JPH1141175A - Distortion compensation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distortion compensation circuit capable of uniformly compensating distortion in a wide band for a frequency multiplexed signal. SOLUTION: The frequency multiplexed signal is branched into a first and a second routes by a branching part 30. A distortion signal is first generated by using the frequency multiplexed signal to propagate the second route by a distortion generation/adjustment part 90. The distortion signal is correlated with non-linear distortion of the frequency multiplexed signal to propagate the first route. After that, amplitude and a delay amount of the generated distortion signal is adjusted to match the amplitude and the delay amount of the non-linear distortion by the distortion generation/adjustment part 90. In this case, the amplitude and the delay amount of the distortion signal included in a frequency band selected by a frequency selection part 80 is adjusted by the distortion generation/adjustment part 90. The distortion signal outputted from the distortion generation/adjustment part 90 and the non-linear distortion included in the frequency multiplexed signal to propagate the first signal are multiplexed in relation that the phases are mutually inverted by a phase inversion multiplexing part 70.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a distortion compensating circuit, and more particularly to a distortion compensating circuit for compensating for nonlinear distortion generated in an output signal due to nonlinearity of an element or the like.

[0002]

2. Description of the Related Art In optical communication, generally, a transmission side transmits an optical modulation signal in which the intensity of light is modulated by a transmission signal, and a reception side demodulates the optical modulation signal to obtain an original signal. The light modulation signal is generated in a light emitting element such as a semiconductor laser by using a phenomenon that when the applied current changes, the power of the light output also changes. However, the optical modulation signal is distorted due to the nonlinearity of the semiconductor laser.
The effect of the distortion is relatively small when the transmission signal is a digital signal, but remarkably appears when the transmission signal is an analog signal, and has a problem of deteriorating the data transmission quality.

One method for solving this problem is a pre-distortion method. In this method, a distortion signal that cancels distortion generated by a semiconductor laser or the like is added to the transmission signal. Therefore, when optical modulation is performed, the distortion signal cancels the distortion due to the non-linearity.
Thus, the data transmission quality is not degraded. Hereinafter, an optical transmission device using a predistortion method will be described with reference to FIG.

In FIG. 6, a branching unit 30 branches a transmission signal (main signal) to be converted into an optical signal by an electric / optical conversion unit 80 composed of a semiconductor laser or the like. One of the two branched main signals propagates through the first path and is input to the phase inversion multiplexing unit 70, and the other is output to the second path. On the second path, the distortion generator 40 and the amplitude adjuster 50
And a delay amount adjusting unit 60. Distortion generator 40
Generates a signal (hereinafter, referred to as a distortion signal) that cancels the distortion generated in the electrical / optical converter 80 when the main signal is input. The amplitude adjustment unit 50 adjusts the amplitude level of the distortion signal so that the amplitude level becomes the same as the distortion generated when the electrical / optical conversion unit 80 generates the optical modulation signal. The delay amount adjusting unit 60 adjusts the delay amount of the distortion signal so that the delay amount becomes the same as that of the main signal propagating through the first path. The phase inversion multiplexing unit 70 converts the main signal and the distortion signal into a phase difference 180
Add together with a degree. Therefore, the output signal from the phase inversion multiplexing unit 70 has the same amplitude level as the main signal and the distortion generated when the optical signal is generated in the electrical / optical conversion unit 80 by the main signal, and has the opposite phase. And a distortion signal. Therefore, in the electrical / optical converter 80, the distortion due to the non-linearity is canceled by the distortion signal. Therefore, this optical modulation signal is converted to an optical / electrical conversion unit (not shown).
When the frequency multiplexed signal is converted into an electric frequency multiplexed signal by the above, the frequency multiplexed signal does not include distortion.

[0005]

In order to compensate for distortion occurring in a frequency-division multiplexed signal as a main signal using the above-described pre-distortion method, the delay on the first path side and the second path side is reduced. The quantities need to match over all of the wide bands that make up the frequency multiplexed signal. However, since there are various components such as non-linear elements on the second path side, it is difficult to match the delay amounts of the first path and the second path, and the delay amount has frequency characteristics. Due to this frequency characteristic, there is a problem that the effect of distortion compensation differs for each frequency component included in the frequency multiplexed signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a distortion compensating circuit capable of uniformly compensating a frequency multiplexed signal over a wide band.

