JP4659584B2 - Digital modulation signal generator - Google Patents

Description

  The present invention converts a baseband digital in-phase component signal and a quadrature component signal output from a baseband signal generation unit into an analog in-phase component signal and a quadrature component signal by a D / A converter, respectively, and performs quadrature modulation. In a digital modulation signal generator that outputs a signal in a predetermined frequency band that is quadrature-modulated with an analog in-phase component signal and a quadrature component signal, it is highly accurate without using a specific calibration baseband signal. The present invention relates to a technique for enabling generation of a digital modulation signal.

  2. Description of the Related Art Conventionally, a digital modulation signal generator using a quadrature modulator has been used as a signal source for testing digital wireless communication devices and the like.

  FIG. 7 shows the basic configuration of the digital modulation signal generator 10, and the baseband digital in-phase component signal I (k) and quadrature component signal Q (k) output from the baseband signal generator 11. Are converted into analog in-phase component signal I (t) and quadrature component signal Q (t) by D / A converters 12 and 13, respectively, and input to quadrature modulator 14, and are orthogonal to in-phase component signal I (t). A signal m in a predetermined frequency band that is orthogonally modulated with the component signal Q (t) is generated and output.

  Here, the analog type quadrature modulator 14 inputs the carrier signal C of the predetermined frequency fc output from the carrier signal generator 14a to the phase shifter 14b, and carries carrier signals Ca and Cb having a phase difference of 90 degrees. One carrier signal Ca is input to the first mixer 14c, and the other carrier signal Cb is input to the second mixer 14d.

  The in-phase component signal I (t) is mixed with the carrier signal Ca by the first mixer 14c, the quadrature component signal Q (t) is mixed with the carrier signal Cb by the second mixer 14d, and both mixed components are combined by the combiner 14e. Thus, a digital modulation output signal m is generated.

here,
Ca = cos ωt, Cb = sin ωt (ω = 2πfc)
Then, the modulation output signal m is
m (t) = I (t) · cos ωt−Q (t) · sin ωt
It can be expressed as.

For example, the frequency of the baseband signal is fb,
I (t) = cos ω′t, Q (t) = sin ω′t (ω = 2πfb)
Then, the modulation output signal m is
m (t) = cos ω′t · cos ωt−sin ω′t · sin ωt
= Cos (ω + ω ') t
Thus, a sine wave signal having a frequency (fc + fb) is obtained.

  The basic configuration of the above-described digital modulation signal generator 10 is described in Patent Document 1, for example.

JP 2001-136216 A

  In the digital modulation signal generating apparatus having the above configuration, it is known that the quality of the modulation output signal m is greatly deteriorated mainly due to the influence of the quadrature error of the quadrature modulator 14 and the carrier leak.

  That is, if the phase difference between the carrier signals Ca and Cb has an error with respect to 90 degrees, or if there is an amplitude difference between the carrier signals Ca and Cb, the modulation accuracy of the modulation output signal m, for example, EVM (Error Vector Magnitude). ) Etc.

  Further, if the mixers 14c and 14d of the quadrature modulator 14 have a DC offset, the carrier signals Ca and Cb leak to the output side, and the carrier component of the frequency fc is generated at a large level in the modulation output signal m.

  Various compensation techniques for preventing the quality deterioration of the modulation output signal m due to the offset error and the quadrature error of the quadrature modulator 14 have been studied.

  For example, Patent Document 2 discloses a technique for compensating for an offset error of a quadrature modulator by adding a DC voltage to an analog in-phase component signal and a quadrature component signal input to the quadrature modulator.

JP 2003-249822 A

  Further, when compensating for the quadrature error of the quadrature modulator, for example, as described above, a baseband signal whose modulation output signal is a single frequency sine wave is used as a calibration signal, and the modulation output signal is generated by the quadrature error. The image component included in the signal is observed by a spectrum analyzer, and the amplitude and phase of the in-phase component signal I and the quadrature component signal Q input to the quadrature modulator 14 are adjusted so that the level of the image component is minimized. .

