JP2001044762A - Noise component measurement device and modulation correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily measure a noise component included in an output of an orthogonal modulator at a low cost and to suppress the noise component on the basis of a result of the measurement. SOLUTION: A noise of a carrier-field-through-component and a noise of an inverse side band component are in existence in a transmission signal that is processed for orthogonal modulation. A frequency conversion section 117 down-converts the transmission signal on the basis of a signal with a frequency corresponding to the frequency of the noise signal that is desirably measured, the down-converted signal passes through a band-pass filter 119 and a detection circuit 121 converts the output of the filter into an effective value of the signal corresponding to the noise component. Since the noise component is observed after being converted into a low frequency component, the measurement circuit is configured with a simple circuit and the measurement is also facilitated. The modulation correction circuit 130 controls an adjustment amount of the amplitude and the phase by a phase.amplitude adjustment sections 102, 103 and a bias voltage applied to a signal wave by DC bias variable circuits 104, 105.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a noise component of a modulated wave, which measures various noise components contained in the modulated wave due to changes in accuracy error, temperature characteristic, etc. of each element constituting a modulation circuit. The present invention relates to a modulation correction device using the same.

[0002]

2. Description of the Related Art A quadrature modulator (vector modulator or I / Q
The modulator can operate as various types of modulators that modulate phase, frequency, amplitude, etc., depending on how the baseband signal is applied.
K, FSK, ASK, etc.). Generally, SSB modulation is often used to evaluate the performance of such a quadrature modulator. This is because the use of SSB modulation makes it possible to easily evaluate important characteristics of the quadrature modulator, such as output power, carrier leak, and image suppression.

FIG. 4 is a diagram showing an example of an SSB modulator which is a kind of a quadrature modulator configured by using a phase shift method. The SSB modulator 500 shown in the figure basically has a configuration of a double balance mixer. That is, the modulator 500 splits a single carrier signal output from the carrier frequency oscillator 501 to generate two carrier signals that are shifted in phase by π / 2 from each other, and is in-phase with the baseband signal. The SSB signal is generated by separately modulating the I signal and the Q signal, which are orthogonal to the baseband signal, with the carrier signals and combining the modulated signals.

[0004] The SSB modulator 500 includes a carrier frequency oscillator 501, phase shifters 502 and 503, and a balanced modulator 50.
4, 505 and a coupler 506. Carrier frequency oscillator 501 outputs a carrier signal having a predetermined frequency. The phase shifter 502 changes the phase of the carrier signal output from the carrier frequency oscillator 501 by π / 4.
Carrier signal A is shifted in the positive direction by
4 is output. Phase shifter 503 shifts the carrier signal output from carrier frequency oscillator 501 in the negative direction by π / 4 and outputs carrier signal B to balanced modulator 505. The carrier signal A is output by the phase shifters 502 and 503.
And the carrier signal B are two carrier signals whose phases are shifted from each other by π / 2. Balanced modulator 504 modulates the I signal by multiplying the I signal that is in phase with the baseband signal by carrier signal A output from phase shifter 502. The balanced modulator 505 modulates the Q signal by multiplying the Q signal that is orthogonal to the baseband signal by the carrier signal B output from the phase shifter 503. The combiner 506 combines the modulated I signal and Q signal output from the balanced modulator 504 and the balanced modulator 505 to output an SSB signal in which one sideband is canceled.

The SSB modulator 500 comprises phase shifters 502 and 503, balanced modulators 504 and 505, and a coupler 5
When 06 operates with ideal characteristics, the SSB modulator 500 generates an SSB signal having an ideal upper sideband component. However, when such an SSB modulator is configured using actual elements, the phase shift characteristics of both the phase shifters 502 and 503 operate stably due to the non-linear operation of the transistors, the asymmetric layout, and the like. Or the characteristics of the balanced modulators 504 and 505 are not the same. Therefore, such an SSB modulator 50
When the SSB amplitude modulation process is performed using
Various noise components are superimposed on the B signal.

FIG. 5 is a diagram showing a frequency spectrum for explaining a noise component superimposed on the SSB signal. As shown in the figure, at the output end of the combiner 506, not only the SSB signal but also the noise of the carrier field through component and the inverse sideband component exist. The noise of the carrier field through component increases when the DC voltage between the I signal and the Q signal is not balanced, and is caused by leakage from a package or a PC board. Indeed, the effect is greater.