[0007]

A first aspect of the present invention is a distortion compensating circuit for compensating for non-linear distortion contained in a frequency multiplexed signal transmitted from a transmitting side. A distorted signal correlated with non-linear distortion included in the frequency multiplexed signal is generated by using a branching unit that inputs and branches the signal to the first and second paths and a frequency multiplexed signal propagated on the second path. A distortion generation unit, an amplitude adjustment unit that adjusts the amplitude of the distortion signal generated by the distortion generation unit, a delay amount adjustment unit that adjusts the delay amount of the distortion signal generated by the distortion generation unit,
The distortion signal whose amplitude and delay amount has been adjusted by the amplitude adjustment unit and the delay amount adjustment unit and the non-linear distortion included in the frequency multiplexed signal propagating through the first path are multiplexed in a mutually inverted phase relationship. A phase inversion multiplexing unit, and a frequency selection unit that selectively extracts a signal of a corresponding frequency from an output signal of the phase inversion multiplexing unit by selecting a frequency, and an amplitude adjustment unit and a delay amount adjustment unit. Switches the adjustment amount of the amplitude and delay amount of the distortion signal in response to the frequency selection operation in the frequency selection unit, whereby the phase inversion multiplexing unit is included in the frequency band selected by the frequency selection unit It is characterized by canceling out nonlinear distortion. According to the first aspect, the phase inversion multiplexing unit inverts the phase of the distortion signal generated by the distortion generation unit and the nonlinear distortion included in the frequency multiplexed signal propagated through the first path. And the nonlinear distortion is cancelled. As a result, distortion compensation is performed. In addition, for the non-linear distortion included in the frequency band selected by the frequency selection unit, the amplitude and delay amount of the distortion signal are adjusted, so that an optimal distortion compensation effect can be obtained. In addition, since the frequency band to be compensated can be selected in the frequency selection unit, the frequency band that can be compensated as a distortion compensation circuit is expanded, and distortion can be compensated without variation for each frequency band. It can be performed. Further, according to the first aspect, since optimal distortion compensation can be performed over the entire frequency band, strict requirements are imposed on components constituting the reception side and transmission side to which the present distortion compensation circuit is applied. No frequency characteristics of delay amount are required.
As a result, manufacturing, maintenance, and other costs of the receiving side and the transmitting side can be reduced.

In a second aspect based on the first aspect, the delay amount adjustment section includes a plurality of delay lines each having a different delay amount and being assigned a different frequency band. In response to the frequency selection operation in the frequency selection unit, one of the plurality of delay lines is selected, and the delay amount of the delay line selected by the delay amount adjustment unit is the frequency assigned to the delay line. In order to make it possible to cancel the nonlinear distortion included in the band, the delay amounts of the first path and the second path are adjusted to be equal. According to the second aspect, since the delay amount adjusting section includes the plurality of delay lines as described above, each delay amount can be easily set, and the number of delay lines can be easily set. Can be changed. Therefore, it is easy to change the frequency band that can be compensated as the distortion compensation circuit and to adjust the distortion compensation circuit.

In a third aspect based on the second aspect, a narrower frequency band is assigned to the plurality of delay lines in the delay amount adjusting section as the frequency becomes higher. Even if the difference between the delay amounts of the first path and the second path is the same at each frequency, the higher the frequency, the larger the phase difference between the nonlinear distortion and the distortion signal. When the phase inversion multiplexing unit performs the phase inversion multiplexing in such a state, the phase of the nonlinear distortion and the distortion signal is largely shifted from the relationship of the opposite phases. Therefore, if a frequency band is allocated as in the third aspect, distortion can be more optimally compensated.

A fourth aspect of the present invention is a distortion compensating circuit for inputting an optical signal intensity-modulated by a frequency multiplex signal from a transmitting side and compensating for nonlinear distortion included in the optical signal. , An optical / electrical conversion unit for converting the frequency multiplexed signal into a frequency multiplexed signal, a branching unit for inputting the frequency multiplexed signal converted by the optical / electrical conversion unit and branching the signal into the first and second paths, Using a frequency multiplexed signal that propagates along the path,
A distortion generator that generates a distortion signal correlated with the non-linear distortion included in the frequency multiplexed signal, an amplitude adjustment unit that adjusts the amplitude of the distortion signal generated by the distortion generator, and a distortion signal generated by the distortion generator. A delay amount adjusting unit that adjusts the delay amount, a distortion signal whose amplitude and delay amount are adjusted by the amplitude adjusting unit and the delay amount adjusting unit, and a nonlinear signal that is included in the frequency multiplexed signal that propagates through the first path. Frequency selection for selectively extracting a signal of a corresponding frequency from an output signal of the phase inversion multiplexing unit by selecting a frequency and a phase inversion multiplexing unit for multiplexing the distortion and the phase inversion relationship with each other. The amplitude adjustment unit and the delay amount adjustment unit switch the adjustment amount of the amplitude and delay amount of the distortion signal in response to the frequency selection operation in the frequency selection unit, whereby the phase inversion multiplexing unit includes frequency Characterized by offsetting the non-linear distortion included in the frequency band selected by the selecting section. According to the fourth aspect, the distortion compensating circuit has the above-described optical-to-electrical conversion unit, so that the optical signal modulated in intensity by the frequency-division multiplexed signal, as in the first aspect,
Optimum distortion compensation can be performed, and manufacturing and maintenance and other costs on the receiving and transmitting sides can be reduced.

In a fifth aspect based on the fourth aspect, the delay amount adjustment section includes a plurality of delay lines each having a different delay amount and being assigned a different frequency band. In response to the frequency selection operation in the frequency selection unit, one of the plurality of delay lines is selected, and the delay amount of the delay line selected by the delay amount adjustment unit is the frequency assigned to the delay line. In order to make it possible to cancel the nonlinear distortion included in the band, the delay amounts of the first path and the second path are adjusted to be equal. According to the fifth aspect, it is easy to change the frequency band that can be compensated as the distortion compensating circuit and adjust the distortion compensating circuit for the optical signal that is intensity-modulated by the frequency multiplexed signal, as in the second aspect. become.