  However, the method of measuring the spectrum of the modulation output signal using the calibration signal as described above and compensating the amplitude and phase so that the image component is minimized requires operator skill and increases the compensation accuracy. There was a problem of variation.

  In addition, during adjustment or readjustment of compensation parameters, only a calibration baseband signal can be output, and there is a problem that an actual test cannot be performed until the adjustment is completed.

  The present invention solves this problem, can maintain high and stable compensation accuracy of offset error and orthogonal error, and can update parameters for compensation when outputting a baseband signal of an arbitrary pattern. An object of the present invention is to provide a digital modulation signal generator.

In order to achieve the above object, a digital modulation signal generator according to claim 1 of the present invention comprises:
A baseband signal generator (11) for outputting a baseband digital in-phase component signal and a quadrature component signal; and D for converting the digital in-phase component signal and the quadrature component signal into an analog in-phase component signal and a quadrature component signal. / A converter (12, 13), and a quadrature modulator (14) for outputting a signal in a predetermined frequency band that is quadrature modulated by the analog in-phase component signal and the quadrature component signal, and
In the digital modulation signal generation device, an error compensation unit (22) for compensating for an offset error and a quadrature error of the quadrature modulator is provided between the baseband signal generation unit and the D / A converter.
The error compensator is
The amplitude ratio between the in-phase component signal output from the baseband signal generation unit and the in-phase component signal obtained by quadrature demodulation of the output signal of the quadrature modulator is Gi, and the quadrature component signal output from the baseband signal generation unit and the The amplitude ratio of the quadrature component signal obtained by quadrature demodulation of the output signal of the quadrature modulator is Gq, the phase error of the carrier signal of the quadrature modulator with respect to the in-phase component signal is θi, the leak level of the carrier signal is Li, and the quadrature component The phase error of the carrier signal of the quadrature modulator with respect to the signal is θq, the leak level of the carrier signal is Lq,
For the input in-phase component signal I and quadrature component signal Q, the following expression I ′ = {(I−Li) cos θq− (Q−Lq) sin θq}
/ {Gi · cos (θq−θi)}
Q ′ = − {(I−Li) sin θi− (Q−Lq) cos θi}
/ {Gq · cos (θq−θi)}
In this way, the in-phase component signal I ′ and the quadrature component signal Q ′ in which the offset error, amplitude error and phase error are compensated are generated.

A digital modulation signal generator according to claim 2 of the present invention is the digital modulation signal generator according to claim 1,
A demodulator (31) that receives the output signal of the quadrature modulator and demodulates the digital baseband in-phase component signal and the quadrature component signal;
The in-phase component signal and the quadrature component signal demodulated by the demodulator are sequentially stored as the coordinate information of the symbol points on the IQ orthogonal coordinates, and are necessary for compensating the offset error from the stored coordinate information of each symbol point. And an error detection unit (32) for obtaining a leak level, amplitude ratios Gi and Gq and phase errors θi and θq necessary for compensation of the orthogonal error, and setting them in the error compensation unit.

Thus, in the digital modulation signal generator of the present invention, the error compensator is
For the input in-phase component signal I and quadrature component signal Q, the following expression I ′ = {(I−Li) cos θq− (Q−Lq) sin θq}
/ {Gi · cos (θq−θi)}
Q ′ = − {(I−Li) sin θi− (Q−Lq) cos θi}
/ {Gq · cos (θq−θi)}
Since the in-phase component signal I ′ and the quadrature component signal Q ′ in which the offset error, the amplitude error, and the phase error have been compensated are generated by performing the above calculation, each error is compensated using each known parameter. Component signals can be obtained, and manual compensation accuracy variation can be eliminated.

