Voltage clamp circuit and power amplifier

Abstract

To provide a voltage clamp circuit with desirable characteristics for preventing damage to high-frequency amplification circuits. [Solution] In the voltage clamp circuit 30, the anode of the second diode 32 is connected to the cathode-side node of the first diode circuit 31, a first impedance element 34 is connected between the cathode of the second diode and a reference potential, and a first current source 35 is connected to the node where the first impedance element and the second diode are interconnected, supplying a current Icont toward the reference potential to the first impedance element. A switching circuit 33 is connected between the output node of the high-frequency amplifier circuit 20 and the reference potential. The first current source includes a temperature-dependent element that changes its electrical characteristics in response to temperature changes, and the switching circuit includes a control node connected to the node where the first diode circuit and the second diode are interconnected, which conducts when the voltage of the control node exceeds a threshold voltage.

Description

Technical Field

[0001] The present invention relates to a voltage clamp circuit and a power amplifier.

Background Art

[0002] The output current and output voltage of a high-frequency power amplifier circuit vary greatly according to fluctuations in load impedance. There is a demand for higher output in the high-frequency power amplifier circuit, and there is also a demand for improvement in the withstand voltage characteristics during load impedance fluctuations. A power amplifier that improves the withstand voltage characteristics by inserting a voltage clamp circuit between the output node of the high-frequency power amplifier circuit and the reference potential is known (Patent Document 1). The voltage clamp circuit disclosed in Patent Document 1 includes a diode circuit composed of a plurality of diodes connected in multiple stages, and a resistor element connected in series to the diode circuit. The resistor element is composed of a part of an epitaxial layer formed on a substrate.

[0003] When an excessive high voltage occurs at the output node of the high-frequency power amplifier circuit, a current flows through the voltage clamp circuit, thereby preventing the breakdown of the transistor of the high-frequency power amplifier circuit. The breakdown voltage of the transistor of the high-frequency power amplifier circuit has temperature dependence, and particularly the breakdown voltage decreases at low temperatures. In order to prevent the breakdown of the transistor at low temperatures, it is preferable that the voltage clamp circuit conducts at a lower voltage at low temperatures.

[0004] However, generally, the forward voltage of a diode has a negative temperature coefficient. That is, the forward voltage of the diode becomes higher at low temperatures. If the number of stages of the diode circuit is set according to the high temperature at which the breakdown voltage is relatively high, sufficient voltage clamping cannot be performed at low temperatures, and the breakdown of the transistor is likely to occur.

[0005] The resistance of the resistive element formed from an epitaxial layer used in the voltage clamp circuit described in Patent Document 1 has a positive temperature coefficient. That is, the voltage drop across the resistive element decreases at low temperatures. Therefore, by connecting a resistive element in series with a diode circuit, the temperature dependence of the forward voltage of the diode circuit can be mitigated. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2023 / 210163 [Overview of the project] [Problems that the invention aims to solve]

[0007] By adopting the voltage clamp circuit configuration described in Patent Document 1, it is possible to mitigate the temperature dependence of the forward voltage of the diode circuit to some extent. However, voltage clamp circuits applied to high-frequency power amplifier circuits require a conduction threshold voltage that is low at low temperatures and high at high temperatures. It is difficult to achieve such characteristics with the voltage clamp circuit described in Patent Document 1.

