There is provided a high-frequency amplifier including a divider, a plurality of amplifiers for amplifying a high-frequency signal distributed by the divider and outputting the amplified high-frequency signal, a combiner for combining amplified high-frequency signals, a base substrate, a conductor pattern that is connected to a ground end of each of the amplifiers, and a ground electrode. Each of the conductor patterns has a first conductive portion. A slot is disposed between the two conductor patterns connected to the corresponding adjacent amplifiers. Between the adjacent amplifiers, two vias are formed so that the slot is sandwiched between the vias. One of the two conductor patterns is connected to the ground electrode via one of the two vias, and the other one of the conductor patterns is connected to the ground electrode via the other one of the two vias.

BACKGROUND

The present invention relates to a high-frequency amplifier for amplifying an input high-frequency signal.

In recent years, high-frequency amplifiers including a Field Effect Transistor (FET) using a gallium arsenide (GaAs) process, a silicon-germanium (SiGe) process, a Complementary Metal Oxide Semiconductor (CMOS) process, or the like have been used for terrestrial microwave communication and satellite communication so as to transmit a radio signal in a microwave range of 1 GHz or higher. Such a high-frequency amplifier generally amplifies an input high-frequency signal using a plurality of amplifiers, combines high-frequency signals amplified by these amplifiers, and outputs a resultant signal so as to obtain high power. These amplifiers in such a high-frequency amplifier each include a group of a plurality of FET elements or FETs, and are arranged in parallel so as to perform power amplification. In such a configuration, a divider distributes an input high-frequency signal equally among a plurality of amplifiers and a combiner combines high-frequency signals output from these amplifiers and outputs a resultant signal.

In current years, F-class amplification is employed in high-frequency amplifiers and the increase in power efficiency is achieved with harmonics. A high-frequency amplifier employing the F-class amplification is a broadband high-frequency amplifier that can handle harmonics such as second and third harmonics of frequencies higher than a target frequency and uses zero power for all harmonics by short-circuiting even harmonics such as a second harmonic and opening odd harmonics such as a third harmonic. This leads to high power efficiency. However, the second and third harmonics have short wavelengths and easily propagate through various signal lines. In order to prevent such a harmonic from outputting from the output end of a combiner, a circuit for reflecting the harmonic is provided. However, for example, when an input high-frequency signal is distributed between two parallel-connected amplifiers by a divider and signals output from these two amplifiers are combined by a combiner, a loop path of the output end of one of the amplifiers, the line of the combiner, the output end of the other one of the amplifiers, the input end of the other one of the amplifiers, the line of the divider, the input end of one of the amplifiers, and the output end of one of the amplifiers is generated. In this loop, oscillation may occur. Therefore, Patent Reference 1 discloses the method of preventing the occurrence of loop oscillation between the input end of a high-frequency amplifier and an amplifier.

FIG. 9is a schematic diagram of a high-frequency amplifier1xdisclosed in Patent Reference 1. The high-frequency amplifier1xillustrated inFIG. 9includes a divider substrate40x, an amplification circuit substrate50x, and a combiner substrate60x. The divider substrate40xhas a conductor pattern including a plurality of branching terminals21x,22x,23x, and24xfor distributing a high-frequency signal input into an input terminal20x. The amplification circuit substrate50xamplifies high-frequency signals output from the branching terminals21x,22x,23x, and24x. The combiner substrate60xcombines high-frequency signals output from the amplification circuit substrate50x. In the conductor pattern of the divider substrate40x, resistive pattern portions41x,42x,43x, and44xare formed between the input terminal20xand the branching terminals21x,22x,23x, and24x, respectively, on an insulating substrate. The resistive pattern portions41x,42x,43x, and44xbetween the input terminal20xof the high-frequency amplifier1xand the amplification circuit substrate50xattenuate high-frequency loop signals and prevent the occurrence of loop oscillation.

PRIOR ART REFERENCE

Patent Reference

Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2011-44812

SUMMARY

For example, when an input high-frequency signal is distributed between two parallel-connected amplifiers including source-grounded FETs by a divider and signals output from these two amplifiers are combined by a combiner, a loop path of the output end (FET's drain) of one of the amplifiers, the line of the combiner, the output end (FET's drain) of the other one of the amplifiers, the input end (FET's gate) of the other one of the amplifiers, the line of the divider, the input end (FET's gate) of one of the amplifiers, and the output end (FET's drain) of one of the amplifiers is generated. In this case, since a high impedance is obtained between the drain and gate of each FET, a high-frequency signal does not propagate through the loop path.

