Distortion compensation circuit, radio transmission device, distortion compensation method, and distortion compensation program

Abstract

To provide a distortion compensation circuit capable of suppressing deterioration in radio characteristic.SOLUTION: A distortion compensation circuit comprises: a memory that stores a look-up-table containing a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation arithmetic part that reads out the distortion compensation coefficient from the look-up-table on the basis of a digital transmission signal to be input, and multiplies the distortion compensation coefficient by the digital transmission signal; a distortion compensation coefficient calculation part that calculates the distortion compensation coefficient for update on the basis of a feedback signal from an output side of the digital transmission signal by which the distortion compensation coefficient is multiplied; a correction part that corrects the distortion compensation coefficient for update; and a determination part that determines whether or not the distortion compensation coefficient for update corrected by the correction part is in an output range of the look-up-table. In the case where the distortion compensation coefficient for update corrected is within the output range of the look-up-table, the look-up-table is updated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a distortion compensation circuit, a radio transmission device, a distortion compensation method, and a distortion compensation program. [Background technology]

[0002] In recent digital high-speed wireless communications, multiple modulation methods such as Code Division Multiple Access (CDMA) modulation and Orthogonal Frequency Division Multiplexing (OFDM) modulation are used. Signals using such multiple modulation methods have very large instantaneous power (peak factor, crest factor) compared to average power. Therefore, it is necessary for the transmitting power amplifier to maintain linearity up to a very high output level, suppress the spread of the transmission spectrum caused by nonlinear distortion, and reduce adjacent channel leakage power.

[0003] As a distortion compensation technique for compensating for nonlinear distortion in such a power amplifier, a digital predistortion (DPD) method is widely adopted. In a DPD distortion compensation circuit, as shown in Patent Document 1, for example, the calculated distortion compensation coefficient is stored in a memory as a lookup table (LUT). With such a configuration, the calculation process for distortion compensation can be performed at high speed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-091115 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the capacity (number of bits) of the lookup table in the memory is limited, and there are upper and lower limits to the value of the distortion compensation coefficient that the lookup table can output. If the calculated distortion compensation coefficient exceeds the output range of the lookup table, an overflow occurs, and the distortion compensation coefficient cannot be correctly represented in the lookup table.

[0006] In this way, if the calculated distortion compensation coefficient exceeds the output range of the lookup table, the distortion compensation circuit cannot compensate for the nonlinear distortion correctly, resulting in degradation of wireless characteristics such as the adjacent channel leakage ratio (ACLR) and the modulation accuracy (EVM). [Means for solving the problem]

[0007] A distortion compensation circuit according to an embodiment of the present disclosure includes: A memory for storing a lookup table including a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation calculation unit that reads out a distortion compensation coefficient from the lookup table based on an input digital transmission signal and multiplies the digital transmission signal by the distortion compensation coefficient; a distortion compensation coefficient calculation unit that calculates an update distortion compensation coefficient based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; A correction unit that corrects the distortion compensation coefficient for update; a determination unit that determines whether or not the update distortion compensation coefficient corrected by the correction unit is within an output range of the lookup table, When the corrected distortion compensation coefficient for update is within an output range of the lookup table, the lookup table is updated.

[0008] A wireless transmission device according to an embodiment of the present disclosure includes: a distortion compensation circuit that performs distortion compensation processing on an input digital transmission signal; a converter for converting the distortion-compensated digital transmission signal into an analog transmission signal; a power amplifier that amplifies the power of the analog transmission signal; The distortion compensation circuit includes: A memory for storing a lookup table including a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation calculation unit that reads out a distortion compensation coefficient from the lookup table based on an input digital transmission signal and multiplies the digital transmission signal by the distortion compensation coefficient; a coefficient update unit that calculates an update distortion compensation coefficient based on a feedback signal fed back from an output of the power amplifier; A correction unit that corrects the distortion compensation coefficient for update; a determination unit that determines whether or not the update distortion compensation coefficient corrected by the correction unit is within an output range of the lookup table, When the corrected distortion compensation coefficient for update is within an output range of the lookup table, the lookup table is updated.

[0009] A distortion compensation method according to an embodiment of the present disclosure includes: Based on the input digital transmission signal, a distortion compensation coefficient is read from the lookup table, and the digital transmission signal is multiplied by the distortion compensation coefficient; calculating an update distortion compensation coefficient for updating the look-up table based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; correcting the updated distortion compensation coefficient; determining whether the corrected update distortion compensation coefficient is within an output range of the look-up table; When the corrected distortion compensation coefficient for update is within an output range of the lookup table, the lookup table is updated by a computer.

[0010] A distortion compensation program according to an embodiment of the present disclosure includes: Based on the input digital transmission signal, a distortion compensation coefficient is read from the lookup table, and the digital transmission signal is multiplied by the distortion compensation coefficient; calculating an update distortion compensation coefficient for updating the look-up table based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; correcting the updated distortion compensation coefficient; determining whether the corrected update distortion compensation coefficient is within an output range of the look-up table; When the corrected distortion compensation coefficient for update is within an output range of the lookup table, the lookup table is updated. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a distortion compensation circuit capable of suppressing deterioration of wireless characteristics. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing an example of a configuration of a distortion compensation circuit according to the present disclosure. [Diagram 2] 1 is a block diagram showing an example of a hardware configuration of a distortion compensation circuit according to the present disclosure. [Diagram 3] 4 is a flowchart illustrating a distortion compensation method according to the present disclosure. [Figure 4] 1 is a block diagram showing an example of a configuration of a distortion compensation circuit according to the present disclosure. [Diagram 5] 13 is a graph showing a schematic relationship between a lookup table LUT of update distortion compensation coefficients Cu and a lookup table LUT of corrected update distortion compensation coefficients Cc. [Figure 6] 11 is a graph showing a schematic diagram of a correction table CT of correction coefficients by which an update distortion compensation coefficient Cu is multiplied. [Figure 7] 13 is a graph showing a schematic relationship between a lookup table LUT of update distortion compensation coefficients Cu and a lookup table LUT of corrected update distortion compensation coefficients Cc. [Figure 8] 11 is a graph showing two correction tables CT before and after updating of correction coefficients to be multiplied by an updating distortion compensation coefficient Cu. [Figure 9] 4 is a flowchart showing steps S3 to S4 in FIG. 3 in more detail. [Figure 10] 1 is a graph showing an example of the AMAM characteristics of a power amplifier PA. [Figure 11] 10 is a flowchart showing an example of details of step ST51 in FIG. 9. [Figure 12] 10 is a flowchart showing an example of details of step ST52 in FIG. 9. [Figure 13] 1 is a block diagram showing an example of a configuration of a wireless transmission device according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the following, specific embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and duplicated descriptions will be omitted as necessary for clarity of explanation.

