JP2001016046A - Feedforward distortion compensating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress carrier components which leak out into an extracted distortion signal over a wider frequency range than conventionally. SOLUTION: A signal branching off from a trunk line and a signal distributed by a distributor D1 via a delay circuit DL1 are coupled (1st loop) by a directional coupler DC2, and then the resulting signal and the signal distributed by the distributor D1 through the delay circuit DL1A are coupled (2nd loop) by a directional coupler DC2A. Thus, a distortion extraction loop is doubled to actualize satisfactory carrier suppression performance over a wide frequency range, without having to precisely set the delay times of the delay circuits DL1 and DL1A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedforward distortion compensation circuit used for removing or suppressing a distortion component generated in a main amplifier.

[0002]

2. Description of the Related Art Since an amplifier generally has nonlinearity, when a signal group distributed over a relatively wide frequency band is amplified, various distortions due to the nonlinearity occur. For example, in a terrestrial digital television broadcasting system scheduled to be implemented in Japan, an OFDM (Orthogonal Orthogonal Frequency Division Multiplexing) system arranges and multiplexes a large number of carriers on the frequency axis so that an orthogonal relationship is established.
gonal Frequency Division Multiplex). When a signal multiplexed according to the OFDM method is amplified, distortion due to intermodulation between carrier components, that is, intermodulation distortion occurs. In particular, when the carrier interval is narrow, it is difficult to separate the carrier component and the intermodulation distortion component in the amplified output by means such as a filter. The problem of non-linearity of the amplifier is caused by CDMA (Code Division Multiple Ac
cess) system, especially its base station
It also occurs during power amplification at the relay station.

[0003] As a device on the circuit for removing or suppressing such a distortion component, a pre-distortion method,
There is a feed forward method and the like. Among these, the feedforward method feeds a part of the input signal to the main amplifier to the output side of the main amplifier to extract a distortion component, and further feedforwards the extracted distortion component to cancel the distortion component in the output. It is based on the principle of eliminating or suppressing.

FIG. 1 shows a configuration of a distortion compensation amplifier having a distortion compensation circuit of a feedforward system. The signals input to the circuit in this figure are the main amplifier A1 and the delay circuit DL.
The signal is output to an antenna or the like (not shown) through 2. Since this input / output path is a path through which the signal to be amplified by the main amplifier A1 and the amplified signal pass, it can be called a main line. The directional coupler DC1 preceding the main amplifier A1 supplies the input signal to the main amplifier A1 for amplification, while having the same frequency configuration as the signal supplied to the main amplifier A1, but having a small amplitude. The signal is branched and the delay circuit D
The signal is supplied to the directional coupler DC2 via L1. The directional coupler DC2 converts the output signal of the main amplifier A1 into a delay circuit D
While the signal is supplied to the directional coupler DC3 via L2, a signal having the same frequency structure as that of the output signal of the main amplifier A1 but having a small amplitude is branched and further divided into a signal supplied via the delay circuit DL1. The combined distortion signal is supplied to a distortion amplifier A2. The directional coupler DC3 generates a distortion-compensated output signal by coupling the signal supplied via the delay circuit DL2 and the input from the distortion amplifier A2 with a predetermined gain, and outputs the signal to an antenna or the like.

The delay time of the delay circuit DL1 composed of a coaxial delay line or the like is equal to the delay time generated on the main line from the directional coupler DC1 to the directional coupler DC2 via the main amplifier A1. , Are to be matched.
Further, a modulator M1 for adjusting the amplitude and phase of the signal or the I and Q component values is provided before or after the path on the main line or the delay circuit DL1. It is assumed that the modulator M1 is set or controlled so that carrier components in two types of signals mutually coupled by the directional coupler DC2 have the same amplitude and opposite phase. In that case, the extracted distortion signal output from the directional coupler DC2 to the distortion amplifier A2 side is:
Generally, the signal includes only a distortion component generated by the non-linearity in the main amplifier A1. Therefore, a loop from the directional coupler DC1 to the directional coupler DC2, that is, a feedforward loop that delays the branched input signal in the delay circuit DL1 and supplies the delayed input signal to the directional coupler DC2 to generate an extracted distortion signal, It can be called a distortion extraction loop.