The high-frequency signal that has flowed from the output end of one of the amplifiers to the output end of the other one of the amplifiers easily passes through a path from the drain to source of an FET. Accordingly, the high-frequency signal propagates through a loop path (hereinafter referred to as “an oscillation loop path between amplifiers”) of the output end (FET's drain) of one of the amplifiers, the line of the combiner, the output end (FET's drain) of the other one of the amplifiers, the ground end (FET's source) of the other one of the amplifiers, the ground end (FET's source) of one of the amplifiers, and the output end (FET's drain) of one of the amplifiers. However, it is difficult to prevent the occurrence of oscillation due to this loop with the method disclosed in Patent Reference 1. When an amplifier amplifies a high-frequency signal, heat is produced. Accordingly, when the spacing between adjacent ones of a plurality of amplifiers in a high-frequency amplifier is reduced for the sake of the size reduction of the high-frequency amplifier, thermal runaway occurs and the electric characteristic of the high-frequency amplifier is deteriorated. Although a case where an FET is used as an amplifier has been described, this difficulty also occurs in a case where a Hetero-junction Bipolar Transistor (HBT) or another transistor is used as an amplifier.

The present invention has been made in view of the above-described difficulty in the related art, and it is an object of the present invention to provide a high-frequency amplifier capable of preventing the occurrence of loop oscillation between an amplifier and a combiner and the deterioration of an electric characteristic due to thermal runaway.

A first feature of a high-frequency amplifier according to the present invention is that the high-frequency amplifier includes a divider for distributing an input high-frequency signal, a plurality of parallel-connected amplifiers for amplifying a high-frequency signal distributed by the divider and outputting the amplified high-frequency signal, a combiner for combining high-frequency signals amplified by the amplifiers, a substrate on which the amplifiers are disposed, a conductor pattern connected to a ground end of each of the amplifiers, and a ground electrode. The conductor pattern has a first conductive portion extending in a direction in which the amplifiers are adjacent to each other. A slot is disposed between two conductor patterns connected to corresponding adjacent ones of the amplifiers. Between the adjacent amplifiers, two vias passing through the substrate are formed so that the slot is sandwiched between the vias. One of the two conductor patterns connected to the corresponding adjacent amplifiers is connected to the ground electrode via one of the two vias. The other one of the two conductor patterns connected to the corresponding adjacent amplifiers is connected to the ground electrode via the other one of the two vias.

According to the present invention having the above-described feature, one of high-frequency signals output from one of the adjacent amplifiers flows to the output end of the other one of the amplifiers via the line of the combiner and then flows to the ground end of the other one of the amplifiers. The slot prevents this high-frequency signal from flowing to one of the amplifiers. The high-frequency signal flows to the ground electrode via the conductor pattern and the via connected to the ground end of the other one of the amplifiers.

As a result, the flow of a high-frequency signal through an oscillation loop path between the above-described amplifiers can be prevented and the occurrence of loop oscillation can be prevented. Heat produced by the amplifiers is dissipated to the ground electrode via the conductor patterns and the vias between the adjacent amplifiers. As a result, the deterioration of the electric characteristics of the amplifiers due to thermal runaway can be prevented.

A second feature of a high-frequency amplifier according to the present invention is that the conductor pattern has, between the adjacent amplifiers, a second conductive portion extending in a direction different from the direction in which the first conductive portion extends, second conductive portions of the two conductor patterns connected to the corresponding ones of the adjacent amplifiers extend in directions away from each other, and the second conductive portions are connected to the corresponding vias.

In order to form two vias, the spacing between the two vias is needed. According to the present invention having the above-described features, however, since the second conductive portions of the two conductor patterns that are connected to the corresponding amplifiers extend in directions away from each other that are different from the direction in which the amplifiers are adjacent to each other and the first conductive portions extend and the vias are connected to the corresponding second conductive portions, the two vias can be formed even if the spacing between the adjacent amplifiers is reduced. Accordingly, the spacing between the adjacent amplifiers can be reduced and a small high-frequency amplifier can be provided.