  Further, the demodulator and the in-phase component signal and the quadrature component signal demodulated by the demodulator are sequentially stored as the coordinate information of the symbol points on the IQ orthogonal coordinates, and the offset error is calculated from the stored coordinate information of each symbol point. Modulation signal having a leak level Li, Lq necessary for compensation of the error, an amplitude detector Gi, Gq and phase error θi, θq necessary for compensation of the quadrature error, and set in the error compensator In the generator, parameters necessary for each compensation can be obtained while a baseband signal having an arbitrary pattern is output without using a specific calibration signal, and high modulation quality can be maintained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of a digital modulation signal generator 20 to which the present invention is applied.

  As shown in FIG. 1, the digital modulation signal generator 20 includes a baseband signal generator 11, D / A converters 12 and 13, and a quadrature modulator that form the basic configuration of the digital modulation signal generator 10 described above. 14.

  An error compensation unit 22 is provided between the baseband signal generation unit 11 and the D / A converters 12 and 13.

  A signal distributor 26 that distributes the modulated output signal m to the output terminal 20 a and the demodulator 31 is provided on the output side of the quadrature modulator 14.

  The demodulating unit 31 converts the modulation output signal m into a digital signal M by the A / D converter 31a, and demodulates the baseband in-phase component signal Ir and the quadrature component signal Qr by the quadrature demodulator 31b to detect error detection described later. To the unit 32.

Next, the compensation principle of this embodiment will be described.
FIG. 2A shows an error model of the basic configuration of the digital modulation signal generator.

  In FIG. 2A, gain error circuits 103 and 104 indicate gains Gi and Gq (ideal value is 1) for each component signal from the baseband signal generation unit 11 to the quadrature modulator 14, and the gain Gi is This corresponds to the amplitude ratio between the in-phase component signal output from the baseband signal generation unit 11 and the in-phase component signal obtained by quadrature demodulation of the output signal of the quadrature modulator 14, and the gain Gq is output from the baseband signal generation unit 11. This corresponds to the amplitude ratio of the quadrature component signal obtained by quadrature demodulation of the quadrature component signal and the output signal of the quadrature modulator 14.

  The baseband ideal component signals I and Q output as digital values from the baseband signal generator 11 are input to the mixers 14c and 14d of the quadrature modulator 14 via the gain error circuits 103 and 104 ( The D / A converters 12 and 13 are omitted, and the component signals I and Q will be described without distinction between digital and analog).

  Further, it is assumed that the carrier signal Ca input from the phase shifter 14b to the mixer 14c has a phase error of θi, the carrier signal Cb input to the mixer 14d has a phase error of θq, and the quadrature modulator 14 itself. The leak level of the carrier signal Ca generated due to the direct current offset to the mixer 14c side is Li, and the leak level of the carrier signal Cb to the mixer 14d side is Lq. However, the leak levels Li and Lq are input conversion values of the quadrature modulator 14.

  In this error model, as shown in FIG. 2B, circuits 107 and 108 having gains 1 / Gi and 1 / Gq which are reciprocals of the gains Gi and Gq are connected from the baseband signal generator 11 to the quadrature modulator. 14 (or D / A converters 12 and 13), the gains for the component signals I and Q are both compensated to unity.

  By performing the gain error compensation, the modulation output signal m becomes as follows.

m (t) = Gi · (1 / Gi) · I · cos (ωt + θi)
-Gq · (1 / Gq) · Q · sin (ωt + θq)
+ (Li) cos (ωt + θi)
− (Lq) sin (ωt + θq)
= (I + Li) cos (ωt + θi)
− (Q + Lq) sin (ωt + θq)
……… (4)

  Further, as shown in FIG. 2C, when the circuits 109 and 110 for subtracting Li and Lq from the component signals I and Q, respectively, are inserted to suppress the leak due to the offset error, the modulation output signal m is It is expressed as

m (t) = (I−Li + Li) cos (ωt + θi)
− (Q−Lq + Lq) sin (ωt + θq)
= I · cos (ωt + θi)-Q · sin (ωt + θq)
......... (5)

  The above equation (5) shows the modulation output in a state where the gain error and the offset error are compensated. Further, when this equation is further decomposed, the following equation (6) is obtained.