Further, the delay time of the delay circuit DL2 constituted by a coaxial delay line or the like coincides with the delay time generated on the path from the directional coupler DC2 to the directional coupler DC3 via the distortion amplifier A2. Shall be kept. Further, before or after this path or the delay circuit DL2, there is provided a modulator M2 for adjusting the amplitude and phase of the signal or the I and Q component values. It is assumed that the modulator M2 is set or controlled so that distortion components in two types of signals mutually coupled by the directional coupler DC3 have the same amplitude and opposite phase.
In this case, the signal output from the directional coupler DC3 as the distortion compensation output signal is generally a signal from which the above-described distortion component has been removed or suppressed. Therefore, the directional coupler DC2
, The feed-forward loop that amplifies the extracted distortion signal by the distortion amplifier A2 and supplies it to the directional coupler DC3 to generate a distortion-compensated output signal can be called a distortion removal loop. .

The control unit CTL controls the operation of the distortion extraction loop, particularly the adjustment operation in the modulator M1, so that the carrier component does not leak into the extracted distortion signal, and controls the distortion component, particularly the intermodulation distortion, in the distortion compensation output signal. The operation of the distortion removal loop, particularly the adjustment operation in the modulator M2, is controlled so that the components do not leak. The control by the control unit CTL is performed using, for example, a technique of inserting and detecting a pilot signal. Alternatively, it is performed using another method, such as using a synchronous detection technique as previously proposed by the present applicant. In addition, the directional couplers DC1 to DC3 are realized by, for example, a hybrid circuit as illustrated. The modulators M1 and M2 are quadrature modulators or a combination of a variable gain amplifier or a variable attenuator and a variable phase shifter.

[0008]

However, in practice, it is difficult to prevent the leakage of the carrier component into the extracted distortion signal over the entire frequency band used.

First, in the circuit shown in FIG. 1, the modulator M1 controls the amplitude and phase under the control of the control unit CTL so that the directional coupler DC2 does not leak the carrier component into the extracted distortion signal. Perform adjustment. For example, 1 GHz
The delay time of the delay circuit DL1 is set and the modulator M is set so that the carrier suppression amount of 40 dB (ie, the ratio of the carrier component in the extracted distortion signal to the output of the main amplifier A1) is obtained.
Control 1 At this time, if an error τ occurs in the delay time in the delay circuit DL1, the delay time setting error τ
Appears as a phase control error 2πfτ. That is, even if the carrier component can be ideally canceled and suppressed at a specific frequency, the phase control error 2πfτ increases and the amount of suppression decreases as the frequency increases.

Therefore, even if the delay time in the delay circuit DL1 is set so as to obtain a carrier suppression amount of 40 dB at 1 GHz, if a setting error τ of 60 psec occurs in the delay time in the delay circuit DL1, for example, At 1.06 GHz, which is 60 MHz away from, the carrier suppression amount can be obtained, for example, only about 36 dB. That is, a non-negligible amount of carrier components leaks into the extracted distortion signal. The error τ of 60 psec is a slight electrical length of 18 mm in a coaxial delay line, and the delay circuit D
This often occurs when L1 is constituted by a coaxial delay line.

As a result, if a sufficiently large carrier suppression amount is to be obtained over a sufficiently wide frequency band extending over several tens of MHz, the delay time setting error τ must be made very small. Furthermore, the members inside or around the distortion extraction loop including the delay circuit DL1 have temperature characteristics. This temperature characteristic also causes a decrease in the amount of carrier suppression.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to reliably suppress a carrier component leaking into an extracted distortion signal over a wider frequency band than before. To allow the delay time to be set roughly as compared to the conventional one, to stabilize the operation of the distortion extraction loop with respect to parameters such as temperature, to be resistant to noise, and to achieve an optimal operating state in a shorter time. Its purpose is to be able to withdraw.

