JP2007282122A - Doherty amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance linearity while securing efficiency in a Doherty amplifier. <P>SOLUTION: A nonlinear amplification unit 140 is provided in parallel with a Doherty amplification unit 130, an output signal of the Doherty amplification unit 130 through an impedance converter 150 and an output signal of the nonlinear amplification unit 140 are composed by a composer 160, and a composed output signal is outputted from an output terminal 170. At such a time, the nonlinear amplification unit 140 performs amplification operation so as to keep linearity by complementing nonlinearity in an area where the Doherty amplification unit 130 performs nonlinear operation, so that a Doherty amplifier 100 can perform linear amplification over a wide area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a Doherty amplifier.

  In recent years, the demand for wireless communication technology has increased, and high-speed data communication has been required in addition to voice communication. Orthogonal Frequency Division Multiplexing (OFDM) using multiple carriers orthogonal to each other in wireless LAN (Local Area Network) and digital terrestrial broadcasting from the viewpoint of high-speed data communication and frequency utilization efficiency ) Has already been adopted.

  By the way, in OFDM modulation, since a large number of carriers are used, the peak power to average power ratio of the signal waveform is high, and in order to amplify such a signal, the difference between the average power and the saturated power in the actual operation of the amplifier It is necessary to operate the given backoff in a sufficiently large state. However, there is a problem that the efficiency of the amplifier generally decreases significantly as the back-off becomes larger.

  A Doherty amplifier is known as a technique for solving such a problem and amplifying a signal having a high peak power to average power ratio such as an OFDM modulated signal. The Doherty amplifier was first devised by W. H. Doherty in 1936 and is disclosed in Non-Patent Document 1 and Patent Document 1.

  Hereinafter, the Doherty amplifier will be described with reference to the drawings. FIG. 3 is a block diagram showing a main configuration of the Doherty amplifier. The Doherty amplifier 10 shown in FIG. 3 includes two amplifiers, a carrier amplifier 13 and a peak amplifier 16.

  The carrier amplifier 13 is an amplifier biased in class A, class AB, or class B, and the peak amplifier 16 is an amplifier biased in class C, that is, biased in class C.

  The radio signal input from the input terminal 11 is divided into two systems by the distributor 12, and then one is output to the carrier amplifier 13 and the other is output to the quarter wavelength network 15 to add a phase difference. Thereafter, it is output to the peak amplifier 16.

  The 1/4 wavelength network 14 is connected to the output side of the carrier amplifier 13, and the radio signal after passing through the 1/4 wavelength network 14 is combined with the radio signal output from the peak amplifier 16 by the combiner 17. And output to the output terminal 18. A load is connected to the output terminal 18.

  At this time, even if the power level of the radio signal is small, the carrier amplifier 13 amplifies the power of the radio signal regardless of the power level. On the other hand, since the peak amplifier 16 is biased to class C, when the power level of the radio signal is small and less than a predetermined threshold, the peak amplifier 16 is turned off and does not perform the amplification operation. In this case, since the power consumed by the peak amplifier 16 is small, the efficiency of the Doherty amplifier 10 as a whole is increased.

  On the other hand, when the power level of the radio signal is equal to or higher than a predetermined threshold, the peak amplifier 16 is turned on, and the power level of the radio signal is amplified by both the carrier amplifier 13 and the peak amplifier 16. Then, by combining the output power of the carrier amplifier 13 and the output power of the peak amplifier 16 by the combiner 17, a large saturation power can be obtained.

  The quarter wavelength network 14 is connected to the output side of the carrier amplifier 13 and plays a role of realizing high efficiency by changing the effective impedance of the carrier amplifier 13 according to the power level of the radio signal. . When the power level of the radio signal is small, the peak amplifier 16 is turned off, so that the output impedance of the peak amplifier 16 is ideally open. In this case, the carrier amplifier 13 can be operated at the maximum efficiency by designing the carrier amplifier 13 so that the efficiency is good.

