Electronic digital logic circuitry – Interface – Current driving
Reexamination Certificate
2000-03-27
2001-10-09
Tokar, Michael (Department: 2819)
Electronic digital logic circuitry
Interface
Current driving
C326S088000, C326S092000
Reexamination Certificate
active
06300797
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device with a power supply circuit mounted thereon, and a liquid crystal device and electronic equipment using the semiconductor device. Particularly, the present invention relates to a technique for the prevention of malfunctions which may occur in the case of power supply emergencies, such as in the case where a battery is taken out.
2. Description of the Related Art
In a liquid crystal device such as a liquid crystal display, a display operation is implemented when a voltage is applied to liquid crystals which are sealed between substrates in which electrodes are formed. This type of liquid crystal display has been widely used in recent years in various electronic equipment such as personal computers, word processors, cellular phones, electronic pocketbooks, and the like.
Such electronic equipment using a liquid crystal display is designed so that the screen becomes blank instantaneously when the power source is cut off according to a prescribed sequence. The phenomenon of instantaneous lighting occurs when the display is turned off by a procedure other than the above-described sequence, such as the case in which the battery is abruptly drawn out during the display operation, or the electronic equipment is forcedly terninated. Specifically, in this phenomenon the screen image instantaneously disappears when the battery is drawn out during display, following which lighting images such as horizontal lines appear for a while.
The present inventors have conducted extensive studies concerning the instantaneous lighting phenomenon and have achieved the present invention.
SUMMARY OF THE INVENTION
Accordingly, an objective of the present invention is to provide a semiconductor device with a power supply circuit mounted thereon, which can prevent malfunctions such as instantaneous lighting which occurs at the time of power supply emergencies, and a liquid crystal device and electronic equipment using the semiconductor device.
In one aspect of the present invention, a semiconductor device including a drive circuit, a drive control circuit which controls the drive circuit, and a power supply circuit which supplies a potential to the drive circuit and drive control circuit,
wherein the power supply circuit comprises:
a boosting circuit, to which a first power supply potential which is a ground potential from an external power supply and a second power supply potential which is a potential other than the ground potential are supplied, and raising the absolute value of the second power supply potential and charging the boosted potential to the capacitor; and
a bias generating circuit generating a potential supplied to the drive circuit and the drive control circuit based on the output potential of the boosting circuit, and
wherein the first power supply potential and a potential from the bias generating circuit are supplied to the drive circuit that outputs a potential selected from potentials supplied in accordance with a control of the drive control circuit during a normal power supply period, and, in the event of a power supply emergency in which an absolute value between the first and the second power supply potentials is lower than a given value, changes all potentials outputted from the drive circuit into the first power supply potential based on the signal activated in the event of the power supply emergency.
When a battery is drawn out and a power supply is forcibly cut off, for example, the first potential and the second potential which are supplied from external power supply sources become equal, e.g. the same potential as the ground potential, after a certain period of time.
Malfunctions such as instantaneous lighting occur because the time period required for the charge to be stored up to the capacitor of the boosting circuit after the forced cutoff of the power supply is longer than the period of time for the first and the second potentials to become equivalent.
In this instance, a potential equivalent to that discharged after cutoff of the power supply is supplied to the drive circuit and drive control circuit which receive a supply of potential from the power supply circuit including this boosting circuit. Malfunctions are caused by such a potential.
Therefore, in the event of a power supply emergency in which the absolute value between the first and the second power supply potentials is lower than a specified value, the drive circuit changes all potentials outputted from the drive circuit to a value equivalent to the first power supply potential (the ground potential) based on-the signals which becomes active when a power supply emergency occurs. This causes all devices which are operated by a potential supplied by the semiconductor device to be completely shutoff without malfunction.
In another aspect of the present invention, a semiconductor device including a drive circuit, a drive control circuit which controls the drive circuit, and a power supply circuit which supplies a potential to the drive circuit and drive control circuit,
wherein the power supply circuit comprises:
a boosting circuit, to which a first power supply potential which is a ground potential from an external power supply and a second power supply potential which is a potential other than the ground potential are supplied, and raising the absolute value of the second power supply potential and charging the boosted potential to the capacitor; and
a bias generating circuit generating a potential supplied to the drive circuit and the drive control circuit based on the output potential of the boosting circuit,
wherein the first power supply potential and a potential from the bias generating circuit are supplied to the drive circuit that outputs a potential selected from potentials supplied in accordance with a control of the drive control circuit, and
wherein in the event of a power supply emergency in which an absolute value between the first and the second power supply potentials is lower than a specified value, the drive control circuit outputs a potential selecting signal that changes all potentials outputted from the drive circuit into the first power supply potential based on the signal activated when the power supply emergency occurs.
In this aspect of the present invention, the operation of the drive circuit in the first-mentioned aspect in the event of a power supply emergency is performed based on the potential selection signals from the drive control circuit.
The drive control circuit preferably comprises:
a logic circuit to which the first and the second power supply potentials are supplied, and outputting various logic levels;
a level shifter group to which a potential from the power supply circuit and the first power supply potential are supplied, including a plurality of level shifters for shifting the logic levels from the logic circuit; and
a potential selection circuit for outputting potential selection signals supplied to the drive circuit based on the output from the level shifter group.
This constitution of the drive control circuit ensures that both the first and the second logic levels from the logic circuit after a battery is drawn out become the same ground potential as each other. In this instance, although the output from the level shifter group may become indefinite, this can be controlled as described above, whereby occurrence of malfunctions can be prevented.
Preferably, the level shifter group has an input level setting circuit for setting the input to the level shifters at a specified value based on the signals which become active in the event of a power supply emergency regardless of the output of the logic circuit.
In this manner, indefinite output of the level shifter group can be prevented by setting the input to the level shifters at a specified value in the event of a power supply emergency. Malfunctions can then be prevented by controlling the device in the Nanner described above based on the specified value inputted to the level shifter group.
Preferably, the pote
Oliff & Berridg,e PLC
Seiko Epson Corporation
Tokar Michael
Tran Anh
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