Matching circuit and multi-band amplifier

A matching circuit includes a demultiplexer for demultiplexing a signal outputted from an amplification device into signals of respective frequency bands, and at least two matching blocks which are connected to the demultiplexer, are respectively fed with the signals of the respective frequency bands, and perform impedance matching in the respective frequency bands of the inputted signals. Impedance matching is performed on each of the demultiplexed signals of the respective frequency bands, thereby achieving a matching circuit capable of efficiently performing impedance matching in the respective frequency bands. With this matching circuit, it is possible to achieve a multi-band amplifier capable of simultaneously amplifying signals of multiple frequency bands with high efficiency and low noise.

TECHNICAL FIELD

The present invention relates to a matching circuit for obtaining impedance matching between an amplification device and a peripheral circuit thereof to efficiently perform amplification. The present invention also relates to multi-band amplifiers which are capable of amplifying signals of multiple frequencies one by one or at the same time.

BACKGROUND ART

The diversification of radio communication service has increased demand for multi-band radio sets for processing signals of multiple frequency bands. In radio sets, an absolutely necessary device is a power amplifier. For efficient amplification, it is necessary to obtain impedance matching between an amplification device for amplifying a signal and a peripheral circuit of the device. Matching circuits are used for this purpose. Here, the input/output impedances of the peripheral circuit are generally set at a fixed value. Hereinafter, the input/output impedance of the peripheral circuit will be referred to as a “system impedance Z0”.

The reflection coefficient (S parameter) of the input and output of an amplification device used for an amplifier can be measured as shown inFIG. 1. Based on the reflection coefficient and the system impedance Z0, the input/output impedance of the amplification device can be measured. “S11” denotes the reflection coefficient of the input side of the amplification device and “S22” denotes the reflection coefficient of the output side of the amplification device.

The input/output impedances of the amplification device have frequency characteristics shown inFIG. 1. When an amplifier is designed using the amplification device, it is necessary to match the input/output impedances in each frequency band to the system impedance Z0.

Therefore, when designing a multi-band power amplifier, it is necessary to match the input/output impedances in each frequency band to the system impedance Z0.

Thus conventionally, when signals of multiple frequency bands are amplified, amplifiers including amplification devices and matching circuits are provided as many as frequency bands to be used and one of the amplifiers is selected according to a used frequency band as in, for example, an amplifier used in “band-sharing mobile equipment” (see, e.g., Non-patent document 1: “Mobile Equipment”, Koji Chiba et al., NTT DoCoMo technical journal, Vol. 10, No. 1). In another method, a matching circuit is designed to obtain a state close to impedance matching over used frequency bands. In still another method, some circuit constants of a matching circuit are changed.

The following will describe the method in which the circuit constants of a matching circuit are changed. The circuit constants of the matching circuit can be changed using variable devices and so on. As a matching circuit having a low loss, a matching circuit700ofFIG. 2is proposed which includes a main matching block701, a delay circuit702having one end connected to the main matching block701, a sub matching block703, and a switching device704connected between the other end of the delay circuit702and one end of the sub matching block703(for example, see Non-patent literature 2: “Multi-band Power Amplifier using MEMS Switch”, Atsushi Fukuda et al., General conference C-2-4, the Institute of Electronics, Information and Communication Engineers, 2004).

The matching circuit700shown inFIG. 2matches an impedance ZL(f) of a circuit connected to a port P2and having frequency characteristics to an input impedance Z0of the port P1. For example, the matching circuit acts as a matching circuit for signals of two frequency bands having frequencies F1and F2ofFIG. 3as center frequencies.

When the switching device704is turned off, the circuit ofFIG. 2acts as a matching circuit for a signal of the frequency band having the frequency F1as the center frequency. When the switching device704is turned on, the circuit ofFIG. 2acts as a matching circuit for a signal of the frequency band having the frequency F2as the center frequency. The states (ON/OFF) of the switching device704are switched thus, so that the matching circuit can be configured for the signals of the two frequency bands. In this case, by using, for example, MEMS technique for the switching device704, both of a low insertion loss and a high isolation can be relatively easily obtained over a wide band, so that a multi-band power amplifier can be configured with excellent characteristics.

In the method in which amplifiers including amplification devices and matching circuits are provided as many as frequency bands to be used and the amplifiers are switched according to a used frequency, it is necessary to provide different amplifiers for the respective frequency bands to be used, resulting in a large circuit size.

On the other hand, in the method using a matching circuit designed for a wide band and the method in which the circuit constants of a matching circuit are changed, there is an advantage in circuit size reduction and so on as compared with the method of switching amplifiers.

However, when using a matching circuit designed for a wide band, it is difficult to optimally design the matching circuit for used frequency bands. Particularly, problems arise in the design of a power amplifier requiring highly efficient operations.

In the method in which the circuit constants of a matching circuit are changed with reference toFIG. 2, the matching circuit can be optimally designed for used frequencies with relative ease, achieving a high power and highly efficient operations at each operating frequency.

However, there is a problem that signals of used frequency bands cannot be efficiently amplified at the same time. To be specific, when signals of multiple frequency bands are to be efficiently amplified at the same time, the same problem as wide-band matching arises, that is, it is difficult to optimally design the matching circuit for each operating frequency. Particularly problems arise in the design of a power amplifier requiring highly efficient operations.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a matching circuit efficiently operating for signals of multiple frequency bands, and a multi-band amplifier capable of efficiently amplifying the signals of the multiple frequency bands at the same time.

A first matching circuit of the present invention includes a demultiplexer for demultiplexing a signal outputted from an amplification device into signals of respective frequency bands, and at least two matching blocks which are connected to the demultiplexer, are respectively fed with the signals of the respective frequency bands, and perform impedance matching in the respective frequency bands of the inputted signals.

A second matching circuit of the present invention includes at least two matching blocks which are respectively fed with signals of respective frequency bands and perform impedance matching in the respective frequency bands of the inputted signals, and a multiplexer which is connected to the at least two matching blocks, multiplexes signals outputted from the matching blocks, and output the multiplexed signal to an amplification device.

A first multi-band amplifier of the present invention includes an amplification device for amplifying an inputted signal and outputting the signal to the demultiplexer of the first matching circuit, and the first matching circuit.