[0008] An object of the present invention is to provide a voltage clamp circuit having desirable characteristics for preventing the breakdown of a high-frequency amplification circuit. Another object of the present invention is to provide a power amplifier having this voltage clamp circuit. [Means for solving the problem]

[0009] According to one aspect of the present invention, A first diode circuit including multiple first diodes connected in multiple stages, the anode node of which is connected to the output node of a high-frequency amplifier circuit, The anode of the second diode is connected to the cathode-side node of the first diode circuit, A first impedance element connected between the cathode of the second diode and the reference potential, A first current source is connected to a node in which the first impedance element and the second diode are interconnected, and the first impedance element is supplied with a current toward a reference potential. A switching circuit connected between the output node of the high-frequency amplifier circuit and the reference potential. Equipped with, The first current source includes a temperature-dependent element that changes its electrical characteristics in response to temperature changes, and supplies a current having a negative temperature coefficient with respect to the temperature change of the temperature-dependent element to the first impedance element. The switching circuit includes a control node connected to a node in which the first diode circuit and the second diode are interconnected, and a voltage clamp circuit is provided that conducts when the voltage of the control node exceeds a threshold voltage.

[0010] According to another aspect of the present invention, The voltage clamp circuit and, The high-frequency amplification circuit and A power amplifier equipped with [this feature] is provided. [Effects of the Invention]

[0011] As the temperature decreases, the current flowing through the first impedance element increases, causing the potential of the node where the second diode and the first impedance element are interconnected to rise. As a result, the voltage at the control node of the switching circuit also rises. Therefore, if the voltage at the output node of the high-frequency amplifier circuit rises excessively, the switching circuit will conduct at a lower voltage. This characteristic of the voltage clamp circuit is desirable for preventing the high-frequency amplifier circuit from being damaged in response to temperature changes. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic equivalent circuit diagram of a power amplifier having a voltage clamp circuit 30 according to the first embodiment. [Figure 2]FIG. 2A is a graph showing an example of the relationship between the temperature of the temperature-dependent element included in the first current source 35 and the current Icont, and FIG. 2B is a graph showing an example of the relationship between the temperature and each of the voltages V1 and V2 when the voltage Vout at the output node 20A of the high-frequency amplifier circuit 20 is constant. [Figure 3] FIG. 3 is a graph showing an example of the relationship between the current Ic flowing through the switching circuit 33 and the voltage Vout at the output node 20A. [Figure 4] FIG. 4 is a schematic equivalent circuit diagram of a power amplifier having the voltage clamp circuit 30 according to the second embodiment. [Figure 5] FIG. 5 is a graph showing an example of the relationship between the current Ic flowing through the switching circuit 33 and the voltage Vout at the output node 20A. [Figure 6] FIG. 6 is a schematic equivalent circuit diagram of a power amplifier having the voltage clamp circuit 30 according to a modified example of the second embodiment. [Figure 7] FIG. 7 is a schematic equivalent circuit diagram of a power amplifier having the voltage clamp circuit 30 according to the third embodiment. [Figure 8] FIG. 8 is an equivalent circuit diagram of the first current source 35 used in the voltage clamp circuit 30 according to the fourth embodiment. [Figure 9] FIG. 9 is an equivalent circuit diagram of a voltage clamp circuit according to a modified example of the fourth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] [First Embodiment] Referring to FIGS. 1 to 3, the voltage clamp circuit according to the first embodiment will be described.

[0014] FIG. 1 is a schematic equivalent circuit diagram of a power amplifier having the voltage clamp circuit 30 according to the first embodiment. The power amplifier includes a high-frequency amplifier circuit 20, a voltage clamp circuit 30, and a surge voltage protection circuit 28. The high-frequency amplifier circuit 20 has a configuration in which a plurality of cells each having a transistor 20Q, an input capacitor 20C, and a ballast resistance element 20R are connected in parallel. In FIG. 1, only one cell is shown.

[0015] As the transistor 20Q, for example, a heterojunction bipolar transistor (HBT) is used. A power supply voltage Vcc is applied to the collector of the transistor 20Q via a choke coil 26. The emitter of the transistor 20Q is connected to a reference potential. A high-frequency signal RFin is input to the base of the transistor 20Q via an input capacitor 20C. A base bias is supplied from a bias circuit 25 to the base of the transistor 20Q via a ballast resistor element 20R. The collector of the transistor 20Q functions as an output node 20A of the high-frequency amplification circuit 20. An amplified high-frequency signal RFout is output from the output node 20A. The voltage of the output node 20A is denoted as Vout.