  On the other hand, when the power level of the radio signal is large, both the carrier amplifier 13 and the peak amplifier 16 operate to amplify the power level of the radio signal. Since the carrier amplifier 13 and the peak amplifier 16 are connected in parallel, the effective impedance at the output terminal of the carrier amplifier 13 is reduced by the quarter wavelength network 14 when the power level is equal to or higher than a predetermined threshold. In other words, the quarter wavelength network 14 can reduce the effective impedance at the output terminal of the carrier amplifier 13 and maintain the voltage applied to the carrier amplifier 13 at a constant level. Can work with.

  By connecting the quarter wavelength network 14 to the output side of the carrier amplifier 13 in this way, the peak amplifier 16 is operated while operating the carrier amplifier 13 at the maximum efficiency. A large saturation power can be obtained, and high efficiency can be maintained.

  FIG. 4 shows input / output characteristics of the Doherty amplifier 10 including the carrier amplifier 13 and the peak amplifier 16 as described above. Further, FIGS. 4 to 7 show the relationship between the input / output characteristics and the efficiency when the operation range of the peak amplifier is changed. 4 and 6, S1 indicates the input / output characteristics of the carrier amplifier 13, S2 indicates the input / output characteristics of the peak amplifier 16, and S3 indicates the combined input / output characteristics. When the operating region ΔP of the peak amplifier 16 is widened as shown in FIG. 4, high efficiency can be maintained in a wide range, but the problem that the linearity of the input / output characteristics deteriorates as shown in FIG. Occurs. On the other hand, when the operating region ΔP of the peak amplifier 16 is narrowed as shown in FIG. 6, linearity is obtained, but there is a problem that the efficiency deteriorates as shown in FIG. The efficiency refers to the ratio between the difference between the output power and the input power and the power consumption.

In order to solve this problem, Patent Document 2 discloses a method in which a distortion compensation circuit is inserted before the Doherty amplifier. FIG. 8 is a diagram showing input / output characteristics when the distortion compensation circuit is inserted in the previous stage of the Doherty amplifier. In the figure, S4 shows the input / output characteristics of the Doherty amplifier, S5 shows the input / output characteristics of the distortion compensation circuit, and S6 shows the input / output characteristics when passing through the distortion compensation circuit and the Doherty amplifier. As shown in FIG. 8, the linearity (S6) of the input / output characteristics is obtained by inserting a distortion compensation circuit having the inverse characteristic (S5) of the distortion (S4) of the Doherty amplifier in the previous stage of the Doherty amplifier. Become.
“A New High Efficiency Power Amplifier For Modulared Waves”, Proceedings of the Institude of Radio Engineers, Vol. 24, No. 9, September 1936. US Patent No. 2210028 JP 2003-037451 A

  However, as disclosed in Patent Document 2, in the method of inserting a distortion compensation circuit in the previous stage of the Doherty amplifier, there is a problem that when the distortion of the Doherty amplifier is large, it is difficult to create an inverse characteristic corresponding to the distortion. Further, when the distortion compensation circuit is inserted, there is a problem that the gain is lowered and the amplification efficiency is deteriorated by inserting the distortion compensation circuit as shown in FIG.

  The present invention has been made in view of this point, and an object of the present invention is to provide a Doherty amplifier capable of improving linearity while ensuring high efficiency in the Doherty amplifier.

  In order to solve this problem, a Doherty amplifier according to the present invention includes a Doherty amplification unit, a nonlinear amplification unit, a distributor that distributes an input radio signal to the Doherty amplification unit and the nonlinear amplification unit, and the Doherty amplification unit. And a synthesizer that synthesizes the output signal of the non-linear amplifier.

  According to this configuration, a non-linear amplification unit is provided in parallel to the Doherty amplification unit, and the radio signal is distributed to the Doherty amplification unit and the non-linear amplification unit, and is amplified with high efficiency by the Doherty amplification unit. In order to maintain the linearity of the input / output characteristics of the combined signal of the radio signal output from the Doherty amplifier and the radio signal output from the nonlinear amplifier, the nonlinearity is reduced in the region where the Doherty amplifier operates nonlinearly. Since it can be supplemented and amplified, the radio signal can be linearly amplified.

