JP5099908B2 - Doherty synthesis circuit and Doherty amplifier - Google Patents

Description

  The present invention relates to an output synthesizer for a Doherty amplifier in the field of high-frequency amplifiers.

  Doherty amplifiers are known to those skilled in the art and were first proposed by Doherty in 1936. FIG. 3 shows a basic configuration of the Doherty amplifier.

  The basic Doherty amplifier includes an input distributor 12, a main amplifier 8 biased in class A or class AB, a peak amplifier 9 biased in class B or class C, a λ / 4 line 10, and λ / It is comprised with the impedance conversion circuit 11 which converts the impedance of 4 lines 9 into an output load impedance (refer nonpatent literature 1).

  As shown in FIG. 3, since the Doherty amplifier is composed of two or more high-frequency amplifiers having different bias classes, individual power supply power lines corresponding to the respective high-frequency transistors are an obstacle to downsizing the device. It was.

  In order to manufacture the Doherty amplifier in an optimal state, it is necessary to adjust each of the main amplifier and the peak amplifier to the optimum characteristics. For example, when adjusting the main amplifier alone, high-frequency interference with the peak amplifier is required. In order to prevent this, it is necessary to disconnect the high-frequency line, and to physically disconnect the power supply circuit in order to measure the efficiency of the main amplifier alone. However, when adjusting by separating the high-frequency line, the load impedance is different from that when the Doherty synthesizer is connected, so that the adjustment with the single amplifier and the total adjustment as the Doherty amplifier are repeated. Furthermore, the power supply circuit in the microwave amplifier has an important role other than the supply of the DC power supply such as suppressing the distortion component generated in the microwave transistor. In order to optimally adjust the operation for suppressing the distortion, It is necessary to strictly control the circuit conditions. In particular, the influence of the capacity of the capacitor connected to the power supply circuit and the mounting position of the capacitor is very large. When the power amplifier is physically separated and the single amplifier is adjusted, and when it is configured as a Doherty amplifier, the power supply Since the physical conditions of the circuit are different, the RF characteristics such as distortion change as compared with the adjustment of the single amplifier.

  As one of these solutions, for example, Non-Patent Document 2 proposes a configuration in which a power supply circuit is connected to the λ / 4 line portion of a Doherty combiner.

  According to this configuration, since the power supply circuits for the main amplifier and the peak amplifier can be integrated into one, the circuit can be reduced in size.

  Further, for example, Patent Document 1 (Japanese Patent Publication No. 2006-500833) includes a power circuit in which a main amplifier and a peak amplifier are integrated into a Doherty synthesis unit, and further controls the bias of a microwave transistor. A configuration with a BIAS CONTROL section is shown.

According to this configuration, by controlling the bias of the main amplifier and the peak amplifier, it is possible to individually set the operation of the ON and OFF states of the respective microwave transistors.
Special table 2006-50083 gazette “A New High Efficiency Power Amplifier for Modulated Waves”, Proceedings of the Institute of Radio Engineers, Vol. 24, no. 9, pp. 1163-1182 September 1936 Hyun-chul Park, Ju-ho Van, Sung-chang Jung, Min-su Kim, Hajin Cho, Sung-work Kwon, Jong-hyuk Jong, Kyung-hoon Lim, Cheon-seok Pong Load Network for Doherty Amplifier Using an Impact Quarter-Wave Line, “Microwave Theory and Techniques, IEEE Transactions on Volume 11”, “Neutral Transactions on Volume 11”. 2007 Page (s): 2313-2319

  However, according to the known technique disclosed in Non-Patent Document 2, since the power line supplied to the main amplifier and the peak amplifier is shared by the Doherty synthesis circuit, the Doherty amplifier can be downsized. Since the drain voltage of the peak amplifier is always supplied to each of them, the main amplifier and the peak amplifier cannot be optimally adjusted while checking the individual operation efficiency with the main amplifier and the peak amplifier being independent from each other.