[0016] A voltage clamp circuit 30 and a surge voltage protection circuit 28 are connected between the output node 20A of the high-frequency amplification circuit 20 and the reference potential. The surge voltage protection circuit 28 includes two diodes connected in two stages. The diodes of the surge voltage protection circuit 28 are connected in a direction opposite from the output node 20A of the high-frequency amplification circuit 20 toward the reference potential.

[0017] The voltage clamp circuit 30 includes a first diode circuit 31, a second diode 32, a switching circuit 33, a first impedance element 34, and a first current source 35. The first diode circuit 31 includes a plurality of first diodes 31D connected in multiple stages. The node on the anode side of the first diode circuit 31 is connected to the output node 20A of the high-frequency amplification circuit 20.

[0018] The anode of the second diode 32 is connected to the cathode-side node of the first diode circuit 31. The first impedance element 34 is connected between the cathode of the second diode 32 and the reference potential. The first current source 35 is connected between the node where the first impedance element 34 and the second diode 32 are interconnected and the reference potential. The first current source 35 supplies the first impedance element 34 with a current Icont directed toward the reference potential. The second diode 32 prevents the current Icont supplied from the first current source 35 from flowing into the switching circuit 33. The voltage generated at the node where the first impedance element 34 and the second diode 32 are interconnected is denoted as V2.

[0019] The first current source 35 includes a temperature-dependent element that changes its electrical characteristics in response to temperature changes. The current Icont supplied from the first current source 35 to the first impedance element 34 has a negative temperature coefficient with respect to the temperature change of the temperature-dependent element. As an example of the electrical characteristics of the temperature-dependent element, when the temperature of the temperature-dependent element rises, the current Icont supplied to the first impedance element 34 decreases, and when the temperature of the temperature-dependent element falls, the current Icont supplied to the first impedance element 34 increases.

[0020] The temperature-dependent element included in the first current source 35 is thermally coupled to the first diode circuit 31. Therefore, the temperature of the temperature-dependent element reflects the temperature of the first diode circuit 31. That is, when the temperature of the first diode circuit 31 rises, the current Icont supplied to the first impedance element 34 decreases, and when the temperature of the first diode circuit 31 falls, the current Icont supplied to the first impedance element 34 increases.

[0021] The switching circuit 33 is connected between the output node 20A of the high-frequency amplifier circuit 20 and the reference potential. The switching circuit 33 includes a control node 33C connected to the node where the first diode circuit 31 and the second diode 32 are interconnected. The voltage generated at the node where the first diode circuit 31 and the second diode 32 are interconnected is denoted as V1. When the voltage V1 at the control node 33C exceeds the threshold voltage, the switching circuit 33 conducts. The current flowing from the output node 20A through the switching circuit 33 to the reference potential is denoted as Ic.

[0022] Figure 2A is a graph showing an example of the relationship between the temperature of a temperature-dependent element included in the first current source 35 (Figure 1) and the current Icont. The horizontal axis represents temperature, and the vertical axis represents the value of the current. When the temperature of the temperature-dependent element rises, the current Icont decreases, and when the temperature of the temperature-dependent element falls, the current Icont increases.

[0023] Figure 2B is a graph showing an example of the relationship between voltages V1 and V2 and temperature when the voltage Vout at the output node 20A of the high-frequency amplifier circuit 20 (Figure 1) is constant. The horizontal axis represents temperature, and the vertical axis represents the voltage value. It is assumed that the first diode circuit 31 and the second diode 32 are in the off state, and that only the current Icont from the first current source 35 is flowing through the first impedance element 34.