A third feature of a high-frequency amplifier according to the present invention is that a length of the slot is substantially equal to or less than a half-wavelength of a high-frequency signal used.

According to the present invention having the above-described features, since the length of the slot is set to the length substantially equal to or less than a half-wavelength of the high-frequency signal used, the slot does not resonate at the frequency of the high-frequency signal used.

As a result, even when the slot is disposed, oscillation does not occur.

A fourth feature of a high-frequency amplifier according to the present invention is that the high-frequency amplifier further includes in parallel with the slot a resistance element connected between the two conductor patterns connected to the corresponding adjacent amplifiers and the adjacent amplifiers are connected to each other via the conductor patterns and the resistance element.

According to the present invention having the above-described features, since in parallel with the slot the resistance element is connected between the two conductor patterns that are connected to the corresponding adjacent amplifiers, the resistance element is present on an oscillation loop path between the amplifiers. Accordingly, a high-frequency signal flowing through the oscillation loop path between the amplifiers passes through the resistance element.

As a result, the high-frequency signal flowing through the oscillation loop path between the amplifiers is attenuated at the resistance element and the occurrence of loop oscillation can be prevented for high-frequency signals in all frequency ranges.

A fifth feature of a high-frequency amplifier according to the present invention is that the high-frequency amplifier further includes in parallel with the slot a resonance circuit connected between the two conductor patterns connected to the corresponding adjacent amplifiers, the adjacent amplifiers are connected to each other via the conductor patterns and the resonance circuit, and the resonance circuit forms a low-pass filter.

According to the present invention having the above-described features, the connected resonance circuit is provided in parallel with the slot and the adjacent amplifiers are connected to each other via the conductor patterns and the resonance circuit. Accordingly, the resonance circuit is present on an oscillation loop path between the amplifiers, and a high-frequency signal flowing through the oscillation loop path between the amplifiers passes through the resonance circuit.

Since the resonance circuit forms a low-pass filter, a harmonic component in the high-frequency signal flowing through the oscillation loop path between the amplifiers can be attenuated. As a result, the occurrence of loop oscillation due to a harmonic component can be prevented.

A sixth feature of a high-frequency amplifier according to the present invention is that the high-frequency amplifier further includes in parallel with the slot a resonance circuit connected between the two conductor patterns connected to the corresponding adjacent amplifiers, the adjacent amplifiers are connected to each other via the conductor patterns and the resonance circuit, the resonance circuit forms a notch filter, and a resonance point of the notch filter is a frequency of a high-frequency signal used.

According to the present invention having the above-described features, the connected resonance circuit is provided in parallel with the slot and the adjacent amplifiers are connected to each other via the conductor patterns and the resonance circuit. Accordingly, the resonance circuit is present on an oscillation loop path between the amplifiers, and a high-frequency signal flowing through the oscillation loop path between the amplifiers passes through the resonance circuit.

The resonance circuit forms a notch filter, and the resonance point of the notch filter is the frequency of a high-frequency signal used. Accordingly, a frequency component in the high-frequency signal used is attenuated by the resonance circuit. As a result, the occurrence of loop oscillation due to a frequency component in a high-frequency signal used can be further prevented.

A seventh feature of a high-frequency amplifier according to the present invention is that an insulating material with which an inside of the slot is filled has a dielectric constant lower than that of an insulating material used around the slot.

According to the present invention having the above-described features, since the insulating material with which the inside of the slot is filled has a dielectric constant lower than that of the insulating material used around the slot, the level of insulation against a high-frequency signal flowing through the oscillation loop path between the amplifiers is increased.

As a result, the occurrence of loop oscillation can be further prevented. In addition, since the level of insulation inside the slot is high, loop oscillation does not occur even when the width of the slot is reduced. The size reduction of a high-frequency amplifier can be therefore achieved.

According to the present invention, there can be provided a high-frequency amplifier capable of preventing the occurrence of loop oscillation between an amplifier and a combiner and the deterioration of an electric characteristic due to thermal runaway.

DETAILED DESCRIPTION OF EMBODIMENTS

Preferred embodiments for implementing the present invention will be described in detail with reference to the drawings. The following description of the embodiments is not intended to limit the present invention. The constituent elements described below include those that a person skilled in the art could easily assume, those that are substantially the same as the constituent elements, or those that fall within the scope of equivalents of the constituent elements. The constituent elements described below may be combined as appropriate. Furthermore, the constituent elements may be omitted, replaced, or modified without departing from the spirit of the present invention.