[0014] (First embodiment) <Distortion compensation circuit configuration> First, an example of the configuration of a distortion compensation circuit according to the present disclosure will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the configuration of a distortion compensation circuit according to the present disclosure. As shown in FIG. 1, a distortion compensation circuit 100 according to the present disclosure includes functional blocks of a distortion compensation calculation unit 11, a memory 12, a distortion compensation coefficient calculation unit 13, a distortion compensation coefficient correction unit 14, and an output range determination unit 15. In FIG. 1, the flow of signals is indicated by arrows, but the signals are not limited to those shown in FIG. 1, and the direction of signal flow is not limited to the direction shown in the figure.

[0015] The distortion compensation calculation unit 11 reads out a distortion compensation coefficient C from a lookup table LUT stored in the memory 12 based on the input digital transmission signal D. For example, the distortion compensation calculation unit 11 calculates a power value of the input digital transmission signal D, and reads out a distortion compensation coefficient C corresponding to the calculated power value. Then, the distortion compensation calculation unit 11 multiplies the input digital transmission signal D by the read distortion compensation coefficient C, and outputs a corrected digital transmission signal Dc.

[0016] The memory 12 stores a lookup table LUT including distortion compensation coefficients C by which the digital transmission signal D is multiplied. For example, the lookup table LUT includes distortion compensation coefficients C corresponding to various power values ​​of the digital transmission signal D.

[0017] The distortion compensation coefficient calculation unit 13 calculates an update distortion compensation coefficient Cu based on a feedback signal Dfb from the output side of the digital transmission signal Dc compensated by the distortion compensation calculation unit 11 .

[0018] The distortion compensation coefficient correction unit 14 corrects the update distortion compensation coefficient Cu calculated by the distortion compensation coefficient calculation unit 13. For example, the distortion compensation coefficient correction unit 14 multiplies the update distortion compensation coefficient Cu by the correction coefficient, and outputs the corrected update distortion compensation coefficient Cc.

[0019] The output range determination unit 15 determines whether or not the distortion compensation coefficient Cc for updating corrected by the distortion compensation coefficient correction unit 14 is within the output range of the lookup table LUT in the memory 12. If the corrected distortion compensation coefficient Cc for updating is within the output range of the lookup table LUT, the output range determination unit 15 updates the lookup table LUT. That is, the output range determination unit 15 outputs the distortion compensation coefficient Cc for updating corrected by the distortion compensation coefficient correction unit 14 to the lookup table LUT. It should be noted that, based on the determination result DR of the output range determination unit 15, the distortion compensation coefficient correction unit 14 may directly output the corrected distortion compensation coefficient Cc for updating to the lookup table LUT.

[0020] On the other hand, if the corrected distortion compensation coefficient Cc for update is not within the output range of the lookup table LUT, the output range determination unit 15 does not update the lookup table LUT. That is, the output range determination unit 15 does not output the distortion compensation coefficient Cc for update corrected by the distortion compensation coefficient correction unit 14 to the lookup table LUT.

[0021] In this case, the distortion compensation coefficient correction unit 14 changes the correction conditions and corrects the update distortion compensation coefficient Cu again based on the judgment result DR of the output range judgment unit 15. Then, the output range judgment unit 15 judges whether or not the update distortion compensation coefficient Cc corrected again by the distortion compensation coefficient correction unit 14 is within the output range of the lookup table LUT in the memory 12. In this manner, the distortion compensation coefficient correction unit 14 repeats the correction of the update distortion compensation coefficient Cu until the update distortion compensation coefficient Cc corrected by the distortion compensation coefficient correction unit 14 falls within the output range of the lookup table LUT.

[0022] FIG. 2 is a block diagram showing an example of a hardware configuration of a distortion compensation circuit according to the present disclosure. 2, the distortion compensation circuit 100 includes, as hardware, a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and an I / O (Input / Output) 104. That is, the distortion compensation circuit 100 has a function as a computer, and performs various processes based on the above-mentioned various programs and the like.

[0023] The CPU 101 is a calculation unit that performs various control processes and calculation processes, for example. The ROM 102 is a memory that stores, for example, a control program and an arithmetic program executed by the CPU 101. The RAM 103 is a memory for temporarily storing processing data and the like. The I / O 104 is an input / output device that inputs data and signals from the outside and outputs data and signals to the outside.

[0024] The memory 12 shown in FIG. 1 is composed of, for example, a RAM 103, but may be composed of a ROM 102. Furthermore, each of the functional blocks of the distortion compensation calculation unit 11, the distortion compensation coefficient calculation unit 13, the distortion compensation coefficient correction unit 14, and the output range determination unit 15 shown in Fig. 1 can be configured in terms of hardware from memories such as the CPU 101, the ROM 102, and the RAM 103 shown in Fig. 2. On the other hand, each of these functional blocks can be realized in terms of software, for example, by a program loaded into a memory such as the ROM 102. Therefore, each functional block can be realized in various forms by computer hardware, software, or a combination thereof.

[0025] As described above, in the distortion compensation circuit 100 according to the present disclosure, the distortion compensation coefficient correction unit 14 corrects the update distortion compensation coefficient Cu calculated by the distortion compensation coefficient calculation unit 13. The output range determination unit 15 determines whether the corrected update distortion compensation coefficient Cc is within the output range of the lookup table LUT. Then, if the corrected update distortion compensation coefficient Cc is within the output range of the lookup table LUT, the lookup table LUT is updated. That is, the update distortion compensation coefficient Cu is corrected so as not to exceed the output range of the lookup table LUT, so that nonlinear distortion can be correctly compensated. As a result, deterioration of wireless characteristics such as adjacent channel leakage power ratio and modulation accuracy can be suppressed.

[0026] <Distortion compensation method> Next, a distortion compensation method according to the present disclosure will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the distortion compensation method according to the present disclosure. The distortion compensation circuit 100 shown in Fig. 1 executes each process constituting the distortion compensation method shown in Fig. 3.

