JP2010278992A - Rf amplification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an RF amplification apparatus which avoids over input and output level reduction in an envelope tracking system. <P>SOLUTION: A power amplifier 111 uses an envelope signal, that is a scalar quantity, of baseband signals generated by a baseband signal generating section 101, as a power supply voltage to perform power amplification on an RF signal that is similarly a vector quantity among the baseband signals. An over input detecting section 200 uses a capture signal of the baseband signals and a capture signal of digital signals fed back from the power amplifier 111 to calculate AM-PM characteristics of the power amplifier 111 and detects an over input state from the calculated AM-PM characteristics. If the over input state is detected, a shift correcting section 120 shifts a power supply voltage to be applied to the power amplifier 111 to a high voltage side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an RF amplifying apparatus using an envelope tracking (ET) system.

  In recent years, in order to improve data transmission speed and increase subscriber capacity, not only multi-valued data but also spreading methods such as CDMA (Code Division Multiple Access) and multi-level such as OFDM The adoption of carrier schemes or modulation schemes combining them is increasing. In these methods, the peak factor, which is the ratio between the average power and the peak power of the modulation signal, tends to increase. In order to transmit these signals without distortion, it is necessary to lower the operating point of the power amplifier and use it in the linear region. For this reason, as the peak factor of the signal increases, the operating point level of the power amplifier decreases, and the power amplifier must be operated in a low efficiency region. Against this background, power amplifiers are highly required to have high linearity and highly efficient characteristics.

  In order to ensure linearity, distortion compensation technology using an analog method or a digital method has been developed. From the viewpoint of improving efficiency, the bias application method has been improved, such as class D, class E, and class F. Developments such as a method, a Doherty method, an envelope tracking method, and an EER method have been made. In these systems, development of an envelope tracking system has been actively carried out in recent years because of the possibility of high efficiency.

  The envelope tracking method is a method in which an envelope signal of an RF signal input to the power amplifier is applied to the power amplifier as a power supply voltage. This envelope signal (power supply voltage of the power amplifier) also changes the average output voltage value according to the average output power value of the power amplifier.

  By the way, in a general power amplifier, the power supply voltage is always a fixed voltage. When the power supply voltage is fixed, all of the power between the power supply voltage and the envelope of the RF signal input to the power amplifier is converted into useless energy such as heat. For this reason, in the area | region where output electric power is small, efficiency falls especially and is disadvantageous.

  On the other hand, since the envelope tracking method always operates in a region close to saturation with respect to the input power, the above-mentioned useless power is eliminated and high efficiency can be achieved.

  As described above, high efficiency is strongly demanded for power amplifiers, and heterojunction devices that are said to be easy to achieve high efficiency are being used. Here, FIG. 1 shows input / output characteristics of the heterojunction device. In the heterojunction device, as the input level increases, the output level also increases at a one-to-one ratio. However, after a certain saturation output level is exceeded, the output level turns down. Hereinafter, an input area in which the output level is lowered in this way is referred to as an over-input area.

  Such a characteristic variation of the power amplifier is considered to occur due to, for example, secular change or an ambient temperature, and can be an excessive input to any power amplifier. When the saturation power value is lowered with respect to a certain power supply voltage value of the power amplifier, the gain is lowered, so that desired characteristics and operation cannot be obtained.

  A general wireless communication apparatus is equipped with a power control function, and operates to increase the gain of the gain control circuit according to a decrease in the output level and to output a constant desired power. For this reason, since the output power level is reduced in the wireless communication device that has become excessively input, the gain of the gain control circuit is increased to correct the reduction amount. As a result, the amount of power input to the power amplifier is increased, leading to further excessive input, which is not preferable. Also, under such circumstances, device breakdown may occur due to a rapid increase in device gate current.

  Such an operation is always performed in a region close to saturation in envelope tracking, so that the influence is larger than that in the fixed voltage method. That is, in the fixed voltage method, an excessive input occurs in a certain output power range, whereas in the envelope tracking method in which the drain voltage changes, the range in which an excessive input occurs may be wide.

  As a technique against the secular change of the power amplifier, for example, techniques disclosed in Patent Document 1 and Patent Document 2 are known. The configuration of the power amplifier disclosed in Patent Document 1 is shown in FIG.

