JP2002132229A - Liquid crystal driving circuit and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that conventionally, an analog signal has been inverted by an inversion circuit arranged in a liquid crystal display device separately from a horizontal driving IC, therefore, it has been necessary to make the inversion circuit speedily operate to correspond to the transfer rate of the analog signal, and a large current has to be consumed. SOLUTION: The analog signal supplied to an input terminal IN is alternately outputted from a 1st system 40 and a 2nd system 50 of a sample-hold circuit 200, namely, it is outputted non-inverted from the 1st system 40, but is outputted with inverted by an inverter circuit 55 arranged at a subsequent stage of a 2nd operational amplifier 53.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sample and hold operation and an output operation of an analog signal for each data line of a liquid crystal panel to be driven every one horizontal period by a first system and a second system. 1. Field of the Invention The present invention relates to a liquid crystal drive device having a sample-and-hold circuit composed of two systems that are alternately operated and a liquid crystal display device using the liquid crystal drive device.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device comprises, as a liquid crystal panel, a rear glass substrate on which pixel electrodes and TFTs (thin film transistors) constituting pixels are formed in a matrix, a common electrode and a color filter. The front side glass substrate is opposed to each other via the liquid crystal, and the TFT and the pixel electrode are provided with a scanning line extending in the horizontal direction and juxtaposed in the vertical direction, and a scanning line extending in the vertical direction and extending in the horizontal direction. The data lines arranged in parallel are connected to each other. A scanning signal was supplied to the liquid crystal panel by connecting a vertical driver IC to a scanning line and a horizontal driver IC to a data line, and supplying a scanning signal line-sequentially to each scanning line from the vertical driver IC. Each TFT connected to the scanning line turns on, and the horizontal driver IC
, The driving voltage supplied to each data line at the same time is supplied to the corresponding pixel electrode via the turned-on TFT, and the liquid crystal is driven by a potential difference from the voltage supplied to the common electrode (hereinafter, referred to as a common voltage).

When the input data signal is an analog signal such as a video signal, the horizontal driver IC has a sample / hold circuit at an output stage. A conventional example of this sample and hold circuit will be described with reference to FIG. In the figure, reference numeral 10 denotes a sample-and-hold circuit provided in a horizontal driver IC corresponding to each data line of a liquid crystal panel. This sample-and-hold circuit 10 is provided for every one horizontal period for scanning one scanning line. It is configured to operate. The sampling switch 11 is turned on by the sampling control signal sequentially supplied from the shift register in the horizontal driver IC to each sample and hold circuit 10 to sample and hold the analog signal supplied to the input terminal IN to the capacitor 12. , Condenser 1
2 inputs and outputs the analog signal sampled and held to the input / output terminal of the operational amplifier 13 connected to a voltage follower (hereinafter, the analog signal is sampled and held by a capacitor and input / output to the operational amplifier connected to a voltage follower. Operation) is referred to as a "sample / hold operation". The output switch 14 is provided by an output control signal which is simultaneously supplied to the respective sample / hold circuits 10 from outside the IC by outputting the analog signal output from the output terminal of the operational amplifier 13. Is turned on and output to the output terminal OUT (hereinafter, “the operation in which the analog signal output to the output terminal of the operational amplifier is output to the output terminal OUT” is referred to as “output operation”).

The sample-and-hold circuit 10 needs to perform the sample-and-hold operation and the output operation during one horizontal period. In the sample-and-hold operation, the operation is performed while the output switch 14 is turned off. It takes time to output a sufficiently stable waveform to the output terminal of the amplifier 13. If this time is insufficient, the output waveform of the output terminal of the operational amplifier 13 will not be sufficiently stabilized, and if the output operation is performed in a state where this output waveform is not sufficiently stable, the liquid crystal panel may not be displayed with high image quality. Therefore, the sample and hold operation of the analog signal output from the output terminal during one horizontal period is performed during the immediately preceding horizontal period to output a sufficiently stable waveform to the output terminal of the operational amplifier. -A hold circuit is used.

