JP2004048174A - Power amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To change over one function as a nonlinear amplifier and another function as a linear amplifier with a bias voltage fixed. <P>SOLUTION: An input signal A from an input terminal 1 is fed via a combiner 7 to an input matching circuit 2 to which a zero or positive fixed bias voltage Vgs is applied. Its output is fed to an active element 3 such as bipolar transistor, FET, etc. to amplify it. Thus, the active element 3 operates as a class B or AB amplifier. When the element 3 functions as a linear amplifier, the input signal A passes through the combiner 7, as it is, so that the output of the element 3 is approximately proportional to its input. When the element 3 functions as a nonlinear amplifier, a harmonic generator circuit 6 generates odd-order harmonic components of the input signal A, and the combiner 7 combines them with the input signal A to form a rectangular wave signal B which is then fed to the active element 3. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power amplifier used for wireless communication and the like.
[0002]
[Prior art]
FIG. 5 is a block diagram showing a conventional example of a power amplifier, wherein 1 is an input terminal, 2 is an input-side matching circuit, 3 is an active element such as a bipolar transistor or an FET (field effect transistor), and 4 is an output-side matching circuit. The circuit 5 is an output terminal.
[0003]
In the figure, an input side matching circuit 2 for setting a matching condition between an input side and an active element 3 in order to minimize a noise figure of the amplifier, an active element 3 for amplifying a signal, and a gain of the amplifier being maximized. And an output-side matching circuit 4 for setting a matching condition between the active element and the output side. The signal input from the input terminal 1 is supplied to the active element 3 via the input side matching circuit 2, amplified there, and output from the output terminal 5 via the output side matching circuit 4.
[0004]
Here, in the input side matching circuit 2, in order to operate the active element 3 in a predetermined state, a bias voltage suitable for the operation is added to the input signal, and the active element 3 is operated with this bias voltage. .
[0005]
By the way, as a power amplifier used in a wireless communication system that performs communication in the UHF, VHF band or the like, for example, as described in Japanese Patent Application Laid-Open No. 9-321550 and Japanese Patent No. A class C amplifier that performs non-linear operation and has high power conversion efficiency is used. That is, in an active element that performs such a class C amplification operation, for example, in a bipolar transistor, when a signal is input, the emitter-collector is saturated and a maximum current flows, but the voltage between them becomes zero, and When no signal is input, the emitter-collector is turned off and no current flows, and a voltage is applied between them. Thus, ideally, between the emitter and the collector, the period during which the current flows and the period during which the voltage is applied are different, and the power consumed here is zero. Further, since the flowing current is maximum, a large amount of power is supplied to the load side.
[0006]
As described above, since the class C amplifier uses a nonlinear region, the waveform of the output signal is distorted. However, the other class A, class B, and AB in which a bias voltage intermediate between them is used. Larger power conversion efficiency can be obtained compared to a class amplifier, and large power can be sent to the load side.
[0007]
In the class C power amplifier having the configuration shown in FIG. 5, in the input side matching circuit 2, a bias voltage (−V _gs ) that is negative with respect to the operation region of the active element 3 is added to the input signal.
[0008]
[Problems to be solved by the invention]
By the way, in the above-mentioned conventional power amplifier, high efficiency is achieved by placing the operating point in a nonlinear region (that is, by using a class C amplifier). However, in such a conventional power amplifier, a large waveform distortion is unavoidable, and a power amplifier capable of increasing the power conversion efficiency while avoiding the occurrence of such large waveform distortion has been developed. Is desired.
[0009]
Depending on the place where the power amplifier is used, there are cases where the power amplifier needs to operate in a non-linear region or in a linear region depending on the input signal handled at that time. Such a variable output power amplifier is not in a desired situation.
[0010]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a variable output power amplifier capable of achieving both reduction of waveform distortion and power conversion efficiency. .
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a harmonic generation circuit that generates an odd harmonic component of an input signal and turns on and off the output thereof, and an odd harmonic component output from the harmonic generation circuit. Is combined with the input signal to output a rectangular wave signal, and when the harmonic generation circuit does not output odd harmonic components, a combiner that outputs the input signal as it is, and an active element that amplifies the output signal of the combiner And it is possible to selectively operate the active element with a linear amplifier and a non-linear amplifier.
[0012]
The harmonic generation circuit includes a frequency converter that generates an odd multiple of the frequency of the input signal and an attenuator that attenuates the output signal of the frequency converter, and generates a harmonic that generates an odd harmonic component of the input signal. And an on / off switch, and supplies the odd-order harmonic component generated by the harmonic generation means to the combiner via the switch.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a power amplifier according to the present invention, in which reference numeral 6 denotes a harmonic generation circuit, reference numeral 7 denotes a combiner, and portions corresponding to those in FIG. Is omitted.
