JP5390495B2 - High frequency amplifier - Google Patents

Description

  Embodiments described herein relate generally to a high-frequency Doherty-type high-efficiency amplifier used for microwave communication and the like.

  As a means for efficiently amplifying high frequency signals such as CDMA (Code Division Multiple Access) and OFDM (Orthogonal Frequency Division Multiplexing) having a large difference between average power and peak power, there is a Doherty type high frequency amplifier. The high frequency amplifier is a main amplifier biased to operate in class B, class AB or class A, a peak amplifier biased to operate in class C, and an input high frequency signal to the main amplifier and peak amplifier. It has a hybrid to distribute.

  Here, since the peak amplifier is sufficiently turned on near the saturation power of the main amplifier, the Doherty type high frequency amplifier can output saturation power equivalent to that of the balanced amplifier. On the other hand, the peak amplifier is turned off in a power operation region in which the saturation power of the main amplifier is sufficiently backed off, so that the Doherty type high frequency amplifier can keep the current consumption of the peak amplifier low. As a result, the Doherty high-frequency amplifier can increase the efficiency at the time of outputting a signal having a large ratio (PAR) between the average power and peak power of CDMA and OFDM.

  As described above, in order to improve the efficiency of the power amplifying apparatus, there is a method of improving the drain efficiency of the final stage by installing a Doherty type high-frequency amplifier in the final stage of the power amplifying apparatus. However, in order to further improve the efficiency of the entire power amplifying device, it is not enough to improve the drain efficiency of the high-frequency amplifier used in the final stage, but by increasing the gain of the high-frequency amplifier in the final stage, It is necessary to reduce the power consumption of the driver amplifier that supplies a signal to the high frequency amplifier.

JP 2008-125044 A

E. James Crescenzi, Jr. et al, “60 Watt Doherty Amplifiers Using High Gain 2-Stage Hybrid Amplifier Modules”, IEEE, 2005

  As described above, in order to improve the efficiency of the power amplifying device, not only the drain efficiency of the high-frequency amplifier used in the final stage is improved, but also the gain of the high-frequency amplifier in the final stage is increased, It is necessary to reduce the power consumption of a driver amplifier that supplies a signal to a high-frequency amplifier.

  Accordingly, an object of the present invention is to provide a Doherty-type high-frequency amplifier used in the final stage that can improve the gain and reduce the power consumption of the driver amplifier that supplies a high-frequency signal.

  According to the embodiment, the high-frequency amplifier has a line impedance of a line to be inserted in advance, a hybrid that distributes the input high-frequency signal to the first signal and the second signal, and the first signal A main amplifier for amplifying; and a peak amplifier for amplifying the second signal. The hybrid outputs a first port to which the high-frequency signal is input, a second port that outputs the first signal toward the main amplifier, and outputs the second signal toward the peak amplifier. And a fourth port that is open-connected. When the input level of the second signal is in the saturation region of the main amplifier, the input impedance of the peak amplifier viewed from the hybrid is equal to the line impedance, and the second port and the The electrical length of the first transmission line between the main amplifier and the electrical length of the second transmission line between the third port and the peak amplifier are adjusted. Further, when the input level of the second signal is in a region where the back-off is taken from the saturation region of the main amplifier, the input impedance of the peak amplifier as seen from the hybrid is larger than the line impedance. In addition, the electrical length of the first transmission line and the electrical length of the second transmission line are set.

It is a block diagram which shows the function structure of the power amplifier which mounts the high frequency amplifier which concerns on 1st Embodiment. It is a figure which shows the connection of the hybrid of FIG. FIG. 3 is a diagram illustrating input impedance viewed from the first port and insertion loss of power output from the first port to the second port when the impedance of the third port changes in FIG. 2. It is a figure which shows the connection of the conventional hybrid. FIG. 5 is a diagram showing the input impedance viewed from the first port and the insertion loss of power output from the first port to the second port when the impedance of the third port changes in FIG. 4. It is a block diagram which shows the function structure of the power amplification apparatus carrying the high frequency amplifier which concerns on 2nd Embodiment. It is a figure which shows the connection of the hybrid of FIG. FIG. 8 is a diagram illustrating the input impedance viewed from the first port and the insertion loss of power output from the first port to the second port when the impedance of the third port decreases in FIG. 7.