A second multi-band amplifier of the present invention includes a second matching circuit and an amplification device for amplifying a signal outputted from the multiplexer of the matching circuit and outputting the amplified signal.

BEST MODES FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 4shows an embodiment of an output-side circuit of a multi-band amplifier. A matching circuit of the present invention is provided on the output side of an amplification device of the multi-band amplifier, so that a power amplifier can be designed with high efficiency and high performance. A multi-band amplifier100shown inFIG. 4amplifies signals of two frequency bands f1and f2. The multi-band amplifier100is made up of an amplification device10and a matching circuit40. The matching circuit40is made up of a demultiplexer20, a matching block30, and a matching block31.

The amplification device10is fed with a combined signal of the signal of the first frequency band f1and the signal of the second frequency band f2. The amplification device10amplifies the inputted signal and outputs the amplified signal to the demultiplexer20. The demultiplexer20demultiplexes the signal having been amplified by the amplification device10into the signal of the frequency band f1and the signal of the frequency band f2, and outputs the signals to the different matching blocks. In this embodiment, the signal of the frequency band f1is outputted to the matching block30and the signal of the frequency band f2is outputted to the matching block31.

This is because regarding the signal of the frequency band f1, an impedance is sufficiently high when viewing the matching block31from the output terminal of the amplification device10through the demultiplexer20. Moreover, this is because regarding the signal of the frequency band f2, an impedance is sufficiently high when viewing the matching block30from the output terminal of the amplification device10through the demultiplexer20.

The matching block30matches a system impedance Z0and the impedance obtained for the signal of the frequency band f1with respect to the demultiplexer20. Further, the matching block31matches the system impedance Z0and the impedance obtained for the signal of the frequency band f2with respect to the demultiplexer20.

In this case, the matching block30and the matching block31only have to obtain matching for the signals of the corresponding frequency bands. The design of one of the matching blocks is not related to the configuration of the other matching block. Thus the matching blocks can be separately designed, so that the most suitable matching blocks can be configured for the respective frequency bands. It is therefore possible to configure a multi-band amplifier with high power and high efficiency in the frequency band f1and the frequency band f2.

Even when the signals of the two frequency bands are simultaneously inputted, each of the matching blocks is fed only with the signal of the corresponding frequency band, thereby achieving high-efficiency and high-power amplification in theory as in the case where the signal of one of the frequency bands is inputted.

The widths of the frequency bands f1and f2can be set as appropriate. For example, the number of frequencies included in the frequency band f1and the number of frequencies included in the frequency band f2may be different from each other. Further, the frequency band f1may include a single frequency F1and the frequency band f2may include a single frequency F2. The smaller the width of the frequency band, it is more easy to design a multi-band amplifier with high power and high efficiency. Moreover, the frequencies F1and F2included in the frequency bands f may have discrete values.

The multi-band amplifier100can be expanded for multiple bands and shared use with multiple bands.FIG. 5shows an embodiment of an output-side circuit of a multi-band amplifier104for multiple bands.

The amplification device11is fed with a combined signal of the signals of the M frequency bands from the first frequency band f1to the M-th frequency band fM. The amplification device11amplifies the inputted signal and outputs the amplified signal to the demultiplexer21. The demultiplexer21demultiplexes the signal having been amplified by the amplification device11into M signals of the frequency band f1to the frequency band fM, and outputs the demultiplexed signals of the respective frequency bands to the different matching blocks. In this embodiment, the signal of the frequency band f1is outputted to the matching block321, the signal of the frequency band fmis outputted to the matching block32m, and the signal of the frequency band fMis outputted to the matching block32M.

This is because regarding the signal of the frequency band fm(1≦m≦M), an impedance is sufficiently high when viewing the matching blocks other than the matching block32mfrom the output terminal of the amplification device11through the demultiplexer21.

Further, each of the matching blocks32m(1≦m≦M) matches the system impedance Z0and an impedance obtained for the signal of the frequency band fmwith respect to the demultiplexer21.

In this case, the matching blocks only have to obtain matching for the signals of the corresponding frequency bands. The design of one of the matching blocks is not related to the configuration of the other matching blocks. Thus the matching blocks can be separately designed, so that the most suitable matching blocks can be configured for the respective frequency bands. It is therefore possible to configure a multi-band amplifier with high power and high efficiency in the frequency bands fm(1≦m≦M).

Even when the signals of the M frequency bands are simultaneously inputted, each of the matching blocks is fed only with the signal of the corresponding frequency, thereby achieving, for example, high-efficiency and high-output amplification in theory as in the case where the signal of one of the frequencies is inputted.

A filter composing the demultiplexer may have the function of changing a frequency to allow the passage of signals of at least one of frequencies (Fm1to Fmp) included in the frequency band fm(p represents an integer not smaller than 2). In other words, signals of some of the frequencies (Fm1to Fmp) included in the frequency band fmmay be passed.

In this case, it is preferable that the matching block has the function of changing a frequency. Thus it is possible to perform impedance matching according to the frequency of the signal passed by a frequency variable filter, achieving operations with high power and high efficiency.

FIG. 6shows an example of a multi-band amplifier including a demultiplexer which uses filters having the function of changing a frequency and matching blocks which have the function of changing a frequency. A multi-band amplifier105includes an amplification device12and a matching circuit45. The amplification device12amplifies a combined signal of a signal of the frequency band f1including two frequencies F11and F12and a signal of the frequency band f2including two frequencies F21and F22. The matching circuit45has a demultiplexer22which includes frequency variable filters28and29having the function of changing a frequency and matching blocks33and34which have the function of changing a frequency.

The frequency variable filter28of the demultiplexer22allows the passage of the signal of one of the frequencies F11and F12. Likewise, the frequency variable filter29of the demultiplexer22allows the passage of the signal of one of the frequencies F21and F22.

The matching block33is preset to perform impedance matching at the frequency of the signal passed by the frequency variable filter28and thus the impedance matching is performed at the frequency of the signal passed by the frequency variable filter28. Likewise, the matching block34is also preset to perform impedance matching at the frequency of the signal passed by the frequency variable filter29and thus the impedance matching is performed at the frequency of the signal passed by the frequency-variable filter29.

