JP2015032841A - Transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter in which correction accuracy of IQ imbalance of a transmission system can be improved in a small additional circuit, without requiring the timing adjustment.SOLUTION: A transmitter 100 that is a device used for predetermined correction generates a modulation signal by performing quadrature modulation for a complex signal consisting of an in-phase signal and an orthogonal signal, and transmitting the modulation signal after power amplification, and generates a feedback signal by performing orthogonal demodulation for the modulation signal after power amplification. The transmitter 100 includes an envelope detector 7 for detecting an amount of variation in the envelope of a modulation signal after power amplification, and a transmission IQ imbalance correcting section 13 for determining correction coefficients on the basis of the amount of variation in the envelope, and correcting the IQ imbalance generated during orthogonal modulation by using the correction coefficients.

Description

  The present invention relates to a transmission apparatus that corrects an imbalance of a complex signal composed of an in-phase signal and a quadrature signal.

  Conventionally, in the field of wireless communication using quadrature modulation, a complex signal (hereinafter referred to as “IQ signal”) composed of an in-phase signal (hereinafter referred to as “I signal”) and a quadrature signal (hereinafter referred to as “Q signal”). A technique for correcting imbalance is known. This technique is disclosed in Patent Documents 1 and 2, for example.

  The transmitter of Patent Literature 1 shifts the phase of a transmission signal that has been orthogonally modulated and power amplified in a transmission path (also referred to as “transmission system”) by 90 degrees in phase shift in the reception path (also referred to as “reception system”). The signal is converted into a signal, and further converted from analog to digital, thereby generating a feedback signal. The transmitter corrects the imbalance (hereinafter referred to as “IQ imbalance”) of the IQ signal included in the quadrature modulator of the transmission path by comparing the feedback signal with the transmission signal before the quadrature modulation. To do.

  The system of Patent Document 2 calculates errors of gain imbalance and phase imbalance, and corrects these values to be zero.

JP 2009-206556 A US Pat. No. 7,382,833

  However, the transmitter of Patent Document 1 and the system of Patent Document 2 each have the following problems.

  FIG. 1 is a diagram illustrating a configuration example of a transmitter disclosed in Patent Document 1. As shown in FIG. 1, the transmitter of Patent Document 1 includes a detection unit 15 including a 90 ° phase shifter 21 and a mixer 22 in the reception path. The 90 ° phase shifter 21 is provided separately from the 90 ° phase shifter 14 for quadrature modulation. For this reason, detection accuracy of amplitude error and phase error generated between the I signal and the Q signal deteriorates due to, for example, dispersion variation during manufacturing. Therefore, there is a problem that the IQ imbalance correction accuracy deteriorates.

  Further, the transmitter of Patent Document 1 includes a detection unit 15 as a dedicated circuit for detecting a feedback amount. Therefore, there is a problem that the circuit scale becomes large.

  Further, the system of Patent Document 2 needs to perform timing adjustment so that transmission data and reception data match when IQ imbalance is corrected. However, there is a possibility that a timing error occurs during the adjustment, resulting in a residual error. is there. Therefore, there is a problem that the IQ imbalance correction accuracy deteriorates.

  An object of the present invention is to provide a transmission apparatus that can improve the IQ imbalance correction accuracy of a transmission system with a small number of additional circuits without requiring timing adjustment.

  The transmission device according to one embodiment of the present invention generates a modulation signal by performing quadrature modulation on a complex signal including an in-phase signal and a quadrature signal, transmits the amplified signal after amplification, and transmits the modulated signal to the amplified modulation signal. A transmission device that generates a feedback signal by performing quadrature demodulation and is used for predetermined correction, an envelope detection unit that detects an amount of fluctuation of an envelope of the modulated signal after amplification, and a minimum amount of fluctuation of the envelope And a first correction unit that corrects an imbalance between the in-phase signal and the quadrature signal generated at the time of the quadrature modulation using the searched correction coefficient.

  The present invention can improve the IQ imbalance correction accuracy of the transmission system with few additional circuits without requiring timing adjustment.

The block diagram which shows the structural example of the transmitter which concerns on patent document 1 The block diagram which shows the structural example of the transmitter which concerns on embodiment of this invention The figure which shows the example of signal arrangement | positioning when the orthogonal modulation part of the transmitter which concerns on embodiment of this invention performs QPSK modulation | alteration The figure which shows the waveform example of the amplitude component of the radio | wireless signal after amplification in the case where there is IQ imbalance in the orthogonal modulation part of the transmitter which concerns on embodiment of this invention, and when it does not exist The figure which shows the waveform example of the power component of the radio | wireless signal after amplification in the case where IQ imbalance exists in the orthogonal modulation part of the transmitter which concerns on embodiment of this invention, and when it does not exist The block diagram which shows the structural example of the transmission IQ imbalance correction part of the transmitter which concerns on embodiment of this invention The figure which shows the circuit structural example of the correction calculation execution part of the transmitter which concerns on embodiment of this invention A graph showing the relationship between the correction coefficients σ and φ and the maximum value of the envelope when there is no IQ imbalance The flowchart which shows the operation example 1 of the correction coefficient search part of the transmitter which concerns on embodiment of this invention. The flowchart which shows the operation example 2 of the correction coefficient search part of the transmitter which concerns on embodiment of this invention The flowchart which shows the operation example 3 of the correction coefficient search part of the transmitter which concerns on embodiment of this invention The block diagram which shows the structural example of the correction coefficient search part of the transmitter which concerns on embodiment of this invention The figure which shows the structural example of the data format of the communication standard which the transmitter which concerns on embodiment of this invention uses

