JP2006148781A - High frequency power amplifying device and its distortion compensation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency power amplifying device having a simpler configuration, excellent in lower power consumption, and capable of compensating nonlinear distortion satisfactorily. <P>SOLUTION: In a high frequency power amplifying device of an EER (Envelope Elimination and Restoration) system, gain adjustment for distortion compensation is not performed, but only phase adjustment is performed. To perform phase adjustment, an analog phase shifter 17 is provided at the prestage of a power amplifier 18. A phase control signal (Vcont) is generated for adjusting the phase-shift amount of the phase shifter, based on a voltage level of a magnitude signal acquired from an audio band amplifier 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high frequency power amplifier and a distortion compensation method thereof.

  In recent years, power amplifiers, particularly high frequency amplifiers, have been used in various portable devices. Among these devices, the power consumption is highest in the power amplifier, and the efficiency of the power amplifier greatly affects the battery life of the portable device. Therefore, it is desired to achieve both high efficiency and low distortion of the power amplifier.

  As power amplifiers with high efficiency, there are power amplifiers of class C, class D, class E, class F, etc., but these are non-linear amplifiers, and can only amplify signals with a constant amplitude.

  In the field of mobile phones and the like, a multi-level modulation method is adopted to improve the data transmission speed. For example, in a modulation method such as 16QAM, phase modulation and amplitude modulation are used in combination.

  In a phase modulation only method such as PSK, it is sufficient that even phase information can be transmitted, and amplitude information is unnecessary. Therefore, a saturation type non-linear power amplifier can also be used. However, with respect to the amplitude-modulated signal, signal loss occurs when the characteristics of the amplifier are nonlinear. Therefore, when the envelope of the signal waveform changes with amplitude modulation, it is necessary to use a linear power amplifier.

  In addition, the baseband signal band tends to be widened not with the improvement in data transmission speed.

  It is known that, for example, a GaAsFET (gallium arsenide field effect transistor) can be used as an amplifier having a wide band and linearity. However, a class A amplifier is inefficient and consumes a large amount of power. In a linear power amplifier, efficiency and linearity are in a trade-off relationship.

  As an improvement measure, there is a polar modulation method (polarity modulation method). With this method, it is said that it is possible to achieve both efficiency and linearity at the same time. The polar modulation method is generally known as EER (Envelope Elimination and Restoration) (for example, see Non-Patent Document 1).

  This method separates the modulation signal (modulation signal based on a modulation method in which amplitude modulation and phase modulation are combined) into a phase signal and an amplitude signal, which are polar components, and has a constant envelope (that is, amplitude is limited by limiting the amplitude). The phase signal from which the information has been removed is used as the input signal of the power amplifier, while the amplitude signal is separately amplified by the amplitude component amplifier, and the power supply voltage of the power amplifier is modulated based on the amplitude signal. The output waveform envelope is changed to restore the same amplitude component as the input signal, thereby recombining the phase component and the amplitude component to obtain an amplified linear signal.

  In the EER system as described above, a general bipolar transistor or FET (field effect transistor) is used as the power amplifier. These general amplifying elements are known to exhibit nonlinear characteristics in a high-level signal region in a high frequency region, and therefore, a sufficient linear property cannot be obtained simply by applying the EER method.

  That is, when the power supply voltage of the power amplifier is modulated by the amplitude signal of the polar component, there is a problem that the output waveform becomes dull in a high-level signal region and sufficient linearity cannot be obtained. This is because, as described above, the gain characteristic and / or phase characteristic of the amplifying element constituting the power amplifier has a characteristic that it is not sufficiently linear with respect to the power supply voltage (collector voltage, drain voltage, etc.). .

  One of the typical techniques for reducing distortion of an output signal caused by nonlinearity of an amplification element constituting a power amplifier is a so-called predistortion type distortion compensation technique. In this method, in order to correct distortion generated in the power amplifier, a distortion having a characteristic opposite to that of the distortion is given in advance to the input signal of the power amplifier.

  There are two types of predistortion methods, a feedback type and a feedforward type. Here, the configuration when the latter method is applied to an EER type power amplifying apparatus will be considered with reference to the drawings.

  FIG. 14 is a block diagram showing an example of a configuration of a power amplifying apparatus having a distortion compensation function (an example studied by the inventor of the present invention before the present invention for consideration of the prior art).