With this configuration, a user of the present invention can select a frequency of the signal to be amplified, from one of the frequencies F11and F12and one of the frequencies F21and F22.

As described above, by providing the filters of the demultiplexer22and the matching blocks with the function of changing a frequency, it is possible to configure a high-efficiency and high-power multi-band amplifier for multiple bands and shared use with multiple bands.

As indicated by a broken line inFIG. 7, a pre-matching circuit9may be provided between the amplification device10and the demultiplexer20. The pre-matching circuit9is, for example, a circuit for changing the output impedance of the amplification device10to a value allowing the demultiplexer20and the matching blocks30and31to be designed with ease. Further, when the pre-matching circuit9is a harmonic processing circuit, a multi-band amplifier101can be further efficient. In this way, the pre-matching circuit9is applicable to various uses.

As shown inFIG. 8, a matching circuit43may include a multiplexer60. The multiplexer60combines the signal of the frequency band f1inputted from the matching block30and the signal of the frequency band f2inputted from the matching block31, and outputs the combined signal. With this configuration, a multi-band amplifier103can be configured with a single output.

FIG. 9Ashows a multi-band amplifier102having an isolator8and an isolator7in a matching circuit42. The isolator8operates in the frequency band f1and is connected to the output terminal of the matching block30. The isolator7operates in the frequency band f2and is connected to the output terminal of the matching block31. A signal amplified by the multi-band amplifier102is fed to an antenna (not shown) and the impedance of the antenna is expected to change with usage conditions. In this case, since the output impedance of the multi-band amplifier102changes, the matching state of the multi-band amplifier102changes and the characteristics deteriorate. By providing the isolator8and the isolator7, it is possible to prevent the changes of the impedance of the antenna from affecting the amplification characteristics of the multi-band amplifier102.

An inexpensive isolator has a narrow operating frequency range and thus the operating frequency band of a radio circuit including the isolator may depend upon the characteristics of the isolator. In the multi-band amplifier102ofFIG. 9A, even when spacing between the frequency band f1and the frequency band f2is wider as compared with the operating frequencies of the isolators, the isolators only have to correspond to the respective frequency bands.

As shown inFIG. 9B, the multiplexer60for multiplexing signals outputted from the isolators8and9is provided in a matching circuit46, so that a multi-band amplifier106can be configured with a single output.

When using a multi-band isolator or a wide-band isolator, as shown inFIG. 8, the isolator6is provided on the output terminal of the multiplexer60for multiplexing the outputs of the matching block30and the matching block31.

In addition to the configuration ofFIG. 9B, the methods of multiple bands1and2, the pre-matching circuit, the multiplexer, and the isolators can be combined as appropriate.

The demultiplexer can be configured by providing, for example, band pass filters (BPFs) in parallel which pass only a signal of a predetermined frequency band or band elimination filters (BEFs) in parallel which eliminate the passage of a signal of a predetermined frequency band. Further, the demultiplexer can be configured by providing in parallel combinations of band pass filters and band elimination filters.FIG. 10Ashows the characteristics of an ideal band pass filter andFIG. 10Bshows the characteristics of an ideal band elimination filter.

FIG. 11shows an example of a demultiplexer23using band elimination filters (hereinafter, will be referred to as BEFs). A BEF230is designed such that the frequency band f2is a rejection band. Conversely, a BEF231is designed such that the frequency band f1is a rejection band. When a combined signal of the signal of the frequency band f1and the signal of the frequency band f2is inputted to the BEF230and the BEF231, the BEF230outputs the signal of the frequency band f1because of the setting of the rejection band. The BEF231outputs the signal of the frequency band f2.

FIG. 12shows an example of a demultiplexer24using band pass filters (hereinafter, will be referred to as BPFs). A BPF241is designed such that the frequency band f1is a pass band. Conversely, a BPF242is designed such that the frequency band f2is a pass band. When a combined signal of the signal of the frequency band f1and the signal of the frequency band f2is inputted to the BPF241and the BPF242, the BPF241outputs the signal of the frequency band f1because of the setting of the pass band. The BPF242outputs the signal of the frequency band f2.

InFIGS. 11 and 12, in some combinations of the frequency band f1and the frequency band f2, it is difficult to design filters such that the signal of one of the frequency bands is reflected and the signal of the other frequency band is passed. In this case, instead of disposing the BPFs or the BEFs in parallel, the BPF and the BEF are cascade-connected, so that the filters can be easily designed.

FIG. 13shows an example of a demultiplexer27using filters having cascade-connected BPFs and BEFs. A signal inputted to the demultiplexer27is inputted to a filter including a BPF241and a BEF230and a filter including a BEF231and a BPF242. The pass band and the rejection band are set as described above, and thus the filter including the BPF241and the BEF230outputs the signal of the frequency band f1. The filter including the BEF231and the BPF242outputs the signal of the frequency band f2. InFIG. 13, the order of connection of the BPF and the BEF is not particularly significant. Further, a filter having at least two cascade-connected BPFs and BEFs may be used as necessary.

FIG. 14shows a structural example of the filter. InFIG. 14, a filter900is a BEF made up of a transmission line901having a length equal to a quarter of a wavelength λ of a frequency to be rejected and an end open line902which is connected to one end of the transmission line and has a length equal to a quarter of the wavelength λ.

FIG. 15shows the frequency characteristics of the filter900.FIG. 15shows a reflection coefficient S11and a transmission coefficient S21when 2 GHz is selected as a frequency to be rejected and the line length is λ/4. A signal incident from a port1at the set frequency (2 GHz) is reflected without being transmitted to a port2.

The transmission line can be made up of, for example, a microstrip line or a coplanar line. Further, the filter may be configured by grounding through a series resonant circuit made up of lumped elements. The filter may have any given configuration according to a filtering theory.

The filter ofFIG. 14can be easily configured for multiple bands.FIG. 16shows a two-band filter910using switching devices.

The two-band filter910is made up of a transmission line911, an open-end line912, and an open-end line913. When frequencies F1and F2have wavelengths λ1and λ2, respectively, the lines have lengths shown inFIG. 16. To be specific, the length of the open-end line912is λ1/4, a length from the end of the transmission line on the signal input side to a portion connected to the open-end line912is λ1/4, the length of the open-end line913is λ2/4, and a length from the end of the transmission line on the signal input side to a portion connected to the open-end line913is λ2/4. A switching device SW1is provided between the transmission line911and the open-end line912. A switching device SW2is provided between the transmission line911and the open-end line913. By switching these switching devices, it is possible to switch connections between the transmission line911and the open-end lines.

