JP2007288545A - Predistortion compensation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pre-distortion compensation circuit, in which the influence to be given to the input/output characteristics of an amplifier is small, even though the attenuation quantity of a variable attenuator for individually adjusting respective levels of predistortion and a main signal changes and a mounting area can be made small. <P>SOLUTION: The predistortion compensation circuit 110 is provided with a distribution/combination device for combining respective distributed signals, obtained by distributing the main signal into a plurality of branches and outputting the combined signal to an amplifier. A predistortion attaching circuit 5 is provided in a "first branch" of the distribution/combination circuit. The distribution/combination circuit includes a predistortion adjuster 3a for adjusting the level of the main signal in the previous stage of the predistortion adjuster 3a of the "first branch", a main signal adjuster 3b for adjusting the level of the main signal in a "second branch", a line 2a for performing quarter-wavelength shift of the main signal at an input end of the "first branch" and a line 2b for performing quarter-wavelength shift of the main signal at the output end of the "second branch". <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a predistortion circuit that outputs a predistortion adjusted to a predetermined level and a main signal.

  The predistortion circuit is a circuit for obtaining an amplified signal whose distortion is compensated from an amplifier. This predistortion compensation circuit is a circuit that preliminarily applies a predistortion for canceling a distortion component generated in an output signal due to input / output characteristics (nonlinear characteristics) of the amplifier to a main signal supplied to the amplifier. Such a predistortion circuit is used in a transmission facility for TV broadcasting, a transmission facility for a radio base station of a mobile phone, or the like.

  As means for applying predistortion to the main signal, a configuration using a non-linear element (for example, a diode) having an input / output characteristic that is an inverse function of the input / output characteristic of the amplifier is known (predistortion applying circuit). (Patent Documents 1 and 2).

  Since such amplifiers and predistortion circuits vary in their input / output characteristics, the predistortion circuit can be adjusted so that the predistortion and main signal contained in the output signal are at a predetermined level. It is desirable that

  As a means for adjusting the predistortion and the main signal level, a configuration for adjusting the ratio of the predistortion given to the main signal by adjusting the level of the main signal supplied to the predistortion circuit (Patent Document) 3) and a configuration for adjusting the (absolute) level of the predistortion and main signal output from the predistortion circuit are known (Patent Document 2). A variable attenuator is generally known as a signal level adjusting means (Patent Document 4).

JP 2000-201099 A JP 2001-230635 A JP 2001-016047 A Japanese Patent Laid-Open No. 11-355011

  It is desirable that the predistortion compensation circuit has a configuration that can individually adjust the levels of the output predistortion and the main signal. As such a configuration, for example, a variable attenuator for adjusting the ratio of the predistortion given to the main signal (as described in Patent Document 3) is provided in the previous stage of the predistortion circuit, A variable attenuator for adjusting the predistortion output from the predistortion circuit (as described in Patent Document 2) and the (absolute) level of the main signal is provided after the predistortion circuit. Configuration is conceivable.

  In the configuration in which the levels of the predistortion and the main signal are individually adjusted as described above, it is desirable that the change in the attenuation amount in the variable attenuator does not affect the input / output characteristics of the amplifier. For example, Patent Document 4 (FIG. 1) proposes a variable attenuator that has a relatively small influence on input / output impedance even if the amount of attenuation changes.

  However, the variable attenuator proposed in Patent Document 4 (FIG. 1) does not consider the parasitic component in the PIN diode, and has an effect on a signal in the microwave band of several hundred MHz to several GHz. Cannot be ignored. As described in Patent Document 4 (FIG. 1), an adjustment terminal may be provided for each PIN diode, but the adjustment is complicated.

  In addition, the (conventional) variable attenuator described in Patent Document 4 (FIG. 4) can cancel the reflected wave at the PIN diode at the input / output terminal, and the microwave band signal as described above. No change in input / output impedance (or very small).

  However, as pointed out in Patent Document 4, such a (conventional) variable attenuator becomes large in scale and individually adjusts the levels of the predistortion and the main signal as described above. Therefore, if the predistortion circuit is arranged before and after the predistortion circuit, the predistortion compensation circuit becomes large and its mounting area becomes large.

  The object of the present invention is to reduce the influence on the input / output characteristics of the amplifier even if the attenuation of the variable attenuator for individually adjusting the levels of the predistortion and the main signal changes, and to reduce the mounting area. The object is to realize a predistortion compensation circuit that can be reduced.

