Protection circuit

Abstract

To provide a protective circuit having high operation precision and preventing overvoltage with respect to a circuit to be protected.SOLUTION: A protective circuit for protecting a circuit to be protected connected with an external output terminal from overvoltage, includes: a current path section connected with the external output terminal and including at least one first element; a reference voltage generation section for generating a reference voltage for output; and an amplifier circuit for outputting a target voltage on the basis of a difference between a first input voltage and a second input voltage. The amplifier circuit operates by taking the reference voltage as the first input voltage and a feedback voltage based on the target voltage as a second input voltage so as to output the target voltage to the current path section. The reference voltage generation section includes at least one second element with operation characteristics corresponding to operation characteristics of at least one first element of the current path section, and generates the reference voltage on the basis of a voltage drop by the at least one second element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a protection circuit, and more particularly to a protection circuit that protects a protected circuit from an overvoltage. [Background technology]

[0002] In the operation of a current output amplifier, if a load larger than expected is applied to the output of the amplifier, an overvoltage state occurs, which may destroy the amplifier. Therefore, in order to protect the amplifier from such overvoltage, a protection circuit is generally used to prevent the occurrence of such overvoltage. A clamp circuit is known as a circuit that protects the circuit to be protected (protected circuit) by fixing the voltage within a certain range so that an overvoltage is not input to the circuit to be protected.

[0003] For example, the following Patent Document 1 discloses a clamp circuit capable of setting a clamp voltage. Specifically, Patent Document 1 discloses a clamp circuit that uses a constant current source and multiple diodes to extract positive and negative clamp voltages centered on a reference voltage, and outputs a stable clamp voltage using two buffer circuits configured with a full feedback amplifier. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 8-23784 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the operational accuracy of the protection circuit is low due to the effects of process variation and temperature characteristics, it is necessary to set the level of the protection voltage to compensate for this, which causes a problem that the dynamic range of the protected circuit is sacrificed. In particular, when the protection circuit is configured using external components, the external components have process variation different from that of the elements that configure the protection circuit, and the temperature characteristics are unstable, which significantly reduces the operational accuracy, and there is a problem that trying to address this results in unnecessarily high costs.

[0006] In addition, the clamp circuit disclosed in Patent Document 1 requires a power supply voltage equal to or higher than the protection voltage for its operation. Furthermore, since the clamp circuit sets positive and negative clamp voltages using a string configuration in which diode elements are simply connected in series, the clamp voltage is easily dependent on the process variation and temperature characteristics of each diode element, and the operation precision is not sufficient. Therefore, an object of the present invention is to provide a protection circuit that is less susceptible to process variations and / or temperature characteristics, has high operational accuracy, and prevents an overvoltage from being applied to a protected circuit.

[0007] Another object of the present invention is to provide a protection circuit that allows the protection voltage to be set to a voltage equal to or higher than the power supply voltage and further allows the protection voltage to be arbitrarily adjusted. [Means for solving the problem]

[0008] The present invention, which aims to solve the above problems, includes the following invention-specific matters and technical features.

[0009] The present invention according to one aspect is a protection circuit that protects a protected circuit connected to an external output terminal from an overvoltage. The protection circuit includes a current path section connected to the external output terminal and including at least one first element, a reference voltage generation section that generates and outputs a reference voltage, and an amplifier circuit that outputs a target voltage based on a difference between a first input voltage and a second input voltage. The amplifier circuit operates with the reference voltage as the first input voltage and a feedback voltage based on the target voltage as the second input voltage, and outputs the target voltage to the current path section. The reference voltage generation section includes at least one second element having operating characteristics corresponding to the operating characteristics of the at least one first element of the current path section, and generates the reference voltage based on a voltage drop caused by the at least one second element.

[0010] The current path section can determine a protection voltage at the external output terminal based on the target voltage and a voltage corresponding to a voltage drop across the at least one first element. Moreover, the reference voltage generating unit may be configured to determine a predetermined voltage for generating the reference voltage. Moreover, the reference voltage generating section can output, as the reference voltage, a voltage that is dropped from the predetermined voltage based on a second current flowing through the at least one second element. Moreover, the reference voltage generating section may further include a second current source that outputs the second current.

