JP2626063B2 - LCD drive circuit - Google Patents

Description

The present invention relates to a liquid crystal drive circuit.

[Conventional technology]

With the spread of liquid crystal TVs and the like, it has become important to reduce the power consumption of the driving circuit of a dry battery driven active matrix liquid crystal panel.

FIG. 3 is a block diagram of an example of a conventional liquid crystal drive circuit.

The video signal output unit 5 inputs the mutually independent RGB signals R, G, B to the input unit of the RGB video line l, and corresponds to each of the RGB signals R, G, B of the sample and hold circuit SH. Are input in parallel, and sequentially output as drive signals R ₁ , G ₁ , B _{1 to} R _2n , G _2n , B _2n to the matrix liquid crystal panel unit 6 during the ON period of the gate for sampling of the sample and hold element. .

[Problems to be solved by the invention]

In the above-described conventional driving circuit, since the parasitic capacitance Cs exists in parallel with the RGB video line, the input impedance of the video line 1 is low, and the power consumption of the video signal output unit in which the number of pixels of the liquid crystal panel unit is large increases. There were drawbacks.

That is, each of the RGB video lines 1 is connected to 2n sample-hold elements. For example, if the number of horizontal pixels is 384, 128 sample-hold elements are connected to each line. Assuming that each parasitic capacitance is 0.5 pF, the total input capacitance is 64 pF for each of the R, G, and B lines.

An object of the present invention is to provide a liquid crystal drive circuit having a high input impedance.

[Means for solving the problem]

The liquid crystal drive circuit according to the present invention is configured such that an RGB signal output from a plurality of output terminals of an RGB video line is input to a corresponding sample hold circuit, and an active matrix liquid crystal is used as a drive signal using the RGB signal during a gate period of the sample hold circuit. In the liquid crystal drive circuit that supplies the circuit,
The sample-and-hold circuit is divided into a plurality of units, and corresponds to the unit including the sample-and-hold circuit in which a gate is operated between an input section of the plurality of units and the output end of the RGB video line. In addition to providing a plurality of unit switches that are divided and controlled, the switching timings of the unit switches are configured by providing a shift period corresponding to each of the RGB video lines.

〔Example〕

According to the present invention, a set of an R signal line, a G signal line, and a B signal line obtained by separating an RGB video signal, and a set of an R signal sample / hold element, a G signal sample / hold element, and a B signal sample / hold element are respectively provided. A first sample and hold unit including a plurality thereof and a second sample and hold unit
, The input side of each R signal sample and hold element of the first sample and hold unit, the input side of each G signal sample and hold element, and the sample and hold element of each B signal. The first connection line, the second connection line, and the third connection line that commonly connect the input sides, respectively, and the input side of each R signal sample and hold element of the second sample and hold unit are commonly used. A fourth connection line, a fifth connection line, and a sixth connection line that commonly connect the input side of the G signal sample and hold element and the input side of each B signal sample and hold element; An R signal switch element and a G signal switch which are respectively arranged between the signal line, the G signal line and the B signal line and the first connection line, the second connection line and the third connection line. A first switch unit comprising a switch element and the B signal for the switch element, the R signal lines, G signal line and the B signal line and the fourth connection line,
A second switch unit including an R signal switch element, a G signal switch element, and a B signal switch element disposed between the fifth connection line and the sixth connection line;
Between the one R signal switch element and the other R signal switch element of the first switch unit and the second switch unit, one G signal switch element and the other G signal switch element;
A liquid crystal drive circuit including a switch control circuit for controlling ON / OFF switching between the signal switch elements, between one B signal switch element and the other B signal switch element is obtained.

Further, according to the present invention, the timing of the switching control of the switch control circuit is such that the R signal sample and hold elements which are close to each other and the G signal which are close to each other at the boundary between the first sample and hold unit and the second sample and hold unit. The signal sample-and-hold element and the sample-and-hold element for the B signal that are close to each other are after the sampling period of the first sample-and-hold unit and before the start of the sampling period of the second sample-and-hold unit. Liquid crystal driving circuit is obtained.

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a timing chart of signals of respective parts for explaining the operation of the block of FIG.

The liquid crystal drive circuit 1 is provided with the sample and hold circuit SH shown in FIG.
Is divided into two units 4 _a and 4 _b by n pairs, and each unit 4
_a, 4 RGB signal of the video to the input of _b R, G, the switch unit 3 _a, 3 _b corresponding provided B, and the timing of the switches R, G, RGB control signal a _R for controlling each B , a _G , a _B 〜b _R , b _G ,
The switch control unit 2 for outputting a b _B has.

