JP5331732B2 - Envelope tracking power amplifier and envelope tracking amplification method - Google Patents

Description

  The present invention relates to an envelope tracking power amplifier using an envelope tracking method and an envelope tracking amplification method thereof.

  As one method for improving the efficiency of a high-frequency power amplifier, an envelope tracking method (hereinafter abbreviated as ET method (amplifier)) in which the drain voltage of an FET, which is an amplifying element of a power amplifier, is varied in synchronization with a signal envelope. There is. That is, when the signal level is low, the drain voltage is lowered to lower the peak power of the amplifier, and the back-off is reduced to increase the efficiency.

FIG. 3 is a functional block diagram for explaining an operation process of an example of a conventional ET amplifier.
In the conventional ET amplifier shown in FIG. 3, a part of the signal input to the input terminal i is branched by the directional coupler 20, and the envelope detector (EDT) 30 detects the envelope of the input signal. The power supply voltage of the RF amplifier 60 that performs power amplification at 40 is controlled in accordance with the amplitude voltage of the envelope. The other input signal is corrected by the delay line (DL) 50 and the delay time generated by the envelope detector 30 and the ET amplifier 40, input to the RF amplifier 60, and output through the output matching circuit (MT) 70. The signal is output from the terminal o toward an external antenna.

  Thus, when the amplitude voltage of the envelope of the input signal is small, the power supply voltage of the RF amplifier 60 is low, and when the amplitude voltage of the envelope of the input signal is large, the power supply voltage of the RF amplifier 60 is controlled high. High-efficiency amplifier operation can be expected.

  One problem with this method is that depending on the type of RF amplifier, the efficiency of the RF amplifier 60 is reduced when the power supply voltage of the RF amplifier 60 is lowered. Here, in the high frequency amplifier of the RF amplifier 60, an impedance matching is performed by providing an output matching circuit (MT) 70 in an input / output portion of an amplifying semiconductor element such as an FET or a bipolar transistor. Since the impedance also changes when it changes, even if the operation of the matching circuit is optimal under a certain bias condition, if the power supply voltage changes, the bias condition changes, and the operation of the matching circuit is not necessarily optimal. Therefore, as a countermeasure, a method of correcting the impedance of the input / output matching circuit according to the envelope of the input signal has been devised (see Patent Document 1).

  An envelope tracking power amplifier according to Patent Document 1 has a configuration in which an amplification semiconductor element and an input / output matching circuit are combined, and a supply bias voltage to the semiconductor element is changed according to an envelope of an amplified signal, By changing the impedance of the input / output matching circuit in accordance with the envelope and in synchronization with the bias voltage, the output impedance is optimized to prevent a reduction in efficiency due to a decrease in power supply voltage.

FIG. 4 is a diagram showing the relationship between the power supply voltage and efficiency of the high-frequency power amplifier (RF amplifier) disclosed in Patent Document 1. In FIG.
If the output is kept at a fixed match without controlling the bias voltage as the amplification control of the ET amplifier, when the power supply voltage of the RF amplifier to which the power of +30 V is applied is reduced to +15 V when the saturated power is output, the efficiency at the time of saturation is about 58 % To about 42%. On the other hand, in the RF amplifier disclosed in Patent Document 1, the output matching circuit is also controlled according to the amplitude voltage of the envelope of the input signal, so that the efficiency at the time of saturation can be achieved even if the power supply voltage of the RF amplifier is reduced to + 15V. Is kept at about 55%.

  Conventionally, efficiency has been improved by setting the peak output level of the RF amplifier to a saturation level. However, in recent modulation systems such as CDMA and OFDM used for mobile phones and broadcasts, a difference between the average output power and the peak output voltage may be about 8 dB. Normally, the control voltage of the ET amplifier decreases the power supply voltage at a power of 10 (X / 20) with respect to the output back-off amount XdB. The power supply voltage at the time of 8 dB backoff is about + 12V.

  If the above measures are not taken, the efficiency falls below 40%, and even if the measures are taken, the efficiency drops below 50%. In such a case, even if the power supply voltage and the bias are simply controlled only by the envelope voltage, the efficiency cannot be ensured sufficiently.

  In other words, if the output voltage difference between the average power and the peak power is large, the operation will be performed with a voltage drop at the average output, which is the majority of the operation time, but at that voltage, the power supply efficiency will decrease and the efficiency will be ensured. There was an inadequate problem.

JP 2008-124947 A

Design of Varactor-Based Tunable Matching Networks for Dynamic Load Modulation of High Power Amplifiers (IEEE TRANSACTION ON MTT 2009 11 No. 5).