[0024] As the temperature rises, the current Icont decreases as shown in Figure 2A, causing the voltage V2 to decrease. Voltage V1 is equal to the value obtained by dividing the voltage Vout-V2 between the output node 20A of the high-frequency amplifier circuit 20 and the cathode of the second diode 32 by the first diode circuit 31 and the second diode 32. Therefore, voltage V1 also decreases as the temperature rises. Also, if the voltage Vout at the output node 20A increases, voltage V1 also increases.

[0025] Figure 3 is a graph showing an example of the relationship between the current Ic flowing through the switching circuit 33 and the voltage Vout at the output node 20A. The horizontal axis represents the voltage Vout at the output node 20A of the high-frequency amplifier circuit 20, and the vertical axis represents the current Ic flowing through the switching circuit 33. The three solid lines in the graph shown in Figure 3 represent the current Ic when the temperature of the temperature-dependent element of the first current source 35 is different.

[0026] As the voltage Vout at output node 20A increases, the voltage V1 also increases. When voltage V1 exceeds the threshold voltage of the switching circuit 33, the switching circuit 33 conducts, and current Ic begins to flow. As the temperature decreases, voltage V1 increases as shown in Figure 2B. Therefore, when voltage V1 increases in conjunction with the increase in voltage Vout, voltage V1 is more likely to exceed the threshold voltage of the switching circuit 33. Consequently, at lower temperatures, the voltage Vout at output node 20A when current Ic begins to flow is lower.

[0027] Next, we will describe the excellent effects of the first embodiment. When the voltage Vout at the output node 20A of the high-frequency amplifier circuit 20 (Figure 1) rises, the voltage V1 also rises, and when the voltage V1 exceeds the threshold voltage of the switching circuit 33, the switching circuit 33 conducts. By setting the number of stages of the first diode circuit 31, the electrical characteristics of the first impedance element 34, the current Icont, and the threshold voltage of the switching circuit 33 so that the switching circuit 33 conducts when the voltage Vout at the output node 20A reaches the breakdown voltage of the transistor 20Q, the breakdown of the transistor 20Q of the high-frequency amplifier circuit 20 can be suppressed.

[0028] Furthermore, in the first embodiment, as shown in Figure 3, when the temperature of the temperature-dependent element of the first current source 35 and the first diode circuit 31 decreases, the voltage Vout when the current Ic of the switching circuit 33 rises decreases. Generally, the breakdown voltage of the transistor 20Q decreases as the temperature decreases. At low temperatures when the breakdown voltage of the transistor 20Q decreases, the voltage Vout when the current Ic of the switching circuit 33 rises becomes low, making it possible to adequately protect the transistor 20Q even at low temperatures.

[0029] [Second Example] Next, a voltage clamp circuit according to the second embodiment will be described with reference to Figures 4 and 5. The following description will omit explanations of components common to the voltage clamp circuit according to the first embodiment, which was described with reference to Figures 1 to 3.

[0030] Figure 4 is a schematic equivalent circuit diagram of a power amplifier having a voltage clamp circuit 30 according to the second embodiment. In the second embodiment, a Darlington connection circuit consisting of a first transistor 33A and a second transistor 33B is used as the switching circuit 33. The first transistor 33A and the second transistor 33B are HBTs formed from the same compound semiconductor as transistor 20Q of the high-frequency amplifier circuit 20. A resistor 34R is used as the first impedance element 34. The pn junctions of the first diode 31D and the second diode 32 are formed from the same semiconductor material as, for example, the pn junction between the base-emitter of the first transistor 33A and the second transistor 33B.

[0031] The node where the first diode circuit 31 and the second diode 32 are interconnected is connected to the base of the first transistor 33A. That is, the base of the first transistor 33A corresponds to the control node 33C of the switching circuit 33. The collectors of the first transistor 33A and the second transistor 33B are connected to the output node 20A of the high-frequency amplifier circuit 20. The emitter of the first transistor 33A is connected to the base of the second transistor 33B. The emitter of the second transistor 33B is connected to a reference potential.

