JP2003087129A - Wireless transmission circuit - Google Patents

Abstract

(57) [Problem] To provide a radio transmission circuit capable of improving adjacent channel leakage power characteristics with a simple configuration without causing a loss in transmission output. SOLUTION: At least a power amplifier for power-amplifying an output of a transmission modulator, a distortion component detector for detecting a distortion component of an output of the power amplifier and outputting a detection voltage, and an output from the distortion component detector And an impedance switch that switches the impedance in response to the detection voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless transmission circuit, and more particularly to a wireless transmission circuit which can improve adjacent channel leakage power characteristics with a simple structure without giving a loss to a transmission output. In mobile communication terminal devices, there are strong demands for device miniaturization and low power consumption, but recently, in order to meet the increasing demand for mobile communication, the frequency band is expanded to increase the line capacity and downsize. The pursuit of low power consumption is being carried out. Moreover, since the line capacity is increased, it is an important matter to secure the adjacent channel leakage power characteristic under low power consumption.

Since the adjacent channel leakage power characteristic relates to non-linear distortion, ensuring the adjacent channel leakage power characteristic is essential for a wireless transmission circuit including a power amplifier that amplifies a transmission output to a high output. It is a matter. Moreover, in the mobile communication terminal device, it is necessary to realize it under the condition of downsizing, which is technically difficult.

[0003]

2. Description of the Related Art FIG. 13 shows the configuration of a conventional wireless transmission circuit using a load matching device. In FIG. 1, 1 is a radio frequency oscillator that generates a carrier wave in the radio frequency band, 2 is a transmission modulator that converts a transmission signal into a transmission signal by the output of the radio frequency oscillator 1, and 3 is an output of the transmission modulator 2. A power amplifier that amplifies a signal to a level required for wireless communication (in the figure, Power Amplifier is abbreviated as "PA". In the following figures, it is also described in the same manner.), And 6 is a power amplifier 3 A load matcher for maintaining good output characteristics of the antenna in the transmission frequency band, 7 is an isolator for stabilizing the load impedance of the power amplifier 3 by absorbing the impedance variation of the antenna, and 8 radiates the transmission output to space. It is an antenna.

Since the impedance variation of the antenna 8 is caused by the surrounding conditions of the mobile communication terminal device such as a building or terrain and the orientation of the antenna itself, it is accompanied by the movement of the mobile communication terminal device. It is normal for the impedance of the antenna to fluctuate. And
In the conventional radio transmission circuit, the load impedance of the power amplifier is set as appropriate as possible by the load matching device 6 having a fixed constant.

In addition to the technique of connecting the load matching device 6 to the output side of the power amplifier 3, there is a means for improving the adjacent channel leakage power characteristic. FIG. 18 shows a distortion correction method for a power amplifier by pre-distortion. In FIG. 18, 9 is a distortion generator and 3 is a power amplifier. In the configuration of FIG. 18, the distortion signal generated by the power amplifier 3 has a polarity opposite to that of the distortion signal generated by the distortion generator 9.
To supply linearly to the power amplifier 3 to suppress the distortion component of the power amplifier 3.

Although the distortion generator 9 generates a preset distortion signal in FIG. 18, when the distortion characteristic of the power amplifier 3 greatly varies due to the fluctuation of the power supply voltage or the ambient temperature, The output of the power amplifier 3 is fed back to the distortion generator 9, the levels of the fundamental wave components of the output of the transmission modulator and the output of the power amplifier 3 are made equal to each other, and the difference is extracted to extract the distortion component. It is preferable that the distortion generator 9 generates a distortion component and supplies it to the power amplifier 3 so as to minimize the level.

As a result, the adjacent channel leakage power characteristic of the power amplifier 3 can be greatly improved. FIG. 19
Is a distortion correction method for a power amplifier by feed forward. In FIG. 19, 10 is a hybrid for branching the signal from the transmission modulator (abbreviated as “H” in the figure by the acronym of Hybrid. In the following, it is also described in the same manner), and 12 is for the hybrid 10. An amplitude / phase adjuster for adjusting the amplitude and phase of one output, 3 is a power amplifier,
Reference numeral 13 is a delay line that delays the other output of the hybrid 10 by a time equal to the delay time in the amplitude / phase adjuster 12 and the power amplifier 3. Reference numeral 11 denotes a distortion circuit that applies distortion to one output of the hybrid 10 (this can be configured by an amplifier and an attenuator that cancels the gain of the amplifier with respect to the fundamental wave).

The reference numeral 10a receives the output of the power amplifier 3 accompanied by the distortion signal and the output of the delay line 13, and outputs the main signal including the fundamental wave component and the distortion component of the power amplifier 3 to the output terminal A side, It is a hybrid that outputs the distortion component of the power amplifier 3 to the output terminal B side. Reference numeral 12a is an amplitude / phase adjuster for adjusting the amplitude and phase of the distortion component of the power amplifier 3 output to the output terminal B side of the hybrid 10a.

