HIGH VOLTAGE DETECTING CIRCUIT

Abstract: A high voltage detecting circuit included in a semiconductor device has a terminal (2) for generating a control signal to start a specific operating mode of the semiconductor device when a potential of a specific mode signal higher by a predetermined value than a normal input voltage having a predetermined range is applied to the terminals (2). The high voltage detecting circuit includes level shift means (4) connected between a blocking transistor (Q3) and a discrimination circuit (5) to lower the potential of the output end by a level shifted value from the potential of the input end. The level shift means (4) prevents the high voltage detecting circuit generating a control signal in error even if the semiconductor device is switched ON and a power line potential (Vcc) of the device is gradually increased while a normal mode signal of the normal input voltage is continuously applied to its terminal (2).

Description: The present invention relates to a high voltage detecting circuit, and in particular, to a high voltage detecting circuit included in a semiconductor device having terminals, for generating a control signal to start a specific operating mode of the semiconductor device, when the potential of a specific mode signal higher by a predetermined value than a normal input voltage having a predetermined range, is applied to at least one of the terminals of the semiconductor device. In general, a high voltage detecting circuit is included in a semiconductor device for detecting a potential of a terminal of the semiconductor device. When the potential of the terminal of the device is higher by a predetermined value than a normal input voltage having a predetermined range, the high voltage detecting circuit generates a control signal for starting a specific mode of the semiconductor device. Upon receiving the control signal, the semiconductor device changes to the specific mode, e.g., a testing mode. Such a high voltage detecting circuit is disclosed in, for example, JP-A-60-124124 and comprises a first power supply means for a high potential; a second power supply means for a low potential; a blocking transistor, having a control electrode and two other electrodes, the control electrode being coupled to the first power supply means and, one of the two other electrodes being connected to the at least one of the terminals, the blocking transistor switching ON when the potential of the control electrode is higher by the threshold voltage of the blocking transistor than the potential of the one of the two other electrodes; and a discrimination circuit, having a first end and a second end, the first end of the discrimination circuit being coupled to the other of the two other electrodes of the blocking transistor for outputting the control signal from the second end of the discrimination circuit when the potential of the first end of the discrimination circuit is higher than a threshold voltage of the discrimination circuit by virtue of the blocking transistor being turned ON. When a potential of a power line (hereinafter referred to as a power line potential) of the semiconductor device is stable the prior high voltage detecting circuit, as in JP-A-60-124124 generates or does not generate the control signal exactly in accordance with the potential applied from an another device to the terminal of the semiconductor device. That is, when the potential of the terminal of the semiconductor device is within the predetermined range of the normal input voltage, the prior high voltage detecting circuit does not generate the control signal for starting the specific mode of the device. However, when the potential of the terminal or the semiconductor device is higher by the predetermined value than the normal input voltage, the prior high voltage detecting circuit generates the control signal and the semiconductor device changes to the specific mode, e.g., to the testing mode. When, however, the power line potential of the semiconductor device is not stable, for example, immediately after the semiconductor device is switched ON, and so when the power line potential of the device gradually increases, while the normal mode signal of the normal input voltage is continuously applied to the terminal of the semiconductor device: the normal mode signal of the terminal of the semiconductor device may be higher by the predetermined value than the increased power line potential. That is, the normal signal of the normal input voltage is considered to be the control signal for starting the specific mode of the semiconductor device. Consequently, the prior high voltage detecting circuit may generate a control signal in error without receiving the specific mode signal, and the semiconductor device may be changed to the specific mode by the erroneous control signal. It is known, for example in JP-A-5719676 to have a device which does not operate until the power supply level reaches Vcc, however such a device would prevent the detection of a specific mode signal while the device is being turned on. According to this invention, a high voltage detecting circuit included in a semiconductor device having terminals, for generating a control signal to start a specific operating mode of the semiconductor device when the potential of a specific mode signal higher by a predetermined value than a normal input voltage having a predetermined range is applied to at least one of the terminals of the semiconductor device, the high voltage detecting circuit comprising: a first power supply means for a high potential; a second power supply means for a low potential; a blocking transistor, having a control electrode and two other electrodes, the control electrode being coupled to the first power supply means and, one of the two other electrodes being connected to the at least one of the terminals, the blocking transistor switching ON when the potential of the control electrode is higher by the threshold voltage of the blocking transistor than the potential of the one of the two other electrodes; and a discrimination circuit, having a first end and a second end, for outputting the control signal from the second end of the discrimination circuit when the potential of the first end of the discrimination circuit is higher than a threshold voltage of the discrimination circuit by virtue of the blocking transistor being turned ON, characterised in that the detecting circuit also includes level shift means having an input end and an output end, the input end being connected to the other of the