JP2007180955A - High frequency amplifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a thermal runaway caused by concentrated current to a small number of transistors, by suppressing unbalanced collector currents among a plurality of transistors connected in parallel. <P>SOLUTION: In a first sub-high frequency amplifier circuit 100 having an identical configuration to a second sub-high frequency amplifier circuit 101, four transistor circuits 4, 5, 6 and 7 are connected in parallel. In each transistor circuit 4, 5, 6, 7, a first signal input terminal 4e is connected to a high frequency input terminal 1 via a transmission line 8, while capacitors 10, 12 and 14 for line connection are connected in series to transmission lines 9, 11 and 13 respectively corresponding thereto, thus forming each pair. The above each pair is connected to between neighboring terminals of the first to a fourth signal input terminals 4e, 5e, 6e and 7e, thereby suppressing the dispersion of the input impedance of the transistor circuits 4, 5, 6 and 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-frequency amplifier circuit, and more particularly, to a high-frequency amplifier circuit configured by connecting a plurality of transistors in parallel to improve operational stability, reliability, and the like.

Conventionally, in a high-frequency amplifier circuit used in a transmission unit of a so-called mobile communication device such as a mobile phone or a wireless LAN, in order to achieve high output power, a circuit configuration is generally provided by providing a plurality of bipolar transistors connected in parallel to each other. (For example, refer to Patent Document 1, Patent Document 2, etc.).
In such a circuit, the temperature difference due to heat generation between the bipolar transistors connected in parallel to each other is fed back to the base bias, and the current flowing through the collectors of some bipolar transistors having a high heat generation temperature increases abnormally. The current flowing in the collectors of the bipolar transistors connected in parallel may concentrate on the collectors of some of the bipolar transistors having high heat generation temperatures, and may eventually be destroyed.
In order to suppress such current concentration in some bipolar transistors, a method of connecting a resistance element, so-called ballast resistor, to the emitter and base of each of the bipolar transistors connected in parallel has been widely used as a conventionally known method. However, this method is simple and reliable, but has a drawback that it causes a reduction in power gain and stability of the high-frequency amplifier circuit.

FIG. 6 shows a specific circuit configuration example of a high-frequency amplifier circuit composed of a plurality of bipolar transistors connected in parallel to each other in order to obtain a high output power characteristic as described above. However, this conventional circuit example will be described.
The high-frequency amplifier circuit shown in FIG. 6 is configured by connecting eight bipolar transistors in parallel.
Specifically, the high-frequency amplifier circuit is configured by connecting a first high-frequency amplifier circuit 160 and a second high-frequency amplifier circuit 161 in parallel. The high frequency amplifier circuits 160 and 161 are configured symmetrically and perform the same operation.

Since the first and second high-frequency amplifier circuits 160 and 161 have basically the same circuit configuration, the first high-frequency amplifier circuit 160 is taken as an example, and a more specific configuration thereof will be described below.
The first high-frequency amplifier circuit 160 includes four bipolar transistors 64a, 65a, 66a, and 67a. The base of the first bipolar transistor 64a is the first capacitor 64b and the first resistor element 64c. Are connected to the high frequency input terminal 61 and the base bias terminal 62, respectively, and the collector is connected to the high frequency output terminal 63. Such a configuration is the same for the second to fourth bipolar transistors 65a, 66a, and 67a. Therefore, detailed description thereof is omitted here, and in FIG. 6, the components correspond to the components described above. The constituent elements are only given reference numerals.

  Then, the four transistor circuits 64, 65, 66, 67 configured as described above centering on the first to fourth bipolar transistors 64a, 65a, 66a, 67a are connected in parallel to each other. ing. The first to fourth capacitors 64b, 65b, 66b, and 67b are set to the same capacitance value.