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

<Configuration Example of Transmitting Device 100>
FIG. 2 is a diagram illustrating a configuration example of the transmission device 100 according to the embodiment of the present invention.

  In FIG. 2, a transmitter 100 includes a DSP (Digital Signal Processor) 1, a DAC (Digital Analog Converter) 2, a quadrature modulation unit 3, a local oscillator 4, a power amplifier 5, a quadrature demodulation unit 6, an envelope detection unit 7, and a switching unit. 8 and ADC (Analog Digital Converter) 9.

  The DSP 1 is a circuit that processes a digital signal, and includes a distortion compensation unit 11, a reception IQ imbalance correction unit 12 (an example of a second correction unit), and a transmission IQ imbalance correction unit 13 (an example of a first correction unit). Have.

  The distortion compensator 11 corrects signal distortion generated in the power amplifier 5. This correction is hereinafter referred to as “distortion compensation”. In the present embodiment, the distortion compensation by the distortion compensator 11 includes transmission imbalance correction by the transmission IQ imbalance correction unit 13 (details will be described later) and reception imbalance correction by the reception IQ imbalance correction unit 12 (details will be described later). It is executed after performing each individually. The operation of this circuit will be described below.

  The distortion compensation unit 11 receives the transmission signal TX_Data. This transmission signal is a baseband signal and includes an IQ signal including an I signal (in-phase signal; also referred to as “in-phase component”) and a Q signal (orthogonal signal; also referred to as “orthogonal component”) having a phase orthogonal thereto. (Complex signal). The transmission signal is a single frequency signal having an amplitude that does not cause distortion in the power amplifier 5.

  When receiving the transmission signal TX_Data, the distortion compensator 11 operates according to one of the following two cases.

  One is a case where the distortion compensation unit 11 has not received a feedback signal from the reception IQ imbalance correction unit 12. In other words, before transmission imbalance correction and reception imbalance correction are performed. The feedback signal here is a signal output from the power amplifier 5 and is a signal that has passed through the quadrature demodulation unit 6, the switching unit 8, the ADC 9, and the reception IQ imbalance correction unit 12. In this case, the distortion compensation unit 11 does not perform distortion compensation, and outputs the input transmission signal TX_Data as it is to the transmission IQ imbalance correction unit 13 as the transmission signal TX_Data_PD.

  The other is a case where the distortion compensation unit 11 receives a feedback signal from the reception IQ imbalance correction unit 12. In other words, after the transmission imbalance correction and the reception imbalance correction are executed. In this case, the distortion compensation unit 11 performs distortion compensation based on the feedback signal and the transmission signal TX_Data. For this distortion compensation, for example, a known technique called digital predistortion is applied.

  Here, a specific example of distortion compensation will be described. First, the distortion compensation unit 11 detects an error between the feedback signal and the transmission signal TX_Data, and obtains a distortion characteristic of the power amplifier 5. Next, the distortion compensation unit 11 calculates a correction coefficient as a correction value that cancels the distortion characteristics. Then, the distortion compensation unit 11 multiplies the transmission signal TX_Data by the correction coefficient. Thereby, the non-linear distortion of the power amplifier 5 is corrected, and the linearity of the amplitude characteristic and the phase characteristic is ensured. Thereafter, the distortion compensation unit 11 outputs the transmission signal TX_Data_PD after distortion compensation to the transmission IQ imbalance correction unit 13.

  The reception IQ imbalance correction unit 12 corrects the IQ imbalance of the orthogonal demodulation unit 6. This correction is hereinafter referred to as “reception imbalance correction”. The IQ imbalance is, for example, a phase error (also referred to as “phase imbalance”) and an amplitude error (also referred to as “amplitude imbalance”) between the I signal and the Q signal. In the present embodiment, the reception imbalance correction by the reception IQ imbalance correction unit 12 is executed after the transmission imbalance correction by the transmission IQ imbalance correction unit 13 and before the distortion compensation by the distortion compensation unit 11. .

  The reception IQ imbalance correction unit 12 receives a feedback signal from the ADC 9. The feedback signal here is an output signal from the power amplifier 5 and is a signal that has passed through the quadrature demodulation unit 6, the switching unit 8, and the ADC 9.

