Clamp Circuit

Abstract

This clamp circuit comprises: a first MOS transistor; and a second MOS transistor that is connected in series to the first MOS transistor. The gate of the first MOS transistor is connected to the drain of the first MOS transistor. The gate of the second MOS transistor is connected to the drain of the second MOS transistor. The clamp circuit is configured such that the first MOS transistor and / or the second MOS transistor exhibits a substrate bias effect.

Description

[Technical field]

[0001] The invention disclosed herein relates to a clamping circuit for clamping a voltage. [Background technology]

[0002] Fig. 9 is a diagram showing a clamp circuit using a Zener diode. When an input voltage VIN larger than a predetermined voltage is applied to a current source 1, the clamp circuit shown in Fig. 9 clamps the voltage applied to the connection node between the current source 1 and the Zener diode ZD1 to the breakdown voltage Vz of the Zener diode ZD1.

[0003] Fig. 10 is a diagram showing a clamp circuit using diodes. When an input voltage VIN larger than a predetermined voltage is applied to a current source 1, the clamp circuit shown in Fig. 10 clamps the voltage applied to the connection node between the current source 1 and diode D1 to m times the forward voltage Vf. Here, m is the number of diodes connected in series.

[0004] In the clamp circuit shown in FIG. 10, a diode-connected bipolar transistor (a bipolar transistor in which the collector and base are short-circuited) may be used as each of the diodes D1 to Dm, or a diode-connected MOS transistor (a MOS transistor in which the drain and gate are short-circuited) may be used as each of the diodes D1 to Dm.

[0005] As an example of the related art, Patent Document 1 can be mentioned. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2012-023912 A Summary of the Invention [Problem to be solved by the invention]

[0007] When a Zener diode is built into a semiconductor integrated circuit device rather than being configured as a discrete component, the breakdown voltage of the Zener diode is generally fixed. Therefore, when the clamp circuit shown in FIG. 9 is built into a semiconductor integrated circuit device, the clamp voltage generally cannot be adjusted.

[0008] On the other hand, in the clamp circuit shown in Fig. 10, the clamp voltage can be adjusted by changing the number of diodes connected in series. However, the more the number of diodes connected in series increases, the worse the variation in the clamp voltage and the temperature characteristics of the clamp voltage become. In addition, the more the number of diodes connected in series increases, the larger the circuit area becomes, which is undesirable. [Means for solving the problem]

[0009] The clamp circuit disclosed in this specification comprises a first MOS transistor and a second MOS transistor connected in series to the first MOS transistor, the gate of the first MOS transistor is connected to the drain of the first MOS transistor, the gate of the second MOS transistor is connected to the drain of the second MOS transistor, and a substrate bias effect is generated in at least one of the first MOS transistor and the second MOS transistor (first configuration).

[0010] In the clamp circuit of the above-mentioned first configuration, the first MOS transistor may be an N-channel MOS transistor, the second MOS transistor may be a P-channel MOS transistor, the source of the first MOS transistor may be connected to the source of the second MOS transistor, and a substrate bias effect may occur in both the first MOS transistor and the second MOS transistor (second configuration).

[0011] In the clamp circuit of the second configuration described above, the back gate of the first MOS transistor may be connected to the drain of the second MOS transistor, and the back gate of the second MOS transistor may be connected to the drain of the first MOS transistor (third configuration).

[0012] In the clamp circuit of the second or third configuration, a resistor or a diode may be provided, and the source of the first MOS transistor may be connected to the source of the second MOS transistor via the resistor or the diode (fourth configuration).

[0013] In the clamp circuit of the first configuration, a configuration (fifth configuration) may be used in which a substrate bias effect occurs in only one of the first MOS transistor and the second MOS transistor.

[0014] Above items 1 to 4 5 In any of the clamp circuits of the configurations, a third MOS transistor may be provided, and the third MOS transistor may be configured so that a first clamp voltage based on the threshold voltage of the first MOS transistor and the threshold voltage of the second MOS transistor is applied to a gate of the third MOS transistor, and the third MOS transistor is configured to generate a second clamp voltage based on the first clamp voltage and the threshold voltage of the third MOS transistor (sixth configuration).