[0007] When the I and Q signals of the baseband signal are combined by the combiner 506, the noise of the opposite sideband component has a slightly different level or a phase difference of π / 2.
It is generated when there is a slight deviation from the frequency, and greatly depends on the frequency, and is also affected by the local power and the power supply voltage. The noise of the inverse sideband component is the difference between the signal components of the upper sideband and the lower sideband, and is called image suppression. In the case where the SSB signal output from the coupler 506 is a signal in the upper sideband existing around the frequency f + a, the noise of the reverse sideband component has a frequency fa lower than the frequency f of the carrier signal by a frequency a. In the center, if the SSB signal is in the lower sideband, it appears in the opposite direction. That is, this noise component is
6, which is one of the sideband signals of the SSB signal that could not be suppressed.

Conventionally, a modulation correction circuit for removing the noise of the carrier field through component and the reverse sideband component as described above is separately provided and externally adjusted.
This modulation correction circuit adjusts the amplitude and phase of the I signal, which is an in-phase component of the baseband signal, and adjusts the amplitude and phase of the Q signal, which is a quadrature component of the baseband signal, so as to be input to the coupler 506. Signals (I signal and Q signal)
), And the noise of the inverse sideband component is removed by making the phase difference between the two signals exactly π / 2. Further, by applying a predetermined bias voltage to the I signal and the Q signal input to the balanced modulators 504 and 505, the noise of the carrier field through component leaking from the balanced modulators 504 and 505 is removed. Have been.

Conventionally, a waveform analyzer (for example, a spectrum analyzer or an FFT analyzer) is connected to the output terminal of the coupler 506, and a frequency spectrum waveform displayed on the waveform analyzer as shown in FIG. 5 is observed. While
Each set value of the modulation correction circuit has been adjusted so that the noise of the carrier field through component and the inverse sideband component included in the SSB signal is reduced.

[0010]

As described above, if a waveform analyzer such as an expensive spectrum analyzer is connected to adjust each set value of the modulation correction circuit, the adjustment requires a lot of time and labor. There was a problem that it took. Also,
Even after the adjustment, if the performance of the element changes due to a temperature change, the adjustment must be performed again.
Further, it is possible to incorporate a waveform analyzer in the quadrature modulator and automatically adjust each set value of the modulation correction circuit based on the observed frequency spectrum waveform. Such a configuration is not preferable in terms of cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a noise component measuring apparatus capable of measuring noise components contained in the output of a quadrature modulator at low cost and easily. Is to provide.

Further, the present invention has been made in view of the above points, and an object of the present invention is to provide an inexpensive and easy-to-use modulation correction device capable of suppressing noise components contained in the output of a quadrature modulator. It is to provide a device.

[0013]

According to a first aspect of the present invention, there is provided a noise component measuring apparatus comprising: an input unit for inputting a transmission signal modulated by a predetermined modulation process; Based on a signal of a predetermined frequency corresponding to a noise signal included in the transmission signal input from the means, frequency conversion means for down-converting the transmission signal, and among the signals down-converted by the frequency conversion means, A filter for passing only a signal in a band corresponding to the noise signal; and a detector for detecting a signal passing through the filter.
The transmission signal modulated by the modulation process includes various noise signals. It is known that these noise signals include noise of a carrier field through component generated by leakage of a carrier wave and noise of an inverse sideband component generated by combining two orthogonal signal waves. . For these noises, the frequency region in which they are generated can be specified according to the frequencies of the signal wave and the carrier wave. Therefore, the noise signal to be measured can be converted into a low-frequency signal by down-converting the transmission signal based on a signal having a frequency corresponding to the frequency of the noise signal to be measured by frequency conversion means. Since only the signal corresponding to the noise signal among the down-converted signals is configured to pass through the filter, the detection means can recognize the magnitude of the noise signal by detecting the value. . Since the noise signal is once converted into a low-frequency signal as described above, the filter means and the detection means can be configured with simple circuits, and the noise component can be easily measured.