[0027] 1 reads out a distortion compensation coefficient C from a lookup table LUT based on an input digital transmission signal D. Then, the distortion compensation calculation unit 11 multiplies the input digital transmission signal D by the read out distortion compensation coefficient C (step ST1).

[0028] Next, the distortion compensation coefficient calculation unit 13 shown in FIG. 1 calculates an update distortion compensation coefficient Cu based on the feedback signal Dfb from the output side of the digital transmission signal Dc compensated by the distortion compensation calculation unit 11 (step ST2).

[0029] Next, the distortion compensation coefficient correcting unit 14 shown in FIG. 1 corrects the distortion compensation coefficient Cu for update (step ST3). Next, the output range determination unit 15 shown in FIG. 1 determines whether or not the update distortion compensation coefficient Cc corrected by the distortion compensation coefficient correction unit 14 is within the output range of the lookup table LUT in the memory 12 (step ST4).

[0030] If the corrected distortion compensation coefficient for update Cc is not within the output range of the lookup table LUT (NO in step ST4), the correction conditions in the distortion compensation coefficient correction unit 14 are changed (step ST5). Then, the process returns to step ST3, and the distortion compensation coefficient for update Cu is corrected again. In this manner, the change of the correction conditions (step ST5) and the correction of the distortion compensation coefficient for update Cu (step ST3) are repeated until the corrected distortion compensation coefficient for update Cc falls within the output range of the lookup table LUT.

[0031] On the other hand, if the corrected distortion compensation coefficients for update Cc are within the output range of the lookup table LUT (YES in step ST4), the lookup table LUT is updated using the corrected distortion compensation coefficients for update Cc (step ST6). As shown in FIG. 3, the lookup table LUT is updated (step ST6), and the distortion compensation method according to the present disclosure ends.

[0032] As described above, in the distortion compensation method according to the present disclosure, the distortion compensation coefficient Cu for updating calculated by the distortion compensation coefficient calculation unit 13 is corrected, and it is determined whether or not the corrected distortion compensation coefficient Cc for updating is within the output range of the lookup table LUT. Then, if the corrected distortion compensation coefficient Cc for updating is within the output range of the lookup table LUT, the lookup table LUT is updated. That is, the distortion compensation coefficient Cu for updating is corrected so as not to exceed the output range of the lookup table LUT, so that nonlinear distortion can be correctly compensated. As a result, deterioration of wireless characteristics such as adjacent channel leakage power ratio and modulation accuracy can be suppressed.

[0033] Second embodiment <Distortion compensation circuit configuration> Next, an example of the configuration of the distortion compensation circuit according to the present disclosure will be described with reference to Fig. 4. Fig. 4 is a block diagram showing an example of the configuration of the distortion compensation circuit according to the present disclosure. Similar to the distortion compensation circuit 100 shown in FIG. 1, the distortion compensation circuit 100 shown in FIG. 4 also includes functional blocks of a distortion compensation calculation unit 11, a memory 12, a distortion compensation coefficient calculation unit 13, a distortion compensation coefficient correction unit 14, and an output range determination unit 15.

[0034] 4, the distortion compensation calculation unit 11 includes a power calculation unit 111 and a multiplication unit 112. Also, in the distortion compensation circuit 100 shown in FIG. 4, the distortion compensation coefficient correction unit 14 includes a multiplication unit 141, a memory 142, and a correction table update unit 143. That is, the distortion compensation circuit 100 shown in FIG. 4 is a more specific example of the distortion compensation circuit 100 shown in FIG.

[0035] As described above, in the distortion compensation circuit 100 shown in FIG. 4, the distortion compensation calculation unit 11 includes the power calculation unit 111 and the multiplication unit 112. The power calculation unit 111 calculates a power value P of the input digital transmission signal D, and outputs it to the memory 12. Here, the digital transmission signal D shown in Fig. 4 is, as an example, digital baseband signals (I signal and Q signal) that are orthogonal to each other.

[0036] The multiplier 112 reads out a distortion compensation coefficient C(Ci, Cq) corresponding to the power value P of the input digital transmission signal D(I, Q) from the lookup table LUT stored in the memory 12. Then, the multiplier 112 multiplies the input digital transmission signal D(I, Q) by the read distortion compensation coefficient C(Ci, Cq) and outputs a corrected digital transmission signal Dc(Ic, Qc).

[0037] The memory 12 stores a lookup table LUT including distortion compensation coefficients Ci, Cq to be multiplied by the digital transmission signals I, Q. For example, the lookup table LUT includes distortion compensation coefficients Ci, Cq corresponding to various power values ​​of the digital transmission signals I, Q. A plurality of lookup tables LUT may be stored in the memory 12. In this case, the distortion compensation calculation unit 11 may switch the lookup table LUT to be read based on, for example, the input digital transmission signals I and Q.

[0038] The distortion compensation coefficient calculation unit 13 calculates an update distortion compensation coefficient Cu (Cui, Cuq) based on a feedback signal Dfb (Ifb, Qfb) fed back from the output side of the digital transmission signal Dc (Ic, Qc) compensated by the distortion compensation calculation unit 11. Here, in the example shown in FIG. 4, the distortion compensation coefficient calculation unit 13 calculates update distortion compensation coefficients Cui, Cuq based on the input digital transmission signals I, Q and feedback signals Ifb, Qfb.

[0039] As will be described in detail later, the feedback signals Ifb and Qfb are signals fed back from the output of a power amplifier provided on the output side of the distortion compensation circuit 100. The distortion compensation coefficient calculation unit 13 may calculate the distortion compensation coefficients Cui and Cuq by other methods.

[0040] The distortion compensation coefficient corrector 14 corrects the distortion compensation coefficients Cu (Cui, Cuq) for updating calculated by the distortion compensation coefficient calculator 13, and outputs the corrected distortion compensation coefficients Cc (Cci, Ccq) for updating to the output range determiner 15. As described above, the distortion compensation coefficient correction unit 14 includes the multiplication unit 141, the memory 142, and the correction table update unit 143.

[0041] The multiplier 141 reads out the correction coefficients CRi and CRq from the correction table CT stored in the memory 142, and multiplies the correction coefficients Cui and Cuq by the correction coefficients CRi and CRq. More specifically, the multiplier 141 multiplies the I signal correction coefficient CRi read out from the correction table CT by the I signal distortion compensation coefficient Cui for updating, and outputs the corrected update distortion compensation coefficient Cci to the output range determiner 15. The multiplier 141 also multiplies the Q signal correction coefficient CRq read out from the correction table CT by the Q signal distortion compensation coefficient Cuq for updating, and outputs the corrected update distortion compensation coefficient Ccq to the output range determiner 15.

