Patent Application
20100079211
(1) Field of the Invention
The present invention relates to a matching circuit, a radio-frequency power amplifier (hereinafter referred to as RF power amplifier), and a mobile phone, and in particular to a matching circuit that matches an input impedance and an output impedance, an RF power amplifier and a mobile phone each including such a matching circuit.
(2) Description of the Related Art
In recent years, there is an increasing demand for mobile communication apparatuses, such as mobile phones to support (i) multiband communication using frequency bands to secure communication capacity and (ii) multimode communication with communication systems through international roaming services. Currently, dominant communication systems are divided into two categories, that is, (i) the second generation system using Global System for Mobile Communication (GSM) standard and (ii) the third generation system using Code Division Multiple Access (CDMA) system. The frequency bands used for transmission in these communication systems includes Band I ranging from 1920 MHz to 1980 MHz, Band II ranging from 1850 MHz to 1910 MHz, Band III ranging from 1710 MHz to 1785 MHz, Band IV ranging from 1710 MHz to 1755 MHz, Band V ranging from 824 MHz to 849 MHz, Band VI ranging from 830 MHz to 840 MHz, Band VIII ranging from 880 MHz to 915 MHz, and Band IX ranging from 1749.9 MHz to 1784.9 MHz. The combinations of the communication systems and these frequency bands differ, depending on a region where the mobile phones are used. In order to support these communication systems, each wireless communication unit included therein needs a plurality of RF power amplifiers, so that there is an increasing demand for miniaturization of the RF power amplifiers.
However, the RF power amplifiers feature the highest power consumption, and input and output of higher electric power, compared with other components included in each wireless communication unit. Thus, devices, such as power amplification transistors included in these RF power amplifiers need to have size corresponding to such high output power, which makes it difficult to simply miniaturize the RF power amplifiers.
Furthermore, resistance values in circuits that are used in wireless communication and are included in mobile phones are set to 50 ohm as the general standard. Furthermore, each of the power amplification transistors included in the RF power amplifiers includes an input matching circuit and an output matching circuit for matching impedances of components in the RF power amplifiers to those of components connected upstream and downstream of the RF power amplifiers. These matching circuits include inductors, capacitors, and microstriplines, and each of the components has limitation in the miniaturization due to each physical length and size.
Thus, much attention is given to the RF power amplifiers that enable the multiband and multimode communication in a single amplification path.
On the other hand, impedances of the matching circuits depend on each frequency because inductors, capacitors, and microstriplines are used in the matching circuits included in the RF power amplifiers, and thus an output power characteristic and an efficiency characteristic depend on each frequency. Accordingly, a multiband matching circuit is suggested which includes switch elements and sub-matching blocks for matching impedances and which converts the impedances (see Japanese Unexamined Patent Application Publication No. 2006-325153 referred to as Patent Reference 1 hereinafter).
Furthermore, as another structure of the matching circuits, the output matching circuits included in the power amplification transistors of the RF power amplifiers preferably include two-stage lowpass filters as main matching circuit units. Such a two-stage lowpass filter includes an inductor connected in series with a signal line and a capacitor that is grounded, or an inductor connected in series with a microstripline and a capacitor that is grounded (for example, see Japanese Unexamined Patent Application Publication No. 2003-298364 referred to as Patent Reference 2 hereinafter).
However, the matching circuit described in Patent Reference 1 needs switch elements additionally including semiconductor devices and other elements, terminals, connection paths, and a control circuit for controlling the switch elements. Thus, the matching circuit has the limitation in the miniaturization and cost reduction.
Furthermore, the lower limit of frequency bands for use in the mobile phones is 824 MHz, and the upper limit is 1980 MHz that is more than double the lower limit. Thus, a circuit structure described in Patent Reference 2 has a problem when one matching circuit amplifies signals in all of these frequency bands. For example, since the second harmonic in Band VIII is within the frequency bands of Band IV and Band IX, the second harmonic cannot be suppressed and an unnecessary emission of a signal in Band VIII cannot be suppressed. In other words, although the structure in
Here, assume that 824 MHz to 915 MHz covering Band V, Band VI, and Band VIII is set to a frequency band X, and 710 MHz to 1980 MHz covering Band I, Band II, Band III, Band IV, and Band IX is set to another frequency band Y. Each of the set frequency bands X and Y never includes any second harmonic. Furthermore, the frequency band X includes the 3 bands of Band V, Band VI, and Band VIII in a lower frequency band, and the frequency band Y includes the 5 bands of Band I, Band II, Band III, Band IV, and Band IX in a higher frequency band. Furthermore, the miniaturization of communication systems can be improved, in a multiband mode operation, with a structure including transmission paths corresponding to the frequency bands X and Y respectively in the lower frequency band and in the higher frequency band. However, broadband matching for multiband communication under the structure of
In this structure, components used as constituent elements of an actual circuit cannot suppress the second harmonic in the higher frequency band, due to self resonant frequencies of the components, and further increases loss of a signal in the higher frequency band having the fundamental.