  Hereinafter, embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a functional configuration of a power amplifying device equipped with a high-frequency amplifier 10 according to the first embodiment. The power amplifying apparatus includes a driver amplifier 20 that amplifies and outputs a high-frequency signal, and a Doherty-type high-frequency amplifier 10 that amplifies the high-frequency signal from the driver amplifier 20.

  The high frequency amplifier 10 includes a hybrid 11, a main amplifier 12, a peak amplifier 13, a first impedance conversion circuit 14, and a second impedance conversion circuit 15.

  The hybrid 11 distributes the high frequency signal from the driver amplifier 20 to the first and second signals, supplies the first signal to the main amplifier 12, and supplies the second signal to the peak amplifier 13. It is.

  The main amplifier 12 is biased to operate in class B, class AB or class A, and amplifies the first signal from the hybrid 11. The main amplifier 12 outputs the amplified first signal to the first impedance conversion circuit 14 having a phase of 90 degrees. The first impedance conversion circuit 14 is composed of a line having a length corresponding to λ / 4.

  The peak amplifier 13 is biased to operate in class C and amplifies the second signal from the hybrid 11. The first signal output from the first impedance conversion circuit 14 and the second signal amplified by the peak amplifier 13 are combined. The combined signal passes through the second impedance conversion circuit 15 having a phase of 90 degrees and is output with a line impedance of 50Ω.

  Although not shown inside, both the input and output portions of both amplifiers are provided with a matching circuit for matching the line impedance to 50Ω, and signals are input and output. Furthermore, the biases of the main amplifier 12 and the peak amplifier 13 are set as described above, but other biases and combinations thereof may be used as long as they operate as a Doherty amplifier.

  Here, the hybrid 11 and the main amplifier 12 are connected by a transmission line L1. The hybrid 11 and the peak amplifier 13 are connected by a transmission line L2.

  FIG. 2 is a schematic diagram illustrating connection of the hybrid 11 according to the first embodiment. The hybrid 11 shown in FIG. 2 includes four ports P1 to P4. The line configuration within the broken line shows an example in which the line impedance connected to the hybrid 11 is 50Ω.

  The first port P1 is connected to the driver amplifier 20, the second port P2 is connected to the main amplifier 12 via the transmission line L1, and the third port P3 is connected to the peak amplifier 13 via the transmission line L2. The fourth port is open. Here, since the peak amplifier 13 is biased so as to operate in class C, the input impedance of the peak amplifier 13 is not constant with respect to the input level of the second signal. In this embodiment, the input impedance on the peak amplifier 13 side viewed from the hybrid 11 is matched to the line impedance of 50Ω when the input level of the second signal is sufficiently high, and the input level of the second signal is compared. It is assumed that the electrical lengths of the transmission lines L1 and L2 are adjusted so as to be higher than 50Ω when the power is low.

  FIG. 3 shows the input impedance viewed from the first port P1 and the second port from the first port P1 when the input impedance on the peak amplifier 13 side (impedance of the third port P3) changes in FIG. The insertion loss of the power output to the port P2 is shown.

  As shown in FIG. 3, when the impedance of the third port P3 is 50Ω, the input impedance viewed from the first port P1 is 50Ω. However, when the impedance of the third port P3 is 500Ω, the input impedance viewed from the first port P1 is about 86Ω. The insertion loss of the power output from the first port P1 to the second port P2 is −3 dB when the impedance of the third port P3 is 50Ω, but the impedance of the third port P3 is 500Ω. Then, the insertion loss of the power output from the first port P1 to the second port P2 is reduced to 1 dB or less.

  Here, for comparison, FIG. 4 shows a schematic diagram showing connection of a conventional hybrid. In FIG. 4, the fourth port P4 is terminated with a standard 50Ω.

  FIG. 5 shows the input impedance viewed from the first port P1 and the power output from the first port P1 to the second port P2 when the impedance of the third port P3 changes in FIG. Indicates insertion loss.

  As shown in FIG. 5, when the impedance of the third port P3 is 50Ω, the input impedance viewed from the first port P1 is 50Ω. However, when the impedance of the third port P3 is 500Ω, the input impedance viewed from the first port P1 changes to about 113Ω. Further, the insertion loss of the power output from the first port P1 to the second port P2 is constant at approximately −3 dB regardless of the impedance of the third port P3.

