JPH0818612A - Quadrature modulator - Google Patents

Abstract

PURPOSE:To adjust carrier leakage and image leakage and to provide a highly accurate quadrature modulator. CONSTITUTION:This modulator is provided with a quadrature modulator 1 provided with a test mode capable of turning all set data to '0' for quadrature modulating and outputting the I channel and Q channel of input, a detection circuit 3 for detecting and outputting the quadrature modulated output, a microprocessor 7 for storing the time lapse value of the detected and outputted test amplitude value and outputting control signals for changing the DC offset and amplitude of I channel or Q channel signals corresponding to a prescribed rule and a voltage generation circuit 8 for outputting the DC offset and amplitude of the I channel and Q channel signals by the control signals of the microprocessor. Then, the output of the voltage generation circuit is changed so as to let the change of the time lapse value of the output of the quadrature modulator at the time of the test mode be less than a set value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature modulator used in a digital communication device or the like and a device for suppressing unnecessary distortion components.

[0002]

2. Description of the Related Art As an example of a conventional circuit for automating suppression of carrier leak, FIG.
There is a circuit shown in the publication. In the figure, 1a is an input terminal 13 for local signals and I and Q signal input terminals 11 and 12
And a quadrature modulator having an RF output terminal 14, 2 is a coupling capacitor, and 3 is a detection circuit. Reference numeral 4 is a switch for opening and closing in synchronization with a control signal from the outside, 5 is a detection voltage holding circuit, 6 is an analog / digital conversion circuit, and 7a is
A microprocessor for generating a control signal, 8 is a voltage generation circuit having a control signal input terminal and DC offset voltage output terminals for I and Q signals.

Prior to the description of the operation of the above configuration, the basic operation of quadrature modulation will be described. FIG. 10 shows the basic configuration of a quadrature modulator. Normally, a quadrature modulator is used in a digital modulation method, and I (Inphase) and Q (Quadra) are used.
The baseband signal is multiplied by the local oscillator signal 21 by the multipliers 23 and 24 and added by the synthesizer 25 to obtain a modulated output signal. At this time, one of the local oscillation signals becomes a signal whose phase is shifted by 90 degrees by the 90 degree phase shifter 22 and is multiplied by the I or Q signal. If the frequency of the local oscillation signal is f _b (or ω _b = 2πf _b ), and the frequencies of the I and Q baseband signals are f _c (or ω _c = 2πf _c ), the characteristics of each device in the circuit of FIG. When the uniform balance is obtained, the output of the following expression (1) is obtained. _{cosω c t · cosω b t +} sinω c t · sinω
_{b t = cos (ω b -ω} c) t = cos (f b -f c)
· As 2.pi.t (1) above quadrature modulator output, shows that the obtained only the carrier frequency of f _b -f _c of equation (1). However, distortion occurs due to variations in the characteristics of each device, external changes such as temperature changes, and unnecessary waves are generated. Among these, there is a so-called carrier leak which is influenced by a local oscillation signal which is a carrier wave as a main unnecessary distortion.

The circuit of FIG. 9 is a circuit for suppressing only the carrier leak component in the above-mentioned unnecessary wave. Quadrature modulator 1
To the I and Q signal input terminals 11 and 12 of a, a signal having an amplitude component only at the time of transmission as shown in FIG. If a carrier is input to the local oscillator signal input terminal 13 in this state, ideally R
A modulated wave is output from the F output terminal 14 at the time of transmission, and the local oscillation signal should be suppressed at the time of transmission stop, and the output should be 0. However, in reality, due to imbalance of internal circuit devices,
There is a carrier leak as shown in FIG.

The output signal from the quadrature modulator 1a is input to the detection circuit 3 via the partial coupling capacitor 2. An input signal is detected and smoothed inside the detection circuit 3, a DC detection voltage is generated and sent to the switch 4. The switch 4 is turned off at the time of transmission and turned on at the time of transmission stop, and among the detection voltages from the detection circuit 3, only the voltage at the time of transmission stop, that is, the detection voltage corresponding to the carrier leak level is sent to the voltage holding circuit 5. While the switch 4 is turned off by the voltage holding circuit 5, the input voltage immediately before turning off is held, the output of the voltage holding circuit 5 is converted into a digital signal by the analog / digital converter 6, and carrier leakage occurs. An output signal which becomes level data is sent to the microprocessor 7a.

