JP2013207782A - Transmitter, signal generating device and calibration method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter capable of precisely correcting a distortion of a signal.SOLUTION: The transmitter includes: a test signal generating section 101; a frequency characteristic correcting section 104 that corrects an amplitude characteristic of a test signal and a phase characteristic; a modulator 105; an envelope detection unit 106; a frequency characteristic calculation section 107 that calculates a frequency characteristic of an envelope signal; and a coefficient calculation section 108 that calculates a correction coefficient for correcting the amplitude characteristic and the phase characteristic of the test signal based on the frequency characteristic. The test signal generating section 101 generates a test signal which is asymmetrical when comparing the trajectory of the signal in at least two quadrants from a first quadrant to a fourth quadrant on an IQ plane.

Description

  The present invention relates to a transmitter, a signal generation device, and a calibration method. In particular, it relates to calibration of frequency characteristics in a transmitter.

  In wireless communication, when up-converting a baseband signal as a transmission signal to a high-frequency signal and down-converting from a high-frequency signal as a reception signal to a baseband signal, distortion occurs according to the frequency of the signal. As an apparatus for correcting signal distortion, for example, a frequency characteristic correcting apparatus disclosed in Patent Document 1 is known.

  The frequency characteristic correction apparatus disclosed in Patent Document 1 extracts a part of a transmission signal by a coupling circuit in signal transmission by a transmission system circuit, divides each band division filter into a low frequency side and a high frequency side, and outputs each filter output ( The power level is detected by each power detector. Further, the frequency characteristic correcting device controls the variable equalizer circuit based on the voltage obtained by comparing the outputs of the respective power detectors with each other in the comparison circuit.

JP 2001-16145 A

  The distortion of the signal with respect to the used frequency tends to appear in an analog circuit including a frequency conversion unit, a power amplifier unit, and an LNA unit that perform frequency conversion on a baseband signal and a high-frequency signal, for example. In particular, in communication that handles a wide frequency (for example, 60 GHz band) of millimeter wave communication, since the signal band is large, there is a possibility that communication characteristics are greatly deteriorated.

  When the frequency characteristic correction apparatus of Patent Document 1 is applied to millimeter wave communication, the frequency characteristic of signal distortion is linearly corrected based on the result of signal detection for several frequency components. However, linear correction is not sufficient for large signal distortion that occurs in the process of frequency conversion of baseband signals and high-frequency signals, or signal amplification of wide-band high-frequency signals. There are things to do. Therefore, signal distortion needs to be corrected with higher accuracy.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a transmitter, a signal generation device, and a calibration method that can correct signal distortion with high accuracy.

  The transmitter of the present invention includes a test signal generation unit that generates a test signal, a frequency characteristic correction unit that corrects amplitude characteristics and phase characteristics of the test signal generated by the test signal generation unit, and the frequency characteristic correction unit. A modulation unit that modulates the corrected correction signal, an envelope detection unit that detects an envelope of the modulation signal modulated by the modulation unit, and a frequency characteristic of the envelope signal detected by the envelope detection unit A frequency characteristic calculation unit that calculates a correction coefficient for correcting the amplitude characteristic and phase characteristic of the test signal by the frequency characteristic correction unit based on the frequency characteristic calculated by the frequency characteristic calculation unit And the test signal generation unit compares the signal trajectories in at least two quadrants from the first quadrant to the fourth quadrant on the IQ plane. To generate a test signal is asymmetric.

  With this configuration, the amplitude characteristic and phase characteristic of the test signal can be acquired by offsetting the test signal from the origin on the IQ plane. Therefore, since the correction coefficient can be obtained based on the amplitude characteristic and the phase characteristic, signal distortion can be corrected with high accuracy.

  The signal generation device of the present invention includes a test signal generation unit that generates a test signal, a frequency characteristic correction unit that corrects amplitude characteristics and phase characteristics of the test signal generated by the test signal generation unit, and the frequency characteristic correction unit. Based on the frequency characteristic calculated by the frequency characteristic calculation unit, the frequency characteristic calculation unit calculates the frequency characteristic of the envelope signal of the modulation signal modulated by the correction signal corrected by the frequency characteristic correction unit A coefficient calculation unit that calculates a correction coefficient for correcting the amplitude characteristic and phase characteristic of the test signal, and the test signal generation unit includes at least two quadrants of the first to fourth quadrants on the IQ plane. When the signal trajectories are compared, a test signal that is asymmetric is generated.

  With this configuration, the amplitude characteristic and phase characteristic of the test signal can be acquired by offsetting the test signal from the origin on the IQ plane. Therefore, since the correction coefficient can be obtained based on the amplitude characteristic and the phase characteristic, signal distortion can be corrected with high accuracy.

