JP4749160B2 - Integrated circuit - Google Patents

Description

  The present invention relates to a protected circuit that causes a malfunction when irradiated with light, and a photodiode connected in reverse bias to detect light that causes the malfunction of the protected circuit. And an integrated circuit configured to limit the operation of the protected circuit in accordance with the cathode potential of the photodiode.

Information stored in a semiconductor integrated circuit such as a memory card or an IC card or the operation of the semiconductor integrated circuit should be kept secret, but an unauthorized user of the semiconductor integrated circuit may give a physical disturbance to the semiconductor integrated circuit. There is a possibility that the semiconductor integrated circuit malfunctions, information stored in the semiconductor integrated circuit is acquired or falsified, or an operation algorithm of the semiconductor integrated circuit is analyzed to imitate or duplicate the semiconductor integrated circuit.
For example, an unauthorized user irradiates light to a semiconductor integrated circuit as a physical disturbance. When light is irradiated to a semiconductor integrated circuit, in particular, a PN junction portion of the semiconductor integrated circuit, a photoelectric reverse current is generated in the PN junction portion due to the photoelectric effect. When a sufficiently large photoreverse current is generated by light irradiation, the irradiated semiconductor integrated circuit malfunctions.

  In order to counter such illegal use, a photodetection circuit deceived by a specific circuit in the semiconductor integrated circuit, and a control for stopping the operation of the protected circuit included in the semiconductor integrated circuit according to the detection signal of the photodetection circuit A semiconductor integrated circuit including a circuit has been proposed (for example, Patent Document 1).

FIG. 8 is a circuit diagram of a semiconductor integrated circuit in Patent Document 1. In FIG.
The semiconductor integrated circuit includes a photodiode 1 connected with a reverse bias, and an inverter 91 connected to the cathode of the photodiode 1. The source of the MOS transistor 90 is connected to the cathode of the photodiode 1, and the drain of the MOS transistor 90 is connected to the power supply potential.

  In the semiconductor integrated circuit configured as described above, the inverter 91 outputs a ground potential when the photodiode 1 is not irradiated with light. When light is irradiated to the photodiode 1 and the cathode potential falls below a predetermined threshold potential, the inverter 91 outputs a light detection signal of the power supply potential. The control circuit stops the operation of the protected circuit in accordance with the output potential of the inverter 91.

FIG. 9 is a circuit diagram of a semiconductor integrated circuit according to another embodiment in Patent Document 1. In FIG.
The semiconductor integrated circuit includes a photodiode 1 connected in reverse bias and a detection circuit 92 connected to the cathode of the photodiode 1.

The detection circuit 92 outputs a ground potential when the photodiode 1 is not irradiated with light, and detects the power supply potential when the photodiode 1 is irradiated with light and the cathode potential falls below a predetermined threshold potential. Output a signal. The control circuit stops the operation of the protected circuit in accordance with the output potential of the detection circuit 92.
JP 2004-206680 A

  However, in the semiconductor integrated circuit according to Patent Document 1, when the photodiode 1 is irradiated with short pulse light having a pulse width of several ns, the detection signal output from the inverter 91 or the detection circuit 92 is also irradiated. Since the signal is an extremely short pulse signal similar to light, the control circuit may not operate normally, and the operation of the protected circuit may not be stopped.

  The present invention has been made in view of such circumstances, and one end is connected to the cathode of the photodiode, the other end is connected to the power supply potential side, and the Schmitt to which the photodiode cathode potential is input. By providing a comparison circuit such as a circuit and a control circuit that limits the operation of the protected circuit when the comparison circuit outputs a predetermined potential, the irradiated short-pulse light is transmitted to a conventional semiconductor integrated circuit. Integrated circuit capable of more reliably detecting and limiting the operation of the protected circuit and effectively preventing the acquisition or falsification of information stored in the integrated circuit, or imitation or duplication of the integrated circuit The purpose is to provide.

  Another object of the present invention is to provide a photodiode having a P-N + junction formed on a P-semiconductor substrate, so that the occupation area can be made smaller than that of a photodiode having a P + N- junction. Therefore, an object of the present invention is to provide an integrated circuit that can increase the degree of freedom of arrangement of the photodiodes and can detect the irradiated light more effectively.

  Another object of the present invention is to provide an integrated circuit that can detect the light emitted more effectively and limit the operation of the protected circuit by providing a plurality of photodiodes.

  Another object of the present invention is to provide an integrated circuit in which unnecessary power consumption can be suppressed by configuring the comparison circuit with a CMOS transistor.