[0011] Moreover, the reference voltage generating section may include a resistive element and a first current source that outputs a first current. The resistive element may be a variable resistive element whose resistance value is adjustable. Moreover, the reference voltage generating section can determine the predetermined voltage based on a value of the first current output from the first current source and the resistance value of the resistive element. Additionally, the first current source may be configured to generate the first current that is inversely proportional to the resistance value. The power supply voltage may further include a gain setting section that generates the feedback voltage based on the target voltage.

[0012] Moreover, the gain setting section may include a voltage dividing resistor, and the feedback voltage may be generated by the voltage dividing resistor. Moreover, the current path portion may include a first parallel connection block in which m1 first elements are connected in parallel, and n1 first parallel connection blocks are connected in series. Moreover, the reference voltage generating section may include a second parallel connection block in which m2 first elements are connected in parallel, and n2 second parallel connection blocks are connected in series.

[0013] Furthermore, the value of the current drawn by the external output terminal can be determined depending on the ratio between the number m1 of the first elements in the current path portion and the number m2 of the second elements in the reference voltage generating portion. In addition, a protection voltage at the external output terminal can be determined depending on a ratio between the number n1 of stages of the first parallel connection blocks in the current path portion and the number n2 of stages of the second parallel connection blocks in the reference voltage generation portion.

[0014] Further, the present invention according to another aspect is a protection circuit for protecting a protected circuit connected to an external output terminal from an overvoltage, comprising a first protection circuit block for protecting the protected circuit from the positive overvoltage and a second protection circuit block for protecting the protected circuit from the negative overvoltage. Each of the first protection circuit block and the second protection circuit block comprises a current path section connected to the external output terminal and including at least one first element, a reference voltage generation section for generating and outputting a reference voltage, and an amplifier circuit for outputting a target voltage based on a difference between a first input voltage and a second input voltage. The amplifier circuit operates with the reference voltage as the first input voltage and a feedback voltage based on the target voltage as the second input voltage, and outputs the target voltage to the current path section. The reference voltage generation section includes at least one second element having operating characteristics corresponding to the operating characteristics of the at least one first element of the current path section, and generates the reference voltage based on a voltage drop caused by the at least one second element.

[0015] In this specification, the term "means" does not simply mean physical means, but also includes cases where the functions of the means are realized by software. The functions of one means may be realized by two or more physical means, or the functions of two or more means may be realized by one physical means. Furthermore, the term "system" refers to a logical collection of multiple devices (or functional modules that realize specific functions), and it does not matter whether each device or functional module is contained within a single housing. Effect of the Invention

[0016] According to the present invention, a protection circuit that is less susceptible to process variations and / or temperature characteristics, has high operating accuracy, and prevents overvoltage to a protected circuit can be obtained. Furthermore, according to the present invention, a protection circuit can be obtained in which the protection voltage can be set to a voltage equal to or higher than the power supply voltage and can be arbitrarily adjusted. Other technical features, objects, and operational effects or advantages of the present invention will become apparent from the following embodiments described with reference to the accompanying drawings. The effects described in this specification are merely examples and are not limited thereto, and other effects may also be present. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a block diagram showing an example of a schematic configuration of a protection circuit according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an example of a specific configuration of a protection circuit according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram showing an example of a specific configuration of a protection circuit according to an embodiment of the present invention. [Figure 4] FIG. 4 is a block diagram showing an example of a schematic configuration of a protection circuit according to one embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram showing an example of a specific configuration of a protection circuit according to an embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of a portion of a specific configuration of a protection circuit according to one embodiment of the present invention. [Figure 7] FIG. 7 is a diagram for explaining the results of a simulation of a protection circuit according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and application of techniques not specified below. The present invention can be implemented by various modifications (for example, combining the respective embodiments) within the scope of the gist of the present invention. In addition, in the following description of the drawings, the same or similar parts are represented by the same or similar reference numerals. The drawings are schematic and do not necessarily correspond to actual dimensions, ratios, etc. The drawings may also include parts with different dimensional relationships and ratios.