  FIG. 5 shows a representative diagram of the known technique disclosed in Patent Document 1. According to the known technique disclosed in Patent Document 1, the Doherty synthesis unit 100 includes a power supply circuit 101 in which power supply circuits of a main amplifier and a peak amplifier are integrated into one, and further controls a bias of a microwave transistor. A configuration including a unit 102 is shown. However, even if the bias of the main amplifier and the peak amplifier can be controlled and the RF device can be turned off as a DC operation, the RF transmission line to which both amplifiers are connected is physically connected. However, there is a problem that the RF characteristics cannot be adjusted to the optimum state completely independently.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems. A main amplifier and a peak amplifier power supply circuit are integrated into one, and a Doherty synthesis circuit and a Doherty circuit capable of optimally adjusting each amplifier completely independently. An object is to provide an amplifier.

  The present invention relates to a λ / 4 line that combines the output signals of two amplifiers by adding a phase difference of 90 degrees, an impedance conversion circuit that converts the impedance of the combined portion of the λ / 4 line into an output load impedance, and impedance conversion A power supply line connected to the circuit, a DC switch A that opens the transmission line of the main amplifier, and a DC switch B that opens the transmission line of the peak amplifier are configured.

As a first aspect of the present invention, an RF input A for inputting an RF signal output from a main amplifier of two high frequency amplifiers constituting a Doherty amplifier, and a peak amplifier of the two high frequency amplifiers are output. The RF input B for inputting the RF signal, the λ / 4 line for synthesizing the output signals of the two high-frequency amplifiers by adding a phase difference of 90 degrees, and the impedance of the synthesizer of the λ / 4 line as the output load impedance an impedance conversion circuit for converting into a power supply line connected to said impedance conversion circuit, which can switch the operation to OPEN and SHORT at the inserted control voltage VcontA between the lambda / 4 lines from the RF input a and DC switches a, between the RF input B of the synthesis of the lambda / 4 line and the impedance conversion circuit Provided is a Doherty synthesis circuit including a DC switch B whose operation can be switched between OPEN and SHORT with an inserted control voltage VcontB, and a harmonic control circuit for suppressing distortion connected to the power supply line. .

  As a second aspect of the present invention, in addition to the above-described Doherty synthesis circuit, an input distributor that separates an input signal by adding a phase difference of 90 degrees, a main amplifier biased to class A or class AB, and class B Alternatively, a Doherty amplifier configured to include a peak amplifier biased in class C and an RF level detection unit that switches and controls the DC switch A and the DC switch B according to the level of an RF input signal is provided. .

As a third aspect of the present invention, an input distributor for separating an input signal by adding a phase difference of 90 degrees, a main amplifier biased to class A or class AB, and a peak biased to class B or class C An amplifier, a λ / 4 line for combining the output signals of the main amplifier and the peak amplifier by adding a phase difference of 90 degrees, and an impedance conversion circuit for converting the impedance of the combining unit of the λ / 4 line into an output load impedance And a power line connected to the impedance conversion circuit, a high frequency short circuit for short-circuiting a high frequency, and an RF input A for inputting an RF signal output from the main amplifier to the λ / 4 line. A DC switch C capable of switching the operation to SHORT and connection to the high-frequency short circuit with the control voltage VcontC, and the peak A DC switch B capable of switching the operation to OPEN and SHORT at the inserted control voltage VcontB between the combining portion of the lambda / 4 line and the impedance converting circuit from RF input B for inputting an RF signal output from the amplifier And a harmonic control circuit that suppresses distortion connected to the power supply line.

  According to the Doherty synthesis circuit of the present invention, since the DC switch A and the DC switch B are simultaneously turned ON only in the output region where the main amplifier and the peak amplifier both perform high-frequency amplification operation, the DC components of both amplifiers interfere unnecessarily. For this reason, the power circuit of the main amplifier and the peak amplifier can be integrated into one and the circuit can be downsized.