According to a second aspect of the present invention, there is provided a noise component measuring device for inputting a transmission signal obtained by modulating and combining two orthogonal signal waves with a carrier wave,
The transmission signal is down based on a signal of a predetermined frequency corresponding to a first noise signal of a carrier field through component included in the transmission signal or a second noise signal generated by combining the two signal waves. Frequency converting means for converting, filter means for passing only signals in a band corresponding to the first noise signal or second noise signal from signals down-converted by the frequency converting means, and the filter means And a detecting means for detecting the passed signal. This noise component measuring apparatus is configured to combine a noise of a carrier field through component included in a transmission signal and a noise of an inverse sideband component generated by combining two orthogonal signal waves.
Each value is measured. The noise of the carrier field through component is noise in the same frequency band as the frequency of the carrier, and the noise of the reverse sideband component is a signal in any one of the frequency bands appearing in the sideband. Therefore, the transmission signal is down-converted by the frequency conversion means based on the signal of the frequency corresponding to the noise of the carrier field through component, so that only the noise signal of the carrier field through component passes through the filter means. On the other hand, by down-converting the transmission signal based on the signal of the frequency corresponding to the noise of the inverse sideband component, only the noise signal of the inverse sideband component passes through the filter means. Therefore, the detection means can easily measure the noise component of the carrier field through component or the inverse sideband component only by detecting the signal passing through the filter means.

According to a third aspect of the present invention, there is provided a noise component measuring apparatus comprising: an input unit for inputting a transmission signal obtained by performing a quadrature modulation process using only a carrier wave without inputting a signal wave; Frequency conversion means for down-converting the transmission signal based on a signal of a predetermined frequency corresponding to the noise signal of the included carrier field through component, and detection means for detecting the signal down-converted by the frequency conversion means It is a thing. It is generally known that noise components generated by performing quadrature modulation processing include noise of a carrier field through component and noise of an inverse sideband component, but the noise of the inverse sideband component is orthogonal. Since it is generated by combining two signal waves, if orthogonal modulation is performed using only a carrier without inputting a signal wave, noise of the inverse sideband component does not occur, only noise of the carrier field through component Will occur. The frequency conversion means down-converts the transmission signal based on a signal having a frequency corresponding to the frequency of the carrier field through component, thereby converting the noise signal of the carrier field through component into a low frequency signal. The detection means only needs to detect the noise signal converted by the frequency conversion means, and the filter means as described above can be omitted.

According to a fourth aspect of the present invention, there is provided a modulation correction device for outputting a transmission signal obtained by modulating a signal wave with a carrier wave, and a modulation signal based on a frequency close to a frequency of a noise signal included in the transmission signal. Frequency conversion means for down-converting the transmission signal output from the modulation means, and passing only a signal in a band corresponding to the noise signal from signals obtained by the down-conversion processing of the frequency conversion means. The apparatus comprises: a filter; a detector for detecting a signal passed through the filter; and an adjuster for adjusting a modulation characteristic of the modulator so that a signal detected by the detector is reduced. In this modulation correction device, the modulation characteristic of the modulation means is adjusted by the adjustment means using the result measured by the noise component measurement device according to the first aspect.

According to a fifth aspect of the present invention, there is provided a modulation correcting apparatus for outputting a transmission signal obtained by modulating and combining two orthogonal signal waves with a carrier wave, and a carrier field included in the transmission signal. The first of the through component
Frequency conversion means for down-converting the transmission signal based on a signal of a predetermined frequency corresponding to a noise signal or a second noise signal generated by combining the two signal waves, and the frequency conversion means Filter means for passing only a signal of a band corresponding to the first noise signal or second noise signal from the down-converted signal; detection means for detecting a signal passed through the filter means; Adjusting means for adjusting the modulation characteristic of the modulating means so that the signal detected by the means becomes small. This modulation correction device
A noise component included in a transmission signal modulated by a quadrature modulator is measured by the noise component measuring device according to claim 2, and the modulation characteristic of the modulation unit is adjusted by an adjustment unit using the result. It is.

According to a sixth aspect of the present invention, in the modulation correction apparatus according to the fifth aspect, the adjusting means may be configured such that the adjusting means adjusts the value of the bias voltage supplied to the two signal waves. Is adjusted to reduce the first noise signal. Since the noise of the carrier field through component can be reduced by adjusting the bias voltage supplied to the two signal waves to be combined, the bias voltage supplied to the two signal waves is used as the modulation characteristic of the modulation means. Was adjusted.

According to a seventh aspect of the present invention, there is provided a modulation correction apparatus according to the fifth or sixth aspect, wherein the adjusting means includes at least one of an amplitude and a phase of the two signal waves. The second noise signal is reduced by adjusting one of them. Since the noise of the reverse sideband component is noise that can be reduced by adjusting the amplitude and phase of the two signal waves to be synthesized, the amplitude and phase are adjusted here as the modulation characteristics of the modulation means.