[0042] FIG. 5 is a graph showing a schematic relationship between the lookup table LUT of the update distortion compensation coefficients Cu and the lookup table LUT of the corrected update distortion compensation coefficients Cc. FIG. 6 is a graph that illustrates a correction table CT of correction coefficients by which the distortion compensation coefficients Cu for update are multiplied.

[0043] 5, when the input exceeds approximately 0.8, the updating distortion compensation coefficient Cu calculated by the distortion compensation coefficient calculation unit 13 exceeds the upper limit threshold A of the output range of the lookup table LUT in the memory 12. Therefore, in FIG. 5, if the updating distortion compensation coefficient Cu before correction is used, correct compensation cannot be performed.

[0044] In contrast, the corrected updated distortion compensation coefficient Cc obtained by multiplying the corrected updated distortion compensation coefficient Cu by the correction coefficient shown in Fig. 6 does not exceed the threshold value A over the entire input range. Therefore, in Fig. 5, when the corrected updated distortion compensation coefficient Cc is used, correct compensation can be achieved over the entire input range.

[0045] The correction table update unit 143 generates and outputs the update correction coefficients CRui, CRuq based on the determination result DR of the output range determination unit 15. Specifically, when the determination result DR indicates that the corrected update distortion compensation coefficients Cci, Ccq are not within the output range of the lookup table LUT, the correction table update unit 143 generates the update correction coefficients CRui, CRuq. The correction table CT stored in the memory 142 is updated by the update correction coefficients CRui, CRuq output by the correction table update unit 143.

[0046] The output range determination unit 15 determines whether or not the update distortion compensation coefficients Cci, Ccq corrected by the distortion compensation coefficient correction unit 14 are within the output range of the lookup table LUT in the memory 12. If the corrected update distortion compensation coefficients Cci, Ccq are within the output range of the lookup table LUT, the output range determination unit 15 updates the lookup table LUT. That is, the output range determination unit 15 outputs the update distortion compensation coefficients Cci, Ccq corrected by the distortion compensation coefficient correction unit 14 to the lookup table LUT. It should be noted that, based on the determination result DR of the output range determination unit 15, the distortion compensation coefficient correction unit 14 may directly output the corrected distortion compensation coefficients Cci and Ccq for updating to the lookup table LUT.

[0047] On the other hand, if the corrected update distortion compensation coefficients Cci, Ccq are not within the output range of the lookup table LUT, the output range determination unit 15 does not update the lookup table LUT. That is, the output range determination unit 15 does not output the update distortion compensation coefficients Cci, Ccq corrected by the distortion compensation coefficient correction unit 14 to the lookup table LUT.

[0048] In this case, the distortion compensation coefficient correction unit 14 changes the correction conditions and corrects the update distortion compensation coefficients Cui, Cuq again based on the judgment result DR of the output range judgment unit 15. Specifically, the correction table update unit 143 generates update correction coefficients CRui, CRuq and updates the correction table CT. Then, the multiplication unit 141 reads out the correction coefficients CRi, CRq again from the updated correction table CT and multiplies them by the update distortion compensation coefficients Cui, Cuq again.

[0049] Furthermore, the output range determination unit 15 determines whether or not the updating distortion compensation coefficients Cci, Ccq corrected again by the distortion compensation coefficient correction unit 14 are within the output range of the lookup table LUT in the memory 12. In this manner, the distortion compensation coefficient correction unit 14 repeats the correction of the updating distortion compensation coefficients Cui, Cuq until the updating distortion compensation coefficients Cci, Ccq corrected by the distortion compensation coefficient correction unit 14 fall within the output range of the lookup table LUT.

[0050] 7 is a graph showing a relationship between the lookup table LUT of the update distortion compensation coefficient Cu and the lookup table LUT of the corrected update distortion compensation coefficient Cc. Here, FIG. 7 shows the lookup tables LUT of the two update distortion compensation coefficients corrected by the pre-update and post-update correction tables CT. FIG. 8 is a graph showing two correction tables CT before and after the update of the correction coefficients by which the distortion compensation coefficients Cu for updating are multiplied.

[0051] 7, when the input exceeds approximately 0.6, the updating distortion compensation coefficient Cu calculated by the distortion compensation coefficient calculation unit 13 exceeds the upper limit threshold A of the output range of the lookup table LUT in the memory 12. Therefore, also in FIG. 7, if the updating distortion compensation coefficient Cu before correction is used, correct compensation cannot be performed.

[0052] Furthermore, the corrected update distortion compensation coefficient Cc (shown as "Cc (before update)" in FIG. 7) obtained by multiplying the update distortion compensation coefficient Cu by the pre-update correction coefficient shown in FIG. 8 also exceeds the threshold value A when the input exceeds approximately 0.6. Therefore, correct compensation cannot be achieved even when the update distortion compensation coefficient Cc corrected using the pre-update correction coefficient shown in FIG. 7 is used.

[0053] In contrast, the corrected update distortion compensation coefficient Cc (shown as "Cc (updated)" in FIG. 7) obtained by multiplying the update distortion compensation coefficient Cu by the update correction coefficient shown in FIG. 8 does not exceed the threshold value A over the entire input range. Therefore, when the update distortion compensation coefficient Cc corrected again using the update correction coefficient shown in FIG. 7 is used, correct compensation can be achieved over the entire input range.

[0054] As described above, in the distortion compensation circuit 100 according to the present disclosure, the distortion compensation coefficient correction unit 14 corrects the update distortion compensation coefficients Cui and Cuq calculated by the distortion compensation coefficient calculation unit 13. The output range determination unit 15 determines whether the corrected update distortion compensation coefficients Cci and Ccq are within the output range of the lookup table LUT. Then, when the corrected update distortion compensation coefficients Cci and Ccq are within the output range of the lookup table LUT, the lookup table LUT is updated. That is, the update distortion compensation coefficients Cui and Cuq are corrected so as not to exceed the output range of the lookup table LUT, so that nonlinear distortion can be correctly compensated. As a result, deterioration of wireless characteristics such as adjacent channel leakage power ratio and modulation accuracy can be suppressed.

[0055] <Distortion compensation method> Next, a distortion compensation method according to the present disclosure will be described with reference to Fig. 9. Fig. 9 is a flowchart showing steps S3 to S4 in Fig. 3 in more detail. As shown in FIG. 9, step ST3 of correcting the updating distortion compensation coefficients Cui and Cuq includes steps ST31 and ST32.