two other electrodes of the blocking transistor, the level shift means obtaining a potential at the output end lower by a level shifted value than the potential at its input end; and, resistor means, having a first end and a second end, the first end being connected to the output end of the level shift means and the second end being connected to the second power supply means, the first end of the discrimination circuit being connected to the output end of the level shift means and to the first end of the resistor means; the resistor means keeping the potential of the first end at the low potential of the second power supply means when the potential of the at least one of the terminals is within the predetermined range of the normal input voltage. The level shift means may include at least one MIS transistor, having a control electrode and two other electrodes. The control electrode is operatively connected to one of the two other electrodes. The other of the two other electrodes is operatively connected to the first end of the resistor means. The level shift value is determined by the threshold voltage of at lest one MIS transistor. The resistor means may include a depletion type MIS transistor, having a control electrode and two other electrodes. The control electrode is operatively connected to one of the two other electrodes and to the second power supply means. The other of the two other electrodes is operatively connected to at least one of the terminals of the semiconductor device, for keeping a leakage current under a predetermined standard current of the semiconductor device. The present invention will now be described and contrasted with the prior art with reference to the accompanying drawings, wherein:- Figure 1 is a block diagram illustrating a semiconductor device including a high voltage detecting circuit; Fig. 2 is a circuit diagram of an example of a conventional high voltage detecting circuit; Fig. 3 is a graph illustrating the conventional high voltage detecting circuit shown in Fig. 2 at the time switching ON the semiconductor device; Fig. 4 is a block circuit diagram illustrating a latch circuit to which a high voltage detecting circuit is applied; Fig. 5 is a block circuit diagram illustrating an EPROM device to which a high voltage detecting circuit is applied; Fig 6 is a block circuit diagram illustrating a semiconductor memory device having an ECC circuit to which a high voltage detecting circuit is applied; Fig. 7 is a block diagram illustrating a high voltage detecting circuit explaining a general concept of the present invention; Fig. 8 is a circuit diagram of a preferred embodiment of a high voltage detecting circuit according to the present invention; and Fig. 9 is a graph illustrating the high voltage detecting circuit shown in Fig. 8 at the time of switching ON the semiconductor device. For a better understanding of the preferred embodiments, the problems in the related art will be first explained. Figure 1 is a block diagram illustrating a semiconductor device including a high voltage detecting circuit. As shown in Fig. 1, a terminal 32 of a semiconductor device 30 is connected to an internal circuit 35 and a signal of the terminal 32 is transmitted directly to the internal circuit 35. The terminal 32 is also connected to a high voltage detecting circuit 31. When a potential of a specific mode signal higher by a predetermined value than a normal voltage having a predetermined range is applied to the terminal 32 of the semiconductor device 30, the high voltage detecting circuit 31 generates a control signal. The control signal is transmitted to a specific mode circuit 33, and the specific mode circuit 33 makes the internal circuit 35, to a specific mode. That is, when the specific mode signal is applied to the terminal 32 of the semiconductor device 30, the semiconductor device 30 changes to the specific mode, e.g., a testing mode. Figure 2 is a circuit diagram of an example of a conventional high voltage detecting circuit. The high voltage detecting circuit is included in a semiconductor device as in the above description with reference to Fig. 1. When a specific mode signal, e.g., 8 volts, higher by a predetermined value than a normal input voltage having a predetermined range, e.g., from 0 volt to 5 volts, is applied to a terminal 12 of the semiconductor device, the high voltage detecting circuit generates a control signal S₀₁ for starting a specific mode of the semiconductor device. A source of a leakage current cutting off transistor Q₁₁ , which is a P-channel type MIS transistor, is connected to the terminal 12 of the semiconductor device, and a gate and drain of the transistor Q₁₁ are connected commonly to a source of a P type MIS transistor Q₁₃. A gate and a drain of the transistor Q₁₃ are connected to a gate and a drain of an N-channel type MIS transistor Q₁₄ , respectively, and a source of the transistor Q₁₄ is connected to a ground GND. A common gate of both transistors Q₁₃ and Q₁₄ is connected to a power line Vcc (the reference mark Vcc also indicates a power line potential). A common drain of both transistors Q₁₃ and Q₁₄ is connected to a common gate of a first inverter circuit 15 consisting of a P type MIS transistor Q₁₅₁ and an N type MIS transistor Q₁₅₂. A common drain of the first inverter circuit 15 is connected to a common gate of a second inverter circuit 16 consisting of a P type MIS transistor Q₁₆₁ and an N type MIS transistor Q₁₆₂. A common drain of the second inverter circuit 16 is an output end 19 of the high voltage detecting circuit and the control signal S₀₁ is transmitted from the output end 19 to the internal circuit through the specific mode circuit of the semiconductor device. In the above description, sources of the transistor Q₁₅₁ and Q₁₆₁ are connected to the power line Vcc and sources of the transistor Q₁₅₂ and Q₁₆₂ are connected to the ground GND. In the above high voltage detecting circuit, when the power line potential Vcc is stabilized, e.g., 5 volts, and a normal mode signal within the normal input voltage, e.g., from 0 volt to 5 volts, is applied to the terminal 12, the high voltage detecting circuit does not generate the control signal. Because a potential of the source of the transistor Q₁₃ is not higher by the threshold voltage of the transistor Q₁₃ than a potential of the gate of the transistor Q₁₃ , the transistor Q₁₃ is not switched ON. Consequently, a potential of the common gate of the first inverter circuit 15 is at a low level, a potential of the common gate of the second inverter circuit 11 is at a high