  The calibration method of the present invention includes a test signal generation step for generating a test signal, a frequency characteristic correction step for correcting amplitude characteristics and phase characteristics of the generated test signal, and the corrected correction signal is modulated. A frequency characteristic calculating step for calculating the frequency characteristic of the envelope signal of the modulated signal, and a coefficient for calculating a correction coefficient for correcting the amplitude characteristic and the phase characteristic of the test signal based on the calculated frequency characteristic And calculating a test signal that is asymmetric when the trajectories of the signals are compared in at least two quadrants from the first quadrant to the fourth quadrant on the IQ plane. To do.

  By this method, the amplitude characteristic and phase characteristic of the test signal can be acquired by offsetting the test signal from the origin on the IQ plane. Therefore, since the correction coefficient can be obtained based on the amplitude characteristic and the phase characteristic, signal distortion can be corrected with high accuracy.

  According to the present invention, signal distortion can be corrected with high accuracy.

The block diagram which shows the structural example of the transmitter in embodiment of this invention (A), (B), (D) is a figure which shows an example of the test signal produced | generated by the test signal generation part in embodiment of this invention, (C) is a figure which shows the phase characteristic of a test signal. The figure which shows an example of the relationship between the component and each amplitude of each angular frequency of the test signal in embodiment of this invention The block diagram which shows the detailed structural example of the frequency characteristic correction | amendment part in embodiment of this invention. The flowchart which shows the 1st operation example in which the transmitter in embodiment of this invention calculates | requires a correction coefficient. The flowchart which shows the 2nd operation example in which the transmitter in embodiment of this invention calculates | requires a correction coefficient. The flowchart which shows the 3rd operation example in which the transmitter in embodiment of this invention calculates | requires a correction coefficient. The figure which shows the simulation result of the amplitude characteristic of the test signal in embodiment of this invention The figure which shows the simulation result of the phase characteristic of the test signal in embodiment of this invention The flowchart which shows the 4th operation example in which the transmitter in embodiment of this invention calculates | requires a correction coefficient. The figure which shows the image which correct | amends the phase characteristic of the test signal in embodiment of this invention to a linear phase characteristic The block diagram which shows the modification structural example of the frequency characteristic correction | amendment part in embodiment of this invention The block diagram which shows the 1st structural example of the radio | wireless apparatus in embodiment of this invention. The block diagram which shows the 2nd structural example of the radio | wireless apparatus in embodiment of this invention.

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

  FIG. 1 is a block diagram illustrating a configuration example of a transmitter 100 according to an embodiment of the present invention. The transmitter 100 includes a test signal generation unit 101, a data generation unit 102, a MUX (Multiplexer) 103, a frequency characteristic correction unit 104, a modulator 105, an envelope detection unit 106, a frequency characteristic calculation unit 107, a coefficient calculation unit 108, and A memory 109 is provided.

  The test signal generation unit 101 generates a test signal for measuring distortion generated by the transmitter 100 and outputs the test signal to the MUX 103. Details of the test signal generation method will be described later.

  The data generation unit 102 generates a baseband signal including data to be transmitted and outputs it to the MUX 103. The transmitted data includes, for example, music data or video data.

  The MUX 103 selects the output of the test signal generation unit 101 or the data generation unit 102 and outputs it to the frequency characteristic correction unit 104. Specifically, in the calibration mode, the test signal that is the output of the test signal generation unit 101 is selected, and in the data transmission mode, the baseband signal that is the output of the data generation unit 102 is selected. The MUX 103 also selects a mode for designating the operation of the transmitter 100.

  The frequency characteristic correction unit 104 corrects the frequency characteristic of the output signal of the MUX 103 based on a parameter (correction coefficient) stored in a LUT (Look Up Table) held by the memory 109 and outputs the correction signal to the modulator 105. . The frequency characteristic includes an amplitude characteristic and a phase characteristic.

出力Ｖ（ｔ）の周波数は、（式１）におけるωに依存し、ｆ＝ω／（２π）によって決定され、例えば６０ＧＨｚである。 The modulator 105 modulates the correction signal output from the frequency characteristic correction unit 104 and outputs a modulation signal (high frequency signal). The output V (t) of the modulator 105 can be expressed by, for example, (Equation 1) below.

The frequency of the output V (t) depends on ω in (Equation 1) and is determined by f = ω / (2π), for example, 60 GHz.

  The envelope detector 106 includes an envelope detector 106A and an AD converter 106B connected in series at the subsequent stage of the envelope detector 106A.

  The envelope detector 106 </ b> A is configured using a detection diode, and detects the envelope of the high-frequency signal output from the modulator 105. The envelope detector 106A receives a part of the output energy of the high frequency signal and detects the size of the envelope of the high frequency signal.

なお、ｃは定数である。 The signal detected by the envelope detector 106A can be expressed by the following (Equation 2).

Note that c is a constant.

  The AD converter 106B converts an analog signal as an envelope detection result into a digital signal, and outputs the digital signal (envelope signal) to the frequency characteristic calculation unit 107.