[0032] When the voltage V1 exceeds the on-voltage of the Darlington connection circuit, current Ic begins to flow through the switching circuit 33. The current amplification factors of the first transistor 33A and the second transistor 33B are set to h. FE When written as such, the base current of the first transistor 33A is (1 / h) of the current Ic. FE ) 2It is twice as large and sufficiently small compared to the current Ic. When the switching circuit 33 conducts, the base current necessary to turn on the first transistor 33A flows through the first diode circuit 31. Therefore, most of the current flowing from the output node 20A of the high-frequency amplifier circuit 20 to the reference potential passes through the switching circuit 33.

[0033] Figure 5 is a graph showing an example of the relationship between the current Ic flowing through the switching circuit 33 and the voltage Vout at the output node 20A. The horizontal axis represents the voltage Vout at the output node 20A of the high-frequency amplifier circuit 20, and the vertical axis represents the current Ic flowing through the switching circuit 33. In the graph shown in Figure 5, the thick solid line, thin solid line, and dashed line represent the current Ic when the temperature of the temperature-dependent element of the first current source 35 is 85°C, 25°C, and -30°C, respectively.

[0034] As the temperature decreases, the voltage Vout at which the current Ic begins to flow also decreases. Note that GaAs heterojunction bipolar transistors (GaAs-HBT) are used as the first transistor 33A and the second transistor 33B. It is also possible to use n-type bipolar transistors as the first transistor 33A and the second transistor 33B.

[0035] Next, we will explain the technical significance of using a Darlington connection circuit of a first transistor 33A and a second transistor 33B as the switching circuit 33. When the switching circuit 33 is constructed with a single HBT, the base of the HBT is subjected to a voltage that is the sum of the voltage V2 due to the voltage drop across the resistor 34R and the forward voltage of the second diode 32.

[0036] Therefore, a voltage higher than the forward voltage of the second diode 32 is applied to the base of the HBT. Since the on-voltage of the HBT is approximately equal to the forward voltage of the second diode 32, the HBT remains constantly on. The on-voltage of the Darlington connection circuit consisting of the first transistor 33A and the second transistor 33B is approximately twice the forward voltage of the second diode 32. Therefore, by changing the voltage V2, it becomes possible to appropriately turn the switching circuit 33 on and off.

[0037] Next, we will describe the excellent effects of the second embodiment. In the second embodiment, as in the first embodiment, the breakdown of transistor 20Q in the high-frequency amplification circuit 20 is suppressed, and transistor 20Q is adequately protected even at low temperatures.

[0038] Next, a voltage clamp circuit according to a modification of the second embodiment will be described with reference to Figure 6. Figure 6 is a schematic equivalent circuit diagram of a power amplifier having a voltage clamp circuit 30 according to a modification of the second embodiment.

[0039] In the second embodiment (Figure 4), a resistor 34R is used as the first impedance element 34. However, in the modified version of the second embodiment shown in Figure 6, a diode 34D is used as the first impedance element 34. The diode 34D is connected in a direction such that the forward direction is towards the reference potential from the second diode 32. The voltage V2 fluctuates according to the forward current-voltage characteristics of the diode 34D and the current Icont supplied from the first current source 35. As in the first embodiment, as the current Icont increases, the voltage V2 increases.

[0040] As shown in the second embodiment (Figure 4) and the modified version of the second embodiment (Figure 6), a resistor 34R or a diode 34D can be used as the first impedance element 34. In addition, a circuit component having the characteristic that the voltage drop increases as the current Icont increases can be used as the first impedance element 34. Furthermore, a circuit configuration in which multiple elements are connected in series or parallel may be used as the first impedance element 34.

[0041] Next, other modifications of the second embodiment will be described. In the second embodiment, a Darlington connection circuit consisting of two HBTs was used as the switching circuit 33 (Figure 4), but other transistors, such as MOSFETs, may also be used. The threshold voltage for turning on the MOSFET can be adjusted, for example, by adjusting the channel dopant profile.