  As shown in the figure, the RF (high frequency signal) input is bisected by the coupler 15, and one signal is guided to the envelope detection circuit 110 to obtain envelope information (amplitude signal), and the envelope information (amplitude) Signal) is applied to the power amplifier 180 via the delay circuit 260, and the power supply voltage is modulated based on the envelope information (amplitude signal), thereby restoring the envelope information (amplitude signal).

  On the other hand, the other half signal is input to the power amplifier 180 in the output stage via the delay circuit 210, the phase adjustment circuit 240, and the gain adjuster 250, and is amplified.

  The phase rotation amount of the phase adjustment circuit 240 and the gain adjustment amount of the gain adjustment circuit 250 are determined by control signals output from the nonlinear phase mapper 220 and the nonlinear gain mapper 230, respectively. The level of this control signal changes appropriately according to the voltage level of the envelope information (amplitude signal) output from the envelope detection circuit 110.

  As a result, the input signal of the power amplifier 180 is preliminarily imparted with distortion that cancels out the nonlinearity of the output signal caused by the modulation of the power supply voltage. An output signal with high linearity can be obtained.

  As in this example, the conventional distortion compensation circuit corrects not only the phase characteristic but also the gain characteristic, and digital signal processing is used to perform more accurate compensation. It has become mainstream.

  For example, in Patent Document 1 (distortion compensation apparatus and distortion compensation method), both the amplitude and the phase are compensated using a lookup table.

  Patent Document 2 (amplitude phase change device) also controls both phase and amplitude under digital control.

  Therefore, in consideration of the tendency of this prior art, it is desirable to correct both the phase and the gain characteristic with respect to the power supply voltage (amplitude signal) of the power amplifier in the high frequency power amplifying apparatus such as the EER system as well. The conclusion is that the control accuracy can be improved by performing digital control.

  However, as a result of further investigation by the inventor of the present invention, the linearity of the gain characteristic with respect to the power supply voltage (amplitude signal) of the power amplifier may be very high depending on the power amplifier device, and correction may not be necessary. I understood it.

  That is, the phase and gain characteristics of various power amplifiers such as GaAsFET, HBT (heterobipolar transistor), and MOSFET with respect to the power supply voltage were measured, and the EER type high frequency power amplifier was evaluated.

  In other words, when considering the gain and phase characteristics with respect to the power supply voltage of the power amplifier, the gain with respect to the power supply voltage has a substantially linear characteristic, but on the other hand, the phase characteristics are not constant and rotate. It was found that the amount of rotation varies greatly depending on each device, and the amount of phase rotation may be 40 degrees or more.

  It was confirmed that the distortion characteristics of the element having a large amount of phase rotation with respect to the power supply voltage of the power amplifier are greatly deteriorated. 15A and 15B are diagrams illustrating specific examples of gain characteristics and phase characteristics with respect to the power supply voltage of the power amplifier. FIG. 15A is a diagram illustrating gain characteristics, and FIG. 15B is a diagram illustrating phase characteristics. .

  As is clear from FIG. 15A, the gain has a substantially linear characteristic with respect to the power supply voltage. On the other hand, as is clear from FIG. 15B, it can be seen that the phase characteristic does not become constant and rotates, and the rotation amount is 40 degrees or more. In such an element, gain correction is not particularly required, and it has been confirmed that a large correction effect can be obtained by controlling only the phase characteristics.

  Further, when both the phase and amplitude are corrected as in the prior art, there is a reality that the required correction accuracy is very high, and that the control is actually very difficult. For example, in the case of the EER method, an amplitude signal is made to correspond to a power supply voltage, but distortion deterioration of about 5 dB occurs even if the linearity deviation with respect to the power supply voltage (amplitude) is about 1%. In addition, a delay shift between the phase signal and the amplitude signal greatly affects the wireless characteristics such as the distortion characteristics.

  For this reason, sufficient distortion cannot be improved if correction is not performed with sufficient accuracy secured, and in some cases, power consumption increases due to deterioration of characteristics and increase in circuit scale and digital operation amount due to correction. However, even if the efficiency of the power amplifier alone is improved, it may not be possible to achieve high efficiency as the entire apparatus.

  For example, Patent Document 3 (a frequency converter and a wireless communication apparatus using the frequency converter) introduces a specific example of a mixer circuit that reduces distortion without greatly increasing the operating current. Even if it sees, it turns out that the concrete circuit for reducing distortion must be a quite complicated structure.

JP 2002-26665 A JP 2001-326541 A JP 2003-17944 A L. R. Kahn, “Single sideband transmission by envelope elimination and restoration”, Proc. IRE, VOL40, No. 7, p803-806, July 1952

  From the above consideration made by the inventors of the present invention, the following matters have been clarified in the correction of nonlinear distortion depending on the power supply voltage (amplitude signal) in the power amplifier of the EER type power amplifier.

