JPH01292489A - High voltage input controller for melting fuse - Google Patents

Abstract

PURPOSE:To prevent a fuse from being carelessly disconnected by impressing a cutting voltage to an input terminal and impressing a supply voltage to a terminal of an IC card when an input pulse is impressed to the input terminal. CONSTITUTION:An IC card power supply voltage (VDD) impressed to a terminal 18 at the time of operation turns on FETs 32, 26 and turns off a switching transistor(TR). When the VDD does not exist and voltage VPP is high, an FET 22 is on, so that an FET 24 is turned on. The FET 24 holds the gate of the switching TR 12 again at a potential level close to the earth level, so that the TR 12 is turned off. When the voltages VPP, VDD and an input pulse exist, FETs 23, 25 are connected, so that the FETs 24, 26 are turned off. When the VPP exists, an FET 31 is turned on and a voltage almost equal to the VPP is impressed to the gate of the TR 12. Thereby, the TR 12 is turned on, the VPP is impressed to the fuse 10 and the fuse 10 is disconnected.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to devices having integrated circuits (in the present invention, r
It's called an IC card. 〉 is used to protect information. It is essential that cards of this type are provided with some form of protection to prevent unauthorized modification of the information stored on them. Thus, once information or programs are placed on the card, the fuse is cut, thereby preventing changes to or additions to the stored information or programs.

[Prior Art] In the conventional technology, a fuse is located in an IC card at a position where stored data can be written or changed only when the fuse is uncut. Once the desired data has been placed on the card, an external power source is connected to the fuse and disconnected.

A problem with this external fuse disconnection mechanism is that the fuse can be disconnected inadvertently and with data not properly stored on the card. Some cards include a small battery as a power source, which is necessary for the operation of the card's circuitry and memory. Other cards that do not have batteries are connected to an external power source while they are in use. If the power supply is not operational, information cannot be input and stored. However, in conventional fuse blowing circuits, the power supply is not part of the circuit. Therefore, an operator may enter data into a card with an inoperable power supply and then disconnect the fuse without checking to see if the power supply is operational.

- Once the fuse is disconnected, data cannot be loaded even if the inoperable power supply is replaced. Therefore, the card becomes nothing more than waste.

[Means for Solving the Problems] The present invention solves these problems by providing an IC card with a CMOS circuit. This circuit consists of a switching transistor that supplies fuse-cutting voltage to the fuse on the IC card, a field effect transistor (FET) coupled to the switching transistor, a fuse-cutting voltage source, a power supply for the IC card, and a fuse-cutting transistor. It is equipped with an input signal for The FET holds the switching transistor in the off position in the absence of IC card power even when the fuse blow voltage is applied. To blow a fuse, IC card power must be applied to the IC card, a fuse cutting voltage must be applied, and a fuse cutting input signal must be present.

The above advantages are obtained with the typical circuit shown in FIG.

This circuit has safety fuse 10. NPN field effect switching transistor 12, fuse cut voltage terminal 14
, a fuse cutting signal input terminal 16, an IC card power supply terminal 18, and a semiconductor switch control circuit 20. The circuit 20 consists of five NPs shown from 22 to 26.
It is equipped with an N-type FET and three PNP-type FETs shown from 30 to 32. It will, of course, be understood that the conductivity type of the switching transistors and various FETs can be varied. This change makes some minor modifications to the circuit, but does not change operation.

[Function] During operation, the IC card power supply voltage (V, o
) turns on FET 32 and FET 26, which holds the gate of switching transistor 12 near ground potential, thus turning off the switching transistor. Fuse cutting voltage applied to terminal 14■
PP, both high (20V) and O, has no effect.

If VDD is not present and vPP is high, FET 22 is on, which turns FET 24 on. FET
24 again holds the gate of switching transistor 12 near ground potential and switches transistor 1
2 is turned off.

vpp, VD[), and in the presence of an input pulse, F
ET23 and 25 are electrically connected, which causes FET24 and 2
6 is turned off. The presence of VPP turns on FET 31 and applies a voltage approximately VPP to the gate of switching transistor 12. Therefore, switching transistor 12 is turned on, causing fuse 10 to have VP
P is added, thereby cutting the fuse 10. F
ET22 is used merely to ensure circuit activation and may be removed for some non-critical applications.

