JP2600372B2 - LCD drive circuit - Google Patents

Description

The present invention relates to a liquid crystal drive circuit.

[Conventional technology]

The display of the active matrix liquid crystal panel is controlled by a drive circuit that inputs a digital image signal.

FIG. 5 is a block diagram of an example of a conventional liquid crystal drive circuit.

The digital image signal v ₃ of m gradation is inputted from the signal input terminal group T _3, by the clock pulse v ₄ which joined the clock pulse input terminal T _4, is transferred shift register 10 _a to 10 _n of the n stages, also , the latch circuit corresponding stage a~n by the latch pulse v ₇ which joined the latch pulse input terminal T ₇ 11 _a
Each of which is transferred to to 11 _n.

The latched holding signals v _{La to} v _Ln are respectively selected by the corresponding _a to _n- stage selectors 23 _a to 23 _n ,
Which one by one the on state of the transistor in each stage per m Ke from the output transistor Q ₁₁ to Q _m1 stage connected to each of the liquid crystal driving voltage output terminal T _18a through T _18n to Q _1n to Q _mn stage giving the LCD display one by one of the power supply voltage V ₁ ~V _m desired one of the power supply voltage terminal T ₂₁ through T _2m as the voltage of m gray scale is to.

Generally, the number of gradations m is 16, and the number of steps n is about 100.

Therefore, the output transistor Q ₁₁ ~Q _mn will be 1600.

[Problems to be solved by the invention]

In the above-described conventional driving circuit, when the number of gradations m is large, the number of output transistors increases, so that when forming an integrated circuit, the output transistors occupy about half of the chip area, the chip size increases, and the cost increases. .

In particular, when the screen of the liquid crystal panel increases, it is necessary to further increase the driving capability of the output transistor. Therefore, the chip size of the output transistor further increases, which is not suitable for an integrated circuit.

Further, voltage power supplies each having a driving power capacity corresponding to the number of gradations of m were required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal drive circuit which is a highly integrated circuit and has a large number of gradations.

[Means for solving the problem]

The liquid crystal driving circuit according to the present invention comprises: (A) a plurality of cascaded shift registers for transferring an input image signal, and a holding signal for holding the image signals transferred from each of the shift registers. (B) a plurality of selectors each of which selects a corresponding reference voltage from the plurality of input reference voltages according to the holding signal and outputs a selected reference voltage; Enter a ramp voltage that changes in proportion to time,
(D) a plurality of source follower circuits for inputting the respective hold voltages of the sampling circuits and outputting a liquid crystal drive voltage; (E) the selection criteria corresponding to the liquid crystal drive voltages, respectively. And a plurality of comparators that drive the corresponding sample switches when the voltages are input, compared, and matched.

〔Example〕

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a waveform diagram of signals of respective parts of the block of FIG. 1, and FIG.
And (b) is a circuit diagram of the comparator and selector of FIG.

The liquid crystal driving circuit includes a conventional selector driving circuit 1 shown in FIG. 5 and reference power supply terminals T _{11 to} T L corresponding to holding signals v _{La to} v _Ln latched by n-stage latch circuits 11 _{a to} 11 _n. a selector 12 _a to 12 _n for selecting one of the reference voltage V ₁₁ ~V _{1 m} as a selection reference voltages from _{1 m,} and the sampling capacitor C _a -C _n of each stage a~n as input a ramp voltage v ₁ a sampling circuit 3 _a to 3 _n consisting of sampling switches 14 _a to 14 _n,
Output transistor Q _a to Q _n and a constant current source I _a ~I and source follower circuit 2 _a to 2 _n of the n stages consisting _n, the liquid crystal drive voltage output of the source follower circuit 2 _a to 2 _n v of each stage 1 pc enter the _18a to v _18n to one compared to corresponding selected reference voltage v _12a to v _12n on the other, by the comparator output voltage v _13a to v _13n, the corresponding sampling switches 14 _a to 14 _n in each stage composed of the opening and closing to the comparator 13 _a to 13 _n.

As shown in FIG. 2, the image signal v ₃ is input from the input terminal T _3, is transferred to the shift register 10 _a to 10 _n in each stage by clock pulses v _6, input to the latch circuit 11 _a to 11 _b data during the next one horizontal period is held by the latch pulse v ₇ to.

The selectors 12 _{a to} 12 _n of the stages _a to _n output the holding signals v _{La to} v _Ln
Reference voltages V ₁ corresponding to the signal to select one of ~V _m, input to each input terminal of the comparator 13 _a to 13 _n in each stage.

Initially, the charging potentials of the sampling capacitors C _{a to} C _n of each stage are all zero, and each of the liquid crystal drive voltage output terminals T
_18a through T _18n of the output voltage V _18a ~V _18n is referred to as being substantially ground potential.

Then, the lamp voltage v ₁ which rises in proportion to time is inputted from the input terminal T _1.

To input start the clock pulse v ₆ to the comparator of each stage.