First Embodiment

FIG. 1is a semiconductor layout chart illustrating the entire configuration of a high-frequency amplifier1according to the first embodiment.FIG. 2is a cross-sectional view taken along the line A-A′ ofFIG. 1.FIG. 3is a cross-sectional view taken along the line D-D′ ofFIG. 1. The high-frequency amplifier1includes a divider3for distributing a high-frequency signal input from an input end2, a plurality of parallel-connected amplifiers6for amplifying a distributed high-frequency signal and outputting the amplified high-frequency signal, a combiner8for combining high-frequency signals amplified by the amplifiers6and outputting a resultant signal from an output end7, a base substrate4on which the amplifiers6are disposed, a conductor pattern9that is connected to the ground end of each of the amplifiers6, and a ground electrode11. Each of the amplifiers6includes a plurality of transistors5. The amplifiers6are connected to the divider3and the combiner8and are connected in parallel to the input end2and the output end7. The divider3, the amplifiers6, and the combiner8are formed on one surface of the base substrate4. The ground electrode11is formed on the other surface of the base substrate4.

Each of the conductor patterns9has a first conductive portion9A that extends in a direction in which the amplifiers6are adjacent to each other and a second conductive portion9B that extends between the adjacent amplifiers6in a direction different from the extending direction of the first conductive portion9A. The second conductive portions9B of the two conductor patterns9that are connected to the corresponding adjacent amplifiers6extend in directions away from each other.

In the high-frequency amplifier1, a slot14is disposed between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6. Between the adjacent amplifiers6, the slot14is sandwiched between two vias10A that pass through the base substrate4. The via10A is connected to the second conductive portion9B. One of the two conductor patterns9that are connected to the corresponding adjacent amplifiers6is connected to the ground electrode11via one of the two vias10A. The other one of the two conductor patterns9that are connected to the corresponding adjacent amplifiers6is connected to the ground electrode via the other one of the two vias10A. Portion of the conductor pattern9opposite to the adjacent amplifiers is connected to the ground electrode11via via10B that passes through the base substrate4. As illustrated inFIGS. 1, 2, and 3, the slot14is disposed between the two conductor patterns9so as to prevent the electric connection between the adjacent amplifiers6via the conductor patterns9. Between the adjacent amplifiers6, the two conductor patterns9are point symmetric with respect to the slot14and the two vias10A are point symmetric with respect to the slot14. The slot14has a function of electrically attenuating a high-frequency signal. As illustrated inFIG. 1, a void having a rectangular shape when viewed in plan is disposed at an angle with respect to a direction in which the first conductive portions9A extend and the slot14is formed by filling the void with an insulating material. The insulating material is the same as an insulating material15to be described later.

The transistors5are field-effect transistors. Each of the amplifiers6is formed by connecting the transistors5in parallel for multiple stages. As illustrated inFIG. 2, each of the transistors5includes a gate electrode5A, a drain5B, a drain electrode5C, a source5D, and a source electrode5E on the base substrate4. The divider3and the gate electrode5A are connected. The drain electrode5C and the combiner8are connected. The source electrode5E and the conductor pattern9are connected. The gate electrode5A corresponds to the input end of the amplifier6. The drain electrode5C corresponds to the output end of the amplifier6. The source electrode5E corresponds to the ground end of the amplifier6.

The surrounding portions of the gate electrodes5A, the drain electrodes5C, the source electrodes5E, the vias10A, and the vias10B are filled with the insulating material15such as polyimide or silicon oxide.