[0019] [First embodiment] 1 is a block diagram illustrating an example of a schematic configuration of a protection circuit according to an embodiment of the present invention. As shown in the figure, the protection circuit 1 generally includes a current path section 11, a reference voltage generating section 12, an amplifier circuit 13, and a gain setting section 14. The protection circuit 1 is a circuit that prevents a voltage (i.e., an overvoltage) higher than a necessary voltage due to, for example, a disturbance from being applied to the protected circuit 2. In this disclosure, the threshold voltage before the overvoltage occurs is defined as a protection voltage (V PROTECT ) In other words, the protection circuit 1 is designed to set an arbitrary protection voltage and protects the protected circuit 2 connected to the external output terminal OUT from an overvoltage. As will be described in other embodiments, the protection voltage can be set on the positive side and the negative side in response to positive and negative overvoltages. The protection circuit 1 of this embodiment is designed to output a desired amount of current to the protected circuit 2 when the output voltage reaches the protection voltage, as will be described below.

[0020] In the figure, the current path section 11 is a circuit in which a path of a current output to the protected circuit 2 is formed. One end of the current path section 11 is connected to the external output terminal OUT, and a current I OUT is drawn in. The current path section 11 is configured to include, for example, at least one element (first element) such as a diode (see FIG. 2). In this embodiment, the current path section 11 is configured by a plurality of diodes connected in series. Such a connection configuration of diodes is called a diode string.

[0021] The reference voltage generating unit 12 is a circuit for generating and outputting a reference voltage VREF for the amplifier circuit 13. The reference voltage generating unit 12 includes, for example, two current sources independent of each other, a variable resistance element, and at least one element (second element) such as a diode (see FIG. 2). As described later, the first current source of the reference voltage generating unit 12 is used to generate a constant voltage VB that is the basis of the reference voltage VREF, while the second current source is used to determine a current IB flowing through the second element. The reference voltage VREF is determined by the voltage VB and a voltage drop due to the current IB flowing through the second element. The second element in the reference voltage generating unit 12 is selected so that its operating characteristics are substantially the same as those of the first element in the current path unit 11.

[0022] The amplifier circuit 13 is a differential amplifier circuit that outputs a predetermined voltage based on the voltage difference between two input voltages. In the present disclosure, the voltage output by the amplifier circuit 13 is referred to as a target voltage V T As will be described later, the target voltage V T By determining the protection voltage V PROTECT is determined. The target voltage V T is fed back as one of the input voltages via a feedback path. That is, the amplifier circuit 13 receives the reference voltage V REF is the first input voltage, and the target voltage V T Feedback voltage based on V FB is set as the second input voltage, and the target voltage V is tracked so that the voltage difference between the first input voltage and the second input voltage becomes zero. T The amplifier circuit 13 outputs a so-called operational amplifier.

[0023] The gain setting unit 14 is provided in a feedback path between the output and input of the amplifier circuit 13, and is a circuit for setting the gain of the amplifier circuit 13. Here, the feedback ratio is set to 1 / β, and the output voltage of the amplifier circuit 13 (the target voltage V T ) is the reference voltage V REFThe gain setting section 14, which becomes β times the gain, includes, for example, at least one resistive element (see FIG. 2).

[0024] Fig. 2 is a diagram showing an example of a specific configuration of a protection circuit according to one embodiment of the present invention, that is, Fig. 2 shows an equivalent circuit of the protection circuit 1 shown in Fig. 1. As shown in the figure, the current path section 11 includes, for example, diodes 111 connected in series. In the present disclosure, the diode 111 is one form of a first element. In this example, four diodes 111(1) to 111(4) are connected in series. The anode of the first-stage diode 111(1) is connected to the external output terminal OUT, and the cathode of the fourth-stage diode 111(4) is connected to the target voltage V T Node N where T In this disclosure, the voltage drop (potential difference between the anode and cathode) of one diode 111 is defined as V D1 Therefore, the potential difference due to the four diodes 111(1) to 111(4) is 4×V D1 Therefore, the target voltage V T The protection voltage is V PROTECT As, V T =V PROTECT -4×V D1 It becomes.

[0025] The reference voltage generating unit 12 includes, for example, a first current source 121, a second current source 122, a resistive element 123, and a diode . The first current source 121 outputs a current I A (I A The resistor element 123 is, for example, a variable resistor element that can be set to an arbitrary resistance value, and outputs a current I A Based on the voltage V B The resistor element 123 may be a fixed resistor element having a predetermined resistance value instead of a variable resistor element. In this example, the current I A Voltage V BThe resistance value of the resistor element 123 when A is a current inversely proportional to the resistance value R. Therefore, if the resistance value of the resistive element 123 is R, the process variations of the resistive elements are cancelled out, and thus the voltage V B You will be able to obtain the following.