  In addition, since the power circuit of the main amplifier and the peak amplifier is integrated into one in the Doherty synthesis circuit of the present invention, the power circuit is exactly the same when adjusting a single amplifier and when configuring a Doherty amplifier. The adjustment of the single amplifier and the adjustment as the Doherty amplifier are unnecessary because the influence on the high-frequency characteristics by the power supply circuit is unchanged even when the amplifier is adjusted.

  Furthermore, the Doherty synthesis circuit according to the present invention operates the mechanical DC switch so that the transmission line is physically disconnected, so that the DC component and the high-frequency signal can be simultaneously disconnected. The peak amplifier can be optimally adjusted completely independently.

  In this embodiment, the power supply circuit is downsized in the Doherty amplifier, and furthermore, when the main amplifier and the peak amplifier are configured as the Doherty amplifier, the RF characteristics do not change and are adjusted independently and optimally. The purpose of doing so was realized with the minimum number of parts.

  The Doherty amplifier is configured by connecting FETs as two amplifiers called a main amplifier and a peak amplifier in parallel. A normal parallel amplifier is used with the gate bias conditions of two FETs being the same, but in the Doherty amplifier, the main amplifier is biased to class AB or class B, and the peak amplifier is biased to class C.

  When the input level is low, since the peak amplifier is biased to class C, it does not consume power in the off state, and the input signal is amplified by the main amplifier. When the input level exceeds a certain value, the main amplifier starts to saturate, but the peak amplifier is turned on and operates to compensate for the gain reduction due to the saturation of the main amplifier. As described above, the Doherty amplifier can operate with high efficiency because the peak amplifier operates only when the signal level is high with respect to a signal having a large average power / peak power ratio.

(Embodiment 1)
FIG. 1 is a diagram showing a Doherty synthesizer according to Embodiment 1 of the present invention. The RF input A18 for inputting the RF signal output from the main amplifier, the RF input B19 for inputting the RF signal output from the peak amplifier, and the output signals of the two high-frequency amplifiers constituting the Doherty amplifier have a phase difference of 90 degrees. Λ / 4 line 1 to be combined, impedance conversion circuit 2 for converting the impedance of the combined portion of λ / 4 line to output load impedance, power supply line 3 connected to the impedance conversion circuit, and control voltage VcontA It is composed of a DC switch A4 whose operation can be switched between OPEN and SHORT, a DC switch B5 whose operation can be switched between OPEN and SHORT with a control voltage VcontB, and a harmonic control circuit 6 which suppresses distortion connected to the power supply line. Yes.

  The operation principle of the Doherty synthesizer configured as described above will be described with reference to FIG. For example, when adjusting the main amplifier, the DC switch B5 is set to OPEN and the DC switch A4 is set to SHORT. By doing so, a power supply voltage is supplied from the power supply line 3 to the main amplifier, but no power is supplied to the peak amplifier. Furthermore, since the RF transmission line is physically disconnected by using a mechanical switch for the DC switch, the RF transmission line to the peak amplifier is also cut off at high frequencies, and the main amplifier has a DC component from the peak amplifier. And high frequency components can be adjusted completely independently without interfering with each other.

  On the other hand, when adjusting the peak amplifier alone, the peak amplifier can be completely independently adjusted like the main amplifier by setting the DC switch B5 to SHORT and the DC switch A4 to OPEN.

  In addition, the power supply circuit in the microwave amplifier has a very important role for high-frequency characteristics in addition to the DC power supply for suppressing the distortion component generated in the microwave transistor. In order to optimally adjust the operation for suppressing the distortion, it is necessary to strictly manage the conditions of the peripheral circuits of the power supply. In particular, the influence of the capacitance of the capacitor connected to the power supply circuit and the physical mounting position of the capacitor is very large. Therefore, when the power supply line connected to the main amplifier or peak amplifier is physically disconnected and the single amplifier on one side is adjusted, and when both power supply lines are simultaneously turned on and configured as a Doherty amplifier, the power supply Since the physical conditions of the circuit are different, the above-described Doherty synthesizer configuration is used for the problem that the RF characteristics such as distortion change as compared with the adjustment of a single amplifier. Even if the DC switch B5 is switched, the physical arrangement and circuit impedance of the power supply line 3 and the harmonic control circuit 6 which are important for suppressing distortion generated in the microwave transistor are not changed. Thus, it is possible to realize an operation in which the conditions of the power supply line relating to the suppression of the distortion component are not changed.