According to another aspect of the present invention, there is provided a modulation correction device for outputting a transmission signal obtained by performing quadrature modulation processing using only a carrier wave without inputting a signal wave, and a modulation signal included in the transmission signal. Frequency conversion means for down-converting the transmission signal based on a signal of a predetermined frequency corresponding to a noise signal of a carrier field through component, and detection means for detecting a signal down-converted by the frequency conversion means; and Adjusting means for adjusting the value of the bias voltage supplied to the signal wave so that the signal detected by the means becomes small. This modulation correction device measures the noise of a carrier field through component generated when quadrature modulation is performed using only a carrier wave without inputting a signal wave, using the noise component measurement device according to claim 3, and measuring the result. The adjusting means adjusts the bias voltage supplied to the two signal waves to suppress the noise.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a noise component measuring device and a modulation correcting device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of a quadrature modulator incorporating a noise component measurement device and a modulation correction device according to the present invention. The quadrature modulator 100
Carrier frequency oscillator 101, phase / amplitude adjustment unit 10
2, 103, DC bias variable circuits 104 and 105, a quadrature modulator 110, and a modulation correction circuit 130.

The carrier frequency oscillator 101 supplies a carrier signal Cin having a predetermined frequency to the quadrature modulator 110. The quadrature modulator 110 includes a phase shifter 111, an I-signal double balance mixer (I-CH DBM) 112, and a Q signal double balance mixer (Q-CH DBM) 11.
3. It includes the coupler 114. Phase shifter 111
Is a carrier signal Cin output from the carrier frequency oscillator 101, the two orthogonal phase signals C 0 and 90 degrees
i and Cq, and outputs the separated phase signal Ci to the I signal double balance mixer 112 and the phase signal Cq to the Q signal double balance mixer 113, respectively.

The phase / amplitude adjustment unit 102 controls the phase and amplitude of the I signal, which is an in-phase component of the baseband signal, by the control unit 12
3 is adjusted according to the phase / amplitude control signal output from
The adjusted baseband signal Isig is output to I signal double balance mixer 112 of quadrature modulator 110. The phase / amplitude adjustment unit 103 adjusts the phase and amplitude of the Q signal, which is also an orthogonal component of the baseband signal, according to the phase / amplitude control signal output from the control unit 123, and outputs the adjusted baseband signal Qsig. The signal is output to the Q signal double balance mixer 113 of the quadrature modulator 110. These phases
By adjusting the phases and amplitudes of the I signal and the Q signal by the amplitude adjustment units 102 and 103, the levels of both signals (I signal and Q signal) input to the coupler 114 are made equal, and the phase difference between the two signals is further increased. Is accurately set to π / 2, and noise of the inverse sideband component can be removed. The phase / amplitude adjustment units 102 and 103 adjust the phase of the baseband signal according to the phase control signal output from the control unit 123, and adjust the amplitude of the baseband signal according to the amplitude control signal. ing.

The DC bias variable circuit 104 outputs a DC bias signal Iref for controlling a bias voltage for determining a DC current in the mixing operation of the I signal double balance mixer 112 to the I signal double balance mixer 112.
Output to Similarly, the DC bias variable circuit 105
A DC bias signal Qref for controlling a bias voltage that determines a DC current during the mixing operation of the Q signal double balance mixer 113 is output to the Q signal double balance mixer 113. Note that the DC bias variable circuit 10
DC bias signals Iref, QR output from
The magnitude of ef is controlled according to the bias control signal output from the control unit 123. This DC bias signal Ire
By setting the magnitudes of f and Qref to appropriate values,
The noise of the carrier field through component leaked and output mainly from the I signal double balance mixer 112 and the Q signal double balance mixer 113 can be suppressed.

The double balance mixer for I signal 112
The baseband signal Isig whose phase and amplitude have been adjusted by the phase / amplitude adjusting unit 102 is mixed with the phase signal Ci output from the phase shifter 111, and the DC bias signal Iref output from the DC bias variable circuit 104
The signal Mi is generated by adjusting the DC current at the time of mixing in accordance with the following formula, and is output to the coupler 114.
Similarly, the Q signal double balance mixer 113 mixes the baseband signal Qsig, the phase and amplitude of which has been adjusted by the phase / amplitude adjustment unit 103, with the phase signal Cq output from the phase shifter 111, and has a DC bias variable circuit. A signal Mq is generated by adjusting a DC current at the time of mixing according to a DC bias signal Qref output from 105, and the signal Mq is output to the coupler 114.