Hereinafter, this sample and hold circuit is shown in FIG.
This will be described with reference to FIG. In the figure, reference numeral 100 denotes a sample-and-hold circuit provided in a horizontal driver IC corresponding to each data line of a liquid crystal panel. This sample-and-hold circuit 100 is connected between input / output terminals IN and OUT.
The hold circuit 10 includes two systems in which a first system 20 and a second system 30 having the same circuit function are connected in parallel. The first system 20 is connected to a first switch 21 for sampling, a first capacitor 22, and a voltage follower. , A first operational amplifier 23 and an output first switch 24, and the second system 3
0 is a second switch 31 for sampling, a second capacitor 32, and a voltage-follower-connected second operational amplifier 3.
3 and an output second switch 34.

Next, the operation of the sample and hold circuit 100 will be described. The sample and hold circuit 100 alternately performs a sample and hold operation and an output operation between the first system 20 and the second system 30 every horizontal period. One
During a horizontal period (hereinafter, referred to as a first horizontal period), the first system 20
Will perform an output operation, and the second system 30 will perform an output operation in the next one horizontal period (hereinafter, referred to as a second horizontal period). In the first horizontal period, the first system 20 outputs the analog signal output to the output terminal of the first operational amplifier 23 in the sample-and-hold operation in the immediately preceding one horizontal period as an output operation from an external horizontal driver IC. The first output switch 24 is turned on by an output control signal simultaneously supplied to each sample-and-hold circuit 100 in the output terminal OU.
T, and the second system 30 converts the analog signal supplied to the input terminal IN from the shift register in the horizontal driver IC into each sample / hold as a sample / hold operation.
The second switch 31 for sampling is turned on by a sampling control signal sequentially supplied to the hold circuit 100 to sample and hold in the second capacitor 32,
The analog signal sampled and held by the capacitor 32 is input / output to the input / output terminal of the second operational amplifier 33. In this first horizontal period, the first switch for sampling 2
1 and the second output switch 34 are controlled to be off.

Next, in the second horizontal period, the first system 2
0 denotes a sampling and holding operation in which the analog signal supplied to the input terminal IN is switched from the shift register in the horizontal driver IC to the sampling first switch 21 by the sampling control signal sequentially supplied to each sample and hold circuit 100. Turn on the first capacitor 22
, And the analog signal sampled and held by the first capacitor 22 is supplied to the first operational amplifier 23.
The second system 30 outputs the analog signal output from the output terminal of the second operational amplifier 33 in the sample-and-hold operation in the first horizontal period to the horizontal driver IC from the outside as an output operation. The second output switch 34 is turned on by an output control signal simultaneously supplied to each sample-and-hold circuit 100, and is output to the output terminal OUT. In the second horizontal period, the sampling second switch 31 and the output first switch 24 are controlled to be off.

[0008]

By the way, the drive voltage supplied to each pixel electrode of the liquid crystal panel must alternately supply a positive voltage and a negative voltage with respect to the common voltage due to the characteristic of the liquid crystal. For example, in the case of the line inversion driving method,
It is necessary to alternately supply a positive voltage and a negative voltage with respect to the common voltage every horizontal period corresponding to each data line of the liquid crystal panel to be driven from the horizontal driver IC. As a method of alternately supplying a positive voltage and a negative voltage to the common voltage,
There are a common symmetric drive system in which the common voltage is kept at a constant voltage, and a common inversion drive system in which the common voltage is inverted at a supply cycle of the positive voltage and the negative voltage. When the horizontal driver IC including the above-described sample-and-hold circuit 100 is used in the line inversion driving method, in both cases, an analog signal is inverted and input to the input terminal IN of the sample-and-hold circuit 100 every horizontal period. There is a need. Conventionally, the inversion of the analog signal has been performed by an inversion circuit and a switch circuit provided in the liquid crystal display device separately from the horizontal driver IC. This inverting circuit needs to operate at a high speed in order to cope with the transfer speed of an analog signal, and there is a problem that a large current is consumed. The present invention has been made in order to solve the above-mentioned problems, and has a structure in which a sample and a sample are obtained every horizontal period.
It is an object of the present invention to provide a liquid crystal driving device in which an inversion circuit which does not need to operate at high speed can be provided by inverting an analog signal after a hold operation, and current consumed in a liquid crystal display device is reduced. I do.