Reference numeral 10b is a hybrid which outputs the difference between the output on the A side of the hybrid 10a and the output of the amplitude / phase adjuster 12a. The configuration of FIG. 19 operates as follows.
That is, the output of the transmission modulator is 2 in the hybrid 10.
It branches and supplies one output of the hybrid to the amplitude / phase adjuster 12 and the power amplifier 3, and gives the other output of the hybrid 10 a delay equal to the delay time of the amplitude / phase adjuster 12 and the power amplifier 3. To the hybrid 10a, and the hybrid signal is separated into the main signal output from the power amplifier 3 and the distortion component output from the power amplifier 3 in the hybrid 10a.

Then, the amplitude and phase of the distortion component output from the hybrid 10a are adjusted by the amplitude / phase adjuster 12a so that the amplitude equal to the distortion component of the main signal output from the hybrid 10a to the output terminal A side is reversed. The phase distortion component is used to cancel the distortion component in the hybrid 10b. This is possible because the information on the distortion component of the power amplifier can be known by experiments or the like performed in advance.

Therefore, the distortion component of the power amplifier 3 can be canceled at the output of the hybrid 10b, and the adjacent channel leakage power characteristic of the power amplifier 3 can be greatly improved.

[0012]

Now, in the power amplifier 3, in order to improve the power efficiency within the determined power consumption, the operating point is not set in the linear region, but in the nonlinear region immediately before the output is saturated. Often put. FIG. 14 illustrates the input / output characteristics of the power amplifier to show the above matters.

In FIG. 14, the horizontal axis is the input power to the power amplifier, the left vertical axis is the output power of the power amplifier, and the right vertical axis is the adjacent channel leakage power of the power amplifier. The output power of the power amplifier increases in proportion to the input power while the input power is relatively small and the power amplifier is operating in the linear region, and the adjacent channel leakage power is relatively small in this region.

On the other hand, when the input power becomes large and the power amplifier operates in the non-linear region, the output power becomes no longer proportional to the input power and finally saturates. Then, the adjacent channel leakage power rapidly increases in the non-linear region. Therefore, in order to keep the power efficiency as high as possible within the determined power consumption and keep the adjacent channel leakage power as small as possible, it is usual to place the operating point in the nonlinear region immediately before the output is saturated.

FIG. 15 is a distortion characteristic in the linear region, FIG.
6 is the distortion characteristic in the non-linear region. In FIGS. 15 and 16, the output of the radio frequency modulator when no transmission signal is applied to the transmission modulator of FIG. 13 and only the carrier of the radio frequency band is applied in order to avoid complication of the drawings. The distortion characteristic in the case of a power amplifier is illustrated. In FIGS. 15 and 16, the horizontal axis is the frequency, and f ₀ on the frequency axis is the frequency of the output of the radio frequency oscillator 1. Therefore, 2f ₀ and 3f ₀ on the frequency axis are the harmonic frequencies of the output of the radio frequency oscillator 1. Generally, there are harmonics of 4 times or more, but FIGS. 15 and 16 show only harmonics of 3 times.

On the other hand, in FIGS. 15 and 16, the vertical axis represents the level of each (frequency) component forming the output of the power amplifier. Incidentally, the ratio of the level of the fundamental wave and the level of each harmonic is expressed in dB (decibels), and the ratio of the harmonic attenuation amount, the level of the fundamental wave and the total level of all distortion components is expressed in dB. The thing is distortion. When the output of the radio frequency oscillator is modulated by the transmission signal, the spectrum of the transmission signal appears around the fundamental wave component and the harmonic component in FIGS. 15 and 16.

In general, the harmonic attenuation amount and distortion factor in the linear region are better than the harmonic attenuation amount and distortion factor in the nonlinear region. Therefore, the distortion characteristic is naturally deteriorated in the power amplifier operating in the non-linear region. As described above, poor distortion characteristics are equivalent to poor adjacent channel leakage power characteristics. Moreover, the adjacent channel leakage power characteristic of the power amplifier is also affected by the load impedance of the power amplifier. This is because when the load impedance is too low, it is necessary to output a large current in order to output a predetermined electric power, and when the load impedance is too high, it is necessary to output a large voltage in order to output a predetermined electric power. This is because the adjacent channel leakage power characteristic deteriorates.

FIG. 17 is an adjacent channel leakage power characteristic of a power amplifier to which a conventional load matching device is applied. In FIG. 17, the horizontal axis represents frequency and the vertical axis represents adjacent channel leakage power characteristics. The smaller the coordinate on the vertical axis, the better the adjacent channel leakage power characteristic. Further, it is assumed that the frequency f ₁ is the frequency at the low end and the frequency f ₂ is the frequency at the high end.