  According to the present invention, it is possible to provide a Doherty amplifier capable of improving linearity while ensuring high efficiency.

  A feature of the present invention is that a nonlinear amplifier is connected in parallel to the Doherty amplifier. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a main configuration of a Doherty amplifier according to an embodiment of the present invention. The Doherty amplifier 100 shown in FIG. 1 includes an input terminal 110, a distributor 120, a Doherty amplification unit 130, a nonlinear amplification unit 140, an impedance converter 150, a combiner 160, and an output terminal 170. .

  The Doherty amplifier 130 includes a carrier amplifier 131, a matching circuit 132, an impedance converter 133, a phase adjuster 134, a peak amplifier 135, a matching circuit 136, and a combiner 137, and the nonlinear amplifier 140 includes The phase adjuster 141, the amplitude adjuster 142, and the non-linear amplifier 143 are provided. As shown in the figure, the non-linear amplifying unit 140 is connected in parallel to the Doherty amplifying unit.

  The distributor 120 distributes the microwave RF (Radio Frequency) signal output from the input terminal 110 to three paths, and outputs the RF signal to the carrier amplifier 131, the phase adjuster 134, and the phase adjuster 141.

  The carrier amplifier 131 amplifies the power level of the RF signal regardless of its magnitude, and outputs the amplified RF signal to the matching circuit 132.

The matching circuit 132 is connected to the output side of the carrier amplifier 131, and matches the amplified RF signal with the load impedance _RL .

The impedance converter 133 is provided in the subsequent stage of the matching circuit 132 connected to the output side of the carrier amplifier 131, performs impedance conversion on the combined RF signal, and outputs the RF signal after the impedance conversion to the combiner 137. . The impedance converter 133 has an impedance _RL similar to the load impedance.

  The phase adjuster 134 adjusts the phase of the distributed RF signal so that the combined output power in the combiner 137 is maximized, and outputs the RF signal after the phase adjustment to the peak amplifier 135.

  The peak amplifier 135 amplifies the power level of the RF signal when the power level of the RF signal is equal to or higher than a predetermined threshold, and outputs the amplified RF signal to the matching circuit 136.

The matching circuit 136 performs matching with the load impedance _RL for the RF signal.

  The combiner 137 combines the RF signal amplified by the carrier amplifier 131 and the RF signal amplified by the peak amplifier 135 and outputs the combined RF signal to the impedance converter 150.

  The impedance converter 150 performs impedance conversion on the combined RF signal using a λ / 4 microstrip line or an equivalent aggregate network, and outputs the RF signal after the impedance conversion to the combiner 160.

  The impedance converters 133 and 150 may be constituted by capacitors, coils, or the like. In particular, when a λ / 4 microstrip line is used, a large amount of power can be supplied with little power loss. Such a microstrip line is a line used for a microwave integrated circuit (MIC), and a low-loss dielectric is placed on a conductor substrate, and a narrow-width conductor (strip conductor) is placed thereon. ) Is pasted. In addition, there is a structure in which a dielectric material is sandwiched between conductive substrates and a conductor called a strip is embedded therein. Such a microstrip line has the advantages of small size and light weight, and has the advantage that L and C can be easily formed in the microwave band by devising the shape processing of the structure in terms of circuit. Can be easily formed.

  By setting the length of the microstrip line to λ / 4, the characteristic impedance is 180 degrees in the Smith diagram of the distributed constant circuit. Therefore, the characteristic impedance is short-circuited and opened (or impedance Z and its inverse Y). ) Can be changed to the opposite characteristics. Therefore, in a microwave transmission circuit, a λ / 4 microstrip line is preferably used as an impedance converter.

  In addition, the characteristic impedance of the microstrip line can be changed considerably easily depending on the conductor width of the strip line, the thickness of the dielectric, and the dielectric constant. In the active element (or active circuit), the circuit characteristics are greatly affected by the operating frequency and the inductive and capacitive load characteristics, so that matching of output impedance is extremely important. Therefore, by connecting a microstrip line to the output terminal of the active circuit, the impedance can be controlled relatively freely, leading to an improvement in transmission efficiency as a whole.