Thus, the present invention has an object of providing a matching circuit, RF power amplifier, and mobile phone whereby the second harmonic can be suppressed and the loss of the fundamental due to the self resonance of the components can be reduced.
In order to achieve the object, the matching circuit according to an aspect of the present invention includes: a transmission line through which a radio-frequency signal is transmitted; and resonators each of which includes a capacitor, the resonators respectively having (i) first terminals connected to substantially a same connecting point on the transmission line and (ii) second terminals that are grounded.
Thereby, a capacitance value for use in each resonator can be made equal to or half thereof. Furthermore, capacitance values are combined in an equivalent circuit obtained by synthesizing resonators, such that capacitance values necessary for matching impedances in a wider frequency band can satisfy a requirement of the matching circuit. Furthermore, a self resonant frequency of a single capacitor can be changed to a frequency equal to or twice a frequency the fundamental, and a radio-frequency signal can be suppressed at a desired frequency in a frequency band including the second harmonic by adjusting component values of the resonators.
Furthermore, each of the resonators may have a resonant frequency within a bandwidth twice a bandwidth of the radio-frequency signal transmitted through the matching circuit.
Thereby, the second harmonic can be further suppressed. Furthermore, one of the resonators may have a resonant frequency different from at least one of the other resonant frequencies of a corresponding one of the resonators.
Thereby, the number of frequency bands can be reduced. For example, 2 frequency bands, 1785 MHz to 1850 MHz and 1910 MHz to 1920 MHz are actually not used in a frequency band of 1710 MHz to 1980 MHz covering Band I, Band II, Band III, Band IV, and Band IX. Thus, in a frequency band twice the frequency band of 1710 MHz to 1980 MHz, that is, a frequency band of 3420 MHz to 3960 MHz, there is no need to suppress 2 frequency bands of 3570 MHz to 3700 MHz and 3820 MHz to 3840 MHz. Thus, the second harmonic can be further suppressed by setting resonant frequencies in a frequency band other than 3570 MHz to 3700 MHz and 3820 MHz to 3840 MHz.
Furthermore, the transmission line may include a first line formed as a microstripline, and each of the resonators may further include a second line that is formed as a microstripline and that is connected in series with a corresponding one of the capacitors.
Thereby, the matching circuit can easily adjust and generate an inductance component using microstriplines.
Furthermore, first terminals of the second lines may be connected to the connecting point, and first terminals of the capacitors may be grounded.
Thereby, the first line connected to the second lines in the resonators will improve flexibility in designing a circuit.
Furthermore, the transmission line may include a first line formed as a microstripline, and each of the resonators may further include an inductor connected in series with a corresponding one of the capacitors.
Thereby, the matching circuit can easily adjust and generate an inductance component without using a specific element.
Furthermore, one of the capacitors included in a corresponding one of the resonators may have a capacitance different from at least one of other capacitances of the other one of the capacitors of the resonators.
Thereby, one of the resonators may have a resonant frequency different from at least one of the other resonant frequencies of a corresponding one of the resonators.
Furthermore, the first line may be formed on a substrate, and the resonators may be arranged in one of areas divided by the first line formed on the substrate.
Thereby, a resonant frequency when only one of the resonators is used matches a resonant frequency when the resonators are used simultaneously, and thus such a matching circuit can be easily designed.
Furthermore, the first line may be right-angled at the connecting point, each of the resonators may be linearly arranged, a longitudinal direction of one of the resonators may be vertical to a longitudinal direction of at least the other one of the resonators, and the longitudinal directions of the resonators may be vertical to the first line.
Thereby, a mounting area of the matching circuit can be reduced. Furthermore, at least one of the resonators may be connected to the connecting point through a via.
Thereby, since a portion or entire of the resonators can be arranged in a layer different from the first line, flexibility in designing a circuit will be improved.
Furthermore, the first line may be formed on a substrate, and one of the resonators may be arranged to be symmetric to the other one of the resonators with respect to the first line.
Thereby, even when the resonators are arranged to be symmetric with each other, a resonant frequency when only one of the resonators is used matches a resonant frequency when the resonators are used together. Thus, such a matching circuit can be easily designed.
An RF power amplifier and a mobile phone each including the matching circuit of the present invention can obtain the same advantages as those of the matching circuit.