  The present invention includes a predistortion circuit that preliminarily applies a predistortion for canceling distortion components generated by input / output characteristics of an amplifier to a main signal supplied to the amplifier, and is adjusted to a predetermined level. And a predistortion circuit for outputting a main signal, including a distribution synthesizer for synthesizing each of the divided signals by distributing the main signal to a plurality of branches and outputting the resultant signal to an amplifier. The circuit is provided in the first branch of the distribution synthesizer, and the distribution synthesizer is provided in the first branch of the predistortion circuit and adjusts the level of the main signal supplied. A predistorter that adjusts the level of predistortion applied to the main signal in the predistortion circuit by outputting to the predistortion circuit, and a main provided and supplied in any other branch The level of the main signal synthesized by adjusting the signal level and output to the amplifier A first signal phase shifter provided at one input end of the first branch and any other branch and phase-shifting the main signal by a quarter wavelength; And a second phase shifter provided at the other output terminal of one of the other branches and phase-shifting the main signal by a quarter wavelength.

  Also, in the present invention, the distribution synthesizer is any other branch, and is provided in a stage subsequent to the main signal adjuster, and is delayed by a time for applying predistortion to the main signal by the predistortion circuit. It is desirable to include a delay device.

  According to the present invention, even if the attenuation amount of the variable attenuator for individually adjusting the levels of the predistortion and the main signal is changed, the influence on the input / output characteristics of the amplifier is small, and the mounting area is reduced. A predistortion circuit that can be reduced can be realized.

  Hereinafter, the predistortion compensation circuit according to the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a power amplifying device on which a predistortion circuit according to the present embodiment is mounted. FIG. 2 is a diagram illustrating a configuration of the predistortion circuit according to the present embodiment.

  A power amplifying apparatus 100 shown in FIG. 1 includes a predistortion compensation circuit 110 and an amplifier 130. The predistortion compensation circuit 110 is a circuit that applies predistortion to the main signal input from the input terminal IN. The predistortion thus applied cancels the distortion component generated in the output signal due to the input / output characteristics (nonlinearity) of the amplifier 130 (or reduces the generated distortion component).

  Therefore, when the main signal to which the predistortion is applied is supplied to the amplifier 130, the amplifier 130 outputs an amplified signal whose distortion is compensated (this amplified signal is fed to the antenna via the output terminal OUT or the like). ) Further, the predistortion and the main signal output from the predistortion circuit are individually adjusted to a predetermined level by an adjustment terminal described later. Details of the configuration of the predistortion circuit 110 will be described later.

  The amplifier 130 amplifies and outputs the input main signal. The amplifier 130 has non-linearity in input / output characteristics (provided that a distortion signal generated by the non-linearity of the amplifier is included when a main signal is supplied). Output main signal). In order to cancel out such distortion components, the predistortion circuit 110 applies predistortion to the main signal.

  Next, details of the configuration of the predistortion circuit 110 will be described with reference to FIG. The predistortion circuit 110 includes a distributor 1 that distributes the main signal into a plurality of (for example, two) branches, and a combiner 9 that combines the distributed signals. Here, the upper branch is referred to as a “first branch”, and the lower branch is referred to as a “second branch”. Further, the distributor 1, the combiner 9, and the configuration connected to the distributor (except for a “predistortion applying circuit 5” described later) are collectively referred to as a “distributor combiner”.

  The “distributor / synthesizer” branches the main signal input from the input terminal IN into a “first branch” and a “second branch”, and from the output terminal OUT at the “first branch”. The level of the predistortion output is adjusted (by a predistortion adjuster 3a and a predistortion applying circuit 5 to be described later), and the level of the main signal output from the output terminal OUT in the “second branch” is adjusted. Adjust (by main signal adjuster 3b described later).

The distributor 1 is a Wilkinson distributor and includes lines 11 a and 11 b and a resistor 13. Lines 11a, 11b is one-quarter wavelength line having a characteristic impedance _{Z 0.} The lines 11a and 11b are connected in series, and an input terminal IN is connected to the connection point. Resistor 13 is the resistance element the resistance value 2Z _0, are connected lines 11a, the other end of 11b.

Here, the principle of distributor 1 which is a Wilkinson distributor will be described (in this case, the impedance of each port of distributor 1 is Z ₀ ). The distributor 1 outputs a signal input from the input terminal IN to the capacitors C1a and C1b described later via the lines 11a and 11b. The distributor 1 combines the two signals supplied through the capacitors C1a and C1b ("reflected wave", which will be described later) in phase with each other and outputs them to the input terminal IN. Offset by Further, the signal (reflected wave) supplied via the capacitor C1a is not output to the capacitor C1b because it is canceled out by the in-phase component via the resistor 13 and the antiphase component via the lines 11a and 11b. . Similarly, the signal supplied via the capacitor C1b is not output to the capacitor C1a.