[0042] [Third Embodiment] Next, the voltage clamp circuit according to the third embodiment will be described with reference to Figure 7. The following description will omit details of components common to the voltage clamp circuit according to the second embodiment, which was described with reference to Figure 4.

[0043] Figure 7 is a schematic equivalent circuit diagram of a power amplifier having a voltage clamp circuit 30 according to the third embodiment. In the second embodiment (Figure 4), the switching circuit 33 is directly connected to the output node 20A of the high-frequency amplification circuit 20, but in the third embodiment, a second impedance element 36 is connected between the switching circuit 33 and the output node 20A. For example, a diode is used as the second impedance element 36. The diode is connected in a direction such that the direction from the output node 20A towards the switching circuit 33 is the forward direction.

[0044] Next, we will describe the excellent effects of the third embodiment. In the third embodiment, current Ic flows through the second impedance element 36 to the switching circuit 33. Due to the voltage drop caused by the second impedance element 36, the voltage applied between the collector and emitter of the second transistor 33B of the switching circuit 33 is reduced.

[0045] In a configuration where the second impedance element 36 is not connected, a voltage approximately equal to the voltage Vout at the output node 20A of the high-frequency amplifier circuit 20 is applied to the second transistor 33B of the switching circuit 33. When the voltage Vout exceeds the breakdown voltage of transistor 20Q, the switching circuit 33 conducts and the voltage Vout decreases. However, during the period before the switching circuit 33 conducts, a voltage temporarily exceeding the breakdown voltage is applied to the second transistor 33B.

[0046] If the voltage Vout, which exceeds the breakdown voltage, is applied for a short period of time, the second transistor 33B will not be destroyed even if the voltage Vout exceeds the breakdown voltage. However, if the time the voltage Vout, which exceeds the breakdown voltage, is applied for a longer period of time, the risk of the second transistor 33B being destroyed increases.

[0047] In the third embodiment, a voltage drop occurs due to the second impedance element 36, reducing the voltage applied to the second transistor 33B. This makes it less likely for the second transistor 33B to be damaged.

[0048] Next, a voltage clamp circuit according to a modification of the third embodiment will be described. In the third embodiment, a diode is used as the second impedance element 36, but other elements that produce a voltage drop, such as a resistor, may also be used.

[0049] [Fourth embodiment] Next, a voltage clamp circuit according to the fourth embodiment will be described with reference to Figure 8. The following description will omit explanations of components common to the voltage clamp circuit according to the first embodiment, which was described with reference to Figures 1 to 3.

[0050] Figure 8 is an equivalent circuit diagram of the first current source 35 used in the voltage clamp circuit 30 according to the fourth embodiment. The first current source 35 includes a current mirror circuit 41 and a second current source 43. The current mirror circuit 41 includes a reference transistor 41R through which a reference current Iref flows and a mirror transistor 41M through which a current Icont flows. PMOSFETs are used as the reference transistor 41R and the mirror transistor 41M. The sources of the reference transistor 41R and the mirror transistor 41M are connected to the power supply voltage.

[0051] The second current source 43 is connected between the drain of the reference transistor 41R and the reference potential, and supplies a reference current Iref from the reference transistor 41R to the reference potential. The drain of the Miller transistor 41M is connected to the first impedance element 34, and the first current source 35 supplies a current Icont to the first impedance element 34.

[0052] The second current source 43 includes an NMOS current mirror circuit 43A and a temperature-dependent current source 43I. The temperature-dependent current source 43I generates a current that depends on the temperature of the first diode circuit 31. More specifically, as the temperature of the first diode circuit 31 rises, the current generated by the temperature-dependent current source 43I decreases. The current generated by the temperature-dependent current source 43I flows through the reference transistor of the NMOS current mirror circuit 43A, and the current flowing through the mirror transistor becomes the reference current Iref. Therefore, the reference current Iref generated by the NMOS current mirror circuit 43A changes depending on the temperature of the first diode circuit 31. The reference current Iref generated by the NMOS current mirror circuit 43A becomes the reference current of the current mirror circuit 41, and the current Icont generated by the current mirror circuit 41 is supplied to the first impedance element 34.