  Another object of the present invention is to provide a first wiring arranged so as to cover a protected circuit, a second wiring branched at one end of the first wiring, and a circuit for supplying a periodic signal to one end of the first wiring. A phase comparison circuit that compares the phase of the signal that has reached the other end of the first wiring with the phase of the signal that has reached the other end of the second wiring, and outputs a potential according to the comparison result. By restricting the operation of the protected circuit according to the output potential, the integrated circuit is made invisible from the outside, and the operation of the protected circuit is limited when the first wiring is cut or short-circuited. Therefore, an object of the present invention is to provide an integrated circuit that can more effectively prevent unauthorized use of the integrated circuit.

Integrated circuit according to the present invention, when light is irradiated includes a circuit to be protected to malfunctions, in order to detect the light which malfunction 該被 protection circuit, and a photodiode connected in reverse bias, the In an integrated circuit configured to limit the operation of the protected circuit in accordance with the cathode potential of the photodiode, an electrical resistance having one end connected to the cathode of the photodiode and the other end connected to the power supply potential side And the input portion is connected to the cathode of the photodiode and one end of the electrical resistance, and has a first threshold potential and a second threshold potential higher than the first threshold potential, respectively, with respect to the cathode potential, If the cathode potential is lower than said first threshold potential, and outputs the Jo Tokoro potential, when the cathode potential increases exceeds said second threshold potential, the output of the predetermined potential A Schmitt circuit for stopping, when the Schmitt circuits outputs a predetermined potential, characterized in that it comprises a control circuit for limiting the operation of the circuit to be protected.

In the present invention, the photodiode is connected in reverse bias, and one end of the electrical resistance is connected to the cathode of the photodiode, and the other end of the electrical resistance is connected to the power supply potential side. When no light is irradiated to the photodiode, no reverse photocurrent flows through the photodiode, and the cathode potential of the photodiode becomes the power supply potential. The Schmitt circuit does not output a predetermined potential when the cathode potential is higher than the first and second threshold potentials. Therefore, the control circuit does not limit the operation of the protected circuit.
When the photodiode is irradiated with light, a reverse photocurrent flows through the photodiode, and the cathode potential of the photodiode drops. Since the Schmitt circuit has the first threshold potential with respect to the decreasing cathode potential, when the cathode potential becomes lower than the first threshold potential, the Schmitt circuit outputs a predetermined potential, and the control circuit Limit the operation of the protection circuit.
When the operation of the protected circuit is restricted, there is no possibility of malfunction due to light irradiation.
Since the electrical resistance is connected in series to the cathode of the photodiode, the cathode potential gradually rises according to the electrical resistance and stray capacitance when light irradiation stops. Since the Schmitt circuit has a second threshold potential higher than the first threshold potential with respect to the rising cathode potential, the Schmitt circuit outputs a predetermined potential until the cathode potential becomes equal to or higher than the first and second threshold potentials.
Therefore, as the difference between the second threshold potential and the first threshold potential is larger, the Schmitt circuit outputs a predetermined potential for a longer time than the light irradiation time, and the control circuit outputs the light irradiation time. Even in a short case, the operation of the protected circuit can be more reliably restricted.
In addition, the lower the first threshold potential, the lower the possibility that the Schmitt circuit outputs a predetermined potential with respect to the input noise potential, and the lower the possibility that the control circuit will erroneously limit the operation of the protected circuit.

  The integrated circuit according to the present invention is characterized in that the photodiode has a PN + junction formed on a P− semiconductor substrate.

  In the present invention, since the photodiode has a PN + junction formed on a P− semiconductor substrate, the photodiode can be made smaller than a photodiode having a P + N− junction. Therefore, the degree of freedom of arrangement of the photodiode for detecting light is high. By arranging a large number of photodiodes at appropriate locations for protecting the protected circuit, it is possible to detect more effectively irradiated light and limit the operation of the protected circuit.

  An integrated circuit according to the present invention includes a plurality of the photodiodes.

  In the present invention, since a plurality of photodiodes for detecting light are provided, it is possible to detect the irradiated light more effectively and limit the operation of the protected circuit.

The integrated circuit according to the present invention is characterized in that the Schmitt circuit is composed of a CMOS transistor.

In the present invention, since the Schmitt circuit is composed of CMOS transistors, when light is not irradiated, the power consumed by the circuit that detects the light irradiation is the CMOS transistor and the photo diode that configure the Schmitt circuit. Only the power consumption due to the diffusion leakage current in the diode.