As described above, the present invention makes it possible to fabricate a matching circuit, RF power amplifier, and mobile phone whereby the second harmonic can be suppressed and the loss of the fundamental due to the self resonant frequency of the components can be reduced.
The disclosure of Japanese Patent Application No. 2008-255801 filed on Sep. 30, 2008 including specification, drawings and claims is incorporated herein by reference in its entirety.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings:
Embodiments of matching circuits as aspects of the present invention will be described with reference to drawings. The same constituent elements are denoted by the same numerals, and the same functions and advantages to be described for the constituent elements will not be repeated.
A matching circuit according to Embodiment 1 of the present invention includes a transmission line through which a radio-frequency signal is transmitted, and resonators. Each of the resonators includes a capacitor, first terminals of the resonators are connected to substantially a same connecting point, and the other terminals that are second terminals of the resonators are grounded.
An RF power amplifier 10 in
The input matching circuit 2 is a circuit for matching an impedance of a transmission line connected to the input terminal 4 to an impedance of the amplification transistor 1 at the next stage.
The input terminal 4 supplies, to the amplification transistor 1, a radio-frequency signal in which the impedances are matched by the input matching circuit 2. The power supply voltage terminal 6 supplies current to the amplification transistor 1 through the output matching circuit 3. Then, the amplification transistor 1 amplifies the radio-frequency signal and transmits the amplified signal to the output matching circuit 3. Here, the amplification transistor 1 may be any one of a Field effect transistor (FET) and a Bipolar Junction Transistor (BJT). The amplification transistor 1 in Embodiment 1 is described as a BIT.
The output matching circuit 3 is a circuit for matching the impedance of the amplification transistor 1 to the impedance of the output terminal 5. More specifically, the output matching circuit 3 includes microstriplines 31, 32, 33, 36, and 37, a bypass capacitor 34, a resonance circuit 35, and a capacitor 38.
A terminal of the microstripline 31 is connected to a collector terminal of the amplification transistor 1, and the other terminal of the microstripline 31 is connected to a terminal of the microstripline 32 and to a terminal of the microstripline 33 that supplies power supply voltage and is for bias. The other terminal of the microstripline 33 is connected to the power supply voltage terminal 6 and a terminal of the bypass capacitor 34. Furthermore, the other terminal of the bypass capacitor 34 is grounded. Furthermore, the other terminal of the microstripline 32 is connected to the resonance circuit 35 at a branch point X.
The resonance circuit 35 is a circuit that resonates at a frequency twice the frequency of the fundamental to shunt the second harmonic. The resonance circuit 35 is connected to the microstriplines 32 and 36 at the branch point X. More specifically, the resonance circuit 35 includes a resonator 35a and a resonator 35b each of which is connected to the branch point X. More specifically, in the resonator 35a, a microstripline 351 is connected in series with a terminal of a capacitor 352, and the other terminal of the capacitor 352 is grounded. Furthermore, a structure of the resonator 35b is the same as that of the resonator 35a. Furthermore, the branch point X is identical to a connecting point in the description.
Here, each of the microstriplines included in the output matching circuit 3 in
The terminal of the microstripline 36 that is not connected to the resonance circuit 35 is connected to the microstripline 37 that is a transmission line for output and to the capacitor 38. The microstripline 37 and the capacitor 38 shunt the third harmonic having a bandwidth triple a bandwidth of the fundamental. More specifically, a terminal of the capacitor 38 is grounded, and the other terminal of the capacitor 38 is connected to a terminal of the microstripline 37, and the other terminal of the microstripline 37 is connected to the output terminal 5.
What is described hereinbefore is the structure of the RF power amplifier 10 including the output matching circuit 3. Component values and characteristics of each component included in the output matching circuit 3 will be described hereinafter.
First, the input impedance and the output impedance of the output matching circuit 3 will be described.
The input impedance is calculated from a required output power and an applied voltage of the amplification transistor 1. First, the required output power is determined based on the GSM standard that requires the highest output. The output power of an antenna terminal should be equal to or smaller than 30 dBm under the GSM standard. A general structure of a connection path from an antenna to the amplification transistor 1 includes a switch for the antenna, a lowpass filter, and the output matching circuit 3 approximately having losses of 0.5 dB, 0.5 dB, and 1.0 dB, respectively. Furthermore, 33 dBm including a margin of 1 dB is required as the output power of the amplification transistor 1 so that output from the antenna terminal always satisfies 30 dBm in consideration of the variations of each component and a degradation characteristic due to temperature change.