  That is, it is not always necessary to control both gain and phase using digital technology. Also, if both gain and phase control using digital technology is performed, a sufficient distortion compensation effect cannot be easily obtained. In reality, there are problems such as circuit complexity and increased power consumption. It may occur, and power consumption may be consumed unnecessarily. In addition, performing useless control may increase the risk of distortion being expanded.

  The present invention has been made based on such considerations, and an object thereof is to provide a high-frequency power amplifying apparatus that has a simple configuration, is excellent in low power consumption, and can sufficiently compensate for nonlinear distortion. To do.

  The high-frequency power amplifying device of the present invention includes a coupler that branches an input signal into a phase signal and an amplitude signal, which are polar components, a limiter that limits the amplitude of one of the branched signals and outputs a phase signal; A detector that detects an amplitude of the other branched signal and outputs an amplitude signal; a power amplifier that amplifies the phase-shifted signal using the amplitude signal as a power supply voltage; and a front stage of the power amplifier; A phase shifter that compensates for phase characteristics of the power amplifier with respect to a power supply voltage, and a phase control signal generator that generates a phase control signal for adjusting the amount of phase shift of the phase shifter according to the voltage level of the amplitude signal The phase signal is input to the power amplifier without gain adjustment.

  With this configuration, paying attention only to the phase characteristics that vary depending on the power supply voltage of the power amplifier, the configuration is simplified because unnecessary gain control is not performed, and power consumption can also be reduced. Further, the configuration of the control system is simple and easy to implement, and in this respect also, the effect of preventing the circuit from becoming complicated and reducing the power consumption can be obtained. Also, by not performing extra control, the risk of distortion expansion due to erroneous correction is also reduced.

  In the high frequency power amplifier according to the present invention, the phase control signal generator outputs a quadrature signal and an in-phase signal as the phase control signal, and the phase shifter is a quadrature modulator that quadrature modulates the phase signal. The phase rotation amount of the quadrature modulator is determined by the quadrature signal and the in-phase signal.

  If an analog type is used for the quadrature modulator, the configuration is simple, and it is a circuit with a proven track record that has been used in the field of communication equipment, etc., and sufficiently follows a wideband modulated wave. Is possible. Then, by changing the value of the I / Q signal, the phase of the input signal can be rotated in the entire phase range. Therefore, a high-speed phase shifter can be realized at low cost, and by using this phase shifter, a high-frequency power amplifying apparatus capable of linear compensation for a high-speed modulation signal can be easily realized.

  The high frequency power amplifying apparatus of the present invention performs at least one of gain adjustment and DC offset adjustment on the quadrature signal and the in-phase signal output from the phase control signal generation unit, and outputs to the quadrature modulator. And a phase control signal adjusting unit.

  In order to perform accurate phase rotation correction, an I / Q signal needs to be ideally input to the phase shifter. However, there may be a deviation in the value of the I / Q signal for some reason. Therefore, in order to correct the deviation, at least one of gain adjustment and DC offset adjustment is performed on the I / Q signal. It ’s what you get. Thereby, highly accurate distortion compensation is always ensured.

  In addition, the high frequency power amplifying apparatus of the present invention uses a modulated signal modulated by an OFDM (Orthogonal Frequency Division Multiplex) modulator as the input signal.

  In OFDM, superposition of subcarriers generates a large amount of power instantaneously at random, and it is necessary to always maintain a large DC power so that a high-frequency signal having such a large power can be linearly amplified. is there. By implementing power amplification by the high-frequency power amplifier of the present invention using the modulation signal from the OFDM modulator (inverse fast Fourier transformer) as an input signal, high-efficiency linear amplification is realized, and there is no wasteful power consumption. Longer battery life in mobile phones and the like can also be achieved.

  The present invention also provides a transmitter equipped with the above high-frequency power amplifier.

  With this configuration, a transmitter with low noise and a long battery life can be realized with a simple configuration.

  The distortion compensation method of the present invention is a distortion compensation method for a power amplifier in a high-frequency power amplifying device, the step of branching an input signal into a phase signal and an amplitude signal that are polar components thereof, Output the phase signal by limiting the amplitude of the signal, detecting the amplitude of the other branched signal and outputting the amplitude signal, and depending on the voltage level of the amplitude signal with respect to the phase signal Adjusting the phase shift amount and compensating the phase characteristic with respect to the power supply voltage of the power amplifier, and using the amplitude signal as the power supply voltage of the power amplifier, the phase characteristics are compensated without performing gain adjustment. Amplifying the signal.

