JPS6230109Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a memory erasing circuit, and in particular, to a device having a volatile memory, it erases data stored in the memory in the event of the device being stolen, etc. This invention relates to a memory erasing circuit intended to prevent others from knowing.

Conventional technology Volatile static RAM using CMOS technology
(hereinafter simply referred to as CMOSRAM) has extremely low power consumption and can maintain memory for a long time (in some cases, several years) by backing up with a small battery even if the main power of the device is cut off. is possible. Due to this characteristic, CMOSRAM has been
It is used for semi-permanent data storage in various electronic devices.

In such devices, strict confidentiality may be required for the data stored in the CMOSRAM, and in particular, a circuit that automatically and promptly erases the stored data even in a situation such as theft of the device is required. The need for

Conventionally, as this type of memory erasing circuit, a method has been devised in which a micro switch or the like is used to cut off the power supply current to the CMOS RAM through mechanical operations such as opening and closing the lid of the device.

Problems to be Solved by the Invention However, although the above method is very simple, it is difficult to miniaturize because it uses mechanical parts. Therefore, it is difficult to implement the microswitch in an ultra-small device, and furthermore, the location of the microswitch is easily discovered, and there is a possibility that a person seeking to illegally obtain data could easily find a preventive measure to erase the memory.

The present invention has been devised in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel memory erasing circuit capable of improving the above-mentioned drawbacks of the conventional system.

Means for Solving the Problems The memory erasing circuit according to the present invention differs from conventional systems in that it uses a photodetector such as a phototransistor or photodiode to detect that the lid of the device has been opened, and detects light from outside the device. The device is characterized in that the output of the photodetection means is used to drive the current cutoff means, cut off the power supply current supplied to the CMOSRAM from the power supply, and erase the stored data. .

Since the present invention uses all electronic means, it is easy to downsize and can be implemented in ultra-small devices. Furthermore, since the circuit is small and can be skillfully hidden within the device, the possibility that others will notice the existence of the circuit is reduced.

Embodiment of the invention Next, a preferred embodiment of the invention will be described in detail with reference to the drawings.

FIG. 1 is a general block diagram showing one embodiment of the present invention. When the light detection means 2 in the figure detects the light beam a1 from outside the device, the current cutoff means 3 is operated by the output v1, and the power supply current l1 supplied from the power supply 1 to the volatile memory 4 is The power is shut off and the data in the volatile memory 4 is erased.

Although various configuration methods are conceivable for the photodetection means 2 and the current interrupting means 3, FIG. 2 shows a specific example of the circuit configuration. A resistor 6, a transistor 7, and a diode 8 are used as the means 3, respectively.

In FIG. 2, when there is no external light beam a2, the phototransistor 5 is in the "OFF" state, and the base potential v2 of the transistor 7 is approximately equal to the output voltage v3 of the power supply 1 due to the resistor 6. Therefore, the transistor 7 is in the "ON" state, the power supply current l2 is supplied to the volatile memory 4, and the stored data is held. Conversely, when the external light beam a2 is incident, the phototransistor 5 enters the “ON” state, so the base potential v2 of the transistor 7
drops to almost ground potential. Therefore, the transistor 7 becomes "OFF", the power supply current l2 to the volatile memory 4 is cut off, and the stored data is erased. The diode 8 is inserted so that when the phototransistor 5 is turned on, the charges accumulated in the volatile memory 4 are quickly discharged, and the stored data can be erased in a short time.

Effects of the invention As described above, in the present invention, the memory erasing circuit is configured entirely using electronic means, so miniaturization is easy, and hybrid ICs can be used together with the memory.
It is also possible to implement it inside. Furthermore, by taking advantage of its small size, unlike conventional microswitches, it can be skillfully hidden within the device, reducing the possibility that others will notice the existence of this circuit.

[Brief explanation of the drawing]

FIG. 1 is a general block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example of a specific circuit configuration of the embodiment of the present invention shown in FIG. DESCRIPTION OF SYMBOLS 1... Power supply, 2... Light detection means, 3... Current interrupting means, 4... Volatile memory, 5... Phototransistor, 6... Resistor, 7... Transistor, 8
... Diode, a1, a2 ... Light beam from outside, v1 ... Output of photodetection means, v2 ... Base voltage of transistor 7, v3 ... Output voltage of power supply 1, l1, l2 ... Power supply current.

Claims (1)

[Scope of utility model registration request] A device having a volatile memory, comprising a light detection means for detecting external light, and a current interrupting means driven by the light detection means, wherein the light from outside the device is detected by the light detection means. The memory erasing circuit is characterized in that the current cutoff means cuts off the power supply current supplied to the volatile memory and erases the stored contents of the volatile memory.