  Comparing the circuit of FIG. 2 with the circuit of FIG. 4, when the input level of the second signal supplied to the peak amplifier 13 is in a sufficiently high saturation region, the impedance of the third port P3 is 50Ω. The circuit 2 and the circuit of FIG. 4 operate in the same manner.

  On the other hand, when the input level of the second signal supplied to the peak amplifier 13 is in a low region sufficiently back-off from the saturation region, the impedance of the third port P3 becomes higher than 50Ω and becomes high. The circuit of FIG. 4 and the circuit of FIG. 4 operate differently.

  As described above, in the first embodiment, the fourth port P4 of the hybrid 11 is opened, and the electrical lengths of the transmission lines L1 and L2 are set to the third when the input level of the second signal is low. The impedance of the port P3 is adjusted in advance so as to be higher than 50Ω. Thereby, when the impedance of the third port P3 deviates from 50Ω, the change in the input impedance viewed from the first port P1 to which the driver amplifier 20 is connected can be reduced as compared with the conventional example. That is, it is possible to suppress the efficiency reduction due to the fluctuation from the optimum efficiency load for the driver amplifier 20.

  Further, when the impedance of the third port P3 deviates from 50Ω, the insertion loss of the power output from the first port P1 to the second port P2 can be reduced as compared with the conventional example, so that the output of the driver amplifier The power consumption can be reduced.

  In other words, according to the Doherty type high frequency amplifier 10 according to the present embodiment, the gain near the average power of the modulated wave can be improved, and the power consumption of the driver amplifier 20 that supplies the high frequency signal to the high frequency amplifier 10 can be reduced. it can.

(Second Embodiment)
FIG. 6 is a block diagram illustrating a functional configuration of a power amplifying device equipped with the high-frequency amplifier 10 according to the second embodiment.

  FIG. 7 is a schematic diagram illustrating connections of the hybrid 11 according to the second embodiment. The fourth port P4 shown in FIG. 7 is connected to the ground.

  Here, in the first embodiment, an example has been shown in which the impedance of the third port P3 viewed from the hybrid 11 increases as the input level of the second signal decreases. In the present embodiment, the input impedance on the peak amplifier 13 side viewed from the hybrid 11 is matched with the line impedance of 50Ω when the input level of the second signal is sufficiently high, and the input level of the second signal is lowered. In this case, it is assumed that the electrical lengths of the transmission lines L1 and L2 are adjusted so as to be smaller than 50Ω.

  FIG. 8 shows the input impedance viewed from the first port P1 and the output from the first port P1 to the second port P2 when the impedance of the third port P3 drops from 50Ω in FIG. Indicates the power insertion loss.

  As shown in FIG. 8, when the impedance of the third port P3 is 50Ω, the input impedance viewed from the first port P1 is 50Ω. However, when the impedance of the third port P3 is 25Ω, the input impedance viewed from the first port P1 changes to about 38Ω. The insertion loss of the power output from the first port P1 to the second port P2 is −3 dB when the impedance of the third port P3 is 50Ω, but the impedance of the third port P3 is 5Ω. Then, it is reduced to 1 dB or less.

  As described above, in the second embodiment, the fourth port P4 of the hybrid 11 is connected to the ground by the transmission line, and the input length of the second signal is reduced in the electrical length of the transmission lines L1 and L2. In this case, the impedance is adjusted in advance so that the impedance of the third port P3 is smaller than 50Ω. Strictly speaking, the electric power of the transmission line L2 between the hybrid 11 and the main amplifier 13 is adjusted in accordance with the adjustment of the electric length of the transmission line L2 so that the outputs of the main amplifier 12 and the peak amplifier 13 are combined in phase. The length is also adjusted. Thereby, when the impedance of the third port P3 deviates from 50Ω, it is possible to reduce the change in the input impedance viewed from the first port P1 to which the driver amplifier 20 is connected as compared with the conventional example. That is, it is possible to suppress the efficiency reduction due to the fluctuation from the optimum efficiency load for the driver amplifier 20.

  Further, when the impedance of the third port P3 deviates from 50Ω, it is possible to reduce the insertion loss of power output from the first port P1 to the second port P2 compared to the conventional example.

  Therefore, according to the high-frequency amplifier 10 according to the present embodiment, the gain near the average power of the modulated wave can be improved, and the power consumption of the driver amplifier 20 that supplies a high-frequency signal to the high-frequency amplifier 10 can be reduced.