level, and the output end 19 of the high voltage detecting circuit is at the low level. That is, the control signal S₀₁ is not generated and the semiconductor device continues in a normal mode operation. When the power line potential Vcc is stabilized, e.g., 5 volts, and the specific mode signal, e.g., 8 volts, higher by a predetermined value than the normal input voltage is applied to the terminal 12, the high voltage detecting circuit generates the control signal. Because a potential of the source of the transistor Q₁₃ is higher by the threshold voltage of the transistor Q₁₃ than a potential of the gate of the transistor Q₁₃ , the transistor Q₁₃ is switched ON. Consequently, a potential of the common gate of the first inverter circuit 15 is at the high level, a potential of the common gate of the second inverter circuit 16 is at the low level, and the output end 19 of the high voltage detecting circuit is at the high level. That is, the staring signal S₀₁ is generated and the semiconductor device changes to the specific mode operation. Figure 3 is a graph illustrating the conventional high voltage detecting circuit shown in Fig. 2 at the time of switching ON the semiconductor device. In Fig. 3, when the power line potential Vcc is stabilized at a time t₁₄ in Fig. 3 of a potential V₁₀ (e.g., 5 volts), and the specific mode signal, shown by a line c₁ in Fig. 3, of a potential V₁₃ (e.g., 8 volts) higher by the predetermined value than the normal input voltage under a potential V₁₀ , is applied to the terminal 12 of the semiconductor device, the high voltage detecting circuit generates the control signal S₀₁. When the semiconductor device including the high voltage detecting circuit is switched ON at a time t₁₀ , the power line potential Vcc is gradually increased from 0 volt at the time t₁₀ to the stabilized power line potential V₁₀ (e.g., 5 volts) at a time t₁₃ , shown by a line a₁ in Fig. 3, until the power line potential Vcc is stabilized. At the same time, the normal mode signal of the normal input voltage (e.g., under 5 volts( is continuously applied to the terminal of the semiconductor device, shown by a line b₁ in Fig. 3, and the high voltage detecting circuit may generate an error control signal for starting the specific mode of the semiconductor device, because when the semiconductor device is switched ON and the power line potential Vcc of the device is gradually increased, the normal mode signal of the normal input voltage is considered to be the staring signal higher by the predetermined value than the increased power line potential a₁ below a potential V₁₂ at a time t₁₂. In Fig. 3, a potential V₁₁ at a time t₁₁ is an operational potential of the device, that is, the potential V₁₁ is an operational potential of the inverter circuit of the device. Therefore, the high voltage detecting circuit may generate the error control signal from the time t₁₁ to the time t₁₂ , when the semiconductor device is switched ON and a power line potential of the device is gradually increased, while the potential of the terminal of the semiconductor device is within a normal input voltage having a predetermined range. Next, problems of semiconductor circuits using the above prior high voltage detecting circuit will be described with reference to Figs. 4, 5, and 6. Figure 4 is a block circuit diagram illustrating a latch circuit to which a high voltage detecting circuit is applied. In Fig. 4, the latch circuit is included in a semiconductor device (not shown), e.g., semiconductor memory device. The latch circuit is useful for setting the semiconductor device to a specific mode continuously, without a specific mode signal being continuously applied to a terminal 2a. A signal of the terminal 2a is transmitted to the internal circuit directly, as shown by reference marks D₁. Signals of the terminals 2b and 2c are transmitted to the internal circuit through the buffers B₂ and B₃ respectively, as shown by reference marks D₂ and D₄. That is, the semiconductor device changes to the specific mode and continues the specific mode by one time receipt of the specific signal, and therefore, all terminals 2a, 2b and 2c can be used as input terminals at the specific mode. In the case of a normal mode operation of the semiconductor device, an output signal D₃ of a NAND gate NG₅ can be changed to a low level or a high level in accordance with a signal of the terminal 2c. On the other hand, in the specific mode operation of the semiconductor device, the output signal D₃ of the NAND gate NG₅ is fixed at the high level independently of the signal of the terminal 2c. That is, the semiconductor device is fixed to the specific mode, e.g., a testing mode, by the high level signal D₃. In the above description, the testing mode is for testing the semiconductor device before forwarding the semiconductor device from a production factory. The prior high voltage detecting circuit may generate an error control signal without receiving the specific mode signal, for example, the semiconductor device is switched ON and the power line potential of the device is gradually increased while the normal mode signal of the normal input voltage is continuously applied to the terminal of the semiconductor device. Consequently, the latch circuit being applied the prior high voltage detecting circuit, may continuously generate the control signal for staring the specific mode of the semiconductor device without the specific signal being continuously applied to a terminal of the semiconductor device. Figure 5 is a block circuit diagram illustrating an EPROM device to which a high voltage detecting circuit is applied. In Fig. 5, the EPROM device has a plurality of terminals T₁ - T j being connected to an address buffer 51. The EPROM device has a function of selecting all word liens WL₁ - WL m and a function of selecting all bit lines BL₁ - BL n for testing all memory cells. The function of selecting all word lines is determined by a first specific mode signal applied to the terminal T₁ , and the function of selecting all bit lines is determined by a second specific mode signal applied to the terminal T j . Note, the first and second specific mode signals should not be applied to the terminal T₁ and T j at the same time. However, the prior high voltage detecting circuits 10a may generate an error control signal S 0a without receiving the first specific mode signal, and at the same time, the prior high voltage detecting circuits 10b may generate an error control signal S 0b without receiving the second specific mode signal, for example, at the time