[0053] Next, we will describe the excellent effects of the fourth embodiment. In the fourth embodiment, the temperature-dependent current source 43I has a temperature dependence, which generates a temperature-dependent current Icont as shown in Figure 2A. As a result, similar to the first embodiment, the breakdown of transistor 20Q in the high-frequency amplifier circuit 20 (Figure 1) is suppressed, and transistor 20Q can be adequately protected even at low temperatures.

[0054] Next, a voltage clamp circuit according to a modified example of the fourth embodiment will be described. In the fourth embodiment, a PMOS transistor is used in the current mirror circuit 41, but a PNP bipolar transistor may also be used. When using a PNP bipolar transistor, in the above description of the fourth embodiment, source, drain, and gate should be read as emitter, collector, and base, respectively.

[0055] Next, with reference to Figure 9, a voltage clamp circuit according to another modification of the fourth embodiment will be described. Figure 9 is an equivalent circuit diagram of a voltage clamp circuit according to another modification of the fourth embodiment. The modification shown in Figure 9 shows one specific configuration of the temperature-dependent current source 43I of the clamp circuit according to the fourth embodiment (Figure 8).

[0056] The temperature-dependent current source 43I includes two PMOS current mirror circuits 43B and 43E. The drain of the PMOS transistor on the reference current side of one of the PMOS current mirror circuits 43B is connected to a reference potential via a series circuit of a resistor 43C and a diode 43D. The diode 43D is connected in a direction such that the forward direction is from the PMOS transistor toward the reference potential. The difference voltage between the drain voltage of the PMOS transistor through which the reference current flows and the silicon bandgap voltage VBG is applied to the gates of the two PMOS transistors in the PMOS current mirror circuit 43B.

[0057] The forward voltage of diode 43D is temperature-dependent. That is, diode 43D functions as a temperature-dependent element of the first current source 35. The output current Iitat of the PMOS current mirror circuit 43B changes depending on the temperature of diode 43D. More specifically, as the temperature of diode 43D rises, the output current Iitat decreases.

[0058] Diode 43D is thermally coupled to the first diode circuit 31. For example, the first diode circuit 31 and diode 43D are formed on the same semiconductor substrate. Alternatively, another semiconductor substrate on which diode 43D is formed may be bonded to the semiconductor substrate on which the first diode circuit 31 is formed, or the semiconductor substrate on which the first diode circuit 31 is formed and the other semiconductor substrate on which diode 43D is formed may be mounted on a common module substrate.

[0059] The drain of the PMOS transistor on the reference current side of the other PMOS current mirror circuit 43E is connected to a reference potential via a resistor 43F. The difference voltage between the drain voltage of the PMOS transistor through which the reference current flows and the silicon bandgap voltage VBG is applied to the gates of the two PMOS transistors of the PMOS current mirror circuit 43E. The output current Iztat of the PMOS current mirror circuit 43E is a constant value that is independent of temperature and depends on the resistance value of the resistor 43F.

[0060] The temperature-dependent current source 43I outputs a current which is the sum of its output current Iitat and output current Iztat. This current becomes the reference current of the NMOS current mirror circuit 43A. Therefore, the reference current Iref generated by the NMOS current mirror circuit 43A is equal to the sum of its output current Iitat and output current Iztat. The reference current Iref generated by the NMOS current mirror circuit 43A becomes the reference current of the current mirror circuit 41, and the current Icont generated by the current mirror circuit 41 is supplied to the first impedance element 34.