In this configuration, voltages corresponding to the base currents of the first to fourth bipolar transistors 64a, 65a, 66a, and 67a are generated at both ends of the first to fourth resistance elements 64c, 65c, 66c, and 67c. Here, if the base current of some of the bipolar transistors increases as the temperature rises, the voltage at both ends of the resistance element connected to the base increases, and conversely, the base-emitter voltage decreases. Therefore, as a result, a rapid increase in the base current of some of the bipolar transistors 64a, 65a, 66a, 67a is suppressed, and so-called thermal runaway is suppressed.
On the other hand, in the high frequency amplifier circuit configured as described above, the input high frequency signal passes through the first to fourth capacitors 64c, 65c, 66c, 67c, and passes through the first to fourth bipolar transistors 64a, 65a, 66a, Since it is input to the corresponding base of 67a, the decrease in power gain is small compared to a configuration in which a high-frequency signal is applied to the base via a resistance element.

  By the way, when the circuit shown in FIG. 6 is actually configured, since it has physical sizes that cannot be ignored, including not only bipolar transistors but also other elements, for example, all bipolar transistors 64a, In practice, it is difficult to make the distance between the bases of 65a, 66a, and 67a and the high-frequency input terminal 61 the same. Therefore, actually, as shown in FIG. 7, the high-frequency input terminal 81 and the input stages of the first to fourth transistor circuits 84, 85, 86, 87 constituting the first high-frequency amplifier circuit 180 In general, transmission lines 88, 89, 90, 91 using conductive members are connected in series.

Japanese Patent Laying-Open No. 2005-184707 (page 6-10, FIGS. 1 to 10) US Pat. No. 5,608,353

However, if the transmission line as described above is provided, a difference occurs in the input impedance to the high-frequency signal between the first to fourth transistor circuits 84, 85, 86, and 87, and so-called imbalance in the operating state. Occurs, causing current concentration in some of the bipolar transistors, causing the occurrence of so-called thermal runaway.
Specifically, for example, the change characteristic of the output power with respect to the input power in the configuration example shown in FIG. 7 is shown in FIG. 8, but according to the figure, when the input power exceeds a certain level, the output power It can be confirmed that the power characteristics change discontinuously (see the dotted box in FIG. 8).

FIG. 9 shows the change characteristic of the collector current of each bipolar transistor 84a, 85a, 86a, 87a with respect to the change of the input power. According to the figure, the output power characteristic shown in FIG. It can be confirmed that the collector current of some of the bipolar transistors rapidly increases at the discontinuous input power. In FIG. 9, Tr1, Tr2, Tr3, and Tr4 represent bipolar transistors 84a, 85a, 86a, and 87a, respectively.
Further, according to FIG. 9, the collector currents of the bipolar transistors 84a, 85a, 86a, 87a differ from each other regardless of whether or not the input state is such that the output power characteristics are discontinuous as described above. It can be confirmed that there is a difference of about 75% at the maximum. Such current imbalance is a cause of current concentration in some bipolar transistors due to the temperature rise of the bipolar transistors.

By the way, in recent years, demand for so-called mobile communication devices such as mobile phones and wireless LANs is rapidly increasing, and accordingly, demands for smaller, higher performance, and higher functionality of the communication device main body are increasing. Yes. Under such circumstances, a high-frequency power amplifier that amplifies a high-frequency signal in the transmitter of the mobile communication device is required to be small and have high power load efficiency.
These high-frequency power amplifiers are often configured using a plurality of bipolar transistors connected in parallel as described above in order to achieve high output power characteristics, but in order to meet the demand for miniaturization, If a structure in which a plurality of bipolar transistors connected in parallel are arranged close to each other, the heat dissipation paths of the bipolar transistors cross each other and the thermal resistance increases, leading to a temperature rise, and the collector of each bipolar transistor as described above. In order to cause current concentration in some bipolar transistors coupled with current imbalance, it is necessary to suppress so-called thermal runaway.

  The present invention has been made in view of the above circumstances, and suppresses the collector current imbalance of a plurality of parallel-connected transistors constituting an amplifier circuit, and current concentration in some transistors due to temperature rise And a high frequency amplifier circuit capable of obtaining a stable output without causing thermal runaway.