[0009]

According to the liquid crystal driving apparatus of the present invention, an analog signal is sampled and held by a capacitor every one horizontal period corresponding to each data line of a liquid crystal panel to be driven, and a voltage follower connection is performed. Sample-and-hold circuit that alternately performs a sample-and-hold operation to be input / output to the input / output terminal of the operational amplifier and an output operation to output an analog signal output to the output terminal of the operational amplifier to the output terminal. In the liquid crystal driving device provided with the above, an inverting circuit is provided in one of the two systems and at a stage subsequent to the operational amplifier. According to the above means, since the analog signal is inverted after the sample and hold operation, there is no need to operate the inverting circuit at high speed, and the current consumed by the inverting circuit can be reduced. A liquid crystal display device according to the present invention is characterized by using the above liquid crystal driving device. According to the above means, since the liquid crystal driving device having the inverting circuit with low current consumption is used, the current consumption can be reduced even in the liquid crystal display device. Further, the liquid crystal display device is driven by a line inversion driving method. The liquid crystal driving device according to the present invention supplies an analog signal corresponding to each data line of the liquid crystal panel to a capacitor by sampling-holding an on / off control of a sampling switch, and supplies the analog signal to a voltage follower-connected operational amplifier. A sample-and-hold circuit, which is output from the output switch by turning on the output switch, is provided for each data line.
In a liquid crystal drive device in which two systems are connected in parallel and the ON control of a sampling switch and an output switch is alternately performed every one horizontal period, an operational amplifier and output for one system sample and hold circuit are used. An inversion circuit is inserted between the switch and the switch.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sample and hold circuit according to an embodiment used in an output stage of a horizontal driver IC which is a liquid crystal driving device for driving a liquid crystal panel line inversion by an analog signal according to the present invention is shown in FIG. This will be described with reference to FIG. In the figure, reference numeral 200 denotes a sample / hold circuit provided in a horizontal driver IC corresponding to each data line of a liquid crystal panel. This sample / hold circuit 200 is a sample / hold circuit 10 between input / output terminals IN and OUT.
And a second system 50 in parallel with a second system 50 in which an inverting circuit is connected between an operational amplifier and an output switch constituting a circuit having the same circuit function as the sample and hold circuit 10. , The first system 40 includes a first switch 41 for sampling, a first capacitor 42,
The first system includes a voltage-follower-connected first operational amplifier 43 and an output first switch 44. The second system 50 includes a sampling second switch 51, a second capacitor 52, and a voltage-follower-connected second switch. It has an operational amplifier 53, a second output switch 54, and an inverting circuit 55. The inverting circuit 55 includes a third operational amplifier 56 and resistors 57 and 58. The resistor 57 is connected between the output terminal of the second operational amplifier 53 and the inverting input terminal of the third operational amplifier 56.
Are connected between the inverting input terminal and the output terminal of the third operational amplifier 56, and the output terminal of the third operational amplifier 56 is connected to the second output switch 54. The non-inverting input terminal of the third operational amplifier 56 is supplied with half the power supply voltage VDD supplied to each of the operational amplifiers 43, 53, 56.

Next, the operation of the sample and hold circuit 200 will be described. The sample and hold circuit 200 alternately performs a sample and hold operation and an output operation between the first system 40 and the second system 50 every horizontal period. One
During a horizontal period (hereinafter, referred to as a first horizontal period), the first system 40
Will perform an output operation, and the second system 50 will perform an output operation in the next one horizontal period (hereinafter, referred to as a second horizontal period). In the first horizontal period, the first system 40 externally outputs the analog signal output to the output terminal of the first operational amplifier 43 in the sample and hold operation of the immediately preceding one horizontal period as an output operation. The first output switch 44 is turned on by an output control signal simultaneously supplied to each sample-and-hold circuit 200 in the output terminal OU.
T, and the second system 50 converts the analog signal supplied to the input terminal IN from a shift register in the horizontal driver IC to each sample / hold operation as a sample / hold operation.
The second switch 51 for sampling is turned on by a sampling control signal sequentially supplied to the hold circuit 200, and the second switch 52 is sampled and held by the second capacitor 52.
The analog signal sampled and held by the capacitor 52 is input to and output from the input / output terminal of the second operational amplifier 53, and the analog signal output from the second operational amplifier 53 is supplied to the inverting circuit 55 and inverted from the inverting circuit 55. And output the analog signal. In the first horizontal period, the first sampling switch 41 and the second output switch 54 are controlled to be off.