[0015] In the clamp circuit of the sixth configuration, the third MOS transistor may be a depletion type MOS transistor (seventh configuration).

[0016] The semiconductor integrated circuit device disclosed in this specification has a configuration (eighth configuration) including a clamp circuit having any one of the first to seventh configurations. Effect of the Invention

[0017] The clamp circuit disclosed herein allows for the generation of an appropriate clamp voltage. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a first embodiment; [Diagram 2] FIG. 1 is a diagram for explaining the substrate bias effect. [Diagram 3] FIG. 1 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a second embodiment; [Figure 4] FIG. 13 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a third embodiment. [Diagram 5] FIG. 13 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a fourth embodiment. [Figure 6] FIG. 13 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a fifth embodiment. [Figure 7] FIG. 13 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a sixth embodiment. [Figure 8] FIG. 13 is a diagram showing a schematic configuration of a semiconductor integrated circuit device according to a seventh embodiment. [Figure 9] Diagram showing a clamp circuit using a Zener diode [Figure 10] Diagram showing a clamp circuit using a diode DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In this specification, a MOS transistor refers to a transistor whose gate structure is composed of at least three layers: "a layer made of a conductor or a semiconductor such as polysilicon with a low resistance value," "an insulating layer," and "a P-type, N-type, or intrinsic semiconductor layer." In other words, the gate structure of a MOS transistor is not limited to a three-layer structure of a metal, an oxide, and a semiconductor.

[0020] First Embodiment FIG. 1 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 101 according to the first embodiment (hereinafter abbreviated as "semiconductor integrated circuit device 101").

[0021] The semiconductor integrated circuit device 101 includes a terminal PVIN, a terminal PGND, a current source 1, a low-voltage circuit 2, and first to third MOS transistors M1 to M3.

[0022] There is no particular limitation on the use of the semiconductor integrated circuit device 101. For example, if the semiconductor integrated circuit device 101 is a semiconductor integrated circuit device for a switching power supply device, the semiconductor integrated circuit device 101 and its external components constitute a switching power supply device. Also, for example, if the semiconductor integrated circuit device 101 is an LED driver, the semiconductor integrated circuit device 101 and its external components constitute an LED lighting device.

[0023] The terminal PVIN is configured to receive the input voltage VIN.

[0024] The terminal PGND is configured to be connected to a ground potential that is lower than the input voltage VIN.

[0025] The first MOS transistor M1 is an enhancement-type N-channel MOS transistor. The first MOS transistor M1 is a diode-connected MOS transistor. That is, as will be described later, the gate of the first MOS transistor M1 is connected to the drain of the first MOS transistor M1.

[0026] The second MOS transistor M2 is an enhancement type P-channel MOS transistor. Like the first MOS transistor M1, the second MOS transistor M2 is also a diode-connected MOS transistor. That is, as will be described later, the gate of the second MOS transistor M2 is connected to the drain of the second MOS transistor M2.

[0027] The third MOS transistor M3 is a depletion-type N-channel MOS transistor.

[0028] One end of the current source 1 and the drain of the third MOS transistor M3 are connected to the terminal PVIN.

[0029] The other end of the current source 1 is connected to the gate and drain of the first MOS transistor M1, the back gate of the second MOS transistor M2, and the gate of the third MOS transistor M3.

[0030] The source of the first MOS transistor M1 is connected to the source of the second MOS transistor M2.

[0031] The gate and drain of the second MOS transistor M2 and the back gate of the first MOS transistor M1 are connected to the terminal PGND.

[0032] The low-withstand voltage circuit 2 is provided between the source of the third MOS transistor M3 and the terminal PGND. The low-withstand voltage circuit 2 operates using a voltage equivalent to the difference between the source voltage of the third MOS transistor M3 and the ground potential as a power supply voltage. The low-withstand voltage circuit 2 is a circuit whose withstand voltage is lower than the expected maximum value of the input voltage VIN. Therefore, when the input voltage VIN becomes excessive, the semiconductor integrated circuit device 101 clamps the source voltage of the third MOS transistor M3 to prevent the low-withstand voltage circuit 2 from being destroyed.