  A power amplifier using the conventional envelope tracking method has a problem of operating at a power supply voltage that reduces power supply efficiency when performing an average output operation when the difference between the average output power and the peak output voltage is large. It was.

  The present invention has been made to solve the above problems, and in a power amplifier using an envelope tracking amplification method, it suppresses a decrease in efficiency when the power supply voltage is decreased, and is highly efficient even when a signal having a high average-peak power ratio is input. It is an object of the present invention to provide an envelope tracking power amplifier and an envelope tracking amplification method capable of various operations.

  In order to achieve the above object, an envelope tracking power amplifier according to the present invention is a power supply that a power supply means supplies to the power amplifier in accordance with a signal level obtained by demultiplexing a high frequency input signal amplified by the power amplifier and detecting an envelope. In an envelope tracking power amplifier whose voltage is controlled, the first and second high-frequency power amplifiers that amplify and output a high-frequency signal and the input signal to the first and second high-frequency power amplifiers A distribution means for branching output; an output means for combining and outputting the outputs of the first and second high-frequency power amplifiers; and a first for supplying power to the first and second high-frequency power amplifiers; The second power supply means and the signal level are monitored and compared with a predetermined level. If the signal level is lower than the predetermined level, the first high-frequency power amplifier includes the first power supply means. A power supply voltage set in advance corresponding to the signal level is supplied from a source supply means, and the branched input signal is amplified and output, while the input signal to the second high-frequency power amplifier is cut off. In addition, a voltage preset in the second power supply means so as to correspond to the impedance formed by the output means preset in the drain-source capacitance of the second high-frequency power amplifier corresponding to the signal level If the input signal is input to both the high-frequency power amplifiers and the operation of the second high-frequency power amplifier is aligned with that of the first high-frequency power amplifier. Control for setting the bias of the gate voltage of the second high-frequency power amplifier and supplying a constant voltage to the first and second power supply means. And control means for performing, characterized in that it comprises.

  An envelope tracking amplification method for an envelope tracking power amplifier according to the present invention includes a distribution means, an output means, first and second high frequency power amplifiers, first and second power supply means, and a control means. The voltage of the power supplied from the power supply means to the high frequency power amplifier is controlled according to the signal level obtained by demultiplexing a part of the high frequency input signal that is input and amplified by both the high frequency power amplifiers and detecting the envelope. In an envelope tracking amplification method of an envelope tracking power amplifier, first and second high frequency power amplifiers that amplify and output a high frequency signal, and the distribution unit are configured to output the input signal to the first and second high frequency powers. The output is branched to the amplifier, and the control means monitors the signal level obtained by extracting the demultiplexed wave and detecting the envelope to obtain a predetermined level. In contrast, when the power level is lower than a predetermined level, a power supply voltage set in advance corresponding to the signal level is supplied from the first power supply means to the first high-frequency power amplifier, and the branched input signal The output means in which the input signal to the second high-frequency power amplifier is cut off and the drain-source capacitance of the second high-frequency power amplifier is preset in accordance with the signal level The second power supply means outputs a preset voltage so as to correspond to the impedance formed by the first and second input power signals to both the high-frequency power amplifiers when the voltage is higher than a predetermined level. The bias of the gate voltage of the second high-frequency power amplifier is set so that the operation of the second high-frequency power amplifier is aligned with that of the first high-frequency power amplifier. To a second power supply means to output a constant voltage, and the output means, and outputs multiplexes the outputs from the first and second high-frequency power amplifier.

  According to the present invention, it is possible to provide an envelope tracking power amplifier and an envelope tracking amplification method that can operate with high efficiency even when a signal having a high average / peak power ratio is input.

The functional block diagram explaining operation | movement of the envelope tracking power amplifier concerning the Example of this invention. The figure which shows the relationship between the control voltage (drain voltage) corresponding to the back-off amount from the saturation level of an envelope tracking power amplifier, and saturation power in connection with the Example of this invention. The functional block diagram explaining the operation processing of an example of the conventional ET amplifier. The figure which shows an example of the relationship between the power supply voltage of a high frequency power amplifier, and efficiency. The figure which shows the relationship between the control voltage (drain voltage) corresponding to the back-off amount from the saturation level of the conventional ET power amplifier, and saturation power.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram illustrating the operation of an ET amplifier in connection with a power amplifier (hereinafter referred to as an ET amplifier) using an envelope tracking amplification method according to an embodiment of the present invention.
In FIG. 1, the ET amplifier of the embodiment uses two RF amplifiers 6 and 12 as power amplifiers. When the input level is low, one RF amplifier 6 is for signal amplification, and the other RF amplifier 12 is It is used to control the output impedance of the other amplifier according to the envelope of the input signal. Further, when the input level is high near the saturation level, the two RF amplifiers 6 and 12 are simultaneously used for signal amplification. The outputs of the RF amplifiers 6 and 12 are combined at an output terminal o via output matching circuits (MC) 7 and 13 and phase adjustment circuits (Φ) 14 and 18. The line lengths of the phase adjustment circuits (Φ) 14 and 18 are adjusted to an appropriate length so that the phases of both the RF amplifiers 6 and 12 are aligned.