[0056] First, as shown in Fig. 9, the initial values ​​of the correction table CT in the memory 142 shown in Fig. 4, that is, the correction coefficients CRi and CRq, are set (step ST31). For example, any fixed value may be used as the initial value, or the correction coefficients at the time of the previous end may be used. Here, in Fig. 9, the correction coefficients CRi and CRq shown in Fig. 4 are indicated as the correction coefficient CR for simplification. Next, as shown in FIG. 9, the multiplication unit 141 shown in FIG. 4 multiplies the correction coefficients CRi, CRq by the update distortion compensation coefficients Cui, Cuq to calculate a lookup table LUT of the corrected update distortion compensation coefficients Cci, Ccq (step ST32).

[0057] As shown in FIG. 9, step ST4 of determining the output ranges of the corrected updating distortion compensation coefficients Cci and Ccq is made up of steps ST41, ST42, and ST43. First, the output range determination unit 15 shown in FIG. 4 determines whether or not the maximum value M of the corrected updating distortion compensation coefficients Cci and Ccq is equal to or less than the upper limit threshold A of the output range of the lookup table LUT in the memory 12 (step ST41).

[0058] If the maximum value M≦threshold value A (YES in step ST41), the output range determination unit 15 determines whether the correction coefficients CRi and CRq are 0 (step ST42). On the other hand, if the maximum value M>threshold value A (NO in step ST41), the correction amount is insufficient, so the correction coefficients CRi and CRq are updated so that the correction amount is increased (step ST51).

[0059] If the correction coefficients CRi, CRq are 0 (YES in step ST42), the output range determination unit 15 determines that the corrected update distortion compensation coefficients Cci, Ccq are within the output range of the lookup table LUT, and updates the lookup table LUT using the corrected update distortion compensation coefficients Cci, Ccq (step ST6).On the other hand, if the correction coefficients CRi, CRq are not 0 (NO in step ST42), it determines whether the maximum value M of the corrected update distortion compensation coefficients Cci, Ccq is equal to or greater than the lower limit threshold B of the output range of the lookup table LUT in the memory 12 (step ST43).

[0060] If the maximum value M≧threshold value B (YES in step ST43), the corrected update distortion compensation coefficients Cci, Ccq are within the output range of the lookup table LUT. Therefore, the lookup table LUT is updated using the corrected update distortion compensation coefficients Cci, Ccq (step ST6). On the other hand, if the maximum value M<threshold value B (NO in step ST43), the amount of correction is excessive, so the correction coefficients CRi, CRq are updated to reduce the amount of correction (step ST52).

[0061] 9, if the corrected distortion compensation coefficients Cci and Ccq for updating are not within the output range of the lookup table LUT (NO in step ST41 or step ST43), the correction conditions in the distortion compensation coefficient correction unit 14 are changed (step ST5). This step ST5 is composed of the above-mentioned steps ST51 and ST52.

[0062] Then, the process returns to step ST32, and the lookup table LUT of the corrected distortion compensation coefficients Cci and Ccq for updating is calculated again. In this manner, steps ST51, ST51, and ST32 are repeated until the corrected distortion compensation coefficients Cci and Ccq for updating fall within the output range of the lookup table LUT.

[0063] As described above, in the distortion compensation method according to the present disclosure, the distortion compensation coefficients Cui and Cuq for updating calculated by the distortion compensation coefficient calculation unit 13 are corrected, and it is determined whether the corrected distortion compensation coefficients Cci and Ccq for updating are within the output range of the lookup table LUT. If the maximum value M of the corrected distortion compensation coefficients Cci and Ccq for updating exceeds the upper threshold A of the lookup table LUT (NO in step ST41), the correction coefficients CRi and CRq are updated so that the correction amount for the input that maximizes the output becomes larger than the current amount (step ST51). If the maximum value M of the corrected distortion compensation coefficients Cci and Ccq for updating falls below the lower threshold B of the lookup table LUT (NO in step ST43), the correction coefficients CRi and CRq are updated so that the correction amount for the input that maximizes the output becomes smaller than the current amount (step ST52).

[0064] In this manner, in the distortion compensation method according to the present disclosure, the distortion compensation coefficient Cu for updating is corrected so as not to exceed the output range of the lookup table LUT, and therefore nonlinear distortion can be compensated correctly, and as a result, deterioration of wireless characteristics such as adjacent channel leakage power ratio and modulation accuracy can be suppressed.

[0065] Now, with reference to FIG. 10, a description will be given of overcompensation of nonlinearity, which is one of the reasons why the distortion compensation coefficients Cui and Cuq for updating do not fall within the output range of the lookup table LUT. Figure 10 is a graph showing an example of the AMAM characteristics of a power amplifier PA. The horizontal axis shows the normalized input amplitude, and the vertical axis shows the ratio of output amplitude to input amplitude. The dots in Figure 10 represent all signal samples at a certain sampling frequency.

[0066] In Fig. 10, the approximation line when the number of samples is large is shown by a solid line, and the approximation line when the number of samples is small is shown by a dashed line. The solid approximation line when the number of samples is large is a normal approximation. On the other hand, the dashed approximation line when the number of samples is small is not a correct approximation due to overcompensation, where the influence of individual samples is large. When the distortion compensation coefficients Cui, Cuq for updating are calculated in the overcompensation state shown by the dashed line in Fig. 10, there is a risk that they will not fall within the output range of the lookup table LUT.

[0067] However, as described above, in the distortion compensation method according to the present disclosure, the correction coefficients are updated and the correction of the update distortion compensation coefficients Cui and Cuq is repeated until the corrected update distortion compensation coefficients Cci and Ccq fall within the output range of the lookup table LUT. Therefore, the dashed line in FIG. 10 can be made closer to the solid line, and nonlinear distortion can be compensated for with higher accuracy even when the number of samples is small. As a result, deterioration of wireless characteristics such as adjacent channel leakage power ratio and modulation accuracy can be suppressed.

[0068] <Detailed Description of Step ST51> Next, details of step ST51 for updating the correction coefficients CRi and CRq so that the correction amount at the input at which the output is maximized becomes larger than the current amount will be described with reference to Fig. 11. Fig. 11 is a flowchart showing an example of details of step ST51 in Fig. 9. Fig. 11 shows an example of a method for calculating the correction coefficients CRi and CRq using a polynomial as an equation representing a correction table.