  When operating as a Doherty amplifier, the DC switch A4 and the DC switch B5 may be simultaneously set to SHORT. Even at that time, since the states of the power supply line 3 and the harmonic control circuit 6 are unchanged, the condition of the power supply line related to distortion suppression does not change from the time of adjusting the single amplifier. For this reason, since the influence of the power supply circuit when adjusting the single amplifier is the same as that when the Doherty amplifier is configured, no backtracking or repeated adjustment occurs in the adjustment of the single amplifier and the adjustment as the Doherty amplifier.

  In FIG. 1, the control of the DC switch A4 and the DC switch B5 is expressed by the control voltage Vcont. However, mechanical manual switching means may be used.

  In the example of FIG. 1, the DC switch A4 and the DC switch B5 imitate a mechanical switch, but it is natural that the switch is composed of a diode, FET, MEMS, or the like having the same effect. The same effect can be obtained even if is used.

(Embodiment 2)
FIG. 2 is a diagram showing a Doherty amplifier according to Embodiment 2 of the present invention. An input distributor 14 for separating an input signal by adding a phase difference of 90 degrees, a main amplifier 15 biased to class A or AB, a peak amplifier 16 biased to class B or C, and a main amplifier 15 And λ / 4 line 1 for combining the output signals of the peak amplifier 16 by adding a phase difference of 90 degrees, an impedance conversion circuit 2 for converting the impedance of the combined part of the λ / 4 line into an output load impedance, and an impedance conversion circuit Connected to the power supply line 3, a DC switch A4 that can be switched between OPEN and SHORT with a control voltage VcontA, a DC switch B5 that can be switched between OPEN and SHORT with a control voltage VcontB, and a power supply line Harmonic control circuit 6 for suppressing distortion, DC switch A and DC switch It comprises an RF level detector 7 for switching and controlling B according to the level of the RF input signal.

  Next, the operation of the Doherty amplifier configured as described above will be described with reference to FIG. The basic operation of the Doherty amplifier is that only the main amplifier 15 operates when the level of the RF input signal is low, and the operation of the peak amplifier 16 is turned off, so that an excessive output margin as the RF amplifier is not secured. It can be operated with high efficiency. The ideal of this operation is that all the RF output power of the main amplifier 15 appears at RF_OUT when the peak amplifier is OFF. In other words, the impedance of the peak amplifier 16 is infinite (OPEN) as seen from the combined part of the λ / 4 line 1 and the impedance conversion circuit 2, and the inflow of the RF output power to the output part of the peak amplifier 16 can be ignored. . According to the configuration of FIG. 2, the RF level detector 7 can switch the DC switch A4 according to the level of the RF input signal. Therefore, at the level of the RF input signal that turns on only the main amplifier 15, the peak amplifier 16 Forcibly disconnected, the impedance of the peak amplifier 16 viewed from the combined portion of the λ / 4 line 1 and the impedance conversion circuit 2 becomes infinite, and an ideal operation state in the low input level region is realized. Further, when the level of the RF input signal becomes high, by setting both DC switches to SHORT, it becomes possible to operate as a normal Doherty amplifier. The RF input level for switching the switch may be arbitrarily set so as to obtain a desired Doherty amplifier characteristic.

  Also, the DC switch is not a simple mechanical switch of only ON and OFF, but a semiconductor switch formed of, for example, an FET whose ON resistance can be varied is used, and a control signal from the RF level detection unit 7 is set according to the RF input level. By changing in steps, the change in the impedance of the peak amplifier as seen from the combined portion of the λ / 4 line 1 and the impedance conversion circuit 2 can be finely controlled from when the peak amplifier is turned on until the saturation operation. Therefore, it is possible to adjust desired characteristics such as linearity and efficiency as the Doherty amplifier.