The combiner 114 includes a double balance mixer 112 for I signal and a double balance mixer 113 for Q signal.
By combining the respective signals Mi and Mq output from the SSB, an SSB signal in which one sideband is canceled is output.

That is, if the carrier signal Cin is Acos (ωt)
, The phase shifter 111 converts the phase signal Ci of Acos (ωt) to I
The phase signal Cq of −Asin (ωt) is output to the signal double balance mixer 112 to the signal double balance mixer 113. The I signal double balance mixer 112 mixes the signal Mi = Isig · Acos (ωt) obtained by mixing the carrier signal Cin and the baseband signal Isig, and the Q signal double balance mixer 113 mixes the carrier signal Cin and the baseband signal. The signal Mq = −Qsig · Asin (ωt) obtained by mixing the signal Qsig is combined with the combiner 114
Output to The combiner 114 combines the signals Mi and Mq, and outputs the output signal S = Mi + M as a combined SSB signal.
q = Isig · Acos (ωt) −Qsig · Asin (ωt) is output.

Here, if the baseband signals Isig and Qsig are set as follows: Isig = cos (φ (t)) Qsig = sin (φ (t)), the output signal S becomes S = cos (φ (t)). ) · Acos (ωt) −sin (φ (t)) · Asin (ωt) = Acos ((ωt) + φ (t)). In the above description of the formula, the description of the DC component is omitted, but it goes without saying that the DC component is actually taken into account.

Phase shifter 1 constituting quadrature modulator 110
11, when the I signal double balancer mixer 112, the Q signal double balance mixer 113, and the coupler 114 operate with ideal characteristics, the quadrature modulator 110 generates an ideal SSB signal. However, when such a quadrature modulator is configured using actual elements,
The phase shift characteristics of the phase shifter 111 do not operate stably,
The characteristics of both the I-signal double balancer mixer 112 and the Q-signal double balance mixer 113 cannot be exactly the same, or the carrier signal Cin is transmitted through one of the paths and leaks. Various noise components are superimposed on the SSB signal.

In the noise component measuring apparatus according to this embodiment, the modulation correction circuit 130 is provided, and the phase / amplitude adjustment unit 10 is provided.
The phase and amplitude adjustment amounts of the DC bias signals 2 and 103 and the values of the DC bias signals Iref and Qref output from the DC bias variable circuits 104 and 105 are controlled so that the noise of the carrier field through component and the reverse sideband component is reduced. are doing. Hereinafter, the configuration of the modulation correction circuit 130 will be described.

The modulation correction circuit 130 includes an oscillator (OSC)
116, frequency converter 117, band pass filter (BP
F) 119, amplifier 120, detection circuit 121, analog-digital converter (A / D converter) 122, control unit 12
3 is included. The oscillator 116 has a frequency f2 corresponding to the frequency of the noise component to be detected, that is, the carrier field through component and the inverse sideband component.
Is output to the frequency conversion section 117. This oscillator 1
The frequency of the signal output by 16 can be appropriately changed according to the noise component to be detected. That is, when the noise to be detected is a carrier field through component, the oscillator 116 has a frequency f2 smaller than that frequency.
If the noise to be detected is a reverse sideband component, the signal of frequency f2A smaller than that frequency is
Each is output to the frequency converter 117. The frequency conversion unit 117 mixes the SSB signal (containing a carrier field through component and a noise of an inverse sideband component) output from the coupler 114 with a signal of a predetermined frequency output from the oscillator 116, and Is down-converted and output.

The band-pass filter 119 is configured to exhibit a steep filter characteristic for passing only a signal in a predetermined frequency band from among the signals down-converted by the frequency converter 117. . Amplifier 120
The signal that has passed through the band-pass filter 119 is amplified. The detection circuit 121 performs a detection process on the signal that has passed through the band-pass filter 119, and outputs an analog signal such as its effective value. The A / D converter 122 includes a detection circuit 121
The analog signal of the effective value output from is converted into a digital signal.

The control unit 123 converts a phase / amplitude control signal relating to the adjustment of the phase and amplitude of the baseband signal based on the digital signal of the effective value output from the A / D converter 122, into the phase / amplitude adjustment unit 102, A bias control signal related to the DC bias signals Iref and Qref is output to DC bias variable circuits 104 and 105, respectively. When removing the noise of the carrier field through component, the control unit 123 sets the frequency of the signal output from the oscillator 116 to be lower than the frequency f of the carrier field through component or to a frequency f2C, and the noise of the reverse sideband component is set. Is removed, the frequency of the signal output from the oscillator 116 is set to a frequency f2A smaller than the frequency fa of the reverse sideband component.