[0033] When an input voltage VIN larger than a predetermined voltage is applied to the terminal PVIN, the current source 1 outputs a current to the first MOS transistor M1 and the second MOS transistor M2. At this time, the drain voltage of the first MOS transistor M1 is equal to the sum of the threshold voltage Vth2' of the second MOS transistor M2 and the threshold voltage Vth1' of the first MOS transistor M1 to the ground potential. In other words, when an input voltage VIN larger than a predetermined voltage is applied to the terminal PVIN, the drain voltage of the first MOS transistor M1 is clamped to the first clamp voltage (=ground potential+threshold voltage Vth2'+threshold voltage Vth1').

[0034] Here, since the back gate of the first MOS transistor M1 is connected to the drain of the second MOS transistor M2 as described above, the back gate voltage of the first MOS transistor M1 is lower than the source voltage of the first MOS transistor M1. Therefore, a substrate bias effect occurs in the first MOS transistor M1 (see FIG. 2). In other words, the threshold voltage Vth1' of the first MOS transistor M1 is higher than the threshold voltage Vth1 of the first MOS transistor M1 when the back gate of the first MOS transistor M1 is connected to the source of the first MOS transistor M1 instead of the drain of the second MOS transistor M2.

[0035] As described above, the back gate of the second MOS transistor M2 is connected to the drain of the first MOS transistor M1, so the back gate voltage of the second MOS transistor M2 is higher than the source voltage of the second MOS transistor M2. Therefore, a substrate bias effect occurs in the second MOS transistor M2 (see FIG. 2). In other words, the threshold voltage Vth2' of the second MOS transistor M2 is higher than the threshold voltage Vth2 of the second MOS transistor M2 when the back gate of the second MOS transistor M2 is connected to the source of the second MOS transistor M2 instead of the drain of the first MOS transistor M1.

[0036] Furthermore, as the threshold voltage Vth2' becomes greater than the threshold voltage Vth2, the influence of the substrate bias effect in the first MOS transistor M1 becomes greater, and as the threshold voltage Vth1' becomes greater than the threshold voltage Vth1, the influence of the substrate bias effect in the second MOS transistor M2 becomes greater.

[0037] As a result, the threshold voltages Vth1 and Vth2 are each about 0.6[V] to 1[V] (the specific values ​​vary depending on the type and size of the MOS transistor), whereas the threshold voltages Vth1' and Vth2' are each about 1[V] to 1.6[V] (the specific values ​​vary depending on the type and size of the MOS transistor). This makes it possible to reduce the number of elements required to generate the above-mentioned first clamp voltage.

[0038] For example, when the above-mentioned first clamp voltage is set to 3 [V], two MOS transistors (first MOS transistor M1, second MOS transistor M2) are connected in series in the semiconductor integrated circuit device 101, whereas when the clamp voltage is set to 3 [V] in the clamp circuit shown in FIG. 10, five diodes need to be connected in series.

[0039] As an example, if the variation in the threshold voltage of the MOS transistor and the variation in the forward voltage of the diode are each ±0.15 [V] and the temperature characteristics of the threshold voltage of the MOS transistor and the temperature characteristics of the forward voltage of the diode are each -2 [mV / °C], then in the clamp circuit shown in FIG. 10, the variation and temperature characteristics of the clamp voltage are ±0.75 [V] and -10 [mV / °C], whereas in semiconductor integrated circuit device 101, the variation and temperature characteristics of the first clamp voltage described above can be suppressed to ±0.3 [V] and -4 [mV / °C].

[0040] When an input voltage VIN larger than a predetermined voltage is applied to the terminal PVIN, the source voltage of the third MOS transistor M3 is clamped to the second clamp voltage. The above-mentioned second clamp voltage is a value obtained by subtracting the threshold voltage Vth3 of the third MOS transistor M3 from the above-mentioned first clamp voltage (=ground potential+threshold voltage Vth2'+threshold voltage Vth1'). Therefore, when considering a case where the temperature characteristic of the threshold voltage of a MOS transistor is -2 [mV / °C], the temperature characteristic of the above-mentioned second clamp voltage can be suppressed to -2 [mV / °C].