  An integrated circuit according to the present invention includes a first wiring arranged so as to cover the protected circuit, a second wiring branched on one end side of the first wiring, and a periodic connection on one end side of the first wiring. The circuit that gives the signal is compared with the phase of the signal that has reached the other end of the first wiring and the signal that has reached the other end of the second wiring, and a potential corresponding to the comparison result is output to the control circuit. And a phase comparator circuit, wherein the control circuit limits the operation of the protected circuit in accordance with the potential output from the phase comparator circuit.

In the present invention, since the first wiring is arranged so as to cover the protected circuit, the protected circuit cannot be visually recognized from the outside.
Further, when a periodic signal is given to one end of the first wiring, the signal reaches the other end of the first and second wirings with a predetermined time difference, so that each signal has a predetermined phase difference. Occurs. When the first wiring is short-circuited or disconnected, the phase difference of each signal changes. The phase comparison circuit detects the change in the phase difference by comparing the phases of the signals, and outputs a potential corresponding to the comparison result to the control circuit.
The control circuit can detect that the first wiring is short-circuited or disconnected in accordance with the potential given by the phase comparison circuit, and can limit the operation of the protected circuit in accordance with the potential. That is, when the first wiring is short-circuited or disconnected, the operation of the protected circuit is limited.

In the present invention, the irradiated short pulse light can be detected more reliably than the conventional semiconductor integrated circuit, and the operation of the protected circuit can be limited and stored in the integrated circuit. Acquisition or alteration of information, or imitation or duplication of a body integrated circuit can be effectively prevented.
In addition, by setting the first threshold potential sufficiently lower than the power supply potential, the Schmitt circuit does not output a predetermined potential even if a noise potential is input to the Schmitt circuit, and the protected circuit is erroneously detected. It is possible to prevent the operation from being restricted.

  In the present invention, since the occupation area can be made smaller than that of a photodiode having a P + N− junction, the degree of freedom of arrangement of the photodiode can be increased, and light irradiation can be performed more effectively. Can be detected.

  In the present invention, by providing a plurality of photodiodes, it is possible to more effectively detect the irradiated light and limit the operation of the protected circuit.

In the present invention, unnecessary power consumption in the Schmitt circuit that is irrelevant to the operation of the protected circuit can be suppressed.

  In the present invention, the first wiring makes the integrated circuit invisible from the outside, and when the first wiring is cut or short-circuited, that is, for irradiating light to a portion where the photodiode is not arranged, When the first wiring is processed, the operation of the protected circuit can be limited, and unauthorized use of the integrated circuit can be more effectively prevented.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(Embodiment 1)
1 is a circuit diagram of a semiconductor integrated circuit according to an embodiment of the present invention, FIG. 2 is a schematic side sectional view of the semiconductor integrated circuit, and FIG. 3 is a circuit layout diagram of the semiconductor integrated circuit.
In the figure, reference numeral 1 denotes a first photodiode connected in reverse bias. The first photodiode 1 is a P− type semiconductor in which low concentration holes are injected into a P− wafer substrate 10 and high concentration carriers are injected. It is configured by an N + type semiconductor PN junction. The PN junction of the first photodiode 1 is disposed between the Nch transistor 7a and the Pch transistor 7b that constitute the first protected circuit 7 to be protected.
The first protected circuit 7 may malfunction when irradiated with light, and information stored in the first protected circuit 7 may be acquired or altered, or imitated or duplicated by analysis of an operation algorithm. Circuit.

  The anode of the first photodiode 1 is grounded, and one end of the first electric resistor 3 is connected to the cathode of the first photodiode 1, that is, the N + type semiconductor, through the first node 4 of the metal wiring. . The first electrical resistor 3 is made of polysilicon, and the other end of the first electrical resistor 3 is connected to the power supply potential Vcc.

  The first node 4 is connected to an input portion of the first Schmitt circuit 2 having hysteresis characteristics, and an output portion of the first Schmitt circuit 2 is connected to the control circuit 6.