  According to this method, the distortion compensation of the EER type high frequency power amplifying apparatus is performed only by analog phase control without performing gain control, so that highly efficient linear distortion compensation can be realized easily.

  According to the present invention, it is possible to provide a high-frequency power amplifying apparatus that has a simple configuration, is excellent in low power consumption, and can sufficiently compensate for nonlinear distortion.

  Next, embodiments of the present invention will be described with reference to the drawings. In the high frequency power amplifier according to the embodiment of the present invention, a phase shifter that compensates for the phase characteristic of the power amplifier with respect to the power supply voltage is inserted in the previous stage of the power amplifier, and the phase amount is analogized according to the amplitude signal level of the modulation signal. By changing to, the distortion characteristics are improved.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of a high-frequency power amplifying apparatus according to the first embodiment of the present invention. As shown in the figure, the high frequency power amplifier includes an envelope detection circuit 11, an audio band amplifier 12, a current amplifier 13, a phase control signal generator 14 such as a converter, a coupler 15, a limiter 16, an analog A phase shifter 17 and a power amplifier 18.

  An RF input (a signal modulated by a multi-level modulation method such as 16QAM) is input to the envelope detection circuit 11 and the limiter 16 via the coupler 15.

  The envelope detection circuit 11 detects envelope information (amplitude signal) of the input modulation signal. The limiter 16 limits the amplitude of the input modulation signal. As a result, the amplitude information is lost and a high-frequency signal having only phase information is obtained.

  The envelope information (amplitude signal) detected by the envelope detection circuit 11 is amplified to a desired amplitude by the audio band amplifier 12. The amplified amplitude signal is input to the current amplifier 13 and the phase control signal generator 14 that perform current amplification.

  The output of the current amplifier 13 becomes a modulation signal of the power supply voltage of the power amplifier 18. Further, the phase control signal generation unit 14 is configured to have, for example, a level converter (converter) that converts the voltage level of the input signal into a level suitable for the control signal of the phase shifter 17. The converter can be constituted by a linear amplifier such as an operational amplifier.

The phase shifter 17 is an analog phase adjuster used in a high-frequency circuit, and is configured using, for example, a coupler and a variable capacitance diode (specific configuration will be described later).
The phase shift amount (phase rotation amount) of the phase shifter 17 is controlled by a phase control signal (Vcont) output from the phase control signal generation unit 14. That is, the amount of phase rotation is controlled to be a phase rotation amount that cancels the phase rotation amount with respect to the power supply voltage in the power amplifier 18.

  The power amplifier 18 amplifies the phase modulation signal whose phase is controlled by the phase shifter 17. The power amplifier 18 includes a switching regulator that generates a power supply voltage, for example (the switching regulator is not shown).

  By switching and controlling the built-in switching regulator according to the output signal of the current amplifier 13, the power supply voltage of the power amplifier 18 can be modulated in accordance with the level of the envelope information (amplitude signal). Due to the modulation of the power supply voltage, the envelope of the output waveform of the power amplifier 18 changes and the amplitude information is restored. That is, the phase signal and the amplitude signal are combined to obtain an input modulated signal that has been linearly corrected.

  Next, a specific configuration of the phase shifter 17 will be described. FIG. 2 is a diagram illustrating an example of a specific configuration and characteristics of the phase shifter according to the first embodiment. FIG. 2A illustrates a circuit configuration, and FIG. 2B illustrates the characteristics. FIG.

  As shown in FIG. 2A, the phase shifter 17 includes a coupler 19 having a hybrid configuration, variable capacitance diodes D1 and D2, and input resistors R1 and R2. As shown in FIG. 2B, the phase rotation amount (Phase) of the phase shifter 17 changes substantially linearly by changing the level of the phase control signal (Vcont). On the other hand, the amount of gain variation (Gain ') is substantially the same.

  Strictly speaking, the phase characteristic of the phase shifter 17 is almost linear over a range of 80 degrees or more with respect to the phase control signal (Vcont). On the other hand, although the gain slightly fluctuates, It can be seen that the value is about 0.1 dB, which is almost negligible.