Next, the operation of the high-frequency amplifier1will be described with reference toFIG. 1. When a high-frequency signal is input into the high-frequency amplifier1, the divider3distributes the high-frequency signal between two portions. The distributed high-frequency signals are input into the input ends of the corresponding amplifiers6and are amplified. The amplified high-frequency signals are output from the corresponding amplifiers6to the output end via the combiner8. However, not only a high-frequency signal to be output to the output end7but also a high-frequency signal to be flowed to the other line (the line connected to the other one of the adjacent amplifiers6) of the combiner8and a high-frequency signal reflected from a matching circuit (not illustrated) connected to the combiner8on the side of the output end7are present at the combiner8. These high-frequency signals flow through the other line of the combiner8and return to the output ends of the adjacent amplifiers6. The high-frequency signals that have returned to the output ends7of the adjacent amplifiers6flow from the drains to the sources (ground ends) of the transistors5in the amplifiers6and then flow to the ground electrode11via the conductor patterns9and the vias10A. Since the slot14is disposed between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6and the adjacent amplifiers6are not electrically connected to each other via the conductor patterns9in the high-frequency amplifier1, the returned high-frequency signals are prevented from flowing to one of the adjacent amplifiers6because of the presence of the slot14and flow to the ground electrode11. As a result, the returned high-frequency signals are attenuated and the occurrence of loop oscillation can be prevented.

When the amplifiers6amplify high-frequency signals, heat is always produced. However, the heat produced by the amplifiers is dissipated from the ground electrode11via the conductor patterns9and the vias10A between the adjacent amplifiers. Accordingly, the deterioration of the electric characteristic of the amplifiers6due to thermal runaway can be prevented. The improvement of a heat dissipation capability is generally proportional to the thickness and perimeter of a via and the number of vias. Accordingly, when the number of vias for connecting the conductor pattern9and the ground electrode11is increased in the high-frequency amplifier1, a heat dissipation capability is improved. Since each of the conductor patterns9and the ground electrode11are connected not only via the via10A but also via the via10B, the high-frequency amplifier1has a good heat dissipation capability.

As described above, the high-frequency amplifier1according to the first embodiment includes the divider3for distributing an input high-frequency signal, the parallel-connected amplifiers6for amplifying a high-frequency signal distributed by the divider3and outputting the amplified signal, the combiner8for combining high-frequency signals amplified by the amplifiers6, the base substrate4on which the amplifiers6are disposed, the conductor pattern9that is connected to the ground end of each of the amplifiers6, and the ground electrode11. Each of the conductor patterns9has the first conductive portion9A extending in a direction in which the amplifiers6are adjacent to each other. The slot14is disposed between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6. Between the adjacent amplifiers6, the vias10A passing through the base substrate4are disposed so that the slot14is sandwiched between the vias10A. One of the two conductor patterns9that are connected to the corresponding adjacent amplifiers6is connected to the ground electrode11via one of the two vias10A. The other one of the two conductor patterns9that are connected to the corresponding adjacent amplifiers is connected to the ground electrode11via the other one of the two vias10A.

One of high-frequency signals output from one of the adjacent amplifiers6flows to the output end of the other one of the amplifiers6via the line of the combiner8and then flows to the ground end of the other one of the amplifiers6. According to the high-frequency amplifier1, the slot14prevents this high-frequency signal from flowing to one of the amplifiers6. The high-frequency signal flows to the ground electrode via the conductor pattern9and the via10A which are connected to the ground end of the other one of the amplifiers6. As a result, the flow of a high-frequency signal through an oscillation loop path between the amplifiers6can be prevented and the occurrence of loop oscillation can be prevented. In addition, heat produced by the amplifiers6is dissipated to the ground electrode11via the conductor patterns9and the vias10A between the adjacent amplifiers. As a result, the deterioration of the electric characteristic of the amplifiers6due to thermal runaway can be prevented.

In the high-frequency amplifier1according to the first embodiment, the conductor pattern9has the second conductive portion9B that extends in a direction different from the extending direction of the first conductive portion9A. The second conductive portions9B of the two conductor patterns9that are connected to the corresponding adjacent amplifiers6extend in directions away from each other. The via10A is connected to the second conductive portion9B. In order to form two vias, the spacing between the two vias is needed. In the high-frequency amplifier1according to the first embodiment, however, since the second conductive portions9B of the two conductor patterns9connected to the corresponding amplifiers6extend in directions away from each other that are different from the direction in which the amplifiers6are adjacent to each other and the first conductive portions9A extend and the via10A is connected to the second conductive portion9B, the two vias10A can be formed even if the spacing between the adjacent amplifiers6is reduced. Accordingly, the spacing between the adjacent amplifiers6can be reduced and a small high-frequency amplifier can be provided.