The first Schmitt circuit 2 has a first threshold potential Vtl with respect to the potential at which the first node 4 drops, that is, the cathode potential Vin at which the first photodiode 1 falls, and with respect to the potential at which the cathode potential Vin increases. Thus, it has a second threshold potential Vth. The second threshold potential Vth is higher than the first threshold potential Vtl and lower than the power supply potential Vcc.
When the falling cathode potential Vin is equal to or higher than the first threshold potential Vtl, the first Schmitt circuit 2 outputs a high-level photodetection signal Vout having the power supply potential Vcc, and the falling cathode potential Vin is the first threshold potential Vtl. When lower, it is configured to output a low-level photodetection signal Vout having a ground potential. Further, when the rising cathode potential Vin is equal to or higher than the second threshold potential Vth, the first threshold potential Vtl outputs a high-level photodetection signal Vout, and the rising cathode potential Vin is lower than the second threshold potential Vth. The low-level photodetection signal Vout is output.

  The control circuit 6 controls the operation of the first protected circuit 7 and stops the operation of the first protected circuit 7 when the low-level photodetection signal Vout output from the first Schmitt circuit 2 is input. A reset processing circuit that performs processing for changing the first protected circuit 7 to a reset state.

  A metal shielding film pattern 5 that shields various circuits from the outside is formed on the upper layer of the first electric resistance 3, the first node 4, the first Schmitt circuit 2, etc., and on the upper layer of the metal shielding film pattern 5, A passivation film (not shown) is formed.

The wafer substrate 10 constituting the semiconductor integrated circuit is substantially square as shown in FIG. 3, and the first protected circuit 7, the first photodiode 1, and the first electric resistance 3 are provided on one side of the wafer substrate 10. Are arranged in order from one vertex side to the other vertex side.
Further, a second protected circuit 17 which is another protection target is disposed at a location apart from the first protected circuit 7 of the wafer substrate 10. A second photodiode 11 having a PN + junction similar to that of the first photodiode 1 is disposed around and inside the second protected circuit 17. The anode of the second photodiode 11 is The cathode is connected to the first node 4 while being grounded.

  In addition, a third photodiode 101 having a PN + junction is disposed around the wafer substrate 10. As with the first photodiode 1, the anode of the third photodiode 101 is grounded, and one end of the second electrical resistor 103 is connected to the cathode of the third photodiode 101 via the second node 104. Has been. The other end of the second electric resistor 103 is connected to the power supply potential Vcc. The second node 104 is connected to the input part of the second Schmitt circuit 102 similar to the first Schmitt circuit 2. The second Schmitt circuit 102 is configured to provide the control circuit 6 with a light detection signal Vout corresponding to the cathode potential Vin of the third photodiode 101.

FIG. 4 is a circuit diagram showing a configuration of the first Schmitt circuit 2.
The first Schmitt circuit 2 includes a first inverter 20, and a first node 4 is connected to an input portion of the first inverter 20. The output part of the first inverter 20 is connected to one input part of the first NAND circuit 21, and the output part of the first NAND circuit 21 is connected to one input part of the second NAND circuit 22. The output part of the second NAND circuit 22 is connected to the other input part of the first NAND circuit 21 and the input part of the second inverter 23. The other input part of the second NAND circuit 22 is connected to the first node 4. The output part of the second inverter 23 is connected to the control circuit 6.
The first threshold potential is adjusted by adjusting the W / L size of the Nch transistor and the W / L size of the Pch transistor constituting the first and second inverters 20 and 23 and the first and second NAND circuits 21 and 22. A first Schmitt circuit 2 having Vtl and a second threshold potential Vth is configured.
The second Schmitt circuit 102 is configured in the same manner as the first Schmitt circuit 2.

FIG. 5 is a schematic diagram showing the metal shielding film pattern 5.
The metal shielding film pattern 5 is branched on one end side of the first wiring 5a and the first wiring 5a arranged to cover various circuits such as the first protected circuit 7 and the second protected circuit 17, The second wiring 5b is arranged at a different location from the first wiring 5a. A signal output circuit 81 is connected to one end of the first wiring 5a. As shown in FIG. 2, the first wiring 5a is exposed to the outside of the first photodiode 1 and forms a hole having an area necessary for the first photodiode 1 to receive light. Similarly, the first wiring 5 a forms a hole for exposing the second photodiode 11 and the third photodiode 101.

  The signal output circuit 81 is a circuit that outputs a periodic signal, for example, a sine wave AC potential, to one end of the first wiring 5a in order to detect cutting or short-circuiting of the metal shielding film pattern 5.

The other end of the first wiring 5a and the other end of the second wiring 5b are connected to the input section of the phase comparison circuit 82, respectively. The phase comparison circuit 82 compares the phase of the signal reaching the other end of the first wiring 5a with the phase of the signal reaching the other end of the second wiring 5b, and supplies a potential according to the comparison result to the control circuit 6. Output.
The control circuit 6 is configured to limit the operations of the first protected circuit 7 and the second protected circuit 17 in accordance with the potential output from the phase comparison circuit 82.