In a sixth aspect based on the fifth aspect, a narrower frequency band is allocated to the plurality of delay lines included in the delay amount adjusting section as the frequency increases.
According to the sixth aspect, more optimal distortion compensation can be performed on an optical signal that has been intensity-modulated by a frequency multiplexed signal, as in the third aspect.

A seventh aspect of the present invention is a distortion compensating circuit for compensating for m-order and n-order nonlinear distortions contained in a frequency multiplexed signal transmitted from a transmitting side, wherein the frequency compensating circuit receives the frequency multiplexed signal. A branching unit for branching into first and second paths;
A second branching unit that branches a frequency multiplexed signal propagating through the third path into third and fourth paths, and a frequency multiplexed signal propagating through the third path, is included in the frequency multiplexed signal. generating an mth-order distortion signal correlated with the mth-order nonlinear distortion,
M for adjusting the amplitude and delay amount of the generated mth-order distortion signal
Using the next-order distortion generation / adjustment unit and the frequency-division multiplexed signal propagating through the fourth path, an nth-order distortion signal correlated with the nth-order nonlinear distortion included in the frequency-division multiplexed signal is generated and generated. n
Generation of nth-order distortion for adjusting the amplitude and delay amount of the second-order distortion signal /
An adjusting unit, an m-order distortion signal generated by the m-order distortion generating / adjusting unit, the amplitude and the delay amount of which are adjusted, and the m-order nonlinear distortion included in the frequency multiplexed signal propagating through the first path. A first phase inversion multiplexing unit that multiplexes the signals in a phase inverted relationship with each other, an nth-order distortion signal generated by the nth-order distortion generation / adjustment unit, the amplitude and the delay amount of which are adjusted, A second phase-inversion multiplexing unit that multiplexes the nth-order nonlinear distortion included in the frequency multiplexed signal obtained by multiplexing the mth-order distortion signal by the phase inversion multiplexing unit in a relationship where the phases are inverted with respect to each other. And a frequency selection unit that selectively extracts a signal of a corresponding frequency from an output signal of the second phase inversion multiplexing unit by selecting a frequency, and includes an mth-order distortion generation / adjustment unit and an nth-order distortion generation / adjustment unit. The distortion generation / adjustment unit responds to the frequency selection operation in the frequency selection unit and outputs the m-th order distortion signal. And the amount of adjustment between the amplitude of the nth-order distortion signal and the amount of delay is switched, so that the first phase inversion multiplexing unit and the second phase inversion multiplexing unit are within the frequency band selected by the frequency selection unit. It is characterized in that the m-th and n-order nonlinear distortions included therein are offset, and one of m and n is 2 and the other is 3.

An eighth invention is a distortion compensating circuit for compensating for m-order and n-order nonlinear distortions contained in a frequency multiplexed signal transmitted from a transmitting side, wherein the frequency compensating circuit receives the frequency multiplexed signal, Using a branching unit for branching into first and second paths and a frequency multiplexed signal propagating through the second path, m-order distortion correlated with m-order nonlinear distortion included in the frequency multiplexed signal A m-order distortion generation / adjustment unit that generates a signal and adjusts the amplitude and delay amount of the generated m-order distortion signal; and an m-order distortion generated by the m-order distortion generation / adjustment unit and whose amplitude and delay amount are adjusted. A first phase inversion multiplexing unit that multiplexes the signal and an m-th order nonlinear distortion included in the frequency multiplexed signal propagating in the first path in a relationship where the phases are inverted with each other; The frequency multiplexed signal obtained by multiplexing the m-order distortion signal by the phase inversion multiplexing unit And a second branching unit that branches to the path of (n) and a frequency-division multiplexed signal propagating through the fourth path. An n-order distortion generation / adjustment unit for adjusting the amplitude and delay amount of the generated and generated n-order distortion signal; and an n-order distortion signal generated by the n-order distortion generation / adjustment unit and having the amplitude and delay amount adjusted. A second phase inversion multiplexing unit that multiplexes the nth-order nonlinear distortion included in the frequency multiplexed signal propagating through the third path in a relationship where the phases are inverted with each other, and by selecting a frequency. A frequency selection unit for selectively extracting a signal of a corresponding frequency from the output signal of the second phase inversion multiplexing unit, wherein the m-order distortion generation / adjustment unit and the n-order distortion generation / adjustment unit perform frequency selection. M-order distortion signal and n-order distortion signal in response to the frequency selection operation in the section The amount of adjustment between the amplitude and the delay amount is switched, so that the first phase inversion multiplexing unit and the second phase inversion multiplexing unit include the mth and nth order included in the frequency band selected by the frequency selection unit. It is characterized by canceling out the following non-linear distortion, wherein one of m and n is 2 and the other is 3.