  The power amplifier shown in FIG. 2 includes a power amplifier 11 that performs power amplification, a power amplifier 12 that serves as a comparison reference for controlling the gate voltage of the power amplifier 11, and a monitor control circuit 13. The monitoring control circuit 13 includes a constant current circuit (not shown), a voltage detection circuit, and a voltage control circuit. It is assumed that the power amplifier 11 and the power amplifier 12 hold gate voltage characteristics for obtaining a certain constant current value with respect to aging, and that the gate voltage characteristics are each linear.

  According to this, the power amplifier 12 monitors the gate voltage with respect to the current value determined by the constant current circuit and sets the gate voltage of the power amplifier 11, thereby suppressing fluctuations in the characteristics of the power amplifier due to secular change. Can do.

  FIG. 3 shows the configuration of the power amplifier disclosed in Patent Document 2. The power amplifier shown in FIG. 3 is generated in the resistor by controlling the gate voltage, the dual gate FET 21 capable of controlling the gain, the FET 22 as the power amplifier, the resistor 23 for converting the gate current of the FET 22 into a voltage, and the resistor. And a conversion circuit 24 that converts the voltage change into the gate voltage of the dual gate FET 21.

  According to this, using the fact that the gate current of the power amplifier 22 increases in the vicinity of the over-input power operation, when the terminal voltage of the resistor 23 inserted in the gate terminal increases, it is determined that an increase in current is detected, and the power The gate voltage of the amplifier 21 can be set to a voltage value that lowers the gain by the conversion circuit 24, and the output level can be lowered.

JP 2001-068948 A Japanese Utility Model Publication No. 5-36923

  However, the method disclosed in Patent Document 1 cannot detect an excessive input and can only deal with a certain current value, and the drain current constantly changes like the envelope tracking method. There is a problem that it is not suitable for such a system.

  Moreover, although the method disclosed in Patent Document 2 can avoid excessive input, there is a problem in that a decrease in output level cannot be avoided.

  The present invention has been made in view of this point, and an object of the present invention is to provide an RF amplification device that avoids excessive input and a decrease in output level in an envelope tracking system.

  The RF amplifying apparatus of the present invention includes a power amplifying unit that amplifies power of an RF signal that is a vector amount of the baseband signal, using an envelope signal that is a scalar amount of the baseband signal as a power supply voltage, and an AM of the power amplifying unit. An over-input detecting means for detecting an over-input state from the PM characteristics, and a shift correcting means for shifting the power supply voltage applied to the power amplifying means to the high voltage side when the over-input state is detected in the over-input detecting means The structure which comprises these is taken.

  According to the present invention, it is possible to avoid excessive input and a decrease in output level in the envelope tracking method.

Diagram showing input / output characteristics of heterojunction devices The figure which shows the structure of the power amplifier disclosed by patent document 1 The figure which shows the structure of the power amplifier disclosed by patent document 2 The figure which shows the structure of RF amplification apparatus which concerns on one embodiment of this invention The figure which shows the internal structure of the excessive input detection part shown in FIG. The figure which shows the internal structure of the overinput determination part shown in FIG. The figure which shows the AM-PM characteristic of the power amplifier used as over input A graph in which the drain voltage against the output power of the power amplifier is defined, and the efficiency characteristics of the power amplifier are superimposed. A graph in which the drain voltage against the output power of the power amplifier is specified, and the gain of the power amplifier is superimposed Diagram showing power supply voltage characteristics with respect to output power before and after correction

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(One embodiment)
FIG. 4 is a diagram showing a configuration of the RF amplifying apparatus 100 according to the embodiment of the present invention. In FIG. 4, a baseband signal generation unit 101 generates a baseband signal in a vector format having an in-phase component and a quadrature component, and among the baseband signals, an envelope signal system that is a scalar quantity is converted into a delay circuit 102 and a capture unit. The RF signal system, which is a vector quantity, is output to the delay circuit 106.

  The envelope signal system output from the baseband signal generation unit 101 is delayed by a predetermined time in the delay circuit 102, and the absolute value calculation unit 103 calculates the absolute value of the delayed envelope signal system and outputs it to the multiplication unit 104. .

  The multiplier 104 multiplies the absolute value of the envelope signal system output from the absolute value calculator 103 by a value set by the shift corrector 120 described later to form an envelope signal, and outputs the envelope signal to the modulation power supply unit 105. . As will be described later, the shift correction unit 120 shifts the voltage of the modulation power supply unit 105 to the high voltage side when it is determined that the operation state of the power amplifier 111 is an excessive input.

