JPS594712B2 - Ekishiyouhiyoujisouchino Kudooseigiyosouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for driving and controlling a liquid crystal display device depending on the magnitude of ambient light.

Liquid crystal display devices are used as display means in many electronic devices because of their low power consumption.

In particular, the combination of CMOS circuit and FEM liquid crystal display device is
It is attracting attention as a display means most suitable for electronic wristwatches because of its extremely low power consumption. However, a liquid crystal display device does not emit light by itself and can only display images depending on the presence of ambient light. Therefore, when the ambient light decreases, the liquid crystal display device effectively stops displaying even though it is being driven. is,
Drive power for display will be consumed unnecessarily.
However, for example, in an electronic wristwatch, etc., the operation as a clock must be performed continuously, and the drive circuit and logic circuit of the liquid crystal display device are integrated into an LSI element, etc. LSI to stop display
If the power supply to the element is stopped, the operation as a clock will also stop, which is inconvenient. Therefore, in order to reduce power consumption, it is necessary to take measures to prevent the operation of other logic circuits from stopping when driving and controlling the liquid crystal display device according to the magnitude of ambient light. The following drive control device for such a liquid crystal display device has already been proposed by the present inventors.

That is, in this device, a decoder output cutoff control gate is provided between the liquid crystal drive circuit and the decoder, and this control gate is opened and closed by a switch that controls the display of the liquid crystal, so that only the liquid crystal display device can be controlled by the drive control gate. It was designed to be controlled. However, in this device, a new LSI element having a gate circuit is required in an LSI element in which a liquid crystal display drive circuit and a logic circuit are integrated, and changes from the element design stage are indispensable. ! The present invention has been made to solve these drawbacks, and provides a simple device that can drive and control a liquid crystal display device using conventional LSI elements as they are.

In order to achieve this objective, the device of the present invention establishes the following relationship between the minimum voltage VCth required for normal operation of the 5LS element and the minimum voltage VLth required for display on the liquid crystal display device. Using this, the drive voltage V supplied to the LSI element can be set to either (2) or
The present invention is characterized in that a means for switching between two values defined by the equation (2) is provided, and the drive of only the liquid crystal display device is controlled depending on the magnitude of ambient light by this switching means.

Note that the LS element and the liquid crystal display device are normally driven at the drive voltage V1 defined by the above equation (2), and the LS element and the liquid crystal display device are driven normally at the drive voltage V2 defined by the above equation (3) below the lighting threshold VLth of the liquid crystal display device. Therefore, the liquid crystal display device does not turn on and only the logic circuit operates normally. The device of the present invention will be explained in more detail below by giving an example related to an electronic wristwatch.
The embodiment shown in FIG. 1 is a block diagram of an electronic wristwatch to which the device of the present invention is applied. Reference numeral 1 denotes an LSI element consisting of a CMOS circuit, which constitutes the electronic circuit section of the timepiece.

2 is a crystal resonator, 3 is a liquid crystal display device, 4 is a power supply, 5 is a D
Shows a C-DC converter.

In the LS element 1, an oscillation circuit 11, first and second frequency dividing circuits 12 and 13 separated into a front stage and a rear stage, and a liquid crystal display device driving circuit are integrated and incorporated.
As the DC-DC converter 5, a CMOS diengel type converter or the like may be used. In the device of this embodiment, this converter 5 includes an oscillation and first frequency dividing circuit section A, and a second frequency dividing circuit section A.
The switching gate 6 according to the present invention is inserted as shown in the figure between the frequency dividing circuit and the liquid crystal display device driving circuit part B, and the voltage Vss supplied to the circuit part A is increased to the voltage VEE necessary for driving the liquid crystal. Boost the pressure. Furthermore, in the drawing, 7 indicates a level sensor, 8 indicates a solar cell for detecting ambient light,
The level sensor 7 detects whether this detected light is above or below a certain level. In this example,
As mentioned above, changes in ambient light are detected using the solar cell 8, and a constant switching level is obtained using the level sensor 7 to control the switching gate 6.

As is well known, the CMOS Diengel converter used in the DC-DC converter 5 requires two driving signals, Q and Q, as inputs, and when V1 is obtained as the output of this converter, either of the inputs Q and Q This circuit is capable of obtaining a potential of approximately V2=V1/2 by setting the voltage to ground potential. Therefore, switching gate 6
is inserted into either the input line Q or Q (Q in the figure), one switching terminal S1 is connected to the frequency divider circuit 12, the other switching terminal S2 is connected to the ground potential, and the level Switching is controlled depending on the output of the sensor 7, and the voltage V1 or V2 is outputted as the output of the converter 5. converter 5
When the output of converter 5 is now 1, it is based on equation (2), so the liquid crystal display device 3 operates normally and lights up.On the other hand, when the output of converter 5 is 2, it is based on equation (3). , the liquid crystal display device 3 does not operate normally and does not turn on.

