JPS59192287A - Display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a liquid crystal display device.

In the voltage averaging method used to drive a liquid crystal display device (hereinafter also referred to as LCD), multiple levels of signals are used. It depends on whether the voltage exceeds the optical threshold voltage.

For example, a signal voltage as shown in FIG. 1 is applied to one electrode of the LCD. The difference voltage between Vo and ■ is the above optical threshold ℃
・The value is selected to be larger than the voltage, Vo−vl+v,
v2. V2 Vs etc. are determined optically and are selected to be smaller than the threshold voltage, so that the voltage can be displayed by the magnitude of the difference between the voltage applied to the other electrode of the LCD and the voltage at multiple levels similar to that shown in Figure 1. .

The hidden state is determined.

Voltages as shown in FIG. 1 are supplied from a common power supply circuit to one and the other electrodes of the LCD via a switching circuit.

Figure 2 shows a power supply circuit 1, a drive circuit 2, and a L
CD is shown. In the circuit shown in Fig. 2, power supply circuit 1
consists of a voltage divider circuit using resistors R8 to R3, and one power supply voltage ■DD to V. or ■3 occurs. LCD
A plurality of voltage levels as shown in FIG. 1 are applied from this common power supply circuit 1 to the drive circuit 2 including switching means.

In the above circuit, the values of the resistors R1 to R3 need to be large (approximately 100Ω) in order to reduce the current (2) flowing through the power supply circuit 1 and reduce power consumption.

By the way, if you change the value of the resistance R+'-R3 in this way (
This means that the output in-beakence becomes large. This also means that the time constant becomes large, coupled with the fact that the LCD is a capacitive load. At the point of change in the LCD1 drive voltage waveform, the waveform becomes blunt, so-called ``accent J'' (see B and D in Figure 1).
, each point of F).

The present invention has been made to solve the above problems.
The purpose is to provide a display device that can eliminate the ``one round'' drive waveform without increasing current consumption.

An embodiment of the present invention for achieving the above object includes a voltage divider circuit in which a plurality of resistors are connected in series, a plurality of insulated gate field effect transistors connected in parallel to the respective resistors, and the insulated gate field effect transistors. The device is characterized by comprising a switching means for intermittently supplying a voltage to the gate of the type field effect transistor.

The present invention will be specifically explained below using Examples.

FIG. 3 is a circuit diagram showing one embodiment of the power supply circuit of the liquid crystal display device of the present invention. This power supply circuit has power supply voltage terminal ■D
Resistors R and -R are connected in series between D (negative voltage) and the ground potential terminal GND, and an enhancement type N-channel insulated gate field effect transistor M1 is connected in parallel to each of the resistors R2 to R3. ~M3 (hereinafter referred to as FET), and a changeover switch 81~S for supplying voltage to the gate of F E 'I'' M and ~M3. The connection point between the resistors R1 and 2 is the terminal (■), the connection point between the resistors R2 and (■t) is the terminal (■1), and the ground potential is the terminal (■).

■Output terminal from this power supply circuit. ～■3 is not shown (・
Connected to the LCD drive circuit. The output of this drive circuit drives the LCD. Note that the changeover switch 81
~S3 is switched to contact B only at the moment when the voltage applied to the LCD changes, and t is brought into contact with contact A at other times. Therefore, when switched to contact B,
FETM, .about.M3 are turned on, and when they contact contact A and reach .degree. C., FETM, .about.M3 are controlled to be turned off.

Moreover, the above-mentioned FETMs to M are those in which the substrate and the source are short-circuited. In this way, this FET
Voltage loss due to substrate effects in M, to M can be prevented.

According to the circuit configured as described above, when the voltage applied to the LCD changes, the switches S, ~S, switch to the contact B, and FET M + ~M3 are turned on. Therefore, the on-resistances of FETMI to M3 are connected in parallel to the voltage dividing resistors R5 to R5, respectively, and the output impedance at each voltage dividing point decreases. As a result, the time constant determined by the impedance of each voltage dividing point and the capacitance of the LCD becomes small, and it is possible to prevent the voltage waveform that drives the LCD from becoming rounded.

