JPH09127271A - Time indicator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an indicator to calculate the present time and automatically set it when power is turned on again even after the power supply is once cut off. SOLUTION: The system measures elapsed time by using the change of threshold value of memory elements such as EPROM element. More specifically, in accordance with notification from a power cut-off notification circuit 1 detecting and notifying the power cut-off, it executes to write in the memory element. Then, the elapsed time is calculated form the change in the threshold value in the memory element 4 during the period (period of power cut-off), the time at the moment is obtained from the time of the power cut-off stored in a time memory part 8 and the calculated elapsed time, and it is set in a clock 3.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a time display device.

[0002]

A time display device such as a clock usually has a constituent element that changes with the passage of time inside the device and reads the amount of change of this constituent element.
The elapsed time is displayed.

Those conventional time display devices are, for example,
Although there are exceptions such as water clocks and hourglasses, in general, components that change over time are used, and in order to make them function as intended, mechanical energy from a motor or electrical energy from a battery, etc. It is necessary to continue supplying some kind of energy such as.

Therefore, there is a problem that if the supply of energy is stopped midway, the correct time cannot be displayed even if the supply of energy is resumed thereafter.

According to the present invention, in the conventional time display device,
It is an object of the present invention to provide a time display device by a new method for solving the problem that the correct time cannot be displayed even if the energy is supplied again after the energy supply is stopped. .

[0006]

In order to solve the above problems, according to the present invention, by utilizing the deterioration characteristics of the memory element over time, even when the energy supply is cut off, the energy is re-supplied thereafter. Provided is a time display device capable of displaying the correct time by measuring the degree of memory deterioration during that time.

According to one aspect of the present invention, there is provided a timepiece device having a display device, a time storage means for storing the time of the timepiece device when the power is cut off, and a writing circuit and a reading circuit. An elapsed time storage element for storing the passage of time,
When the power is cut off, it is detected and the write-off circuit is notified, and the memory state of the memory element is read when the power is turned on again, and the current time is calculated based on the read contents. And a current time calculation circuit that supplies the time to the time storage means and sets the current time calculated by activating the timepiece device.

According to another aspect of the present invention, in the time display device, the elapsed time storage element has a deterioration characteristic over time of memory, and the current time calculation circuit calculates a current time based on the deterioration characteristic. There is provided a time display device configured to do so.

According to still another aspect of the present invention, in the time display device, the elapsed time storage element is an EPROM or an EEPROM semiconductor non-volatile storage element, and the time deterioration characteristic is a threshold change. provide.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the time display device of the present invention will be described below with reference to the accompanying drawings. FIG.
FIG. 3 shows an example of a time storage element used in an embodiment of the present invention, which is an EPROM semiconductor nonvolatile storage element.

The structure of this EPROM semiconductor nonvolatile memory element is, for example, in the case of an n-channel EPROM, as shown in the figure, an n + layer is formed on a p-type substrate 21 as shown in the figure, and a source electrode 22 and The drain electrode 23 is provided,
This is a normal structure in which a gate electrode is provided between the source and the drain. The gate electrode includes a control gate 27 and a floating gate 25, which are surrounded by an insulating film.

When an EPROM (erasable PROM) is used as an ordinary memory device, a control gate is connected to a word line and a drain is connected to a bit line. To write information to the EPROM cell, a high voltage is applied to the control gate 27 and the drain 23 and a current is passed through the cell.

A part of the electrons flowing in the cell is accelerated by a high electric field in the vicinity of the drain to obtain energy, and the energy exceeds the energy barrier of the gate insulating film.
Is injected into. Since the floating gate is not connected to other circuit parts, the charge can be stored here semipermanently.

Information is read from the cell as follows. That is, select a cell with a word line and a bit line,
Apply current. At this time, the threshold value of the cell transistor changes due to the electric charge stored in the floating gate, and therefore the current flowing through the selected cell changes according to the information. Therefore, the information is read out by detecting and amplifying this current. . To erase the contents of the cell, the cell is exposed to UV light.

In one embodiment of the present invention, this E
Since the PROM is used as a memory element and the conductive electrode 25 called a floating gate is surrounded by the first and second two gate insulating films 24 and 26 and is electrically insulated, Inject charge into it,
This is performed by changing the threshold value of the storage element.

When the charge is stored in this way, the charge injected into the floating gate will be over time due to the inability to completely insulate the floating gate. As a result, the threshold value also changes over time and the stored value is gradually lost, as shown in FIG.
Memory deterioration occurs.