[0026] The second current source 122 controls the current I B In the figure, two second current sources 122 are shown. That is, the second current sources 122 cause a current I B The second current source 122 is configured to be able to operate independently of the first current source 121.

[0027] The diode 124 has its anode connected to the output terminal of the second current source 122 and its cathode connected to the node N REF The diode 124 is connected to the first input of the amplifier circuit via a first resistor R111. In the present disclosure, the diode 124 is one form of the second element. The diode 124 is selected such that its operating characteristics are substantially the same as those of the diode 111.

[0028] Here, the current I B When current flows through diode 124, the potential difference due to diode 124 is V D2 The output terminal of the upper second current source 122 is connected to the output terminal of the first current source 121, and the current I B does not flow to the resistor element 123, and the node N REF (i.e., the reference voltage V REF ) is the voltage V B and voltage V D2 This is the difference between the two.

[0029] As described above, the amplifier circuit 13 is a differential amplifier circuit. The first input terminal of the amplifier circuit 13 is connected to the node N REF, while the second input terminal is connected to node N FB , and the output terminal is connected to the gate of the MOSFET 131. That is, the amplifier circuit 13 has a node N REF The reference voltage V that appears at REF is the first input voltage, and the node N FB The feedback voltage V that appears at FB is the second input voltage, and the target voltage V is tracked so that the voltage difference between the first input voltage and the second input voltage becomes zero. T The function operates to output the following. The MOSFET 131 is, for example, an N-channel MOSFET that constitutes the amplifier circuit 13. The drain of the MOSFET 131 is connected to a node N T and the gate of the diode 111(4) is connected to the output terminal of the amplifier circuit 13.

[0030] The gain setting section 14 may be configured to include, for example, a voltage dividing resistor made up of a plurality of resistor elements 141 connected in series. In this example, four resistor elements 141(1) to 141(4) are connected in series, and a node N FB to feedback voltage V FB That is, the feedback voltage V FB V T ×1 / 4. In addition, the voltage V α is shown as a voltage at which the current source 142 can operate. Therefore, the power supply voltage of the protection circuit 1 is V DD Then, the protection circuit 1 is as follows: V DD >V T +V α It operates under the following conditions.

[0031] In the protection circuit 1 configured as above, the operation characteristics of the diode 111 and the diode 124 are substantially the same. As described above, the reference voltage V REF teeth, V REF=V B -V D2 As shown in the figure. In addition, due to the operating characteristics of the amplifier circuit 13, V FB =V REF and the target voltage V T teeth, V T =4×V FB It becomes. Therefore, the output voltage V OUT teeth, V OUT =V T +4×V D1 =4×V B +4×V D1 -4×V D2 It becomes.

[0032] In other words, the protected circuit 2 is normally connected to 4×V B Smaller range of output voltage V OUT (V OUT <4×V B ) and the output voltage V OUT is 4×V B More than (V OUT ≧4×V B ) is applied to the protected circuit 2, the protection circuit 1 functions to protect the protected circuit 2. In other words, when the output voltage V OUT is 4×V B When it reaches the current I B and the output current I OUT The relationship between I OUT =I B As described above, in this example, the operating characteristics of the diode 111 and the diode 124 are substantially the same. Therefore, the output voltage V OUT is 4×V B If so, the current I B The output current I is equal to OUT This will be obtained.

[0033] As described above, according to this embodiment, the protection circuit 1 sets a protection voltage for protecting the protected circuit 2 from an overvoltage to a power supply voltage V DD In other words, the protection circuit 1 can be set to a voltage higher than the target voltage V T The voltage difference according to the number of diodes 111 (4 × V in this example) D1 ) higher. In addition, according to this embodiment, the output voltage V OUT is the voltage V B This is a circuit configuration that depends on the voltage V B is determined by the resistance R, so the output voltage V OUT Unlike the conventional configuration in which the voltage is set according to the number of connected stages (number of diodes), it is possible to set the voltage with high precision (for example, in units of several mV).

[0034] In addition, in protection circuit 1, the target voltage V T (V PROTECT -4×V D1 ) and feedback voltage V FB ((V PROTECT -4×V D1 ) / 4) can be taken into consideration when selecting the MOSFET 131, so that the MOSFET 131 with a low rated voltage can be adopted, ensuring design freedom. Similarly, the options for the amplifier circuit 13 and the current source 142 are expanded, ensuring design freedom.