[0041] In the semiconductor integrated circuit device 101, since the third MOS transistor M3 is a depletion-type N-channel MOS transistor, even when the input voltage VIN is small and the current source 1 does not operate, the third MOS transistor M3 can be turned on to supply the power supply voltage to the low-withstand voltage circuit 2.

[0042] Unlike the present embodiment, the third MOS transistor M3 may be an enhancement type N-channel MOS transistor or an NPN bipolar transistor. Furthermore, unlike the present embodiment, when clamping to the power supply side, a P-channel MOS transistor or a PNP bipolar transistor may be used as the third MOS transistor M3.

[0043] Furthermore, although semiconductor integrated circuit device 101 includes a first clamp circuit (clamp circuit including first and second MOS transistors M1 and M2) that generates the above-mentioned first clamp voltage and a second clamp circuit (clamp circuit including first to third MOS transistors M1 to M3) that generates the above-mentioned second clamp voltage, the above-mentioned first clamp circuit may be used alone. In other words, unlike this embodiment, the semiconductor integrated circuit device may be configured to include the above-mentioned first clamp circuit and not include the third MOS transistor M3.

[0044] <Second embodiment> FIG. 3 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 102 according to the second embodiment (hereinafter, abbreviated as "semiconductor integrated circuit device 102").

[0045] The semiconductor integrated circuit device 102 differs from the semiconductor integrated circuit device 101 in that the back gate of the first MOS transistor M1 is connected to the source of the first MOS transistor M1, but has the same configuration as the semiconductor integrated circuit device 101 in other respects.

[0046] In the semiconductor integrated circuit device 102, a body bias effect occurs in the second MOS transistor M2, but no body bias effect occurs in the first MOS transistor M1. As a result, in the semiconductor integrated circuit device 102, the above-mentioned first clamp voltage and the above-mentioned second clamp voltage can be made smaller than those in the semiconductor integrated circuit device 101. In other words, if it is desired to set the clamp voltage lower, it is sufficient to employ, for example, the semiconductor integrated circuit device 102 instead of the semiconductor integrated circuit device 101.

[0047] <Third embodiment> FIG. 4 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 103 according to the third embodiment (hereinafter, abbreviated as "semiconductor integrated circuit device 103").

[0048] The semiconductor integrated circuit device 103 differs from the semiconductor integrated circuit device 102 in that it includes a fourth MOS transistor M4 instead of the first MOS transistor M1, but has the same configuration as the semiconductor integrated circuit device 102 in other respects.

[0049] The fourth MOS transistor M4 is an enhancement type P-channel MOS transistor. The source and back gate of the fourth MOS transistor M4 are connected to the other end of the current source 1, the gate of the third MOS transistor M3, and the back gate of the second MOS transistor M2. The gate and drain of the fourth MOS transistor M4 are connected to the source of the second MOS transistor M2. The fourth MOS transistor M4 corresponds to the "first MOS transistor" in the claims.

[0050] In the semiconductor integrated circuit device 103, a substrate bias effect occurs in the second MOS transistor M2, but no substrate bias effect occurs in the fourth MOS transistor M4. As a result, in the semiconductor integrated circuit device 103, the above-mentioned first clamp voltage and the above-mentioned second clamp voltage can be made smaller than those in the semiconductor integrated circuit device 101. In other words, when it is desired to set the clamp voltage lower, it is sufficient to employ, for example, the semiconductor integrated circuit device 103 instead of the semiconductor integrated circuit device 101.

[0051] <Fourth embodiment> FIG. 5 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 104 according to a fourth embodiment (hereinafter, abbreviated as "semiconductor integrated circuit device 104").

[0052] The semiconductor integrated circuit device 104 differs from the semiconductor integrated circuit device 101 in that the back gate of the second MOS transistor M2 is connected to the source of the second MOS transistor M2, but has the same configuration as the semiconductor integrated circuit device 101 in other respects.

[0053] In the semiconductor integrated circuit device 104, a substrate bias effect occurs in the first MOS transistor M1, but no substrate bias effect occurs in the second MOS transistor M2. As a result, in the semiconductor integrated circuit device 104, the above-mentioned first clamp voltage and the above-mentioned second clamp voltage can be made smaller than those in the semiconductor integrated circuit device 101. In other words, if it is desired to set the clamp voltage lower, the semiconductor integrated circuit device 104, for example, should be adopted instead of the semiconductor integrated circuit device 101.