  Next, the reception IQ imbalance correction unit 12 performs reception imbalance correction so that the IQ imbalance in the feedback signal is minimized. Then, the reception IQ imbalance correction unit 12 outputs the feedback signal after the reception imbalance correction to the distortion compensation unit 11. This feedback signal is used for distortion compensation of the distortion compensator 11 as described above.

  The transmission IQ imbalance correction unit 13 corrects an IQ imbalance that occurs between the I signal and the Q signal when the quadrature modulation unit 3 performs quadrature modulation. This correction is hereinafter referred to as “transmission imbalance correction”. In the present embodiment, the transmission imbalance correction by the transmission IQ imbalance correction unit 13 is executed before the reception imbalance correction by the reception IQ imbalance correction unit 12 and the distortion compensation by the distortion compensation unit 11.

  The transmission IQ imbalance correction unit 13 receives the transmission signal TX_Data_PD from the distortion compensation unit 11. As described above, this transmission signal is either a transmission signal before distortion compensation or a transmission signal after distortion compensation.

  First, when the transmission signal TX_Data_PD is a transmission signal before distortion compensation and the envelope value FB_ENV has not yet been detected, the transmission IQ imbalance correction unit 13 uses the transmission signal TX_Data_PD as it is as the transmission signal TX_Data_CR as DAC2 Output to. This transmission signal is used as a test signal for detecting the envelope value in the envelope detector 7. The envelope value FB_ENV is the value of the envelope (envelope) of the test signal output from the power amplifier 5 and is detected by the envelope detector 7. A specific example of this envelope will be described later with reference to FIGS.

  Thereafter, the transmission IQ imbalance correction unit 13 inputs the envelope value FB_ENV via the switching unit 8 and the ADC 9. Then, the transmission IQ imbalance correction unit 13 optimizes the correction coefficient based on the envelope value FB_ENV. That is, the transmission IQ imbalance correction unit 13 searches for a correction coefficient that can minimize the fluctuation of the envelope value FB_ENV. A specific example of the correction coefficient search will be described in operation examples 1 to 3 described later.

  After optimization of the correction coefficient, the transmission IQ imbalance correction unit 13 newly inputs a transmission signal TX_Data_PD (transmission signal before distortion compensation). Then, the transmission IQ imbalance correction unit 13 performs transmission imbalance correction on the newly input transmission signal TX_Data_PD using the optimized correction coefficient. Thereby, for example, the amplitude level and the phase shift amount of the I signal are corrected, and the IQ imbalance of the quadrature modulation unit 3 is suppressed to the minimum. Thereafter, the transmission IQ imbalance correction unit 13 outputs the transmission signal TX_Data_CR after the transmission imbalance correction to the DAC 2. As described above, this transmission signal is used as a feedback signal for reception imbalance correction in the reception IQ imbalance correction unit 12.

  After the transmission imbalance correction, the transmission IQ imbalance correction unit 13 receives a transmission signal TX_Data_PD that is a transmission signal after distortion compensation. Then, the transmission IQ imbalance correction unit 13 performs transmission imbalance correction on the transmission signal TX_Data_PD using the previously optimized correction coefficient, and outputs the corrected signal to the DAC 2 as the transmission signal TX_Data_CR.

  The DAC 2 receives the transmission signal TX_Data_CR from the transmission IQ imbalance correction unit 13. As described above, this transmission signal is either a transmission signal (test signal) before distortion compensation and before transmission imbalance correction, a transmission signal before distortion compensation and after transmission imbalance correction, or a transmission signal after distortion compensation. It is.

  Then, the DAC 2 converts any one of the transmission signals TX_Data_CR from digital to analog and outputs it to the quadrature modulation unit 3.

  The quadrature modulation unit 3 inputs the analog-converted transmission signal from the DAC 2. Next, the quadrature modulation unit 3 frequency-mixes the analog-converted transmission signal, the in-phase carrier signal output from the local oscillator 4 and the quadrature carrier signal obtained by shifting the carrier signal by 90 °. As a result, a modulation signal having a desired frequency (hereinafter referred to as “radio signal”) is generated. Then, the quadrature modulation unit 3 outputs a radio signal to the power amplifier 5.

  The power amplifier (power amplifier) 5 receives a radio signal from the quadrature modulation unit 3 and amplifies it. Then, the power amplifier 5 outputs the amplified radio signal to a signal distributor (not shown). The signal distributor outputs the radio signal from the power amplifier 5 to an antenna (not shown), the quadrature demodulator 6 and the envelope detector 7. The radio signal output to the antenna is radiated as a radio wave from the antenna.

  The orthogonal demodulator 6 receives a radio signal from the signal distributor. Next, the quadrature demodulator 6 frequency-mixes the input radio signal with the in-phase carrier signal output from the local oscillator 4 and the quadrature carrier signal obtained by shifting the carrier signal by 90 °. As a result, a demodulated signal (baseband signal) is generated. Then, the quadrature demodulation unit 6 outputs the demodulated signal to the switching unit 8. As described above, this demodulated signal is input to the reception IQ imbalance correction unit 12 and used as a feedback signal.

