Electronic devices and low-voltage detection method

Details Electronic devices and low-voltage detection method Electronic devices and low-voltage detection method

1999-11-19

2001-05-08

Fears, Terrell W. (Department: 2824)

Static information storage and retrieval

Powering

Data preservation

C365S189070, C365S207000

Reexamination Certificate

active

06229751

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic devices equipped with electronic circuits that are driven by power supply means such as a battery, and a low-voltage detection method for detecting low voltage.
2. Description of Related Art
Portable electronic devices are well known. Many of these portable electronic devices are battery driven and driven by a primary or secondary battery. Some examples of these kinds of electronic devices are, portable game devices, portable audio devices and cellular telephones.
There are some battery driven electronic devices that have a mechanism for monitoring, displaying the amount of remaining charge of the battery. In these kinds battery such as electronic devices, there is a low-voltage detection circuit for monitoring the power-supply voltage supplied to the internal circuits.
FIG. 1
is a block diagram showing the configuration of a conventional low-voltage detection circuit. As shown in
FIG. 1
, the low-voltage detection circuit
101
is equipped with a BGR circuit
102
and a comparator
103
.
The BGR circuit
102
is a constant-voltage output circuit called the “Band Gap Reference.” The BGR circuit
102
outputs a predetermined absolute reference voltage Vref.
The comparator
103
compares the reference voltage Vref and the actual power-supply voltage Vlevel, and when the power-supply voltage Vlevel drops below the reference voltage Vref, it outputs a low-voltage detection signal Vdd_Low. The system uses this Vdd_Low signal as a trigger to perform necessary processing such as displaying “Battery End” or to save data for the application being executed.
However, there is error in the accuracy of the reference voltage output by the BGR circuit
102
and the threshold voltage of the comparator
103
. Since electronic devices are designed for the worst-case condition which takes this error into consideration, “Battery End” is sometimes displayed for batteries that may still be used.
Moreover, the reference voltage Vref is generally determined to correspond to the lowest operable voltage for the internal circuits, however, the actual lowest operable voltage of the elements of the internal circuits, such as the semiconductors or the like, may vary depending on the manufacturing process or operating conditions. Therefore, depending on the variation of elements and operating conditions, “Battery End” was sometimes displayed for batteries that may still be used.
In other words, in conventional electronic devices, the effective battery capacity is not always completely used.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an electronic device and low-voltage detection method which makes it possible to use battery capacity effectively.
The electronic device according to the present invention comprises an electronic circuit which is driven by a drive voltage supplied from a power-supply unit, a memory unit which is driven by the drive voltage, a comparison unit which writes data to the memory unit, after which it reads the data that have been written and compares the written data with the read data, and a judgment unit which judges whether or not the electronic circuit is operating properly based on the comparison results of the comparison unit.
The low-voltage detection method according to the present invention monitors the drive voltage that is supplied to an electronic circuit of an electronic device, comprises a comparison step wherein data are written to the memory unit that is driven by the drive voltage, thereafter the data that have been written are read and the written data are then compared with the read data, and includes a judgment step wherein the value of the drive voltage is judged based on the comparison results as to whether or not it has dropped below the minimum operable voltage value for the electronic circuit.
A second electronic device according to the present invention comprises a memory that is driven by voltage supplied from a battery, and a CPU that is driven by the voltage. The CPU performs a write test for the memory, and based on the results of this write test, judges whether or not the voltage has dropped below the minimum operable voltage.
Moreover, a second low-voltage detection method according to the present invention is a low-voltage detection method which monitors the voltage supplied to the electronic device, and it comprises a step that performs a write test for the memory that is driven by the voltage, and a judgment step that judges, based on the results of the write test, whether or not the voltage has dropped below the minimum operable voltage.


REFERENCES:
patent: 4327422 (1982-04-01), Imazeki et al.
patent: 4399524 (1983-08-01), Maguruma et al.
patent: 4422163 (1983-12-01), Oldenkamp
patent: 4631724 (1986-12-01), Shimizu

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