(Other embodiments)
In the first and second embodiments, the case where the real part of the impedance on the side of the peak amplifier 13 viewed from the hybrid 11 increases and decreases as the input level of the second signal increases is described as an example. . However, the present invention is not limited to this. For example, depending on the adjustment value of the electrical length of the transmission lines L1 and L2, not only the real part of the impedance, that is, the pure resistance component, but also the imaginary part of the impedance may change.

  In such a case, a tip open transmission line having an electrical length such that the impedance on the peak amplifier 13 side becomes a pure resistance component is connected to the fourth port P4 (not shown), or the peak amplifier 13 side is connected. An effect similar to that of the above embodiment can be obtained by connecting a short-circuited short transmission line having an electrical length such that the impedance becomes a pure resistance component (not shown). By doing so, the impedance on the side of the peak amplifier 13 can be changed according to the pure resistance such as 30Ω to 150Ω, for example, along with the increase / decrease of the input level of the second signal.

  When there is no space for mounting the tip open transmission line or the tip short transmission line at the fourth port P4, the same effect can be obtained by connecting a lumped constant element such as an inductor or a capacitor.

  Further, in the hybrid 11 according to the first and second embodiments, the transmission lines L1 and L2 are constructed in the pattern shape of the signal path of the circuit forming the high frequency amplifier 10, or the functions of the delay elements and the like. Parts may be used.

  In the hybrid 11 according to the first and second embodiments, the case where an equally distributed coupler such as a branch line coupler is used has been described as an example. However, the present invention is not limited to this. For example, the same application can be made when using couplers that distribute unevenly.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... High frequency amplifier 11 ... Hybrid 12 ... Main amplifier 13 ... Peak amplifier 14 ... 1st impedance conversion circuit 15 ... 2nd impedance conversion circuit 20 ... Driver amplifier P1-P4 ... 1st thru | or 4th port L1, L2 ... Transmission line

Claims (6)

A line impedance of a line to be inserted is set in advance, a hybrid that distributes the input high-frequency signal to the first signal and the second signal, a main amplifier that amplifies the first signal, and the second In a Doherty type high frequency amplifier comprising a peak amplifier for amplifying a signal,
The hybrid is
A first port to which the high-frequency signal is input;
A second port for outputting the first signal toward the main amplifier;
A third port for outputting the second signal toward the peak amplifier;
A fourth port that is open-connected,
When the input impedance of the peak amplifier viewed from the hybrid is equal to the line impedance when the input level of the second signal is in the saturation region of the main amplifier, the input of the second signal is When the level is in a region where the back-off is taken from the saturation region of the main amplifier, the electrical length of the transmission line between the second port and the main amplifier is set to be larger than the line impedance; A high-frequency amplifier, wherein an electrical length of a transmission line between the third port and the peak amplifier is set.   2. The high-frequency amplifier according to claim 1, wherein a tip open transmission line having an electrical length is connected to the fourth port so that an input impedance of the peak amplifier is a pure resistance.   The high-frequency amplifier according to claim 1, wherein the fourth port is in an open connection state by a lumped constant element in which an input impedance of the peak amplifier is a pure resistance. A line impedance of a line to be inserted is set in advance, a hybrid that distributes the input high-frequency signal to the first signal and the second signal, a main amplifier that amplifies the first signal, and the second In a Doherty type high frequency amplifier comprising a peak amplifier for amplifying a signal,
The hybrid is
A first port to which the high-frequency signal is input;
A second port for outputting the first signal toward the main amplifier;
A third port for outputting the second signal toward the peak amplifier;
A fourth port shorted to ground,
When the input impedance of the peak amplifier viewed from the hybrid is equal to the line impedance when the input level of the second signal is in the saturation region of the main amplifier, the input of the second signal is When the level is in a region where the backoff is taken from the saturation region of the main amplifier, the electrical length of the transmission line between the second port and the main amplifier is set to be smaller than the line impedance; A high-frequency amplifier, wherein an electrical length of a transmission line between the third port and the peak amplifier is set.   5. The high frequency amplifier according to claim 4, wherein a tip short transmission line having an electrical length is connected to the fourth port so that an input impedance of the peak amplifier is a pure resistance.   5. The high frequency amplifier according to claim 4, wherein the fourth port is short-circuited to the ground by a lumped constant element in which the input impedance of the peak amplifier is a pure resistance.

Images