FIG. 17 shows an example in which the adjacent channel leakage power characteristics are deteriorated at the low band edge and the high band edge, and the adjacent channel leakage power characteristics are best near the center of the band. This is a case where the output impedance of the power amplifier and the impedance of the load matching device are matched near the center of the band, and the output impedance of the power amplifier and the impedance of the load matching device are mismatched at the band end.

For example, if the impedance of the load matching device is high at the low band end and the impedance of the load matching device is low at the high band end, the impedance of the load matching device is lowered at the low band end and the load matching is performed at the high band end. If variably controlled so as to increase the impedance of the device, it should be possible to ensure good adjacent channel leakage power characteristics in a wide band. However, since the conventional load matching device has a fixed circuit constant,
The above control is impossible, and after all, the constant of the load matching device must be determined so that the adjacent channel leakage power characteristic becomes an average characteristic in the band.

On the other hand, the means for improving the adjacent channel leakage power characteristics by pre-distortion or feed forward has a circuit scale large enough to be finally realized on a large printed board, and in particular, a pre-loop having a feedback loop is used. Distortion also requires relatively large scale software processing. Therefore, pre-distortion and feed
Although it is possible to apply the means for improving the adjacent channel leakage power characteristic by forward, it is not possible to apply pre-distortion or feed-forward in a device such as a mobile communication terminal device where small size is the highest priority. It is impossible.

In view of the above problems, the present invention relates to a radio transmission circuit, and more particularly, to a radio transmission circuit which can improve adjacent channel leakage power characteristics with a simple structure without giving a loss to a transmission output. The purpose is to provide.

[0023]

SUMMARY OF THE INVENTION A first invention is at least a power amplifier for power-amplifying the output of a transmission modulator, and a distortion component detection for detecting a distortion component of the output of the power amplifier and outputting a detection voltage. And a impedance switching device that switches impedance by receiving a detection voltage output from the distortion component detector.

According to the first aspect of the present invention, the impedance changer switches the impedance according to the detection voltage which the distortion component detector detects and outputs the harmonic component of the output of the power amplifier. The matching state at the terminal can be made variable depending on the frequency, and the adjacent channel leakage power characteristic can be improved in a wide band within the pass band.

A second invention is the radio transmission circuit according to the first invention, wherein the distortion component detector is inserted in parallel with the output line of the power amplifier, and the fundamental wave component output by the power amplifier is lost. Is a distortion component detector that rectifies an output of a circuit capable of extracting only a distortion component without generating a signal and generates a detection voltage. According to the second invention, since the distortion component detector rectifies the output of the circuit capable of extracting only the distortion component output from the power amplifier to generate the detection voltage, the power for generating the detection voltage is detected. The adjacent channel leakage power characteristic can be improved within the pass band without giving a loss to the fundamental wave component of the output of the amplifier, that is, the output of the wireless transmission circuit.

A third aspect of the present invention is the radio transmission circuit of the first aspect, wherein the impedance switching device receives the detection voltage output from the distortion component detector and is turned on / off by a switch that is turned on / off to control the power amplifier. The wireless transmission circuit is an impedance switcher that switches an impedance connected to an output terminal. According to the third aspect of the invention, the impedance switcher switches the impedance connected to the output terminal of the power amplifier by a switch that is controlled to be turned on and off by receiving the detection voltage output by the distortion component detector, The load impedance of the power amplifier can be varied depending on the frequency with a simple configuration, and the adjacent channel leakage power characteristic can be improved within the pass band without complicating the configuration of the wireless transmission circuit.

[0027]

DETAILED DESCRIPTION OF THE INVENTION The technique of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram for explaining the principle of distortion reduction of a power amplifier according to the present invention, and illustrates the components from the power amplifier to the load matching device in the wireless transmission circuit. In FIG. 1, 3 is a power amplifier that amplifies the output of a transmission modulator (not shown) to a level required for wireless communication, and 4 is a predetermined level or higher by extracting only harmonic components from the output of the power amplifier 3. When a harmonic component of is detected, a detection voltage is output and the fundamental component is passed through with low loss. A distortion component detector 5 receives the fundamental component passed by the distortion component detector 4 at its input terminal to detect the distortion component. An impedance switching device that receives the detection voltage output from the device 4 at its control terminal and switches the impedance with respect to the fundamental wave component, and a load matching device 6 that maintains good output characteristics of the power amplifier 3 in the transmission frequency band.

In the configuration of FIG. 1, since the distortion component detector 4 can reduce the loss presented to the fundamental wave component of the output of the power amplifier 3, the load from the output terminal of the power amplifier 3 via the impedance of the impedance switching device 5 can be achieved. The impedance looking into the input terminal of the matching device 6 can be seen. Now, the detection voltage that the distortion component detector 4 detects and outputs a harmonic component of a predetermined level or higher is supplied to the control terminal of the impedance switching device, and is not shown in FIG. 1 (details of the configuration of the impedance switching device will be described later. The switching element which is connected to the input terminal of the load matching unit 6 is switched by driving the switching element. Therefore, when the distortion component detector 4 outputs the detection voltage, the impedance seen from the output terminal of the power amplifier 3 changes.