[0069] First, the formula used in the calculation method will be described. The correction table can be expressed as a polynomial with the signal amplitude |x(t)| at a certain time t as a variable. The n-th order polynomial function table(|x(t)|) that represents this correction table has a correction coefficient c k Using the above, it is expressed by the following formula (1). k and n are exponents and are integers that satisfy 0≦k≦n. Note that the correction coefficient c k (=c0, c1, . . ., c n ) correspond to the correction coefficients CRi and CRq shown in FIG. TIFF2025019775000002.tif13150

[0070] In step ST51, the correction coefficient c is set so that the amount of correction at the input at which the output is maximized is larger than the current amount. k Specifically, the current correction coefficient c k c' k Then, a step coefficient α is added to increase the correction amount at the input where the output is maximized. m The updated correction factor c k Here, m is the number of steps and is an integer equal to or greater than 0. TIFF2025019775000003.tif6150Note that each correction coefficient c k (=c0, c1, . . ., c n The initial value of ) is set in step ST31 in FIG.

[0071] 11, in the case of the first update (YES in step ST511), the update target is the first correction coefficient c0, the current correction coefficient c0 is set to c'0, and the first step coefficient α0 is added to set the new correction coefficient c0 (step ST512). That is, in equation (2), c0=c'0+α0. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0072] On the other hand, as shown in FIG. 11, in the case of the second or subsequent update (NO in step ST511), it is determined whether or not the maximum value M of the update distortion compensation coefficient Cc corrected using the updated correction coefficient is equal to or less than the previous maximum value M′ (step ST513).

[0073] Here, if the maximum value M≦maximum value M′ (YES in step ST513), the previously updated correction coefficient c kOn the other hand, if the maximum value M>the maximum value M' (NO in step ST513), there is no improvement, so the previously updated correction coefficient c k The correction coefficient c' before updating k (step ST514b).

[0074] Next, the final correction factor c n If the correction coefficient c k from the following correction factor c k+1 At this time, the current correction coefficient c k+1 c' k+1 Then, add the current step coefficient α m Add the new correction coefficient c k+1 (Step ST516). That is, in the formula (2), c k+1 =c' k+1 +α m Let us assume that. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0075] On the other hand, the final correction factor c n When all the correction coefficients c0, c1, . . . , c n It is determined whether or not there is any that has been updated in step ST514a (step ST517).

[0076] The correction factor c that has been updated k If there is no step coefficient α m The next step coefficient α m+1 (step ST518). Then, the update target is the final correction coefficient c n Return the initial correction coefficient c0 to c'0, and update the step coefficient α m+1 In other words, in the formula (2), c0=c'0+α m+1 Let us assume that. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0077] On the other hand, the correction coefficient c k If there is (NO in step ST517), the step coefficient α m The update target is the last correction coefficient c n Return to the initial correction coefficient c0, set the current correction coefficient c0 to c'0, and set the current step coefficient α m In other words, in the formula (2), c0=c'0+α m Let us assume that. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0078] Note that step ST51 for updating the correction coefficients CRi and CRq so as to increase the correction amount is not limited to the above calculation method. For example, the memory 142 may store a plurality of correction tables CT in advance, and the current correction table CT may be switched to another correction table CT in which the correction amount at the input that maximizes the output is larger than the current one.

[0079] <Detailed Description of Step ST52> Next, details of step ST52 for updating the correction coefficients CRi and CRq so that the correction amount at the input at which the output is maximized becomes smaller than the current amount will be described with reference to Fig. 12. Fig. 12 is a flowchart showing an example of details of step ST52 in Fig. 9. Like Fig. 11, Fig. 12 shows an example of a method for calculating the correction coefficients CRi and CRq using the polynomial shown in formula (1) as a formula representing the correction table.

[0080] In step ST52, the correction coefficient c is set so that the correction amount at the input where the output is maximized is smaller than the current amount. k Specifically, the current correction coefficient ck c' k Then, a step coefficient β is added to reduce the correction amount at the input where the output is maximized. l The updated correction factor c k Here, l is also the number of steps and is an integer equal to or greater than 0. TIFF2025019775000004.tif6150As mentioned above, each correction coefficient c k (=c0, c1, . . ., c n The initial value of ) is set in step ST31 in FIG.

[0081] 12, in the case of the first update (YES in step ST521), the update target is the first correction coefficient c0, the current correction coefficient c0 is set to c'0, and the first step coefficient β0 is added to set the new correction coefficient c0 (step ST522). That is, in equation (3), c0=c'0+β0. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0082] On the other hand, as shown in FIG. 12, in the case of the second or subsequent update (NO in step ST521), it is determined whether the maximum value M of the update distortion compensation coefficient Cc corrected using the updated correction coefficient is equal to or greater than the previous maximum value M' (step ST523).

[0083] Here, if the maximum value M is greater than or equal to the maximum value M' (YES in step ST523), the previously updated correction coefficient c k On the other hand, if the maximum value M is smaller than the maximum value M' (NO in step ST523), no improvement has been made, so the previously updated correction coefficient c k The correction coefficient c' before updating k (step ST524b).

[0084] Next, the final correction factor c n If the correction coefficient ck from the following correction factor c k+1 Then, the current correction coefficient c k+1 c' k+1 Then, add the current step coefficient β l Add the new correction coefficient c k+1 (Step ST526). That is, in the formula (3), c k+1 =c' k+1 +β l Let us assume that. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0085] On the other hand, the final correction factor c n When all the correction coefficients c0, c1, . . . , c n It is determined whether or not there is any that has been updated in step ST524a (step ST527).

[0086] The correction factor c that has been updated k If there is no step coefficient β l The next step coefficient β l+1 (step ST528). Then, the update target is the final correction coefficient c n Return the initial correction coefficient c0 to c'0, and update the step coefficient β l+1 That is, in the formula (3), c0=c'0+β is added to obtain a new correction coefficient c0 (step ST529). l+1 Let us assume that. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0087] On the other hand, the correction coefficient c k If there is a step coefficient β l The update target is the last correction coefficient c nReturn to the initial correction coefficient c0, set the current correction coefficient c0 to c'0, and set the current step coefficient β l That is, in the formula (3), c0=c'0+β is added to obtain a new correction coefficient c0 (step ST529). l Let us assume that. Then, the process returns to step ST32 shown in FIG. 9, and the lookup table LUT of the corrected updated distortion compensation coefficients Cc is calculated again using the updated correction coefficients.