  The phase adjuster 141 adjusts the phase of the distributed RF signal and outputs the RF signal after the phase adjustment to the amplitude adjuster 142.

  The amplitude adjuster 142 adjusts the amplitude of the RF signal and outputs the RF signal after the amplitude adjustment to the nonlinear amplifier 143.

  The nonlinear amplifier 143 amplifies the power level of the RF signal and outputs it to the combiner 160 when the power level of the RF signal is equal to or higher than a predetermined threshold. Here, the non-linear amplifier 143 has characteristics similar to those of the peak amplifier 135 of the Doherty amplifying unit 130, and the input / output characteristics are opposite to those of the Doherty amplifying unit 130 as shown by a solid line (S12) in FIG. The bias is adjusted so as to obtain characteristics. 2A shows the input / output characteristics of the Doherty amplifier 130, and FIG. 2C shows the input / output characteristics after synthesis.

  Specifically, a reverse bias is applied between the base and emitter of the transistors constituting the nonlinear amplifier 143 to adjust the period during which the collector current flows. By doing so, the non-linear amplifier 143 is turned off when the power level of the RF signal is small, does not perform an amplification operation, and the power level of the RF signal is equal to or higher than a predetermined threshold, similarly to the peak amplifier 135. Only in this case, the nonlinear amplification operation is performed. By doing so, the power consumption of the nonlinear amplifier 143 can be reduced and high efficiency can be maintained. Further, by appropriately adjusting the values of the load resistance and collector resistance connected to the transistor, the slope of the input / output characteristic is controlled, so that the input / output characteristic of the nonlinear amplifier 143 is opposite to the nonlinear characteristic of the Doherty amplification unit 130. By doing so, since the nonlinear amplifier 143 operates so as to supplement and amplify the nonlinearity in the region where the Doherty amplification unit 130 performs nonlinear amplification, the Doherty amplifier 100 as a whole can transmit the RF signal in a wide region. It becomes possible to perform linear amplification.

  The combiner 160 combines the RF signal amplified by the Doherty amplification unit 130 and impedance-converted with the RF signal amplified by the nonlinear amplifier 143, and outputs the combined signal to the output terminal 170. As described above, the phase adjuster 141 and the amplitude adjuster 142 adjust the phase and amplitude of the RF signal, and the input / output characteristics of the nonlinear amplifier 143 are opposite to the characteristics of the nonlinear operating region of the Doherty amplification unit 130. By adjusting the bias of the nonlinear amplifier 143 as described above, the Doherty amplifier 100 can linearly amplify even in a high power region, as shown in FIG.

  Next, the operation of the Doherty amplifier 100 configured as described above will be described again using the input / output characteristics of FIG.

  The microwave RF signal output from the input terminal 110 is distributed to three paths by the distributor 120, and the distributed RF signal is output to the carrier amplifier 131, the phase adjuster 134, and the phase adjuster 141.

  Then, the carrier amplifier 131 amplifies the RF signal regardless of the power level, and outputs the amplified RF signal to the combiner 137 via the matching circuit 132 and the impedance converter 133.

  On the other hand, the RF signal output to the phase adjuster 134 is phase-adjusted by the phase adjuster 134 and then output to the peak amplifier 135. When the power level is equal to or higher than a predetermined threshold by the peak amplifier 135, the power is The level is amplified and output to the combiner 137 via the matching circuit 136. FIG. 2A shows input / output characteristics by a solid line (S11). As shown in the figure, the input / output characteristics become nonlinear as the power level of the RF signal increases.

  Then, the combiner 137 combines the output power of the carrier amplifier 131 and the peak amplifier 135 and outputs the combined RF signal to the impedance converter 150.