  The frequency characteristic calculation unit 107 receives the signal (envelope signal) detected by the envelope detection unit 106 and calculates the frequency characteristic of the envelope signal.

  The coefficient calculation unit 108 calculates a correction coefficient for correcting the frequency characteristic of the test signal, that is, the amplitude characteristic and the phase characteristic, based on the frequency characteristic calculated by the frequency characteristic calculation unit 107. The coefficient calculation unit 108 stores the obtained correction coefficient in the LUT 109 held by the memory 109.

  Note that the frequency characteristic calculation unit 107 and the coefficient calculation unit 108 implement each function by executing a program stored in the memory 109. Details of operations of the frequency characteristic calculation unit 107 and the coefficient calculation unit 108 will be described later.

  The transmitter 100 may be configured using a first integrated circuit and a second integrated circuit. The first integrated circuit includes a test signal generation unit 101, a data generation unit 102, a MUX 103, a frequency characteristic correction unit 104, a frequency characteristic calculation unit 107, a coefficient calculation unit 108, and a memory 108. The second integrated circuit includes a modulator 105 and an envelope detector 106. Moreover, all the components in the transmitter 100 may be configured by one integrated circuit.

  In addition, when the transmitter 100 is in the calibration mode, the detection system including the envelope detection unit 106, the frequency characteristic calculation unit 107, and the coefficient calculation unit 108 operates.

  Next, the test signal generation unit 101 will be described.

（式３）において、ω_ｍ,ｎは角周波数、ｄはオフセット量を示す定数、Ｋは振幅を表す定数である。 For example, the test signal generation unit 101 generates a test signal S that can be expressed by the following (Equation 3).

In (Expression 3), ω _{m, n} is an angular frequency, d is a constant indicating an offset amount, and K is a constant indicating an amplitude.

Further, the frequency of the test signal S generated by the test signal generation unit 101 depends on the term “ω _m, nt” in (Expression 3), and is determined by f = ω _m, nt / (2π), For example, 100 MHz or 500 MHz. That is, the angular frequency ω _{m, n} in (Expression 3) is a sufficiently small value as compared with the angular frequency ω in (Expression 1).

  FIG. 2A is a diagram showing the test signal S of (Expression 3) on the IQ plane. The test signal S is indicated by a circle offset from the distance d when compared to a circle C centered at the origin O in the IQ plane and having the same amplitude as the test signal S. Further, the test signal S may or may not rotate on the circle at a constant speed.

  Further, the test signal generation unit 101 generates an IQ signal that is symmetric with respect to the I axis shown in FIG. 2B, even if the test signal is other than the IQ signal represented by (Equation 3). That's fine. Further, an IQ signal that is symmetric with respect to the Q axis may be generated.

  Further, the test signal generation unit 101 may generate an IQ signal rotated around the origin O on the IQ plane from a state that is symmetric with respect to the I axis or the Q axis. Even in these cases, the center of the test signal S is offset from the origin O by a predetermined amount. The test signal S may or may not be rotated on the line at a constant speed. The I axis and the Q axis are examples of the reference axis.

  The test signal generated by the test signal generation unit 101 is in any of the cases of FIG. 2A and FIG. 2B, and passes through a symmetric line (the origin O as shown in FIG. 2C). When the phase of the reference axis is Φ, the amplitude monotonously changes from Φ to Φ + 180 °. FIG. 2D shows a case where the phase of the symmetrical line is Φ in FIG.

  That is, it is sufficient if the trajectories of the test signals in at least two quadrants are compared in the first quadrant to the fourth quadrant on the IQ plane.

  For example, in FIG. 2A, the first quadrant and the second quadrant are asymmetric, the first quadrant and the third quadrant are asymmetric, the second quadrant and the fourth quadrant are asymmetric, and the first quadrant and the fourth quadrant are symmetric. The second quadrant and the third quadrant are symmetric.

  In FIG. 2B, the first quadrant and the second quadrant are asymmetric, the first quadrant and the third quadrant are asymmetric, the second quadrant and the fourth quadrant are asymmetric, the first quadrant and the fourth quadrant are symmetrical, The second quadrant and the third quadrant are symmetric.

  In FIG. 2D, all quadrants are asymmetric.

  If the test signal C of FIG. 2A that draws a circle centered on the origin O on the IQ plane is used, the size of the envelope detected by the envelope detector 106 becomes constant. Therefore, since the test signal C does not have an AC signal, it is difficult to obtain phase characteristics.

  The test signal generation unit 101 can change the size of the envelope by generating the test signal S offset by a predetermined amount from the origin O. Therefore, the amplitude characteristic and the phase characteristic can be acquired by using the test signal S.

In FIG. 3, the test signal generation unit 101 sequentially sweeps (sweeps) the angular frequency ω _{m, n} of the test signal S from n = 1 to n = N. FIG. 3 is a diagram illustrating an example of the relationship between the components of each angular frequency ω _{m, n} of the test signal S and the amplitude. In FIG. 3, the sweep range of the frequency (= ω _m / 2π) of the test signal S is, for example, −1 GHz to 1 GHz, and the interval between adjacent test signals is, for example, 100 MHz.