[0014]
In the figure, a signal A inputted from an input terminal 1 is supplied to a combiner 7, combined with a harmonic component supplied from a harmonic generation circuit 6, and supplied to an input side matching circuit 2. The harmonic generation circuit 6 generates an odd-order harmonic component of the input signal A. The harmonic component of the input signal A is synthesized, so that the input signal A is output from the synthesizer 7. The signal is converted into a rectangular wave signal B and output.
[0015]
The rectangular wave signal B is supplied to the active element 3 via the input side matching circuit 2 and is amplified there and output to the output side matching circuit 4. In this case, the input signal B A zero or positive bias voltage (+ V _gs ) is applied to the active element 3 so that the active element 3 operates as a class B or class AB amplifier.
[0016]
When no harmonic component is supplied from the harmonic generation circuit 6 to the combiner 7, the input signal A from the input terminal 1 passes through the combiner 7 as it is, and the same bias voltage (+ V _gs) ) Is supplied to the active element 3. That is, the bias voltage (+ V _gs ) is fixed to zero or a constant positive voltage value.
[0017]
Therefore, when no harmonic component is supplied from the harmonic generation circuit 6 to the synthesizer 7, the input signal A from the input terminal 1 is amplified as it is by the active element 3 performing the class B or class AB amplification operation. In this case, the active element 3 outputs a signal whose waveform is substantially proportional to the input signal A, and functions as a linear amplifier operating in a linear region. At this time, since the active element 3 operates as a class B or class AB amplifier, the power conversion efficiency is relatively high.
[0018]
On the other hand, when the harmonic component of the input signal A is supplied from the harmonic generation circuit 6 to the combiner 7, the amplitude is larger than that of the input signal A because the harmonic component is combined with the input signal A. The large rectangular wave signal B is supplied to the active element 3 as a class B or class AB amplifier. For this reason, the active element 3 is saturated during the signal period of substantially half cycle of the rectangular wave signal B, and performs a switching operation similar to that of the class C amplifier to output a rectangular wave signal whose rising and falling are steep. That is, the active element 3 functions as a nonlinear amplifier that operates in a nonlinear region where the output signal is not proportional to the input signal A.
[0019]
When the active element 3 functions as a non-linear amplifier in this way, it operates as shown in FIG. 2, similarly to the conventional class C amplifier. That is, the active element 3 as a class B or class AB amplifier operates approximately every half cycle of the rectangular wave signal B. If the active element 3 is a bipolar transistor, for example, the rectangular wave signal B the signal period of the half cycle of, ideally, the collector - the collector and the emitter is saturated (oN) - emitter voltage V _CE becomes zero, flows a collector current I _C is. In another nearly half cycle period of the square wave signal B, the collector - emitter region is the collector current I _C is turned off becomes zero, the collector - becomes the voltage V _CE generated not zero between the emitters. And thus the collector current I _C and the collector - emitter voltage V _CE is the time non-overlapping in time, the power consumption in this bipolar transistor 3 becomes zero, the voltage conversion efficiency is 100%. This is the same when the active element 3 is an FET.
[0020]
However, in practice, the active element 3 has an ON resistance (for example, a non-zero resistance between the drain and the source when it is turned on in the case of an FET, and a collector-emitter when it is turned on in the case of a bipolar transistor). it is not a zero resistance) is present between, and since the rectangular wave signal B obtained by the synthesizer 7 also, that not a perfect square wave, for example, in the case of a bipolar transistor, a rectangular wave signal flowing collector current I _C A non-zero voltage _VCE is generated between the collector and the emitter during a part of the period of almost half the period of B. In terms of Figure 2, it will be overlapping and duration of the period and the current I _C of the voltage V _CE part, so that the power consumption occurs in the overlap period.
[0021]
For this reason, even when the active element 3 is operated as a non-linear amplifier, power is consumed there, but the power consumption is negligible. Therefore, the voltage conversion efficiency is lower than when the active element 3 is operated as a linear amplifier. Will be large.
[0022]
As described above, in this embodiment, by controlling the output of the harmonic component in the harmonic generation circuit 6, the active element 3 can be used as a linear amplifier or a non-linear amplifier without changing the bias voltage. Can also function, and a variable output power amplifier can be obtained.
[0023]
FIG. 3 is a block diagram showing a specific example of the harmonic generation circuit 6 in FIG. 1, wherein 8 and 9 are frequency converters, 10 and 11 are attenuators, 12 is a synthesizer, 13 is a switch, and 14 is a delay circuit. The same reference numerals are given to portions corresponding to those in FIG. 1 and duplicate description will be omitted.
[0024]
FIG. 4 is a waveform diagram showing signals of respective parts in FIG. 3, and the same reference numerals are given to the signals corresponding to FIG.