By the way, since the distortion characteristic of the power amplifier 3 changes according to the frequency characteristic of the load impedance, it is possible to improve the distortion characteristic of the power amplifier 3 according to the change of the impedance of the impedance switching device 5. That is, this is the principle of distortion reduction of the power amplifier of the present invention. Hereinafter, detailed configurations of the distortion component detector and the impedance switching unit and reduction of the distortion characteristic of the power amplifier by the configuration of FIG. 1 will be described in detail.

FIG. 2 shows the configuration (1) of the distortion component detector. In FIG. 2, reference numeral 4-1 is a capacitor, 4-2 is an inductor, which is a series circuit that resonates with the harmonic component of the output of the power amplifier 3 of FIG. 1 by the capacitor 4-1 and the inductor 4-2 to extract the harmonic component. Configure a resonant circuit. 4-
Reference numeral 3 is a diode for rectifying the harmonic component extracted by the series resonance circuit, and 4-4 is a capacitor for storing the charge rectified by the diode 4-3.

Reference numeral 4-5 is an inductor, and 4-6 is a resistor, which is a smoothing circuit for smoothing the voltage rectified by the inductor 4-5 and the resistor 4-6 and stored in the capacitor 4-4 to generate a detection voltage. Constitute. A choke coil 4-7 takes out the detected voltage with low resistance in terms of direct current and high impedance in terms of high frequency. That is, the distortion component detector having the configuration of FIG. 2 is inserted in parallel between the power amplifier 3 and the impedance switch 5 of FIG.

Here, for example, if the resonance frequency of the series resonant circuit is matched with the frequency of the third harmonic component of the output of the power amplifier 3 of FIG. 1, the impedance exhibited by the series resonant circuit as the fundamental wave component is shown. Can be made sufficiently high, so that even if the distortion component detector having the configuration of FIG. 2 is connected to the output terminal of the power amplifier 3 of FIG. 1, the loss of the fundamental wave component output by the power amplifier 3 is extremely small. Becomes Therefore, the distortion component detector configured as shown in FIG. 2 can extract the harmonic component with almost no influence on the fundamental component output from the power amplifier 3.

In the above description, the resonance frequency of the series resonance circuit is made to match the frequency of the third harmonic component, but it may be made to match the frequency of any harmonic component. However, in the case of matching with the second harmonic component, there is a slight risk of giving a loss to the fundamental component when the quality factor of the series resonance circuit (so-called Q of the circuit) is low, and When the output waveform of the power amplifier 3 in FIG. 1 is oddly symmetrical with respect to zero crossing, the level of the even-order harmonic component becomes low, and the level of the harmonic component originally having a high order is low. Considering this, it can be said that the third harmonic is optimal when detecting a single harmonic.

Also, instead of detecting a single harmonic,
It is also possible to detect the power of all distortion components. In this case, instead of the series resonance circuit of FIG. 2, a high-pass filter that blocks the fundamental wave component may be arranged, and the output of the high-pass filter may be square-law detected to obtain a detection voltage. However, in this configuration, it is necessary to design the high-pass filter so as not to complicate the configuration.

In any case, the distortion component detector described with reference to FIG. 2 is generally inserted in parallel to the output line of the power amplifier, and the fundamental wave component output by the power amplifier is lost. Can be said to be a distortion component detector that rectifies the output of a circuit capable of extracting only the distortion component without generating the above and generates a detection voltage. Next, FIG. 3 shows a configuration (No. 1) of the impedance switching device.

In FIG. 3, 5-1 is a diode and 5-
2 is a choke coil and 5-3 is a capacitor. In FIG. 3, the detection voltage output from the distortion component detector is supplied to the control terminal, and a current flows through the diode 5-1 and the choke coil 5-2. As a result, when the detection voltage is not supplied, the capacitor 5-3 is not connected to the line between the distortion component detector and the load matching device, and when the detection voltage is supplied, the capacitor 5-3 distorts the distortion component. Connected to the line between the detector and the load matcher.

That is, the impedance presented by the impedance switching device can be variably controlled depending on whether or not the detection voltage is applied. Therefore, the impedance of the load matching device can be variably controlled in the sense that it includes the impedance of the impedance switching device, and the distortion characteristic of the power amplifier can be improved. FIG. 4 shows the distortion component detector shown in FIG.
4 is an embodiment of the distortion mitigation of the power amplifier of the present invention, in which the distortion component detector having the configuration described above is applied and the impedance switching device having the configuration illustrated in FIG. 3 is applied to the impedance switching device.