  Since the phase rotation characteristic of the power amplifier 18 in FIG. 1 and the phase rotation characteristic of the phase shifter 17 are known, the relational expression between the output signal level of the audio band amplifier 12 and the phase control signal (Vcont). Can be easily obtained. Since the rotation direction of the phase characteristic with respect to the power supply voltage of the phase shifter 17 and the power amplifier 18 is the same, if an inverting gain amplifier is used as the phase control signal generation unit 14, the phase rotation amount of the power amplifier 18 is corrected. Therefore, the phase control signal (Vcont) necessary for this can be easily obtained.

  In the above description, the amplitude signal is generated by the envelope detection circuit 11 and the phase signal is generated by the limiter 16. However, a signal separated in advance in the baseband unit is generated and input to the audio band amplifier 12 and the phase shifter 17. It is good also as a structure.

  As described above, linear compensation is possible with a simple configuration. The linearly compensated signal waveform has the same low distortion as that of the input RF signal, and unnecessary distortion components are not generated, so that high efficiency can be achieved.

  3A and 3B are diagrams showing distortion compensation effects in the high-frequency power amplification device according to the first embodiment. FIG. 3A is a diagram showing characteristics before performing distortion compensation, and FIG. 3B is a diagram after distortion compensation. It is a figure which shows the characteristic. In FIG. 3, the horizontal axis represents the frequency band, and the vertical axis represents the distortion level. As shown in FIG. 3, it can be seen that the characteristic shown in FIG. 3B is a low distortion characteristic as a whole over the entire frequency band as compared with FIG.

  According to the high frequency power amplifying apparatus of the first embodiment of the present invention as described above, linear compensation of the phase characteristic phase characteristic is performed without using table data or the like based on the power supply voltage (amplitude signal) in the power amplifier. By using only the circuit, an effect that the distortion characteristic can be greatly improved is obtained. Further, by not performing the gain control of the power amplifier with respect to the power supply voltage (amplitude signal), it is possible to reduce the circuit scale and power consumption and to reduce the possibility of a reduction in correction accuracy.

(Second Embodiment)
FIG. 4 is a block diagram showing a schematic configuration of the high-frequency power amplifying apparatus according to the second embodiment of the present invention. The basic configuration of the high frequency power amplifier of FIG. 4 is the same as that of the high frequency power amplifier of FIG. However, the configuration of the phase shifter 17 is different (and correspondingly, the phase control signal Vcont output from the phase control signal generation unit 14 becomes two systems of signals (I, Q)).

  FIG. 5 is a circuit diagram showing a specific configuration of the phase shifter 17 of the second embodiment. The phase shifter 17 shown in FIG. 5 includes a quadrature modulator. This quadrature modulator includes mixers (multipliers) 26 a and 26 b, a 90 ° phase shifter 27, and an adder 28.

  As described above, the phase control signal (Vcont) has two signals, an in-phase signal (I signal) and a quadrature signal (Q signal) orthogonal to the I signal, and these I / Q signals are cos θ and sin θ. By applying a voltage, the RF output signal becomes a signal whose phase is rotated by θ with respect to the RF input signal.

  FIG. 6 is a diagram illustrating an example of the characteristic of the phase output with respect to the control set value of the quadrature modulator. FIG. 7 is a diagram illustrating an example of frequency response characteristics of the quadrature modulator.

  From FIG. 6, it can be seen that the phase can be rotated in the entire phase range by the value of the set value I / Q to the phase shifter 17. An algorithm for linear compensation using the I / Q signal will be described later. In FIG. 7, the frequency characteristic for the I / Q signal is measured up to 20 MHz for the convenience of the measuring instrument. However, in actuality, it has a band of several hundreds of MHz or more, and the followability to a wideband modulated wave is sufficient. It can be confirmed that

  Through the operation as described above, the phase shifter 17 adjusts the phase of the phase modulation signal so as to cancel the phase rotation amount corresponding to the power supply voltage of the power amplifier 18. Thereby, the linearity of the output signal of a power amplifier can be improved.

  Thus, with a simple configuration, the high-frequency power amplifier according to the present invention can linearly compensate for a high-speed modulated signal. The corrected signal waveform has the same low distortion as that of the input RF signal, and an unnecessary distortion component is not generated, so that high efficiency can be achieved. Further, by using an I / Q quadrature modulator as a phase shifter, a high-speed phase shifter can be realized at a low cost.

  Next, the compensation algorithm of this embodiment will be described. The phase rotation amount θ output from the power amplifier 18 in the EER type high frequency power amplifier can be expressed as θ = f (amp), where f is the phase transfer function of the power amplifier 18. Here, “amp” is a power supply voltage applied to the power amplifier 18.