The operation and effect of the semiconductor integrated circuit configured as described above will be described.
FIG. 6 is a timing chart showing changes in the cathode potential Vin of the first photodiode 1 irradiated with light and the potential of the light detection signal Vout.
When the first photodiode 1 is irradiated with a short pulse light of a predetermined light amount or more from time t1a to t2a, a reverse photocurrent flows through the first photodiode 1 as shown in FIG. The cathode potential Vin of the first photodiode 1 drops. When the decreasing cathode potential Vin becomes equal to or lower than the first threshold potential Vtl at time t1b, the first Schmitt circuit 2 outputs a low-level photodetection signal Vout, as shown in FIG. 6B.

  When the irradiation of light stops after the time t2a has elapsed, the reverse photocurrent does not flow through the first photodiode 1, and the cathode potential Vin is determined according to the resistance value and the stray capacitance value of the first electric resistance 3. Will gradually rise according to the charging curve. When the rising cathode potential Vin becomes equal to or higher than the second threshold potential Vth at time t2b, the first Schmitt circuit 2 outputs a high-level photodetection signal Vout.

  Note that when the amount of light applied to the first photodiode 1 is small, a sufficient reverse photocurrent does not flow, and the cathode potential Vin falls to the first threshold potential Vtl or lower as shown by the broken line in FIG. The first Schmitt circuit 2 does not output the low-level photodetection signal Vout.

  In the semiconductor integrated circuit configured as described above, the larger the difference between the first threshold potential Vtl and the second threshold potential Vth, the longer the irradiation time of the irradiated short pulse light (t2a-t1a). Since the low-level photodetection signal Vout is output to the control circuit 6 for the time (t2b-t1b), the control circuit 6 can more reliably detect the light irradiation and is stored in the semiconductor integrated circuit. It is possible to effectively prevent acquisition or alteration of information, or imitation or duplication of a semiconductor integrated circuit.

  Further, by setting the first threshold potential Vtl sufficiently lower than the power supply potential Vcc, when the noise potential is input to the first and second Schmitt circuits 2 and 102, the first and second Schmitt circuits 2 and 102 are used. Outputs a low-level photodetection signal Vout to the control circuit 6, thereby preventing a malfunction in which the control circuit 6 stops the operation of the first and second protected circuits 7 and 17.

  Furthermore, since the first to third photodiodes 1, 11, 101 can be configured to have a smaller occupied area than the photodiode having the P + N− junction, the first to third photodiodes 1, 11, 101 can be configured. The degree of freedom of arrangement can be increased, and light irradiation can be detected more effectively.

  Furthermore, by providing a plurality of first to third photodiodes 1, 11, 101, it is possible to more effectively detect the irradiated light and limit the operation of the first and second protected circuits 7, 17. can do.

  Furthermore, since the first and second Schmitt circuits 2 and 102 are composed of CMOS transistors, the first and second Schmitt circuits 2 and 102 which are not related to the operation of the first and second protected circuits 7 and 17 are unnecessary. Power consumption can be reduced.

  Furthermore, since the first protected circuit 7 and the second protected circuit 17 are covered with the first wiring 5a of the metal shielding film pattern 5, even when the passivation film of the semiconductor integrated circuit is removed. The first protected circuit 7 and the second protected circuit 17 can be made invisible.

  Furthermore, in order for an unauthorized user to visually recognize the first and second protected circuits 7 and 17 or to irradiate light other than the first to third photodiodes 1, 11 and 101, the first wiring 5 a Is processed, the phase difference between the signals reaching the other ends of the first wiring 5a and the second wiring 5b changes, and the potential applied to the control circuit 6 by the phase comparison circuit 82 changes. Then, when the phase difference changes, for example, in accordance with the potential output from the phase comparison circuit 82, the control circuit 6 restricts the operation of the first and second protected circuits 7, 17 in order to limit the first wiring 5 a. Unauthorized use of the semiconductor integrated circuit due to processing can be prevented more effectively.

(Embodiment 2)
FIG. 7 is a circuit layout diagram of a portion constituting the semiconductor integrated circuit according to the second embodiment.
Since the semiconductor integrated circuit according to the second embodiment is different from the semiconductor integrated circuit according to the first embodiment only in the configuration of the photodiode, the difference will be mainly described below.