  The envelope detection unit 7 includes a detector 71 and an LPF (Low Pass Filter) 72.

  When receiving a radio signal from the signal distributor, the detector 71 detects an envelope value FB_ENV of the radio signal and outputs it to the switching unit 8 via the LPF 72.

  In the envelope, when IQ imbalance occurs in the quadrature modulation unit 3, fluctuation (also referred to as “variation”) occurs. Here, the fluctuation of the envelope will be described.

  FIG. 3 is a diagram illustrating an example of signal arrangement (constellation map) when the quadrature modulation unit 3 performs QPSK (Quadrature Phase Shift Keying) modulation. When IQ imbalance does not occur in the orthogonal modulation unit 3, a signal point exists at a position indicated by a white circle as shown in FIG. In this case, the trajectory OR1 connecting the four signal points is an ideal constellation trajectory. On the other hand, when IQ imbalance occurs in the quadrature modulation unit 3, a signal point exists at a position indicated by a black circle as shown in FIG. In this case, the trajectory OR2 connecting the four signal points becomes a distorted constellation trajectory. In FIG. 3, σ represents amplitude imbalance, and φ represents phase imbalance.

  FIG. 4A shows an example of the waveform of the amplitude component of the radio signal amplified by the power amplifier 5 when IQ imbalance occurs in the quadrature modulation unit 3. On the other hand, FIG. 4B shows an example of the waveform of the amplitude component of the radio signal amplified by the power amplifier 5 when no IQ imbalance occurs in the orthogonal modulation unit 3. In the waveform shown in FIG. 4A, an envelope variation, that is, fluctuation occurs in the time direction, but in the waveform shown in FIG. 4B, fluctuation does not occur in the time direction.

  FIG. 5A shows an example of the waveform of the power component of the radio signal amplified by the power amplifier 5 when IQ imbalance occurs in the orthogonal modulation unit 3. On the other hand, FIG. 5B shows an example of the waveform of the power component of the radio signal amplified by the power amplifier 5 when IQ imbalance does not occur in the orthogonal modulation unit 3. In the waveform shown in FIG. 5A, fluctuation occurs in the time direction, but in the waveform shown in FIG. 5B, fluctuation does not occur in the time direction.

  The switching unit 8 switches so that either the demodulated signal from the orthogonal demodulation unit 6 or the envelope value FB_ENV from the envelope detection unit 7 is output to the ADC 9. A specific example of switching is as follows.

  When the envelope value FB_ENV is not detected and transmission imbalance correction is not performed, the switching unit 8 switches so that the envelope value FB_ENV from the envelope detection unit 7 is output to the ADC 9. On the other hand, when the envelope value FB_ENV has been detected and transmission imbalance correction has been performed, the switching unit 8 switches so that the demodulated signal from the orthogonal demodulation unit 6 is output to the ADC 9.

  The ADC 9 receives either the demodulated signal or the envelope value FB_ENV from the switching unit 8 and converts it from analog to digital. First, when the envelope value FB_ENV is input, the ADC 9 digitally converts the envelope value FB_ENV and outputs it to the transmission IQ imbalance correction unit 13. The envelope value FB_ENV is used for optimization of the correction coefficient as described above. Thereafter, when a demodulated signal is input, the ADC 9 digitally converts the demodulated signal and outputs the digital signal to the reception IQ imbalance correction unit 12. As described above, this demodulated signal is used for reception imbalance correction as a feedback signal.

  By providing the above configuration, transmitting apparatus 100 of the present embodiment has the following operational effects.

  The first effect is as follows. Since transmitting apparatus 100 performs transmission imbalance correction based on fluctuations in the envelope of a radio signal (output signal after power amplification), it is not necessary to provide a demodulating mixer in the detector of the receiving path. Therefore, transmission imbalance correction can be realized with a small number of additional circuits.

  The second effect is as follows. In the prior art (for example, the system of Patent Document 2), in order to calculate the IQ imbalance of the quadrature modulator, the calculation of the difference between the transmission signal, which is a baseband signal, and the demodulated data at the timing corresponding thereto, that is, the timing adjustment Had to do. However, if the timing adjustment is not performed accurately, a timing error occurs and a residual error occurs, resulting in a problem that the IQ imbalance correction accuracy deteriorates. On the other hand, the transmitting apparatus 100 only needs to detect the fluctuation of the envelope of the radio signal (output signal after power amplification), and therefore does not require timing adjustment when correcting transmission imbalance. Therefore, the transmission apparatus 100 does not have a possibility of causing a timing error and a residual error unlike the conventional technique, and the IQ imbalance correction accuracy does not deteriorate. As a result, the transmission device 100 can improve transmission characteristics.

