JP2007195158A - Radio frequency power amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration in the power load efficiency of a transistor that causes non-linear amplification in a method for controlling output power by controlling a collector voltage of the transistor. <P>SOLUTION: A radio frequency power amplifier 1 includes a former-stage transistor 2, a latter-stage transistor 3, and an inter-stage matching circuit 4 for connecting the former-stage transistor 2 and the latter-stage transistor 3. The inter-stage matching circuit 4 includes a high-pass filter circuit including a transfer line m1, a capacitor C1 and a capacitor C2, and a transfer line m2 whose passage phase of a secondary harmonic signal is 15° or greater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-frequency power amplifier that includes a plurality of stages of transistors and is suitable for power amplification of a high-frequency signal.

  High frequency power amplifiers used in wireless communication are desired to be designed with low distortion and high efficiency. In many communication systems, an orthogonal modulation method is used to improve the communication speed, and in order to suppress frequency spreading of the modulation signal, the communication signal is subjected to amplitude modulation in addition to phase modulation. For this reason, a linear amplifier capable of faithfully reproducing the amplitude modulation of the input signal is used as the high frequency power amplifier.

  On the other hand, in GMSK (Gaussian filtered Minimum Shift Keying) modulation used in GSM (Global System for Mobile Communications), a modulation signal generates an amplitude component by changing a binary value due to the positive / negative phase change. do not have. Therefore, the high frequency power amplifier used in the GSM system does not need to reproduce the power amplitude, and can be used as either a linear amplifier or a nonlinear amplifier. In general, a nonlinear amplifier capable of obtaining high efficiency is used. As described above, the high-frequency power amplifier used in wireless communication differs depending on the modulation method used.

  As is well known, high-frequency power amplifiers can be improved in efficiency by increasing the amount of gain compression, and further improved in efficiency by matching harmonic frequencies. However, the optimum conditions for effectively improving this efficiency differ depending on the method for controlling the output power of the high-frequency power amplifier and whether the high-frequency power amplifier is a linear amplifier or a nonlinear amplifier.

  For example, in Non-Patent Document 1, the efficiency at high gain compression is such that the second harmonic is opened and the third harmonic is released compared with a class F amplifier that short-circuits the second harmonic and opens the third harmonic. It is reported that an inverse class F amplifier with a short circuit is higher. Non-Patent Document 2 discloses that the efficiency at the time of 1 dB gain compression is higher for an inverse class F amplifier than a class F amplifier when the idle current is large, and when the idle current is small, the efficiency of the class F amplifier is higher than that of an inverse class F amplifier. Is reported to be higher. As described above, the high-frequency power amplifier can achieve high efficiency by optimally adjusting the harmonic matching conditions according to the communication system.

  In the GSM system, a high-efficiency nonlinear high-frequency power amplifier is used, and two methods are used for controlling the output power. The first method is a method of adjusting the output power by changing the power gain by controlling the base voltage of the transistor. The second method is a method of adjusting the output power by varying the power gain by controlling the collector voltage of the transistor.

  In the first method, since the output power changes logarithmically with respect to the base voltage, the sensitivity of the output power with respect to the base voltage increases, and it becomes difficult to control the output power. On the other hand, in the second method, since the output power changes in a linear function with respect to the collector voltage, the output power can be easily controlled.

FIG. 9 is a diagram showing a basic circuit configuration example of the high-frequency power amplifier 101 using the second method.
This high-frequency power amplifier 101 connects two transistors 102 and 103 in multiple stages in order to increase the power gain. Usually, the rear stage side transistor 103 has a large element size because of the large power to be amplified. For this reason, the rear-stage transistor 103 has a larger parasitic capacitance or the like than the front-stage transistor 102 and has a lower impedance than the front-stage transistor 102. For this reason, when transistors are connected in multiple stages, an interstage matching circuit 104 is provided for matching the impedances of the collector of the front-stage transistor 102 and the base of the rear-stage transistor 103.

  The interstage matching circuit 104 has a high-pass filter type composed of a grounded inductor Lp and a capacitor Cs connected in series shown in FIG. 10, or is connected in series with a grounded capacitor Cp shown in FIG. A low-pass filter type including the inductor Ls is used. However, the interstage matching circuit 104 needs to supply biases to the collector of the front-stage transistor 102 and the base of the rear-stage transistor 103 in addition to impedance matching, and separates the DC components of these biases. There is a need to.