For example, a test signal having an angular frequency ω _{m, 1} is used as the first test signal S ₁ , and a test signal having an angular frequency ω _{m, n} is used as the nth test signal S _n . Finally, a test signal having an angular frequency ω _{m, N} is used as the Nth test signal S _N. The test signal S _n indicates a component of the angular frequency ω _{m, n} in the test signal S.

The value N is the number of samples for obtaining the frequency characteristics of the test signal S _n. It is preferable that the test signal generation unit 101 sets the value N in consideration of how much frequency interval the frequency characteristic is to be analyzed and how much resolution the frequency characteristic is to be corrected. Further, the value N may be set in advance.

Next, the frequency characteristic correction unit 104 will be described.
FIG. 4 is a block diagram illustrating a detailed configuration example of the frequency characteristic correction unit 104.
The frequency characteristic correction unit 104 includes a Fourier transform unit 204, a multiplier 205, and an inverse Fourier transform unit 206.

  The Fourier transform unit 204 converts a time-domain signal that is an output signal of the MUX 103 into a frequency-domain signal. Since the output signal of the MUX 103 is an IQ signal, the Fourier transform unit 204 performs Fourier transform as complex number data. In the calculation by the Fourier transform unit 204, for example, Fast Fourier Transform (FFT) is used.

  The multiplier 205 multiplies the frequency domain signal output from the Fourier transform unit 204 by the correction coefficient stored in the LUT held by the memory 109.

  The inverse Fourier transform unit 206 converts the frequency domain signal that is the signal output from the multiplier 205 into a time domain signal. In the calculation by the inverse Fourier transform unit 206, for example, an inverse fast Fourier transform (IFFT) is used.

  Next, an operation example in which the transmitter 100 obtains a correction coefficient for correcting the frequency characteristic from the test signal will be described.

FIG. 5 is a flowchart illustrating a first operation example in which the transmitter 100 obtains a correction coefficient for correcting the frequency characteristic from the test signal S. In the example of FIG. 5, it is assumed that the coefficient z _n at each angular frequency ω _{m, n} is obtained by one frequency sweep. In FIG. 5, the coefficient z _n is a correction coefficient.

  First, the test signal generation unit 101 sets a variable n to an initial value 1 (step S401).

Subsequently, the test signal generation unit 101 generates a test signal S _, and sets the angular frequency of the test signal S to ω _{m, n} (step S402).

During the period in which the test signal generation unit 101 performs frequency sweep, the frequency characteristic correction unit 104 does not correct the frequency characteristic, or corrects the frequency characteristic by setting the coefficient z _n stored in the LUT to 1. To do.

Then, the frequency characteristic calculation section 107 receives the envelope signal corresponding to the test signal _{S n} of the angular frequency omega _{m, n,} a Fourier transform (step S403). That is, the frequency characteristic calculation unit 107 has a Fourier transform unit. The frequency characteristic calculation unit 107 uses, for example, fast Fourier transformation (FFT) in order to make the calculation more efficient.

Subsequently, the frequency characteristic calculation unit 107 extracts “a _n + jb _n ” that is the complex number data of the components of the angular frequencies ω _{m and n} in the IQ plane (step S404).

Further, the frequency characteristic calculation unit 107 may calculate the amplitude _mn by (Equation 4) and the phase θ _n by (Equation 5) from the extracted “a _n + jb _n ”.

That is, the frequency characteristic including the amplitude characteristic and the phase characteristic in the component of the angular frequency ω _{m, n} can be acquired by the process of step S404. The frequency characteristic is a frequency characteristic of the transmitter 100 itself, and specifically, is a frequency characteristic of distortion caused by, for example, an analog circuit included in the transmitter 100.

Subsequently, the coefficient calculation unit 108 calculates a coefficient z _n which is complex data for correcting the frequency characteristics of the transmitter 100, and temporarily stores information on the coefficient z _{n in} the coefficient calculation unit 108 (step S1). S405). The coefficient z _n can be expressed by the following (formula 6).

The coefficient z _n can also be expressed by the following (Equation 7) using the amplitude m _n and the phase θ _n .

That is, the coefficient calculation unit 108 calculates the coefficient z _n that is the reciprocal of “a _n + jb _n ” that is the complex number data of the components of the angular frequency ω _{m and n} of the test signal S. The coefficient z _n is the inverse characteristic of the frequency characteristic of the transmitter 100.

Subsequently, the test signal generation unit 101 determines whether or not the test signal _SN having the last angular frequency component has been swept (step S406). That is, the test signal generation unit 101 determines whether n ≧ N.