Next, in the second horizontal period, the first system 4
0 is a sample-and-hold operation in which the first switch 41 for sampling is controlled by a sampling control signal sequentially supplied from the shift register in the horizontal driver IC to each of the sample-and-hold circuits 200 as an analog signal supplied to the input terminal IN. Turn on the first capacitor 42
The first operational amplifier 43 samples and holds the analog signal sampled and held by the first capacitor 42.
The second system 50 outputs, as an output operation, the sample / output signal of the first horizontal period to the output terminal of the inverting circuit 55 as an output operation.
The output second switch 54 is turned on by the output control signal simultaneously supplied from the outside to the respective sample and hold circuits 200 in the horizontal driver IC to output the inverted analog signal output by the hold operation to the output terminal OUT. Output. In the second horizontal period, the sampling second switch 51 and the output first switch 44 are controlled to be off.

As described above, the analog signal supplied to the input terminal IN is supplied to the sample-and-hold circuit 200.
Are alternately output from the first system 40 and the second system 50 every one horizontal period, and are output from the first system 40 in a non-inverted manner.
From the system 50, the output is inverted. Inverting circuit 55
Needs only to invert the sampled and held analog signal, it does not need to correspond to the transfer rate of the analog signal supplied to the input terminal IN, does not need to operate at high speed, and is independent of the horizontal driver IC. Since the current consumption can be reduced as compared with the provided inversion circuit, the current consumption of the liquid crystal display device can be reduced. In addition, analog signals are transferred to a horizontal driver IC.
When the inversion is performed by another circuit before the signal is supplied to the sample and hold circuit 200, a switch for switching between inversion and non-inversion is required. However, when the inversion is performed in the sample and hold circuit 200, a new switch is not required.

[0014]

According to the liquid crystal driving device according to the present invention,
2 of the sample and hold circuit to which the analog signal is supplied
Since an inversion circuit is provided in one of the systems and at a stage subsequent to the operational amplifier, it is not necessary to operate the inversion circuit at high speed, and the current consumption of the liquid crystal display device using this liquid crystal driving device can be reduced. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a sample and hold circuit used in a horizontal driver IC according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional one-system sample / hold circuit.

FIG. 3 is a circuit diagram of a conventional two-system sample-hold circuit.

[Explanation of symbols]

 Reference Signs List 40 First system 41 First sampling switch 42 First capacitor 43 First operational amplifier 44 First switch for output 50 Second system 51 Second switch for sampling 52 Second capacitor 53 Second operational amplifier 54 Second switch for output 55 inversion circuit 200 sample and hold circuit

Claims (4)

[Claims] An analog signal is sampled and held by a capacitor and input / output to / from an input / output terminal of a voltage-follower-connected operational amplifier for each horizontal line corresponding to each data line of a liquid crystal panel to be driven. A liquid crystal driving device including a sample and hold circuit that alternately performs a sample and hold operation and an output operation in which an analog signal output to an output terminal of an operational amplifier is output to an output terminal in two systems, A liquid crystal driving device, wherein an inverting circuit is provided in one system and at a stage subsequent to the operational amplifier. 2. A liquid crystal display device using the liquid crystal drive device according to claim 1. 3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is driven by a line inversion driving method. 4. An analog signal corresponding to each data line of the liquid crystal panel is sampled and held by a capacitor by turning on a sampling switch, and supplied to a voltage follower-connected operational amplifier. Sample output by ON control of
In the liquid crystal driving device, two hold circuits are connected in parallel corresponding to each data line, and the ON control of the sampling switch and the output switch is alternately performed every two horizontal periods between the two systems. A liquid crystal drive circuit comprising an inversion circuit inserted between an operational amplifier and an output switch of a sample and hold circuit of a system.