  The modulation power supply unit 105 converts the envelope signal output from the multiplication unit 104 into a predetermined voltage amplitude and current value, and applies them to the power amplifier 111 as a power supply. Further, the modulation power supply unit 105 includes a table for outputting a drain voltage corresponding to the output power of the power amplifier 111. Note that, instead of this table, an approximate expression coefficient using a polynomial may be used.

  On the other hand, the RF signal system output from the baseband signal generation unit 101 is delayed by a predetermined time in the delay circuit 106, and the distortion compensation output from the adaptive control unit 119 described later is changed to the delayed RF signal system in the multiplication unit 107. A baseband signal that multiplies the coefficient and cancels the distortion characteristic generated in the power amplifier 111 is generated and output to the DAC 108.

  The DAC 108 converts the baseband signal output from the multiplication unit 107 into an analog signal and outputs the analog signal to the modulation unit 109. The modulation unit 109 converts the analog signal output from the DAC 108 into an IF signal and supplies the IF signal to the upmixer 110. Output.

  The upmixer 110 converts the IF signal output from the modulation unit 109 into an RF signal and outputs the RF signal to the power amplifier 111. The power amplifier 111 is applied by the modulation power supply unit 105 and output from the upmixer 110. Is amplified and output to the coupler 112.

  The coupler 112 outputs a part of the RF signal output from the power amplifier 111 to the outside of the RF amplifying apparatus 100 and outputs it to the downmixer 113 while monitoring a part of the RF signal.

  The downmixer 113 converts the RF signal output from the coupler 112 into an IF signal and outputs the IF signal to the demodulator 114. The demodulator 114 converts the IF signal output from the downmixer 113 into a baseband signal, and generates an alias. The data is output to the ADC 116 through the filter 115.

  The ADC 116 converts the baseband signal output via the alias filter 115 into a digital signal and outputs the digital signal to the capture unit 117, and the capture unit 117 captures the digital signal output from the ADC 116 and sends it to the adaptive control unit 119. Output.

  The capture unit 118 captures the envelope signal system output from the baseband signal generation unit 101 and outputs the captured envelope signal system to the adaptive control unit 119.

  The adaptive control unit 119 performs three types of control: distortion compensation (hereinafter referred to as “DPD”) control, delay control, and over-input control. In the DPD control, the amount of error between the baseband signal and the feedback signal from the power amplifier is detected, and the output distortion is suppressed by operating so that the difference becomes zero. In the delay control, the delay characteristic between the envelope signal and the feedback signal is calculated, and the delay amount is controlled to be zero. These operations are indispensable processes in the ET method, but are not related to avoiding excessive input and a decrease in output level. Hereinafter, DPD control, delay control, and over-input control will be briefly described.

  In the DPD control, the adaptive control unit 119 determines an error in the signal amplitude of the data between captures based on the capture signal of the baseband signal output from the capture unit 118 and the capture signal of the digital signal output from the capture unit 117. Is calculated. The signal to the power amplifier 111 is multiplied by the distortion compensation data using the multiplication unit 107 so that the calculated error becomes zero. As a result, the output data of the power amplifier 111 has the same signal characteristics as the baseband signal, and the distortion characteristics are improved.

  In the delay control, the adaptive control unit 119 performs a correlation operation between the baseband signal output from the capture unit 118 and the digital signal output from the capture unit 117, and calculates a delay difference between the envelope signal and the RF signal. The calculated delay difference is converted into a set value of the delay circuits 102 and 106, and control is performed so that the delay difference between the envelope signal in the power amplifier 111 and the RF signal becomes zero.

  For overinput control, the adaptive control unit 119 includes an overinput detection unit 200 that detects an overinput state from the baseband signal output from the capture unit 118 and the baseband signal output from the capture unit 118. The overinput detection unit 200 determines whether or not the power amplifier 112 is overinput, and controls the shift correction unit 120 and the modulation power supply unit 105 according to the determination result. With respect to signal capture, it is possible to use capture data used in DPD control, which is essential in the ET method, and an increase in circuit scale can be avoided. The over-input operation is a state in which the allowable power is exceeded with respect to the power supply voltage of the power amplifier, and the gain of the power amplifier is lowered and the phase characteristic is rapidly changed. For this reason, in order to avoid an excessive input state, it is necessary to raise the power supply voltage of the power amplifier 111. When the excessive input detection result indicates an excessive input state of the power amplifier, the shift correction unit 120 shifts the power supply voltage of the power amplifier 111 (that is, the voltage of the modulation power supply unit 105) to the high voltage side. The over-input judgment method is shown below.

