JP2004343296A - Distortion compensation circuit using diode linearizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distortion compensation circuit which more expands the dynamic range, whereas having a compact and simple structure utilizing a diode linearizer. <P>SOLUTION: When the level of an input signal to a power amplifier 3 ranges below or over a reference level, a bias resistance R<SB>b1</SB>is taken to change a bias voltage to a first, or another bias resistance R<SB>b2</SB>is taken to change the bias voltage to a second bias voltage value, respectively. The first bias voltage is higher than the second bias voltage enough to compensate the output distortion while the input signal level ranges below the specified reference level. The second bias voltage is higher than the first bias voltage enough to compensate the output distortion while the input signal level ranges over the reference level. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a distortion compensation circuit using a diode linearizer that is provided at an input stage of a power amplifier that amplifies an input signal in a radio frequency band and compensates for output distortion of the power amplifier.
[0002]
[Prior art]
2. Description of the Related Art In recent years, RF signals (signals in a radio frequency band) such as microwaves are frequently used in wireless communication devices for terrestrial communication such as satellite communication and mobile phones. A wireless communication device using such an RF signal is equipped with a power amplifier that amplifies the RF signal. FIG. 4 is a graph showing input / output characteristics of a power amplifier used for communication using an RF signal.
[0003]
As shown in Y ₁ in FIG. 4, the input signal level and output signal level of the power amplifier, linear, i.e., he ideal to be in a linear relationship, but in the power amplifier realistically this kind, In the figure, as indicated by V ₁ ′, when the input signal level becomes higher than a predetermined level, distortion occurs and linearity is lost. Such output distortion is not preferable because it generates a radio frequency that is not permitted to use or causes interference. Therefore, a circuit for compensating for such distortion is often provided in the input stage of the power amplifier. In particular, a linearizer using a diode (hereinafter also referred to as a diode linearizer) is often used as a distortion compensation circuit because of its small size and simple configuration.
[0004]
FIG. 5 is a block circuit diagram related to a distortion compensation circuit using a conventional diode linearizer. As shown in FIG. 5, a linearizer 1 'as a distortion compensation circuit is connected via a buffer amplifier 2 to a stage preceding a power amplifier 3 for amplifying an input signal in a radio frequency band.
[0005]
The linearizer 1 ′ includes a diode D having one end grounded, an input-side bias blocking capacitor C ₁ and an output-side bias blocking capacitor C ₂ connected to the other end of the diode D, and the other end of the diode D and a bias voltage. It includes a bias resistor _Rb interposed between the power supply + _Vcc .
[0006]
In operation of the distortion compensating circuit having such a configuration, in FIG. 1, the radio frequency signals inputted to the input terminal IN passes through the input side bias blocking capacitor C _1, is input to the diode D . A bias voltage fixedly determined by the bias resistor _Rb is applied to the diode D. At this time, the signal of the radio frequency band, is the level compensated by the diode D which the bias voltage is applied, via the output-side bias blocking capacitor C _2, the buffer amplifier 2, is supplied to the power amplifier 3. Then, as shown in FIG. 4, a signal in the radio frequency band in which the characteristic represented by V ₁ ′ is compensated as represented by _Vb is output from the output terminal OUT. Note that the distortion compensation circuit as shown in FIG. 5 is also shown in Non-Patent Document 1 below.
[0007]
[Non-patent document 1]
IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 45, NO. 12, DECEMBER 1997 (pp. 2431-2432, FIG. 1).
[0008]
[Problems to be solved by the invention]
By the way, the distortion compensation circuit using the diode linearizer has the advantages of being small and simple in configuration, but also has the disadvantage that the dynamic range is narrow. That is, according to the above-described conventional distortion compensation circuit, as shown by _Vb in FIG. 4, the input signal level capable of maintaining the linearity is improved to be slightly higher. That is, although the dynamic range is increased to some extent, There is a problem that a sufficient dynamic range cannot be obtained yet.
[0009]
Therefore, in view of the above situation, it is an object of the present invention to provide a distortion compensation circuit that has a small and simple configuration using a diode linearizer and can further expand a dynamic range.