If the test signal S _N has not been swept up to the last test signal S _N , the test signal generator 101 sweeps the angular frequency ω _{m, n} of the test signal S _{n in} order to analyze the frequency of the next test signal (step S407). That is, 1 is added to the variable n. Then, the process proceeds to step S402.

On the other hand, when the sweep is performed up to the last test signal S _N , the coefficient calculation unit 108 stores information on each coefficient z _n at each angular frequency ω _{m, 1 to} ω _{m, N} temporarily stored therein in the memory 109. (Step S408).

According to the process of FIG. 5, analyzes the frequency of the test signal S _n at each angular frequency omega _{m, n,} by calculating the coefficients z _n, the frequency characteristic obtained by adding the amplitude characteristics and phase characteristics of the test signal S _n Can be corrected. Further, by generating a modulation signal from the corrected baseband signal, it is possible to transmit a signal having a flat amplitude characteristic and phase characteristic. Further, since the inverse of the frequency characteristic of the transmitter 100 is used as the inverse characteristic, it can be easily calculated.

In FIG. 5, as the timing of the coefficient writing to LUT, to store all of the angular frequency ω _m, 1 ~ω _m, after calculating the coefficient _{z n} at _n, the coefficients _{z n} in the memory 109 Indicated. That is, after sweeping the angular frequency ω _{m, n} of the test signal S _n N times, the coefficient calculation unit 108 stores the obtained coefficients z _n in the LUT. Other than this _, the coefficient z _n at the angular frequency ω _{m, n} may be stored in the memory 109 each time it is calculated.

FIG. 6 is a flowchart illustrating a second operation example in which the transmitter 100 obtains a correction coefficient for correcting the frequency characteristic from the test signal S. In the example of FIG. 6, the coefficient z _n at each angular frequency ω _{m, n} is repeatedly obtained, and the coefficient y _n based on the coefficient z _n is stored in the LUT. Coefficient _{y n} is sequentially updated.

In Figure 6, the coefficients z _n, a coefficient representing the residual error correction is a coefficient for determining the coefficient y _n. Coefficient _{y n} is a correction coefficient. The coefficient w is a coefficient representing weighting for adding the residual error z _n and is selected between 0 and 1, for example. For example, the coefficient w is set to 0.5.

First, the test signal generation unit 101 sets a variable n to an initial value 1, to set the variable _{y n} to an initial value 0 (step S501).

Subsequently, the transmitter 100 performs the processes of steps S402 to S406 in FIG. When the frequency characteristic is analyzed to the last test signal S _N and the coefficient z _n is obtained, the process proceeds to step S502.

Coefficient calculating unit 108, each _{z n} calculated weighted by a factor w, it is added to each coefficient _{y n} (step S502). Specifically, the coefficient calculation unit 108 calculates y _n = y _n + w × z _n .

Subsequently, the coefficient computation unit 108, the information for each coefficient _{y n} calculated, and stored in the LUT memory 109 holds (step S503). Moreover, if the already stored information of the coefficient y _n is updates the information of the coefficient y _n.

Then, the coefficient calculation unit 108 calculates the difference between the coefficient y _n where the last calculated calculation of coefficients y _n, is smaller than a predetermined threshold value terminates the process of FIG. 6, is larger, the flow returns to step S402 (Step S504).

In the process of FIG. 6, the coefficient calculation unit 108 repeats the calculation of coefficients y _n as the correction coefficient, continue to update the coefficients y _n stored in the LUT. For example, the result of adding by weighted coefficients z _n in the coefficient y _n, updating the coefficients y _n.

According to the process of FIG. 6, the repeatedly calculates the coefficients z _n at each angular frequency omega _{m, n,} the correction accuracy of the coefficient y _n as the correction coefficient is improved. Further, repeated calculation of coefficients z _n, by calculating the coefficients y _n with coefficients w, residual error because approaches asymptotically to 0, it is improved further correction accuracy.

  Further, by generating a modulation signal from the corrected baseband signal, it is possible to transmit a signal having a flat amplitude characteristic and phase characteristic.

FIG. 7 is a flowchart illustrating a third operation example in which the transmitter 100 obtains a correction coefficient for correcting the frequency characteristic from the test signal S. Here, the difference from FIG. 6 will be described. In FIG. 7, the coefficient z _n at each angular frequency ω _{m, n} is repeatedly obtained R times.

First, in step S505, the test signal generation unit 101 sets a variable n to an initial value 1, and set the variable y _n to an initial value 0, sets the variable r to the initial value 1.

Further, in step S506, the coefficient calculator 108, a predetermined number of times the calculation of the coefficient _{y n} (R times) to determine whether it has performed. Specifically, the coefficient calculation unit 108 determines whether r ≧ R.

In step S507, the case where the calculation of the coefficient y _n not performed R times, the coefficient calculating unit 108 adds 1 to the variable r, it sets a variable n to 1 to initialize. On the other hand, if the calculation of the coefficient y _n was carried R times, the transmitter 100 terminates the processing of FIG.