[0035] [Second embodiment] This embodiment is a modification of the first embodiment, and is characterized in that the protection voltage and the magnitude of the drawn current can be optimized by the configuration of a first element in the current path section and the configuration of a second element in the corresponding reference voltage generating section. 3 is a diagram showing an example of a specific configuration of a protection circuit according to an embodiment of the present invention. As shown in the figure, the current path section 11 has a configuration in which a group of a plurality of diodes 111 connected in parallel is connected in series. Similarly, the reference voltage generation section 12 has a configuration in which a group of a plurality of diodes 124 connected in parallel is connected in series. Also, in the figure, the voltage dividing resistors in the gain setting section 14 are shown as resistance elements 141(1) and 141(2).

[0036] That is, the current path section 11 of the present embodiment has a configuration in which n1 parallel connection blocks (first parallel connection blocks) each configured by connecting m1 diodes 111 in parallel are connected in series. That is, the current path section 11 is configured to include m1×n1 diodes 111.

[0037] On the other hand, the reference voltage generating unit 12 has a configuration in which n2 parallel connection blocks (second parallel connection blocks) each configured by connecting m2 diodes 124 in parallel are connected in series. That is, the current path unit 11 is configured to include m2×n2 diodes 124. Note that the operation characteristics of each diode 111 and each diode 124 are substantially the same.

[0038] The resistance values ​​of the resistive elements 141(1) and 141(2) in the gain setting unit 14 are R FB1 and R FB2 The feedback voltage V FB teeth, V FB =V T ×R FB2 / (R FB1 +R FB2 ) Therefore, the relationship between the number of parallel connected blocks, n1 and n2, is as follows: n2 / n1=R FB2 / (R FB1 +R FB2 ) So that R FB1 and R FB2 The resistance value of each of these is determined. Therefore, the output voltage V OUT teeth, V OUT =V B ×(n1 / n2) When I OUT =I B ×(m1 / m2) It becomes.

[0039] In other words, by increasing the ratio of the number of parallel-connected blocks, n1 and n2 (n1 / n2), the voltage V B In addition, by setting the ratio (m1 / m2) of the number m1 of the diodes 111 and the number m2 of the diodes 124 connected in parallel to a large value, the protection voltage can be increased with respect to the current I B Current I drawn by protection circuit 1 OUT can be made larger. The protection circuit 1 of the first embodiment has a configuration where m1 / m2=1 and n1 / n2=4.

[0040] As described above, according to this embodiment, it is possible to obtain the same advantages or effects as those of the first embodiment. In particular, according to this embodiment, it is possible to arbitrarily adjust the protection voltage and the amount of current drawn by the protection circuit 1 based on the ratio (n1 / n2) of the number of parallel-connected blocks in the current path section 11 and the reference voltage generating section 12, and the ratio (m1 / m2) of the number of diodes 111 connected in parallel to the number of diodes 124.

[0041] [Third embodiment] This embodiment is a modification of the first embodiment, and is characterized in that it is possible to set positive and negative protection voltages in response to positive (upper limit) and negative (lower limit) overvoltages of the protected circuit. 4 is a diagram showing an example of a schematic configuration of a protection circuit according to an embodiment of the present invention. As shown in the diagram, the protection circuit 1 of this embodiment is configured to include two circuit blocks, that is, a first protection circuit block 10 and a second protection circuit block 10'. The first protection circuit block 10 and the second protection circuit block 10' are configured symmetrically to each other so as to correspond to positive and negative voltages, as described below.

[0042] Fig. 5 is a diagram showing an example of a specific configuration of a protection circuit according to an embodiment of the present invention. In the diagram, a first protection circuit block 10 has the same circuit configuration as that shown in Fig. 2, and therefore a description thereof will be omitted. The second protection circuit block 10' has the same basic circuit configuration as the first protection circuit block 10, but in order to set a negative protection voltage, the orientation of the diode 111' in the current path section 11' is reversed, and accordingly, some elements are also configured symmetrically with respect to positive and negative voltages.

[0043] In the second protection circuit block 10′, the reference voltage V REF 'teeth, V REF '=V B '+V D2 ' It is shown that: In addition, the feedback voltage V FB 'teeth, V FB '=V T '+3 / 4×V DD -3 / 4×V T ' =3 / 4×V DD +V T ' / 4 Therefore, the output voltage V OUT teeth, V OUT '=V T '-4×V D1 It becomes. Also, V B '+V D2 '=3 / 4×V DD +V OUT' / 4+V D1 ' Therefore, V OUT '=-3×V DD +4×V B '-4×V D1 '+4×V D2 ' It becomes.