  FIG. 5 is a diagram showing an internal configuration of the overinput detection unit 200 shown in FIG. In FIG. 5, an AM-PM calculation unit 201 calculates an AM-PM characteristic based on the capture signal of the envelope signal output from the capture unit 118 and the capture signal of the digital signal output from the capture unit 117. The calculated AM-PM characteristic is output to the over-input determination unit 202. Note that the AM-PM characteristic due to the drain voltage being applied to the power amplifier 111 is obtained by dividing the output signal of the power amplifier 111 by the input signal.

  The overinput determination unit 202 determines whether or not there is an excessive input by determining whether the AM-PM characteristic output from the AM-PM calculation unit 201 has a steep fluctuation (distortion), and determines the determination result. The data is output to the shift correction unit 120.

  FIG. 6 is a diagram illustrating an internal configuration of the over-input determination unit 202 illustrated in FIG. In FIG. 6, the weighting unit 301 performs a weighting process on the AM-PM characteristic output from the AM-PM calculating unit 201, and outputs the weighted AM-PM characteristic to the first threshold value determining unit 303.

  The first threshold setting unit 302 sets a predetermined first threshold, and outputs the set first threshold to the first threshold determination unit 303.

  The first threshold determination unit 303 performs threshold determination between the AM-PM characteristic output from the weighting unit 301 and the first threshold output from the first threshold setting unit 302, and uses the threshold determination result as a flag as the second threshold The data is output to the determination unit 305. For example, if it is determined that the AM-PM characteristic exceeds the first threshold, flag = 1 is set as over-input, and if it is determined that the AM-PM characteristic is less than the first threshold, flag = 0 is set as not over-input. .

  The second threshold setting unit 304 sets a predetermined threshold and outputs the set threshold to the second threshold determination unit 305.

  The second threshold determination unit 305 performs threshold determination between the amount of the flag (flag = 1) indicating the excessive input output from the first threshold determination unit 303 and the second threshold output from the second threshold setting unit 304. If it is determined that the flag amount exceeds the second threshold value, it is assumed that the frequency of excessive input is high, and the shift correction unit 120 outputs that shift correction is to be performed. If it is determined that the flag amount is less than the second threshold, it is assumed that the frequency of overinput is low, and shift correction is not performed.

  Here, the reason why the weighting unit 301 of the overinput determination unit 202 performs the weighting process will be described. The AM-PM characteristic often includes a large error when the amplitude of a signal input to and output from the power amplifier 111 is small. For this reason, in order to accurately calculate the AM-PM characteristic in the power amplifier 111, the time-series timing of the absolute value or power value of the baseband signal input to the power amplifier 111 is matched with the output signal of the power amplifier 111. It is desirable to perform the weighting process by multiplying. Thereby, even when the amplitude of the signal input / output to / from the power amplifier 111 is small, errors included in the AM-PM characteristics can be reduced.

  By the way, the reason why the AM-PM characteristic is used as the characteristic of the power amplifier is that the characteristic of the power amplifier that has become excessively input particularly has a steep fluctuation in the AM-PM characteristic. FIG. 7 shows the AM-PM characteristics of the power amplifier that is over-input. As disclosed in Patent Document 2, a method of monitoring the gate current value is known as the over-input detection. However, since the output characteristics of the power amplifier are not directly monitored, the presence / absence of occurrence of over-input is detected. In addition, it is impossible to accurately grasp the output deterioration of the power amplifier. On the other hand, the AM-PM characteristic of the power amplifier is the input / output characteristic itself of the power amplifier and can be easily grasped.

  Next, the operation principle of the RF amplification device 100 described above will be described. FIG. 8 is a graph in which efficiency characteristics of the power amplifier are superimposed on a graph defining the drain voltage with respect to the output power of the power amplifier. The thin solid line shown in FIG. 8 shows the efficiency characteristics of the power amplifier to be operated in contour lines. In the envelope tracking method, in order to achieve high efficiency, the voltage of the power amplifier is applied so that the efficiency is the best with respect to the output power. For this reason, it is desirable to operate the voltage applied to the power amplifier so as to coincide with the ridge (best value) of the contour line of the efficiency characteristic as shown by the thick solid line in FIG.