Next, simulation of frequency characteristic correction will be described.
FIG. 8 is a diagram illustrating a simulation result of the amplitude characteristic of the test signal. FIG. 9 is a diagram illustrating a simulation result of the phase characteristics of the test signal. FIG. 8 and FIG. 9 show the results of simulation by the operation of FIG. 5, FIG. 6, or FIG.

In the simulation, when generating the test signal, the test signal generation unit 101 sets the sampling frequency to 3.52 GHz and sets the coefficients used in (Equation 3) to K = 1 and d = 0.1. Further, the test signal generation unit 101 sweeps f _m (= 2πω _m ) at intervals of 100 MHz from −1.1 GHz to +1.1 GHz.

  As a filter simulating the frequency characteristics of the transmitter 100, a second-order Butterworth filter having a cutoff frequency of 300 MHz and a passing frequency shifted in the negative direction of 352 MHz is assumed.

  8 and 9, the solid line L1 indicates the filter characteristic, and the white point D1 indicates the frequency characteristic (detection characteristic) of the test signal measured by the frequency characteristic calculation unit 107. Referring to FIGS. 8 and 9, it can be understood that the filter characteristics and the detection characteristics match. Therefore, it can be confirmed that the amplitude characteristic and the phase characteristic can be accurately detected by the detection system of the transmitter 100.

  8 and 9, the dotted line L2 indicates the frequency characteristic (correction characteristic) of the signal corrected by the frequency characteristic correction unit 104 after the correction coefficient is obtained. The dotted line L2 is on a line indicating “0” as the phase characteristic. That is, as a result of the frequency characteristic correction unit 104 correcting the signal using the correction coefficient as the inverse characteristic and modulating the correction signal, the phase characteristic and frequency characteristic of the transmitted signal are flat.

  Further, even if the filter characteristic is offset from the center of the frequency range to be measured and is asymmetric, the frequency characteristic can be analyzed suitably.

  Next, a case where the frequency characteristic of the transmitter 100 is corrected to be a linear phase characteristic will be described.

FIG. 10 is a flowchart illustrating a fourth operation example in which the transmitter 100 obtains a correction coefficient for correcting the frequency characteristic from the test signal S. In FIG. 10, the coefficient _xn is a correction coefficient. In the example of FIG. 10, correction is not performed until the phase characteristic of the signal output from the transmitter 100 becomes flat (similar to the dotted line L2 in FIG. 9) (see FIG. 9), but the phase characteristic becomes a linear characteristic. Correct as follows.

First, steps S401 to S403 in FIG. 5 are performed. When the Fourier transform of the test signal at the angular frequency ω _{m, n} is completed, the process proceeds to step S601.

The frequency characteristic calculation unit 107 extracts “a _n + jb _n ” that is the complex number data of the components of the angular frequency ω _{m, n} in the IQ plane. Further, the frequency characteristic calculation unit 107 calculates the amplitude _mn by (Expression 4) from the extracted “a _n + jb _n ”, and calculates the phase θ _n by (Expression 5) (Step S601).

Then, the coefficient calculation unit 108 calculates the difference △ theta _n the phase theta _n and linear phase characteristics theta _{i, n} (step S602). That is, the coefficient calculation unit 108 calculates Δθ _n = θ _n −θ _{i, n} . In FIG. 11, the linear phase characteristic θ _{i, n} is a characteristic in which the phase decreases linearly as the frequency increases. The memory 109 holds information on the linear phase characteristics θ _{i, n in} advance.

Subsequently, the coefficient calculation unit 108 calculates a coefficient _xn , which is complex data for correcting the frequency characteristics of the transmitter 100, and temporarily stores information on the coefficient _{xn in} the coefficient calculation unit 108 (step S1). S405). The coefficient x _n can be expressed by the following (formula 8) using the amplitude m _n and the phase difference Δθ _n .

That is, the coefficient calculation unit 108, a difference △ theta _n the phase theta _n and linear phase characteristics theta _{i, n} of a complex data of the component of the angular frequency omega _{m, n} of the test signal S _{"a n} + jb n" Based on the amplitude _mn , a coefficient _xn as a correction coefficient is calculated.

  In the transmitter 100, since the transmission system normally has a positive delay time, the phase of the test signal is delayed as the frequency increases (see FIG. 9). The transmission system includes a test signal generation unit 101, a data generation unit 102, a MUX 103, a frequency characteristic correction unit 104, and a modulator 105.

According to the processing in FIG. 10, the coefficient _xn can be brought closer to a linear phase characteristic considering some phase delay without making the frequency characteristic of the transmitter 100 completely opposite in phase. Therefore, the transmitter 100 can obtain good amplitude characteristics and phase characteristics without preparing a filter having a negative delay time.