  The phase transfer function of the power amplifier 18 is obtained by actual measurement. Since amp is an input signal value, θ can be determined. The phase control signal generator 14 creates an I / Q signal (Vcont) so as to cancel out this θ.

  Further, the phase rotation amount with respect to the voltage level of the I / Q signal can be known by actual measurement.

If the phase rotation amount y is a function of the phase setting value x of the modulator,
^{_{y = C 1 × x n +}} C 2 × x (n-1) + ··· + C (n-1) Equation (1)
It is represented by Expression (1) is an approximate expression of the phase rotation amount y, and C and n are coefficients C of an expression representing an approximate expression of the phase rotation amount y of the power amplifier with respect to the phase setting value x (drain voltage of the power amplifier). And the order n.

  Since the phase rotation amount with respect to the phase setting value x can measure the characteristics of the power amplifier with a network analyzer or the like, the coefficient C can be calculated using the least square method or the like based on the value. Further, the order n tends to increase the accuracy of the approximate expression as the number increases, and the calculation time tends to increase. The order n can be increased or decreased in view of the calculation result of the approximate expression. In this way, by determining the order n and calculating C, the phase rotation amount y at each phase setting value x can be calculated.

If the y value is the same as the rotation amount θ of the power amplifier 18 and the rotation angle is opposite, the phase rotation can be canceled. If the phase setting value x is obtained, the I / Q signal input voltage of the phase shifter 17 is
I = cos (−θ), Q = sin (−θ)
It becomes.

  When this algorithm is executed by an arithmetic unit such as a CPU, if there is a possibility that a delay time may occur, a reference table may be created and an I / Q signal (phase control signal Vcont) corresponding to the amplitude signal may be generated. . In the description of the present embodiment, the phase compensation is performed based on the signal amplitude, but the same compensation can be performed for the input power.

  According to such a high frequency power amplifying device of the second embodiment of the present invention, a high-speed phase shifter can be realized at low cost by using an analog quadrature modulator as a phase shifter. By using this device, it is possible to easily realize a high-frequency power amplifying apparatus capable of linear compensation with respect to a high-speed modulation signal.

(Third embodiment)
FIG. 8 is a block diagram showing a schematic configuration of a high-frequency power amplifying device according to the third embodiment of the present invention. The basic configuration of the high-frequency power amplifier of FIG. 8 is the same as that of the above-described embodiment. However, the difference is that a gain / offset adjustment circuit 21 is provided in the previous stage of the phase control signal generation unit 14.

  The I / Q signal (phase control signal Vcont) input to the phase shifter 17 needs to have its gain and DC offset accurately controlled. FIG. 9 is a diagram for explaining the necessity of adjusting the gain and DC offset of the I / Q signal, and FIG. 9A is a diagram showing ideal phase characteristics of the I / Q signal. (B) is a figure which shows the characteristic containing the error of I / Q signal.

  In order to accurately perform phase rotation on the amplitude signal, the gain and DC offset of the I / Q signal to the phase shifter 17 must be ideally adjusted. However, for some reason, an error may occur between the gain and the DC offset. In this case, an incorrect phase rotation amount θ2 (see FIG. 9B) is set with respect to the phase rotation amount θ1 (see FIG. 9A) to be originally set. With this, sufficient distortion correction cannot be performed.

  Therefore, in the high frequency power amplifier of FIG. 8, a gain / offset adjustment circuit 21 is provided. By inserting the gain / offset adjustment circuit 21, more accurate phase compensation can be performed, and further improvement in distortion characteristics can be achieved.

  FIG. 10 is a diagram illustrating an example of a specific configuration of the gain / offset adjustment circuit according to the third embodiment. As shown in the figure, the gain / offset adjustment circuit is composed of a gain adjustment amplifier (resistors R3, R4 and an operational amplifier OP1) and an offset adjustment amplifier (variable resistor R5 and an operational amplifier OP2) in the previous stage. And).

  According to the high frequency power amplifying apparatus of the third embodiment of the present invention, it is possible to perform high precision by enabling at least one of gain adjustment and DC offset adjustment to the I / Q signal. Is always guaranteed.

(Fourth embodiment)
FIG. 11 is a block diagram showing a schematic configuration of a high-frequency power amplifying device according to the fourth embodiment of the present invention.

  The basic configuration is the same as that of the above-described embodiment, but in this embodiment, an OFDM (Orthogonal Frequency Division Multiplex) using an inverse fast Fourier transformer (IFFT) as an input signal of the high-frequency power amplifier is used. It is characterized in that it uses a modulation signal from a (division multiplexing) modulator.