[0013]

In order to achieve the above object, the present invention provides (1) a main amplifier for amplifying and outputting an input signal containing a carrier component, which is caused by nonlinearity of the main amplifier. A distortion compensation circuit used to remove or suppress the distortion component from the output signal of the main amplifier, and (2) feed forward a signal branched from the input signal and combine the signal with a signal branched from the output signal. A distortion extraction loop that generates an extracted distortion signal, feed-forwards the extracted distortion signal and combines it with the output signal to generate a distortion-compensated output signal, and a signal in a distortion extraction loop and a distortion removal loop. And a control unit for controlling the adjustment operation, so that leakage of the carrier component to the extracted distortion signal is suppressed and leakage of the distortion component to the distortion compensation output signal is provided. In feedforward distortion compensating circuit wherein the control unit executes the control so that pressure,
(3) a distortion extraction loop, (4) a branching member for dividing the input signal into N branches (N: a natural number of 3 or more) and supplying one of them to a main amplifier for amplification;
-1 corresponding one is sequentially combined with a signal branched from the output signal or a signal output from the preceding coupling member, and the resulting signal is output to the next coupling member or distortion removal loop. (6) The output of the last-stage coupling member is used as the extracted distortion signal.

More preferably, a stabilizing amplifier for amplifying the signal is provided on a path for supplying a signal from an arbitrary coupling member to a subsequent coupling member. And
A feedforward distortion compensating amplifier according to the present invention includes the main amplifier and the feedforward distortion compensating circuit according to the present invention.

Here, also in the prior art, a member for branching the input signal is provided in the distortion extraction loop (FIG. 1).
Directional coupler DC1). On the other hand, in the present invention, the number of branches in the branch member in the distortion extraction loop is three or more. For example, in the prior art, the delay circuit DL1
The above-described N-branch is executed by, for example, further branching the signal supplied to the directional coupler DC2 via the above into two or more. One of the N branches is fed to the main amplifier as before. In the present invention, the remaining N-1 branches are respectively supplied to corresponding ones of the N-1 stages of cascaded connecting members.

In the prior art, a coupling member for generating an extracted distortion signal is provided (the directional coupler D in FIG. 1).
C2). On the other hand, in the present invention, a total of N-1 stages of coupling members are provided corresponding to each of the remaining N-1 branches except for the branch supplied to the main amplifier, and these N-1 stages of coupling members are provided. Are cascaded. The coupling member located at the first stage of the cascade connection couples the signal branched from the output signal of the main amplifier and the signal related to the corresponding one of the above-mentioned N-1 branches. The resulting signal is
It is supplied to the next-stage coupling member. The coupling member of the next stage is
The signal supplied from the preceding or first stage coupling member and the remaining N
-The signal relating to one of the two branches is combined.
The signal obtained as a result is further supplied to the next coupling member. The same operation is sequentially performed by each coupling member, and an extraction distortion signal is output from the final-stage coupling member.

As described above, according to the present invention, the branching member and the coupling member constituting the distortion extraction loop are deformed, and an extracted distortion signal is generated by cooperation of the N-1 cascade-connected coupling members. It has such a configuration. In other words, in the related art, the distortion extraction loop is a single loop, but in the present invention, the distortion extraction loop is a loop having a configuration in which N-1 loops are multiplexed.

[0018] Issues that have been a problem in the prior art,
That is, the problem that the frequency band in which a sufficient amount of carrier suppression can be obtained is narrow has been caused by the phase frequency characteristics of the members constituting the distortion extraction loop. In other words, since the distortion extraction loop is composed of a single loop, the phase frequency characteristic of the loop, which is generally steep, is the phase frequency characteristic of the entire distortion extraction loop, and as a result, sufficient carrier suppression is achieved. The frequency band over which the amount could be obtained was also narrow.
On the other hand, in the present invention, by multiplexing N-1 loops, even if the gradient of the phase frequency characteristic of each loop is steep as in the related art, the distortion extraction loop as a whole has the phase frequency characteristic of the loop. The gradient is made gentler, thereby expanding the frequency band in which a sufficient amount of carrier suppression can be obtained.

As a result, the circuit constituting the distortion extraction loop, for example, the delay circuit can be designed and set more roughly than in the past, and the circuit becomes stable with respect to temperature. Further, since the carrier suppression amount per coupling member is smaller than the carrier suppression amount in the conventional coupling member (directional coupler DC2), it is less affected by noise than in the conventional technology, and the optimum adjustment state can be achieved. The time required for retraction is also reduced. In particular, by providing a stabilizing amplifier for amplifying the signal on a path for supplying a signal from an arbitrary coupling member to the next coupling member, the level of the signal supplied to the next coupling member is reduced. Since the height is higher, it is more resistant to noise and the like, and the pull-in time is shorter.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The same or corresponding components as those of the conventional technology shown in FIG. 1 are denoted by the same reference numerals, and duplicate description will be omitted.