m (t) = I {cos ωt · cos θi−sin ωt · sin θi}
-Q {sin ωt · cos θq + cos ωt · sin θq}
= {I · cos θi-Q · sin θq} cos ωt
− {I · sin θi + Q · cos θq} sin ωt
= Ia ・ cos ωt−Qa ・ sin ωt
However,
Ia = I · cos θi−Q · sin θq
Qa = I · sin θi + Q · cos θq
………… (6)

  In the above equation (6), if Ia and Qa of the modulation output signal m are equal to the original component signals I and Q, respectively, the phase error is compensated.

  Here, assuming that the baseband signals that are correctly compensated for the phase error and input to the quadrature modulator 14 are Ia ′ and Iq ′, the following equations are established.

Ia = I = Ia ′ · cos θi−Qa ′ · sin θq
Qa = Q = Ia ′ · sin θi + Qa ′ · cos θq
............ (7)

  Solving the above equation (7) with respect to the phase compensation outputs Ia ′ and Qa ′, the following result is obtained (the intermediate equation is omitted).

Ia ′ = (I · cos θq−Q · sin θq) / cos (θq−θi)
Qa ′ = − (I · sin θi−Q · cos θi) / cos (θq−θi)
............ (8)

Therefore, as shown in FIG. 2D, if the arithmetic circuits 111 and 112 perform the arithmetic processing of the above equation (8) on the input component signals I and Q, respectively, and input the signals to the quadrature modulator 14, the modulation is performed. The output signal m is
m (t) = I · cos ωt−Q · sin ωt
And can be in an ideal state.

  In the embodiment shown in FIG. 1, the error compensation unit 22 performs subtraction processing of the circuits 109 and 110 in FIG. 2 and the circuit 107 for each component signal I and Q output from the baseband signal generation unit 11. , 108, 109, and 110, the following calculation process is performed to suppress the carrier leak and the image component included in the modulation output signal m (t).

I ₁ = {(I−Li) cos θq− (Q−Lq) sin θq}
/ {Gi · cos (θq−θi)}
Q ₁ = − {(I−Li) sin θi− (Q−Lq) cos θi}
/ {Gq · cos (θq−θi)}
............ (9)

  By the compensation calculation processing of the equation (9), a highly accurate modulation output signal free from quality deterioration due to offset error and orthogonal error can be obtained.

  The gains (amplitude ratios) Gi and Gq, leak levels Li and Lq, and phase errors θi and θq, which are parameters necessary for correctly performing the above-described compensation processes, are obtained by the demodulator 31 and the error detector 32 described above. .

  The error detection unit 32 sequentially stores the component signals Ir and Qr demodulated by the demodulation unit 31 as coordinate information of symbol points on IQ orthogonal coordinates, and compensates for offset errors from the stored coordinate information of each symbol point. The gain levels Gi and Gq and the phase errors θi and θq necessary to compensate for the leak levels Li and Lq, the quadrature error, are obtained.

  For example, in the case where the modulation scheme is QPSK and the absolute value of Q is 1, the ideal symbol point obtained by demodulating an ideal digital modulation signal is IQ, as shown in FIG. Square vertex Sa (1, 1), Sb (-1, 1), Sc (-1, -1), Sd (1, -1) centered on the origin of Cartesian coordinates, and time As the time passes, the symbol points Sa to Sd are moved.

  Here, if it is assumed that there is only an offset error and no other errors among the errors, leak levels Li and Lq are added to the demodulated symbol points. As described above, the reception symbol points Sa1 to Sd1 respectively corresponding to the ideal symbol points Sa to Sd move by Li in the I-axis direction and Lq in the Q-axis direction.