According to the seventh and eighth aspects of the invention, both the second-order and third-order nonlinear distortions contained in the frequency-division multiplexed signal are compensated while exhibiting the same effects as those described in the first aspect. And a distortion compensating circuit capable of performing the same.

[0016]

FIG. 1 is a block diagram showing a schematic configuration of a communication system to which a distortion compensation circuit according to first to third configuration examples of the present invention is applied. In FIG. 1, one transmission device 1 and a plurality of reception devices 2 (one shown) are communicably connected to the communication system via an optical fiber 4. The transmission device 1 uses a semiconductor laser or another non-linear element (not shown) to transmit an optical signal, which is intensity-modulated by a frequency multiplexed signal as an electric signal, to the optical fiber 4. In this optical signal, nonlinear distortion occurs at the time of the intensity modulation. Although the conventional distortion compensation circuit is provided on the transmission device 1 side, the transmission device 1 shown in FIG. 1 does not necessarily need to be provided with a distortion compensation circuit. Each receiving device 2 is provided with a distortion compensating circuit 3 for compensating for nonlinear distortion included in an optical signal transmitted by the optical fiber 4.

FIG. 2 is a block diagram showing a first configuration example of the distortion compensation circuit 3 shown in FIG. In FIG. 2, a distortion compensation circuit 3 (see inside a two-dot chain line) includes an optical / electrical conversion unit 10,
Amplitude level adjustment unit 20, branch unit 30, distortion generation / adjustment unit 9
0, a phase inversion multiplexing unit 70, and a frequency selection unit 80.

The optical / electrical converter 10 receives an optical signal transmitted by the optical fiber 4 and converts it into a frequency multiplexed signal (electrical signal). Amplitude level adjuster 20
Adjusts the amplitude level of the frequency multiplexed signal converted by the optical / electrical conversion unit 10 to a predetermined amplitude level. The branching unit 30 branches the frequency-division multiplexed signal whose amplitude level has been adjusted by the amplitude level adjusting unit 20 into two paths, a first path and a second path. Here, the first path is a path for directly inputting one of the frequency-division multiplexed signals branched by the branching unit 30 to the phase inversion multiplexing unit 70, and the second path is a path for branching by the branching unit 30 into two. The other frequency-division multiplexed signal is transmitted to the phase inverting / multiplexing unit 7 via the distortion generation / adjustment unit 90.
This is a path for inputting 0.

The distortion generating / adjusting section 90 uses the frequency multiplexed signal propagating through the second path to obtain the second or third order nonlinear distortion included in the frequency multiplexed signal propagating through the first path. 2 and adjusts the amplitude and delay amount of the generated distortion signal, and includes a distortion generation unit 40, an amplitude adjustment unit 50, and a delay amount adjustment unit 60 (see FIG. 2). See inside the dotted line). Hereinafter, the process of generating the distortion signal will be described in more detail. The distortion generating section 40 includes a semiconductor diode, an FET, and other non-linear elements.
The above distortion signal is generated. Since the distortion generator 40 is often used in the pre-distortion method, it will not be described in detail here. The amplitude adjustment unit 50 includes a variable attenuation type attenuator and the like, and the distortion generation unit 40
Of the distortion signals input from the
The amplitude of the distortion signal included in the frequency band selected by 0 is the same as the amplitude of the second- or third-order nonlinear distortion (nonlinear distortion to be compensated) included in the same frequency band. Adjust to The reason why the amplitude adjusting unit 50 is disposed after the distortion generating unit 40 is that the nonlinearity between the semiconductor laser and other non-linear elements used in the transmitting apparatus 1 and the non-linear elements in the distortion generating unit 40 is high. Is generally different, and there is an amplitude difference between the non-linear distortion generated by the semiconductor laser or the like and the distortion signal generated by the FET or the like. Delay amount adjustment unit 60
In the distortion signal input from the amplitude adjustment unit 50, the delay amount of the distortion signal included in the frequency band selected by the frequency selection unit 80 (the frequency band whose amplitude level has been adjusted by the amplitude adjustment unit 50) is: The adjustment is made so that the delay amount of the second-order or third-order nonlinear distortion included in the same frequency band becomes the same. The phase inversion multiplexing unit 70 receives a signal from the first path and the delay amount adjusting unit 60, and outputs second-order or third-order nonlinear distortion included in the frequency multiplexed signal propagating through the first path. And the distortion signal output from the delay amount adjustment unit 60 are multiplexed in such a relationship that the phases are inverted with each other (hereinafter, referred to as phase inversion multiplexing). In other words, these two
The two signals are added so as to have a phase difference of 180 degrees. Thereby, 2 included in the frequency multiplexed signal is obtained.
The secondary or tertiary nonlinear distortion is canceled out and the distortion is compensated. In particular, in the frequency band selected by the frequency selector 80, the amplitude and delay amount between the distortion signal and the secondary or tertiary nonlinear distortion are reduced. Since the adjustments are made to be the same, the nonlinear distortion is most effectively canceled and the distortion is compensated. The frequency selection unit 80 includes a frequency variable filter (not shown) and the like, and selects and passes only a predetermined frequency component from the frequency-multiplexed signal output from the phase inversion multiplexing unit 70 and distortion-compensated. At the same time (frequency selection operation), the frequency band including the frequency component is notified to the amplitude adjustment unit 50 and the delay amount adjustment unit 60 described above.