The microprocessor 7a calculates the DC offset voltage applied to the quadrature modulator 1a in order to minimize the carrier leak of the quadrature modulator 1a based on the carrier leak data. Then, a control signal for minimizing the carrier leak is sent to the voltage generation circuit 8. As a concrete method, the DC offset voltage value is slightly changed. If the result is good, the change in that direction is continued. If the result is not good, the change is made in the opposite direction. The voltage generation circuit 8 receives DC signals for I and Q inputs based on a control signal for controlling the direction.
Offset voltage (control signal) is set to I, Q
Input to the input signal terminal. The carrier leak is minimized by repeating the above operation, and when the carrier leak is minimized, the final bias is held and the setting of the DC offset is completed.

[0007]

Since the conventional quadrature modulator is constructed as described above, it is possible to automatically adjust the carrier leak due to the deviation of the DC offset voltage, but it is a cause of the vector error of the signal. There is a problem that it is not possible to adjust such image leaks. Also, a switch for switching in synchronization with the transmission mode was required.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a highly accurate quadrature modulation device by adjusting not only carrier leak but also image leak.

[0009]

A quadrature modulator according to the present invention has a quadrature modulator which has a test mode in which all setting data can be set to 0, and which quadrature-modulates an input I channel and Q channel signal and outputs the quadrature modulator. A detection circuit for detecting and outputting the modulated output, and a time-lapsed value of the test amplitude value thus detected and output are stored, and D of the I channel or Q channel signal is stored.
The test mode includes a microprocessor that outputs a control signal that changes the C offset and the amplitude according to a predetermined rule, and a voltage generation circuit that outputs the DC offset and the amplitude of the I channel and Q channel signals according to the control signal of the microprocessor. The output of the voltage generating circuit is changed so that the change of the elapsed time value of the output of the quadrature modulator at the time becomes equal to or less than the set value.

Furthermore, an amplifier for amplifying the detection output is provided, and the output of this amplifier is input to the microprocessor.

Furthermore, the amplification degree of the amplifier can be switched.

Further, the amplifier inputs the reference subtraction value, amplifies the difference between the detection output and the reference value, and outputs the amplified difference to the microprocessor.

The microprocessor first changes the DC offset to issue a control signal so that the change of the test amplitude value over time becomes equal to or less than the set value, and then changes the amplitude of the I channel or Q channel signal. The control signal is output so that the change of the test amplitude value over time becomes equal to or less than the set value, or conversely, the amplitude of the channel signal is first changed to monitor the set value, and then the DC offset is changed. The set value is monitored to determine the control signal.

[0014]

In the quadrature modulator according to the present invention, the test amplitude value of the output of the quadrature modulator is monitored for a certain time in the test mode, and the time variation width of the test amplitude value is set within the set value. The DC offset of the channel and the amplitude of the I and Q signals change, and I,
The amplitude of the Q signal and the DC offset are defined.

Further, the time variation width of the test amplitude value is amplified and input to the microprocessor, and a more precise change is detected.

In addition, the time variation width of the test amplitude value is sequentially amplified in the closed loop control by changing the amplification degree and input to the microprocessor to detect the stable and more precise variation.

Further, the time variation width of the test amplitude value is further expanded and inputted to the microprocessor, and a more precise change is detected.

In the closed loop control, first, either the amplitude of the I, Q signals or the DC offset is first determined, and then the other is determined, so that the amplitude and the offset are stably determined.