  Next, consider a case where the saturation output level of the power amplifier is lowered. As shown by the broken line in FIG. 8, the power supply voltage characteristic with respect to the output power when the saturated output level is lowered cannot match the ridge (best value) of the contour line of the efficiency characteristic when the saturated output level is lowered.

  FIG. 9 is a graph in which the gain of the power amplifier is superimposed on a graph defining the drain voltage with respect to the output power of the power amplifier. The thin solid line shown in FIG. 9 shows the efficiency characteristics of the power amplifier to be operated in contour lines. As can be seen from FIG. 9, in the region where the voltage is lower than the thick solid line that achieves the desired operation, the gain reduction proceeds abruptly (region surrounded by the dotted frame in FIG. 9).

  Here, as in the above case, consider a case where the saturation output level of the power amplifier is lowered. The power supply voltage characteristic with respect to the output power when the saturation output level is reduced is a characteristic indicated by a broken line in FIG. As can be seen from the thin solid line indicating the gain characteristic, the gain characteristic is drastically lowered when the saturation output level is lowered. This is because, as shown in FIG. 8, in the over-input region, the output power decreases even if the input power increases.

  FIG. 10 shows power supply voltage characteristics with respect to output power of the power amplifier before and after correction. The thick solid line in FIG. 10 indicates the power supply voltage characteristic with respect to the output power at which both efficiency and gain are optimized at the time of factory shipment. Further, the broken line in FIG. 10 indicates the power supply voltage characteristic with respect to the output power when the saturated output power is decreased due to aging or the like. In order to achieve optimum efficiency and gain when the saturation output level is lowered, the operating point may be shifted and reset so as to have the characteristics of the black solid line. That is, the shift correction unit 120 corrects the set value of the power supply voltage, corrects the drain voltage for the same output power from the broken line to the thick solid line as shown in FIG. 10, and increases the power supply voltage. Thereby, the saturation output level, gain, and efficiency can be improved. The correction amount is determined by continuing the correction up to an area where the AM-PM characteristic does not change. Thereby, even if there is individual variation, it can be appropriately corrected.

  However, since the region where the AM-PM characteristic does not change is not excessive input, the output power monotonously increases with respect to the input power. For this reason, even when transmission power control and distortion compensation are performed, the operation does not become unstable. In addition, since over-input can be avoided, device destruction does not occur.

  As described above, according to the present embodiment, the AM-PM characteristic of the power amplifier is directly monitored, and when an excessive input is detected, the set value of the power supply voltage is increased and corrected until no excessive input is detected. Even if the current value is changed, an excessive input can be avoided and a decrease in the output level can be avoided.

  The present invention is applicable to adjustment at the time of factory shipment and adjustment at the time of actual operation after shipment.

  The RF amplification device according to the present invention can be applied to, for example, a radio communication base station device, a digital television transmitter, and the like.

101 baseband signal generation unit 102, 106 delay circuit 103 absolute value calculation unit 104, 107 multiplication unit 105 modulation power supply unit 108 DAC
109 Modulator 110 Upmixer 111 Power Amplifier 112 Coupler 113 Downmixer 114 Demodulator 115 Alias Filter 116 ADC
117, 118 Capture unit 119 Adaptive control unit 120 Shift correction unit 200 Over input detection unit 201 AM-PM calculation unit 202 Over input determination unit 301 Weighting unit 302 First threshold setting unit 303 First threshold determination unit 304 Second threshold setting unit 305 Second threshold value determination unit

Claims (3)

Power amplifying means for amplifying the power of the RF signal, which is the vector amount of the baseband signal, using the envelope signal, which is the scalar amount of the baseband signal, as a power supply voltage;
An overinput detection means for detecting an overinput state from the AM-PM characteristic of the power amplification means;
A shift correction unit that shifts a power supply voltage applied to the power amplification unit to a high voltage side when an overinput state is detected in the overinput detection unit;
An RF amplifying apparatus comprising: The over-input detection means includes
AM-PM calculating means for calculating an AM-PM characteristic of the power amplifying means using a capture signal of the envelope signal and a capture signal of a digital signal fed back from the power amplifying means;
An over-input determination unit that weights the calculated AM-PM characteristic and determines whether or not there is an over-input based on the weighted AM-PM characteristic;
The RF amplification device according to claim 1, comprising:   2. The RF amplifying apparatus according to claim 1, wherein the shift correction unit shifts the power supply voltage so that a power supply voltage characteristic with respect to output power of the power amplifying unit coincides with a contour ridge of the efficiency characteristic of the power amplifying unit.

Images