  The phase and amplitude of the RF signal output to the phase adjuster 141 are adjusted by the phase adjuster 141 and the amplitude adjuster 142, and the adjusted RF signal is output to the nonlinear amplifier 143. FIG. 2B shows the input / output characteristics of the non-linear amplifier 140 by a solid line (S12). As shown in the figure, in the nonlinear amplifying unit 140, when the nonlinear amplifier 143 is biased to class C and the power level of the RF signal is equal to or higher than a predetermined threshold value, the input / output of the Doherty amplifying unit 130 described above is performed. It is adjusted by the load resistance, collector resistance value, phase adjuster 141 and amplitude adjuster 142 constituting the nonlinear amplifier 143 so as to be opposite to the characteristic (FIG. 2 (a) S11).

  By doing so, the RF signal that has been amplified by the Doherty amplifier 130 and then passed through the impedance converter 150 and the RF signal that has been amplified by the nonlinear amplifier 140 are combined by the combiner 160. Even in the region where the power level is high, the Doherty amplifier 100 as a whole can linearly amplify the RF signal. FIG. 2C shows input / output characteristics (S13) after the synthesis of the RF signal amplified by the Doherty amplification unit 130 by the synthesizer 160 and the RF signal amplified by the nonlinear amplification unit 140.

  That is, the nonlinear amplifier 140 is provided in parallel with the Doherty amplifier 130, and the input / output characteristics of the region where the power level of the nonlinear amplifier 140 is high are opposite to those of the Doherty amplifier 130. By adjusting the bias, load resistance, collector resistance, etc., and synthesizing the output signal of the Doherty amplification unit 130 and the output signal of the nonlinear amplification unit 140, the Doherty amplifier 100 can be operated linearly even in a high power level region. Will be able to.

  As described above, according to the present embodiment, the non-linear amplifying unit 140 whose bias is adjusted so as to have a characteristic opposite to the characteristic of the non-linear region of the Doherty amplifying unit 130 is connected in parallel to the Doherty amplifying unit 130. Since the output signal of the amplifying unit 130 is combined with the output signal of the non-linear amplifying unit 140, the non-linear amplifying unit 140 amplifies the signal so as to compensate for the linearity in a region where only the Doherty amplifying unit 130 is nonlinearly amplified. Thus, the RF signal can be amplified linearly even at a high power level. Further, since the nonlinear amplifying unit 140 is biased to class C, it does not operate when the power level is low, and operates only when the power level is equal to or higher than a predetermined threshold value. Can be maintained.

  A Doherty amplifier according to a first aspect of the present invention includes a Doherty amplification unit, a nonlinear amplification unit, a distributor that distributes an input radio signal to the Doherty amplification unit and the nonlinear amplification unit, and an output of the Doherty amplification unit And a synthesizer that synthesizes the signal and the output signal of the nonlinear amplifying unit.

  According to this configuration, a non-linear amplification unit is provided in parallel to the Doherty amplification unit, and the radio signal is distributed to the Doherty amplification unit and the non-linear amplification unit, and is amplified with high efficiency by the Doherty amplification unit. In order to maintain the linearity of the input / output characteristics of the combined signal of the wireless signal output from the Doherty amplifier and the wireless signal output from the nonlinear amplifier, the nonlinearity is supplemented in the region where the Doherty amplifier operates nonlinearly. Thus, the radio signal can be linearly amplified.

  The Doherty amplifier according to a second aspect of the present invention employs a configuration in which, in the first aspect, the non-linear amplification unit has a characteristic that compensates for a characteristic of a peak amplifier provided in the Doherty amplification unit.

  According to this configuration, a non-linear amplifier can be used that is biased to class C, like the peak amplifier that constitutes the Doherty amplifier, and the nonlinear amplifier is used only when the power level is equal to or higher than a predetermined threshold. When the power level is low, the power consumed is small and high efficiency can be realized.

  The Doherty amplifier according to a third aspect of the present invention is the Doherty amplifier according to the second aspect, wherein the non-linear amplification unit is configured such that the combined radio signal output from the combiner has a linear amplification characteristic. The configuration of compensating for the characteristics of the peak amplifier provided in FIG.