[0054] <Fifth embodiment> FIG. 6 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 105 according to a fifth embodiment (hereinafter abbreviated as "semiconductor integrated circuit device 105").

[0055] The semiconductor integrated circuit device 105 differs from the semiconductor integrated circuit device 104 in that it includes a fifth MOS transistor M5 instead of the second MOS transistor M2, but has the same configuration as the semiconductor integrated circuit device 104 in other respects.

[0056] The fifth MOS transistor M5 is an enhancement type N-channel MOS transistor. The source and back gate of the fifth MOS transistor M5 are connected to the terminal PGND, the back gate of the first MOS transistor M1, and the low-voltage circuit 2. The gate and drain of the fifth MOS transistor M5 are connected to the source of the first MOS transistor M1. The fifth MOS transistor M5 corresponds to the "second MOS transistor" in the claims.

[0057] In the semiconductor integrated circuit device 105, a substrate bias effect occurs in the first MOS transistor M1, but no substrate bias effect occurs in the fifth MOS transistor M5. As a result, in the semiconductor integrated circuit device 105, the above-mentioned first clamp voltage and the above-mentioned second clamp voltage can be made smaller than those in the semiconductor integrated circuit device 101. In other words, when it is desired to set the clamp voltage lower, it is sufficient to employ, for example, the semiconductor integrated circuit device 105 instead of the semiconductor integrated circuit device 101.

[0058] Sixth embodiment FIG. 7 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 106 according to a sixth embodiment (hereinafter, abbreviated as "semiconductor integrated circuit device 106").

[0059] The semiconductor integrated circuit device 106 differs from the semiconductor integrated circuit device 101 in that it includes a resistor R1 and the source of the first MOS transistor M1 is connected to the source of the second MOS transistor M2 via the resistor R1, but otherwise has the same configuration as the semiconductor integrated circuit device 101. In this embodiment, it is preferable to use a constant current source as the current source 1 in order to suppress fluctuations in the clamp voltage.

[0060] In this embodiment, the potential difference across resistor R1 causes the influence of the substrate bias effect in each of first MOS transistor M1 and second MOS transistor M2 to be greater than in the first embodiment. As a result, in semiconductor integrated circuit device 106, the above-mentioned first clamp voltage and second clamp voltage can be made greater than those in semiconductor integrated circuit device 101. In other words, when it is desired to set the clamp voltage higher, for example, semiconductor integrated circuit device 106 may be used instead of semiconductor integrated circuit device 101.

[0061] Unlike this embodiment, a diode (for example, a diode-connected bipolar transistor, a diode-connected MOS transistor, etc.) may be used instead of the resistor R1. However, since the resistor R1 has a positive temperature characteristic, by providing the resistor R1 instead of a diode between the source of the first MOS transistor M1 and the source of the second MOS transistor M2, the temperature characteristic values ​​[V / °C] of the first clamp voltage and the second clamp voltage described above can be reduced.

[0062] Seventh embodiment FIG. 8 is a diagram showing a schematic configuration of a semiconductor integrated circuit device 107 according to the seventh embodiment (hereinafter, abbreviated as "semiconductor integrated circuit device 107").

[0063] The semiconductor integrated circuit device 107 differs from the semiconductor integrated circuit device 101 in that the back gate of the second MOS transistor M2 is connected to the terminal PVIN, but has the same configuration as the semiconductor integrated circuit device 101 in other respects.

[0064] In this embodiment, the back gate voltage of the second MOS transistor M2 is higher than the drain voltage of the first MOS transistor M1, so that the influence of the substrate bias effect in the second MOS transistor M2 is greater than in the first embodiment. As a result, in the semiconductor integrated circuit device 107, the above-mentioned first clamp voltage and the above-mentioned second clamp voltage can be made higher than those in the semiconductor integrated circuit device 101. In other words, when it is desired to set the clamp voltage higher, it is sufficient to employ, for example, the semiconductor integrated circuit device 107 instead of the semiconductor integrated circuit device 101.