[0088] Note that step ST52 for updating the correction coefficients CRi and CRq so as to reduce the amount of correction is not limited to the above calculation method. For example, the memory 142 may store a plurality of correction tables CT in advance, and the current correction table CT may be switched to another correction table CT in which the amount of correction at the input that maximizes the output is reduced from the current one. The other configuration is similar to that of the first embodiment, and therefore the description will be omitted.

[0089] (Third embodiment) <Configuration of wireless transmitting device> Next, an example of a configuration of a wireless transmission device according to the present disclosure will be described with reference to Fig. 13. Fig. 13 is a block diagram showing an example of a configuration of a wireless transmission device according to the present disclosure. The wireless transmitting device shown in FIG. 13 includes, in addition to the distortion compensation circuit 100 shown in FIG. 1, a quadrature modulation unit QM1, a quadrature demodulation unit QM2, a digital / analog converter DAC, an analog / digital converter ADC, and a power amplifier PA.

[0090] Of course, the wireless transmission device shown in Fig. 13 may include the distortion compensation circuit 100 shown in Fig. 4 instead of the distortion compensation circuit 100 shown in Fig. 1. That is, this embodiment may be combined with either the first or second embodiment.

[0091] The quadrature modulation unit QM1 quadrature-modulates the compensated digital transmission signals Ic and Qc output from the distortion compensation calculation unit 11, and outputs the result as a digital IF (Intermediate Frequency) signal to a digital / analog converter DAC. The digital / analog converter DAC converts the digital IF signal into an analog transmission signal and outputs it to the power amplifier PA. The power amplifier PA is a power amplifier for transmission. The power amplifier PA amplifies an input analog transmission signal and outputs it as an output signal OUT.

[0092] The analog / digital converter ADC converts the output signal OUT, which is an analog signal, into a digital IF signal and outputs it to the quadrature demodulation unit QM2. The orthogonal demodulation unit QM2 demodulates the digital IF signal and outputs it to the distortion compensation coefficient calculation unit 13 as feedback signals Ifb and Qfb.

[0093] 13, the distortion compensation coefficient calculation unit 13 calculates update distortion compensation coefficients Cui and Cuq based on the input digital transmission signals I and Q and feedback signals Ifb and Qfb. More specifically, the distortion compensation coefficient calculation unit 13 compares the input digital transmission signals I and Q with the feedback signals Ifb and Qfb, and calculates update distortion compensation coefficients Cui and Cuq that indicate the inverse characteristics of the nonlinear distortion of the power amplifier PA based on the comparison result.

[0094] With this configuration, the wireless transmission device shown in FIG. 13 can compensate for nonlinear distortion in the transmission power amplifier PA by using the distortion compensation circuit 100. The other configurations are similar to those of the first and second embodiments, and therefore the description will be omitted.

[0095] In the above examples, the program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray® disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, the transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0096] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-mentioned embodiments. Various modifications that can be understood by a person skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure.

[0097] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes.

[0098] (Appendix 1) A memory for storing a lookup table including a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation calculation unit that reads out a distortion compensation coefficient from the lookup table based on an input digital transmission signal and multiplies the digital transmission signal by the distortion compensation coefficient; a distortion compensation coefficient calculation unit that calculates an update distortion compensation coefficient based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; A correction unit that corrects the distortion compensation coefficient for update; a determination unit that determines whether or not the update distortion compensation coefficient corrected by the correction unit is within an output range of the lookup table, updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table; Distortion compensation circuit.

[0099] (Appendix 2) when the corrected distortion compensation coefficient for update is not within an output range of the lookup table, the lookup table is not updated, and the correction condition is changed in the correction unit to correct the distortion compensation coefficient for update again. 2. The distortion compensation circuit according to claim 1.

[0100] (Appendix 3) The correction unit is a correction memory for storing a correction table including a correction coefficient to be multiplied by the distortion compensation coefficient for update; and an update unit that updates the correction table when the corrected update distortion compensation coefficient is not within an output range of the lookup table. 3. The distortion compensation circuit according to claim 1 or 2.

[0101] (Appendix 4) When the corrected distortion compensation coefficient for update exceeds an upper limit of an output range of the lookup table, The update unit updates the correction table so that a correction amount becomes larger than a current amount. 4. The distortion compensation circuit according to claim 3.

[0102] (Appendix 5) The correction memory stores a plurality of correction tables in advance, When the corrected distortion compensation coefficient for update exceeds an upper limit of an output range of the lookup table, the update unit switches from a correction table currently in use to a correction table with a larger correction amount; 4. The distortion compensation circuit according to claim 3.

[0103] (Appendix 6) When the corrected update distortion compensation coefficient falls below a lower limit of an output range of the lookup table, The update unit updates the correction table so that a correction amount becomes smaller than a current amount. 4. The distortion compensation circuit according to claim 3.

[0104] (Appendix 7) The correction memory stores a plurality of correction tables in advance, When the corrected update distortion compensation coefficient falls below a lower limit of an output range of the lookup table, the update unit switches from a correction table currently in use to a correction table having a smaller correction amount; 4. The distortion compensation circuit according to claim 3.

[0105] (Appendix 8) a distortion compensation circuit that performs distortion compensation processing on an input digital transmission signal; a converter for converting the distortion-compensated digital transmission signal into an analog transmission signal; a power amplifier that amplifies the power of the analog transmission signal; The distortion compensation circuit includes: A memory for storing a lookup table including a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation calculation unit that reads out a distortion compensation coefficient from the lookup table based on an input digital transmission signal and multiplies the digital transmission signal by the distortion compensation coefficient; a coefficient update unit that calculates an update distortion compensation coefficient based on a feedback signal fed back from an output of the power amplifier; A correction unit that corrects the distortion compensation coefficient for update; a determination unit that determines whether or not the update distortion compensation coefficient corrected by the correction unit is within an output range of the lookup table, updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table; Radio transmitting device.

[0106] (Appendix 9) when the corrected distortion compensation coefficient for update is not within an output range of the lookup table, the lookup table is not updated, and the correction condition is changed in the correction unit to correct the distortion compensation coefficient for update again. 9. The wireless transmitting device according to claim 8.

[0107] (Appendix 10) The correction unit is a correction memory for storing a correction table including a correction coefficient to be multiplied by the distortion compensation coefficient for update; and an update unit that updates the correction table when the corrected update distortion compensation coefficient is not within an output range of the lookup table. 10. The wireless transmitting device according to claim 8 or 9.