Further, since it is sufficient to correct the phase characteristic of the signal output from the transmitter 100 to the linear phase characteristic, the amount of calculation is smaller than the correction amount of the inverse characteristic, and the time resource or the bit width resource can be effectively used. Therefore, even when a frequency characteristic having a steep change in a specific frequency such as quantization noise is included, the correction accuracy is improved by providing one parameter (Δθ _n ) and correcting it to the linear phase characteristic. improves.

FIG. 11 is a diagram showing an image for correcting the phase characteristic of the test signal to the linear phase characteristic.
In FIG. 11, the solid line L <b> 1 indicates the filter characteristics of a filter simulating the frequency characteristics of the transmitter 100. A white point D1 indicates a detection characteristic. A dotted line L2 indicates a linear phase characteristic, and indicates a correction characteristic corrected by the coefficient _xn obtained by the process of FIG. 10 at a predetermined frequency.

Next, a modification of the frequency characteristic correction unit 104 will be described.
FIG. 12 is a block diagram illustrating a modified configuration example of the frequency characteristic correction unit 104.
In FIG. 12, the frequency characteristic correction unit 104 includes a digital filter 901. When the digital filter 901 is used, the coefficient stored in the LUT is the coefficient of the digital filter 901. Coefficients of the digital filter 901, for example, coefficient calculator 108, may be obtained by inverse Fourier transform coefficients z _n as the correction coefficient.

  By providing the digital filter 901, the frequency characteristic correction unit 104 does not need to include a Fourier transform unit and an inverse Fourier transform unit, and the configuration can be simplified.

  Next, the operation of the transmitter 100 after calibration is described.

  When the calibration is completed, the transmitter 100 ends the calibration mode. When the calibration mode ends, the transmitter 100 switches to the data transmission mode. Specifically, the MUX 103 in FIG. 1 selects the output of the data generation unit 102.

  Subsequently, the frequency characteristic correction unit 104 refers to the LUT that stores the correction coefficient calculated by the coefficient calculation unit 108 and corrects the IQ signal output from the data generation unit 102. Subsequently, the modulator 105 modulates the correction signal and transmits the modulated signal.

  According to the transmitter 100, the amplitude characteristic and phase characteristic of the signal can be corrected with high accuracy, and distortion of the transmission signal can be reduced. Note that the correction of the frequency characteristics of the transmitter 100 is performed, for example, when the transmitter 100 is turned on, when starting from the sleep mode, and before starting data transmission.

  That is, according to the transmitter 100, for example, in wireless communication that handles a wideband frequency, it is possible to accurately correct frequency characteristics generated by frequency conversion between a baseband signal and a high-frequency signal. In addition, it is possible to realize a transmitter that is compensated so that amplitude characteristics, phase characteristics, and frequency characteristics are flat in wireless communication that handles a wideband frequency.

Next, the wireless device 1200 including the transmitter 100 will be described.
FIG. 13 is a block diagram illustrating a configuration example of the wireless device 1200. The wireless device 1200 includes a transmitter 100, a receiver 1202, a duplexer 1203, and an antenna 1204.

  The transmitter 100 corrects frequency characteristics, modulates desired data, and transmits a modulated signal. The receiver 1202 receives data from other communication devices. The duplexer 1203 separates the transmission signal and the reception signal and shares the antenna 1204 during transmission and reception.

  The wireless device 1200 can transmit data with less distortion.

  As illustrated in FIG. 14, the wireless device 1300 may include a transmission antenna 1303 and a reception antenna 1304 separately.

  The present invention is not limited to the configuration of the above-described embodiment, and can be applied to any configuration that can achieve the functions shown in the claims or the functions of the configuration of the present embodiment. Is possible.

  In the above-described embodiment, the case where the present invention is configured using hardware has been described as an example. However, the present invention can also be realized by software in cooperation with hardware.

  Each functional block used in the description of the above embodiment is typically realized as an LSI that is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. Here, it may be an LSI, or may be referred to as an IC, a system LSI, a super LSI, or an ultra LSI depending on the degree of integration.

  Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. For example, a Field Programmable Gate Array (FPGA) that can be programmed after manufacturing the LSI, connection of circuit cells in the LSI, or a reconfigurable processor whose settings can be reconfigured may be used.

  Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied.

  The present invention is useful for a transmitter, a signal generation device, and a calibration method that can correct distortion of a signal with high accuracy.