In order to achieve the above object of the present invention, a high frequency amplifier circuit according to the present invention comprises:
The first sub-high frequency amplifier circuit and the second sub high-frequency amplifier circuit connected in parallel with each other, each of the first and second sub high-frequency amplifier circuits includes n transistors that perform an amplification operation. A high-frequency amplifier circuit configured by connecting circuits in parallel,
Each of the n transistor circuits includes a bipolar transistor or a field effect transistor, and each bipolar transistor or field effect transistor has collectors or drains, emitters or sources connected in parallel to each other. One end of each resistor and base capacitor is connected to each base or gate, and the other end of each resistor is a DC bias input terminal. The end is a signal input terminal,
Among the n transistor circuits, the signal input terminal of the first transistor circuit is connected to a high frequency input terminal via a first transmission line,
Between the signal input terminals adjacent to each of the first to n-th transistor circuits, a transmission line and a line connection capacitor which are connected in series to form a pair respectively form the pair on the first transmission line side. Each transmission line is connected so as to be positioned, and a plurality of pairs of transmission lines and line connecting capacitors are vertically connected to the high-frequency input terminal.
In this configuration, the capacitance of each of the base capacitors of the second to n-th transistor circuits and the capacitance of the capacitor for line connection connected in series between the other end of the base capacitor and the high-frequency input terminal. It is also preferable that a capacitor having a capacitance is newly used as the base capacitor of each of the second to nth transistor circuits, and the base capacitor also serves as the line connection capacitor.
In addition, the first sub-high frequency amplifier circuit and the second sub high-frequency amplifier circuit connected in parallel with each other, each of the first and second sub-high frequency amplifier circuits perform n amplification operations. A high-frequency amplifier circuit composed of transistor circuits connected in parallel,
Each of the n transistor circuits includes a bipolar transistor or a field effect transistor, and each bipolar transistor or field effect transistor has collectors or drains, emitters or sources connected in parallel to each other. One end of each resistor and base capacitor is connected to each base or gate, and the other end of each resistor is a DC bias input terminal. One end of the transmission line is connected to the end, and the other end of the transmission line is a signal input terminal.
Among the n transistor circuits, the signal input terminal of the first transistor circuit is connected to a high frequency input terminal,
The signal input terminals of the second to n-th transistor circuits are connected to bipolar transistors or electric fields of adjacent transistor circuits so that the first to n-th transistor circuits are sequentially cascade-connected to the high-frequency input terminal. A configuration in which the transistor is sequentially connected to the base or gate of the effect transistor is also preferable.

  According to the present invention, by connecting the transmission line and the line connection capacitor, the inductance component of the transmission line is canceled out by the line connection capacitor, and a difference occurs in the input impedance of each transistor circuit connected in parallel to each other. Therefore, it is possible to suppress the so-called imbalance in the operating state, avoid the current concentration in some transistors, and suppress or prevent the occurrence of so-called thermal runaway, providing a high-frequency amplifier circuit with stable output characteristics can do.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.
The members and arrangements described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.
First, a first configuration example of the high-frequency amplifier circuit according to the embodiment of the present invention will be described with reference to FIG.
This high-frequency amplifier circuit is configured by connecting a first sub-high-frequency amplifier circuit 100 and a second sub-high-frequency amplifier circuit 101 in parallel, and the first and second sub-high-frequency amplifier circuits 100 and 101 are connected. Are configured symmetrically and perform the same operation.
Since the first and second sub high frequency amplifier circuits 100 and 101 have the same circuit configuration, here, the first sub high frequency amplifier circuit 100 is taken as an example, and a more specific configuration thereof will be described. The description will be replaced with the description of the second sub-high frequency amplifier circuit 101.

The first sub-high frequency amplifier circuit 100 has four transistor circuits 4 to 7, which are connected in parallel to each other as will be described later, and the first to fourth transistor circuits 4 to 7 have their inputs. The side is configured to be connected to a high frequency input terminal 1 to which a high frequency signal from the outside is applied via a transmission line (details will be described later).
The first sub high frequency amplifier circuit 100 is connected in parallel between the second sub high frequency amplifier circuit 101 having the same configuration and the high frequency input terminal 1 and the high frequency output terminal 3. It has become.