[0065] In this embodiment, if the input voltage VIN fluctuates, the degree of influence of the substrate bias effect in the second MOS transistor M2 fluctuates, and the threshold voltage Vth2' of the second MOS transistor M2 fluctuates. As a result, if the input voltage VIN fluctuates, the first clamp voltage and the second clamp voltage fluctuate as well. Therefore, if importance is attached to the stability of the first clamp voltage and the second clamp voltage, for example, the semiconductor integrated circuit devices 101 to 105 or the semiconductor integrated circuit device 106 using a constant current source as the current source 1 may be employed.

[0066] <Other> In addition to the above-described embodiment, the configuration of the present invention can be modified in various ways without departing from the spirit of the invention.

[0067] For example, modifications described in one embodiment may be applied as modifications to other embodiments as long as the circuitry operates without problems.

[0068] Also, for example, like the seventh embodiment, in the second, third and sixth embodiments, the back gate of the second MOS transistor M2 may be connected to the terminal PVIN instead of the drain of the first MOS transistor M1.

[0069] Also, instead of being limited to the terminal PVIN, the back gate of the first MOS transistor M1 may be connected to a predetermined location in the semiconductor integrated circuit device so that the substrate bias effect occurs in the first MOS transistor M1. Similarly, the back gate of the second MOS transistor M2 may be connected to a predetermined location in the semiconductor integrated circuit device so that the substrate bias effect occurs in the second MOS transistor M2.

[0070] As such, the above-described embodiments should be considered to be illustrative in all respects and not restrictive, and the technical scope of the present invention is indicated by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that are within the meaning and scope of the claims. [Explanation of symbols]

[0071] 1 current source 2. Low-voltage circuit M1 to M3 1st to 3rd MOS transistors PVIN and PGND terminals

Claims

1. A first MOS transistor; a second MOS transistor connected in series to the first MOS transistor; Equipped with the gate of the first MOS transistor is connected to the drain of the first MOS transistor; the gate of the second MOS transistor is connected to the drain of the second MOS transistor; the first MOS transistor is an N-channel MOS transistor, the second MOS transistor is a P-channel MOS transistor, the source of the first MOS transistor is connected to the source of the second MOS transistor; A clamp circuit configured to generate a substrate bias effect in both the first MOS transistor and the second MOS transistor.

2. a back gate of the first MOS transistor is connected to a drain of the second MOS transistor; 2. The clamp circuit according to claim 1, wherein a back gate of the second MOS transistor is connected to a drain of the first MOS transistor.

3. A resistor or a diode is provided, 3. The clamp circuit according to claim 1, wherein the source of said first MOS transistor is connected to the source of said second MOS transistor via said resistor or said diode.

4. a third MOS transistor; 4. The clamp circuit according to claim 1, wherein the third MOS transistor is configured to apply a first clamp voltage based on a threshold voltage of the first MOS transistor and a threshold voltage of the second MOS transistor to a gate of the third MOS transistor, and is configured to generate a second clamp voltage based on the first clamp voltage and the threshold voltage of the third MOS transistor.

5. A first MOS transistor; a second MOS transistor connected in series to the first MOS transistor; A third MOS transistor; Equipped with the gate of the first MOS transistor is connected to the drain of the first MOS transistor; the gate of the second MOS transistor is connected to the drain of the second MOS transistor; the third MOS transistor is configured to apply a first clamp voltage based on a threshold voltage of the first MOS transistor and a threshold voltage of the second MOS transistor to a gate of the third MOS transistor, and to generate a second clamp voltage based on the first clamp voltage and the threshold voltage of the third MOS transistor; A clamp circuit configured to generate a substrate bias effect in at least one of the first MOS transistor and the second MOS transistor.

6. 6. The clamp circuit according to claim 5, configured such that a substrate bias effect occurs in only one of the first MOS transistor and the second MOS transistor.

7. 7. The clamp circuit according to claim 4, wherein the third MOS transistor is a depletion type MOS transistor.

8. A semiconductor integrated circuit device comprising the clamp circuit according to any one of claims 1 to 7.

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