100 Transmitter 101 Test Signal Generation Unit 102 Data Generation Unit 103 MUX
104 frequency characteristic correction unit 105 modulator 106 envelope detection unit 106A envelope detector 106B AD converter 107 frequency characteristic calculation unit 108 coefficient calculation unit 109 memory 204 Fourier transform unit 205 multiplier 206 inverse Fourier transform unit 901 digital filter 1200 wireless device 1202 Receiver 1203 Duplexer 1204 Antenna 1300 Radio equipment 1302 Receivers 1303 and 1304 Antenna

Claims (15)

A test signal generator for generating a test signal;
A frequency characteristic correction unit that corrects amplitude characteristics and phase characteristics of the test signal generated by the test signal generation unit;
A modulation unit that modulates the correction signal corrected by the frequency characteristic correction unit;
An envelope detector for detecting an envelope of the modulated signal modulated by the modulator;
A frequency characteristic calculator that calculates the frequency characteristic of the envelope signal detected by the envelope detector;
Based on the frequency characteristic calculated by the frequency characteristic calculation unit, a coefficient calculation unit that calculates a correction coefficient for correcting the amplitude characteristic and phase characteristic of the test signal by the frequency characteristic correction unit;
With
The test signal generator generates a test signal that is asymmetric when comparing signal trajectories in at least two quadrants of the first to fourth quadrants on the IQ plane. The transmitter of claim 1, comprising:
The test signal generation unit is a transmitter that generates a test signal that is offset by a predetermined amount in an IQ plane, is symmetric with respect to a reference axis, and rotates on a line indicating a locus of the signal. The transmitter of claim 1, comprising:
The transmitter is a transmitter that rotates at a constant speed on a line indicating a locus of the signal. The transmitter according to claim 2, wherein
The test signal generator is a transmitter that generates a test signal that rotates on a circle that is offset by a predetermined amount in the IQ plane. The transmitter according to claim 4, wherein
The transmitter is a transmitter that rotates at a constant speed on a circle offset by a predetermined amount on the IQ plane. The transmitter according to any one of claims 1 to 5,
The test signal generation unit sweeps the frequency of the test signal in a predetermined frequency range,
The frequency characteristic calculation unit extracts each complex number data from each envelope signal based on each angular frequency component of the test signal,
The coefficient calculation unit is a transmitter that calculates each correction coefficient based on each complex number data extracted by the frequency characteristic calculation unit. The transmitter according to claim 6, wherein
The coefficient calculation unit is a transmitter that calculates an inverse of the complex data as the correction coefficient. The transmitter according to claim 6, wherein
The transmitter is a transmitter that calculates the correction coefficient based on a difference between a phase characteristic and a linear phase characteristic of the complex number data and an amplitude characteristic of the complex number data. The transmitter according to any one of claims 6 to 8, further comprising:
A storage unit for storing the correction coefficient;
The coefficient calculation unit is a transmitter that repeats calculation of each correction coefficient and updates each correction coefficient stored in the storage unit. The transmitter according to claim 9, wherein
The coefficient calculator is
Based on each complex number data extracted by the frequency characteristic calculation unit, calculates a coefficient for calculating each correction coefficient,
The coefficient calculation unit updates each correction coefficient stored in the storage unit according to a result of weighting and adding the coefficient calculated by the coefficient calculation unit to each correction coefficient stored in the storage unit. Machine. The transmitter according to any one of claims 1 to 10,
The frequency characteristic correction unit is
A conversion unit for converting the test signal from a time domain signal to a frequency domain signal;
A multiplier for multiplying the frequency domain signal by the coefficient calculated by the coefficient calculator;
An inverse converter that converts the signal output from the multiplier from a signal in the frequency domain to a signal in the time domain;
Transmitter with. The transmitter according to any one of claims 1 to 10,
The frequency characteristic calculation unit is a transmitter including a conversion unit that converts the envelope signal from a time domain signal to a frequency domain signal. The transmitter according to any one of claims 1 to 10, further comprising:
A baseband signal generator for generating a baseband signal;
A transmitter for transmitting the modulated signal;
With
The frequency characteristic correction unit corrects the baseband signal based on the correction coefficient calculated by the coefficient processing unit, and generates the correction signal. A test signal generator for generating a test signal;
A frequency characteristic correction unit that corrects amplitude characteristics and phase characteristics of the test signal generated by the test signal generation unit;
A frequency characteristic calculation unit that calculates the frequency characteristic of the envelope signal of the modulation signal obtained by modulating the correction signal corrected by the frequency characteristic correction unit;
Based on the frequency characteristic calculated by the frequency characteristic calculation unit, a coefficient calculation unit that calculates a correction coefficient for correcting the amplitude characteristic and phase characteristic of the test signal by the frequency characteristic correction unit;
With
The test signal generator generates a test signal that is asymmetric when comparing signal trajectories in at least two quadrants of the first to fourth quadrants on the IQ plane. A test signal generation step for generating a test signal;
A frequency characteristic correction step for correcting the amplitude characteristic and phase characteristic of the generated test signal;
A frequency characteristic calculating step of calculating a frequency characteristic of an envelope signal of a modulation signal obtained by modulating the corrected correction signal;
A coefficient calculating step for calculating a correction coefficient for correcting the amplitude characteristic and phase characteristic of the test signal based on the calculated frequency characteristic;
Have
In the test signal generation step, a calibration method for generating an asymmetric test signal when signal trajectories are compared in at least two quadrants of the first to fourth quadrants on the IQ plane.

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