Since the characteristic of this memory deterioration is not affected by the absence of energy supply from the outside, the threshold change of the cell due to this memory deterioration has good reproducibility. Therefore, the elapsed time can be known by reading the change in the threshold value at any time.

The principle of the present invention has been described above by taking the EPROM semiconductor nonvolatile memory element as an example. However, the deterioration characteristic over time of memory is basically present in all memory elements, and other memory elements also. With the same idea, the elapsed time can be measured.

FIG. 1 shows a system configuration diagram of the time display device of the present invention. According to this system configuration, even if the energy supplied from the outside such as the power source is cut off in the middle, the correct time can be displayed by restarting the energy supply.

EPROM will be used as a memory element in the following description.
A case where a semiconductor nonvolatile memory element is used will be described as an example.

In the normal use state, when the time display device is powered on, the conventional normal timepiece 3
, The time is displayed on the display device 7. When the power is cut off for some reason from this state, the power cutoff notification circuit 1 issues a notification signal to activate the EPROM element writing circuit 2 to write to the EPROM element 4.
That is, the threshold is set to a certain value.

At the same time, the time storage unit 8 receives the notification from the power cutoff notification circuit 1 and stores the current time at that time. After a lapse of time in this state, and thereafter, when the failure, battery replacement, or other cause is eliminated, the power is turned on again.

When the power source is turned on again, the read circuit 5 is set to EP
The threshold value of the ROM element 4 is read and sent to the current time calculation circuit 6. The current time calculation circuit compares the threshold value sent from the read circuit 5 with the threshold value at the time of the previous writing, calculates the elapsed time from the power-off time, and stores it in the time storage unit 8. The current time is calculated based on the time when the power is turned off.

The calculated time is sent to the normal timepiece 3 and the timepiece 3 is set to the current time. As a result, the correct time can be displayed even after the power is turned on again.

FIG. 3 shows the deterioration characteristics with time of the threshold voltage of the EPROM element. This characteristic is basically determined by the material and film thickness of the first and second gate insulating films of the EPROM element. FIG. 3 shows the deterioration characteristics over time of the two cases.

First, the material of the first gate insulating film is an oxide film, and the film thickness is 30 nm. The material of the second gate insulating film is an oxide film, and the film thickness is 30 nm or more, which is indicated by (a) in the figure.

Secondly, the material of the first gate insulating film is an oxide film having a film thickness of 10 nm, and the material of the second gate insulating film is an oxide film having a film thickness of 20 nm or more. , (B) in the figure.

In the first case, the value is 0.5 in 1000 days.
The deterioration characteristic of V is observed, and the elapsed time of several years can be measured. Further, in the second case, the value of 0.
A deterioration characteristic of 5 V is seen, and it is possible to measure the elapsed time on the order of several days.

[0029]

According to the time display device of the present invention, even if energy such as electrical energy is not supplied by shutting off the power, the elapsed time can be correctly measured when the power is turned on again.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an embodiment of a time display device of the invention.

FIG. 2 is an element schematic diagram showing an example of an elapsed time storage element applied to the present invention.

FIG. 3 is a characteristic diagram showing a change in threshold value with respect to elapsed time of an element.

[Explanation of symbols]

 1 Power-off notification circuit 2 EPROM element writing circuit 3 Normal type clock 4 EPROM element 5 EPROM element reading circuit 6 Time calculation circuit 7 Display device 8 Time storage unit

Claims (3)

[Claims] 1. A timepiece device provided with a display device, a time storage means for storing the time of the timepiece device when the power is cut off, and an elapsed time memory provided with a writing circuit and a reading circuit for storing the passage of time from the time of writing. The device, the power cutoff notification circuit that detects it when the power is turned off and notifies the writing circuit, and the storage state of the storage device when the power is turned on again, and reads the current time based on the read contents. And a current time calculation circuit which sets the current time calculated by supplying the time to the time storage means and starting the timepiece device. 2. The time display device according to claim 1, wherein the elapsed time storage element has a aging memory deterioration characteristic, and the current time calculation circuit calculates a current time based on the deterioration characteristic. Time display device. 3. The time display device according to claim 1, wherein the elapsed time storage element is an EPROM or EEPRO.
A time display device, which is an M semiconductor nonvolatile storage element, and whose memory deterioration characteristic over time is a threshold change.