  The first to fourth transistor circuits 4 to 7 basically have the same configuration. Here, the configuration of the first transistor circuit 4 will be described, and the description will be replaced with the description of the configuration of the second to fourth transistor circuits 5 to 7. In the following description, the reference numerals of the corresponding components of the second to fourth transistor circuits 5 to 7 are shown in parentheses after the reference numerals of the constituent elements of the first transistor circuit 4.

In the first transistor circuit 4, the first bipolar transistor 4a (5a, 6a, 7a) includes, on its base, a first base capacitor 4b (5b, 6b, 7b) and a first resistor 4c (5c, 6c, 7c) is connected to one end, while the emitter is connected to the ground and the collector is connected to the collector terminal 4d (5d, 6d, 7d).
In this configuration example, the npn type is used as the bipolar transistor.

The other end of the first base capacitor 4b (5b, 6b, 7b) is connected to the first signal input terminal 4e (5e, 6e, 7e), and the first resistor 4c (5c, 6c, 7c). ) Is connected to the first DC input terminal 4f (5f, 6f, 7f).
The first to fourth DC input terminals 4f, 5f, 6f, and 7f are connected to the base bias terminal 2 in parallel with each other, while the first to fourth collector terminals 4d, 5d, 6d, and 7d are The high frequency output terminals 3 are connected in parallel to each other.

Between the signal input terminals 4e, 5e, 6e, and 7e of the transistor circuits 4 to 7 and the high frequency input terminal 1, the transmission lines 8, 9, 11, and 13 and the line connecting capacitor 10 are described as described below. , 12 and 14 are provided.
That is, the first signal input terminal 4e and the high-frequency input terminal 1 are connected via the first transmission line 8, and the connection point between the first signal input terminal 4e and the first transmission line 8 is One end of the second transmission line 9 is connected, the other end of the second transmission line 9 is connected to the other end of the second line connection capacitor 10, and the second line connection capacitor 10 is further connected. Is connected to the second signal input terminal 5e.

The other end of the second line connecting capacitor 10 is connected to one end of the third transmission line 11, and the other end of the third transmission line 11 is connected to the third line connecting capacitor 12. To the third signal input terminal 6e.
The other end of the third line connecting capacitor 12 is further connected to one end of the fourth transmission line 13, and the other end of the fourth transmission line 13 is connected to the fourth line connecting capacitor. 14 is connected to the fourth signal input terminal 7e.
That is, in other words, the transmission lines 9, 11, 13 and the second to fourth line connecting capacitors 10, 12, 14 connected in series corresponding to each of the transmission lines 9, 11, 13 form a pair, and each pair is the first The first signal input terminal 4e and the fourth signal input terminal 7e are connected between adjacent terminals, whereby the pair is connected in cascade to the high frequency input terminal 1. ing.
The transmission lines 8, 9, 11, and 13 are specifically made of microstrip lines, wiring materials having inductance, or inductance elements.

Here, in the transmission lines 8, 9, 11, and 13 described above, the dominant element of the impedance is an inductance component. In particular, if the inductance components in the second to fourth transmission lines 9, 11, and 13 are not negligible, the first to fourth transistor circuits 4 to 7 have different input impedances. Differences will also occur in the signal being transmitted.
Therefore, in the embodiment of the present invention, the second to fourth line connecting capacitors 10, 11, and 14 have inductance components of the second to fourth transmission lines 9, 11, and 13 connected in series, respectively. It has a capacity to cancel out.

Since the amplification operation in such a configuration is basically the same as that of the conventional circuit, detailed description thereof will be omitted, and the output characteristics in comparison with the conventional circuit will be described below with reference to FIGS. 2 and 3. Explain the difference. In the following description, FIGS. 8 and 9 which are conventional characteristic diagrams are referred to as appropriate.
First, the change characteristics of the output power with respect to the input power will be described with reference to FIG. 2. From FIG. 2, the high-frequency amplifier circuit according to the embodiment of the present invention described above is different from the conventional one (see FIG. 8). It can be confirmed that the output change does not become discontinuous regardless of the magnitude of the power.
According to FIG. 3, in the above-described high-frequency amplifier circuit according to the embodiment of the present invention, although there is a difference in the collector current of each bipolar transistor 4a, 5a, 6a, 7a with respect to the change in input power, the maximum But it is suppressed to about 25%.
In this regard, for example, in the characteristic example of the conventional circuit shown in FIG. 9, there is a difference of about 75% at the maximum, so that the high-frequency amplifier circuit according to the embodiment of the present invention has a marked improvement in characteristics. It can be confirmed that it was made.
In FIG. 3, Tr1, Tr2, Tr3, and Tr4 represent bipolar transistors 4a, 5a, 6a, and 7a, respectively.