[0044] In other words, the protected circuit 2 is normally connected to 4×V B '-3×V DD Larger range of output voltage V OUT (V OUT >4×V B '-3×V DD ) and the output voltage V OUT is 4×V B '-3×V DD Below (V OUT ≦4×V B '-3×V DD When a negative overvoltage, such as the output voltage V OUT is 4×V B '-3×V DD When it reaches the current I B ' and the output current I OUT The relationship between I OUT '=I B ' It becomes. That is, the second protection circuit block 10′ that sets the negative protection voltage is OUT ' is 4 × V B '-3×V DD If so, the current I B The output current I is equal to OUT ' can be obtained.

[0045] As described above, according to this embodiment, it is possible to obtain the same advantages and effects as the above-mentioned embodiments. In particular, according to this embodiment, since the protection circuit block 10' in which the negative protection voltage for the protected circuit 2 is set is further provided, it is possible to reliably protect the protected circuit 2 from positive and negative overvoltages.

[0046] [Fourth embodiment] This embodiment is a modification of the above embodiment, and is characterized in that it is possible to set positive and negative protection voltages in response to positive and negative overvoltages of the protected circuit, while optimizing the magnitude of the protection voltages and the draw current. 6 is a diagram showing an example of a part of a specific configuration of a protection circuit according to an embodiment of the present invention. That is, the diagram shows only the second protection circuit block 10' of the protection circuit 1 including the first protection circuit block 10 for setting a positive protection voltage and the second protection circuit block 10' for setting a negative protection voltage. The first protection circuit block 10 has the same circuit configuration as that shown in FIG. 3, so a description thereof will be omitted. Although not shown, as would be understood by a person skilled in the art upon reading this disclosure, the second protection circuit block 10' includes a current path section 11', a reference voltage generating section 12', an amplifier circuit 13', and a gain setting section 14'.

[0047] As shown in the figure, in the protection circuit 1 of this embodiment, the current path section 11' of the second protection circuit block 10' has a configuration in which a group of a plurality of parallel-connected diodes 111' is connected in series (cascade). Similarly, the reference voltage generating section 12' has a configuration in which a group of a plurality of parallel-connected diodes 124' is connected in series. Also, in the figure, the voltage dividing resistors in the gain setting section 14' are shown as resistance elements 141(1)' and 141(2)'.

[0048] That is, the current path section 11' in this embodiment has a configuration in which n1 (n1≧1) parallel connection blocks, each of which is configured by connecting m1 (m1≧1) diodes 111' in parallel, are connected in series. That is, the current path section 11 is configured to include m1×n1 diodes 111'.

[0049] On the other hand, the reference voltage generating unit 12' has a configuration in which n2 (n2≧1) parallel connection blocks, each of which is configured by connecting m2 (m2≧1) diodes 124' in parallel, are connected in series. That is, the current path unit 11 is configured to include m2×n2 diodes 124'. Note that the operation characteristics of each diode 111' and each diode 124' are substantially the same.

[0050] The reference voltage V REF 'teeth, V REF '=V B '+n2×V D2 ' As shown in the figure. Here, the relationship between the number of parallel-connected blocks, n1 and n2, is as follows: n2 / n1=R FB1 ' / (R FB1 '+R FB2 ') So that R FB1 ' and R FB2 The resistance value of each of the resistors .times. ...

[0051] In addition, the resistance values ​​of the resistive elements 141(1)' and 141(2)' in the gain setting unit 14' are R FB1 ' and R FB2 The feedback voltage V FB 'teeth, V FB '=V T '+R FB2 ' / (R FB1 '+R FB2 ')×(V DD -V T ') ={(n1-n2) / n1}×V DD +n2 / n1×V T ' Therefore, the target voltage V T 'teeth, V T '=n1 / n2×V FB '+{(n2-n1) / n2}×V DD It becomes.

[0052] Therefore, the output voltage V OUT 'teeth, V OUT '=V T '-n1×V D1 ' = n1 / n2 × V B '+{(n2-n1) / n2}×V DD +n1×V D2 '-n1×V D1 ' Therefore, the output voltage V OUT 'teeth, V OUT '=n1 / n2×V B '+{(n2-n1) / n2}×V DD When I OUT '=I B '×(m1 / m2) It becomes.