  For this reason, in the low-pass filter type configuration, an impedance conversion element such as a transmission line for supplying a bias and an inductor is newly required to separate the high-frequency signal from the DC power source for driving the transistor. Furthermore, in order to separate the collector of the front-stage transistor 102 and the base of the rear-stage transistor 103, a series-connected capacitor is required, which increases the circuit scale.

On the other hand, in the high-pass filter type configuration, it is possible to supply a bias by grounding the inductor Lp via a capacitor, and bias separation can be performed by a capacitor Cs connected in series. For this reason, an impedance conversion element is unnecessary and a miniaturization design can be performed easily. For this reason, a high-pass filter type configuration is usually preferred. FIG. 12 is a diagram showing a configuration example of a conventional high-frequency power amplifier 101 using the high-pass filter type interstage matching circuit 104. In FIG. 12, the inductor L1 (= Lp) is grounded via the capacitor C1, and the collector of the front-stage transistor 102 and the base of the rear-stage transistor 103 are galvanically separated by the capacitor C2 (= Cs).
Inoue et al., “Analysis of Class F and Inverse Class F Amplifiers”, TECHNICICAL REPORT OF IEICE, ED2000-231, MW2000-180, ICD2000-191 (2001-01) "Comparison of efficiency between class F and inverse class F amplifiers", IEICE Electronics Society Conference (C-10-13), 2004

  However, the interstage matching circuit 104 configured as a high-pass filter type has a characteristic that the reflection of the harmonic signal in the interstage matching circuit 104 is small and most of the harmonic signal passes therethrough. For this reason, the impedance of the harmonic signal is not impedance-matched by the interstage matching circuit 104, and the harmonic load impedance characteristic of the front stage side transistor 102 becomes equal to the harmonic load impedance characteristic of the rear stage side transistor 103. Therefore, the impedance of the harmonic signal is a low impedance of the rear stage side transistor 103, and the impedance of the fundamental wave signal is a high impedance of the front stage side transistor 102.

  FIG. 13 is a diagram showing output power-efficiency characteristics of the front-stage transistor 102 in the conventional high-frequency power amplifier 101 using the interstage matching circuit 104 having a high-pass filter type configuration. In FIG. 13, the broken line indicates the relationship between output power and efficiency when the base voltage is controlled, and the solid line indicates the relationship between output power and efficiency when the collector voltage is controlled. As shown in FIG. 13, the efficiency gradually decreases when the base voltage is controlled, but there is a region where the efficiency decreases sharply when the collector voltage is controlled. The cause of this will be described with reference to FIGS.

  FIG. 14 is a diagram showing input power-output power characteristics in the conventional high-frequency power amplifier 101 using the interstage matching circuit 104 having a high-pass filter type configuration. The horizontal axis in FIG. 14 indicates input power, and the vertical axis indicates output power. The plurality of characteristic lines V1 to V6 are input / output characteristics indicating characteristics of output power with respect to input power of the high-frequency power amplifier at a plurality of collector voltages. The characteristic line V1 has the highest collector voltage, and the collector voltage decreases in the order of the characteristic lines V2, V3, V4, V5, and V6. In the method of controlling the collector voltage, the input power of the transmission signal input to the high frequency power amplifier 101 is constant, and the output power is adjusted along the line indicated by the broken line by adjusting the collector voltage. At this time, it can be confirmed that the input / output characteristics are in an excessive gain compression state in a region where the collector voltage is small.

  FIG. 15 is a diagram showing the input power-efficiency characteristics of the front-stage transistor 102 in the conventional high-frequency power amplifier 101 using the interstage matching circuit 104 having a high-pass filter type configuration. In FIG. 15, the horizontal axis indicates the input power, and the vertical axis indicates the efficiency of the pre-stage transistor 102. A plurality of characteristic lines V1 to V4 indicate the efficiency with respect to the input power of the high-frequency power amplifier at a plurality of collector voltages. The characteristic line V1 has the highest collector voltage, and the collector voltage decreases in the order of the characteristic lines V2, V3, and V4.

  In FIG. 15, when the input power is increased, it can be confirmed that the efficiency is sharply reduced due to an excessive gain compression state from the input / output characteristics shown in FIG. Further, in the case where such a characteristic is shown, if the collector voltage is controlled while the input power is fixed to the value of the broken line, the efficiency shown in FIG. 13 sharply decreases.