In FIG. 4, 3 is a power amplifier. Four
Is a distortion component detector, and its constituent elements are as follows. That is, 4-1 is a capacitor, 4-2 is an inductor, 4-3
Is a diode that rectifies the harmonic component extracted by the series resonance circuit formed by the capacitor 4-1 and the inductor 4-2,
4-4 is a capacitor for accumulating charges rectified by the diode 4-3, 4-5 is an inductor, 4-6 is a resistor, 4-7
Is a choke coil that extracts the detected voltage with low resistance in terms of direct current and high impedance in terms of high frequency.

Reference numeral 5 is an impedance switch, and its constituent elements are as follows. That is, 5-1 is a diode, 5
-2 is a choke coil and 5-3 is a capacitor.
6 is a load matching device. FIG. 7 is a Smith chart explaining the distortion correction in the present invention. The Smith chart is used by those skilled in the wireless communication technology on a daily basis for designing and studying characteristics.
The description of the chart itself is omitted.

Now, the frequency f in the low band of the transmission band₁In the vicinity
The power amplifier is point P in FIG.₁Adjacent in load corresponding to
Good channel leakage power characteristics and high transmission band
Frequency f₂In the vicinity, the power amplifier is point P in FIG.₂Against
Adjacent channel leakage power characteristics are
Suppose there is. At such times, the load impedance of the power amplifier
If the dance is determined only by the impedance of the load matcher
For example, the adjacent channel leakage power characteristic of the power amplifier is frequency f
₁Even if the frequency is good in the vicinity, the frequency f₂Adjacent
The channel leakage power characteristics will deteriorate. Avoid this
Frequency f₁In the vicinity, P in FIG.₁Load corresponding to
The impedance of the matcher terminates the power amplifier and the frequency
f₂In the vicinity, P in FIG. ₂With impedance corresponding to
The power amplifier should be terminated.

Now, based on the above assumption, at frequency f ₁ ,
Since the load impedance corresponding to the point P ₁ in FIG. 7 gives the power amplifier a good adjacent channel leakage power characteristic, the distortion component detector of FIG. 4 does not output the detection voltage. Therefore, the capacitor 5-3 in FIG. 4 is not connected to the line between the power amplifier 3 and the load matching device 6, and the power amplifier 3 is terminated under good conditions.

On the other hand, based on the above assumption, at frequency f ₂ ,
If the power amplifier 3 is terminated by the impedance corresponding to the point P ₂ in FIG. 7, the adjacent channel leakage power characteristic of the power amplifier 3 will be good. For this purpose, the load impedance of the power amplifier 3 may be changed from the impedance corresponding to the point P ₁ to the impedance corresponding to the point P ₂ , which is parallel to the input terminal of the load matching device 6 near the frequency f _2. It can be realized by connecting a capacitor to.

[0043] Now, when the load impedance of the power amplifier at the frequency f ₂ vicinity is different from the impedance corresponding to P _2, the adjacent channel leakage power characteristic of the power amplifier 3 is deteriorated, the distortion component detector 4 detects Output voltage. The detected voltage turns on the diode 5-1 of the impedance switching device 5 and connects the capacitor 5-3 to the line between the power amplifier 3 and the load matching device 6. Therefore,
Can be connected to the capacitor in parallel to the input terminal of the load matching unit 6 at the frequency f ₂ vicinity, it is possible to improve the adjacent channel leakage power characteristic of the power amplifier 3 at frequency f ₂ vicinity.

FIG. 5 shows the adjacent channel leakage power characteristic (No. 1) of the power amplifier to which the present invention is applied, showing the characteristic in the vicinity of frequency f _1. FIG. 6 is the adjacent channel of the power amplifier to which the present invention is applied. Leakage power characteristics (2), frequency f
_It shows the characteristics in the vicinity of ₂ . 5 and 6, the horizontal axis represents frequency and the vertical axis represents adjacent channel leakage power characteristics.

Based on the above assumption, adjacent channel leakage power characteristics are good in the vicinity of frequency f ₁ . Here, when the load impedance of the power amplifier 3 in FIG. 4 is determined only by the impedance of the load matching device 6, the adjacent channel leakage power characteristics deteriorate near the frequency f ₂ as indicated by the broken line in FIG. . However, since the load impedance of the power amplifier 3 is changed in the vicinity of the frequency f _{2 in} the configuration of FIG. 4, the adjacent channel leakage power characteristics can be improved even in the vicinity of the frequency f _{2 as} shown in FIG. The characteristic of the broken line shown in FIG. 6 is the adjacent channel leakage power characteristic of the power amplifier 3 when the load impedance of the power amplifier 3 is determined only by the impedance of the load matching device 6.