FIG. 2 shows a circuit configuration according to an embodiment of the present invention. This embodiment has a configuration in which a distributor D1, a delay circuit DL1A, a modulator M1A, a directional coupler DC2A, and a stabilizing amplifier A3 are added to the conventional technique shown in FIG. The distributor D1 is provided with a directional coupler DC1.
Divides the signal branched from the main line into two, one of which is supplied to the directional coupler DC2 via the delay circuit DL1, and the other is supplied to the directional coupler DC via the delay circuit DL1A and the modulator M1A.
2A. That is, in the present embodiment, the directional coupler DC1 and the distributor D1 correspond to the aforementioned branching member for N branching. N is set to 3.

The directional coupler DC2A is, for example, a hybrid. The directional coupler DC2A is coupled to a signal input via the delay circuit DL1A and the modulator M1A and a signal branched from the main line via the directional coupler DC2 and transmitted via the delay circuit DL1. The signal input via the stabilizing amplifier A3 is coupled. The directional coupler DC2A supplies the resulting signal to the distortion removal loop as an extracted distortion signal. That is, in the present embodiment, the directional coupler D is used as the N-1 stage coupling member described above.
C2 and DC2A are provided.

The delay time in the delay circuit DL1 is determined by a signal delay in a path from a branch point in the directional coupler DC1 to a coupling point in the directional coupler DC2 via the modulator M1 and the main amplifier A1, and a directional characteristic. The directional coupler DC from the branch point in the coupler DC1 via the distributor D1 and the delay circuit DL1
2 are set so that the signal delay on the path to the connection point in 2 is equal. Further, the delay time in the delay circuit DL1A is changed from the branch point in the directional coupler DC1 to the coupling point in the directional coupler DC2A through the modulator M1, the main amplifier A1, the directional coupler DC2, and the stabilizing amplifier A3. And the signal delay in the path from the branch point in the directional coupler DC1 to the coupling point in the directional coupler DC2A via the distributor D1, the delay circuit DL1A and the modulator M1A. It is set to be equal.

The control unit CTL controls the modulator M1 so that the carriers in the signals coupled by the directional coupler DC2 have the same amplitude and opposite phase. The control unit CTL controls the modulator M1A so that the carriers in the signals coupled by the directional coupler DC2A have the same amplitude and opposite phase. Note that the modulator M1A may have the same circuit configuration as the modulator M1.
Further, as a method of controlling the modulators M1 and M1A by the control unit CTL, various methods can be adopted, such as diverting the control method of the modulator M1 in the related art.

In the prior art, unless the delay time in the delay circuit DL1 is precisely set, a sufficient carrier suppression amount cannot be obtained in the frequency band in which the amplifier is used. One of the advantages of this embodiment is that the delay circuit DL1
And that the frequency band in which a sufficient amount of carrier suppression can be obtained can be expanded without setting the delay time in DL1A so precisely. That is, if the distortion extraction loop is doubled as in the present embodiment, even if the phase frequency characteristic of each loop constituting the distortion extraction loop has a gradient similar to that of the distortion extraction loop in the related art. , The gradient of the phase frequency characteristic in the entire distortion extraction loop becomes gentle.
As a result, the frequency band in which the carrier suppression by the coupling under the amplitude / phase adjustment works sufficiently, that is, the frequency band in which the carrier suppression amount in the distortion extraction loop is sufficiently large is widened. In other words, even if the delay time setting is rougher than in the related art, it is possible to preferably suppress the carrier over a frequency band equal to or more than that of the related art.

Further, by using the distortion extraction loop multiplexed as described above, a change in delay time due to a change in environment such as a change in temperature becomes strong. In addition, since the amount of amplitude / phase adjustment in the N-1 loops constituting the distortion extraction loop is reduced when viewed per loop, the control by the control unit CTL becomes more stable, and the operation to the optimal operation state is performed. Retrieval is also quick. In particular, the directional coupler D
By amplifying and increasing the level of the signal supplied from C2 to the directional coupler DC2A, a more stable distortion extraction loop against noise can be obtained.