[0061] Next, we will explain the excellent effects of the modified example of the fourth embodiment shown in Figure 9. In a modified version of the fourth embodiment, a current Icont having a temperature dependence as shown in Figure 2A is generated by the diode 43D thermally coupled to the first diode circuit 31. As a result, similar to the first embodiment, the breakdown of transistor 20Q in the high-frequency amplifier circuit 20 (Figure 1) is suppressed, and transistor 20Q can be adequately protected even at low temperatures.

[0062] The embodiments described above are illustrative, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. Similar effects and benefits from similar configurations in multiple embodiments will not be mentioned sequentially for each embodiment. Furthermore, the present invention is not limited to the embodiments described above. For example, it will be obvious to those skilled in the art that various modifications, improvements, and combinations are possible. [Explanation of Symbols]

[0063] 20 High-frequency amplification circuit Output node of a 20A high-frequency amplifier circuit 20C Input Capacitor 20Q Transistor 20R ballast resistor element 25 Bias Circuit 26 Choke coil 28. Surge voltage protection circuit 30 Voltage clamp circuit 31. First Diode Circuit 31D First Diode 32. Second Diode 33 Switching Circuits 33A First Transistor 33B Second Transistor 34. First Impedance Element 34D diode 34R Resistor 35 1st current source 36. Second Impedance Element 41 Current Mirror Circuit 41M Miller-side transistor 41R Reference transistor 43 Second current source 43A NMOS Current Mirror Circuit 43B PMOS Current Mirror Circuit 43C Resistor 43D diode 43E PMOS Current Mirror Circuit 43F Resistor 43I Temperature dependent current source

Claims

1. A first diode circuit including multiple first diodes connected in multiple stages, the anode node of which is connected to the output node of a high-frequency amplifier circuit, A second diode whose anode is connected to the cathode-side node of the first diode circuit, A first impedance element connected between the cathode of the second diode and the reference potential, A first current source is connected to a node in which the first impedance element and the second diode are interconnected, and the first impedance element is supplied with a current toward a reference potential. A switching circuit connected between the output node of the high-frequency amplifier circuit and the reference potential. Equipped with, The first current source includes a temperature-dependent element that changes its electrical characteristics in response to temperature changes, and supplies a current having a negative temperature coefficient with respect to the temperature change of the temperature-dependent element to the first impedance element. The switching circuit includes a control node connected to a node in which the first diode circuit and the second diode are interconnected, and a voltage clamp circuit that conducts when the voltage of the control node exceeds a threshold voltage.

2. The aforementioned switching circuit is A first transistor whose base functions as the control node and whose collector is connected to the output node of the high-frequency amplification circuit, A second transistor whose base is connected to the emitter of the first transistor, whose collector is connected to the output node of the high-frequency amplifier circuit, and whose emitter is connected to a reference potential. A voltage clamp circuit according to claim 1, including the following:

3. The voltage clamp circuit according to claim 1 or 2, wherein the first impedance element is a resistive element, or a diode whose forward direction is toward the reference potential from the second diode.

4. Furthermore, the voltage clamp circuit according to any one of claims 1 to 3, further comprising a second impedance element inserted between the switching circuit and the output node of the high-frequency amplification circuit.

5. The first current source is, A current mirror circuit including a reference transistor through which the reference current flows and a mirror transistor through which the output current flows, Second current source and Includes, The source or emitter of the reference transistor and the source or emitter of the mirror transistor are connected to the power supply voltage. The second current source is connected between the drain or collector of the reference transistor and the reference potential. The voltage clamp circuit according to any one of claims 1 to 4, wherein the drain or collector of the mirror-side transistor is connected to the first impedance element.

6. The voltage clamp circuit according to any one of claims 1 to 5, wherein the temperature-dependent element is thermally coupled to the first diode circuit.

7. A voltage clamp circuit according to any one of claims 1 to 6, The high-frequency amplification circuit and A power amplifier equipped with [a specific feature].

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