Since the impedance switching device having the configuration shown in FIG. 4 is adapted to select whether or not to connect the capacitor 5-3 according to the detected voltage, the frequencies f ₁ and f ₂
Adjacent channel leakage power characteristics may deviate from the optimum characteristics near the middle of. However, in the impedance switching device 5, it is possible to adopt a configuration in which the capacitors having different capacitances can be connected to the line between the power amplifier 3 and the load matching device 6 by the diodes having different ON characteristics.
The load impedance of the power amplifier 3 can be gradually changed according to the change of the detection voltage output from the distortion component detector 4, and the frequency characteristic of the adjacent channel leakage power characteristic of the power amplifier 3 can be improved. . This is
The same applies to the case of using the distortion component detector and impedance switching device described below.

The technique of the present invention has been described above by showing the specific configurations of the distortion component detector and the impedance switching device. After that, another configuration example of the distortion component detector and the impedance switching device will be described. FIG. 8 is a configuration (No. 2) of the distortion component detector. In FIG. 8, 4-8 is a planar circuit element electrostatically coupled to the line between the power amplifier and the impedance switch, 4-3 is a diode for rectifying the harmonic component extracted by the planar circuit element, 4- Reference numeral 4 is a capacitor that stores the charges rectified by the diode 4-3.

Reference numeral 4-5 is an inductor, and 4-6 is a resistor, which is a smoothing circuit for smoothing the voltage rectified by the inductor 4-5 and the resistor 4-6 and stored in the capacitor 4-4 to generate a detection voltage. Constitute. A choke coil 4-7 takes out the detected voltage with low resistance in terms of direct current and high impedance in terms of high frequency. In the configuration of FIG. 8, the planar circuit element 4-8 is electrostatically coupled to the line between the power amplifier and the impedance switch, and forms an inductor between the upper end and the lower end of the planar circuit element 4-8. Therefore, the plane circuit element 4-8 constitutes a series resonance circuit. If the resonance frequency of the series resonance circuit is matched with the frequency of the harmonic component of the output of the power amplifier, the harmonic component, that is, the distortion component is extracted without affecting the transmission characteristic for the fundamental wave component output by the power amplifier. be able to. That is, the distortion component detector having the configuration shown in FIG. 8 is also inserted in parallel to the output line of the power amplifier, does not give a loss to the fundamental wave component output from the power amplifier, and can extract only the distortion component. It can be said that the distortion component detector rectifies the output to generate a detection voltage.

FIG. 9 shows the configuration (No. 3) of the distortion component detector. In FIG. 9, 4-9 are directional couplers coupled to the line between the power amplifier and the impedance switch, 4
-10 is a resistor that terminates one end of the directional coupler 4-9, 4
-3 is a diode that rectifies the component extracted by the directional coupler 4-9, and 4-4 is a capacitor that stores the charge rectified by the diode 4-3.

Reference numeral 4-5 is an inductor, and 4-6 is a resistor, which is a smoothing circuit for smoothing the voltage rectified by the inductor 4-5 and the resistor 4-6 and stored in the capacitor 4-4 to generate a detection voltage. Constitute. A choke coil 4-7 takes out the detected voltage with low resistance in terms of direct current and high impedance in terms of high frequency. In the configuration of FIG. 9, in the directional coupler 4-9, the fundamental wave component of the output of the power amplifier does not branch from the line between the power amplifier and the impedance switcher, and the harmonic component included in the output of the power amplifier. Is branched from the line between the power amplifier and the impedance switch. For example, in order to branch the third harmonic component, the length of the directional coupler 4-9 may be made equal to 1/4 of the wavelength of the third harmonic component. Therefore, the distortion component detector of FIG. 9 is also inserted in parallel to the output line of the power amplifier, and the output of the circuit capable of extracting only the distortion component without giving a loss to the fundamental wave component output from the power amplifier is output. It can be said that the distortion component detector rectifies and generates a detection voltage.

The distortion component detector having the structure shown in FIGS. 8 and 9 can be applied to the structure shown in FIG. 1 similarly to the distortion component detector having the structure shown in FIG. FIG. 10 shows a configuration (No. 2) of the impedance switching device. In FIG. 10, 5-1 is a diode, 5-2 is a choke coil, 5-4 is an inductor, and 5-5 is a battery of a predetermined voltage.

In the configuration of FIG. 10, the detection voltage output from the distortion component detector is supplied to the control terminal and the diode 5-
1 and choke coil 5-2. As a result, when the detection voltage is not supplied, the diode 5
Since the inductor 5-1 is turned on, the inductor 5-4 is short-circuited, and when the detection voltage is supplied, the diode 5-1 is turned off. Therefore, the inductor 5-4 is connected to the distortion component detector and the impedance switching device. It is inserted in series between the lines. That is, the impedance presented by the impedance switching device can be variably controlled depending on whether or not the detection voltage is applied.