[0025]
3 and 4, the input signal A of the frequency f _C input from the input terminal 1 is delayed by the delay circuit 14 and supplied to the synthesizer 7, and is also supplied to the harmonic generation circuit 6.
[0026]
In the harmonic generation circuit 6, the input signal A is supplied to the frequency converter 8 to multiply the frequency by 3, and further supplied to the attenuator 10 to attenuate the amplitude to 1/3. As a result, a signal C having a frequency 3 f _C that is three times the frequency of the input signal A and an amplitude that is 振幅 times as large as the frequency of the input signal A is obtained from the attenuator 10 as the third harmonic component of the input signal A. The input signal A is also supplied to the frequency converter 9 where the frequency is multiplied by 5, and further supplied to the attenuator 11 where the amplitude is attenuated to 1/5. Thus, from this attenuator 11, amplitude 5 times the frequency 5f _C of the frequency of the input signal A is the 1/5 of the signal D is obtained as a fifth-order harmonic component of the input signal A. The third harmonic component C and the fifth harmonic component D are combined by the combiner 12.
[0027]
The switch 13 is closed (turned on) when operating the active element 3 (FIG. 1) as a nonlinear amplifier, and is opened (turned off) when operating the active element 3 (FIG. 1) as a linear amplifier. When the switch 13 is on, a combined signal of the harmonic components C and D from the combiner 12 is supplied to the combiner 7 via the switch 13. On the other hand, the input signal A is delayed by the delay circuit 14 for a time equal to the processing time in the harmonic generation circuit 6, supplied to the combiner 7, and combined with the combined signal from the combiner 12. Thereby, a rectangular wave signal B is obtained from the synthesizer 7.
[0028]
Thus, in this specific example, the input signal A can be converted into a rectangular wave signal and supplied to the input side matching circuit 2. When operating the active element 3 (FIG. 1) as a linear amplifier, the switch 13 is set to an off state. Thereby, the input signal A from the input terminal 1 is supplied to the input side matching circuit 2 as it is via the delay circuit 14 and the combiner 7. Therefore, the switch 13 has a function of selecting one of the input signal A and a rectangular wave signal obtained by converting the input signal A and supplying the selected signal to the active element 3.
[0029]
Here, in this specific example, two types of harmonic components of the third harmonic component C and the fifth harmonic component D are used as the harmonic components of the input video signal A, but one odd harmonic component is used. A component, for example, only the third harmonic component may be used. However, when the types of the odd-order harmonic components to be used are small, the output signal B of the combiner 7 at that time is a rectangular wave signal having a rectangular wave shape but a waveform whose amplitude fluctuates to some extent. , May slightly cause a reduction in voltage conversion efficiency in the active element 3 (FIG. 1) operated as a non-linear amplifier. In order to prevent this, higher-order odd-order harmonic components may be generated and combined with the input signal A.
[0030]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a variable output power amplifier capable of switching between a linear amplification function and a non-linear amplification function while maintaining a constant bias voltage. Thus, it can be used for either one of these amplification functions.
[Brief description of the drawings]
FIG. 1 is a block diagram showing one embodiment of a power amplifier according to the present invention.
FIG. 2 is a diagram showing an ideal timing relationship between a collector-emitter voltage and a collector current in an active element during a nonlinear amplification operation of the embodiment shown in FIG. 1;
FIG. 3 is a block diagram showing a specific example of a harmonic generation circuit in FIG. 1;
FIG. 4 is a waveform chart showing signals of respective units in FIG. 4;
FIG. 5 is a diagram illustrating a configuration of a class C power amplifier.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Input terminal 2 Input side matching circuit 3 Active element 4 Output side matching circuit 5 Output terminal 6 Harmonic generation circuit 7 Synthesizer 8, 9 Frequency converter 10, 11 Attenuator 12 Synthesizer 13 Switch 14 Delay circuit

Claims (2)

A harmonic generation circuit that generates an odd harmonic component of the input signal and turns on and off the output of the odd harmonic component;
When the odd-order harmonic component output from the harmonic generation circuit is combined with the input signal to output a rectangular wave signal, and when the harmonic generation circuit does not output the odd-order harmonic component, the input signal is And a synthesizer that outputs
A power amplifier, comprising: an active element for amplifying an output signal of the combiner, wherein the active element is selectively operated by a linear amplifier and a non-linear amplifier. The power amplifier according to claim 1,
The harmonic generation circuit,
A frequency converter that receives the input signal and generates an odd multiple of the frequency of the supplied input signal; and an attenuator that attenuates an output signal of the frequency converter, wherein the odd-order harmonic of the input signal is provided. Harmonic generation means for generating a component;
A power amplifier, comprising: a switch that performs an on / off operation, wherein the odd-order harmonic component generated by the harmonic generation means is supplied to the combiner via the switch.

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