[0010]
[Means for Solving the Problems]
A distortion compensating circuit according to claim 1, which is provided to solve the above-mentioned problem, includes a diode linearizer provided before the power amplifier 3 for amplifying an input signal in a radio frequency band and compensating for output distortion of the power amplifier 3. A distortion compensating circuit using the bias voltage of the diode linearizer based on a level of the input signal supplied to the power amplifier, at least a first bias voltage value or a second bias voltage different from the first bias voltage value. Switching control means for switching to a value, wherein the first bias voltage is a value that compensates for the output distortion more than the second bias voltage in a range where the level of the input signal is equal to or lower than a predetermined reference level. , The second bias voltage is set such that the level of the input signal is higher than the reference level. The switching control means compares the input signal with a predetermined reference level, and when the level of the input signal is equal to or less than the reference level, the switching control means adjusts the bias voltage. Is switched to the first bias voltage value, and when the level of the input signal is higher than the reference level, the bias voltage is switched to the second bias voltage.
[0011]
According to the first aspect of the present invention, the bias voltage is switched to the first bias voltage value in a range where the level of the input signal to the power amplifier 3 is equal to or lower than the reference level, and is changed to the second bias voltage in a range higher than the reference level. Switch. Here, the first bias voltage is a value that compensates for the output distortion more than the second bias voltage in a range where the level of the input signal is equal to or lower than a predetermined reference level. In a range where the signal level is higher than the reference level, the value is a value that compensates for the output distortion more than the first bias voltage. As described above, by switching the bias voltage to a value that compensates for the output distortion more greatly in each range, the output distortion of the power amplifier 3 can be compensated to a higher input level.
[0012]
According to a second aspect of the present invention, there is provided a distortion compensation circuit according to the first aspect, wherein the switching control unit has a first bias resistor or a second bias resistor having different resistance values. Wherein the bias voltage is switched by selectively interposing any one of the components between a diode included in the diode linearizer and a bias voltage supply source for supplying a constant voltage.
[0013]
According to the second aspect of the present invention, any one of the first bias resistor and the second bias resistor having a different resistance value is selectively supplied to the diode included in the diode linearizer and the bias for supplying a constant bias voltage. Since the bias voltage is switched by interposing the bias voltage source, the bias voltage source itself does not need to be changed.
[0014]
According to a third aspect of the present invention, there is provided a distortion compensation circuit according to the first or second aspect, wherein each of the bias voltages increases the output distortion more than others in a predetermined range. Three or more kinds of values to be compensated are set, and the switching control means switches the bias voltage to the largest value among the three or more kinds of values for compensating the output distortion for each range. It is characterized by.
[0015]
According to the third aspect of the present invention, the bias voltage is set to three or more values that are larger than the others in the predetermined range and that compensate for the output distortion. Since the value is largely switched to a value that compensates for the output distortion, it is possible to compensate for the output distortion more widely and more accurately.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block circuit diagram according to a distortion compensation circuit according to one embodiment of the present invention. As shown in FIG. 1, this distortion compensation circuit is connected via a buffer amplifier 2 to a stage preceding a power amplifier 3 that amplifies an input signal in a radio frequency band. This distortion compensation circuit includes a linearizer 1, a distributor 4, a detector 5, and a comparator 6.
[0017]
Here, linearizer 1, the Schottky diode D, capacitor connected to the input side bias blocking the other end of the diode D C ₁ and the output side bias blocking capacitor C ₂ whose one end is _grounded, and the other end of the diode D It includes bias resistors R _b1 and R _b2 provided between the bias voltage supply source + V _cc and the switch 11. The switch 11 is a switch circuit composed of, for example, a transistor, and selectively switches either the bias resistor R _b1 or R _b2 to the other end of the diode D in response to a switch control signal from the comparator 6. And a bias voltage supply source + _Vcc .
[0018]
Each of the bias resistors R _b1 and R _b2, the voltage of the bias voltage supply + V _cc as the first bias voltage and the second bias voltage is set to a value to be applied to the diode D. The first bias voltage is a value that compensates for the output distortion of the power amplifier 3 to a greater extent than the second bias voltage in a range where the level of the input signal is equal to or lower than the predetermined reference level _Ir1. The voltage is a value that compensates for the output distortion more than the first bias voltage in a range where the level of the input signal is higher than the reference level _Ir1 . Note that larger and the compensation output distortion, output distortion of the power amplifier 3, a means of compensating as approximated by the ideal to characteristics shown in Y ₁ in FIG. The approximation calculation may use a known least square method or the like.