The above-described carrier frequency oscillator 101 and quadrature modulator 110 serve as input means and modulation means,
6 and the frequency conversion unit 117 correspond to the frequency conversion unit, the bandpass filter 119 corresponds to the filter unit, and the detection circuit 121 and the A / D converter 122 correspond to the detection unit.
Further, the phase / amplitude adjustment units 102 and 103, the DC bias variable circuits 104 and 105, and the control unit 123 correspond to an adjustment unit.

Next, the operation of the modulation correction circuit 130 according to this embodiment will be described. For example, SSB existing at a frequency of 422.01 [MHz] as shown in FIG.
It is assumed that the signal is output from the combiner 114 of the quadrature modulator 110. For example, this SSB signal includes 421.
It is assumed that noise of a carrier field through component existing at a frequency of 4 [MHz] and noise of an inverse sideband component existing at a frequency of 420.79 [MHz] are included. The pass frequency band of the band-pass filter 119 is set to about 21.4 [MHz]. In this case, the band-pass filter 119 has ± 610
It has a filter characteristic enough to remove a [KHz] signal.

First, when removing the noise of the carrier field through component existing near the frequency of 421.4 [MHz] shown in FIG. 2, the oscillator 116 operates at 400 [MHz].
Is set by the control unit 123 so as to output a signal of the frequency Frequency converter 117
Converts the signal of each frequency component from the coupler 114 into the oscillator 1
16 is down-converted based on a signal of a frequency of 400 [MHz] output from the 16. That is, the frequency conversion unit 117 outputs the signal frequency (400
[MHz]), the noise of the carrier field through component (frequency 421.4 [MHz]) is reduced to 21.4 [M].
Hz] and convert the SSB signal (frequency 422.01 [MHz]) to 22.01 [MH].
z], and the noise (frequency 420.79 [MHz]) of the reverse sideband component is reduced to 20.79.
Down-convert to a noise signal of [MHz]. Each signal down-converted by the frequency conversion unit 117 is input to the band-pass filter 119.

Since the pass frequency band of the band-pass filter 119 is around 21.4 [MHz], it is 21.4 [MHz].
Only the noise of the carrier field-through component downconverted to the vicinity passes through the band-pass filter 119,
22.01 [MHz] corresponding to other SSB signals
20 and the noise of the inverse sideband component.
The signal of 79 [MHz] is cut off here. The noise of the carrier field through component in the vicinity of 21.4 [MHz] that has passed through the band-pass filter 119 is amplified by the amplifier 120 and then input to the detection circuit 121. The detection circuit 121 performs an RMS detection process and outputs an effective value of the noise of the carrier field through component. This effective value is converted into a digital signal by the A / D converter 122 and input to the control unit 123.

The control unit 123 controls the DC bias variable circuits 104 and 10 so that the effective value of the noise of the carrier field through component output from the A / D converter 122 is reduced.
5 to adjust the bias control signal. As a result, the DC bias component of the signal Mi output from the I signal double balance mixer 112 and the DC bias component of the signal Mq output from the Q signal double balance mixer 113 change, and the noise of the carrier field through component changes accordingly. I will be. The control unit 123 performs such closed loop control until the bias control signal that minimizes the effective value of the noise of the carrier field through component is output to the DC bias variable circuits 104 and 105.

FIG. 2 shows 420.79 [MHz].
When removing the noise of the reverse sideband component having the frequency of .times..times..times..times..times..times..times..times..times..times..times..times..tim- es. Frequency converter 117
Down-converts the signal of each frequency component output from the combiner 114 in the same manner as described above. That is, the frequency conversion unit 117 generates the noise signal (frequency 420.79) of the inverse sideband component based on the frequency (399.39 [MHz]) of the signal output from the oscillator 116.
[MHz]) is down-converted to a noise signal of 21.4 [MHz], and a noise signal (frequency 421.4 [MHz]) of a carrier field through component is 22.01 [MH]
z], and down-converts the SSB signal (frequency 422.01 [MHz]) to 22.62 [MHz].
Down-converted to a signal. Thereby, 21.
Only the noise of the inverse sideband component down-converted into a signal of 4 [MHz] passes through the band-pass filter 119 and is amplified by the amplifier 120, and then the detection circuit 12
1 will be input. The detection circuit 121 is an RMS
The detection processing is performed, and the effective value of the noise signal of the reverse sideband component is output. This effective value is converted into a digital signal by the A / D converter 122 and output to the control unit 123.