[0053] Therefore, the output voltage V OUT 'but, V OUT '=(n1 / n2)×V B '+{(n2-n1) / n2}×V DD When B ' and the output current I OUT The relationship between I OUT '=I B '×(m1 / m2) It becomes.

[0054] In other words, by increasing the ratio of the number of parallel-connected blocks, n1 and n2 (n1 / n2), the voltage V B In addition, by setting the ratio (m1 / m2) of the number m1 of the diodes 111' and the number m2 of the diodes 124' connected in parallel to each other to a large value, the current I B Current I drawn by protection circuit 1 relative to OUT ' can be made larger on the negative side.

[0055] In this embodiment, the configuration of the diodes 111' in the current path section 11' in the second protection circuit block 10' (i.e., the number of parallel connections and the number of stages) and the configuration of the diodes 124' in the reference voltage generating section 12' (i.e., the number of parallel connections and the number of stages) are the same as those in the first protection circuit block 10, respectively, but are not limited to this.

[0056] (Simulation results) A simulation was performed on the operating characteristics (process variation and temperature variation) of the protection circuit 1 according to the present invention (see FIG. 2). For comparison, a simulation was performed on the operating characteristics of a protection circuit with a conventional diode string configuration (hereinafter referred to as the "conventional protection circuit"). Note that the diode string configuration was four stages in both the conventional protection circuit and the protection circuit 1 according to the present invention.

[0057] In the simulation, a protection circuit consisting of process fast and process slow diodes was used to evaluate process and temperature variations. A process fast semiconductor (diode in this example) is one with a high doping amount at the PN junction in the semiconductor manufacturing process, and a process slow semiconductor is one with a low doping amount at the PN junction in the semiconductor manufacturing process.

[0058] 7 is a diagram for explaining the results of a simulation of a protection circuit according to an embodiment of the present invention. First, FIG. 7(a) is a graph showing the relationship between temperature and output voltage in a conventional protection circuit. As shown in FIG. 7(a), the output voltage difference between the conventional protection circuit with a fast process and the conventional protection circuit with a slow process was about 0.1V. In addition, the change in output voltage with respect to a temperature change from -40 degrees to +120 degrees was about 0.7V.

[0059] In contrast, Fig. 1(b) is a graph showing the relationship between temperature and output voltage in the protection circuit 1 according to the present invention (see Fig. 2). As shown in Fig. 1(b), almost no process variation or temperature variation was observed in the protection circuit 1 according to the present invention. As described above, in the protection circuit 1 according to the present invention, the process variations and temperature variations could be suppressed by 99% or more.

[0060] As described above, according to this embodiment, it is possible to obtain the same advantages and effects as the above-mentioned embodiments. In particular, according to this embodiment, even in the protection circuit block 10' in which a negative protection voltage for the protected circuit 2 is set, it is possible to arbitrarily adjust the negative protection voltage of the protection circuit 1 and the amount of current drawn. The above-described embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments. The present invention can be embodied in various forms without departing from the spirit of the present invention.

[0061] For example, in the methods disclosed herein, steps, operations, or functions may be performed in parallel or in a different order, provided that the results are consistent. The steps, operations, and functions described are provided merely as examples, and some of the steps, operations, and functions may be omitted or combined into one, or other steps, operations, or functions may be added, without departing from the spirit of the invention. In addition, although various embodiments are disclosed in this specification, specific features (technical matters) in one embodiment can be added to or replaced with specific features in other embodiments, with appropriate modifications, and such forms are also included in the spirit of the present invention.

[0062] The functions of the elements disclosed herein may be implemented using circuitry or processing circuitry including general purpose processors, special purpose processors, integrated circuits, ASICs ("application specific integrated circuits"), conventional circuitry, and / or combinations thereof configured to execute the disclosed elements or programmed to execute the disclosed functions. A processor is considered to be a processing circuitry or circuitry when it includes transistors and other circuitry therein. In this disclosure, a circuitry, unit, or means is hardware that performs the recited function or hardware that is programmed to perform the recited function. The hardware may be any hardware disclosed herein or other known that is programmed to perform the recited function or configured to perform the recited function. When the hardware is a processor, which may be considered as a type of circuitry, the circuitry, means, or unit is a combination of hardware and software, software used to configure the hardware, and / or processor. [Explanation of symbols]