When the switching device SW1is turned on, the frequency F1is a rejection frequency. When the switching device SW2is turned on, the frequency F2is a rejection frequency.

The two-band filter910can be used as the frequency-variable filters28and29of the multi-band amplifier105shown inFIG. 6.

The two-band filter910can be easily expanded for two bands or more. For example, when a frequency Fito be rejected has a wavelength of λi, an open-end line having a length of λi/4 is disposed at a distance of λi/4 from the end of the transmission line on the signal input side. This arrangement is used for each frequency Fito be rejected, so that the filter can be configured for multiple bands.

When a variable capacitor is disposed on one end of the open-end line on the side not connected to the transmission line, frequency to be rejected can be finely adjusted by changing the value of the variable capacitor.

Further, with a single amplification device, the matching circuits may be switched using a switch with one input and multiple outputs. However, in the case of a large frequency difference and a large number of switching systems, it is generally difficult to obtain compatibility between a preferable insertion loss and isolation characteristics of the switch, resulting in difficulty in achieving an efficient switch.

When a demultiplexer of elimination type is used instead of a switch as in the present invention, a power loss is reduced as compared with the case where a switch is used. Thus an advantageous effect of a small circuit size can be obtained. This is because the demultiplexer of elimination type has a simple configuration and reduces the number of components. Moreover, even in the case of multiple bands, only a simple switch having one input and one output is basically used, achieving an efficient switch.

FIG. 17shows a structural example of a variable matching circuit having the function of changing a frequency. The variable matching circuit920shown inFIG. 17is a variable matching circuit described in Non-patent document 2. For example, for the signals of the frequency F1and the frequency F2, matching can be obtained between a target impedance and a system impedance by selecting on/off states of a switching device SW3. A variable matching circuit920is made up of a transmission line921, an open-end line922, and an open-end line923. InFIG. 17, the variable matching circuit920becomes a matching circuit for the frequency F1when the switching device SW3is turned off, and the variable matching circuit920becomes a matching circuit for the frequency F2when the switching device SW3is turned on. The variable matching circuit920can be used as, for example, the matching blocks33and34of the multi-band amplifier105shown inFIG. 6. Further, the variable matching circuit920can be easily expanded for two or more bands (e.g., see Non-patent document 2).

Second Embodiment

In the first embodiment, the matching circuits and the multi-band amplifiers are disposed on the output side. A similar matching circuit may be used on the input side of a multi-band amplifier. By disposing the matching circuit of the present invention on the input side, an amplifier can be designed with high efficiency. In the following explanation, the same parts as those of the first embodiment are indicated by the same reference numerals and the explanation thereof is omitted.

FIG. 18shows an example of a multi-band amplifier in which the matching circuit of the first embodiment is used on the input side of the multi-band amplifier. A multi-band amplifier500shown inFIG. 18amplifies the signals of two frequency bands f1and f2. The multi-band amplifier500is made up of an amplification device10and a matching circuit501. The matching circuit501includes, for example, a multiplexer60, a matching block530, and a matching block531.

Of the input signals of the frequency bands f1and f2to the multi-band amplifier500, the signal of the frequency band f1is inputted to the matching block530and the signal of the frequency band f2is inputted to the matching block531. The matching block530matches a system impedance Z0and an impedance obtained for the signal of the frequency band f1with respect to the multiplexer60, and outputs the signal to the multiplexer60. The matching block531matches the system impedance Z0and an impedance obtained for the signal of the frequency band f2with respect to the multiplexer60, and outputs the signal to the multiplexer60.

The multiplexer60multiplexes the signals outputted from the matching blocks530and531and outputs, to the amplification device10, a combined signal of the signal of the frequency band f1and the signal of the frequency band f2.

In this case, the matching blocks530and531only have to achieve matching for the signals of the corresponding frequency bands. Further, the design of one of the matching blocks is not related to the configuration of the other matching block. Thus the matching blocks can be separately designed, so that the most suitable matching blocks can be configured for the respective frequency bands. It is therefore possible to achieve a design with high power and high efficiency in the frequency bands f1and f2, so that the multi-band amplifier can be configured with high efficiency.

Even when the signals of the two frequency bands are simultaneously inputted, each of the matching blocks is fed only with the signal of the corresponding frequency band, thereby satisfying the same matching conditions in theory as in the case where the signal of one of the frequency bands is inputted.

The multi-band amplifier500of a second embodiment can be modified as the modifications of the multi-band amplifier of the first embodiment. For example, a configuration for multiple bands can be achieved by providing three or more matching blocks having different target impedances. Further, the multi-band amplifier500can be designed with one input and one output by providing a demultiplexer20in the matching circuit501. The demultiplexer20, the matching blocks, and the multiplexer may be provided with the function of changing a frequency. Furthermore, the output terminal of the multiplexer may be provided with a pre-matching circuit9. These modifications may be combined.

Third Embodiment

A multi-band amplifier of a third embodiment is obtained by combining the matching circuit and the amplification device of the first embodiment and the matching circuit of the second embodiment. For example, a multi-band amplifier600shown inFIG. 19includes a matching circuit501described in the second embodiment, the amplification device10for amplifying a signal outputted from the matching circuit501, and the matching circuit40for performing, for each frequency band, impedance matching on a signal outputted from the amplification device10in the first embodiment.

The configurations and functions of the parts are similar to those of the first and second embodiments. Thus the same parts are indicated by the same reference numerals and the explanation thereof is omitted. As in the first and second embodiments, the matching circuit501and the matching circuit40can be configured for multiple bands and may include the demultiplexer20, the multiplexer60, the isolators7and8, and the pre-matching circuit9as appropriate.

By disposing the matching circuits of the present invention on the input side and the output side, the multi-band amplifier can be designed with high efficiency, high power, and low noise.