  Further, of the errors, for example, assuming that there are errors of gain Gi> 1, Gq <1, and no other errors, the I and Q coordinates of each demodulated symbol point are Gi times and Gq, respectively. Therefore, as shown in FIG. 3C, the absolute values of the I coordinates of the reception symbol points Sa2 to Sd2 corresponding to the ideal symbol points Sa to Sd respectively become larger than 1, and the reception symbol points Sa2 to Sd2 The absolute value of the Q coordinate is smaller than 1, and the quadrilateral formed by connecting the four points is a horizontally long rectangle.

Further, of the errors, for example, when there is only the phase error θi and there is no other error, from the above equation (6), the I and Q coordinates of the demodulated symbol points Sa3 to Sd3 are
Ia = I · cos θi
Qa = I · sin θi + Q
It is represented by

Here, if the absolute values of I and Q are 1, the coordinates of the reception symbol point Sa3 are (cos θi, sin
θi + 1), the coordinates of the received symbol point Sb3 are (−cos θi, −sin θi + 1), and the slope k with respect to the I axis of the line segment connecting the two points Sa3 and Sb3 is
k = (sin θi + 1 + sin θi−1) / (cos θi + cos θi)
= Sin θi / cos θi = tan θi
It becomes. In addition, the inclination with respect to the I axis of the line segment connecting the reception symbol points Sc3 and Sd3 has the same result.

  That is, as shown in FIG. 3D, the line segment connecting the reception symbol points Sa3 and Sb3 and the line segment connecting the reception symbol points Sc3 and Sd3 are inclined by the phase error θi with respect to the I axis.

At this time, the I coordinates of the received symbol points Sa3 and Sd3 are both equal to cos θi, and the I coordinates of the received symbol points Sb3 and Sc3 are both -cos.
It is equal by θi.

Further, of the errors, for example, when it is assumed that there is only the phase error θq and there is no other error, from the equation (6), the I coordinate and Q coordinate of the demodulated symbol points Sa4 to Sd4 are
Ia = I−Q · sin θq
Qa = Q · cos θq
It is represented by

Here, if the absolute values of I and Q are 1, the coordinates of the reception symbol point Sa4 are (1-sin θq, cos
θq), the coordinates of the received symbol point Sd4 are (1 + sin θq, −cos θq), and the slope k with respect to the Q axis of the line segment connecting the two points Sa4 and Sd4 is
k = (1 + sin θq−1 + sin θq) / (cos θq + cos θq)
= Sin θq / cos θq = tan θi
It becomes. In addition, the inclination with respect to the Q axis of the line segment connecting the reception symbol points Sb4 and Sc4 has the same result.

  That is, as shown in FIG. 3E, the line segment connecting the reception symbol points Sa4 and Sd4 and the line segment connecting the reception symbol points Sb4 and Sc4 are inclined by the phase error θq with respect to the Q axis.

At this time, the Q coordinates of the received symbol points Sa4 and Sb4 are both equal to cos θq, and the Q coordinates of the received symbol points Sc4 and Sd4 are both -cos.
It is equal by θq.

  Therefore, the theoretical figure obtained by connecting the received symbol points Sa ′ to Sd ′ in order when all the errors described above are included is a parallelogram as shown in FIG. The coordinates of the center of gravity, which is the intersection of the two, correspond to the leak levels Li and Lq, and ½ of the length of the line segment connecting the reception symbol points Sa ′ and Sb ′ (or Sc ′ and Sd ′) corresponds to the gain Gi. The angle of the line segment with respect to the I axis corresponds to the phase error θi, and ½ of the length of the line segment connecting the reception symbol points Sa ′ and Sd ′ (or Sb ′ and Sc ′) corresponds to the gain Gq. The angle of the line segment with respect to the Q axis corresponds to the phase error θq.

  However, since the positions of the received symbol points Sa ′ to Sd ′ obtained with respect to the actually demodulated baseband signal vary due to the influence of noise or the like, the error detector 32 is demodulated by the demodulator 31. Each component signal Ir, Qr is sequentially stored as coordinate information of symbol points on IQ orthogonal coordinates, and the received symbol points respectively corresponding to the four ideal symbol points Sa to Sd are averaged, and obtained by the averaging. By performing each calculation described above for the coordinate information of the four symbol points Sa ″ to Sd ″, leak levels Li and Lq necessary for offset error compensation, gains Gi and Gq necessary for quadrature error compensation, and phase error θi and θq are obtained, and these compensation parameters are set in the error compensator 22.