  The effects of the third eye are as follows. Conventionally, there are IEEE802.15.4g and IEEE802.11ah currently being developed in the 920MHz band used for sensor wireless, and considering the future, there is a demand to minimize power leakage to other channels. . Therefore, it is necessary to improve the performance of digital predistortion and transmission imbalance correction and improve the transmission characteristics. However, in the conventional transmission apparatus, distortion compensation is performed using a feedback signal including all of the distortion of the power amplifier, the IQ imbalance of the quadrature modulation unit, and the IQ imbalance of the quadrature demodulation unit. The effect remains, and the IQ imbalance correction accuracy deteriorates. As a result, transmission characteristics are degraded. Therefore, the transmission apparatus 100 individually performs transmission imbalance correction, reception imbalance correction, and distortion compensation in this order. As a result, IQ imbalance does not remain, and IQ imbalance correction accuracy does not deteriorate. As a result, the transmission device 100 can improve transmission characteristics.

  The fourth effect is as follows. The conventional technique (for example, the system of Patent Document 2) estimates the gain imbalance and the phase imbalance by calculation and directly corrects them, so that the amount of calculation increases. On the other hand, the transmitting apparatus 100 only needs to detect envelope fluctuations, and therefore requires a smaller amount of calculation than the prior art.

<Configuration Example of Transmission IQ Imbalance Correction Unit 13>
FIG. 6 is a diagram illustrating a configuration example of the transmission IQ imbalance correction unit 13.

  In FIG. 3, the transmission IQ imbalance correction unit 13 includes a correction calculation execution unit 131 and a correction coefficient search unit 132.

  The correction calculation execution unit 131 inputs correction coefficients σ and φ from a correction coefficient search unit 132, which will be described later, and performs a correction calculation (transmission imbalance correction) on the baseband signal (transmission signal TX_Data_PD) based on the correction coefficients. Do. Then, the correction calculation execution unit 131 outputs the corrected baseband signal (transmission signal TX_Data_CR) to the DAC 2.

Considering that IQ imbalance occurs in the transmission output, it is possible to cancel IQ imbalance as a total characteristic if the reverse characteristic is given in the baseband region in advance. If the transmission characteristics shown in FIG. 3 are obtained due to the influence of IQ imbalance, for example, the relationship between the signals (Iout, Qout) and the baseband signals (IDT, QDT) considered by shifting the transmission output to the baseband signal is as follows. As shown in equation (1).

In the above formula (1), A is a scalar. Therefore, if an inverse characteristic of X can be given to the baseband signal in advance, it is possible to cancel the IQ imbalance of the transmission apparatus 100. The inverse matrix of X can be given by the following equation (2).

  Δ is a scalar and is approximately 1. Here, the correction calculation execution unit 131 has a circuit configuration shown in FIG. 7 in order to realize the calculation of Expression (2). Therefore, the correction calculation execution part 131 can give the reverse characteristic of IQ imbalance with respect to a baseband signal by using the circuit structure of FIG. For this purpose, it is necessary to obtain in advance in the correction coefficient search unit 132 σ and φ that are sources of the correction coefficient.

  The correction coefficient search unit 132 receives the envelope value FB_ENV of the transmission signal from the ADC 9 and searches for optimum values of the correction coefficients σ and φ based on the envelope value. Then, the correction coefficient search unit 132 outputs the correction coefficients σ and φ as the optimum values to the correction calculation execution unit 131.

  The envelope value FB_ENV input to the correction coefficient search unit 132 is, for example, a value corresponding to the constellation trajectory shown in FIG. Specifically, when there is no IQ imbalance, the envelope value FB_ENV is a value corresponding to the trajectory OR1 that is a perfect circle. On the other hand, when there is IQ imbalance, the envelope value FB_ENV is a value corresponding to the orbit OR2 which is an ellipse.

  Therefore, (σ, φ) is used as a parameter to check the change in the envelope value of the transmission signal (hereinafter referred to as “transmission envelope”), and if the maximum value (σ, φ) can be detected, Can be considered as an optimum value for correcting IQ imbalance. As an example, FIG. 8 shows an example of the result of calculating what value the maximum value of the transmission envelope becomes by changing (σ, φ) when there is no IQ imbalance.

  FIG. 8A is a graph plotting the relationship between σ and the maximum value of the transmission envelope when φ is swung from -3 to +3 (an example of a search range). FIG. 8B is a graph plotting the relationship between the maximum value of the transmission envelope and φ when σ is swung from −0.5 to +0.5 (an example of a search range). From the graphs of FIGS. 8A and 8B, the maximum value of the transmission envelope is minimum when σ is 0 regardless of the value of φ, and when φ is 0 regardless of the value of σ. I understand. That is, when there is no IQ imbalance, (σ, φ) = (0, 0) can be said to be the optimum value. Even if there is IQ imbalance, it is possible to retrieve the optimum value by sweeping σ and φ independently.

  For this reason, it is possible to search the optimum values for the correction coefficients σ and φ by operating the correction coefficient search unit 132 according to any one of the operation examples 1 to 3 described below.

<Operation Example 1 of Correction Coefficient Search Unit 132>
Hereinafter, an example (operation example 1) of the operation of the correction coefficient search unit 132 will be described with reference to the flowchart of FIG.