  Therefore, an object of the present invention is to provide a high frequency power amplifier capable of adjusting output power while suppressing a decrease in efficiency in a system for controlling a collector voltage.

  The present invention is directed to a high-frequency power amplifier in which transistors for nonlinear amplification are connected in multiple stages. In order to achieve the above object, a high-frequency power amplifier according to the present invention includes a front-stage transistor that inputs a signal to a base, a rear-stage transistor that outputs a signal from a collector, a collector of the front-stage transistor, and a rear-stage transistor. An interstage matching circuit that connects to the base is provided at least, and the interstage matching circuit includes a high-pass filter circuit and an impedance conversion element that sets the passing phase of the second harmonic signal to 15 degrees or more.

  Typically, a transmission line, an inductor, or a circuit in which an inductor and a capacitor are connected in parallel is used as the impedance conversion element.

  According to the present invention, it is possible to suppress a reduction in power load efficiency of a nonlinear amplification transistor that adjusts the output power by controlling the collector voltage of the transistor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a high-frequency power amplifier 1 according to an embodiment of the present invention. In FIG. 1, the high-frequency power amplifier 1 of the present embodiment includes a front-stage transistor 2, a rear-stage transistor 3, and an interstage matching circuit 4 that connects the front-stage transistor 2 and the rear-stage transistor 3. The interstage matching circuit 4 is a high-pass filter type circuit, and includes transmission lines m1 and m2 and capacitors C1 and C2.

  The pre-stage transistor 2 inputs a high frequency signal to the base and outputs the amplified high frequency signal from the collector. The emitter of the pre-stage transistor 2 is grounded. The amplified high-frequency signal output from the collector of the pre-stage transistor 2 is input to the base of the post-stage transistor 3 via the transmission line m2 and the capacitor C2. A collector bias is supplied to the connection point between the transmission line m2 and the capacitor C2 via the transmission line m1. One terminal of the transmission line m1 to which the collector bias is applied is grounded via the capacitor C1. A base bias is supplied to the base of the rear stage side transistor 3. The post-stage transistor 3 further amplifies the amplified high frequency signal input to the base, and then outputs it from the collector. The emitter of the rear stage side transistor 3 is grounded.

The present invention is characterized in that a transmission line m2 for adjusting harmonic impedance is provided in the interstage matching circuit 4 in order to suppress a decrease in amplification efficiency. This transmission line m2 has a function of controlling the reflection and passage of the second harmonic signal inside the interstage matching circuit 4, and preferably has a line length such that the passage phase of the second harmonic signal is 15 degrees or more. It is formed.
The effects produced by providing this transmission line m2 will be described with further reference to FIGS.

FIG. 2 is a diagram showing the input power-efficiency characteristic of the front-stage transistor 2 in the high-frequency power amplifier 1 when the interstage matching circuit 4 is provided with a transmission line m2 having a passing phase of 20 degrees. In FIG. 2, the horizontal axis represents the input power of the front-stage transistor 2, and the vertical axis represents the efficiency of the front-stage transistor 2. The plurality of characteristic lines V1 to V4 indicate the efficiency with respect to the input power of the high-frequency power amplifier 1 at a plurality of collector voltages. The characteristic line V1 has the highest collector voltage, and the collector voltage decreases in the order of the characteristic lines V2, V3, and V4.
As described above, even when the transmission line m2 is provided, the efficiency is lowered when the input power is increased, but the efficiency is gradually changed as compared with the conventional case (FIG. 15).

FIG. 3 is a diagram showing the output power-efficiency characteristics of the front-stage transistor 2 in the high-frequency power amplifier 1 when the interstage matching circuit 4 is provided with a transmission line m2 having a passing phase of 20 degrees. In FIG. 3, the broken line shows the relationship between the output power and efficiency of the front-stage transistor 2 (same as the solid line in FIG. 13) when the interstage matching circuit 104 (FIG. 12) without the conventional transmission line m2 is used. The solid line shows the relationship between the output power and the efficiency of the pre-stage transistor 2 when the interstage matching circuit 4 having the transmission line m2 of the present invention is used. The input power is fixed.
Thus, when there is the transmission line m2, the efficiency is improved as compared with the conventional case, and there is no region where the efficiency drops sharply.