The control unit 123 outputs a phase / amplitude control signal that minimizes the effective value of the noise of the inverse sideband component output from the A / D converter 122 to the phase / amplitude adjustment unit 10.
2, 103. That is, the control unit 123
The amplitude control signal that minimizes the effective value of the noise of the reverse sideband component output from the / D converter 122 is phase-
Output to the amplitude adjustment unit 102 and the A / D converter 122
A phase control signal that minimizes the effective value of the noise of the inverse sideband component output from the
Output to As a result, when the execution value of the noise of the inverse sideband component is minimized, the control unit 123 then executes A / A
An amplitude control signal that minimizes the effective value of the noise of the inverse sideband component output from the D converter 122 is output to the phase / amplitude adjustment unit 102 and the inverse sideband output from the A / D converter 122 is output. A phase control signal that minimizes the effective value of the component noise is output to phase / amplitude adjustment section 103. The control unit 123 executes such a series of closed loop operations to minimize the effective value of the noise of the inverse sideband component output from the A / D converter 122. Note that the order of this processing is an example, and any order may be used as long as the effective value of the noise of the inverse sideband component can be finally minimized. When the phase is adjusted, it is needless to say that one of the phase / amplitude adjusting units 102 and 103 may be adjusted because the phase is relative.

Modulation correction circuit 130 according to this embodiment
The frequency converter 117 down-converts a high-frequency signal including a noise component into a signal in a frequency band that can be controlled by a simple circuit, and passes only a noise component to be detected from the signal through a band-pass filter 119. And the coupler 1
The effective value of the noise of the carrier field through component and the noise of the inverse sideband component to be removed from the noise components included in the signal output from the signal 14 can be easily measured with a simple circuit. Further, based on the measured effective value of noise, the degree of phase adjustment and amplitude adjustment performed by the phase / amplitude adjustment units 102 and 103 is controlled, and the DC bias signals Iref and Iref output from the DC bias variable circuits 104 and 105 are controlled. By controlling the level of Qref,
The noise of the carrier field through component and the noise of the reverse sideband component can be easily suppressed. That is,
Since it is not necessary to use an expensive waveform analyzer such as a spectrum analyzer as in the related art, cost can be reduced.

Further, as in the prior art, the measurer views the frequency spectrum of the carrier field through component and the inverse sideband component displayed on the display unit of the waveform analyzer, and adjusts the phase adjustment amount and amplitude of the phase / amplitude adjustment unit. Since there is no need to adjust the adjustment amount or change the levels of the DC bias signals Iref and Qref output from the DC bias variable circuits 104 and 105, the work load on the measurer can be reduced.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the modulation correction circuit 130 shown in FIG. 1, the case where the carrier field through component and the reverse sideband component are removed by various control processes by the control unit 123 has been described.
40, the control unit 12 is connected to the output terminal of the A / D converter 122.
The display unit 223 is connected in place of 3, and the measurer observes the effective value (analog value or digital value) of the noise of the carrier field through component and the noise of the reverse sideband component displayed on the display unit 223. Phase / amplitude adjustment unit 10
2, 103, the phase adjustment amount and the amplitude adjustment amount are changed.
The levels of the DC bias signals Iref and Qref output from the C bias variable circuits 104 and 105 may be appropriately changed.

In the embodiment corresponding to FIGS. 1 and 3, a case has been described in which both the noise of the carrier field through component and the noise of the inverse sideband component are removed, but only the noise of the carrier field through component is removed. In order to remove the sideband signal, the sideband signal (SSB signal) is not output from the coupler 114 if a predetermined modulation process is performed without inputting two orthogonal I and Q signals. That is, the quadrature modulator 100 shown in FIG.
Alternatively, by performing quadrature modulation processing without inputting the I signal and the Q signal to the quadrature modulator 200 shown in FIG. 3,
The coupler 114 outputs only the noise of the carrier field through component. Therefore, in such a case, the band pass filter 119 of FIG. 1 or 3 can be omitted.

[0045]

As described above, according to the present invention, it is possible to measure a noise component using an inexpensive and simple circuit configuration without providing a waveform analyzer such as an expensive spectrum analyzer. As a result, the noise component can be removed, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a quadrature modulator incorporating a modulation correction device according to the present invention.