In the high-frequency amplifier1according to this embodiment, a void portion corresponding to the slot14is filled with an insulating material. However, the slot14may be a void portion that is not filled with an insulating material. In the high-frequency amplifier1, the slot14is disposed at an angle to the direction in which the first conductive portions9A extend. However, the slot14may be disposed so that the long side of the slot14is perpendicular to the extending direction of the first conductive portions9A. In the high-frequency amplifier1, the slot14has a rectangular shape when viewed in plan, but may have another shape.

In the high-frequency amplifier1according to this embodiment, the slot14is disposed between the two conductor patterns9connected to the corresponding adjacent amplifiers6so that the adjacent amplifiers6are not electrically connected to each other via the conductor patterns9. However, parts of the two conductor patterns9may be electrically connected to each other around the slot14and the adjacent amplifiers6may be electrically connected to each other via the conductor patterns9. Even in that case, the slot14has a function of electrically attenuating a high-frequency signal. Accordingly, in a case where the slot14is disposed between the two conductor patterns9, the flow of a high-frequency signal through an oscillation loop path between the amplifiers6can be prevented and the occurrence of loop oscillation can be prevented.

For the simplification of explanation, a common configuration example including the divider3for distributing a high-frequency signal between two portions, the two amplifiers6, and the combiner8for combining two distributed paths has been described in this embodiment. However, a layout configuration other than that of a high-frequency amplifier according to this embodiment may be employed. The transistors5included in the amplifiers6may not be field-effect transistors according to the first embodiment, and may be, for example, bipolar transistors. Although the high-frequency amplifier1according to this embodiment has a semiconductor layout, the high-frequency amplifier may be configured with modules.

Second Embodiment

In the second embodiment, only an additional configuration part to the first embodiment will be described. More specifically, in a high-frequency amplifier according to the second embodiment, the long side of the slot14having a rectangular shape when viewed in plan inFIG. 1is equal to or less than a half-wavelength of a high-frequency signal used. When the slot14is used, resonance generally occurs at the frequency of a high-frequency signal used and oscillation occurs at the slot14. However, by setting the length of the slot to the length equal to or less than a half-wavelength of the high-frequency signal used, resonance does not occur. Accordingly, even when the slot14is disposed, oscillation does not occur.

Third Embodiment

In the third embodiment, a configuration part different from that described in the first embodiment will be described. More specifically, a high-frequency amplifier300according to the third embodiment includes in parallel with the slot14a resistance element16connected between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6. The adjacent amplifiers6are connected to each other via the conductor patterns9and the resistance element16.FIG. 4is a diagram illustrating the top view of a layout of the high-frequency amplifier300.FIG. 5is a cross-sectional view taken along the line B-B′ ofFIG. 4. As illustrated inFIGS. 4 and 5, the resistance element16is disposed on the lower layer of the slot14(the upper surface of the base substrate4) and is connected via vias10C to the two conductor patterns9that are connected to the corresponding adjacent amplifiers6. The resistance element16may not be disposed directly below the slot14as long as in parallel with the slot14the resistance element16is connected. The resistance value of the resistance element16is set as appropriate in accordance with the magnitude of a high-frequency signal that returns to the ground ends of the amplifiers6.

The operation of the high-frequency amplifier300will be described. Since in parallel with the slot14the resistance element16is connected between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6, the resistance element16is present on an oscillation loop path between the amplifiers6. Accordingly, a high-frequency signal flowing through the oscillation loop path between the amplifiers6passes through the resistance element16. As a result, the high-frequency signal flowing through the oscillation loop path between the amplifiers6is attenuated at the resistance element16and the occurrence of loop oscillation can be prevented for high-frequency signals in all frequency ranges.

Fourth Embodiment

In the fourth embodiment, a configuration part different from that described in the first embodiment will be described. More specifically, a high-frequency amplifier400according to the fourth embodiment includes in parallel with the slot14a resonance circuit18connected between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6. The adjacent amplifiers6are connected to each other via the conductor patterns9and the resonance circuit18.FIG. 6is a diagram illustrating the top view of a layout of the high-frequency amplifier400.FIG. 7is a cross-sectional view taken along the line C-C′ ofFIG. 6. As illustrated inFIGS. 6 and 7, the resonance circuit18is disposed on the lower layer of the slot14and is connected via the vias100to the two conductor patterns9that are connected to the corresponding adjacent amplifiers6. The resonance circuit18forms a low-pass filter and attenuates a harmonic component in a high-frequency signal used. The resonance circuit18may not be disposed directly below the slot14as long as in parallel with the slot14the resonance circuit18is connected.