Here, regarding the delay amount adjusting section 60,
This will be described in more detail. For example, the delay amount of the first path is a constant delay amount D in a frequency band to be used. On the other hand, the delay amount of the second path has frequency characteristics, and different delay amounts D1 to D3 for different frequency bands Δf1 to Δf3 (frequency deviation of delay amount). In such a case, in the related art, the delay amount of the first path and the delay amount of the second path are matched at a certain frequency, so that the delay amounts are shifted at other frequencies. For example, if the first path and the second path have the same delay amount in the frequency band Δf3, the delay amount will be shifted by D3-D1 in the frequency band Δf1, and D3-D2 in the frequency band Δf2. These delay amounts D1 to D3 and D are obtained in advance by measurement or the like. Delay amount adjusting section 6 having a configuration as shown in FIG.
Numeral 0 is composed of a plurality of delay lines 61 to 63 having delay amounts DD1, DD2 and DD3, and two switches 64a and 64b (see inside the two-dot chain line in FIG. 3). The delay lines 61 to 63 have frequency bands Δf
1 to Δf3 are assigned. The switches 64a and 64b are provided so that the frequency selection unit 80 controls the frequency band (Δf1 to Δf1).
When any one of f3) is selected, a delay line (one of delay lines 61 to 63) corresponding to the frequency band is connected.

A delay amount adjusting unit 60 as shown in FIG.
Can easily adjust the amount of delay given to the delay line, so that even if the second path has a frequency deviation in the amount of delay, the frequency band selected by the frequency The delay amount given to the second-order or third-order nonlinear distortion included in the frequency multiplexed signal on the first path and the delay amount given to the distortion signal on the second path can be exactly matched. Further, even if the difference between the delay amount of the first path and the delay amount of the second path is the same at each frequency, as the frequency increases, the phase of the nonlinear distortion and the phase of the distortion signal become higher. The deviation increases. If the phase inversion multiplexing unit performs phase inversion multiplexing in such a state, the phase between the nonlinear distortion and the distortion signal included in the frequency multiplexed signal greatly deviates from the relationship of the opposite phases, and the distortion compensation circuit 3 , The effect of distortion compensation becomes smaller. Therefore, as the frequency increases, each of the delay lines 61 to 63
Is preferably assigned a narrow frequency band.
Further, each delay line may be prepared in a number corresponding to the number of frequency components of the frequency multiplexed signal, and a narrow frequency band corresponding to each frequency component may be allocated, but a wide frequency band including a plurality of frequency components may be allocated. Even if the frequency band is assigned and the number of delay lines is relatively reduced, a sufficient distortion compensation effect can be obtained.

A delay amount adjusting unit 60 as shown in FIG.
Is not to make the delay amount of the first path and the delay amount of the second path coincide with each other over a wide band.
Both are matched only in a certain specific frequency band. In other words, the delay amount adjustment unit 60 can narrow the frequency band assigned to each delay line, so that the delay amount difference can be easily eliminated in that frequency band, and the optimal distortion compensation can be performed. The effect can be obtained. Further, since the delay amount adjusting section 60 has a plurality of delay lines, if the number of delay lines is increased and an appropriate delay amount is given, the frequency band in which distortion can be compensated can be widened. Then, the delay amount adjustment unit 60 can optimally adjust the delay amount for the frequency band selected by the frequency selection unit 80.
For example, recent cable TVs have 90 MHz to 750 MH
The z frequency band is often used. It is difficult to collectively adjust the delay amount over such a wide frequency band in view of the performance of components used in the transmission device 1 and the reception device 2 and the like. Moreover, the audience
In most cases, the user watches a television program or other information broadcast on a certain channel, so that it is not always necessary to adjust the delay amount over the entire wide frequency band. Therefore, the delay amount adjustment unit 60 is configured such that the delay amount can be adjusted over the entire wide frequency band, but the delay amount is particularly optimally adjusted for the frequency band required by the viewer. Is valid. Further, according to the delay amount adjusting unit 60, the components used in the transmission device 1 and the reception device 2 do not need to have strict frequency characteristics of the delay amount.
And the cost of the receiving device 2 can be reduced.

The first configuration example is a configuration in which the secondary or tertiary nonlinear distortion is compensated for according to the operating conditions of the distortion generator 40. Second and third configuration examples are conceivable. FIG. 4 is a block diagram showing a second configuration example of the distortion compensation circuit 3 shown in FIG. FIG.
, The distortion compensation circuit 3 includes an optical / electrical conversion unit 10, an amplitude level adjustment unit 20, first and second branching units 410 and 420, a secondary distortion generation / adjustment unit 430, and a tertiary distortion generation / Adjustment unit 440 and first and second phase inversion multiplexing unit 45
0 and 460, and a frequency selection unit 80. Of these configurations, the optical / electrical conversion unit 10 and the amplitude level adjustment unit 20 are the same as the corresponding configurations in the first configuration example, and thus description thereof is omitted, and the first The following description focuses on the differences from the configuration example.