[0019]
In addition, the characteristics of the linearizer change depending on the value of the bias voltage applied to the diode D (described later with reference to FIG. 3). By positively utilizing the characteristics of such a linearizer, a bias voltage for compensating the output distortion of the power amplifier to a greater extent is selectively switched in accordance with the input signal level. The reference level _Ir1 for switching the value of the bias voltage is determined in advance by experiments or the like in consideration of the characteristics of the power amplifier 3 and the linearizer 1 to be used. Since the value of the bias voltage is switched by selectively switching the bias resistors R _b1 and R _b2 , there is no need to make any change to the bias voltage supply source itself, which unnecessarily complicates the circuit configuration. Nothing.
[0020]
The distributor 4 distributes an input signal in a radio frequency band input to the input terminal IN and supplies the signal to the linearizer 1 and the detector 5. The detector 5 detects the signal from the distributor 4, detects at least the signal level of the input signal, and supplies this to the comparator 6. The comparator 6 is composed of, for example, an operational amplifier, compares the detected signal level with the reference level _Ir1, and outputs the switching control signal for controlling the switching unit 11. The distributor 4, the detector 5, the comparator 6, the switch 11, the bias resistors _Rb1 and _Rb2 correspond to the switching control means in the claims.
[0021]
An example of improving the operation and input / output characteristics of the distortion compensation circuit having such a configuration will be described with reference to FIGS. FIG. 2 is a flowchart illustrating a bias voltage switching process according to an embodiment of the present invention. FIG. 3 is a graph showing an example of improvement in input / output characteristics according to the present invention.
[0022]
In FIG. 1, a signal in a radio frequency band input to an input terminal IN and distributed by a distributor 4 is detected by a detector 5 at a signal level thereof and reaches a comparator 6. The signal level, in FIGS. 1 and 2, when in the comparator 6 is compared with the reference level I _r1, the input signal level I _i is equal to or less than the reference level I _r1 (Y in step S1), the The bias resistor _Rb1 is selected by the switch 11, and the value of the bias voltage applied to the diode D is set to the first bias voltage (Step S2). When the value of the bias voltage is set to the first bias voltage (when the input signal level Ii is equal to or lower than the reference level _Ir1 ), the input / output characteristics of the power amplifier are as shown by _Vb1 in FIG. become.
[0023]
On the other hand, when the input signal level Ii is higher than the reference level _Ir1 (N in step S1), the bias resistor _Rb2 is selected by the switch 11, and the bias voltage applied to the diode D is increased. The value is set to the second bias voltage (Step S3). When the value of the bias voltage is set to the second bias voltage (when the input signal level Ii is higher than the reference level _Ir1 ), the input / output characteristics of the power amplifier are as shown by _Vb2 in FIG. become. Then, returning to step S1, the level of the signal input to the input terminal IN is constantly monitored, and the bias voltage is controlled according to this level.
[0024]
On the other hand, the radio frequency signals inputted to the input terminal IN, in FIG. 1, after passing through the distributor 4, through the input side bias blocking capacitor C ₁ of the linearizer 1, is input to the diode D. A bias voltage set to the above value, that is, either the first bias voltage or the second bias voltage is applied to the diode D. At this time, the signal of the radio frequency band, is the level compensated by diode D the bias voltage as described above is applied, via the output-side bias blocking capacitor C _2, supplied to a buffer amplifier 2, power amplifier 3 Is done. By controlling the switching of the bias voltage, even if the level of the input signal is in a range equal to or lower than the reference level _Ir1, or in a range higher than the reference level _Ir1 , a more linear characteristic (for example, ideal). A signal in the radio frequency band whose distortion has been compensated for by the characteristic line Y ₁ ) is output from the output terminal OUT.
[0025]
In the above-described embodiment, an example in which the bias voltage is switched in two stages has been described. However, the bias voltage may be switched in two or more stages. For example, the above embodiment adds a reference level, as shown by I _r2 in FIG. 3, when the input signal level Ii is greater than the reference level I _r2 is, the input-output characteristic of the power amplifier, V _b3 in FIG. 3 Is selected such that the bias voltage becomes as shown by As a result, input-output characteristics of the power amplifier, when the input signal level Ii is below the reference level I _r1 is now represented by V _b1 in FIG. 3, when the input signal level Ii is greater than the reference level I _r1 to become as shown by V _b2 of FIG. 3, it is as shown by V _b3 in Figure 3 when the input signal level Ii is greater than the reference level I _r2. This makes it possible to compensate for output distortion in a wider range and with higher accuracy.