Fourth Embodiment

A multi-band amplifier1000according to a fourth embodiment inFIG. 20includes the two dual-system multi-band amplifiers (hereinafter, will be referred to as an amplifier1002and an amplifier1003) described in the first embodiment and combining circuits75and76for combining the signal outputs of the same frequency band out of the outputs of the systems.

In this configuration, the amplifier1002has a high saturation output power and the amplifier1003has a low saturation output power. Generally, an amplifier can efficiently amplify a signal around the saturation output power and thus the efficiency decreases when, for example, a signal at a low output level is amplified by an amplifier having a high saturation output power. Therefore, in the multi-band amplifier1000, a signal at a high output power level is amplified by the first amplifier1002and a signal at a low output power level is amplified by the second amplifier1003. Thus efficient operations can be achieved at all output levels.

An output power level is detected by control means made up of a comparator77, switches72and73, and a power supply78. The comparator77compares the power level of an input signal with a predetermined value. The input signal is divided by a divider1004and is inputted to the comparator77. For example, the predetermined value is set beforehand at a value between the saturation output powers of the amplifiers1002and1003.

When the power level of the input signal is higher than the predetermined value, the comparator77turns on the switch72and turns off the switch73. Thus the power of the power supply78is supplied to the amplification device10of the amplifier1002to operate the amplifier1002. When the predetermined value is lower than the power level of the input signal, the comparator77turns on the switch73and turns off the switch72. Thus the power of the power supply78is supplied to the amplification device10of the amplifier1003to operate the amplifier1003.

In this configuration, the amplifiers1002and1003each include output terminals of two systems for the respective frequency bands, and the combining circuits75and76combine signals of the same frequency bands out of signals outputted from the amplifiers. To be specific, the signals of a frequency band f1from the matching block30of the amplifier1002and the matching block30of the amplifier1003are combined and outputted by the combining circuit75, and the signals of a frequency band f2from the matching block30of the amplifier1002and the matching block31of the amplifier1003are combined and outputted by the combining circuit76. In this case, the combining circuit75is designed for each frequency band.

Since the different amplifiers are turned on according to the output levels, the output impedances of the amplifiers also fluctuate. In this case, the combining circuits75and76are designed in consideration of the output impedances of the amplifiers1002and1003.

As indicated by a broken line inFIG. 20, a multiplexer60may be provided for multiplexing the signal of the frequency band f1from the combining circuit75and the signal of the frequency band f2from the combining circuit76and outputting a multiplexed signal.

Further, as in the first and second embodiments, the amplifier1002and the amplifier1003can be configured for multiple bands and may include the demultiplexer20, the multiplexer60, the isolators7and8, and the pre-matching circuit9as appropriate.

Moreover, two or more amplifiers having different saturation output powers may be provided and control means may be provided for selecting one of the two or more amplifiers according to the power of an inputted signal and driving only the selected amplifier. For example, based on a plurality of predetermined threshold values, the control means selects one of the amplifiers according to the power of the inputted signal. For example, when N amplifiers An(n=1, . . . N) having different saturation output powers are used, N−1 different threshold values an(n=1, . . . , N−1) are prepared. Control can be performed such that an amplifier A1is used when the input signal has a power W<a1, an amplifier Akis used for ak-1<W<akwhere k=2, . . . , N−1, and an amplifier ANis used for aN-1<W. The threshold value ancan be set as appropriate.

In the multi-band amplifier1000ofFIG. 20, the amplifiers1002and1003are the output-side multi-band amplifiers described in the first embodiment. The amplifiers1002and1003may be the input-side multi-band amplifier500described in the second embodiment with reference toFIG. 18or the multi-band amplifier600described in the third embodiment with reference toFIG. 19. When the input-side multi-band amplifier500described in the second embodiment is used as the amplifiers1002and1003, it is preferable that a signal outputted from the divider1004is inputted to the demultiplexers of the multi-band amplifiers500and signals outputted from the amplification devices10(seeFIG. 18) of the multi-band amplifiers500are combined by one of the combining circuits75and76.

In this way, the two or more amplifiers having different saturation output powers are provided and the most suitable amplifier is selected according to the power of an inputted signal, so that a multi-band amplifier can be designed with higher efficiency and higher power.

Fifth Embodiment

A plurality of dividers, a plurality of amplifiers according to the present invention, and a plurality of combiners are cascade-connected, so that a signal of each frequency is divided into multiple signals by dividers designed for corresponding frequencies, the divided signals are amplified by the amplifiers of respective systems, and the amplified signals are combined by combiners designed for the corresponding frequencies. As examples of an amplifier achieved with this configuration, a multi-port amplifier and a Doherty amplifier will now be described. The multi-port amplifier will now be discussed as a fifth embodiment. The Doherty amplifier will be described later.

First, a Butler matrix used as a divider and a combiner in the multi-port amplifier will be described below. The simplest Butler matrix includes, for example, a 90 degree hybrid.FIG. 21illustrates the configuration of the 90 degree hybrid. A 90 degree hybrid801is a circuit having four ports (ports802to805). A signal inputted from the port802passes through the 90 degree hybrid801, so that the signal is equally divided with a 90-degree phase difference and is outputted to the port804and the port805. Similarly, a signal inputted from the port803passes through the 90 degree hybrid801, so that the signal is equally divided with a 90-degree phase difference and is outputted to the port804and the port805.

FIG. 22shows that a similar Butler matrix810is connected to the port804and the port805. A signal outputted from the port804is inputted to a port812and is outputted to a port814and a port815. Similarly, a signal outputted from the port805is inputted to a port813and is outputted to the port814and the port815. In this case, the input signal to the port803is transmitted to the port814without a loss and the input signal to the port802is transmitted to the port815without a loss.

In the configuration of a typical multi-port amplifier, as indicated by broken lines inFIG. 22, unit amplifiers820and821having the same characteristics are connected between the port804and the port812and between the port805and the port813, respectively. In a Butler matrix800, even when signal powers inputted to the port802and the port803are different, input powers to the unit amplifiers are equalized, that is, signal powers on the port804and the port805are equalized.

By using the multi-band amplifier of the present invention as the unit amplifiers820and821indicated by the broken lines inFIG. 22, a multi-port amplifier for multiple bands can be configured. To be specific, as shown inFIG. 23, two multi-band amplifiers including the demultiplexers20and the multiplexers60according to the third embodiment are respectively provided as the unit amplifier820and the unit amplifier821between the Butler matrix800and the Butler matrix810. The configurations and functions of the parts of the unit amplifiers820and821are similar to those described above. Thus the same parts are indicated by the same reference numerals and the explanation thereof is omitted.