the EPROM device is switched ON and the power line potential of the EPROM device is gradually increased, while the normal mode signal of the normal input voltage is continuously applied to the terminals T₁ and T j of the EPROM device. When the high voltage detecting circuits 10a and 10b generate error staring signals S 0a and S 0a at the same time, all word lines WL₁ - WL m are selected and, further, all bit lines BL₁ - BL n are selected, and therefore, a certain current (e.g., about 1 µA) flows in all of the memory cells of the EPROM device. For example, if a memory capacity of the EPROM is 64 K bits and the current flowing in each cell is 1 µA, then the current flowing in the EPROM device is 64 mA, and if a memory capacity of the EPROM is 256 K bits and the current flowing in each cell is 1 µA, then the current flowing the EPROM device is about 260 mA. If such a large current flows in the EPROM device, peripheral circuits, i.e., power supply 54, of the EPROM device cannot supply such large currents. Thus, a power line potential cannot be increased to the normal potential, and the power line potential remains at a certain value under the normal power line potential. When the power line potential remains at a certain value, the normal mode signal of the normal input voltage is continuously considered to be the specific mode signal higher by the predetermined value than the power line potential. Consequently, the flowing of the large current in the EPROM device is continued, until the EPROM device is destroyed. Figure 6 is a block diagram illustrating a semiconductor memory device having an error checking and correction (ECC) circuit to which a high voltage detecting circuit is applied. In Fig. 6, the ECC circuit has a switching means S₁ - S₇ and a register 68 for setting signals in order to control the switching of the switching means by a latch control signal. There are three modes in the semiconductor memory device having the ECC circuit in accordance with a state of the register 68, as follows; 1 ○ a normal mode for normal operation with correcting the error, 2 ○ a testing mode for testing information bits, and 3 ○ a testing mode for testing inspection bits. As a result of the above three modes, the information bits and the inspection bits can be tested independently without the normal operation mode. The register 68 is controlled by the output signal S 0c of the high voltage detecting circuit 10. That is, when the high voltage detecting circuit 10 generates a control signal for the testing mode of the ECC circuit, the ECC circuit changes to the testing mode for testing information bits or the testing mode for testing inspection bits from the normal mode for normal operation with correcting the error. But the prior high voltage detecting circuits may generates an error control signal without receiving the specific mode signal, when the semiconductor memory device having the ECC circuit is switched ON and the power line potential of the device is gradually increased. Then the ECC circuit may change to the testing mode for testing information bits or the testing mode for testing inspection bits form the normal mode for normal operation with correcting the error, by the error control signal. Referring to Figs. 7, 8 and 9, the preferred embodiments according to the present invention will be described. Figure 7 is a block diagram illustrating a high voltage detecting circuit explaining a general concept of the present invention. As shown in Fig. 7, a high voltage detecting circuit of the present invention is included in a semiconductor device having terminals 2, for generating a control signal S₀ in order to start a specific mode of the semiconductor device when a potential of a specific mode signal higher by a predetermined value than a normal input voltage having a predetermined range is applied to at least one of the terminals 2 of the semiconductor device. The high voltage detecting circuit includes a first power supply means 7, a second power supply means 8, a blocking transistor 3, a level shift means 4, a resistor means 6, and a discrimination circuit 5. The first power supply means 7 is used for a high potential and the second power supply means 8 is used for a low potential. The blocking transistor 3 has a control electrode and two other electrodes, the control electrode being operatively connected to the first power supply means 7 and one of the two other electrodes being operatively connected to at least one of the terminals 2 of the semiconductor device, for switching ON the blocking transistor 3 when a potential of the control electrode is higher than a potential of the one of the two other electrodes 2 by a threshold voltage of the blocking transistor 3. The level shift means 4 has an input end and an output end, the input end being operatively connected to the other of the two other electrodes of the blocking transistor 3 for obtaining a potential of the output end lower by a level shift value than a potential of the input end. The resistor means 6 has a first end and a second end, the first end being operatively connected to the output end of the level shift means 4, and the second end being operatively connected to the second power supply means 8, for keeping the potential of the first end to the low potential of the second power supply means 8 when a potential of at least one of the terminals 2 of the semiconductor device is within the predetermined range of the normal input voltage. The discrimination circuit 5 has a first end and a second end, the first end of the discrimination circuit 5 being operatively connected to the output end of the level shift means 4 and to the first end of the resistor means 6, for outputting the control signal S₀ to the second end of the discrimination circuit 5, when a potential of the first end of the discrimination circuit 5 is higher than a threshold voltage of the discrimination circuit 5. Figure 8 is a circuit diagram of a preferred embodiment of a high voltage detecting circuit according to the present invention. The high voltage detecting circuit is included in the semiconductor device as in the above description. When a specific mode signal, e.g., 8 volts, higher by a predetermined value than a normal input voltage having a predetermined range, e.g., from 0 volt to 5 volts, is applied to the terminal 2 of the semiconductor device, the high voltage detecting circuit generates a control signal S₀ for starting a specific mode of the semiconductor device. A source of leakage current cutting off transistor Q₁ , which is a P type MIS