Fuse 10 cannot be inadvertently blown, but if for some reason the circuit does not start properly, it will need to be tried again.

[Effects of the Invention] Thus, when the input pulse is applied to the input terminal 16, the cutting voltage is applied to the terminal 14, and the supply voltage is applied to the IC
Since it must be applied to the terminal 18 of the card, inadvertent cutting of the fuse 10 cannot occur. If all these voltages are not present, fuse 10 will not blow. Also, since the fuse 10 cannot be cut unless a supply voltage is present, cutting the fuse cannot cause the IC to become waste if it does not contain data or programs due to the lack of supply voltage. Since the CMOS circuit is contained in the IC card, virtually no extra space or manufacturing steps are required.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a CMOS fuse disconnection circuit for an IC card. FIG. 2 is a top plan view of the IC card safety fuse. 10... Safety fuse, 12... Switching transistor, 14... Fuse cutting voltage terminal, 16... Signal input terminal for fuse cutting, 18... I
C card voltage terminal. Patent applicant Motorola Japan Co., Ltd.

Claims (4)

[Claims] 1. A CMOS circuit that is used in connection with an IC card that has a power supply terminal for connecting a power supply voltage and that cuts a safety fuse includes: a safety fuse, a switching transistor coupled in series with the fuse, and a switching transistor and a fuse. a fuse blow voltage terminal coupled in series and adapted to receive the supplied fuse blow voltage; an input terminal adapted to receive the applied fuse blow signal pulse; and a switching transistor, a fuse blow voltage terminal. ,
Coupled with the power supply terminal, and the input terminal of the IC card, the switching transistor is turned off when voltage is supplied to the fuse-cutting voltage terminal, but not to the power supply terminal, and the voltage is supplied to the fuse-cutting voltage terminal, the power supply terminal, and A CMOS circuit comprising: a semiconductor circuit that turns on a switching transistor when supplied to an input terminal; 2. 2. A CMOS circuit according to claim 1, which is used in conjunction with an IC card to cut a safety fuse, wherein the circuit and the fuse are included in the IC card. 3. A CMOS circuit according to claim 1 for use in conjunction with an IC card to blow a safety fuse, wherein the switching transistor has its gate coupled to the semiconductor circuit and its source at a fuse cutting voltage. A CMOS circuit comprising a field effect transistor (FET) of a first conductivity type coupled to the terminal and having its drain coupled to one terminal of a safety fuse. 4. A CMOS circuit according to claim 3 for use in conjunction with an IC card to cut a safety fuse, the semiconductor circuit comprising four semiconductor circuits of a first conductivity type, each having a gate, a source, and a drain. FET and three FETs of the second conductivity type, the first FET among the four FETs has its gate coupled to the input terminal, its source coupled to the first connection point, and its A second of the four FETs has its drain coupled to the reference potential, its gate coupled to the first node, its source coupled to the gate of the switching transistor, and its drain coupled to the reference potential. The third FET of the four FETs is coupled to the potential.
has its gate coupled to the input terminal, its source coupled to the second node, and its drain coupled to the reference potential, and the fourth of the four FETs has its gate coupled to the second node.
, its source is coupled to the gate of the switching transistor, its drain is coupled to the reference potential, and the first of the three FETs has its gate coupled to the gate of the switching transistor. A second of the three FETs has its source coupled to the fuse breaker voltage terminal, its drain coupled to the first node, and a second FET with its gate coupled to the first node. , its source is coupled to the fuse-break voltage terminal, its drain is coupled to the gate of the switching transistor, and the third of the three FETs has its gate coupled to the input terminal and its source coupled to the power supply terminal. C coupled to the terminal, the drain of which is coupled to the second connection point.
MOS circuit.