The circuit shown in FIG. 2 is only an embodiment of the present invention. The present invention can be implemented as a circuit obtained by applying various modifications to the circuit shown in FIG. For example, the stabilizing amplifier A3 in FIG. 2 can be omitted if sufficient stability can be obtained without it. Further, although N = 3 in FIG. 2, N = 4 may be set as shown in FIG. In FIG. 3, D2 is a distributor having the same configuration as the distributor D1, DL1B is a delay circuit, M1B is a modulator, DC2
B is a directional coupler, A4 is a stabilizing amplifier, and the control unit CTL also controls the modulator M1B. Like the stabilizing amplifier A3, the stabilizing amplifier A4 can be omitted. Of course,
N> 4. Further, the modulator M1 may be moved to the delay circuit DL1 as shown in FIG. FIG.
As shown by symbols X1 to X4, delay circuits DL1 and D1
L1A may be moved. Delay circuits DL1 and DL1
A can be combined with one or all of them in one delay circuit. Then, N-1 constituting a distortion extraction loop
The loops are designed so that the amount of carrier suppression by the loop alone is maximized at any frequency within the frequency band in which the amplifier is used, that is, the frequency band in which carriers are distributed. It is not necessary to exactly match the frequency of the maximum carrier suppression amount between the loops.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a circuit according to a conventional technique.

FIG. 2 is a block diagram illustrating a configuration of a circuit according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a modified example of this embodiment, particularly a distortion extraction loop portion thereof.

FIG. 4 is a block diagram showing another modified example of the embodiment, particularly a modulator arrangement thereof.

FIG. 5 is a block diagram showing still another modified example of the embodiment, particularly, a delay circuit arrangement thereof.

[Explanation of symbols]

A1 main amplifier, A2 distortion amplifier, A3, A4 stabilizing amplifier, CTL controller, D1, D2 distributor, DC
1 to DC3, DC2A, DC2B Directional coupler, DL
1, DL1A, DL1B, DL2 delay circuit, M1, M
1A, M1B, M2 modulator.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ryoji Ito 5-1-1 Shimorenjaku, Mitaka-shi, Tokyo Japan Radio Co., Ltd. F-term (reference) 5J090 AA04 AA41 CA21 CA27 CA62 FA08 FA20 GN02 GN05 GN07 HA25 HN03 KA15 KA16 KA23 KA53 KA68 MA14 SA14 TA01

Claims (3)

[Claims] 1. A distortion compensator attached to a main amplifier for amplifying and outputting an input signal including a carrier component and used for removing or suppressing a distortion component caused by nonlinearity of the main amplifier from an output signal of the main amplifier. A distortion extraction loop that feed-forwards a signal branched from the input signal and combines the signal with a signal branched from the output signal to generate an extracted distortion signal, and feed-forwards the extracted distortion signal to generate the output signal. And a control unit for controlling the signal adjustment operation in the distortion extraction loop and the distortion removal loop, whereby the leakage of the carrier component to the extracted distortion signal is suppressed. The feed-forward distortion compensation in which the control unit performs the control so that the leakage of the distortion component to the distortion compensation output signal is suppressed. In the path, a distortion extracting loop includes a branching member for branching the input signal into N branches (N: a natural number of 3 or more) and supplying one branch to the main amplifier for amplification, and a branch member corresponding to each of the remaining N-1 branches. Things, in order,
A cascaded N-1 stage coupling member that combines a signal branched from the output signal or a signal output from a preceding coupling member and outputs the resulting signal to a next stage coupling member or a distortion removal loop. And a feedforward distortion compensating circuit, wherein an output of the final-stage coupling member is used as the extracted distortion signal. 2. The feedforward distortion compensation circuit according to claim 1, wherein a stabilizing amplifier for amplifying the signal is provided on a path for supplying a signal from an arbitrary coupling member to a coupling member at the next stage. A feedforward distortion compensation circuit characterized by the following. 3. A feed-forward distortion compensation amplifier comprising the main amplifier and the feed-forward distortion compensation circuit according to claim 1.