transistor, is connected to a terminal 2 of the semiconductor device. A gate and a drain of the transistor Q₁ are connected commonly to a source of a blocking transistor Q₃ , which is a P type MIS transistor. The leakage current cutting off transistor Q₁ is for keeping a leakage current under a predetermined standard current of the semiconductor device. Therefore, a potential of the source of the transistor Q₃ is lower by the threshold voltage of the transistor Q₁ than a potential of the terminal 2. A gate of the blocking transistor Q₃ is connected to a power line Vcc and a drain of the transistor Q₃ connected to an input end of a level shift circuit 4. When a potential of the gate of the transistor Q₃ is higher by the threshold voltage of the blocking transistor Q₃ than a potential of the source of the transistor Q₃ , the blocking transistor Q₃ is switched ON. The level shift circuit 4 includes k pieces of MIS transistors Q₄₁ , ..., Q 4k . In a first transistor Q₄₁ of the level shift circuit 4, a gate and a drain of the transistor Q₄₁ is commonly connected to the drain of the blocking transistor Q₃ as the input end of the level shift circuit 4. A source of the first transistor Q₄₁ is connected to a gate and a drain of a second transistor of the level shift circuit 4, and a source of the second transistor is connected to a gate and a drain of a third transistor of the level shift circuit 4 as same as the first transistor Q₄₁. A source of a final transistor Q 4k is connected as the input end of the level shift circuit 4 to a drain of a resistor transistor Q₆ and to a first end of a discrimination circuit 5. The level shift circuit 4 is used for obtaining a potential of the output lower by a level shift value than a potential of the input end. The level shift value is determined by a sum of the threshold voltage of the k pieces of MIS transistors Q₄₁ , ..., Q 4k in the level shift circuit 4. The discrimination circuit 5 includes a first inverter circuit 5a and a second inverter circuit 5b, the first inverter circuit 5a consists of a P type MIS transistor Q₅₁ and an N type MIS transistor Q₅₂ , and the second inverter circuit 5b consists of a P type MIS transistor Q₅₃ and an N type MIS transistor Q₅₄. The first end of a discrimination circuit 5, which is a common gate of a first inverter circuit 5a, is connected to the output end of the level shift circuit 4 and to the drain of a resistor transistor Q₆. The discrimination circuit 5 is for outputting the control signal S₀ in order to start the specific mode of the semiconductor device to a second end of the discrimination circuit 5, which is a common drain of the inverter circuit 5b. That is, the discrimination circuit 5 generates the control signal S₀, when a potential of the common gate of the first inverter circuit 5a is higher than the threshold voltage of the first inverter circuit 5a. In the above description, the second inverter circuit 5b is for completing and inverting the output signal of the first inverter circuit 5a, sources of the transistor Q₅₁ and Q₅₃ are connected to the power line Vcc, and source of the transistor Q₅₂ and Q₅₄ are connected to the ground GND. The resistor Q₆ is a depletion type MIS transistor, and a gate and a source of the transistor Q₆ is commonly connected to the ground GND. The resistor transistor Q₆ is for keeping the potential of the drain of the transistor Q₆ to the low potential of the ground GND, when a potential of the terminal 2 of the semiconductor device is within the predetermined range of the normal input voltage. That is, the resistor transistor Q₆ flows an unnecessary electrical charge at the input end of the discrimination circuit 5 to the ground GND, when the potential of the input end changes from the high level to the low level. Referring to Fig. 8, the operation of the high voltage detecting circuit will be described when the power line potential Vcc of the semiconductor device is stabilized, e.g., 5 volts. First, the normal mode operation of the semiconductor device will be described. When the semiconductor device including the high voltage detecting circuit is used as the normal mode operation, that is, the normal mode signal within the predetermined range of the normal input voltage, e.g., 0 - 5 volts, which is not higher than the power line potential Vcc of 5 volts, supplied by another device, is applied to the terminal 2 of the semiconductor device. The potential of the input signal of the terminal 2 is dropped to the threshold voltage of the transistor Q₁ by cutting off the leakage current to transistor Q₁ and applying it to the source of the blocking transistor Q₃. Therefore, the blocking transistor Q₃ is switched OFF, since the transistor Q₃ is switched ON only when the potential of the source of the transistor Q₃ is higher by the threshold voltage of the transistor Q₃ , than the potential of the gate of the transistor Q₃ which is power line potential Vcc. Therefore, the input end of the level shift circuit 4 is at the low level and the common gate of the first inverter circuit 5a is also at the low level, and thus the common drain of the second inverter circuit 5b is at the low level. This is, when the power line potential Vcc is stabilized while the normal mode signal is applied to the terminal 2, the high voltage detecting circuit will not generate the control signal S₀ for starting the specific mode of the semiconductor device. Next, the specific mode operation of the semiconductor device will be described. When the semiconductor device including the high voltage detecting circuit is used as the specific mode operation, e.g., testing mode operation. That is, the specific mode signal, e.g., 8 volts, higher by the predetermined value than the normal input voltage, is applied to the terminal 2 of the semiconductor device. The potential of the source of the transistor Q₃ is higher by the threshold voltage of the transistor Q₃ than the potential of the gate of the transistor Q₃ , but the potential of the input signal of the terminal 2 is dropped to the threshold voltage of the transistor Q₁ by cutting off the leakage current at the transistor Q₁ and applying it to the source of the blocking transistor Q₃. Consequently, the blocking transistor Q₃ is switched ON and the input end of the level shift circuit 4 is at the high level. Although the potential of the input end of the level shift circuit 4 is dropped to the sum of the threshold voltages of k pieces of MIS transistors Q₄₁ , ..., Q 4k in the level shift circuit 4 by the transistors Q₄₁ , ..., Q 4k , which is the threshold voltage