[0063] 1…Protection circuit 10...First protection circuit block 10'...Second protection circuit block 11, 11'...Current path section 111,111'...Diode 12, 12': Reference voltage generating section 121,121'…First current source 122,122'…Second current source 123, 123'...Resistance element 124,124'...Diode 13,13'...Amplification circuit 131,131'...MOSFET 14,14'...Gain setting section 141, 141'...resistance element 142,142'...Current source

Claims

1. A protection circuit for protecting a protected circuit connected to an external output terminal from an overvoltage, comprising: a current path portion connected to the external output terminal and including at least one first element; a reference voltage generating unit that generates and outputs a reference voltage; an amplifier circuit that outputs a target voltage based on a difference between a first input voltage and a second input voltage; the amplifier circuit operates using the reference voltage as the first input voltage and a feedback voltage based on the target voltage as a second input voltage, and outputs the target voltage to the current path portion; The reference voltage generating unit is at least one second element having an operational characteristic corresponding to an operational characteristic of the at least one first element of the current path portion; generating the reference voltage based on a voltage drop across the at least one second element; protection circuit.

2. the current path unit determines a protection voltage at the external output terminal based on the target voltage and a voltage corresponding to a voltage drop caused by the at least one first element.

2. The protection circuit of claim 1.

3. The reference voltage generating unit is configured to determine a predetermined voltage for generating the reference voltage.

3. The protection circuit according to claim 1 or 2.

4. the reference voltage generating unit outputs, as the reference voltage, a voltage obtained by dropping the voltage from the predetermined voltage based on a second current flowing through the at least one second element; 4. The protection circuit of claim 3.

5. the reference voltage generating unit further includes a second current source that outputs the second current.

5. The protection circuit of claim 4.

6. The reference voltage generating unit is A resistive element; a first current source that outputs a first current; 6. A protection circuit according to claim 1.

7. The resistive element is a variable resistive element whose resistance value is adjustable.

7. The protection circuit of claim 6.

8. the reference voltage generating unit determines the predetermined voltage based on a value of the first current output from the first current source and the resistance value of the resistive element. A protection circuit according to claim 7 which recites claim 3.

9. the first current source is configured to generate the first current inversely proportional to the resistance value; 9. A protection circuit according to claim 7 or 8.

10. a gain setting unit that generates the feedback voltage based on the target voltage, A protection circuit according to any one of claims 1 to 9.

11. the gain setting section includes a voltage dividing resistor; generating the feedback voltage by the voltage divider resistor; The protection circuit of claim 10.

12. the current path portion includes a first parallel connection block in which m1 first elements are connected in parallel, and n1 first parallel connection blocks are connected in series; A protection circuit according to any one of claims 1 to 11.

13. the reference voltage generating unit includes a second parallel connection block in which m2 first elements are connected in parallel, and n2 second parallel connection blocks are connected in series.

13. The protection circuit of claim 12.

14. a value of a current drawn into the external output terminal is determined depending on a ratio between a number m1 of the first elements in the current path portion and a number m2 of the second elements in the reference voltage generating portion; 14. The protection circuit of claim 13.

15. a protection voltage at the external output terminal is determined depending on a ratio between a number n1 of stages of the first parallel-connected blocks in the current path section and a number n2 of stages of the second parallel-connected blocks in the reference voltage generating section; 15. A protection circuit according to claim 13 or 14.

16. A protection circuit for protecting a protected circuit connected to an external output terminal from an overvoltage, comprising: a first protection circuit block for protecting the protected circuit from the positive overvoltage; a second protection circuit block for protecting the protected circuit from the negative overvoltage; Each of the first protection circuit block and the second protection circuit block includes: a current path portion connected to the external output terminal and including at least one first element; a reference voltage generating unit that generates and outputs a reference voltage; an amplifier circuit that outputs a target voltage based on a difference between a first input voltage and a second input voltage; the amplifier circuit operates using the reference voltage as the first input voltage and a feedback voltage based on the target voltage as a second input voltage, and outputs the target voltage to the current path portion; The reference voltage generating unit is at least one second element having an operational characteristic corresponding to an operational characteristic of the at least one first element of the current path portion; generating the reference voltage based on a voltage drop across the at least one second element; A protection circuit configured as follows.

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