The first branching section 410 branches the frequency-division multiplexed signal whose amplitude level has been adjusted by the amplitude level adjusting section 20 into two, and connects one of the two to the first path (connected to the first phase inversion multiplexing section 450). The other is output to a second path (a path connected to the second branching unit 420).
The second branching unit 420 branches the other frequency multiplexed signal propagating through the second path into two, and sets one of the two to the third path (path connected to the secondary distortion generation / adjustment unit 430). The other is output to a fourth path (a path connected to the third-order distortion generation / adjustment unit 440).

The secondary distortion generation / adjustment section 430 includes a distortion generation section, an amplitude adjustment section, and a delay amount adjustment section, but includes a distortion generation / adjustment section 90 indicated by a dotted line in FIG. Since the configuration is the same, illustration of the configuration is omitted in FIG. The distortion generator receives the frequency multiplexed signal propagating through the third path and generates a secondary distortion signal using the frequency multiplexed signal. The second-order distortion signal is correlated with the second-order nonlinear distortion included in the frequency-division multiplexed signal that propagates through the first path and is input to the first phase-inversion multiplexing unit 450. Furthermore, the amplitude and delay amount of the secondary distortion signal are
In the same manner as described in the first embodiment, the adjustment is performed by the amplitude adjustment unit and the delay amount adjustment unit (see FIG. 3 for the configuration).

The first phase inversion multiplexing section 450 receives a signal from the first path and the second-order distortion generating / adjusting section 430 and is included in the frequency multiplexed signal propagating through the first path. The second-order nonlinear distortion and the second-order distortion signal output from the second-order distortion generation / adjustment section 430 are phase-inverted and combined. As a result, in the frequency multiplexed signal, the second-order nonlinear distortion included in the frequency band selected by the frequency selection unit 80 is optimally compensated.

The frequency multiplexed signal propagating through the fourth path is input to a third-order distortion generator / adjuster 440. The third-order distortion generation / adjustment unit 440 has the same configuration as the second-order distortion generation / adjustment unit 430, but differs in that this frequency-multiplexed signal is input and a third-order distortion signal is generated and adjusted. . Other than this, there is no difference between the two, and the description of the third-order distortion creating unit 440 is omitted. Note that the third-order distortion signal is correlated with the third-order nonlinear distortion included in the frequency multiplexed signal input to the second phase-inversion multiplexing unit 460 via the first phase-inversion-multiplexing unit 450. ing. Second phase inversion multiplexer 460
Receives signals from the first phase inversion multiplexing section 450 and the third-order distortion generating / adjusting section 440 and outputs the third-order nonlinear distortion included in the frequency-multiplexed signal in which the second-order nonlinear distortion is compensated. And the third-order distortion signal output from the third-order distortion generation / adjustment section 440 is phase-inverted and multiplexed. Thus, in the frequency multiplexed signal, the third-order nonlinear distortion included in the frequency band selected by the frequency selection unit 80 is optimally compensated.
The frequency multiplexed signal in which the second-order and third-order nonlinear distortions have been compensated as described above is output from the second phase inversion multiplexing unit 460 to the frequency selection unit 80.

As described above, the distortion compensating circuit 3 according to the second configuration example can compensate for both the second-order and third-order nonlinear distortion included in the frequency multiplexed signal. Note that the distortion compensating circuit 3 according to the second configuration example includes two components included in the frequency multiplexed signal.
Although the configuration is such that the next non-linear distortion is compensated first, the effect of distortion compensation does not change even if the configuration is to compensate the third-order nonlinear distortion first.

FIG. 5 is a block diagram showing a third configuration example of the distortion compensation circuit 3 shown in FIG. In FIG. 5, the distortion compensating circuit 3 includes the same components as those in the second configuration example. Therefore, corresponding components are denoted by the same reference numerals. However, the distortion compensation circuit 3 according to this configuration example is
In the second configuration example, the second-order distortion generation / adjustment unit 430 and the third-order distortion generation / adjustment unit 440 are connected in parallel, whereas the second-order distortion generation / adjustment unit 440 is apparent as shown in FIG. / Adjustment section 430 and third-order distortion generation / adjustment section 440 are connected in series. However, the operation of each component is the same as that of the second configuration example, and can be easily understood with reference to FIG. 5, so that the detailed description is omitted. The distortion compensating circuit 3 according to the third configuration example can also compensate for both the second-order and third-order nonlinear distortion included in the frequency multiplexed signal. In this configuration example, the effect of distortion compensation does not change even if the third-order nonlinear distortion is compensated first.