  In the conventional ET amplifier, a single power amplifier is used at the final stage, and the power supply voltage is set so that the output is close to the saturation level when the input signal reaches a peak value. On the other hand, in the ET amplifier of the embodiment of the present application, when two input power amplifiers with low output are used at the final stage and the input signal level is low, only one unit is operated for ET amplification. For most of the operation time when the input level is at the average level, a single low-power power amplifier is operated near the maximum efficiency, and the power amplifier is added only at the momentary large input level to greatly increase the back-off. However, the efficiency of the entire amplifier is improved by narrowing the control range of the power supply voltage.

  Hereinafter, although the case where the RF amplifier 6 and the RF amplifier 12 are amplifier elements having the same saturation power will be described, the scope of the present proposal is not limited thereto. Here, an example will be described in which the signal range of the input level is divided into two regions of −3 dB or less and −3 dB or more from the saturation power of the entire proposed amplifier.

(1) Region in which output level is −3 dB or less from the saturation power level of the entire power amplifier In this region, the first RF amplifier 6 operates as an amplifier that amplifies the input signal, but the second RF amplifier 12 is RF Used as a circuit for controlling the output impedance of the amplifier 6.

  The signal input to the input terminal i is divided by the hybrid (directional coupler, distributor: H) 2, and one signal is input to the envelope amplifier 4 after detection by the envelope detector (EDT) 3, and RF The power supply voltage of the amplifier 6 is controlled according to the voltage of the detection signal. The other divided signal is further divided into two by a divider (Div) 9 through a delay line (DL) 5, and one is input to an RF amplifier 6 through a variable phase shifter (hereinafter abbreviated as Φ) 10. After being amplified and supplied to the output terminal o through the output matching circuit (MC) 7 and Φ18.

  The RF amplifier 6 is affected by the output impedance by a circuit constituted by the RF amplifier 12 connected via the output matching circuit (MC) 13 and Φ14. Here, the operation of the RF amplifiers 6 and 12 will be described.

  The output of the EDT 3 input to the envelope amplifier 4 is input to the level comparator (COM) 16, and here it is determined by a determination value that is 3 dB lower than the input level corresponding to the saturation level, but the envelope detection signal A switching signal is generated according to the level of the signal and supplied to the switch (SW) 11 and the gate bias setting circuit 17.

  The RF amplifier 6 is supplied with a low power supply voltage (drain voltage) when the input level is low by the envelope amplifier 4 and is supplied with a high voltage when the input level is high. The operation of the RF amplifier 6 in this case is newly added with a distributor 9 and a phase adjustment circuit Φ10 on the input side, but is basically the same as the operation of the conventional ET amplifier shown in FIG.

  The other output of the hybrid 2 is further distributed by the distributor (Div) 9 as described above, and one of the signals is input to the RF amplifier 6, and the other is input to the RF amplifier 12 via the switch (SW) 11. Entered. Here, in the region of −3 dB or less from the saturation power of the entire amplifier, the switch (SW) 11 is turned off by the comparator 16 and the input signal to the RF amplifier 12 is cut off.

  Further, the comparator 16 sets the gate bias setting circuit (when the RF amplifier is an FET) (BC) 17 to set the gate voltage of the RF amplifier 12 so that the drain of the RF amplifier 12 (when the FET is used) does not flow.

  The signal detected by the envelope detector (EDT) 3 is also input to the drain voltage control circuit (DC) 15 that controls the power supply voltage applied to the RF amplifier 12 in the same manner as the envelope amplifier 4. In general, the capacitance (Cds) between the drain and the source of an FET changes by controlling the drain voltage. Then, by controlling the output voltage of the drain control circuit 15 according to the input level and changing the Cds of the RF amplifier 12, the output impedance viewed from the RF amplifier 6 is controlled according to the input power so that the efficiency is optimized. To do.