  The RF level detection unit 7 can be simply configured by a detection circuit using a diode, for example, but it goes without saying that a thermal detection circuit or other power detection means may be used.

  The relationship between the control signal from the RF level detection unit 7 and the RF level may be any relationship such as proportional, inversely proportional, logarithmic proportionality, and inverse logarithmic proportionality so as to obtain desired characteristics.

(Embodiment 3)
FIG. 4 is a diagram showing a Doherty amplifier according to Embodiment 3 of the present invention. An input distributor 14 for separating an input signal by adding a phase difference of 90 degrees, a main amplifier 15 biased to class A or AB, a peak amplifier 16 biased to class B or C, and a main amplifier 15 And λ / 4 line 1 for combining the output signals of the peak amplifier 16 by adding a phase difference of 90 degrees, an impedance conversion circuit 2 for converting the impedance of the combined part of the λ / 4 line into an output load impedance, and an impedance conversion circuit The power supply line 3 connected to the high frequency circuit 13, the high frequency short circuit 13 for short-circuiting the high frequency, the DC switch C17 capable of switching the operation to SHORT and the high frequency short circuit with the control voltage VcontC, and the operation to the OPEN and SHORT with the control voltage VcontB Possible DC switch B5 and high to suppress distortion connected to the power line The harmonic control circuit 6 includes an RF level detection unit 7 that controls switching of the DC switch C17 and the DC switch B5 according to the level of the RF input signal.

Next, the operation of the Doherty amplifier configured as described above will be described with reference to FIG. According to the configuration of FIG. 4, as described in the second embodiment, the RF level detection unit 7 switches the DC switch B5 and turns on only the main amplifier 15 in the region where the level of the RF input signal is small. An ideal operating state of the Doherty amplifier in the low input level region is realized.
Further, when the level of the RF input signal becomes high, it is possible to operate as a normal Doherty amplifier by setting both DC switches to SHORT.

  In order to operate the peak amplifier 16 alone as a single amplifier, the DC switch B5 is switched to SHORT and the DC switch C17 is switched to the high frequency short circuit 13. By doing so, the λ / 4 line 1 viewed from the output of the peak amplifier 16 and the combining unit of the impedance conversion circuit 2 becomes a short stub of λ / 4, and the impedance with respect to the frequency of the RF main signal appears to be open. Therefore, the output of the peak amplifier 16 and the λ / 4 line 1 viewed from the combining unit of the impedance conversion circuit 2 do not affect the high frequency characteristics. In FIG. 4, the high-frequency short-circuit circuit 13 is simply expressed by a capacitor whose one electrode is grounded to GND, but the same effect can be obtained by using a λ / 4 open stub.

  When operating as a Doherty amplifier, the DC switch C12 and the DC switch B5 may be set to SHORT at the same time.

  Also, the DC switch to be used is not a simple mechanical switch of only ON and OFF, but a semiconductor switch formed of, for example, an FET with variable ON resistance is used, and a control signal from the RF level detection unit 7 is set according to the RF level. Thus, the change in the impedance of the peak amplifier 16 as seen from the combined portion of the λ / 4 line 1 and the impedance conversion circuit 2 is changed from when the peak amplifier 16 is turned on until the saturation operation is performed. Since it can be finely controlled, it is possible to adjust desired characteristics such as linearity and efficiency as a Doherty amplifier.

  Further, according to this configuration, not only is the effect obtained when the main amplifier 15 and the peak amplifier 16 are adjusted independently, but also when either the main amplifier 15 or the peak amplifier 16 is operated as a single amplifier, It can be used without loss of high frequency power.

  The RF level detection unit 7 can be constituted by a detection circuit using a diode, for example, but it goes without saying that a heat detection circuit or other detection means may be used.

  The relationship between the control signal from the RF level detection unit 7 and the RF level may be any relationship such as proportional, inversely proportional, logarithmic proportionality, and inverse logarithmic proportionality so as to obtain desired characteristics.