of the level shift circuit 4, the output end of the level shift circuit 4 is still at the high level. That is, the potential of the output of the level shift circuit 4 is higher than the threshold voltage of the first inverter circuit 5a, and the potential of the specific mode signal is determined by the threshold voltages of the transistors Q₁ and Q₃ , the level shift circuit 4, and the first inverter circuit 5a. Therefore, the common gate of the first inverter circuit 5a is at the high level, and thus the common drain of the second inverter circuit is at the high level. That is, when the power line potential Vcc is stabilized and the specific mode signal is applied to the terminal 2, the high voltage detecting circuit generates the control signal S₀ for starting the specific mode of the semiconductor device. Referring to Fig. 9, the operation of the high voltage detecting circuit will be described when the power line potential Vcc of the semiconductor device is not stabilized, e.g., when the semiconductor device is switched ON. Figure 9 is a graph illustrating the high voltage detecting circuit shown in Fig. 8 at the time of switching ON the semiconductor device. When the semiconductor device including the high voltage detecting circuit is switched ON at a time t₀ , the power line potential Vcc is gradually increased from the time t₀ to a time t₃ until the power line potential is stabilized, a shown by a line a in Fig. 9. When the normal mode signal of the normal input voltage is continuously applied to the terminal of the semiconductor device, shown by a line b in Fig. 9, and at the same time the semiconductor device is switched ON, the normal mode signal having the potential of the line b is considered to be the specific mode signal. Because the potential of the source of the blocking transistor Q₃ which has the potential lower by the threshold voltages of the transistor Q₁ than the potential of the normal mode signal, is higher by the threshold voltages of the transistor Q₃ than the potential of the gate of the transistor Q₃ , which is the increasing power line potential of the line a . Therefore, the blocking transistor Q₃ is switched ON from the time t₀ to a time t₂ , that is, the blocking transistor Q₃ is switched ON until the time that the normal mode signal is not considered to be the specific mode signal. However, when the potential of the output end of the level shift circuit is at the low level, the blocking transistor Q₃ is switched ON. Note, the inverter circuits 5a and 5b cannot be operated until the power line potential exceeds an operable voltage V₁ of the inverter circuits. Consequently, it is possible to generate an error control signal for starting the specific mode of the semiconductor device from a time t₁ to the time t₂ in the high voltage detecting circuit. But in the high voltage detecting circuit shown in Fig. 8, the potential of the drain of the blocking transistor is dropped the predetermined value by the level shift circuit 4, and the potential of the common gate of the first inverter circuit 5a is not higher than the threshold voltage of the inverter circuit 5a (i.e., the threshold voltage of the transistor Q₅₁ of the first inverter circuit 5a). Consequently, the error control signal for starting the specific mode of the semiconductor device is not generated, even if the potential of the source of the blocking transistor Q₃ is higher by the threshold voltages of the transistor Q₃ than the increasing power line potential. Note, the predetermined voltage value of the level shift circuit 4 is indicated by a reference mark α, the threshold voltages of the transistors Q₁ and Q₃ are indicated by reference marks Vth₁ and Vth₃ respectively, the threshold voltage of the transistor Q₅₁ of the first inverter circuit 5a is indicated by a reference mark Vth₅₁ , the increasing power line voltage is indicated by a reference mark V X , the potential of the input end of the first inverter circuit 5a is indicated by a reference mark V G , and the potential of the normal input signal is indicated by a reference mark V₀. The potential of the normal input signal applied to the terminal 2 is V₀ , e.g., 5 volts, and the potential V G is indicated by the following formula. V G = V₀ - Vth₁ - Vth₃ - α (A) Furthermore, a condition in which the discrimination circuit 5 does not generate the control signal S₀ for starting the specific mode of the semiconductor device, is the potential V X being applied to the source of blocking transistor Q₃ is higher by the threshold voltage Vth₅₁ of the transistor Q₅₁ than the potential V G being applied to the gate of blocking transistor Q₃. Therefore the potential V G is indicated by the following formula. V G ≦ V X - Vth₅₁ (B) From the above two formulas (A) and (B), the predetermined voltage value α is indicated by the following formula. α ≧ V₀ - V X + Vth₅₁ - Vth₁ - Vth₃ (C) In the increasing power line voltage V X , the possibility of generating the error control signal is in a range of V₁ ≦ V X ≦ V₂ , and the predetermined voltage value α is indicated by the following formula. α ≧ V₀ - V₁ + Vth₅₁ - Vth₁ - Vth₃ (D) It is necessary that the predetermined voltage value α, dropped by the level shift circuit 4, be determined as satisfying the above formula (D). When the value α is determined by the formula (D), the potential of the output of the level shift circuit 4 is not higher than the threshold voltage of the first inverter circuit 5a, even when the semiconductor device is switched ON while the normal mode signal of the normal input voltage is continuously applied to the terminal of the semiconductor device. This is, the potential V G of the input end of the first inverter circuit 5a is not higher than the threshold voltage Vth₅₁ of the transistor Q₅₁ in the first inverter circuit 5a, the P type MIS transistor Q₅₁ is switched ON and the transistor Q₅₂ is switched OFF. Therefore, the potential of the output end of the first inverter 5a is at the high level and the potential of the output end of the second inverter 5b is at the low level, that is the control signal S₀ is not generated. Next, the potential β of the specific mode signal applied to the terminal of the semiconductor device will be described, as shown by reference mark c in Fig. 9. The potential V G of the input end of the first inverter circuit 5a should be at the high level, e.g., the potential V₀ of the normal input signal, when the potential β of the specific mode signal is applied to the terminal of the semiconductor device. The normal input signal V₀ is equal to the power line