The port802of the Butler matrix800in a multi-port multi-band amplifier1100is fed with a combined signal (hereinafter, will be referred to as a signal f11f21) of the signal of a frequency band f1(hereinafter, will be referred to as a signal f11) and the signal of a frequency band f2(hereinafter, will be referred to as a signal f21), and the port803is fed with a combined signal (hereinafter, will be referred to as a signal f12f22) of the signal of the frequency band f1(hereinafter, will be referred to as a signal f12) and the signal of the frequency band f2(hereinafter, will be referred to as a signal f22).

According to the characteristics of the Butler matrix, a combined signal f11f21f12f22(first signal) of the signal f11f21having been shifted in phase by 90 degrees and the signal f12f22is outputted from the port804(first output terminal) of the Butler matrix800. Further, a combined signal f11f21f12f22(second signal) of the signal f11f21and the signal f12f22having been shifted in phase by 90 degrees is outputted from the port805(second output terminal).

The unit amplifier820amplifies the first input signal f11f21f12f22and outputs the amplified signal to the port812of the Butler matrix810. The unit amplifier821amplifies the second input signal f11f21f12f22and outputs the amplified signal to the port813of the Butler matrix810.

From the Butler matrix810fed with the first amplified signal f11f21f12f22from the port812and the second amplified signal f11f21f12f22from the port813, the signal f12f22is outputted to the port814and the signal f11f21is outputted to the port815.

The unit amplifiers820and821can be configured for multiple bands by the same methods as those of the first to third embodiments and may include pre-matching circuits, isolators, and the function of changing a frequency.

A Butler matrix usable in the present embodiment is not limited to a matrix with two inputs and two outputs. The present embodiment is applicable to a Butler matrix having B input ports and B output ports where B represents an integer not smaller than 3. For example, in the case of B output ports, it is preferable that unit amplifiers are provided in parallel as many as the B output ports, between an input-side Butler matrix and an output-side Butler matrix.

Sixth Embodiment

An actual Butler matrix including a 90 degree hybrid has frequency characteristics. In this case, the Butler matrix exerts the foregoing effect only at a design frequency. Thus as shown inFIG. 24, Butler matrixes90and91(92,93) designed to efficiently operate in each frequency band are used as a divider and combiner and the multi-band amplifier1201and the amplifier1202of the third embodiment are used, so that the amplifier1201and the amplifier1202can be shared in multiple frequency bands. Thus a multi-port and multi-band amplifier can be achieved with a small size.

The Butler matrixes90and91are designed to efficiently operate in a frequency band f1and the Butler matrixes92and93are designed to efficiently operate in a frequency band f2.

The Butler matrix90combines a signal f11of the frequency band f1from a port901and a signal f12of the frequency band f1from a port902through a 90 degree hybrid, and outputs a first signal f11f12from a port903(first output terminal). Further, the Butler matrix90outputs a second signal f11f12from a port904(second output terminal). Likewise, the Butler matrix92combines a signal f21of the frequency band f2from a port921and a signal f22of the frequency band f2from a port922through a 90 degree hybrid, and outputs a first signal f21f22from a port923(first output terminal). Further, the Butler matrix90outputs a second signal f21f22from a port924(second output terminal).

The first signal f11f12and the first signal f21f22that are respectively outputted from the Butler matrixes90and92are inputted to a matching circuit1203of the amplifier1201. The second signal f11f12and the second signal f21f22that are outputted from the Butler matrixes90and92are inputted to a matching circuit1205of the amplifier1202.

The amplifiers1201and1202amplify the inputted signals f11f12and f21f22and output signals of the respective frequency bands. The functions, configurations, and processing of the parts of the amplifiers1201and1202are similar to those of the first to third embodiments and thus the explanation thereof is omitted.

The Butler matrix91is fed with the signal f11f12of the frequency band f1from a matching circuit1204of the amplifier1201and the signal f11f12of the frequency band f1from a matching circuit1206of the amplifier1202. The Butler matrix93is fed with the signal f21f22of the frequency band f2from the matching circuit1204of the amplifier1201and the signal f21f22of the frequency band f2from the matching circuit1206of the amplifier1202. In other words, each of the Butler matrixes is fed with the signals of the same frequency band out of the signals outputted from the matching circuits of the respective amplifiers (that is, the respective matching circuits).

The Butler matrix91outputs the inputted signal through a 90 degree hybrid, so that the signal f12is outputted from a port913and the signal f11is outputted from a port914. The Butler matrix93outputs the inputted signal through a 90 degree hybrid, so that the signal f22is outputted from a port933and the signal f21is outputted from a port934.

The amplifiers1201and1202can be configured for multiple ports by the same methods as those of the first to third embodiments and may include pre-matching circuits, isolators, and the function of changing a frequency.

A Butler matrix usable in the present embodiment is not limited to a matrix with two inputs and two outputs. The present embodiment is also applicable to a Butler matrix having B input ports and B output ports where B represents a natural number not smaller than 3. For example, in the case of B output ports, it is preferable that the amplifiers of the third embodiment are provided in parallel as many as the B output ports, between an input-side Butler matrix and an output-side Butler matrix. In this case, as in the foregoing embodiments, the first signals outputted from the input-side Butler matrixes are inputted to the same amplifier and the second signals outputted from the input-side Butler matrixes are inputted to the other amplifier. The third and subsequent signals are inputted in a similar manner. Further, of the signals outputted from the amplifiers, the signals of the same frequency band are inputted to the same output-side Butler matrix in the above manner.

When increasing the number of frequency bands to be amplified, it is preferable that the input side Butler matrixes and the output-side Butler matrixes are provided as many as the frequency bands. In this case, it is necessary to increase the number of matching blocks in each amplifier with the number of frequency bands.

Seventh Embodiment

In a seventh embodiment, the matching circuit and the multi-band amplifier of the present invention are applied to a Doherty amplifier.