Switch 3 _a, 3 _b by, for example sampling on the operation in the unit 4 _b other units 4 _a of the switch unit
3 _a of S _R, S _G, can be disconnected between the input end and the unit 4 _a of the RGB signal by turning off any of the S _B.

Switch switching timing to the next unit 4 _b from unit 4 _a, it is necessary to shift the off timing of the sampling gate of the sample-and-hold device of the sample-and-hold circuit SH _b connected to the RGB video line l.

Otherwise, charge / discharge noise at the time of switching of each unit switch affects the sample and hold circuits SH _a and SH _b .

For example, as for the R signal R, the time when the sampling gate r _n of the sample-and-hold element corresponding to the unit 4 _a is turned off at the time t _{1 and} shifted by the period τ ₁
In t _2, controls the R switch S _R of the switch unit 3 _a signal a _R
Off at the same time as the R switch of switch unit 3 _b
Turn on S _R.

Next, the sample and hold circuit SH at t ₃ after time tau _2
The drive signal R _{n + 1} is output by the sampling gate r _{n + 1} of the sample and hold element _b .

Thus, the R signal R is shifted R switch S switching point _R t ₂ and the gate r ₁ ~r _2n on-off time t _3.

Hereinafter, the video signals G and B operate at the same timing.

Therefore, during the period when the unit _4b is operating, the other unit _4a is separated from the input unit of the liquid crystal drive circuit 1, and when the number of horizontal pixels is 384, n = 64. The total input capacitance per signal is 37 pF, which is the sum of 32 pF, which is half the total of the conventional parasitic capacitance Cs, and 5 pF, the switch parasitic capacitance of one MOS.

In this embodiment, the liquid crystal drive circuit is a one-chip integrated circuit, but the switch control unit 2 may be divided into two chips corresponding to each unit.

〔The invention's effect〕

The present invention divides the sample-and-hold circuit into a plurality of units, and disconnects units other than the unit performing the sampling operation by a switch, thereby greatly reducing the input capacity of the video line, and reducing the power consumption of the video signal output unit and the driving circuit. This is effective in reducing the amount of rust.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
FIG. 3 is a timing chart of signals of respective parts for explaining the operation of the block shown in FIG. 3, and FIG. 1 ... LCD drive circuit, 2 ... Switch control unit, _3a , _3b ...
… Switch unit, 4 _a , 4 _b … Unit, 5… Video signal output unit, 6… Liquid crystal panel unit, a _R , a _G , a _B … RGB
Control signal, l ...... RGB signal video line, l _a, l _b ...... unit switch control signals, R, G, B ...... RGB _{signals, R 1, G 1, B} 1 ~
R _2n , G _2n , B _2n ... Drive signal, SH _a , SH _b .

Claims (2)

(57) [Claims] An R signal line for separating an RGB video signal;
A first sample and hold unit and a second sample and hold unit each including a plurality of sets of a G signal line and a B signal line, a plurality of sets of an R signal sample and hold element, a G signal sample and hold element, and a B signal sample and hold element; The input side of each R signal sample and hold element of the first sample and hold unit is commonly used, the input side of each G signal sample and hold element is commonly used, and the input side of each B signal sample and hold element is commonly used. A first connection line, a second connection line, and a third connection line to be connected to each other; and an input side of each of the R signal sample and hold elements of the second sample and hold unit, each G signal sample and hold. The input side of the element is commonly connected and the input side of each B signal sample-and-hold element is commonly connected. 4, the fifth connection line, the sixth connection line, and between the R signal line, the G signal line, and the B signal line, and the first connection line, the second connection line, and the third connection line. A first switch unit including a R-signal switch element, a G-signal switch element, and a B-signal switch element, respectively; and a fourth connection line with the R signal line, the G signal line, and the B signal line; A second switch unit including an R signal switch element, a G signal switch element, and a B signal switch element disposed between the fifth connection line and the sixth connection line; and the first switch unit and the second switch unit. 2 switch unit, between one R signal switch element and the other R signal switch element, one G signal switch element and the other G signal switch element.
A liquid crystal drive circuit including a switch control circuit that controls ON / OFF switching between the signal switch elements, between one B signal switch element and the other B signal switch element. 2. The switching control timing of the switch control circuit is such that an R-signal sample-hold element which is close to the second sample-hold unit and a G-signal which is close to each other at a boundary between the second sample-hold unit and the second sample-hold unit. The sample-and-hold element and the sample-and-hold element for the B signal that are close to each other are after the sampling period of the first sample-and-hold unit and before the start of the sampling period of the second sample-and-hold unit. The liquid crystal drive circuit according to claim 1.