potential Vcc when the semiconductor device is stabilized, and therefore, the potential V G of the input end of the first inverter circuit 5a is indicated by the following formula. V G = β - Vth₁ - Vth₃ - α (A₀) V G ≧ V₀ - Vth₅₁ (B₀) From the above two formulas (A₀) and (B₀), the potential β the specific mode signal is indicated by the following formula. β ≧ V₀ + α + Vth₁ + Vth₃ - Vth₅₁ (C₀) It is obviously that the potential β of the specific mode signal should be determined in accordance with the voltage value α of dropped by the level shift circuit 4 as shown in the formula (C₀). That is, if the predetermined voltage value α is established as the higher value, the potential β should be determined as the higher value. Consequently, the predetermined voltage value α should not be established as the higher value unless absolutely necessary. Next, applications of semiconductor circuits using the embodiment of the high voltage detecting circuit according to the present invention will be described with reference to Figs. 4, 5, and 6. Figure 4 is a block circuit diagram illustrating a latch circuit to which a high voltage detecting circuit is applied. In Fig. 4, the latch circuit, included in a certain semiconductor device (not shown), e.g., semiconductor memory device, has three terminals 2a, 2b, and 2c, a logic circuit 40, and a high voltage detecting circuit 10. The terminal 2a is connected to an internal circuit of the semiconductor device, and the terminal 2a is also connected to a high voltage detecting circuit 10. The terminal 2b is connected through a buffer B₁ to the logic circuit 40 and through a buffer B₂ to the internal circuit of the semiconductor device. The terminal 2c is connected through a buffer B₃ to the logic circuit 40 and to the internal circuit of the semiconductor device. In a normal mode operation of the semiconductor device, a signal of the terminal 2a is transmitted to the internal circuit directly, as shown by reference marks D₁ , and signals of the terminal 2b and 2c are transmitted to the internal circuit through the buffer B₂ and B₃ respectively, as shown by reference marks D₂ and D₄. In the above description, each potential of the signal D₁ , D₂ , and D₄ is within a normal input voltage and a power line potential is stabilized. In normal operation mode, the high voltage detecting circuit 10 does not generate a control signal S₀ , that is, an output signal of the high voltage detecting circuit 10 is at a low level. When a specific mode signal higher by a predetermined value than the normal input voltage is applied to the terminal 2a while the power line potential is stabilized, a control signal S₀ for starting a specific mode of the semiconductor device is generated from the high voltage detecting circuit 10. While the control signal, which is at a high level, is generated from the high voltage detecting circuit 10, at the same time, a high level signal within a normal input voltage is applied to the terminal 2b, an output signal of an NAND gate NG₂ is at the low level and an output signal of an NAND gate NG₁ is at the high level. Therefore, an output signal of an NAND gate NG₄ is at the high level and an output signal of an NAND gate NG₃ is at the low level. That is, in the specific mode operation, the output signal of the NAND gate NG₃ is at the low level. Therefore, an output signal of an NAND gate NG₅ is at the high level as shown by a reference mark D₃ and the output signal of the NAND gate NG₅ which is at the high level is applied to the internal circuit. In the above description, the output signal D₃ of the NAND gate NG₅ is continuously at the high level without applying a specific mode signal to the terminal 2a. When the internal circuit received the low level signal D₃ of the output of the NAND gate NG₅ , the semiconductor device including the internal circuit changes to a certain specific mode, for example, a testing mode for testing the semiconductor device. Figure 5 is a block circuit diagram illustrating an EPROM device to which a high voltage detecting circuit is applied. In Fig. 5, the EPROM device has a function of selecting all word lines WL₁ - WL m and a function of selecting all bit lines BL₁ - BL n for testing all memory cells. The EPROM device has a plurality of terminals T₁ - T j connected to an address buffer 51. The terminal T₁ of the terminals T₁ - T j are connected to a high voltage detecting circuit 10a and an output 9a of the high voltage detecting circuit 10a is applied to a word line decoder 52. The terminal T j of the terminals T₁ - T j is connected to a high voltage detecting circuit 10b and an output 9b of the high voltage detecting circuit 10b is applied to a bit line decoder 53. The word line decoder 52 has a plurality of word lines WL₁ - WL m , the bit line decoder 53 many bit lines BL₁ - BL n , and there are a plurality of memory cells MC at each cross point of the word lines WL₁ - WL m and the bit lines BL₁ - BL n . In the above description, the function of selecting all word lines and the function of selecting all bit lines are used to give stress to the memory cells, and thereby test them. The function of selecting all word lines is determined by a first specific mode signal applied to the terminals T₁ , and the function of selecting all bit lines is determined by a second specific mode signal applied to the terminal T j . Note, the first and second specific mode signals should not be applied to the terminals T₁ and T j , at the same time. In Fig. 5, reference numeral 54 denotes a power supply. In a normal mode operation of the EPROM device, a signal of each terminal T₁ - T j is transmitted to the word line decoder 52 and the bit line decoder 53 through the address buffer 51. In the normal mode operation of the EPROM device, normal address signals within a normal input voltage are applied to the terminals T₁ - T j , and the high voltage detecting circuits 10a and 10b do not generate starting signals S 0a and S 0b , respectively. In the specific mode operation of the EPROM device, the first specific signal or the second specific signal is applied to the terminals T₁ - T j , and then one of the high voltage detecting circuits 10a and 10b generates a control signal S 0a or S 0b . In this case, the high voltage detecting circuits 10a and 10b should not generate a control signal at the same time. Figure 6 is a block circuit diagram illustrating a semiconductor memory device having an error checking and correction (ECC) circuit to which a high voltage detecting circuit is applied. In Fig. 6, the ECC circuit has a switching