Next, the operation of the digital modulation signal generator 20 of this embodiment will be described.
First, the apparatus is operated in a state where the compensation operation of the error compensator 22 is stopped, that is, in the state of the error model described above, and the demodulation processing for the modulation output signal m (t) output from the quadrature modulator 14 is demodulated. The baseband signals Ir and Qr obtained by the demodulation unit 31 are input to the error detection unit 32, and the received symbol point coordinates determined by the in-phase component signal Ir and the quadrature component signal Qr are stored. The averaging process is performed to obtain four symbol points Sa ″ to Sd ″ that form the vertices of the parallelogram as shown in FIG.

  Then, the coordinates of the center of gravity G of the parallelogram are set as the leak levels Li and Lq necessary for offset error compensation and set in the error compensator 22.

  Further, the error detection unit 32 is configured to ½ the length between the symbol points Sa ″ and Sb ″ (or between Sc ″ and Sd ″) and between the symbol points Sa ″ and Sd ″ (or between Sb ″ and Sc ″). ) Is obtained as gains Gi and Gq, respectively, and the inclination angle θi with respect to the I axis of the line segment connecting the symbol points Sa ″ and Sb ″ (or Sc ″ and Sd ″) and the symbol point The inclination angle θq with respect to the Q axis of the line segment connecting Sa ″ and Sd ″ (or Sb ″ and Sc ″) is obtained as a phase error, and set in the error compensator 22 together with the gains Gi and Gq.

  By setting each of the above parameters, the offset error and the quadrature error are compensated, the carrier leak and the image component included in the output signal of the quadrature modulator 14 are suppressed, and each received symbol point obtained when demodulating this is as follows. As shown in FIG. 5, correction is performed so as to overlap the corresponding ideal symbol points Sa to Sd, and as a result, a highly accurate digital modulation signal is obtained.

  Note that the operation for obtaining and setting the compensation parameters as described above can be made closer to the ideal state by repeating not only once but also a plurality of times.

  As described above, the digital modulation signal generator 20 according to the embodiment does not require a specific signal for calibration, and is necessary for compensating for an offset error and an orthogonal error while outputting a baseband signal having an arbitrary pattern. The parameters can be acquired and set, and the complicated and skillful work of adjusting the parameters while observing the spectrum waveform as in the prior art is unnecessary.

  In addition, new parameters can be acquired and set at an arbitrary timing during measurement, quality deterioration due to environmental changes such as temperature can be prevented, and high modulation quality can be maintained.

  In the above embodiment, the demodulator 31 and the error detector 32 are provided inside the apparatus. However, as in the digital modulation signal generator 20 ′ shown in FIG. 6, the demodulator 31 and the error detector 32 are included in the apparatus. A configuration may be adopted in which the compensation parameters obtained by the demodulation process and the error detection process at the time of factory shipment are stored in the parameter storage unit 35 in the apparatus without being provided.

  In the above-described embodiment, the case of the modulation method QPSK has been described as the error detection process. However, the present invention can also be applied to other modulation methods such as 16QAM and 64QAM.

  In other words, in a general form including the above-described QPSK, when detecting a leak level necessary for offset error compensation, among ideal symbol points determined by the modulation method, a regular n-gonal shape with the coordinate origin as the center of gravity ( n is an n-gonal shape formed by selecting ideal symbol points located at respective vertices of 4) and connecting received symbol points corresponding to the selected ideal symbol points (or points obtained by averaging thereof). The I and Q coordinates of the center of gravity are obtained as leak levels Li and Lq.