  In OFDM, superposition of subcarriers generates a large amount of power instantaneously at random, and it is necessary to always maintain a large DC power so that a high-frequency signal having such a large power can be linearly amplified. is there.

  By implementing power amplification by the high-frequency power amplifier of the present invention using the modulation signal from the OFDM modulator (inverse fast Fourier transformer) as an input signal, high-efficiency linear amplification is realized, and there is no wasteful power consumption. Longer battery life in mobile phones and the like can also be achieved.

  As shown in FIG. 11, the high-frequency power amplifier has n (n = 2 in the example of FIG. 11) input signal paths. OFDM signal modulated by an OFDM modulator 22 (including n (in the example of FIG. 11, n = 2) IFFTs (Inverse Fast Fourier Transformers) 20A and 20B) is input to each signal path.

  There are also n (= 2) limiters and phase shifters (limiters 16A and 16B and phase shifters 17A and 17B). The subcarriers are combined by a combiner (AD) and amplified by a power amplifier 18.

  FIG. 12 is a diagram illustrating phase characteristics of the power amplifier with respect to the power supply voltage (Vdd). As shown in the figure, the phase characteristics of the power amplifier 18 differ in phase rotation characteristics depending on the frequencies f1 to fn. When the data transmission speed is increased in wireless communication, the signal bandwidth is widened.

  For this reason, even if phase characteristic distortion compensation at the transmission frequency point is performed, if the signal bandwidth is wide, sufficient compensation characteristics cannot be obtained. Therefore, in order to obtain the best distortion characteristics when amplifying an OFDM modulated signal, it is necessary to correct each phase over all frequencies within the signal bandwidth.

  In order to realize this, in the high frequency power amplifier of FIG. 11, compensation is performed by inserting a plurality of phase shifters having different phase rotation amounts. Or you may compensate by inserting the phase shifter which has the same characteristic as the phase control signal generation part 14 from which a sensitivity characteristic differs.

  Next, the specific operation of the high-frequency power amplifier of FIG. 11 will be described. The OFDM modulator 22 modulates the I / Q signal by performing IFFT (Inverse Fast Fourier Transform). In OFDM modulation, a modulated signal can be divided into an arbitrary number of subcarriers. Further, for example, in the case of an OFDM modulated wave having a total number of subcarriers of 52, when carrier sequences are grouped into four carrier groups such as 1 to 13, 14 to 26, 27 to 39, and 40 to 52, any carrier It is also possible to modulate only the group. For this reason, the signal bandwidth can be divided into arbitrary bandwidths on the frequency axis and transmitted.

  FIG. 13 is a diagram illustrating an example of a configuration of a data string to be subjected to OFDM modulation. Here, for convenience of explanation, consider a case where an input data string is divided into two series of A and B. When the data string is input to the inverse fast Fourier transformers (IFFT) 20A and 20B, the value in B1 to B20 is set to 0 in the data string A, and the value in A1 to A20 is set to 0 in the data string B. When the data sequences A and B are subjected to inverse fast Fourier transform, the frequency band can be divided as shown on the right side of FIG.

  The signals divided on the frequency axis are respectively input to the limiter (16A, 16B) and the phase shifter (17A, 17B), and the phase characteristics are compensated based on the amplitude signal as in the above-described embodiment.

  The compensated signal is synthesized by a synthesizer (AD), and a signal having only the phase of the data string signal having the original frequency bandwidth is generated. On the other hand, a part of the signal divided on the frequency axis is taken out by the coupler 15 and recombined in the previous stage of the envelope detection circuit 11 to reproduce the original signal information.

  Therefore, in the loop for detecting the amplitude signal, the amplitude information of the original signal information is generated. The generated amplitude signal information is combined with the phase signal in the power amplifier 18 and reproduced as an OFDM modulated signal. Since the reproduced signal is phase-compensated, it has good distortion characteristics.

  According to the fourth embodiment of the present invention, by using an OFDM modulated signal as an input signal, high-efficiency and highly linear amplification is realized, and the battery life of a portable device or the like is extended. You can also.

  As described above, the high-frequency device according to the embodiment of the present invention can be used for a high-speed, wide-band wireless data communication device or the like that employs a modulation scheme that performs both amplitude modulation and phase modulation. Stations, terrestrial digital transceivers, wireless LAN base stations, terminal stations, etc. can achieve low noise and low power consumption.