  The semiconductor integrated circuit according to Embodiment 2 is provided in parallel with the first protected circuit 207, and includes a first photodiode 201 and a second photodiode 211 connected with reverse bias. The first photodiode 201 has a P + N− junction, and the second photodiode 211 has a P−N + junction. The anodes of the first photodiode 201 and the second photodiode 211 are grounded, and the cathodes are connected to the first node 204.

  Since the photoelectromotive force generated when light is irradiated is higher when the impurity concentration in the semiconductor is lower, the first photodiode 201 detects the irradiated light with higher sensitivity than the second photodiode 211. Can do.

However, as shown in FIG. 7, the interval (d _{p + n−} + d _n− ) necessary for element separation between the first photodiode 201 having the P + N− junction and the first protected circuit 207 is P−N +. The second photodiode 211 is smaller than the first photodiode 201 because it is longer than the interval (d _{n +} ) necessary for element isolation between the first photodiode 201 having a junction and the first protected circuit 207. Can be configured. Therefore, the second photodiode 211 has a higher degree of freedom in arrangement. For example, the second photodiode 211 can be arranged at a higher density than the first photodiode 201 at an appropriate location for protecting the first protected circuit 207.

  In the semiconductor integrated circuit according to the second embodiment, when the first photodiode 201 is arranged at a place where the arrangement space is large and the second photodiode 211 is arranged at a place where the arrangement space is small, Light irradiation can be reliably detected, and acquisition or falsification of information stored in the semiconductor integrated circuit, or imitation or duplication of the semiconductor integrated circuit can be effectively prevented.

1 is a circuit diagram of a semiconductor integrated circuit according to an embodiment of the present invention. 1 is a schematic side sectional view of a semiconductor integrated circuit. 1 is a circuit layout diagram of a semiconductor integrated circuit. It is a circuit diagram which shows the structure of a 1st Schmitt circuit. It is a schematic diagram which shows a metal shielding film pattern. 6 is a timing chart showing changes in the cathode potential of the first photodiode irradiated with light and the potential of the light detection signal. FIG. 6 is a circuit layout diagram of a part constituting a semiconductor integrated circuit according to a second embodiment. 2 is a circuit diagram of a semiconductor integrated circuit in Patent Document 1. FIG. FIG. 10 is a circuit diagram of a semiconductor integrated circuit according to another embodiment in Patent Document 1.

Explanation of symbols

1,201 First photodiode 2 First Schmitt circuit 3 First electric resistance 4 First node 5 Metal shielding film pattern 5a First wiring 5b Second wiring 6 Control circuit 7 First protected circuit 10 Wafer substrate 11 Second photo Diode 17 Second protected circuit 81 Signal output circuit 82 Phase comparison circuit 101 Third photodiode 102 Second Schmitt circuit 103 Second electric resistance 104 Second node Vtl First threshold potential Vth Second threshold potential

Claims (5)

When light is irradiated, and the protection circuit malfunction, in order to detect the light which malfunction 該被 protection circuit, and a connected photodiode in the reverse bias, in accordance with the cathode potential of the photodiode In an integrated circuit that limits the operation of the protected circuit,
One end is connected to the cathode of the photodiode, the other end is connected to the power supply potential side, an electrical resistance;
An input portion is connected to the cathode of the photodiode and one end of the electric resistance, and has a first threshold potential and a second threshold potential higher than the first threshold potential with respect to the cathode potential, respectively, and a falling cathode If the potential is lower than said first threshold potential, and outputs the Jo Tokoro potential, when the cathode potential increases exceeds said second threshold potential, and Schmitt circuit stops outputting the predetermined potential,
An integrated circuit comprising: a control circuit that restricts the operation of the protected circuit when the Schmitt circuit outputs a predetermined potential. The photodiode is
The integrated circuit according to claim 1, further comprising a PN + junction formed on a P− semiconductor substrate. The integrated circuit according to claim 1, comprising a plurality of the photodiodes. The integrated circuit according to any one of claims 1 to 3, wherein the Schmitt circuit is configured by a CMOS transistor. A first wiring arranged to cover the protected circuit;
A second wiring branched on one end side of the first wiring;
A circuit for applying a periodic signal to one end of the first wiring;
A phase comparison circuit that compares the phase of the signal reaching the other end side of the first wiring and the phase of the signal reaching the other end side of the second wiring and outputs a potential corresponding to the comparison result to the control circuit. ,
The control circuit includes:
The integrated circuit according to claim 1, wherein an operation of the protected circuit is limited according to a potential output from the phase comparison circuit.

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