Next, a second configuration example will be described with reference to FIG.
The same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. Hereinafter, different points will be mainly described.
In this second configuration example, the second to fourth line connection capacitors 10, 11, and 14 in the first configuration example shown in FIG. 1 are combined with the corresponding base capacitors 5b, 6b, and 7b. Thus, the second to fourth line connecting capacitors 10, 11, and 14 can be eliminated.

That is, the second base capacitor 25b has a combined capacitance of the capacitance of the second base capacitor 5b shown in FIG. 1 and the capacitance value of the second line connection capacitor 10 shown in FIG. It has become.
Similarly, the third base capacitor 26b has a combined capacitance of the capacitance of the third base capacitor 6b (see FIG. 1) and the capacitance value of the third line connection capacitor 12 (see FIG. 1). ing.
Further, similarly, the fourth base capacitor 27b has a combined capacitance of the capacitance of the fourth base capacitor 7b (see FIG. 1) and the capacitance value of the fourth line connection capacitor 14 (see FIG. 1). It has become.
Accordingly, the operation and characteristics of the circuit are the same as those of the first configuration example, and detailed description thereof is omitted here.

  If the difference between the high-frequency amplifier circuit in the second configuration example and the conventional circuit shown in FIG. 7 is described, the two seem to be similar circuits at first glance, but the conventional circuit In this case, the first to fourth capacitors 84b, 85b, 86b, 87b have the same capacity, whereas in the case of the configuration example shown in FIG. 4, first, the capacity of the first base capacitor 4b, The capacities of the second to fourth base capacitors 25b, 26b, and 27b are different. Further, the capacitances of the second to fourth base capacitors 25b, 26b, and 27b cancel out the inductance components of the corresponding second to fourth transmission lines 9, 11, and 13, respectively, in addition to the capacitance of the original base capacitor. The capacity is taken into consideration, and therefore the first to fourth base capacitors 4b, 25b, 26b, and 27b are not the same capacity.

Next, a third configuration example will be described with reference to FIG.
The same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. Hereinafter, different points will be mainly described.
This third configuration example eliminates the first to fourth base capacitors 4a, 5a, 6a, and 7a in the first configuration example shown in FIG. 1, while newly adding a first line connection capacitor. 49, and the capacities of the first to fourth line connecting capacitors 49, 51, 53, and 55 are set as described later.
First, a first line connection capacitor 49 is provided between the first transmission line 8 and the first bipolar transistor 4a.
The first to fourth line connecting capacitors 49, 51, 53, and 55 remove the DC components in the base biases of the corresponding first to fourth bipolar transistors 4a, 5a, 6a, and 7a (DC cut). And the role of canceling out the inductance components of the corresponding first to fourth transmission lines 8, 9, 11, and 13, respectively. For this reason, the first to fourth line connecting capacitors 49, 51, 53, and 55 are set to capacitance values in which the capacitance necessary for DC cut is added to the capacitance necessary for canceling the inductance component. Yes.

  In any of the above-described configuration examples, the npn type bipolar transistor is used. However, it is needless to say that the present invention is not limited to this, and a pnp type bipolar transistor may be used. An effect transistor may be used. Note that when a field effect transistor is used instead of the bipolar transistor, the base, collector, and emitter of the bipolar transistor may correspond to the gate, drain, and source of the field effect transistor, respectively.

  The first and second sub-high frequency amplifier circuits 100 and 101 are each configured by connecting four transistor circuits in parallel to each other, but needless to say, the present invention is not limited to this. As long as a plurality of transistor circuits are connected in parallel, the number thereof may be arbitrarily selected as desired.