[0019]

【Example】

Example 1. An embodiment of a quadrature modulator having a distortion component suppressing mechanism according to the present invention will be described with reference to the configuration diagram of FIG.
In the present embodiment, the carrier leak and the image leak, which are the output distortion of the quadrature modulator, occur due to the imbalance of the I and Q channel elements in the quadrature modulator and the imbalance of the input signal. An example will be described in which the signal amplitude of the Q signal and the DC offset are adjusted to cancel each other. In this consideration, all the setting data are set to 0, and adjustment is performed so that the distortion component of the output of the quadrature modulator is minimized, that is, the amplitude change is minimized. In the figure, 1 is an input terminal 13 for a local oscillator signal.
And I and Q signal input terminals 11 and 12, and RF output terminal 1
4 is a quadrature modulator, 2 is a coupling capacitor, 3 is a detection circuit, 6 is an analog / digital conversion circuit, 7 is a microprocessor for generating a control signal, 8 is a control signal input terminal and I, Q signal output terminals. It is a voltage generation circuit that has. The switch and voltage holding circuit required in the conventional example are unnecessary.

Next, the operation of carrier leak and image leak suppression adjustment of the apparatus having the above configuration will be described. First,
In the quadrature modulator 1, ALLO data is set as setting data. When distortion components such as carrier leak and image leak are sufficiently suppressed, even if the input I and Q signals are orthogonally modulated and a modulated wave is continuously output in this state, the amplitude of the modulated wave is Is constant. But,
When the carrier leak and the image leak are not sufficiently suppressed by the DC offset or the amplitude shift of the I and Q analog signals, the amplitude of the modulated wave fluctuates with time.
Therefore, carrier leak and image leak can be suppressed by suppressing the temporal amplitude change of the modulated wave. By the way, the distortion is affected by both the difference between the I and Q channels or the amplitude difference of the quadrature modulator and the difference between the DC offsets of the I and Q channel signals. During normal operation, the I and Q signal input terminals 11 and 12 of the quadrature modulator 1 have the I and Q signals shown in FIG.
A signal is input. However, during the adjustment test for distortion suppression of the present embodiment, the input signal is always applied,
I and Q baseband signals are continuously input. A carrier is input to the local oscillator signal input terminal 13 as usual, and a modulated wave modulated by ALLO data is continuously transmitted from the RF output terminal 14 of the quadrature modulator 1.

An output signal from the quadrature modulator 1 obtains an amplitude value through a partial coupling capacitor 2 and a detection circuit 3, the analog / digital converter 6 converts the amplitude value into a digital value, and the microprocessor 7 receives the amplitude value. Sent. The microprocessor 7 stores the digital amplitude value from the analog / digital converter 6. Then, a control value for changing the offset or the amplitude of the I and Q signals is set, and the control value is sent to the voltage generating circuit 8. The voltage generation circuit 8 inputs the DC offset of the I and Q inputs or the amplitude voltage of the I and Q signals based on this control value to the I and Q input signal terminals of the quadrature modulator 1. The digital amplitude value corresponding to the next measurement time is input to the microprocessor 8, and the next control value is set and output. By repeating the above operation, the distortion component due to carrier leak and image leak can be suppressed.

The above operation will be described with reference to a flowchart. As described above, the control signal calculation method in the microprocessor 7 is, for example, the maximum value of the amplitude for every fixed time,
The operation based on the flowchart is performed while calculating the difference between the minimum values, that is, the amplitude fluctuation at regular time intervals. An example in which the DC offset is changed to minimize the carrier leak will be described in the procedure of the flowchart of FIG. The DC offset voltage of either I or Q is changed by a constant value n in step S31. Step S at the next measurement time
At 32, the detection circuit 3 is used rather than the amplitude fluctuation within the fixed time last time.
It is determined whether the amplitude value of the output of 1 has decreased, and steps S31 and S32 are repeated until the amplitude fluctuation is minimized. On the contrary, when it is necessary to reduce the DC offset voltage in order to minimize the carrier leak, steps S33 and S3 are performed.
At 4, the voltage decrease is repeated until the amplitude fluctuation is minimized. Finally, since steps S31 to S34 are performed, the DC offset voltage is lower than the optimum value by n. Therefore, the DC offset voltage is increased to the optimum value in step S35. Thus the final DC
The offset voltage is determined and the value is held thereafter.