The distortion compensating circuits 3 according to the first to third configuration examples are applied to an optical communication system, and convert an optical signal into a frequency multiplexed signal which is an electric signal, and then convert the optical signal into a nonlinear signal included therein. It is configured to compensate for distortion.
However, even in a communication system to which a normal frequency division multiplexing method is applied, the transmitting apparatus transmits a frequency multiplexed signal to a transmission path using an amplifier which is a non-linear element. Includes distortion.
Therefore, the first to third communication systems are also provided in such a communication system.
The distortion compensating device 3 according to the above configuration example can be applied.
However, in this case, the optical / electrical converter 10 shown in FIGS. 2, 4, and 5 is not required.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a communication system to which a distortion compensation circuit according to first to third configuration examples of the present invention is applied.

FIG. 2 is a block diagram showing a first configuration example of a distortion compensation circuit 3 shown in FIG.

FIG. 3 is a diagram illustrating a detailed configuration of a delay amount adjusting unit 60 illustrated in FIG. 2;

FIG. 4 is a block diagram showing a second configuration example of the distortion compensation circuit 3 shown in FIG.

FIG. 5 is a block diagram showing a third configuration example of the distortion compensation circuit 3 shown in FIG.

FIG. 6 is a block diagram showing a configuration of a conventional distortion compensation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transmission apparatus 2 ... Receiving apparatus 3 ... Distortion compensation circuit 4 ... Optical fiber 10 ... Optical / electrical conversion part 20 ... Amplitude level adjustment part 30 ... Branch part 40 ... Distortion generation part 50 ... Amplitude adjustment part 60 ... Delay amount adjustment part 61 to 63 delay line 64a, 64b switch 70 phase inversion multiplexing section 80 frequency selection section 90 distortion generation / adjustment section 410 first branch section 420 second branch section 430 secondary distortion generation / Adjustment unit 440 ... third-order distortion generation / adjustment unit 450 ... first phase inversion multiplexing unit 460 ... second phase inversion multiplexing unit

Claims (8)