Therefore, the impedance of the load matching device can be variably controlled in a sense including the impedance of the impedance switching device, so that the distortion characteristic of the power amplifier can be improved. FIG. 11 is a Smith diagram for explaining the distortion correction when the impedance switching device having the configuration of FIG. 10 is applied.
It is a chart.

Now, it is assumed that the power amplifier has good adjacent channel leakage power characteristics in the load corresponding to the point P ₃ in FIG. 11 near the frequency f _{1 in} the low band of the transmission band, and the frequency f _{2 in} the high band of the transmission band. In the vicinity, it is assumed that the power amplifier has good adjacent channel leakage power characteristics at the load corresponding to the point P ₄ in FIG. 7. In such a case, if the load impedance of the power amplifier is determined only by the impedance of the load matching device, the adjacent channel leakage power characteristic of the power amplifier is good in the vicinity of frequency f ₁ , but the adjacent channel leakage power is in the vicinity of frequency f _2. The power characteristics will deteriorate. In order to avoid this, the power amplifier is terminated with the impedance of the load matching device corresponding to P ₃ in FIG. 11 near the frequency f ₁ , and the power amplifier is terminated with the impedance corresponding to P ₄ in FIG. 11 near the frequency f ₂ . You can do it.

By the above assumption, at frequency f ₁ ,
Since the load impedance corresponding to point P ₃ in FIG. 11 gives the power amplifier good adjacent channel leakage power characteristics,
The distortion component detector does not output the detection voltage. Therefore, FIG.
The inductor 5-4 does not affect the impedance between the power amplifier 3 and the load matcher 6, and the power amplifier is terminated under good conditions.

On the other hand, based on the above assumption, at frequency f ₂ ,
If the power amplifier is terminated by the impedance corresponding to the point P ₄ in FIG. 11, the adjacent channel leakage power characteristic of the power amplifier will be good. Therefore, the load impedance of the power amplifier is changed from the impedance corresponding to the point P ₃ to the point P _3.
It may be changed to an impedance corresponding to ₄ , which can be realized by connecting an inductor in series with the input terminal of the load matching device 6 in the vicinity of the frequency f ₂ .

When the load impedance of the power amplifier is different from the impedance corresponding to P ₄ in the vicinity of the frequency f ₂ , the adjacent channel leakage power characteristic of the power amplifier is deteriorated and the distortion component detector detects the detected voltage. Output. The detected voltage turns off the diode 5-1 of the impedance switching device configured as shown in FIG. 10 and connects the inductor 5-4 to the line between the power amplifier 3 and the load matching device 6.

[0058] Accordingly, it is possible to connect the inductor in series with the input terminal of the load matching unit at the frequency f ₂ vicinity, it is possible to improve the adjacent channel leakage power characteristic of the power amplifier at the frequency f ₂ vicinity. FIG. 12 shows a configuration (No. 3) of the impedance switching device. In FIG. 12, 5-1
4 and 5-15 are transmission lines with different lengths, 5-6, 5
-7, 5-8 and 5-9 are diodes 5 which are on / off controlled by a detection voltage supplied from the distortion component detector,
-10, 5-11, 5-12 and 5-13 are chokes.
It is a coil. In the configuration of FIG. 12, the detection voltage supplied by the distortion component detector seems to be directly supplied to the line between the power amplifier and the load matching device, but the output of the detection voltage of the distortion component detector described above is output. There is no problem because a choke coil is inserted in series with the terminal.

In the configuration of FIG. 12, one of the transmission lines having different lengths depending on the detection voltage output from the distortion component detector is inserted between the power amplifier and the load matching device, so that the power amplifier and the load matching device are connected. Adjust the transmission delay time of. This is equivalent to inserting a capacitor in parallel or inserting an inductor in series in the configuration of the impedance switcher already described. Therefore, it will be omitted to explain again that the adjacent channel leakage power characteristic of the power amplifier can be improved even if the impedance switch having the configuration of FIG. 12 is applied.

The impedance switching device shown in FIGS. 3, 11 and 12 is connected to the output terminal of the power amplifier by a switch which is controlled to be turned on and off by receiving the detection voltage output from the distortion component detector. It can be said that it is an impedance switching device that switches the impedance. Lastly, the configuration in which the load matching device is provided as the configuration of the wireless transmitter has been mainly described, but the load matching device is not necessarily provided in all cases. Such a configuration is used when the variation of the impedance of the antenna is small, but in this case as well, the variation of the impedance of the antenna is not completely eliminated. Therefore, the impedance switching device of the present invention may be directly connected to the isolator and used. Then, any of the configurations of the impedance switching device shown in FIGS. 3, 10, and 11 can be used.

Therefore, according to the present invention, at least a power amplifier that power-amplifies the output of the transmission modulator, a distortion component detector that detects a distortion component of the output of the power amplifier and outputs a detection voltage, and the distortion component. It can be said that the wireless transmission circuit includes an impedance switching device that switches the impedance in response to the detection voltage output from the detector.