1 is a circuit diagram illustrating a first circuit configuration example of a high-frequency amplifier circuit according to an embodiment of the present invention. It is a characteristic diagram which shows the change characteristic of the output electric power with respect to the input electric power of the high frequency amplifier circuit in embodiment of this invention. It is a characteristic line figure which shows the change characteristic of the collector current of each bipolar transistor with respect to the input power of the high frequency amplifier circuit in embodiment of this invention. It is a circuit diagram which shows the 2nd circuit structural example of the high frequency amplifier circuit in embodiment of this invention. It is a circuit diagram which shows the 3rd circuit structural example of the high frequency amplifier circuit in embodiment of this invention. It is a circuit diagram which shows the conventional circuit structural example. It is a circuit diagram which shows the other conventional circuit structural example. It is a characteristic diagram which shows the change characteristic of the output power with respect to the input power in the conventional circuit shown in FIG. FIG. 8 is a characteristic diagram showing a change characteristic of collector current of each bipolar transistor with respect to input power in the conventional circuit shown in FIG. 7.

Explanation of symbols

4-7 ... 1st thru | or 4th transistor circuit 8 ... 1st transmission line 9 ... 2nd transmission line 10 ... 2nd line connection capacitor | condenser 11 ... 3rd transmission line 12 ... 3rd line connection use Capacitor 13 ... Fourth transmission line 14 ... Fourth line connecting capacitor 100 ... First sub-high frequency amplifier circuit 101 ... Second sub-high frequency amplifier circuit

Claims (3)

The first sub-high frequency amplifier circuit and the second sub high-frequency amplifier circuit connected in parallel with each other, each of the first and second sub high-frequency amplifier circuits includes n transistors that perform an amplification operation. A high-frequency amplifier circuit configured by connecting circuits in parallel,
Each of the n transistor circuits includes a bipolar transistor or a field effect transistor, and each bipolar transistor or field effect transistor has collectors or drains, emitters or sources connected in parallel to each other. One end of each resistor and base capacitor is connected to each base or gate, and the other end of each resistor is a DC bias input terminal. The end is a signal input terminal,
Among the n transistor circuits, the signal input terminal of the first transistor circuit is connected to a high frequency input terminal via a first transmission line,
Between the signal input terminals adjacent to each of the first to n-th transistor circuits, a transmission line and a line connection capacitor which are connected in series to form a pair respectively form the pair on the first transmission line side. A high-frequency amplifier circuit, wherein each transmission line is connected to be positioned, and a plurality of pairs of transmission lines and line-connecting capacitors are vertically connected to the high-frequency input terminal.   A capacitance of a base capacitor of each of the second to nth transistor circuits, and a combined capacitance of the capacitance of the line connection capacitor connected in series between the other end of the base capacitor and the high-frequency input terminal. 2. The high frequency amplifier circuit according to claim 1, wherein a capacitor is newly used as a base capacitor of each of the second to nth transistor circuits, and the base capacitor also serves as the line connecting capacitor. The first sub-high frequency amplifier circuit and the second sub high-frequency amplifier circuit connected in parallel with each other, each of the first and second sub high-frequency amplifier circuits performing n transistor circuits for performing an amplification operation. Is a high-frequency amplifier circuit configured by being connected in parallel,
Each of the n transistor circuits includes a bipolar transistor or a field effect transistor, and each bipolar transistor or field effect transistor has collectors or drains, emitters or sources connected in parallel to each other. One end of each resistor and base capacitor is connected to each base or gate, and the other end of each resistor is a DC bias input terminal. One end of the transmission line is connected to the end, and the other end of the transmission line is a signal input terminal.
Among the n transistor circuits, the signal input terminal of the first transistor circuit is connected to a high frequency input terminal,
The signal input terminals of the second to n-th transistor circuits are connected to bipolar transistors or electric fields of adjacent transistor circuits so that the first to n-th transistor circuits are sequentially cascade-connected to the high-frequency input terminal. A high-frequency amplifier circuit characterized by being sequentially connected to the base or gate of an effect transistor.

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