JPH0315023A - Liquid crystal driving circuit - Google Patents

Abstract

PURPOSE:To constitute the liquid crystal driving circuit with a smaller area by using two transistors(TR) for the output buffer part of a segment signal output circuit without any deterioration in display quality. CONSTITUTION:The substrate potential of a TR Pa is fixed basically at the VA same as the source potential of the Pa, and a short discharge period is provided by a signal T in the beginning of each duty of both a segment and backplate output signal. Consequently, the output buffer part of the segment signal output circuit consists of the two TRs Pa and Na similarly to a normal output buffer without any deterioration in display quality. Consequently, the liquid crystal driving circuit with the smaller area can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a liquid crystal drive circuit constituted by MOS transistors.

<Prior Art> As shown in FIG. 3, a limb crystal drive circuit sends segment output signals i1, . ．． ．． , 1n, and a banok plate output signal H.
l.・・・． The bank plate signal output circuit 3 outputs Hm.

Conventional segment and banok plate output signals are as shown in FIG. 4, and a circuit for outputting these signals has a configuration as shown in FIG. 5. In FIG. 5, fat is a segment signal output circuit, and FIG. 5 (bl is a banok plate signal output route.

VA of this segment signal output circuit. VBl”ll..
At frame 1 (S=H) (dVA=AA1.vn
=VBB,7L/-mu2(S=L)TUVA=AAz
．． It is controlled so that Vn = vD2. At each duty, when the signal is l to H, transistors Pa and Nb turn on in frame 1 and output -VAI level, and in frame 2, transistor Pb1Na turns on and outputs -Vllll level, and the liquid crystal display lights up. , when the signal i=L, the transistors Pb and Na turn on in frame 1 and output the -Vllll level, and in the frame 2, the transistors Pa and Nb turn on and output the full VA2 level, turning off the light.

In this segment signal output circuit, transistor Pa.
Nb and Pb. Na is conjugated. Normal output Banoff rPa. With only Na, does Na turn on at frame l and the VII1 level is output? When Pa is turned on in frame 2 and outputs the VA2 level, a panoch gate bias is applied to the transistors Na and Pa (the source potential of Na is as high as VBI with respect to the substrate potential VB2 of Na). The substrate potential VA of Pa
Since the source potential of Pa becomes low (V2 compared to I), the on-resistance of the transistor becomes large, and the night crystal, which is the load, cannot be driven completely, and the voltage changes from VAI level to VB level in frame 1 and to VB level in frame 2. The output signal waveform from VB ■l level to V person 2 level becomes dull,
The display quality deteriorates (see Figure 6).

In order to compensate for the deterioration of the on-resistance due to this Banok gate bias, two transistors, Pb and Nb, are added, and as transistor gates, the level can be output with a small on-resistance in any case, and the output signal waveform is This prevents unnecessary charges and maintains good display quality.

<Problems to be Solved by the Invention> In the conventional method, four transistors were required in the output buffer section of the segment signal output circuit, which required a very large area.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method in which the output vanofer section of a segment signal output circuit can be configured with two transistors in the same way as a normal output vanofa, without deteriorating the display quality.

Means for Solving the Problems> The liquid crystal drive circuit of the present invention has each output circuit for a segment output signal and a panoch plate output signal, and is configured to have a short discharge period at the beginning of each duty of the output signal. It is characterized by:

<Example> Hereinafter, the present invention will be explained in detail based on examples.

The segment and banok plate signal output circuit according to the present invention is shown in FIG. (To be exact, the potential of the N well) is fixed at VA, which is the same as the source potential of Pa,
Furthermore, the structure is such that the signal T provides a short discharge period at the beginning of each digital of the segment and banok plate output signals.

Figure 2 shows the output signal from this circuit.

As a countermeasure for banok gate bias of transistor Pa of segment signal output circuit. Pa's substrate potential C is exactly PaN
The well potential) is fixed to the same potential as the source of Pa. By configuring only Pa in a single well, separated from the internal Ojinoku, it is possible to set the well potential to VA. Even if VA2 changes, the substrate (well) and the well have the same potential, so a structure can be created in which no banok gate bias is applied. However, since the substrate potential of the transistor Na is fixed at the iVn2 level, unlike Pa, the potentials of the substrate (N well) and the source cannot be made the same, and it is not possible to prevent the gate bias. Therefore, the circuit structure is made as shown in FIG. 1, and the signal T is used to provide a short destination period at the beginning of each duty of the segment and banok plate output signals. That is, the segment and banok plate signals shown in FIG. 2 are output. If such a signal is output, the charge annoborated to the liquid crystal at the time of V person 1 level output will be in the state a (when T = H, n = VB2) during the discharge period, where no banok gate bias is applied. ) with small on-resistance N
It is discharged for a short time at a, and then vn=Vn
+, and the VB1 level is output by Na. Therefore, there is no need to drive the liquid crystal as a load with Na, which has a large on-resistance when a banok gate bias is applied, and the waveform never drops, resulting in good display quality.

Effects of the Invention> As described above, according to the present invention, the output vanofer section of the segment signal output circuit can be configured with two transistors without deteriorating the display quality, and the output can be configured with a smaller area. It is possible to configure a liquid crystal drive circuit, and is extremely effective in practice.

[Brief explanation of drawings]

? 1 is a circuit diagram of a segment signal output circuit and a banok plate signal output circuit according to the invention, FIG. 2 is a waveform diagram of a segment output signal and a banok plate output signal according to the invention, and FIG. 3 is a bronc diagram of a liquid crystal display system. Fig. 4 is a waveform diagram of a conventional segment output signal and banok plate output signal, Fig. 5 is a circuit diagram of a conventional segment signal output circuit and banok plate signal output circuit, and Fig. 6 is a waveform diagram of a conventional segment output signal and banok plate signal output circuit.
FIG. 6 is a segment output signal waveform diagram of a poem with only a and Na.

Claims (1)

[Claims] 1. A liquid crystal drive circuit characterized in that it has an output circuit for a segment output signal and a back plate output signal, and is configured to have a short discharge period at the beginning of each duty of the output signal.