  Prior to step S11, the correction coefficient search unit 132 determines a predetermined σ in a predetermined search range of σ as a set value (initial value).

  In step S11, the correction coefficient search unit 132 detects the maximum value MAX of the transmission envelope FB_ENV. The search range here is, for example, the range of “−0.5 to +0.5” described above. The maximum value MAX here is, for example, the MAX shown in FIGS. 4A and 5A.

  In step S12, the correction coefficient search unit 132 determines whether or not the maximum value MAX detected this time is smaller than the maximum value MAX of the past transmission envelope FB_ENV. As a result of the determination, when the maximum value MAX detected this time is not smaller than the maximum value MAX of the past transmission envelope FB_ENV (step S12: NO), the flow proceeds to step S14. On the other hand, as a result of the determination, if the maximum value MAX detected this time is smaller than the maximum value MAX of the past transmission envelope FB_ENV (step S12: YES), the flow proceeds to step S13.

  In step S13, the correction coefficient search unit 132 holds the maximum value MAX of the transmission envelope FB_ENV detected this time and the current set value σ.

  In step S14, the correction coefficient search unit 132 determines whether or not the search range of σ has ended. As a result of the determination, if the search range of σ is completed (step S14: YES), the flow proceeds to step S17. On the other hand, as a result of the determination, the search range of σ has not ended (step S14: NO), the flow proceeds to step S15.

  In step S15, the correction coefficient search unit 132 updates the current set value σ to another value within the search range.

  In step S16, the correction coefficient search unit 132 stands by for a time during which the updated σ is reflected in the feedback envelope. Thereafter, the flow returns to step S11.

  In step S <b> 17, the correction coefficient search unit 132 outputs the held σ as an optimum value, for example, to the correction calculation execution unit 131.

  After step S17, steps S18 to S24 are performed as a search for the optimum value of φ.

  Similar to the search for the optimum value of σ described above, the correction coefficient search unit 132 determines a predetermined φ in a predetermined search range of φ as a set value (initial value) before step S18.

  In step S18, the correction coefficient search unit 132 detects the maximum value MAX of the transmission envelope FB_ENV. The search range here is, for example, the range of “−0.5 to +0.5” described above. The maximum value MAX here is, for example, the MAX shown in FIGS. 4A and 5A.

  In step S19, the correction coefficient search unit 132 determines whether or not the maximum value MAX detected this time is smaller than the maximum value MAX of the past transmission envelope FB_ENV. As a result of the determination, if the maximum value MAX detected this time is not smaller than the maximum value MAX of the past transmission envelope FB_ENV (step S19: NO), the flow proceeds to step S21. On the other hand, as a result of the determination, if the maximum value MAX detected this time is smaller than the maximum value MAX of the past transmission envelope FB_ENV (step S19: YES), the flow proceeds to step S20.

  In step S20, the correction coefficient search unit 132 holds the maximum value MAX of the transmission envelope FB_ENV detected this time and the current set value φ.

  In step S21, the correction coefficient search unit 132 determines whether or not the search range of φ has ended. As a result of the determination, if the search range of φ is ended (step S21: YES), the flow proceeds to step S24. On the other hand, as a result of the determination, the search range of φ has not ended (step S21: NO), the flow proceeds to step S22.

  In step S22, the correction coefficient search unit 132 updates the current set value φ to another value within the search range.

  In step S23, the correction coefficient search unit 132 stands by for a time during which the updated φ is reflected in the feedback envelope. Thereafter, the flow returns to step S18.

  In step S24, the correction coefficient search unit 132 outputs the held φ as an optimum value to, for example, the correction calculation execution unit 131.

  According to the operation example 1 described above, the correction coefficient search unit 132 can search for the optimal correction coefficients σ and φ.

<Operation Example 2 of Correction Coefficient Search Unit 132>
In the operation example 1, the sweep coefficient is used to search for the correction coefficient (σ, φ) that minimizes the maximum value of the transmission envelope. In this operation example, the correction coefficient (σ, φ) that maximizes the minimum value of the transmission envelope. ). Thereby, also in this operation example, the same effect as that of the operation example 1 can be obtained.

  Hereinafter, an example (operation example 2) of the operation of the correction coefficient search unit 132 will be described with reference to the flowchart of FIG.

  Prior to step S31, the correction coefficient search unit 132 determines a predetermined σ in a predetermined search range of σ as a set value (initial value).

  In step S31, the correction coefficient search unit 132 detects the minimum value MIN of the transmission envelope FB_ENV. The search range here is, for example, the range of “−0.5 to +0.5” described above. The minimum value MIN here is, for example, the MIN shown in FIGS. 4A and 5A.

  In step S32, the correction coefficient search unit 132 determines whether or not the minimum value MIN detected this time is larger than the minimum value MIN of the past transmission envelope FB_ENV. As a result of the determination, if the minimum value MIN detected this time is not larger than the minimum value MIN of the past transmission envelope FB_ENV (step S32: NO), the flow proceeds to step S34. On the other hand, as a result of the determination, if the minimum value MIN detected this time is larger than the minimum value MIN of the past transmission envelope FB_ENV (step S32: YES), the flow proceeds to step S33.