Next, assuming that a starting voltage of a battery that supplies power to the amplification transistor 1 is 3.5 V, and a sum of (i) a voltage drop of a control circuit for controlling a power supply voltage on the connection path and (ii) a voltage drop of a conductor on the connection path is 0.3 V, 3.2 V is applied to the amplification transistor 1. The input impedance estimated under these two conditions is approximately 50 ohm.
Furthermore, the output impedance is assumed to be 50 ohm that is generally used as an impedance for radio-frequency engineering.
The component values of each component included in the output matching circuit 3 are determined as follows to satisfy the aforementioned conditions for the input impedance and the output impedance.
Here, the microstripline 31 had a width of 200 μm and a length of 0.57 mm. The microstripline 32 had a width of 200 μm and a length of 1.0 mm. The microstripline 33 for bias had a width of 150 μm and a length of 9.0 mm. A 0603 surface mount device (SMD) chip component was used as the bypass capacitor 34, and had a capacitance of 100 pF. The microstripline 36 had a width of 200 μm and a length of 5.7 mm. The microstripline 37 had a width of 200 μm and a length of 0.3 mm. Another 0603 SMD chip component was used as the capacitor 38, and had a capacitance of 2.3 pF. The microstriplines 351 and 353 had a width of 200 μm and a length of 0.5 mm. The other 0603 SMD chip components were used as the capacitors 352 and 354, and had a capacitance of 3.5 pF.
In
An output matching circuit including the resonance circuit 35 including one resonator will hereinafter be described in comparison with Embodiment 1.
An output matching circuit according to the conventional technique was examined in comparison with that of the present invention.
The output impedance of the main matching circuit unit needs to be limited to no larger than 50 ohm that is a value in which characteristic impedance is independent of frequencies in a 50-ohm matched circuit, as a condition for widening a bandwidth in
Here, the result of our examination shows that a capacitor C2 had a capacitance of 2.86 pF, an inductor L2 had an inductance of 2.51 nH, a capacitor C1 had a capacitance of 10.22 pF, and an inductor L1 had an inductance of 0.7 nH, as component values.
Most noteworthy is that the capacitor C1 had a capacitance of 10.22 pF that is a larger value. In the case of matching impedances at a single frequency, there is no problem that the capacitor C1 has a smaller value. However, when the impedances over the wider bandwidth are adjusted to be an identical impedance and the capacitor C1 has a smaller value, the impedances cannot be matched. Thus, the capacitance needs to have a larger value. The reasons will be described with reference to
Next,
Thus, when an impedance is converted using the inductor L2, an admittance having a real part in a higher frequency is converted to an impedance having a smaller real part in a capacitive impedance region. Conversely, when an impedance is converted to a inductive impedance, an imaginary part of the impedance reverses in sign, and the real part of the admittance becomes larger.
In this way, since the impedance of the capacitor C1 is converted to a lower impedance, the impedance needs to have a larger value obtained by the impedance conversion to cover an inductive region to a capacitive region. Furthermore, as wider a frequency band in which impedances match is, the capacitor C1 needs to have a larger capacitance.
However, there is a problem in a larger capacitance of the capacitor C1 when an output matching circuit is actually fabricated.
Currently, SMD chip components each with a length of 0.6 mm, a width of 0.3 mm, and a height of 0.3 mm are mainly used as components of matching circuits for RF power amplifiers. However, these components normally have parasitic inductance due to each physical length. For example, when a capacitor that is numbered GRM0332C1E100JD01 of Murata Manufacturing Co., Ltd. and has a capacitance of 10 pF is used as the capacitor C1, the capacitor had a self resonant frequency of 2.33 GHz.
Furthermore, when such a chip component is connected on a dielectric substrate, there is a possibility that another parasitic inductance will occur through a connection path to the ground, and the chip component will resonate at a frequency lower than 2.33 GHz. Here, since the self resonant frequency is close to a frequency band of 1710 MHz to 1980 MHz that is the frequency band for the fundamental, the loss of the fundamental increases and the efficiency of the RF power amplifiers is sharply reduced.
In contrast, the output matching circuit 3 of Embodiment 1 includes resonators each including a capacitor as a replacement for the capacitor C1 of the resonance circuit 35 in
As described above, the output matching circuit 3 of Embodiment 1 can suppress the second harmonic and reduce the loss of fundamental due to the self resonant frequency of the components.
Here, the resonators included in the resonance circuit 35 may be 3 or more to match frequencies in a wider bandwidth.