The synthesizer 9 is a Wilkinson synthesizer, similar to the distributor 1, and includes lines 91 a and 91 b and a resistor 93. Lines 91a, 91b is one-quarter wavelength line having a characteristic impedance _{Z 0.} The lines 91a and 91b are connected in series, and an output terminal OUT is connected to the connection point. Resistor 93 is the resistance element the resistance value 2Z _0, are connected lines 91a, the other end of 91b. Since the principle of the synthesizer 9 is the same as that of the distributor 1, the description thereof is omitted.

Line 2a is a quarter-wave line characteristic impedance _{Z 0.} That is, the line 2a shifts the input signal by a quarter wavelength. The line 2a is provided at the input end of the “first branch”. By this line 2a, the reflected wave in the predistorter 3a to be described later and the reflected wave in the main signal adjuster 3b are reversed in phase to the distributor 1 which is a Wilkinson distributor (through the capacitors C1a and C1b). Supplied. Therefore, the reflected wave in the predistorter 3a and the reflected wave in the main signal adjuster 3b are canceled by the input terminal IN and are not output (or even if output, the level is very small). ).

Moreover, line 2b is a quarter-wave line characteristic impedance Z ₀ is provided to the output end of the "second branch". Similar to the line 2a, the line 2b is a Wilkinson synthesizer (through capacitors C5a and C5b) for the reflected wave in the predistorter 3a described later and the reflected wave in the main signal adjuster 3b. Input to the device 9 in reverse phase. As a result, the reflected wave in the predistorter 3a, which will be described later, and the reflected wave in the main signal adjuster 3b are canceled at the output terminal OUT and are not output (or even if output, the level is Very small).

The predistorter 3a is a variable attenuator that is provided in the preceding stage of the “first branch” predistortion circuit 5, and adjusts and outputs the level of the main signal to be supplied. The predistortion regulator 3a is a variable resistor and a diode 31a and 35a made of, and the line 33a is a quarter-wave line characteristic impedance _{Z 0,} the diode 31a and supplies a bias current to the diode 31a and 35a And a coil 37a which is an adjustment terminal for changing the resistance value of 35a. The diodes 31a and 35a and the line 33a form a π-type attenuator.

The predistorter 3a can change the amount of attenuation by changing the bias current supplied from the coil 37a to the diodes 31a and 35a to change the resistance values of the diodes 31a and 35a. Further, by setting R1 = R2 + _{Z 0} when the resistance value of the diode 31a and the resistance value of the diode 35a and R1 R2 input and output impedances of the (by the impedance conversion by the line 33a) predistortion regulator 3a _{Z 0} (Ie, zero reflection coefficient).

The main signal adjuster 3b is a variable attenuator that is provided in the “second branch” and adjusts and outputs the level of the supplied main signal. The main signal adjuster. 3b, and the line 33b is a front is a predistortion regulator 3a similar construction (i.e., a diode 31b and 35b serving as a variable resistor, a quarter wave line of characteristic impedance Z _0, A coil 37b for supplying a bias current to the diodes 31b and 35b to vary the resistance value of the diodes 31b and 35b, and the diodes 31b and 35b and the line 33b form a π-type attenuator. ing).

  The predistortion applying circuit 5 is a circuit that preliminarily applies a predistortion for canceling a distortion component generated by the input / output characteristics of the amplifier to the main signal supplied to the amplifier 130. This predistortion circuit 5 has a diode 51 having an input / output characteristic that is an inverse function (or an approximate function thereof) with respect to the input / output characteristic of the amplifier 130, and the diode 51 has the input / output characteristic as described above. And a coil 53 for supplying a bias current.

  The delay device 7 is a circuit that delays an input signal. The delay amount in the delay unit 7 is set to the same amount (or the same level) as the delay amount received by the predistortion circuit 5 on the main signal supplied to the “first branch”. Capacitors C1a and C1b, C3a and C3b, C5a and C5b are capacitors that disconnect the portions where the bias current flows in a DC manner.

  With the above-described configuration, the predistortion compensation circuit 110 according to the present embodiment can adjust the levels of the predistortion and the main signal individually (the predistorter 3a and the main signal). Even if the attenuation of the adjuster 3b) changes, the influence on the input / output characteristics of the amplifier 130 is small, and the mounting area can be reduced.