  The high frequency power amplifying apparatus of the present invention employs a modulation scheme that performs both amplitude modulation and phase modulation with a simple configuration, excellent in low power consumption, and capable of sufficiently compensating for nonlinear distortion. It is useful for high-speed and wide-band wireless data communication devices, such as mobile communication bases, terminal stations, terrestrial digital transceivers, wireless LAN base stations, terminal stations, and the like.

1 is a block diagram showing a schematic configuration of a high-frequency power amplifying device according to a first embodiment of the present invention. The figure which shows an example of the concrete structure of the phase shifter of 1st Embodiment, and its characteristic The figure which shows the distortion compensation effect in the high frequency power amplifier of 1st Embodiment The block diagram which shows schematic structure of the high frequency power amplifier which concerns on the 2nd Embodiment of this invention. The circuit diagram which shows the concrete structure of the phase shifter 17 of 2nd Embodiment. The figure which shows the example of the characteristic of the phase output with respect to the control setting value of a quadrature modulator Diagram showing examples of frequency response characteristics of quadrature modulator The block diagram which shows schematic structure of the high frequency power amplifier which concerns on the 3rd Embodiment of this invention. The figure for demonstrating the necessity of adjustment of the gain of an I / Q signal, and DC offset The figure which shows an example of the specific structure of the gain / offset adjustment circuit of 3rd Embodiment. The block diagram which shows schematic structure of the high frequency power amplifier which concerns on the 4th Embodiment of this invention. The figure which shows the phase characteristic with respect to power supply voltage (Vdd) of a power amplifier The figure which shows an example of a structure of the data sequence used as the object of OFDM modulation A block diagram showing an example of a configuration of an EER system power amplifier having a distortion compensation function The figure which shows the concrete example of the gain characteristic and the phase characteristic with respect to the power supply voltage of the power amplifier

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Envelope detection circuit 12 Audio band amplifier 13 Current amplifier 14 Phase adjustment signal generation part 15 Coupler 16 Limiter 17 Phase shifter (phase adjuster)
18 Power Amplifier 19 Coupler 20 Inverse Fast Fourier Transformer 21 Gain / Offset Adjustment Circuit 22 OFDM Modulator 26a, 26b Mixer 28 Adder

Claims (6)

A coupler that branches an input signal into a phase signal and an amplitude signal, which are polar components,
A limiter that limits the amplitude of one of the branched signals and outputs a phase signal;
A detector for detecting an amplitude of the other branched signal and outputting an amplitude signal;
A power amplifier that amplifies the phase-shifted signal using the amplitude signal as a power supply voltage;
A phase shifter provided in a preceding stage of the power amplifier to compensate for a phase characteristic of the power amplifier with respect to a power supply voltage;
A phase control signal generator for generating a phase control signal for adjusting the amount of phase shift of the phase shifter according to the voltage level of the amplitude signal;
With
A high-frequency power amplifying apparatus in which the phase signal is input to the power amplifier without gain adjustment. The high-frequency power amplifying device according to claim 1,
The phase control signal generation unit outputs a quadrature signal and an in-phase signal as the phase control signal,
The phase shifter includes a quadrature modulator that quadrature modulates the phase signal, and a phase rotation amount of the quadrature modulator is determined by the quadrature signal and the in-phase signal. A high-frequency power amplifying device according to claim 2,
A high-frequency power further comprising a phase control signal adjustment unit that performs at least one of gain adjustment and DC offset adjustment on the quadrature signal and the in-phase signal output from the phase control signal generation unit and outputs them to the quadrature modulator Amplification equipment. A high-frequency power amplifying device according to any one of claims 1 to 3,
A high-frequency power amplifying apparatus that uses a modulation signal modulated by an OFDM (Orthogonal Frequency Division Multiplex) modulator as the input signal.   A transmitter equipped with the high-frequency power amplifier according to any one of claims 1 to 4. A method for compensating for distortion of a power amplifier in a high-frequency power amplifier,
Branching the input signal into a phase signal and an amplitude signal which are polar components;
Limiting the amplitude of one of the branched signals and outputting a phase signal;
Detecting the amplitude of the other branched signal and outputting an amplitude signal;
Adjusting a phase shift amount according to a voltage level of the amplitude signal with respect to the phase signal, and compensating a phase characteristic with respect to a power supply voltage of the power amplifier;
Using the amplitude signal as a power supply voltage of the power amplifier, amplifying the phase signal with compensated phase characteristics without performing gain adjustment;
A distortion compensation method comprising:

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