  In step S33, the correction coefficient search unit 132 holds the minimum value MIN of the transmission envelope FB_ENV detected this time and the current set value σ.

  Steps S34 to S37 are the same as steps S14 to S17 in FIG. Further, after step S37 (including the setting of the initial value φ), steps S38 to S44 are performed as a search for the optimal value of φ. The flow is the same as the search for the optimal value of σ in steps S31 to S37. Therefore, explanation here is omitted.

<Operation Example 3 of Correction Coefficient Search Unit 132>
In the operation example 2, the sweep coefficient is used to search for the correction coefficient (σ, φ) that maximizes the minimum value of the transmission envelope. However, in this operation example, the correction that minimizes | maximum value−minimum value | of the transmission envelope is minimized. Search for coefficients (σ, φ). Thereby, also in this operation example, the same effect as in the operation example 2 can be obtained.

  Hereinafter, an example (operation example 3) of the operation of the correction coefficient search unit 132 will be described with reference to the flowchart of FIG.

  Prior to step S51, the correction coefficient search unit 132 determines a predetermined σ within a predetermined search range of σ as a set value (initial value).

  In step S51, the correction coefficient search unit 132 detects the absolute value | MAX−MIN | of the difference between the maximum value MAX and the minimum value MIN of the transmission envelope FB_ENV. The search range here is, for example, the range of “−0.5 to +0.5” described above. The absolute value | MAX−MIN | here is an absolute value of the difference between MAX and MIN shown in FIGS. 4A and 5A, for example.

  In step S52, the correction coefficient search unit 132 determines whether or not the absolute value | MAX−MIN | detected this time is smaller than the absolute value | MAX−MIN | of the past transmission envelope FB_ENV. If the absolute value | MAX-MIN | detected this time is not smaller than the absolute value | MAX-MIN | of the past transmission envelope FB_ENV as a result of the determination (step S52: NO), the flow proceeds to step S54. On the other hand, if the absolute value | MAX-MIN | detected this time is smaller than the absolute value | MAX-MIN | of the past transmission envelope FB_ENV as a result of the determination (step S52: YES), the flow proceeds to step S53.

  In step S53, the correction coefficient search unit 132 holds the absolute value | MAX−MIN | of the transmission envelope FB_ENV detected this time and the current set value σ.

  Steps S54 to S57 are the same as steps S14 to S17 in FIG. 9, and a description thereof will be omitted here. Further, after step S57 (including setting of the initial value φ), steps S58 to S64 are performed as a search for the optimal value of φ, and the flow is the same as the search for the optimal value of σ in steps S51 to S57. Therefore, explanation here is omitted.

<Configuration Example of Correction Coefficient Search Unit 132>
The above-described correction coefficient searching unit 132 may be able to select the correction coefficients σ and φ according to temperature and power supply fluctuations. A configuration example for realizing this will be described below. FIG. 12 is a block diagram illustrating a configuration example of the correction coefficient search unit 132.

  In FIG. 12, the correction coefficient search unit 132 includes an execution unit 1321, a learning unit 1322, a table unit 1323, and a selection unit 1324. Further, the correction coefficient search unit 132 is connected to the temperature / power supply fluctuation detection unit 133.

  The temperature / power supply fluctuation detection unit 133 detects the temperature state of the transmission device 100 and the power supply state of the transmission device 100, and outputs them to the correction coefficient search unit 132.

  The execution unit 1321 executes the flow of any one of the operation examples 1 to 3.

  The learning unit 1322 associates the correction coefficient input from the execution unit 1321 with the temperature and power supply state input from the temperature / power supply fluctuation detection unit 133 and writes them in the table unit 1323.

  The table unit 1323 receives the correction coefficient corresponding to the temperature and the power supply state from the learning unit 1322 and stores it. By this storage, a correction coefficient corresponding to the temperature and the power supply state is learned.

  The selection unit 1324 selects the correction coefficient input from the execution unit 1321 during learning of the correction coefficient, and outputs the correction coefficient to the correction calculation execution unit 131. On the other hand, when the learning of the correction coefficient is completed, the selection unit 1324 selects the correction coefficient corresponding to the temperature and power supply state input from the temperature / power supply fluctuation detection unit 133 from the table unit 1323, and the correction calculation execution unit. It outputs to 131.

  According to the above configuration, the optimum IQ imbalance correction can be performed with respect to the current temperature and power supply state. Note that fine adjustment can be further performed by performing interpolation processing on the correction coefficient stored in the table unit 1323.

<Operation Timing of Correction Coefficient Search Unit 132>
The timing when the correction coefficient search unit 132 described above executes the above-described operation flow will be described.

  In a general communication standard, a known pattern is embedded in the header portion of a transmission signal. 13 is a diagram illustrating a configuration example of a data format of a communication standard (IEEE.802.11ah) used by the transmission apparatus 100. In FIG. 13, training areas called STF (Short Training Field) and LTF (Long Training Field) are provided at the top.