  Also, the sum of the I coordinates of each received symbol point (or the point obtained by averaging) corresponding to all ideal symbol points determined by the modulation method is obtained, and this is obtained as the sum of the leak levels Li and Q coordinates. This may be the leak level Lq.

  When obtaining the amplitude, the ideal symbol point determined by the modulation method is selected from the ideal symbol points located at the vertices of the square with the coordinate origin as the center of gravity, and the received symbol corresponding to each of the selected ideal symbol points is selected. What is necessary is just to obtain | require the length of the side of the rectangle formed by connecting the points (or the points obtained by the averaging), and obtain the amplitude based on the length of the sides.

  Further, when obtaining the phase error, the inclination with respect to the I-axis of the line segment connecting the two reception points respectively corresponding to the two ideal symbol points having the same Q coordinate among the ideal symbol points determined by the modulation method is defined as the phase error θi. The inclination with respect to the Q axis of the line segment connecting the two received symbol points respectively corresponding to the two ideal symbol points having the same I coordinate may be obtained as the phase error θq.

Configuration diagram of an embodiment of the present invention The figure which shows the relationship between the error model of embodiment, and compensation Diagram showing the relationship between error and figure drawn by symbol point The figure which shows the figure which the symbol point which is obtained when demodulating the signal which has the offset error and the quadrature error draws Figure showing the figure obtained by averaging received symbol points and the change in symbol points due to compensation The figure which shows the structure of other embodiment. Configuration diagram of conventional equipment

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Baseband signal generator, 20, 20 '... Digital modulation signal generator, 22 ... Error compensation part, 12, 13 ... D / A converter, 14 ... Quadrature modulator, 31 ... Demodulation Part, 32 ... error detection part, 35 ... parameter storage part

Claims (2)

A baseband signal generator (11) for outputting a baseband digital in-phase component signal and a quadrature component signal; and D for converting the digital in-phase component signal and the quadrature component signal into an analog in-phase component signal and a quadrature component signal. / A converter (12, 13), and a quadrature modulator (14) for outputting a signal in a predetermined frequency band that is quadrature modulated by the analog in-phase component signal and the quadrature component signal, and
In the digital modulation signal generation device, an error compensation unit (22) for compensating for an offset error and a quadrature error of the quadrature modulator is provided between the baseband signal generation unit and the D / A converter.
The error compensator is
The amplitude ratio between the in-phase component signal output from the baseband signal generation unit and the in-phase component signal obtained by quadrature demodulation of the output signal of the quadrature modulator is Gi, and the quadrature component signal output from the baseband signal generation unit and the The amplitude ratio of the quadrature component signal obtained by quadrature demodulation of the output signal of the quadrature modulator is Gq, the phase error of the carrier signal of the quadrature modulator with respect to the in-phase component signal is θi, the leak level of the carrier signal is Li, and the quadrature component The phase error of the carrier signal of the quadrature modulator with respect to the signal is θq, the leak level of the carrier signal is Lq,
For the input in-phase component signal I and quadrature component signal Q, the following expression I ′ = {(I−Li) cos θq− (Q−Lq) sin θq}
/ {Gi · cos (θq−θi)}
Q ′ = − {(I−Li) sin θi− (Q−Lq) cos θi}
/ {Gq · cos (θq−θi)}
A digital modulation signal generator that generates the in-phase component signal I ′ and the quadrature component signal Q ′ in which the offset error, the amplitude error, and the phase error are compensated for by performing the above calculation. A demodulator (31) that receives the output signal of the quadrature modulator and demodulates the digital baseband in-phase component signal and the quadrature component signal;
The in-phase component signal and the quadrature component signal demodulated by the demodulator are sequentially stored as the coordinate information of the symbol points on the IQ orthogonal coordinates, and are necessary for compensating the offset error from the stored coordinate information of each symbol point. And an error detection unit (32) that obtains leak levels Li and Lq, amplitude ratios Gi and Gq and phase errors θi and θq necessary for compensation of the quadrature error, and sets them in the error compensation unit. The digital modulation signal generator according to claim 1.

Images