  In the Doherty synthesis circuit of the present invention, the DC switch A and the DC switch B are provided, and the power supply circuits of the main amplifier and the peak amplifier are integrated into one, so that the circuit can be reduced in size. In addition, since the DC switch A and the DC switch B are simultaneously turned ON only in the output region where the main amplifier and the peak amplifier both perform a high frequency amplification operation that requires power supply, the DC component applied between the two amplifiers interferes. Can be suppressed.

  The Doherty synthesizing circuit of the present invention operates the mechanical DC switch A (or DC switch B), so that the high frequency signal can be separated simultaneously with the DC component, so that the main amplifier and the peak amplifier are completely independent. Can be adjusted optimally.

  In addition to the field of high-frequency amplifiers, the present invention can be applied to a power amplification system in which a plurality of transistors are operated in parallel.

Explanatory drawing showing Embodiment 1 of the present invention Explanatory drawing showing Embodiment 2 of the present invention Diagram showing basic configuration of Doherty amplifier Explanatory drawing showing Embodiment 3 of the present invention The figure of the prior art shown in the special table 2006-5000883

Explanation of symbols

1 λ / 4 line 2 impedance conversion circuit 3 power supply line 4 DC switch A
5 DC switch B
6 Harmonic control circuit 7 RF input level detector 8 Main amplifier 9 Peak amplifier 10 λ / 4 line 11 Impedance conversion circuit 12 Input distributor 13 High frequency short circuit 14 Input distribution circuit 15 Main amplifier 16 Peak amplifier 17 DC switch C
18 RF input A
19 RF input B
DESCRIPTION OF SYMBOLS 100 90 degree phase conversion circuit 101 Impedance conversion circuit provided with power supply circuit 102 Bias control circuit

Claims (3)

RF input A for inputting an RF signal output from the main amplifier of the two high-frequency amplifiers constituting the Doherty amplifier;
RF input B for inputting an RF signal output from a peak amplifier of the two high-frequency amplifiers;
A λ / 4 line that combines the output signals of the two high-frequency amplifiers with a phase difference of 90 degrees;
An impedance conversion circuit that converts the impedance of the combined portion of the λ / 4 line into an output load impedance;
A power supply line connected to the impedance conversion circuit;
A DC switch A capable of switching operation to OPEN and SHORT at the inserted control voltage VcontA between the lambda / 4 lines from the RF input A,
A DC switch B capable of switching the operation to OPEN and SHORT at the inserted control voltage VcontB between the combining portion of the lambda / 4 line and the impedance converting circuit from the RF input B,
A harmonic control circuit for suppressing distortion connected to the power supply line;
A Doherty synthesis circuit comprising: In addition to the Doherty synthesis circuit according to claim 1,
An input distributor for separating an input signal by adding a phase difference of 90 degrees;
A main amplifier biased to class A or class AB,
A peak amplifier biased to Class B or Class C;
An RF level detector that controls the DC switch A and the DC switch B according to the level of an RF input signal;
A Doherty amplifier comprising: An input distributor for separating an input signal by adding a phase difference of 90 degrees;
A main amplifier biased to class A or class AB,
A peak amplifier biased to Class B or Class C;
A λ / 4 line that combines the output signals of the main amplifier and the peak amplifier by adding a phase difference of 90 degrees;
An impedance conversion circuit that converts the impedance of the combined portion of the λ / 4 line into an output load impedance;
A power supply line connected to the impedance conversion circuit;
A high-frequency short circuit that short-circuits the high frequency; and
DC switch capable of switching operation to SHORT and connection to the high-frequency short circuit by a control voltage VcontC inserted between an RF input A for inputting an RF signal output from the main amplifier and the λ / 4 line. C
DC switch capable of switching the operation between OPEN and SHORT with a control voltage VcontB inserted between the λ / 4 line and the synthesis unit of the impedance conversion circuit from the RF input B for inputting the RF signal output from the peak amplifier B and
A harmonic control circuit for suppressing distortion connected to the power supply line;
A Doherty amplifier comprising:

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