;

FIG. 5 is a circuit diagram of a signal processing circuit following FIG. 4;

FIG. 6 is a circuit diagram of a signal processing circuit following FIG. 5;

7 is an explanatory diagram showing input / output characteristics of a gamma correction circuit in the signal processing circuit of FIG.

FIG. 8 is a graph in which the transmittance of a liquid crystal element is plotted with respect to an applied voltage.

FIG. 9 is a waveform chart showing an operation of the gamma correction circuit of FIG.

FIG. 10 is a block diagram illustrating a schematic configuration of a signal processing circuit of a conventional liquid crystal display device.

11 is a waveform chart showing an operation of the signal processing circuit of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Variable voltage generator 2 Clamp circuit (1st clamp circuit) 3 Slice circuit 4 Switch circuit (1st switch circuit) 5 Gamma correction circuit 6 Clamp circuit (2nd clamp circuit) 7 Inverting amplifier (1st inversion) Amplifier) 8 clamp circuit (third clamp circuit) 9 switch circuit (second switch circuit) 10 amplifier circuit 11 buffer (first buffer) 12 detection circuit 13 inverting amplifier (second inverting amplifier) 14 analog multiple Xer (third switch circuit) 15 buffers (second buffer)

Claims (2)

(57) [Claims] 1. A variable voltage generator, a first clamp circuit for clamping a pedestal level of a video signal to an output voltage of the variable voltage generator, and a back porch of a signal pedestal clamped by the first clamp circuit. A first switch circuit for inserting a beacon pulse of a predetermined first voltage into the signal, a gamma-correction circuit for gamma-correcting the signal into which the beacon pulse has been inserted by the first switch circuit, and a signal gamma-corrected by the gamma-correction circuit First inverting amplifier, a second clamp circuit for clamping the pedestal level of the signal gamma-corrected by the gamma correction circuit to a predetermined second voltage, and a pedestal of the inverted signal from the first inverting amplifier -For signals with gamma-corrected levels
A third clamping circuit for clamping the third voltage to the difference between the pedestal level constant, a second, a second switch circuit for selecting and outputting an output signal of the third clamp circuits alternately, a Amplify the output signal from the second switch circuit
Amplifier circuit that performs impedance conversion after amplification
The first bus that outputs a signal to the driver that drives the crystal element
And Ffa was amplified from the output of the amplifier circuit of the labeling pulse
A voltage signal corresponding to the output voltage of the variable voltage generator
A second inverting amplifier for inverting an output signal of the detection circuit; a second inversion amplifier for inverting an output signal of the detection circuit;
A third switch circuit that alternately selects and outputs an inverted signal from the inverting amplifier of
Impedance conversion and signal to common electrode of liquid crystal element
The signal processing circuit of the liquid crystal display device, characterized in that is provided with a second buffer for outputting. 2. A signal processing apparatus according to claim 1, further comprising a slice circuit for clipping a signal smaller than the pedestal level from the signal pedestal-clamped by the first clamp circuit. circuit.