FIG. 25shows a structural example of a typical Doherty amplifier251. The Doherty amplifier251includes, for example, an input-side Doherty network252, an output-side Doherty network253, a carrier amplifier254, and a peak amplifier255.

The input-side Doherty network252includes one input terminal (port256) and two output terminals (ports257and258). Further, the input-side Doherty network252includes a divider259which divides a signal inputted from the port256and outputs the divided signals respectively to the port257and the port258and a λ/4 wavelength line260which is disposed between the divider259and the port258and shifts by 90 degrees the phase of the signal to be outputted to the port258.

The output-side Doherty network253includes two input terminals (ports262and263) and one output terminal (port264). Further, the output-side Doherty network253includes a combiner266which combines a signal inputted from the port262and a signal inputted from the port263and a λ/4 wavelength line265which is disposed between the combiner266and the port262, shifts by 90 degrees the phase of the signal inputted from the port262, and outputs the signal to the combiner266.

The carrier amplifier254is disposed between the port257and the port262. The carrier amplifier254is biased to, for example, class F.

The peak amplifier255is disposed between the port258and the port263. The peak amplifier255is biased to, for example, class C.

A signal inputted from the port256to the input-side Doherty network252is divided to two paths by the divider259. One of the divided signals is outputted from the port257and is amplified by the carrier amplifier254. The other signal passes through the λ/4 wavelength line260, so that the signal is shifted in phase by 90 degrees from the signal outputted from the port257. After that, the signal is outputted from the port258and is amplified by the peak amplifier255.

The signal amplified by the carrier amplifier254is inputted to the output-side Doherty network253from the port262and passes through the λ/4 wavelength line265, so that the signal is shifted in phase by 90 degrees from the signal amplified by the peak amplifier255and is outputted to the combiner266. The signal amplified by the peak amplifier255is inputted from the port263to the output-side Doherty network253and is outputted to the combiner266. The combiner266combines the two amplified input signals.

As long as the input signal is present, the carrier amplifier254amplifies and outputs the signal. In other words, even in the case of a small instantaneous input signal, the signal is amplified and outputted.

The peak amplifier255is biased to class C. In the case of a small instantaneous input signal, the input level is not high enough to turn on the peak amplifier255. Thus the peak amplifier255is turned off and does not output any signals. Since the DC power consumption of the peak amplifier255is sufficiently low, the overall Doherty amplifier251has high efficiency. In the case of a large instantaneous input signal, not only the carrier amplifier254but also the peak amplifier255are turned on, so that the peak amplifier255also amplifies and outputs a signal.

In other words, in the Doherty amplifier251, the peak amplifier255operates when the input signal has a high power, so that the two output powers of the carrier amplifier254and the peak amplifier255are combined to increase a saturation power and an apparent load impedance applied to the carrier amplifier254fluctuates with the power of the input signal. Thus efficient operations can be achieved.

In this case, the λ/4 wavelength lines260and265of the Doherty amplifier251have frequency characteristics and the above effect can be obtained in theory only at a frequency having a wavelength λ. Thus as shown inFIG. 26, input-side Doherty networks2521and2522designed for the respective frequency bands are used as dividers, output-side Doherty networks2531and2532designed for the respective frequency bands are used as combiners, and the multi-band amplifiers of the third embodiment are connected in parallel as a carrier amplifier1301and a peak amplifier1302between the input-side Doherty network and the output-side Doherty network, so that a Doherty multi-band amplifier1300can be configured with a small size.

The Doherty network multi-band amplifier1300shown inFIG. 26includes the input-side Doherty network2521, the input-side Doherty network2522, the output-side Doherty network2531, the output-side Doherty network2532, the carrier amplifier1301, and the peak amplifier1302.

The input-side Doherty network2521includes a port401to which the signal of a frequency band f1is inputted, a divider2591which divides the signal inputted from the port401to two paths and outputs the divided signals respectively to a port402and a port403, and a λ/4 wavelength line2601which is provided between the divider2591and the port403and shifts the phase of a passed signal by 90 degrees. Of the divided signals, the signal outputted from the port402is used as a first signal and the signal outputted from the port403is used as a second signal.

The input-side Doherty network2522includes a port411to which the signal of a frequency band f2is inputted, a divider2592which divides the signal inputted from the port411to two paths and outputs the divided signals respectively to a port412and a port413, and a λ/4 wavelength line2602which is provided between the divider2592and the port413and shifts the phase of a passed signal by 90 degrees. Of the divided signals, the signal outputted from the port412is used as a first signal and the signal outputted from the port413is used as a second signal.

The first signal outputted from the port402of the input-side Doherty network2521and the first signal outputted from the port412of the input-side Doherty network2522are inputted to a matching circuit1303of the carrier amplifier1301. In other words, the first signals outputted from the input-side Doherty networks are inputted to the matching circuit1303of the carrier amplifier1301.

The second signal outputted from the port403of the input-side Doherty network2521and the second signal outputted from the port413of the input-side Doherty network2522are inputted to a matching circuit1305of the peak amplifier1302. In other words, the second signals outputted from the input-side Doherty networks are inputted to the matching circuit1305of the peak amplifier1302.

The carrier amplifier1301is biased to, for example, class F. The carrier amplifier1301amplifies the first signal (the signal of the frequency band f1) outputted from the input-side Doherty network2521and the first signal (the signal of the frequency band f2) outputted from the input-side Doherty network2522and outputs the signals for the respective frequency bands. To be specific, a matching block30of a matching circuit1304in the carrier amplifier1301outputs the signal of the frequency band f1, and a matching block31of the matching circuit1304in the carrier amplifier1301outputs the signal of the frequency band f2. The functions, configurations, and processing of the carrier amplifier1301are similar to those of the first to third embodiments and thus the explanation thereof is omitted.

The peak amplifier1302is biased to, for example, class C. The peak amplifier1302amplifies the second signal (the signal of the frequency band f1) outputted from the input-side Doherty network2521and the second signal (the signal of the frequency band f2) outputted from the input-side Doherty network2522and outputs the signals for the respective frequency bands. To be specific, a matching block30of a matching circuit1306in the peak amplifier1302outputs the signal of the frequency band f1, and a matching block31of the matching circuit1306in the peak amplifier1302outputs the signal of the frequency band f2. The functions and configurations of the peak amplifier1302are similar to those of the first to third embodiments and thus the explanation thereof is omitted.