FIG. 2 is a diagram illustrating an SSB signal, a carrier field through component, and a frequency spectrum component of an inverse sideband component input to a frequency conversion unit from a coupler.

FIG. 3 is a diagram illustrating a modification of the modulation correction circuit of FIG. 1;

FIG. 4 is a diagram illustrating an example of an SSB modulator that is a type of a quadrature modulator configured by using a phase shift method.

FIG. 5 is a diagram showing a frequency spectrum for explaining what noise component is superimposed on the SSB signal.

[Explanation of symbols]

Reference Signs List 100, 200 Quadrature modulator 101 Carrier frequency oscillator 102, 103 Phase / amplitude adjustment unit 104, 105 DC bias variable circuit 110 Quadrature modulator 111 Phase shifter 112 Double balance mixer for I signal (I-CH D)
BM) 113 Double balance mixer for Q signal (Q-CH D
BM) 114 Coupler 116 Oscillator 117 Frequency converter 119 Band-pass filter (BPF) 120 Amplifier 121 Detection circuit 122 Analog-digital converter (A / D converter) 123 Control unit 130, 140 Modulation correction circuit 223 Display unit

Claims (8)

[Claims] 1. An input unit for inputting a transmission signal modulated by a predetermined modulation process, and based on a signal of a predetermined frequency corresponding to a noise signal included in the transmission signal input from the input unit, Frequency conversion means for down-converting a transmission signal, filter means for passing only signals in a band corresponding to the noise signal from signals down-converted by the frequency conversion means, and detection of a signal passing through the filter means A noise component measuring device, comprising: 2. An input means for inputting a transmission signal obtained by modulating and combining two orthogonal signal waves with a carrier, and a first noise signal of a carrier field through component included in the transmission signal or the input signal. Frequency conversion means for down-converting the transmission signal based on a signal of a predetermined frequency corresponding to a second noise signal generated by combining the two signal waves; and A noise component comprising: filter means for passing only a signal in a band corresponding to the first noise signal or the second noise signal from the inside; and detection means for detecting a signal passing through the filter means. measuring device. 3. An input means for inputting a transmission signal obtained by performing a quadrature modulation process using only a carrier wave without inputting a signal wave, and corresponding to a noise signal of a carrier field through component included in the transmission signal. A noise component measuring device, comprising: frequency conversion means for down-converting the transmission signal based on a signal having a predetermined frequency, and detection means for detecting a signal down-converted by the frequency conversion means. 4. A modulating means for outputting a transmission signal obtained by modulating a signal wave with a carrier wave, and an output from the modulation means based on a signal of a predetermined frequency corresponding to a noise signal included in the transmission signal. Frequency conversion means for down-converting the transmission signal to be passed, filter means for passing only signals in a band corresponding to the noise signal from signals down-converted by the frequency conversion means, A modulation correction device comprising: a detection unit that detects a signal; and an adjustment unit that adjusts a modulation characteristic of the modulation unit so that a signal detected by the detection unit is reduced. 5. A modulating means for outputting a transmission signal obtained by modulating and combining two orthogonal signal waves with a carrier wave; and a first noise signal of a carrier field through component included in the transmission signal or the first noise signal. Frequency conversion means for down-converting the transmission signal based on a signal of a predetermined frequency corresponding to a second noise signal generated by combining two signal waves; and a signal down-converted by the frequency conversion means. Filter means for passing only a signal in a band corresponding to the first noise signal or the second noise signal, detection means for detecting a signal passed through the filter means, and detection means for detecting An adjustment unit for adjusting a modulation characteristic of the modulation unit so that a signal is reduced. 6. The modulation correction device according to claim 5, wherein the adjustment unit reduces the first noise signal by adjusting a value of a bias voltage supplied to the two signal waves. . 7. The modulation correction according to claim 5, wherein the adjustment unit reduces the second noise signal by adjusting at least one of a phase and an amplitude of the two signal waves. apparatus. 8. A modulating means for outputting a transmission signal obtained by performing quadrature modulation processing using only a carrier wave without inputting a signal wave, and corresponding to a noise signal of a carrier field through component included in the transmission signal. Frequency conversion means for down-converting the transmission signal based on the signal having the predetermined frequency, detection means for detecting the signal down-converted by the frequency conversion means, and a signal detected by the detection means being reduced. Adjusting means for adjusting a value of a bias voltage supplied to the signal wave.