  Next, the operation will be described. The main signal input via the input terminal IN is distributed by the distributor 1 into the above-described “first branch” and “second branch”. That is, the main signal distributed to the “first branch” is supplied to the line 2a via the capacitor C1a, and the main signal distributed to the “second branch” is supplied to the main signal adjuster via the capacitor C1b. 3b.

  The main signal supplied to the “first branch” is phase-shifted by a quarter wavelength by the line 2a and supplied to the predistorter 3a. Here, the level of the main signal is adjusted (attenuated) by the predistorter 3a. The level of the main signal supplied to the “second branch” is adjusted (attenuated) by the main signal adjuster 3b.

  The main signal whose level is adjusted by the predistorter 3 a is supplied to the predistorter circuit 5. The predistortion applying circuit 5 applies predistortion to the input main signal and outputs it. The predistortion applied by the predistortion applying circuit 5 is applied at a level corresponding to the level of the supplied main signal. For this reason, the level of the predistortion given to the main signal can be adjusted by adjusting the level of the main signal with the predistorter 3a. The main signal to which the predistortion is added in this way is supplied to the synthesizer 9.

  The main signal whose level is adjusted by the main signal adjuster 3b is supplied to the combiner 9 via the line 2b and the delay unit 7 (as will be described later, the level of the main signal by the main signal adjuster 3b). To adjust the level of the main signal output from the output terminal OUT). In this way, the first branch main signal, the second branch main signal, and the output terminal OUT which are input to the combiner 9 are combined.

  The main signal supplied from the input terminal IN to the output terminal OUT via the “first branch” passes through the lines 11a, 2a, 33a, 91a, and is thus shifted by 360 degrees. Further, the main signal supplied from the input terminal IN to the output terminal OUT via the “second branch” passes through the lines 11b, 2b, 33b, 91b, and is thus shifted by 360 degrees. .

  Therefore, at the output terminal OUT, the main signal supplied via the “first branch” and the main signal supplied via the “second branch” are combined in phase. Further, the predistortion is applied to the main signal of the “first branch” as described above. For this reason, the main signal with predistortion is output from the output terminal OUT. Further, as described above, the main signal adjuster 3 b can adjust the level of the “second branch” main signal. For this reason, the level of the main signal output from the output terminal OUT can be adjusted by adjusting the level of the main signal with the main signal adjuster 3b.

  As described above, the level of the predistortion output from the output terminal OUT can be adjusted by adjusting the level of the main signal supplied to the predistortion applying circuit 5 with the predistortion adjuster 3a. The level of the main signal output from the output terminal OUT can be adjusted by adjusting the level of the main signal supplied to the combiner 9 by the main signal adjuster 3b (that is, predistortion compensation). The circuit 110 can individually adjust the predistortion and the main signal).

When the adjustment as described above, the matching can not be taken against the predistortion regulator input impedance 3a is (due to the influence of the unbalance and parasitics resistance value of the diode 31a and 35a) the characteristic impedance Z ₀ Then, the main signal (a part thereof) is reflected by the input terminal (the diode 31a) of the predistorter 3a. Similarly, when the input side impedance of the main signal adjuster 3b is not is consistent for the characteristic impedance Z _0, main signal (a part of) is reflected at the input end of the main signal conditioner 3b (diode 31b) of The

  The main signal reflected at the input end of the predistorter 3a in this way (a part thereof) is further phase-shifted by a quarter wavelength by the line 2a and supplied to the distributor 1 via the capacitor C1a. Is done. Similarly, (a part of) the main signal reflected at the input terminal of the main signal adjuster 3b is supplied to the distributor 1 via the capacitor C1b.

As described above, the main signal reflected at the input end of the predistorter 3a reciprocates along the line 2a, and thus the main signal reflected at the input end of the main signal adjuster 3b. The phase is supplied with a delay of 180 degrees with respect to (part of). Accordingly, the main signal (a part of) reflected by the predistorter 3a and the main signal adjuster 3b is synthesized in the opposite phase at the input terminal IN and canceled. Therefore, no reflected wave is output from the input terminal IN. The attenuation amounts of the predistorter 3a and the main signal adjuster 3b described above are individually adjusted, so the levels of the reflected waves are strictly different, but these attenuations are practically about the same. Therefore, even if the signal is output from the input terminal IN, its level is very small so as not to cause a practical problem. In addition, the “first branch” and the “second branch” differ in the presence or absence of the predistortion circuit 5, but the impedance of the diode 51 forming the predistortion circuit 5 is the characteristic impedance Z. If it is sufficiently large with respect to ₀ , it does not particularly affect the reflected wave output from the input terminal IN.