  For this control, for example, the drain voltage control circuit (DC) 15 previously stores the correspondence between the detection voltage and the output voltage in a table and stores it in a memory not shown in the figure, and allows the internal CPU to control the detection voltage. This is implemented by setting the input / output characteristics with a CR circuit to which is inputted or a semiconductor non-linear circuit.

  The design method for varying the output impedance viewed from the RF amplifier 6 will not be described in detail here. However, as an example, in Non-Patent Document 1, a varactor diode is used to change the capacitance according to the input level. A method for controlling the output impedance efficiency to be optimum is described, and the same effect can be obtained in terms of circuit operation.

  The above is the description of the operation of “operation in a region where the output level is −3 dB or less from the saturated power of the entire amplifier”.

(2) Region where output level is −3 dB or more from saturation power of entire power amplifier In this case, level detector (COM) 16 detects that the output level is from −3 dB or more from saturation power of the entire power amplifier. Then, the switch 11 is turned on to input a signal to the RF amplifier 12 which is the second amplifier. In addition, the gate bias setting circuit applies a setting voltage comparable to that of the RF amplifier 6 to the RF amplifier 12. The phase adjustment circuits (Φ) 10 and 19 are for adjusting the phase so that signals of the RF amplifier 6) and the RF amplifier 12 are combined in phase with the output.

  The envelope amplifier 4 is set to supply the maximum drain voltage to the RF amplifier 6 at an operating point where the output power is -3 dB from the saturated power, and is set to hold the voltage in the operating region (2). The same drain voltage as that of the amplifier 6 is supplied. As a result, in this region, the RF amplifier 6 and the RF amplifier 12 operate as a balanced amplifier.

  In other words, at an output power of −3 dB or more from the saturation power, the outputs of two RF amplifiers having the same output applied with a constant power supply voltage are combined and added and output toward an antenna (not shown). The

  Next, the operation of the ET amplifier according to the present embodiment will be compared with the operation of the ET amplifier in Document 1 (Japanese Patent Laid-Open No. 2008-124947).

2 and 5 show the control voltage (drain voltage) and saturation power of the amplifier corresponding to the back-off amount from the saturation level in this embodiment and the conventional method. Here, as an example, the existing circuit whereas the using device of saturation power 100W, the present embodiments and to obtain an output of 100W using two devices of saturation power 50 W. Further, the maximum value to which the drain voltage (indicated as the control voltage in FIGS. 2 and 5) can be applied is + 30V.

  In the ET amplifier of the embodiment, as shown in FIG. 2, at the operating point where the output level is 9 dB backoff from the saturation level, the drain voltage of the RF amplifier 6 is 15 V, and the RF amplifier 12 is OFF. Is shifted by 3 dB. In the conventional method, when the back-off of 9 dB is taken, the drain voltage is as low as 11 V. However, in this embodiment, the drain voltage is 15 V as described above, which is equal to the drain voltage at the time of the conventional 6 dB back-off.

  As shown in FIG. 4, the efficiency corresponds to the drain voltage. In this embodiment, the efficiency at the operating point where the output level is 9 dB back-off from the saturation level is 55%. An efficiency equivalent to the efficiency at the operating point can be expected, and the efficiency can be improved over the efficiency at the operating point with the 9 dB back-off in the conventional method (45% when impedance matching is performed, and 35% when not). it can.

  In the embodiment of the present application, even at the operating point where the output level is 3 dB back-off from the saturation level, the drain voltage quickly reaches 30 V at the maximum and the saturation output is 100 W, which is more than necessary, and the operation using the conventional method with 3 dB back-off. It seems to be degraded compared to the efficiency when the voltage is lowered at the point.

  However, in general, a signal having a ratio of average power to peak power of about 8 dB has a low probability of existence of a high-power signal with an output of 3 dB backoff or higher, and the RF amplifier 12 operates only in a short period, and within a main operation period. Then, since only the RF amplifier 6 operates, high efficiency can be maintained.

  In the present invention, the combination of the above configuration and processing procedure may be changed without departing from the spirit of the present invention. For example, when the input signal is lower than 3 dB from the saturation level, the power supply voltage to the RF amplifier 6 is applied to 15 V even at 9 dB back-off simply by turning off the RF amplifier 12 and keeping the output impedance constant. Therefore, a reduction in efficiency can be prevented as compared with the conventional method.

  In other words, by configuring the RF amplifier in multiple configurations, it is not necessary to widen the maximum power supply voltage of the power supply means for supplying power to the RF amplifier and the cover range of the envelope amplifier, and one RF amplifier at the time of low level input By turning the signal OFF to use it for output impedance matching in the same manner as a varactor diode, an effect of obtaining high efficiency can be obtained.