[0026]
The bias voltage may be switched and controlled in more stages. In this case, the bias voltage may be set to a value that compensates for the output distortion more than the others in the range corresponding to each stage, and the bias voltage may be switched to the bias voltage assigned to each range. This makes it possible to compensate for output distortion in a wider range and with higher accuracy.
[0027]
As described above, according to the embodiment of the present invention, the output distortion of the power amplifier 3 is compensated to a higher input level by switching the bias voltage to a value that compensates for the output distortion more greatly according to the level of the input signal. it can. That is, the dynamic range can be further expanded while having a small and simple configuration using the diode linearizer.
[0028]
The switching control performed by the comparator 6 may be performed using a microcomputer instead of the operational amplifier. The present invention includes those modified without departing from the gist thereof.
[0029]
【The invention's effect】
As described above, according to the first aspect of the present invention, the input voltage having a higher output distortion of the power amplifier 3 is changed by switching the bias voltage to a value that compensates for the output distortion more greatly in accordance with the level of the input signal. Can compensate up to the level. That is, the dynamic range is extended.
[0030]
According to the second aspect of the present invention, any one of the first bias resistor and the second bias resistor having a different resistance value is selectively supplied to the diode included in the diode linearizer and the bias for supplying a constant bias voltage. Since the bias voltage is switched by interposing the bias voltage source, the bias voltage source itself does not need to be changed. That is, the effect of the first aspect of the present invention can be obtained with a simple configuration in which only the bias resistor is selected.
[0031]
According to the third aspect of the present invention, the bias voltage is set to three or more values that are larger than the others in the predetermined range and that compensate for the output distortion. Since the value is largely switched to a value that compensates for the output distortion, it is possible to compensate for the output distortion more widely and more accurately.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram according to a distortion compensation circuit according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a bias voltage switching process according to an embodiment of the present invention.
FIG. 3 is a graph showing an example of improving input / output characteristics according to the present invention.
FIG. 4 is a graph showing input / output characteristics and the like of a power amplifier used for communication using an RF signal.
FIG. 5 is a block circuit diagram related to a conventional distortion compensation circuit.
[Explanation of symbols]
1 linearizer (diode linearizer)
2 buffer amplifier 3 power amplifier 4 distributor 5 detector 6 comparator 11 switch R _b1 , R _b2 bias resistor D diode

Claims (3)

A distortion compensation circuit using a diode linearizer that is provided before a power amplifier that amplifies an input signal in a radio frequency band and compensates for output distortion of the power amplifier,
A switching control unit configured to switch a bias voltage of the diode linearizer to at least a first bias voltage value or a second bias voltage value different from the first bias voltage value based on a level of the input signal supplied to the power amplifier;
The first bias voltage is a value that compensates for the output distortion more than the second bias voltage in a range where the level of the input signal is equal to or lower than a predetermined reference level,
The second bias voltage is a value that compensates for the output distortion more than the first bias voltage in a range where the level of the input signal is higher than the reference level,
The switching control means,
Comparing the input signal with a predetermined reference level,
When the level of the input signal is equal to or less than the reference level, the bias voltage is switched to the first bias voltage value;
In a range where the level of the input signal is higher than the reference level, the bias voltage is switched to the second bias voltage.
A distortion compensation circuit using a diode linearizer. The distortion compensation circuit according to claim 1,
The switching control means,
Selectively interposing one of a first bias resistor and a second bias resistor having different resistance values between a diode included in the diode linearizer and a bias voltage supply for supplying a constant voltage. By switching the bias voltage,
A distortion compensation circuit using a diode linearizer. The distortion compensation circuit according to claim 1, wherein
Each of the bias voltages is set to three or more values that compensate for the output distortion more than others in a predetermined range,
The switching control means switches the bias voltage to a value that compensates for the output distortion largest among the three or more values for each range.
A distortion compensation circuit using a diode linearizer.

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