In this embodiment, in this way, the driving voltage supplied to the circuit section B of the LSI element 1 is switched by detecting the magnitude of ambient light, and the driving of only the liquid crystal display device is controlled. Nao L
The operating voltage V in the SI element 1 is low except for the liquid crystal display device drive circuit 14. , h, the voltage V1 for driving the liquid crystal display device 3 once should ideally be applied only to the liquid crystal display device drive circuit 14.
Due to the design of the LSI element 1, the voltage may be applied to the circuit section B including the frequency dividing circuit as in the device of this embodiment. In Figure 1, Vs
s indicates the voltage applied to the circuit section A, and VEE indicates the voltage applied to the circuit section B. In this embodiment, as described above, this voltage EE is expressed as Vl,
The drive control of the liquid crystal display device is performed by controlling between V2. Figure 2 shows the CMOS in the block diagram shown in Figure 1.
This is a diagram showing specific circuits of the diengel converter 5, the switching gate 6, and the level sensor 7.To explain each circuit and its operation with reference to this diagram, the level sensor 7 has a high voltage on both the p and n channel sources. CMOS inverters 71, 71...... with resistance
The stages are connected in series, and an ordinary CMOS inverter 72 with low output impedance is further connected in series as the final stage.

Note that 73 is a variome for adjusting the level of the detection signal of the solar cell 8, and if n is an odd number in this level sensor 7, the final stage CMOS inverter 7
A non-inverter circuit including 2 is configured. Therefore, when the surroundings are bright, a low level signal is output from the sensor 7, and when the surroundings are dark, a high level signal is outputted and input to the switching gate 6. In this level sensor 7, CMOS inverters 71, 71...
. . . are connected in series in multiple stages in order to reduce power consumption in the level sensor and to sharpen the transfer characteristic to perform level detection with excellent sensitivity.

The switching gate 6 includes a first CMOS inverter 61 for obtaining signals P and P from the output signal P of the level sensor 7, and two CMOS inverters for configuring a switching switch.
It is composed of MOS inverters 62 and 63, and turns the Q signal on and off depending on the signals P and 'p.

That is, when the output signal P of the level sensor 7 is at a high level (
(When the light input to the solar cell 8 is small), the terminals N2 and 0UT of the two CMOS inverters 62 and 63 that make up the changeover switch are conductive, whereas the terminals 1N1 and 0UT are cut off, and the diengel converter 5 is One input terminal is at ground potential and voltage V2 is output.

On the other hand, when the output signal P of the level sensor 7 is low level (
When the light power to solar cell 8 is large), terminals 1N1 and 0U
T is conductive, and on the other hand, terminals IN2 and 0UT are cut off, and one input terminal of the Schierken converter 5 is connected to Q.
Voltage V1 is output. If the level sensor 7 has an odd number of stages including the final stage CMOS inverter 72, the terminal 1N1 of the switching gate 6 is set to the ground potential, and the IN2 is set to the Q
If you connect it to , you will get the same result as above.

In this way, when the output of the Diengel converter 5 is switched to the voltages Vl and V2 depending on the level of ambient light, the voltage V
As mentioned above, between V2' and V2, there are V2'-V1/2 and V1.
〉Lth. Because of the relationship Vcth<V2<VL,h, when the voltage V1 is output, both the electronic circuit section and the liquid crystal display device 3 are driven, but when the voltage V2 is output, the electronic circuit section and the liquid crystal display device 3 are both driven. The LCD device 3 is driven, and the liquid crystal display device 3 is driven and controlled to stop displaying. As described above in detail with reference to the embodiments, in the device of the present invention, the voltage supplied to the electronic circuit section (for example, integrated into an LSI etc.) including the circuit that drives the liquid crystal display device is controlled by ambient light. This configuration controls the drive of the liquid crystal display by controlling the size of without changing the internal circuit of the LSI element.
It is a very useful device because it can perform one-drive control of a liquid crystal display using the current LS element as it is, reducing power consumption of electronic equipment and extending the operating life of the liquid crystal display device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an electronic wristwatch according to an embodiment of the present invention, and FIG. 2 is a partial circuit diagram of the block diagram shown in FIG. 1. 1... LSI element, 14... Liquid crystal display device drive circuit, 3... Liquid crystal display device, 5...
...DC-DC converter, 6...Switching gate, 7...Level sensor, 8...Solar cell.

Claims (1)

[Claims] 1. In a driving device for a liquid crystal display device including a CMOS circuit for display driving a liquid crystal display device, the operating voltage supplied to the CMOS circuit is set to a binary voltage of V_1 and V_2, and the binary voltage is set to V_1≧ V_Lth, V_Cth≦V
It is determined within the range of _2≦V_Lth (V_Lth is the lowest voltage necessary for display driving of the liquid crystal display device, V_Cth is the lowest voltage necessary for operation of the CMOS circuit), and V
A liquid crystal display device characterized in that the voltage supplied to the liquid crystal display device can be switched to a display drive voltage or less during the operation period of the CMOS circuit by providing a switching means for selectively supplying _1 and V_2. drive control device.