[0062]

As described in detail above, according to the present invention, a radio transmission circuit which can improve adjacent channel leakage power characteristics in a transmission band with a simple structure without giving a loss to a transmission output is realized. It becomes possible to do.
That is, according to the first aspect of the invention, since the distortion component detector detects that the harmonic component of the output of the power amplifier is equal to or higher than a predetermined level and the detected voltage is output, the impedance switcher switches the impedance. The matching state at the output terminal of the power amplifier can be made variable depending on the frequency, and the adjacent channel leakage power characteristic of the power amplifier can be improved within the pass band.

According to the second aspect of the invention, the distortion component detector rectifies the output of the circuit having the resonance characteristic with respect to the harmonics output from the power amplifier to generate the detection voltage. It is possible to improve the adjacent channel leakage power characteristic of the power amplifier within the pass band without causing a loss in the output of the power amplifier, that is, the output of the wireless transmission circuit due to the voltage generation.

Furthermore, according to the third aspect of the invention, the impedance switching device is connected to the output terminal of the power amplifier by a switch which is controlled to turn on and off by receiving the detection voltage output from the distortion component detector. Since the impedance is switched, the load impedance of the power amplifier can be varied depending on the frequency with a simple configuration, and the adjacent channel leakage power characteristics of the power amplifier within the pass band can be obtained without complicating the configuration of the wireless transmission circuit. Can be improved.

[Brief description of drawings]

FIG. 1 is a principle of distortion reduction of a power amplifier according to the present invention.

FIG. 2 is a configuration of a distortion component detector (No. 1).

FIG. 3 shows a configuration of an impedance switching device (No. 1).

FIG. 4 is an embodiment of distortion mitigation of a power amplifier according to the present invention.

FIG. 5 is an adjacent channel leakage power characteristic of the power amplifier to which the load matching device of the present invention is applied (Part 1).

FIG. 6 is an adjacent channel leakage power characteristic of the power amplifier to which the load matching device of the present invention is applied (Part 2).

FIG. 7 is a Smith chart illustrating distortion correction in the configuration of FIG.

FIG. 8 shows a configuration of a distortion component detector (2).

FIG. 9 is a configuration of a distortion component detector (3).

FIG. 10 shows a configuration of an impedance switching device (part 2).

FIG. 11 is a Smith chart illustrating distortion correction when the impedance switch having the configuration of FIG. 10 is applied.

FIG. 12 is a configuration of an impedance switching device (3).

FIG. 13 is a configuration of a wireless transmission circuit using a conventional load matching device.

FIG. 14 is an input / output characteristic of a power amplifier.

FIG. 15 shows strain characteristics in a linear region.

FIG. 16 shows strain characteristics in a non-linear region.

FIG. 17 is an adjacent channel leakage power characteristic of a power amplifier to which a conventional load matching device is applied.

FIG. 18 is a distortion correction method for a power amplifier by pre-distortion.

FIG. 19 is a distortion correction method of a power amplifier by feed forward.

[Explanation of symbols]

1 Radio Frequency Oscillator 2 Transmission Modulator 3 Power Amplifier 4 Distortion Component Detector 5 Impedance Switcher 6 Load Matcher 7 Isolator 8 Antenna 9 Distortion Generator 10, 10a, 10b Hybrid 11 Distortion Circuit 12 Amplitude / Phase Adjuster 4-1 Capacitor 4-2 Inductor 4-3 Diode 4-4 Capacitor 4-5 Inductor 4-6 Resistor 4-7 Choke coil 4-8 Planar circuit element 4-9 Directional coupler 4-10 Resistor 5-1 Diode 5- 2 choke coil 5-3 capacitor 5-4 inductor 5-5 battery 5-6, 5-7, 5-8, 5-9 diode 5-10, 5-11, 5-12, 5-13 choke
Coil 5-14, 5-15 Transmission line

Claims (3)

[Claims] 1. A power amplifier for power-amplifying the output of a transmission modulator, a distortion component detector for detecting a distortion component of the output of the power amplifier and outputting a detection voltage, and the distortion component detector for outputting. And a impedance switching device that switches the impedance in response to the detected voltage. 2. The radio transmission circuit according to claim 1, wherein the distortion component detector is inserted in parallel with an output line of the power amplifier, and a fundamental wave component output from the power amplifier is not lost. A wireless transmission circuit, which is a distortion component detector that rectifies an output of a circuit capable of extracting only a distortion component and generates a detection voltage. 3. The wireless transmission circuit according to claim 1, wherein the impedance switching device is connected to an output terminal of the power amplifier by a switch that is turned on / off by receiving a detection voltage output from the distortion component detector. A wireless transmission circuit, which is an impedance switching device for switching the impedance to be controlled.