Furthermore, resonators included in the resonance circuit 35 may be configured to resonate at different frequencies in a frequency band twice the bandwidth of the fundamental, so that the second harmonic can be suppressed as an application of the structure according to an aspect of the present invention. As an example, FIG. 12 shows a passing characteristic when, in the resonator 35a of the resonance circuit 35 in
Embodiment 2 embodies a layout of the output matching circuit according to Embodiment 1.
The branch point X1 in
Similarly, the capacitor 352 is removed from the resonator 35a of the resonance circuit 350a so that a terminal of the microstripline 351 is open. When a resonant frequency of the resonance circuit 350a with only the resonator 35b and the microstripline 351 is calculated, the resonant frequency becomes 3.475 GHz as shown in
Although the resonance circuit 350a in
In the resonator 35a of the resonance circuit 350a, the microstripline 351 had a length of 0.3 mm, the capacitor 352 had a capacitance of 3.8 pF, the microstripline 353 of the resonator 35b had a length of 0.3 mm, and the capacitor 354 had a capacitance of 3.2 pF.
Furthermore, under these conditions, a resonant frequency of the resonator 35a alone is 3.580 GHz, while a resonant frequency of the resonator 35b alone is 3.900 GHz. These values are deviated from a resonant frequency calculated with the combination of the resonators 35a and 35b by equal to or larger than 100 MHz, and thus a difficulty lies in designing the resonance circuit 350a to give a desirable frequency.
The branch point X2 in
Thus, the resonators 35a and 35b can resonate at an identical frequency in the resonance circuit 350b in
Furthermore, similarly as the application of Embodiment 1, resonators included in the resonance circuit 350b are resonated at different frequencies in a frequency band including the second harmonic to suppress the second harmonic over a wider bandwidth.
In the resonator 35a, the capacitor 352 had a capacitance of 3.2 pF and the microstripline 351 had a length of 0.4 mm while in the resonator 35b, the capacitor 354 had a capacitance of 3.8 pF and the microstripline 353 had a length of 0.36 mm.
Thus, the resonator 35a is desirably adjacent to the resonator 35b in the resonance circuit 350b as illustrated in
Here, arranging the resonators in one of areas divided by a transmission line provided on a substrate may have the same advantage as described above.
Embodiment 3 is another embodiment for embodying a layout of the output matching circuit according to Embodiment 1, and one of resonators included in the output matching circuit is arranged to be symmetric to the other one of the resonators with respect to the first line.
The resonator 35f is connected in series with the via hole VIA 1, the microstripline 358, a via hole VIA 2, and the capacitor 354 having a terminal grounded. The other structure is the same as that of
Here, when one resonator is connected to a branch point through a via hole, a pair of resonators including the one resonator and included in a resonance circuit may be laid out so as to be adjacent to each other without being separated by a transmission line. Furthermore, the microstripline 358 may be replaced with a transmission line that is formed as a strip line arranged in a dielectric layer lower than the microstripline 351. Furthermore, a portion of a resonator may be formed as a strip line and another portion of the resonator may be formed as a microstripline.
The component values of the resonators 35a and 35b are adjusted so that the resonators 35a and 35b resonate at different frequencies in a frequency band including the second harmonic as an application of the above circuit structure. Thereby, the second harmonic can be suppressed over a wider bandwidth.
Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
For example, the branch point X desirably includes: a first connecting point connected to the center of an edge of the second line included in the first resonator out of resonators; a second connecting point connected to the center of an edge of the second line included in the second resonator out of the resonators; and a third line formed between the first connecting point and the second connecting point as a microstripline. Furthermore, a length of the third line is desirably equal to or shorter than 80 μm when a width of the third line and widths of the second lines included in both the first and second resonators are respectively 200 μm. The reason will be described hereinafter.
Next, a case where the X-length is 1.0 mm will be described.
However, when the X-length is 1.0 mm, a length of the microstripline 351 in the resonator 35a and a length of the microstripline 353 in the resonator 35b become 0.19 mm. Actually, the capacitors 352 and 354 for use in mounting a matching circuit of the present invention on a substrate have a chip size of 0.6 mm×0.3 mm. Thus, the capacitors 352 and 354 cannot be connected to the microstriplines 351 and 353 having the length of 0.19 mm.
Thus, the X-length is desired to be equal to or smaller than 0.8 mm.
Furthermore, the output matching circuit according to the present invention may be used in an RF power amplifier and a mobile phone including such an RF power amplifier as illustrated in
Although Embodiments 1 to 3 are described for an output matching circuit, these may be applied to an input matching circuit.
The matching circuit, RF power amplifier, and mobile phone according to the present invention are applicable to an circuit for matching impedances, and a wireless transmitter and a circuit for transmitting a radio-frequency signal.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-255801 | Sep 2008 | JP | national |