In addition, in the above circuit, when the driving voltage of the LCD does not change, the FETM, ~M, are turned off, so the current increases only slightly at the moment when the driving voltage changes, so the current consumption is unnecessarily reduced. It will not increase.

Further, since FETs MI to M3 connected between the substrate and the source are used, there is no voltage loss due to the substrate effect.

FIG. 4 is a circuit diagram showing another embodiment of the power supply circuit of the liquid crystal display device of the present invention. This power supply circuit is unique in that the switches S, .about.S in FIG. 3 are constructed using FETs. N-channel FETM and M are connected in series, and P-channel FETM is connected to the above FE.
A switch S is configured by connecting FETM4 and M in parallel, and the connection point between FETM4 and M is an N-channel FETM.
.

Connect to the gate. In addition, N-channel FET M6 and M7 are connected in series, and P-channel FET
M, o and M1□ are connected in series, and the series-connected connection points are commonly connected to configure switch S2,
The above common connection point is connected to the gate of N channel 281M2. Furthermore, by connecting the N-channel FETM, 2 and the P-channel FETM, 2 in parallel, and connecting the P-channel FETM, , to the source side of the FETM, 2, the switch S, FETM, 2. The connection point of M, , is connected to the gate of N-channel FET M3.

In addition, the board of the above N-channel FET M, -M8 has P-channel FET M, -M, 3 connected to the power terminal ■DD.
The board is grounded.

The above FETM, ~M7. Of these, 84 N-channel FETs. , M7 and P channel F E T M +. 2M
, 2, as shown in Fig. 5 '1-, the voltage VL applied to the LCD becomes high level 'H' (GND level) only when the voltage VL changes, and at other times it becomes low level 'L I+ (-■ D
D level) is applied.

Other FETM A, M, M8. M,, ~i,,
, Ni13 is applied with an inverted signal T (inverted by the inverter IN) of the above control signal.

According to the circuit with the above configuration, when the voltage applied to the LCD changes, the control signal T becomes H°'' level, which turns on FETM5, M, , Mヮ+Mll+M1., and turns on the other FETMs. TM, , M6.M,
o.

M8. Since M, , is turned off, N channel F
ETM, ~M, is turned on. As a result, output terminal 7■o~
■The output impedance of 3 decreases. Also, when the voltage applied to the LCD does not change, M71MIo9MI
2 is turned off, thus the N-channel FETM, ~
M, turns off (at this time, other FETM4.M, ,
M, o, M8. M,, turns on, and FETM, ~
M, and contributes to speeding up the off-operation). As a result, the output impedance of the output terminals vo to (3) is large and the current consumption is small.

In addition, since the switches S and ~s3 described above have a C-MOS (complementary MO8) transfer configuration, there is almost no voltage loss based on the substrate effect.

According to the present invention as described above, a display device that consumes low power and does not cause waveform distortion can be obtained.

The present invention is applicable to display devices that require the above-mentioned effects.
Available.

[Brief explanation of drawings]

Fig. 1 is a drive waveform diagram of the LCD, Fig. 2 is a circuit diagram for explaining a power supply circuit that outputs three-value levels, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is a diagram of the present invention. FIG. 5, which is a circuit diagram showing the other side of the invention, is a waveform diagram of the drive signal of the switch in the invention. 1...Power supply circuit, 2...LCD driver, R8-R
3...Resistance, M1-M13...FET, S...~S
,...Switch, LCD...Liquid crystal display device. Figure 1 Figure 3 ↓ Figure 5

Claims (1)

[Claims] 1. Consisting of (a) a display element driven by a plurality of voltages, and (b) a power supply circuit that outputs a pulse-like driving voltage to the display element, the impedance of the power supply circuit is equal to the output voltage. A display device characterized in that the value is set to a low value when the value fluctuates.