means S₁ - S₇ and a register 68 for setting signals in order to control the switching of the switching means by a latch control signal. There are three modes in the semiconductor memory device in accordance with a state of the register 68, as follows; 1 ○ a normal mode for normal operation with correcting the error, 2 ○ a testing mode for testing information bits, and 3 ○ a testing mode for testing inspection bits. As a result of the above three modes, the information bits and the inspection bits can be inspected independently without the normal operation mode. In Fig. 6, reference normal 10 denotes a high voltage detecting circuit (HD), reference numeral 61 denotes data input (Din), reference numeral 62 denotes a plurality of address input (Ain), a reference numeral 63 denotes a encorder (COD), reference numeral 64 denotes information bits (IB), reference numeral 65 denotes inspection bits (PB), reference numeral 66 denotes a decoder (DEC), reference numeral 67 denotes an error checking and correction circuit having data output (Do), and reference numeral 68 denotes a register. In 1 ○, the normal mode for normal operation with correcting the error, the switching means are as follows: S₁ = ON, S₂ = ON, S₃ = R, S₄ = ON, S₅ = ON, S₆ = ON, S₇ = R, and therefore, the ECC circuit is operated and corrected data is output. In 2 ○, the testing mode for testing information bits, the switching means are as follows: S₁ = OFF, S₂ = ON, S₃ = R, S₄ = OFF, S₅ = OFF, S₆ = OFF, S₇ = R, and therefore, the ECC circuit is not operated and the information bits can be tested. In 3 ○, the testing mode for testing inspection bits, the switching means are as follows: S₁ = OFF, S₂ = OFF, S₃ = L, S₄ = OFF, S₅ = OFF, S₆ = OFF, S₇ = L, and therefore, the ECC circuit is not operated and the inspection bits can be tested. In Fig. 6, the switching of the switching means is controlled by the register 68, which is provided with predetermined information of the switching state of the above three modes. In the above description referring to Figs. 4, 5, and 6, the semiconductor circuits using the embodiments of the high voltage detecting circuit according to the present invention are not started in testing mode by the error control signal for starting the testing mode of the semiconductor circuit generated from the high voltage detecting circuit.

Claims: A high voltage detecting circuit included in a semiconductor device having terminals (2), for generating a control signal to start a specific operating mode of the semiconductor device when the potential of a specific mode signal higher by a predetermined value than a normal input voltage having a predetermined range is applied to at least one of the terminals (2) of the semiconductor device, the high voltage detecting circuit comprising: a first power supply means (Vcc) for a high potential; a second power supply means (GND) for a low potential; a blocking transistor (3), having a control electrode (G) and two other electrodes (S,D), the control electrode (G) being coupled to the first power supply means (Vcc) and, one (S) of the two other electrodes (S, D) being connected to the at least one of the terminals (2), the blocking transistor (3) switching ON when the potential of the control electrode (G) is higher by the threshold voltage of the blocking transistor (3) than the potential of the one (S) of the two other electrodes (S, D); and a discrimination circuit (5), having a first end and a second end, for outputting the control signal from the second end of the discrimination circuit (5) when the potential of the first end of the discrimination circuit is higher than a threshold voltage of the discrimination circuit (5) by virtue of the blocking transistor (3) being turned ON, characterised in that the detecting circuit also includes level shift means (4) having an input end and an output end, the input end being connected to the other (D) of the two other electrodes (S,D) of the blocking transistor (3), the level shift means (4) obtaining a potential at the output end lower by a level shifted value than the potential at its input end; and, resistor means (6), having a first end and a second end, the first end being connected to the output end of the level shift means (4) and the second end being connected to the second power supply means (GND), the first end of the discrimination circuit (5) being connected to the output end of the level shift means (4) and to the first end of the resistor means (6); the resistor means (6) keeping the potential of the first end at the low potential of the second power supply means (GND) when the potential of the at least one of the terminals (2) is within the predetermined range of the normal input voltage. A high voltage detecting circuit according to claim 1, wherein the level shift means (4) comprises: at least one MIS transistor (Q41) having a control electrode (G) and two other electrodes (S,D), the control electrode (G) and one (D) of the two other electrodes (D,S) being connected to the input end of the level shift means (4) and the other (S) of the two other electrodes (S,D) being coupled to the first end of the resistor means (6), the level shifted value being determined by the threshold voltage of the at least one MIS transistor (Q41). A high voltage detecting circuit according to claim 1 or 2, wherein the resistor means (6) comprises: a depletion type MIS transistor (Q6) having a control electrode (G) and two other electrodes (S,D), the control electrode (G) being connected to one (S) of the two other electrodes (S,D) and to the second power supply means (GND) and the other (D) of the two other electrodes (S,D) being connected to the output end of the level shift means (4) and to the first end of the discrimination circuit (5). A high voltage detecting circuit according to any one of the preceding claims, further comprising: a leakage current cutting off transistor (Q1) having a control electrode (G) and two other electrodes (S,D), the control electrode (G) being connected to one (D) of the two other electrodes (S,D) and to the one (S) of the two other electrodes (S,D) of the blocking transistor (3), the other (s) of the two other electrodes (S,D), of the leakage current cutting off transistor (Q1) being connected to the at least one of the terminals (2) for keeping a leakage current under a predetermined standard current of the semiconductor device.

Inventors: KAWASHIMA, HIROMI, TAKEUCHI, ATSUSHI
Applicants: FUJITSU LIMITED
Application year: 1987
Main classification: G01R19
IPC codes: H01L27, G01R31, H03K5, G01R19, H03K17