FIG. 4 is a diagram showing the relationship between the passing phase of the transmission line m2 and the efficiency reduction rate. In FIG. 4, the horizontal axis indicates the passing phase of the second harmonic signal of the transmission line m2, and the vertical axis indicates the efficiency at the time of the maximum voltage given to the collector of the front-stage transistor 2 and the maximum voltage / 2. The ratio to the efficiency is shown.
Thus, as the passing phase of the second harmonic signal increases, the decrease in efficiency is suppressed and becomes substantially constant at 15 degrees or more.

As other configuration examples of the interstage matching circuit 4, the configurations shown in FIGS.
FIG. 5 shows a configuration in which the transmission line m1 of the interstage matching circuit 4 is replaced with an inductor L1. FIG. 6 shows a configuration in which the transmission lines m1 and m2 of the interstage matching circuit 4 are replaced with inductors L1 and L2, respectively. FIG. 7 shows a configuration in which the transmission line m1 of the interstage matching circuit 4 is replaced with an inductor L1, and the transmission line m2 is replaced with a parallel circuit of an inductor L3 and a capacitor C3. Whichever configuration is used, the same effect as that of the configuration of FIG. 1 can be obtained.

  In addition, as shown in FIG. 8, the input circuit 10 may be provided at the base of the front-side transistor 2, and the output circuit 20 may be provided at the collector of the rear-side transistor 3. Note that the input circuit 10 may be a high frequency power amplifier composed of one or more stages of transistors.

  The high-frequency power amplifier 1 shown in each drawing is an example and does not limit the circuit configuration of the present invention. As described above, the same effect can be obtained by providing an impedance conversion element in which the passing phase of the second harmonic signal is 15 degrees or more in any place of the interstage matching circuit 4.

  The high-frequency power amplifier of the present invention can be used for power amplification of a high-frequency signal, particularly when it is desired to suppress a decrease in power load efficiency of a nonlinear amplification transistor that adjusts output power by controlling the collector voltage of the transistor. Useful.

The figure which shows schematic structure of the high frequency power amplifier 1 which concerns on one Embodiment of this invention. The figure which shows an example of the input power-efficiency characteristic of the front | former stage side transistor 2 in the high frequency power amplifier 1 The figure which shows an example of the output power-efficiency characteristic of the front | former stage side transistor 2 in the high frequency power amplifier 1 The figure which showed the relationship between the passage phase of transmission line m2, and an efficiency fall rate The figure which shows schematic structure of the other high frequency power amplifier 1 which concerns on one Embodiment of this invention. The figure which shows schematic structure of the other high frequency power amplifier 1 which concerns on one Embodiment of this invention. The figure which shows schematic structure of the other high frequency power amplifier 1 which concerns on one Embodiment of this invention. The figure which shows schematic structure of the other high frequency power amplifier 1 which concerns on one Embodiment of this invention. The figure which shows the basic circuit structural example of the high frequency power amplifier 101 The figure which shows the structural example of the high-pass filter type interstage matching circuit 104 The figure which shows the structural example of the low-pass filter type interstage matching circuit 104. The figure which shows the structural example of the conventional high frequency power amplifier 101 using the high pass filter type interstage matching circuit 104. The figure which shows an example of the output power-efficiency characteristic of the front | former stage side transistor 102 in the conventional high frequency power amplifier 101 The figure which shows an example of the input power-output power characteristic of the front | former stage side transistor 102 in the conventional high frequency power amplifier 101 The figure which shows an example of the input power-efficiency characteristic of the front | former stage side transistor 102 in the conventional high frequency power amplifier 101

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 High frequency power amplifier 2, 3, 102, 103 Transistor 4, 104 Interstage matching circuit 10 Input circuit 20 Output circuit C1-C3, Cp, Cs Capacitance L1-L3, Lp, Ls Inductor m1, m2 Transmission line

Claims (4)

A high-frequency power amplifier in which transistors for nonlinear amplification are connected in multiple stages,
A pre-stage transistor that inputs a signal to the base;
A rear-stage transistor that outputs a signal from the collector;
An interstage matching circuit connecting at least a collector of the front side transistor and a base of the rear side transistor;
The interstage matching circuit is
A high-pass filter circuit;
A high-frequency power amplifier comprising: an impedance conversion element that sets a passing phase of a second harmonic signal to 15 degrees or more.   The high-frequency power amplifier according to claim 1, wherein the impedance conversion element is a transmission line.   The high-frequency power amplifier according to claim 1, wherein the impedance conversion element is an inductor.   The high-frequency power amplifier according to claim 1, wherein the impedance conversion element is a circuit in which an inductor and a capacitor are connected in parallel.

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