[0108] (Appendix 11) When the corrected distortion compensation coefficient for update exceeds an upper limit of an output range of the lookup table, The update unit updates the correction table so that a correction amount becomes larger than a current amount. 11. The wireless transmitting device of claim 10.

[0109] (Appendix 12) The correction memory stores a plurality of correction tables in advance, When the corrected distortion compensation coefficient for update exceeds an upper limit of an output range of the lookup table, the update unit switches from a correction table currently in use to a correction table with a larger correction amount; 11. The wireless transmitting device of claim 10.

[0110] (Appendix 13) When the corrected update distortion compensation coefficient falls below a lower limit of an output range of the lookup table, The update unit updates the correction table so that a correction amount becomes smaller than a current amount. 11. The wireless transmitting device of claim 10.

[0111] (Appendix 14) The correction memory stores a plurality of correction tables in advance, When the corrected update distortion compensation coefficient falls below a lower limit of an output range of the lookup table, the update unit switches from a correction table currently in use to a correction table having a smaller correction amount; 11. The wireless transmitting device of claim 10.

[0112] (Appendix 15) Based on the input digital transmission signal, a distortion compensation coefficient is read from the lookup table, and the digital transmission signal is multiplied by the distortion compensation coefficient; calculating an update distortion compensation coefficient for updating the look-up table based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; correcting the updated distortion compensation coefficient; determining whether the corrected update distortion compensation coefficient is within an output range of the look-up table; a process of updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table, the process being performed by a computer; Distortion compensation method.

[0113] (Appendix 16) Based on the input digital transmission signal, a distortion compensation coefficient is read from the lookup table, and the digital transmission signal is multiplied by the distortion compensation coefficient; calculating an update distortion compensation coefficient for updating the look-up table based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; correcting the updated distortion compensation coefficient; determining whether the corrected update distortion compensation coefficient is within an output range of the look-up table; causing a computer to execute a process of updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table; Distortion compensation program. [Explanation of symbols]

[0114] 11 Distortion compensation calculation section 12. Memory 13 Distortion compensation coefficient calculation section 14 Distortion compensation coefficient correction section 15 Output range determination section 100 Distortion compensation circuit 111 Power calculation section 112 Multiplication section 141 Multiplication section 142 Memory 143 Correction table update unit ADC Analog / Digital Converter CT correction table DAC Digital to Analog Converter LUT Lookup Table PA Power Amplifier QM1 Quadrature Modulation Section QM2 Quadrature demodulation section

Claims

1. A memory for storing a lookup table including a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation calculation unit that reads out a distortion compensation coefficient from the lookup table based on an input digital transmission signal and multiplies the digital transmission signal by the distortion compensation coefficient; a distortion compensation coefficient calculation unit that calculates an update distortion compensation coefficient based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; A correction unit that corrects the distortion compensation coefficient for update; a determination unit that determines whether or not the update distortion compensation coefficient corrected by the correction unit is within an output range of the lookup table, updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table; Distortion compensation circuit.

2. when the corrected distortion compensation coefficient for update is not within an output range of the lookup table, the lookup table is not updated, and the correction condition is changed in the correction unit to correct the distortion compensation coefficient for update again. The distortion compensation circuit according to claim 1 .

3. The correction unit is a correction memory for storing a correction table including a correction coefficient to be multiplied by the distortion compensation coefficient for update; and an update unit that updates the correction table when the corrected update distortion compensation coefficient is not within an output range of the lookup table.

3. The distortion compensation circuit according to claim 1 or 2.

4. When the corrected distortion compensation coefficient for update exceeds an upper limit of an output range of the lookup table, The update unit updates the correction table so that a correction amount becomes larger than a current amount. The distortion compensation circuit according to claim 3 .

5. The correction memory stores a plurality of correction tables in advance, When the corrected distortion compensation coefficient for update exceeds an upper limit of an output range of the lookup table, the update unit switches from a correction table currently in use to a correction table with a larger correction amount; The distortion compensation circuit according to claim 3 .

6. When the corrected update distortion compensation coefficient falls below a lower limit of an output range of the lookup table, The update unit updates the correction table so that a correction amount becomes smaller than a current amount. The distortion compensation circuit according to claim 3 .

7. The correction memory stores a plurality of correction tables in advance, When the corrected update distortion compensation coefficient falls below a lower limit of an output range of the lookup table, the update unit switches from a correction table currently in use to a correction table having a smaller correction amount; The distortion compensation circuit according to claim 3 .

8. a distortion compensation circuit that performs distortion compensation processing on an input digital transmission signal; a converter for converting the distortion-compensated digital transmission signal into an analog transmission signal; a power amplifier that amplifies the power of the analog transmission signal; The distortion compensation circuit includes: A memory for storing a lookup table including a distortion compensation coefficient to be multiplied by a digital transmission signal; a distortion compensation calculation unit that reads out a distortion compensation coefficient from the lookup table based on an input digital transmission signal and multiplies the digital transmission signal by the distortion compensation coefficient; a coefficient update unit that calculates an update distortion compensation coefficient based on a feedback signal fed back from an output of the power amplifier; A correction unit that corrects the distortion compensation coefficient for update; a determination unit that determines whether or not the update distortion compensation coefficient corrected by the correction unit is within an output range of the lookup table, updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table; Radio transmitting device.

9. Based on the input digital transmission signal, a distortion compensation coefficient is read from the lookup table, and the digital transmission signal is multiplied by the distortion compensation coefficient; calculating an update distortion compensation coefficient for updating the look-up table based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; correcting the updated distortion compensation coefficient; determining whether the corrected update distortion compensation coefficient is within an output range of the look-up table; a process of updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table, the process being performed by a computer; Distortion compensation method.

10. Based on the input digital transmission signal, a distortion compensation coefficient is read from the lookup table, and the digital transmission signal is multiplied by the distortion compensation coefficient; calculating an update distortion compensation coefficient for updating the look-up table based on a feedback signal from an output side of the digital transmission signal multiplied by the distortion compensation coefficient; correcting the updated distortion compensation coefficient; determining whether the corrected update distortion compensation coefficient is within an output range of the look-up table; causing a computer to execute a process of updating the lookup table when the corrected update distortion compensation coefficient is within an output range of the lookup table; Distortion compensation program.

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