  Similarly, the signal reflected at the output end (diode 35a) of the predistorter 3a and the signal reflected at the output end (diode 35b) of the main signal adjuster 3b are supplied to the combiner 9. However, since the signal reflected at the output end of the main signal adjuster 3b reciprocates on the line 2a, the signals reflected by the predistorter 3a and the main signal adjuster 3b are out of phase at the output terminal OUT. Synthesized. For this reason, the signal reflected by the predistorter 3a and the main signal adjuster 3b is not output from the output terminal OUT (the level is very high even if it is output for the same reason as described above). small).

  Therefore, when the predistortion and main signal level output from the predistortion compensation circuit 110 are individually adjusted, the impedance of the predistortion adjuster 3a and the main signal adjuster 3b is changed in order to change the attenuation. Even if the input / output impedance is changed, the input / output impedance of the predistortion circuit 110 itself does not change (because the input / output reflection coefficient does not change) and does not affect (or give) the input / output characteristics of the amplifier 130. Less impact). Further, as described above, since the distributor 1 and the combiner 9 are of the Wilkinson type, it is possible to ensure isolation between the branches.

  As described above, the predistortion compensation circuit 110 according to the present embodiment does not include the variable attenuator described in Patent Document 4 (FIG. 4) before and after the predistortion application circuit as described above. ) Even if the attenuation amount of the variable attenuator (predistortion adjuster 3a and main signal adjuster 3b) for individually adjusting the levels of the predistortion and the main signal is changed, the input / output characteristics of the amplifier 130 are changed. The influence is small, and the mounting area can be reduced. Moreover, even if there is a reflection due to the influence of a parasitic component or the like in the predistorter 3a and the main signal adjuster 3b, it is canceled by the input / output terminal, so that the signal in the microwave band of several hundred MHz to several GHz is used. Also effective.

  In the present embodiment, the delay unit 7 that delays the same amount as the delay amount in the predistortion circuit 5 in the “first branch” is provided in the “second branch”. Other configurations may be used as long as the above can be obtained. For example, a second predistortion applying circuit may be provided. Furthermore, in the present embodiment, the number of branches is 2, but it may be 2 or more. For example, two branches for adjusting the level of predistortion may be prepared, two branches for adjusting the level of the main signal may be prepared, or any number of combinations may be used. Also good. Further, the line 2a may be provided in the “second branch” and the line 2b may be provided in the “first branch” (even in such a configuration, the predistorter 3a and the main signal adjustment may be provided. The reflected wave in the device 3b is canceled at the input / output terminal).

It is a figure showing the structure of the predistortion circuit and amplifier which concern on embodiment of this invention. It is a figure showing the structure of the predistortion compensation circuit which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Divider, 2a, 2b Line, 3a Predistorter, 3b Main signal adjuster, 5 Predistortion circuit, 7 Delay device, 9 Synthesizer.

Claims (2)

A predistorter circuit that pre-applies a predistortion for canceling distortion components generated by the input / output characteristics of the amplifier to the main signal supplied to the amplifier;
A predistortion circuit that outputs a predistortion and a main signal adjusted to a predetermined level,
A distribution synthesizer that divides the main signal into a plurality of branches and synthesizes the divided signals and outputs them to an amplifier;
The predistortion circuit is provided in the first branch of the distribution synthesizer,
The distribution synthesizer
The first branch is provided to the main signal in the predistortion circuit by adjusting the level of the main signal provided and provided in the preceding stage of the predistortion circuit and outputting the adjusted signal to the predistortion circuit. A predistorter for adjusting the level of predistortion,
A main signal adjuster that adjusts the level of the main signal that is combined and adjusted and output to the amplifier by adjusting the level of the main signal that is provided and supplied in any other branch;
A first phase shifter provided at one input end of the first branch and any other branch and phase-shifting the main signal by a quarter wavelength;
A second phase shifter provided at the other output terminal of the first branch and any other branch and phase-shifting the main signal by a quarter wavelength;
A predistortion compensation circuit comprising: The predistortion circuit according to claim 1,
The distribution synthesizer is:
A predistorter including any other branch and a delay unit provided at a subsequent stage of the main signal adjuster and delaying by a time for adding a predistortion to the main signal by a predistortion circuit; Compensation circuit.

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