  According to this configuration, the input / output characteristics of the combined signal of the radio signal output from the Doherty amplifier and the radio signal output from the nonlinear amplifier can be kept linear, and the radio signal can be linearly amplified.

  A Doherty amplifier according to a fourth aspect of the present invention employs a configuration including the phase adjuster provided between the distributor and the nonlinear amplifier in the first aspect.

  According to this configuration, the input / output characteristics of the nonlinear amplifier can be adjusted without affecting the input / output characteristics of the Doherty amplifier by the phase adjuster provided between the distributor and the nonlinear amplifier. Therefore, the input / output characteristics of the Doherty amplifier can be adjusted relatively easily.

  A Doherty amplifier according to a fifth aspect of the present invention employs a configuration including an amplitude adjuster provided between the distributor and the nonlinear amplifier in the first aspect.

  According to this configuration, the input / output characteristics of the nonlinear amplifier can be adjusted without affecting the input / output characteristics of the Doherty amplifier by the amplitude adjuster provided between the distributor and the nonlinear amplifier. The input / output characteristics of the Doherty amplifier can be adjusted relatively easily.

  A Doherty amplifier according to a sixth aspect of the present invention employs a configuration including an impedance converter provided between the distributor and the combiner in the first aspect.

  According to this configuration, the apparent load impedance of the Doherty amplification unit is changed by the impedance converter provided between the distributor and the combiner, and the entire Doherty amplification unit can be made more efficient.

  The high-efficiency Doherty amplifier of the present invention can improve the linearity while ensuring high efficiency, and is useful, for example, for an amplifier used in communication equipment that requires low power consumption.

The block diagram which shows the principal part structure of the highly efficient Doherty amplifier which concerns on embodiment of this invention (A) Diagram showing the input / output characteristics of the Doherty amplifier according to the above embodiment (b) Diagram showing the input / output characteristics of the nonlinear amplifier according to the above embodiment (c) High-efficiency Doherty according to the above embodiment Diagram showing input / output characteristics of amplifier The block diagram which shows the principal part structure of the conventional Doherty amplifier Diagram for explaining input / output characteristics of a conventional Doherty amplifier Diagram for explaining the efficiency characteristics of a conventional Doherty amplifier Diagram for explaining input / output characteristics of a conventional Doherty amplifier Diagram for explaining the efficiency characteristics of a conventional Doherty amplifier Diagram for explaining input / output characteristics of a conventional Doherty amplifier

Explanation of symbols

DESCRIPTION OF SYMBOLS 110 Input terminal 120 Divider 130 Doherty amplifier 131 Carrier amplifier 132 Matching circuit 133 Impedance converter 134 Phase adjuster 135 Peak amplifier 136 Matching circuit 137 Synthesizer 140 Non-linear amplifier 141 Phase adjuster 142 Amplitude adjuster 143 Non-linear amplifier
150 Impedance converter 160 Synthesizer 170 Output terminal

Claims (6)

Doherty amplification unit,
A non-linear amplifier,
A distributor for distributing an input radio signal to the Doherty amplification unit and the nonlinear amplification unit;
A combiner that combines the output signal of the Doherty amplifier and the output signal of the nonlinear amplifier;
A Doherty amplifier comprising: 2. The Doherty amplifier according to claim 1, wherein the nonlinear amplification unit has a characteristic that compensates for a characteristic of a peak amplifier provided in the Doherty amplification unit. 3. The Doherty amplifier according to claim 2, wherein the nonlinear amplification unit compensates for a characteristic of a peak amplifier provided in the Doherty amplification unit so that a combined radio signal output from the combiner has a linear amplification characteristic. The Doherty amplifier according to claim 1, further comprising a phase adjuster provided between the distributor and the nonlinear amplifier. The Doherty amplifier according to claim 1, further comprising an amplitude adjuster provided between the distributor and the nonlinear amplifier. The Doherty amplifier according to claim 1, further comprising an impedance converter provided between the distributor and the combiner.

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