[Claims] 1. A distortion compensation circuit for compensating for non-linear distortion contained in a frequency multiplexed signal transmitted from a transmission side, wherein the frequency multiplexed signal is input and branched to first and second paths. A branching unit, a distortion generating unit that generates a distortion signal that is correlated with the nonlinear distortion included in the frequency multiplexed signal using the frequency multiplexed signal that propagates through the second path, An amplitude adjustment unit that adjusts the amplitude of the distortion signal; a delay amount adjustment unit that adjusts the delay amount of the distortion signal generated by the distortion generation unit; and an amplitude and delay amount that is adjusted by the amplitude adjustment unit and the delay amount adjustment unit. A phase inversion multiplexing unit that multiplexes the obtained distortion signal and the non-linear distortion included in the frequency multiplexed signal propagating through the first path in a relationship where the phases are inverted with each other; , The phase inversion A frequency selection unit that selectively extracts a signal of a corresponding frequency from an output signal of the wave unit, wherein the amplitude adjustment unit and the delay amount adjustment unit respond to a frequency selection operation in the frequency selection unit, Switching the adjustment amount of the amplitude and delay amount of the distortion signal, whereby the phase inversion multiplexing unit cancels out nonlinear distortion included in the frequency band selected by the frequency selection unit. Distortion compensation circuit. 2. The delay amount adjusting section includes a plurality of delay lines each having a different delay amount and being assigned a different frequency band, and responding to a frequency selecting operation in the frequency selecting section. And selecting one of the plurality of delay lines. The delay amount of the delay line selected by the delay amount adjustment unit cancels the nonlinear distortion included in the frequency band allocated to the delay line. 2. The distortion compensation circuit according to claim 1, wherein the delay amount of the first path and the second path is adjusted to be equal to enable the delay amount. 3. 3. The distortion compensation circuit according to claim 2, wherein a narrower frequency band is assigned to the plurality of delay lines in the delay amount adjustment unit as the frequency increases. 4. A distortion compensating circuit for inputting an optical signal intensity-modulated by a frequency multiplex signal from a transmitting side and compensating for nonlinear distortion included in the optical signal. An optical-to-electrical conversion unit that converts the signal into a frequency-multiplexed signal; a branching unit that receives the frequency-multiplexed signal converted by the optical-to-electrical conversion unit and splits the signal into first and second paths; A distortion generating unit that generates a distortion signal correlated with non-linear distortion included in the frequency multiplexed signal using a frequency multiplexed signal that propagates, and an amplitude adjustment unit that adjusts the amplitude of the distortion signal generated in the distortion generating unit. A delay amount adjustment unit that adjusts a delay amount of a distortion signal generated by the distortion generation unit; a distortion signal whose amplitude and delay amount are adjusted by the amplitude adjustment unit and the delay amount adjustment unit; Frequency that propagates the route A phase inversion multiplexing unit that multiplexes the nonlinear distortion included in the multiplexed signal in a relationship where the phases are inverted with each other; and selecting a frequency, the output signal of the phase inversion and multiplexing unit corresponds to A frequency selection unit for selectively extracting a frequency signal, wherein the amplitude adjustment unit and the delay amount adjustment unit respond to a frequency selection operation in the frequency selection unit, and determine the amplitude and delay amount of the distortion signal. A distortion compensation circuit, wherein the amount of adjustment is switched, whereby the phase inversion multiplexing unit cancels out nonlinear distortion included in the frequency band selected by the frequency selection unit. 5. The delay amount adjusting unit includes a plurality of delay lines each having a different delay amount and being assigned a different frequency band, and responding to a frequency selecting operation in the frequency selecting unit. And selecting one of the plurality of delay lines. The delay amount of the delay line selected by the delay amount adjustment unit cancels the nonlinear distortion included in the frequency band allocated to the delay line. The distortion compensation circuit according to claim 4, wherein the delay amount of the first path and the second path are adjusted so as to be equal to each other. 6. The distortion compensation circuit according to claim 5, wherein a narrower frequency band is assigned to the plurality of delay lines in the delay amount adjuster as the frequency becomes higher. 7. A distortion compensating circuit for compensating m-order and n-order nonlinear distortions contained in a frequency multiplexed signal transmitted from a transmitting side, comprising: And a branching unit for branching to a second path; a second branching unit for branching a frequency multiplexed signal propagating in the second path to third and fourth paths; and a frequency to propagate in the third path. Using the multiplexed signal, generate an m-th order distortion signal correlated with the m-th order nonlinear distortion included in the frequency multiplexed signal, and adjust the amplitude and delay amount of the generated m-order distortion signal. A generation / adjustment unit, and an nth-order distortion signal correlated with the nth-order nonlinear distortion included in the frequency multiplexed signal, using the frequency multiplexed signal propagating through the fourth path, and generating n An nth-order distortion generation / adjustment unit for adjusting the amplitude and delay amount of the next-order distortion signal; The m-th order distortion signal generated by the m-th order distortion generation / adjustment unit, the amplitude and the delay amount of which are adjusted, and the m-order nonlinear distortion included in the frequency multiplexed signal propagating through the first path. A first phase inversion multiplexing unit that multiplexes the signals in a relationship where their phases are inverted with each other; an nth-order distortion signal generated by the nth-order distortion generation / adjustment unit and having an amplitude and a delay amount adjusted; A second phase inversion for multiplexing the nth-order nonlinear distortion included in the frequency multiplexed signal obtained by multiplexing the mth-order distortion signal by the 1 phase inversion multiplexing unit in a relationship where the phases are inverted with respect to each other; A multiplexing unit; and a frequency selecting unit that selectively extracts a signal of a corresponding frequency from an output signal of the second phase inversion multiplexing unit by selecting a frequency, wherein the m-order distortion generation / adjustment is performed. Unit and the nth-order distortion generation / adjustment unit, In response to the selection operation, an adjustment amount between the amplitude and the delay amount of the m-order distortion signal and the n-order distortion signal is switched, whereby the first phase inversion multiplexing unit and the second phase inversion multiplexing are switched. The unit is characterized in that m-th and n-th nonlinear distortion included in the frequency band selected by the frequency selection unit are offset, and one of the m and n is 2, and the other is Is 3, a distortion compensation circuit. 8. A distortion compensating circuit for compensating m-order and n-order nonlinear distortions contained in a frequency multiplexed signal transmitted from a transmission side, comprising: A branching unit for branching to a second path, and an m-order distortion signal correlated with an m-order nonlinear distortion included in the frequency-multiplexed signal, using the frequency-multiplexed signal propagating in the second path. An m-order distortion generation / adjustment unit that adjusts the amplitude and delay amount of the generated and generated m-order distortion signal; and an m-order distortion signal generated by the m-order distortion generation / adjustment unit and whose amplitude and delay amount are adjusted. A first phase-inversion multiplexing unit that multiplexes the m-order nonlinear distortion included in the frequency-division multiplexed signal propagating in the first path in a phase-inverted relationship with each other; The frequency multiplexed signal obtained by multiplexing the m-order distortion signal by the phase inversion multiplexing unit 1 A second branching unit that branches into third and fourth paths, and a frequency-division multiplexed signal propagating through the fourth path, which is correlated with the nth-order nonlinear distortion included in the frequency-division multiplexed signal. an nth-order distortion generation / adjustment unit that generates an nth-order distortion signal and adjusts the amplitude and the delay amount of the generated nth-order distortion signal; and the n-th order distortion generation / adjustment unit generates and adjusts the amplitude and the delay amount. A second phase inversion multiplexing unit that multiplexes the nth-order distortion signal and the nth-order nonlinear distortion included in the frequency multiplexed signal propagating through the third path in a relationship where the phases are inverted with respect to each other. A frequency selection unit for selectively extracting a signal of a corresponding frequency from an output signal of the second phase inversion multiplexing unit by selecting a frequency, wherein the m-order distortion generation / adjustment unit and the n The secondary distortion generation / adjustment unit selects the frequency in the frequency selection unit. Switching the amount of adjustment between the amplitude and the amount of delay of the m-order distortion signal and the n-order distortion signal in response to the operation, whereby the first phase inversion multiplexing unit and the second phase inversion multiplexing unit Is characterized in that m-order and n-order nonlinear distortion included in the frequency band selected by the frequency selection unit are offset, and one of the m and n is 2, and the other is 3. A distortion compensation circuit.