The operation of the high-frequency amplifier400will be described. Since in parallel with the slot14the resonance circuit18is connected between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6, the resonance circuit18is present on an oscillation loop path between the amplifiers6. Accordingly, a high-frequency signal flowing through the oscillation loop path between the amplifiers6passes through the resonance circuit18. When high-frequency signals are amplified by the amplifiers6, harmonics are generated. However, since the resonance circuit18forms a low-pass filter, a harmonic component in the high-frequency signal flowing through the oscillation loop path between the amplifiers6can be attenuated. As a result, the occurrence of loop oscillation due to a harmonic component in a high-frequency signal used can be prevented.

Fifth Embodiment

In the fifth embodiment, a configuration part different from that described in the fourth embodiment will be described. More specifically, in a high-frequency amplifier according to the fifth embodiment, the resonance circuit18in the high-frequency amplifier400according to the fourth embodiment forms a notch filter. The resonance point of the notch filter is the frequency of a high-frequency signal used. The resonance circuit18preferably forms a notch filter including, for example, a resonator for resonating an L and a C in parallel.

The operation of a high-frequency amplifier according to the fifth embodiment will be described. Since in parallel with the slot14the resonance circuit18is connected between the two conductor patterns9that are connected to the corresponding adjacent amplifiers6, the resonance circuit18is present on an oscillation loop path between the amplifiers6. Accordingly, a high-frequency signal flowing through the oscillation loop path between the amplifiers6passes through the resonance circuit18. The resonance circuit18forms a notch filter, and the resonance point of the notch filter is the frequency of a high-frequency signal used. Accordingly, a frequency component in the high-frequency signal used is attenuated by the resonance circuit18. As a result, the occurrence of loop oscillation due to a frequency component in a high-frequency signal used can be further prevented.

Sixth Embodiment

In the sixth embodiment, a configuration part different from that described in the first embodiment will be described. More specifically, in a high-frequency amplifier according to the sixth embodiment, the inside of the slot14is filled with an insulating material with a dielectric constant lower than that of the insulating material15used around the slot14. The insulating material with which the inside of the slot14is filled is preferably an insulating material with a dielectric constant of 3.0 or less, for example, a Low-k material. By filling the inside of the slot14with an insulating material of a low dielectric constant, the level of insulation against a high-frequency signal flowing through the oscillation loop path between the amplifiers is increased and the high-frequency signal does not pass through the slot14. As a result, the occurrence of loop oscillation can be further prevented. In addition, by filling the inside of the slot14with an insulating material of a low dielectric constant, a wavelength-shortening effect acts and the width of the slot14can be reduced. As a result, the size reduction of a high-frequency amplifier can be achieved.

Exemplary Simulation

Simulations of the isolation between the adjacent amplifiers6were performed on high-frequency amplifiers according to the first to fifth embodiments and a high-frequency amplifier that is a comparative example and has the same configuration as that of the high-frequency amplifier1according to the first embodiment except for the elimination of the slot14using an Advanced Design System (ADS) of Agilent Technologies. Results of the simulations are illustrated inFIG. 8. ADS ideal elements were individually used for the resistance element16and the resonance circuit18. Referring toFIG. 8, fosc indicates the frequency of a high-frequency signal used.

Since the slot14is not present in the comparative example, the isolation is poor over the entire frequency band and it is apparent from the result that loop oscillation easily occurs. In the first and second embodiments in which a slot is formed, the isolation is achieved particularly in a low frequency band. In the third embodiment, the isolation is achieved on average over the entire frequency band. In the fourth embodiment, the isolation is good particular in a high frequency band and it is apparent from the result that harmonics can be attenuated in particular. In the fifth embodiment, a specific frequency component, that is, a component of the fosc, can be attenuated. It is apparent from the result that the occurrence of loop oscillation due to a frequency component in a high-frequency signal used can be prevented.

Simulation results according to the first to fifth embodiments have been described. The methods of preventing the occurrence of loop oscillation in a high-frequency amplifier can be used as appropriate in these embodiments in accordance with a use or a purpose.

As described previously, a high-frequency amplifier according to the present invention can be used as an amplifier in, for example, a radio communication apparatus.

REFERENCE SIGNS LIST