  If the difference between the peak level and the average level is large and the probability of peak level is low, the RF amplifier 12 is turned on, the level is increased, and the RF amplifier 6 is made an amplifier that operates at a lower voltage and with higher efficiency. May be taken.

  Although detailed explanation is omitted, the present invention has been described by taking the case where two power amplifiers are used at the final stage as an example, but additional power amplifiers are added in stages, such as three or four. It may be something to go.

  As described above, the present invention can provide an envelope tracking power amplifier and an envelope tracking amplification method that can operate with high efficiency even when a signal having a high average / peak power ratio is input.

10, 14, 18, 19 Variable phase shifter (Φ)
11 Switch (SW)
15 Drain voltage control circuit (DC)
2 Hybrid (directional coupler: H)
3 Envelope detector (EDT)
4 Envelope amplifier 5 Delay line (DL)
6, 12 RF amplifier 7, 13 Output matching circuit (MC)
16 level detector (COM)
17 Gate bias setting circuit (BC)

Claims (6)

In the envelope tracking power amplifier in which the voltage of the power source supplied to the power amplifier by the power supply means is controlled according to the signal level obtained by demultiplexing and detecting the envelope of the high frequency input signal amplified by the power amplifier,
First and second high-frequency power amplifiers that amplify and output high-frequency signals;
Distribution means for branching and outputting the input signal to the first and second high-frequency power amplifiers;
Output means for combining and outputting the outputs of the first and second high-frequency power amplifiers;
First and second power supply means for supplying power to the first and second high-frequency power amplifiers;
If the signal level is monitored and compared with a predetermined level, and lower than the predetermined level,
While supplying a preset power supply voltage corresponding to the signal level from the first power supply means to the first high-frequency power amplifier and amplifying and outputting the branched input signal,
The input signal to the second high-frequency power amplifier is cut off, and the drain-source capacitance of the second high-frequency power amplifier corresponding to the signal level corresponds to the impedance formed by the output means. And performing control to output a preset voltage to the second power supply means,
If it is higher than a given level,
Each of the input signals is input to both the high frequency power amplifiers, and the bias voltage of the gate voltage of the second high frequency power amplifier is set so that the operation of the second high frequency power amplifier is aligned with the first high frequency power amplifier. And a control means for controlling the supply by outputting a constant voltage to the first and second power supply means.
An envelope tracking power amplifier comprising:   2. The envelope tracking power amplifier according to claim 1, wherein the predetermined level corresponds to an average value of the input signals with reference to a saturation level of the combined output.   2. The envelope tracking power amplifier according to claim 1, wherein the predetermined level corresponds to a level in which an average value of the input signals is 3 dB lower than a saturation level of the combined output. A high-frequency input that includes a distribution unit, an output unit, first and second high-frequency power amplifiers, first and second power supply units, and a control unit, and that is input and amplified by both the high-frequency power amplifiers. In an envelope tracking amplification method of an envelope tracking power amplifier, wherein a voltage of a power source supplied to the high frequency power amplifier by a power supply means is controlled according to a signal level obtained by demultiplexing a signal and detecting an envelope,
First and second high-frequency power amplifiers that amplify and output high-frequency signals;
The distribution means branches and outputs the input signal to the first and second high-frequency power amplifiers,
The control means monitors the signal level obtained by extracting the demultiplexed wave and detecting the envelope, compares it with a predetermined level, and if lower than the predetermined level,
Supplying a first power supply voltage corresponding to the signal level from the first power supply means to the first high-frequency power amplifier, amplifying the branched input signal, and outputting the amplified signal;
The input signal to the second high-frequency power amplifier is cut off, and the drain-source capacitance of the second high-frequency power amplifier corresponding to the signal level corresponds to the impedance formed by the output means. In the same manner, the second power supply means outputs a preset voltage,
If it is higher than a given level,
Each of the input signals is input to both the high frequency power amplifiers, and the bias voltage of the gate voltage of the second high frequency power amplifier is set so that the operation of the second high frequency power amplifier is aligned with the first high frequency power amplifier. And outputting a constant voltage to the first and second power supply means,
The envelope tracking amplification method for an envelope tracking power amplifier, wherein the output means combines and outputs the outputs from the first and second high frequency power amplifiers.   5. The envelope tracking amplification method according to claim 4, wherein the predetermined level corresponds to an average value of the input signals based on a saturation level of the combined output.   5. The envelope of an envelope tracking power amplifier according to claim 4, wherein the predetermined level corresponds to a level in which an average value of the input signals is 3 dB lower than a saturation level of the combined output. Tracking amplification method.

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