JP2947438B2 - LCD drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving circuit in which an output circuit is formed of an integrated circuit having a plurality of power supply voltages and applies a video signal which is inverted at a vertical or horizontal period to a liquid crystal panel.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal drive circuit for applying a video signal which is inverted at a vertical or horizontal cycle to a liquid crystal panel includes
Some of them are configured using an integrated circuit having a small withstand voltage.
FIG. 4 is an example of a liquid crystal drive circuit configured using a conventional integrated circuit. FIG. 5 is an example of a signal waveform of each part of the liquid crystal driving circuit.

In FIG. 4, reference numeral L denotes a buffer amplifier in an integrated circuit indicated by a two-dot chain line, and M denotes an operational amplifier (hereinafter referred to as an operational amplifier) other than the integrated circuit. As shown in FIG. 4, the buffer amplifier L has a power supply voltage of 5 V (Vcc).
-8V (Vee), the input signal is 1 and the output signal is m. This output signal m is input to the operational amplifier M. An example of the input signal 1 and the output signal m is shown in FIG.
It becomes as shown in.

The operational amplifier M has a power supply voltage of 5 V and -10 V
As a source driver for applying a video signal to the liquid crystal panel. The source driver performs amplification of the video signal (the amplification rate is determined by the characteristic resistances ra and rb) and level shift (the reference voltage is determined by the voltage division resistances rc and rd). An example of an output signal of the source driver is as shown in FIG. Here, the withstand voltage of the power supply voltage of the integrated circuit is 13V (5V to -8V). On the other hand, the power supply voltage of the source driver is 5V and -10V.

[0005]

Therefore, the output signal m of the integrated circuit is -1.5 V, as shown in FIG.
(1 V higher than -2.5 V) and 9 Vpp (Vpp
5 represents a peak-to-peak voltage), the video signal to be applied to the liquid crystal must have an amplitude of 10 Vpp or more around -2.5 V as shown in FIG. 5B. Therefore, like the source driver, amplification and DC
Since the level shift must be performed and the amplifier circuit is provided outside the integrated circuit, the number of components is increased and the cost is increased. On the other hand, if an amplifier circuit is provided on an integrated circuit, the withstand voltage of the integrated circuit must be increased, resulting in an increase in cost.

In a liquid crystal driving circuit for a color screen, conventionally, an amplifying circuit for amplifying a video band requires three or more circuits of red (R), green (G) and blue (B). It is expensive, and each amplifier circuit must be adjusted, which is complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and a large dynamic range can be obtained with a small number of components without changing the withstand voltage of an integrated circuit. It is an object of the present invention to provide a liquid crystal driving circuit capable of obtaining an amplitude video signal.

[0008]

The present invention has the following configuration to achieve the above object. The present invention relates to a liquid crystal driving circuit in which an output circuit section is formed of an integrated circuit having a plurality of power supply voltages, and applies a video signal that is inverted in a vertical or horizontal cycle to a liquid crystal panel. An inverting operational amplifier to be switched, a changeover switch for switching and connecting a video signal or an inverted video signal inverted by the inverting operational amplifier at a predetermined cycle, and an amplifying operational amplifier for amplifying a video signal or an inverted video signal output from the changeover switch. Voltage generating means for generating a Zener voltage by applying a reverse voltage to a Zener diode outside the output circuit portion, the Zener voltage generating means having an inverting operational amplifier and at least one pair of power supply terminals for applying a power supply voltage to the amplifying operational amplifier. Power supply signal that changes at the same cycle as the changeover switch A liquid crystal driving circuit and applying to at least one pair of power supply terminal of the output circuit with the Zener voltage from the stage.

[0009]

According to the present invention, a video signal capable of driving a liquid crystal panel can be obtained without using an amplification and level shift circuit. Accordingly, a large-amplitude video signal with a wide dynamic range and little distortion can be obtained with a small number of components without changing the withstand voltage of the integrated circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows a liquid crystal panel drive circuit according to an embodiment of the present invention. FIG. 2 shows reference numerals a to a of the liquid crystal panel driving circuit.
7 is an example of a signal waveform of each part indicated by g. In FIG. 1, reference numeral A denotes a buffer, B denotes an inverting amplifier having a gain of -1, and C denotes an operational amplifier, each of which is formed of a well-known operational amplifier (operational amplifier). Also, D
Are switches, and these buffers A, inverting amplifiers B,
The operational amplifier C and the switch D are configured on the integrated circuit 10. Further, an output circuit section is configured in a range indicated by a chain line OC on the integrated circuit 10. Reference numerals 1 to 8 indicate terminals of the integrated circuit 10. R1 to R8 are resistors, D
Reference numeral 1 denotes a Zener diode. The power supply voltage of the source driver including the operational amplifier C of the liquid crystal panel drive circuit is 5V and -10V. Further, the integrated circuit 1
The withstand voltage of 0 is 12V.

Next, the liquid crystal panel drive circuit will be described with reference to the circuit configuration of FIG. 1 and the signal waveform of FIG. 2 as an example. The buffer A operates at a power supply voltage of −5 V to GND. The input of the buffer A is a and the output is b. This output b is applied to the inverting input (-) of the inverting amplifier B.