Next, the image leak is minimized by the procedure shown in the flowchart of FIG. The image leak can be minimized by adjusting the I and Q amplitude voltages, but the actual monitoring is performed so that the time-varying value of the same output amplitude value of the quadrature modulator 1 is minimized. Therefore, it is preferable to adjust the other of the DC offset and the I and Q amplitudes after the adjustment of the other is completed. The procedure is the same as when adjusting the DC offset voltage. That is, when it is necessary to increase the amplitude voltage in order to minimize the image leak, steps S36 and S37 are repeated, and conversely, when it is necessary to decrease the amplitude voltage,
By repeating steps S38 and S39, the voltage generation circuit 8 is controlled so that the amplitude fluctuation of the modulated wave output from the quadrature modulator 1 is minimized.
Control value to control. Finally, in step S40, the amplitude voltage is adjusted to the optimum value, and the I or Q final amplitude voltage is held thereafter. By the above operation, the distortion components of carrier leak and image leak are suppressed to a minimum.

Relationship between carrier leak and image leak,
The relationship between the carrier leak and the like and the time change value of the output of the quadrature modulator will be described. FIG. 8 is a diagram showing frequency vs. output level, and is a diagram corresponding to FIG. 12 of the related art. Figure 8
This is the output level of the quadrature modulator 1 when there are I and Q signal inputs. Minimizing the time variation of the output of the quadrature modulator 1 in FIG. 1 is equivalent to decreasing the peak values of carrier leak and image leak in FIG. In this way, if the output level of only the frequency components of the I and Q signals which are the desired waves is increased, the modulation characteristic is improved.

Example 2. In the above embodiment, the microprocessor 7 adjusts the DC offset voltage and the amplitude voltage of the I and Q baseband signals once by the procedure of the flowcharts of FIGS. 2 and 3 to perform the adjustment to suppress the distortion component. . However, the other distortion component may increase to some extent during the adjustment of one distortion component. Therefore, if the steps of the flowcharts of FIGS. 2 and 3 are repeated many times, the amplitude fluctuation of the modulated wave is minimized. , The distortion component can be minimized more accurately.

Example 3. In this embodiment, an example will be described in which the time variation of the output amplitude value of the quadrature modulator is expanded and the offset and the I and Q signal amplitudes are controlled more accurately. FIG. 4 is a circuit configuration diagram of the distortion component suppressing quadrature modulator of the present embodiment. In the figure, 9 is an amplifier, which is provided between the detection circuit 3 and the analog / digital converter 6. In this way, when the output voltage of the detection circuit 3 is small, amplification is performed by the amplifier 9, and it becomes possible to detect the amplitude fluctuation of the modulated wave more precisely.

Example 4. Further, in this embodiment, the amplifier is a variable gain amplifier. FIG. 5 is a block diagram of the quadrature modulator of the present embodiment, in which the amplifier between the detection circuit 3 and the analog / digital converter 6 is a variable gain amplifier 10 whose gain is switched by a signal from the microprocessor 7. . When the amplitude variation of the modulated wave cannot be detected in the current measurement time, the gain switching control signal is issued from the microprocessor 7 to increase the amplification factor of the variable gain amplifier 10, and the amplitude variation of the modulated wave can be detected more accurately. Becomes

As a detailed configuration of the variable amplifier 10, there is a circuit shown in FIG. 6, for example. Analog multiplexer 24, 2
5 is switched by a control signal from the microprocessor 7 to switch the amplification factor.

Embodiment 5 FIG. Another embodiment for detecting the time variation of the output amplitude value of the quadrature modulator to be monitored more precisely will be described. FIG. 7 is a circuit configuration diagram of the quadrature modulator of this embodiment. In the figure, the amplifier 9 is a differential amplifier and provides 28 reference values as a differential input. That is, the quadrature modulator 1
The output amplitude value of is subtracted by the reference value 28, and the time variation is amplified and input to the microprocessor 7. The subsequent control operation of the microprocessor 7 is similar to that of the other embodiments. It should be noted that the present embodiment and the fourth embodiment are combined so that the amplifier 10 is a variable gain differential amplifier, and the difference input is 28.
It may be configured to give the reference value of.