The comparators 13 _{a to} 13 _n of each stage are connected to the selected reference voltage v ₁₂ a selected by one of the selectors 12 _{a to} 12 _n of the stage corresponding to the liquid crystal drive output voltage v _{18 a to} v _{18 n} of each stage. ~ V _12n
Compare with one of

First selected reference voltage v _i, the lamp voltage v higher than _i, the output voltage v of the comparator 13 _a to 13 _n in each stage a~n
_13a to v _13n closes each time point t ₀ sampling switches 14 _a ... 14 _n, the sampling capacitor C _a -C _n in each stage was charged with lamp voltage v _1, the constant current source I _a ~I _n in each stage , Source follower circuits 2 _a to 2 _n composed of output transistors Q _{a to} Q _n at each stage.
It is output to the output terminal T _18a through T _18n.

Time ramp voltage v ₁ rises elapsed, the output voltage of each stage
v _{18a to} v _18n also increase in proportion to v _1, and ₁ of the reference voltages V _{1 to} V _m
One of exceeding respectively selected selector voltage, for example V _i, the V _j.

At that time t _i , t _j , the comparator output voltage v
_13a to v _13n is reversed, the sampling switches 14 _a ~ of each stage
14 _{Make n} open.

As a result, driving the output voltage v _18a to v _18n of each stage, the values corresponding to each held signal to the latch 11 _a to 11 _n of each stage, to obtain a v _i and v _j here.

Output transistor Q _a to Q _n of the circuit of FIG. 1, each stage a~
a one month to n, Figure 3 also comparators 13 _a to 13 _n as shown in (a) can be easily configured by the NOT circuit of the three hair switches and 1 pc capacitor and 1 Ke, FIG. 3 (b selector as shown in) 12 _a to 12 _n is also the transfer gate TG for small small-signal influence on the chip area of the decoder 4 and m Ke
Can be configured. In this embodiment, each of the output transistors Q _{11 to} Q _mn occupies about half of the chip area.
In the present embodiment, the number x × n is required is reduced to _n of Q _{a to} Q _n . For example, when m is 16, the area occupied by the chip of the integrated circuit is reduced to about 60%. This has the effect that a small integrated circuit can be achieved.

FIG. 4 is a waveform diagram of a lamp voltage according to a second embodiment of the present invention.

Generally, in driving an active matrix liquid crystal, the voltage range in which the transmittance greatly changes is small.

In the present embodiment, in order to increase the temporal resolution (the number of comparator clock pulses v6) corresponding to the voltage ranges ΔV _L1 and ΔV _L2 , the ramp voltage v ₁ has a low rise rate time τ _L1 and τ _L2. A linear voltage v _NL is given.

This makes it possible to obtain a liquid crystal drive circuit that supplies an accurate drive voltage to the liquid crystal.

[Effects of the Invention] As described above, the present invention provides a sampling circuit, a source follower circuit, and a comparator circuit for outputs of a plurality of stages, and transfers a ramp voltage input simultaneously to each stage to each stage. By outputting the liquid crystal drive voltage by charging up to the reference voltage selected according to the data signal value, the number of output transistors corresponding to the number of gradations, which conventionally occupied a large chip area, is not required. In addition, only one output transistor having only a source follower is required, and high integration of the IC is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a waveform diagram of each part of the block of FIG. 1, and FIGS. 3 (a) and (b) are comparators and selectors of FIG. FIG. 4 is a waveform diagram of a lamp voltage according to a second embodiment of the present invention, and FIG. 5 is a block diagram of an example of a conventional liquid crystal drive circuit. 1... Selector drive unit, 2 _a to 2 _n ... Source follower circuit,
3 _{a to} 3 _n ... sampling circuit, 10 _a to 10 _n ... shift register, 11 _{a to} 11 _n ... latch circuit, 12 _{a to} 12 _n ... selector, 13 _{a to} 13 _n ... comparator, 14 _a ~ 14 _n ...... Sampling switch, C _a ~ C _n ...... Sampling capacitor, Q _a
~ Q _n …… Output transistor, T ₂ …… Reference voltage terminal, T _18a
~T _18n ...... liquid crystal driving voltage output terminal, V ₁ ~V _m ...... reference voltage, v ₁ ...... ramp voltage, v ₃ ...... image signal, v ₄ ...... clock pulse, v ₆ ...... comparator clock pulses, v ₇ ……
Latch pulse, v _12a ...... selected reference voltage, v _13a ...... comparator output signal, v _18a ~v _18n ...... liquid crystal driving voltage, v _La ...
... Hold signal.

Claims (1)

(57) [Claims] 1. A shift register in which n stages corresponding to the number of horizontal pixel electrodes are connected in cascade to transfer an input image signal, and the image signal transferred from each of the shift registers is held. A selector driving unit having n latch circuits for outputting a holding signal, and (B) inputting m reference voltages corresponding to the number of gradations, and from among the m reference voltages, the holding signal corresponds to the gradation signal by the holding signal. N selectors for selecting a reference voltage to be output and outputting a selected reference voltage, respectively. (C) Commonly input a ramp voltage rising in proportion to time, and corresponding n samplings by n sampling switches (D) input each hold voltage of the sampling circuit and input a corresponding liquid crystal drive voltage (E) n comparators for inputting and comparing the liquid crystal drive voltage and the corresponding selection reference voltage, and driving the corresponding sampling switch when they match. A liquid crystal driving circuit characterized by the above.