A reference voltage determined by the resistors R3 and R4 is supplied to a non-inverting input terminal (+) of the inverting amplifier B via a terminal 2.
The inverting amplifier B inverts the output b around the voltage of the terminal 2 to produce an output c. At this time, the resistance R3
When R4 is equal, the midpoint potential is -2.5V, and-
A signal c centered at 2.5 V can be obtained. The output c of the inverting amplifier B and the output b of the buffer A are applied to the L terminal and the H terminal of the switch D. The output of the switch D is selected by the horizontal signal or vertical signal e output from the timing generation circuit, and is -2.5 V
To obtain a signal d centered on. The output signal d is applied to the non-inverting input terminal of the operational amplifier C, and is amplified to a predetermined amplitude by the operational amplifier C.

Here, in order to obtain a predetermined amplitude required for the liquid crystal panel, it is necessary to increase the power supply voltage. The power supply terminal 7 of the output circuit unit OC and the lowest power supply terminal 4 (substrate) of the terminals of the integrated circuit 10 are separated from the power supply voltage in another integrated circuit (such as IC1 or IC2). These circuits can be represented as shown in FIG.
Therefore, it is possible to synchronize the signal f input to the integrated circuit IC2 with the signal e and swing the power supply terminals 7 and 4 according to the horizontal or vertical signal.

That is, a signal f having the same period as the signal e is input to the cathode of the Zener diode D1, and in this case, the signal f is applied to the integrated circuit IC1 and the integrated circuit IC1 provided on another substrate. the circuit IC2 Zener - diode - signal frequency lower potential and become a waveform f Zener voltage V _D1 de D1 is applied. Accordingly, the potential of the same waveform as f is input to the power supply terminal 7 via the IC ₁ , and the potential of the waveform f which is lower than the Zener voltage V _D1 is input to the power supply terminal 4. For this reason, FIG.
As described above, the output g of the operational amplifier C becomes a large-amplitude signal obtained by shaking the input d of the operational amplifier C as a horizontal signal or a vertical signal due to a change in the potential (signal) of the potential terminals 7 and 4. As a result, the output signal is swung with a large amplitude.

On the side of the Zener diode D1 connected to the integrated circuit IC2, a constant current source is provided between the Zener diode D1 and a power supply of -12V. This constant current source is provided to prevent the Zener voltage from fluctuating even when the current flowing through the Zener diode D1 fluctuates between the high level and the low level of the signal f. However, in the circuit of FIG. 1, a resistor can be provided instead of the constant current source.

Further, both the integrated circuits IC1 and IC2 perform impedance conversion by a voltage follower and serve as a power supply for the output circuit unit OC. The reason for performing the impedance conversion of the power supply in this manner is as follows. That is, the other integrated circuit IC1 supplies power on the “+” side of the output circuit unit OC. In addition, the integrated circuit IC2 has a “−”
Side, and is always at the lowest voltage level (connected to the substrate) among the power supplies in the integrated circuit IC. On the other hand, the DC voltage level of the video signal passing through the inverting amplifier B and the operational amplifier C inside the integrated circuit 10 is the DC voltage level applied to the non-inverting input (+) terminal and the inverting input (-) terminal of the amplifiers B and C, respectively. And does not depend on the power supply voltage. Therefore, if the voltage of the terminal denoted by reference numeral 2 and the resistances R6 and R7 are managed, the waveform of the output signal g is a symmetrical waveform based on the center voltage of 5V and -10V, and the output circuit has a large amplitude signal. Even when the (liquid crystal panel drive signal) is output, the impedance conversion is performed because there is no need to adjust the power supply voltage.

As described above, since the video signal is inverted at the horizontal or vertical cycle, the voltage of the output section circuit OC power supply and the substrate is swung at the same cycle at the same cycle as that of the video signal, thereby obtaining a large amplitude signal. Video signals can be extracted from the integrated circuit 10 having a low withstand voltage.

[0018]

As described above, according to the present invention, a wide dynamic range can be obtained with a small number of components without changing the withstand voltage of the integrated circuit, and a large-amplitude video signal with little distortion can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a liquid crystal drive circuit according to an embodiment of the present invention.

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

3A is a conceptual diagram of an output circuit in FIG. 1, and FIG.
FIG. 4 is an explanatory diagram of an example of a change in an output signal as a change in a power supply voltage.

FIG. 4 is an explanatory diagram of a conventional liquid crystal drive circuit.

FIG. 5 is a signal waveform diagram of each part of the circuit of FIG. 4;

[Explanation of symbols]

 Reference Signs List A buffer B inverting amplifier C operational amplifier D switch OC output circuit section 1 to 8 terminals of integrated circuit 10 integrated circuit

Claims (1)

(57) [Claims] 1. A liquid crystal driving circuit in which an output circuit section is composed of an integrated circuit having a plurality of power supply voltages and applies a video signal that is inverted at a vertical or horizontal cycle to a liquid crystal panel. For inversion to invert the signal
And an inversion by the operational amplifier and the video signal or the inverting operational amplifier.
To switch the inverted video signal
Switch and a video signal or inverted video output from the switch.
The amplifier operational amplifier for amplifying the video signal, and the power supply voltage to the inverting operational amplifier and the operational amplifier
And at least one pair of power supply terminals for applying a reverse voltage to the Zener diode outside the output circuit section.
Zener voltage generating means for generating a Zener voltage by adding
And changes at the same cycle as the switching cycle of the changeover switch.
A power supply signal from the Zener voltage generating means;
At least one pair of power supply terminals of the output circuit unit together with a voltage
A liquid crystal driving circuit characterized in that the liquid crystal driving circuit applies the voltage to a pixel.