The signal of the frequency band f1from the matching block30of the matching circuit1304in the carrier amplifier1301is inputted from a port421to the output-side Doherty network2531. The signal of the frequency band f1from the matching block30of the matching circuit1306in the peak amplifier1302is inputted from a port422to the output-side Doherty network2531. The signal of the frequency band f2from the matching block31of the matching circuit1304in the carrier amplifier1301is inputted from a port431to the output-side Doherty network2532. The signal of the frequency band f2from the matching block31of the matching circuit1306in the peak amplifier1302is inputted from a port432to the output-side Doherty network2532. In this way, of the signals outputted from the matching blocks on the output side of the amplifiers, the signals of the same frequency band are outputted to the same output-side Doherty network.

The output-side Doherty network2531has a λ/4 wavelength line2593and a combiner2603. The combiner2603combines the signal of the frequency band f1from the port422and the signal of the frequency band f1, the signal having been inputted from the port421and shifted in phase by 90 degrees through the λ/4 wavelength line2593. And then, the combiner2603outputs the combined signal from a port423.

The output-side Doherty network2532has a λ/4 wavelength line2594and a combiner2604. The combiner2604combines the signal of the frequency band f2from the port432and the signal of the frequency band f2, the signal having been inputted from the port431and shifted in phase by 90 degrees through the λ/4 wavelength line2594. And then, the combiner2604outputs the combined signal from a port433.

When increasing the number of frequency bands to be amplified, it is preferable that the input-side Doherty networks and the output-side Doherty networks are provided as many as the frequency bands. In this case, it is necessary to increase the number of matching blocks in the amplifiers with the number of frequency bands.

In this case, as in the foregoing embodiments, the first signals outputted from the input-side Doherty networks are inputted to the carrier amplifier and the second signals outputted from the input-side Doherty networks are inputted to the peak amplifier. Further, of the signals outputted from the amplifiers, the signals of the same frequency band are inputted to the same output-side Doherty network in the above manner.

The first signals may be inputted to the peak amplifier and the second signals may be inputted to the carrier amplifier.

In the Doherty multi-band amplifier1300, when the input signal has a low power, the peak amplifier1302does not operate and thus the saturation power is low, whereas when the input signal has a high power, the peak amplifier1302operates and thus the saturation power increases. Therefore, the Doherty multi-band amplifier1300efficiently operates regardless of the power of the input signal.

The carrier amplifier1301and the peak amplifier1302can be configured for multiple bands by the same methods as those of the first to third embodiments and may include pre-matching circuits, isolators, and the function of changing a frequency.

Since the plurality of Doherty networks designed for the respective frequency bands are used, the circuit size may become a problem. The circuit size can be reduced by, for example, disposing dividers and combiners in the layers of a multilayer board as shown inFIG. 27. In the example ofFIG. 27, the divider and the combiner of the frequency band f1are provided in a first layer272formed on one of the surfaces of a ground layer271and the divider and the combiner of the frequency band f2are provided in a second layer273formed on the other surface of the ground layer271.

Another Embodiment

As a matter of course, the matching circuit of the present invention is applicable to uses other than amplifiers. In other words, the matching circuit of the present invention is applicable to the overall circuit in which an impedance changes with a frequency.

Only signals of some of design frequency bands may be inputted to the matching circuit and the multi-band amplifier of the present invention. In other words, it is not necessary to input the signals of all the design frequency bands. For example, although the design frequency of the multi-band amplifier100described with reference toFIG. 4is a frequency band f1and a frequency band f2, only a signal of the frequency band f1may be inputted out of the design frequencies. This holds true in other embodiments.

EXPERIMENTAL EXAMPLE

FIG. 28shows a design example of the multi-band amplifier for 1.5 GHz/2.5 GHz according to the present invention. A multi-band amplifier6000ofFIG. 28includes a matching circuit623, an amplification device601, a transmission line614having a length of 3.423 mm, a demultiplexer602, a matching block605for performing impedance matching in a 2.5 GHz frequency band, and a matching block606for performing impedance matching in a 1.5 GHz frequency band.

The matching circuit623includes an open-end line610having a length of 4.823 mm, a transmission line611having a length of 2.886 mm, an open-end line612having a length of 9.205 mm, and a transmission line having a length of 4.823 mm. The matching circuit623is designed to obtain matching in each band.

The demultiplexer602includes a filter603and a filter604. The filters603and604are designed based on the configuration ofFIG. 14. To be specific, the filter603includes a transmission line615having a length of 19.75 mm and an open-end line616having a length of 19.75 mm. The filter604includes a transmission line617having a length of 11.83 mm and an open-end line618having a length of 11.83 mm.

The matching blocks605and606are configured such that for a signal of each frequency, a transmission line and an open-end line have an impedance equal to a system impedance with respect to the demultiplexer. To be specific, the matching block605includes a transmission line619having a length of 0.14 mm and an open-end line620having a length of 18.45 mm. The matching block606includes a transmission line621having a length of 0.04 mm and an open-end line622having a length of 0.2 mm.

FIG. 29shows the frequency characteristics of the circuit. InFIG. 29, S21indicates transmission characteristics from a port607to a port608and S31indicates transmission characteristics from the port607to a port609. InFIG. 29, S21has the maximum gain at around 2.5 GHz and the multi-band amplifier operates as an amplifier of the 2.5 GHz band. S31has the maximum gain at around 1.5 GHz and the multi-band amplifier operates as an amplifier of the 1.5 GHz band. On the other hand, S21has a sufficiently small gain at around 1.5 GHz and S31similarly has a sufficiently small gain at around 2.5 GHz. In other words, when signals of 2.5 GHz and 1.5 GHz are inputted to the multi-band amplifier6000, the signals are amplified and outputted to the port608and the port609, respectively. As is evident fromFIG. 29, the signals of the two frequencies can be simultaneously amplified.

A matching circuit of the present invention performs impedance matching on each demultiplexed signal of each frequency band, thereby efficiently performing impedance matching in each frequency band. Further, according to the multi-band amplifier of the present invention, signals of multiple frequency bands can be simultaneously amplified with high efficiency and low noise by means of the matching circuits of the multi-band amplifier.