[0030]

As described above, according to the present invention, a quadrature modulator having a test mode of setting data 0, a detection circuit, a processor for issuing a control signal based on a change with time of detected amplitude, an offset, and I, Q signals. Since a voltage generation circuit that outputs the amplitude of is provided, it is effective in suppressing distortion that is a combination of carrier leak and image leak.

Furthermore, since an amplifier for amplifying the detection output is provided, there is an effect that a more precise time change of the amplitude of the detection waveform can be detected and a more precise distortion suppression can be performed.

Furthermore, since the amplification degree of the amplifier is switched, there is an effect of stabilizing the process until the distortion suppression value is determined.

Furthermore, since the amplifier with the reference subtraction value for amplifying the detection output is provided, there is an effect that a more precise time change of the amplitude of the detection waveform can be detected and more precise distortion suppression can be performed.

Furthermore, since the processor firstly changes one control output to obtain a result and then changes the other control output, it has an effect of stabilizing the process up to the determination of the distortion suppression value.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a quadrature modulation device that is an embodiment of the present invention.

2 is a flowchart showing a procedure for adjusting a DC offset voltage of I and Q baseband signals in the quadrature modulator of FIG.

3 is a flowchart showing a procedure for adjusting the amplitude voltage of the I and Q baseband signals in the quadrature modulator of FIG.

FIG. 4 is a configuration diagram of a quadrature modulator according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a quadrature modulator according to a fourth embodiment of the present invention.

FIG. 6 is a detailed circuit diagram showing an example of the variable gain amplifier of FIG.

FIG. 7 is a configuration diagram of a quadrature modulator according to a fifth embodiment.

FIG. 8 is a diagram showing frequency versus output level of a quadrature modulator.

FIG. 9 is a block diagram of a conventional quadrature modulator.

FIG. 10 is a diagram illustrating a basic configuration of a quadrature modulator.

FIG. 11 is a diagram showing the relationship between I and Q signals, modulator output, and output waveform after detection.

FIG. 12 is a diagram showing a relationship between an output and a carrier leak when a transmission of a conventional quadrature modulator is OFF.

[Explanation of symbols]

1 quadrature modulator, 2 coupling capacitors, 3 detection circuit,
4 switches, 5 voltage holding circuit, 6 analog / digital converter, 7 microprocessor, 8 voltage generation circuit, 9 amplifier, 10 variable gain amplifier, 11 I signal input terminal, 12 Q signal input terminal, 13 local signal input terminal , 14 RF output terminal, 21 resistor, 22 resistor, 23 resistor, 24 analog multiplexer, 2
5 Analog multiplexer, 26 Inverter, 27
Operational amplifier, 28 reference value terminal.

Claims (5)

[Claims] 1. A quadrature modulator which has a test mode in which all setting data can be set to 0, outputs a quadrature modulation of input I channel and Q channel signals, a detection circuit which detects and outputs the quadrature modulation output, and the detection output. Memorize the elapsed time value of the test amplitude value
A microprocessor that outputs a control signal that changes the DC offset and amplitude of the I channel or Q channel signal according to a predetermined rule; and a DC offset and amplitude of the I channel and Q channel signal that is output by the control signal of the microprocessor. A quadrature modulation device comprising a voltage generation circuit and changing the output of the voltage generation circuit so that the change of the elapsed time value of the output of the quadrature modulator in the test mode is equal to or less than a set value. 2. The quadrature modulator according to claim 1, further comprising an amplifier for amplifying the detection output, wherein the amplifier output is input to a microprocessor. 3. The quadrature modulator according to claim 2, wherein the amplification degree of the amplifier can be switched. 4. Further, the amplifier receives the reference subtraction value, amplifies the difference between the detection output and the reference value, and outputs the difference to the microprocessor.
The quadrature modulator described. 5. The microprocessor first sets the DC
Change the offset to output a control signal so that the change of the test amplitude value over time becomes less than or equal to the set value, and then change the amplitude of the I channel or Q channel signal to set the change of the test amplitude value over time. The control signal is output so that it becomes less than or equal to the value, or conversely, the amplitude of the channel signal is first changed to monitor the set value, and then the DC offset is changed to monitor the set value to determine the control signal. The quadrature modulator according to claim 1, characterized in that.