  The STF is an area where the envelope is almost constant and can be used for transmission power control and the like. The LTF is an area used for AGC (Automatic Gain Control) or the like of a receiving system where there is a large fluctuation of the envelope.

  The correction coefficient search unit 132 can perform IQ imbalance correction (transmission imbalance correction) in the initial state of communication by executing any one of the above-described operation flows in the STF having a substantially constant envelope. As a result, communication processing can be realized with high quality.

  While the present embodiment has been described above, the above embodiment is an example, and various modifications can be made.

  As described above, the transmission device of the present disclosure generates a modulated signal by performing quadrature modulation on a complex signal composed of an in-phase signal and a quadrature signal, transmits the amplified signal after amplification, and performs quadrature demodulation on the amplified modulated signal. Is a transmitter that generates a feedback signal and performs a predetermined correction, and includes an envelope detector that detects an amount of fluctuation of the envelope of the modulated signal after amplification, and a correction that minimizes the amount of fluctuation of the envelope A first correction unit that searches for a coefficient and corrects an imbalance between the in-phase signal and the quadrature signal generated during the quadrature modulation using the searched correction coefficient.

  In the transmission device of the present disclosure, the first correction unit searches for a correction coefficient that minimizes the maximum value of the envelope variation.

  In the transmission device according to the present disclosure, the first correction unit searches for a correction coefficient that maximizes the minimum value of the envelope variation.

  In the transmission device according to the present disclosure, the first correction unit searches for a correction coefficient that minimizes the absolute value of the difference between the maximum value and the minimum value of the fluctuation amount of the envelope.

  Further, in the transmission device of the present disclosure, the first correction unit learns in advance the correspondence between the searched correction coefficient and the temperature and power supply state, and calculates the correction coefficient based on the detected temperature and power supply state. select.

  In the transmission device according to the present disclosure, the first correction unit performs correction using the correction coefficient using a training signal in which a transmission envelope is constant.

  Further, in the transmission device of the present disclosure, based on the feedback signal, a second correction unit that corrects an imbalance that occurs during the quadrature demodulation, an output from the second correction unit, and a complex signal before the quadrature modulation And a distortion compensator for correcting distortion generated at the time of amplification.

  The present invention is useful for a technique (for example, an apparatus, a system, a method, and a program) that corrects an imbalance of a complex signal composed of an in-phase signal and a quadrature signal.

1 DSP
2 DAC
3 Quadrature Modulation Unit 4 Local Oscillator 5 Power Amplifier 6 Orthogonal Demodulation Unit 7 Envelope Detection Unit 8 Switching Unit 9 ADC
DESCRIPTION OF SYMBOLS 11 Distortion compensation part 12 Reception IQ imbalance correction part 13 Transmission IQ imbalance correction part 14, 21 90 degree phase shifter 15 Detection part 22 Mixer 71 Detector 72 LPF
DESCRIPTION OF SYMBOLS 100 Transmission apparatus 131 Correction calculation execution part 132 Correction coefficient search part 133 Temperature / power supply fluctuation | variation detection part 1321 Execution part 1322 Learning part 1323 Table part 1324 Selection part

Claims (7)

A modulated signal is generated by performing quadrature modulation on a complex signal composed of an in-phase signal and a quadrature signal, transmitted after amplification, and a feedback signal is generated by performing quadrature demodulation on the modulated signal after amplification. A transmission device used for predetermined correction,
An envelope detector for detecting the amount of fluctuation of the envelope of the modulated signal after amplification;
A first correction unit that searches for a correction coefficient that minimizes the amount of fluctuation of the envelope, and corrects an imbalance between the in-phase signal and the quadrature signal generated during the quadrature modulation using the searched correction coefficient; Having
Transmitter device. The first correction unit includes:
Searching for a correction coefficient that minimizes the maximum value of the fluctuation amount of the envelope;
The transmission device according to claim 1. The first correction unit includes:
Searching for a correction coefficient that maximizes the minimum value of the fluctuation amount of the envelope;
The transmission device according to claim 1. The first correction unit includes:
Search for a correction coefficient that minimizes the absolute value of the difference between the maximum value and the minimum value of the fluctuation amount of the envelope,
The transmission device according to claim 1. The first correction unit includes:
Learn in advance the correspondence between the searched correction coefficient and the temperature and power supply status,
Selecting the correction factor based on the detected temperature and power supply status;
The transmission device according to any one of claims 2 to 4. The first correction unit includes:
Correction using the correction coefficient is performed using a training signal in which the transmission envelope is constant.
The transmission device according to any one of claims 2 to 4. A second correction unit that corrects an imbalance that occurs during the quadrature demodulation based on the feedback signal;
A distortion compensation unit that corrects distortion generated during amplification based on the output from the second correction unit and the complex signal before the quadrature modulation;
The transmission device according to any one of claims 1 to 6.

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