JP2942553B1 - Distortion compensation circuit for broadband optical fiber communication system - Google Patents

Abstract

A distortion compensation circuit used in a broadband optical fiber communication system is provided. SOLUTION: This distortion compensating circuit is a CSO (Composite Second) of a transmission signal generated due to intermodulation of harmonics by a non-linear element in a system.
Order) / CTB (Composite Tir)
d Beat) distortion can be compensated. The distortion compensation circuit includes split means such as a directional coupler for dividing an input signal into a first signal and a second signal. The first signal is sent on a first path and the second signal is sent on a second path.
The CSO / CTB generator generates the second signal to receive the second signal.
The second signal is coupled to a path to selectively generate a compensated COS / CTB output from the second signal. Further, coupling means, such as another directional coupler, are located at the ends of the first and second paths and combine the compensated CSO / CTB output of the CSO / CTB generator with the first signal. The compensated CSO / CTB output is the CSO / CTB generated in the fiber optic communication system.
Used to offset strain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber optic communication system, and more particularly, to a wide band for compensating for transmission signal distortion caused by analog non-linear (non-linear) elements in the system and leaving the transmission signal essentially free of distortion. The present invention relates to a distortion compensation circuit for an optical fiber communication system.

[0002]

BACKGROUND OF THE INVENTION Optical fiber systems are widely used in the area of communications, such as cable television systems (CATV), for the simultaneous transmission of multiple frequency division multiplex channels of signals and information. In CATV systems, the bandwidth of the carrier is increased to increase the power so that the broadcast signal is provided to more subscribers, or to increase the number of channels over which a single cable link can send more programs to the subscribers. And it is desired to increase the number. However, distortion caused by non-linear elements in the system is problematic for providing high quality image transmission.

CAT based on multi-carrier analog communication
In V, the transmission signal needs to have low noise and low distortion in order to achieve the purpose of high quality image transmission. One way to make the transmitted signal low noise is
To increase the output of the modulated signal so that the signal-to-noise ratio (S / N ratio) increases. However, this will increase the distortion of the transmitted signal caused by the non-linear characteristics of the light emitting and receiving elements in the system.

In optical systems that carry a single radio frequency (RF) or microwave carrier, many non-linear optical or electrical components result in the generation of undesirable harmonics in the carrier, as shown in FIG. When a carrier wave, which is a sine wave signal of frequency f ₀ , passes through the nonlinear element 10, the output of the nonlinear element 10 is an infinite series of harmonics whose frequency is an integer multiple of the input signal frequency (called the base frequency) f _0. Will contain waves. The first harmonic has the same frequency f ₀ as the input signal and the second harmonic has the frequency 2
f ₀ and the third harmonic has a frequency 3f ₀ . The amplitude of these harmonics usually decreases as the order increases. Generally, the amplitude of the fourth or higher harmonic is small enough to be negligible. Therefore, the first to third harmonics are worth considering.

In a multiple RF (or microwave) carrier system, a so-called CSO (Composite) is used.
Second Order) and CTB (Comp
RF (or microwave) where the site triple beat passes through the nonlinear elements in the system
Occurs due to intermodulation between carriers. CSO and CT
B causes so-called intermodulation distortion (IMD) and degrades the quality of transmitted information. For a detailed technical background on this, refer to the IE
EE Journal (November 1989, No. 11, Vo
l. 7)] will be helpful.

[0006] CSO and CTB become more important as the power or number of RF (or microwave) carriers used in the system is increased. CSO
And to some extent the CTB will have a detrimental effect on the quality of the transmitted video information over the CATV system.

A conventional method of compensating for CSO / CTB distortion is to split the input signal into a first signal sent on a first path (called the main path) and a second signal sent on a second path. In particular, CSO or C
A so-called distortion generator is provided which can compensate for distortion such as TB or both. CS
When compensating for O strain, refer to Taiwan (ROC) Publication No. 2
A CSO strain generator (also referred to as a secondary circuit) as disclosed in US Pat. No. 76842 is placed on the second path. On the other hand, when compensating for CTB distortion, US Pat. C as disclosed in US Pat. No. 5,210,633
A TB strain generator is located on the second path. further,
The final output of the second path and the final output of the first path are combined to obtain the difference between them, thereby reducing the undesired C
SO and CTB components can be deleted.

Further, when compensating for both CSO and CTB distortion, a third path is added to the first path and the second path described above. FIG. 2 schematically shows a circuit configuration in this case. The input signal is first sent to the first path 20
Primary signal sent to (main path) and second path 2
It is split into two of the secondary signals sent to 1. Next, the secondary signal is further sent to the first sub-path where the CSO distortion generator 22 is arranged and the second sub-signal is sent to the second sub-path where the CTB distortion generator 23 is arranged. It is divided into sub-signals. CSO strain generator 22
Is used to cancel the CSO component of the primary signal, while the output of the CTB distortion generator 23 is used to cancel the CTB component of the primary signal. Thus, this method can compensate for both CSO and CTB distortion of the input signal. A conventional distortion compensation circuit used in this method is disclosed, for example, in US Pat.
No. 5,132,639 and U.S. Pat. 5,42
No. 4,680.

However, one disadvantage of this method is that
2 called CSO strain generator and CTB strain generator
It requires two separate strain generators. This leads to a complicated circuit configuration. Therefore, the input signal C
Both SO strain and CTB strain or CSO
There is a need for a distortion compensation circuit that includes a single distortion generator that can be adjusted to compensate for either distortion or CTB distortion.

[0010]

SUMMARY OF THE INVENTION The main object of the present invention is to provide:
It is an object of the present invention to provide a distortion compensating circuit for a broadband optical fiber communication system capable of compensating for distortion of a transmission signal caused by an optical or electrical analog non-linear element in a system and having an essentially distortion-free transmission signal. .

Another object of the present invention is to provide a distortion compensation circuit for a broadband optical fiber communication system that is tunable to compensate for both the CSO and CTB distortions of the input signal, or either the CSO and CTB distortions. It is to be.

[0012] Based on the above and other objects of the present invention, a distortion compensation circuit for a broadband optical fiber communication system is provided.

In general, the distortion compensating circuit of the present invention includes the following components: (a) split means for dividing an input signal into a first signal sent to a first path and a second signal sent to a second path; b) located on a second path for receiving a second signal;
CSO / CT for selectively generating compensated CSO / CTB output
B generating means; and (c) a compensating CSO / CTB output from the CSO / CTB generating means located at the end of the first and second paths for canceling the CSO / CTB distortion generated in the optical fiber communication system. Coupling means for coupling to the first signal;

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Principle of the Invention In the following embodiments, the distortion compensating circuit of the present invention uses a CSO of a transmission signal in a broadband optical fiber communication system.
Used to compensate for / CTB distortion. First, FIG.
The principle of the present invention will be described below with reference to FIG.

FIGS. 3 and 4 are schematic diagrams showing the principle of a pre-distortion compensating circuit and a post-distortion compensating circuit, respectively, having the ability to cancel undesirable harmonic components generated by a non-linear element.

As described in the prior art disclosure section of this specification, when a sinusoidal signal of frequency f ₀ passes through a non-linear element such as a laser diode or an optical receiver in a broadband optical fiber communication system, its output is basically It contains a series of harmonic components having a frequency that is an integer multiple of the frequency. Therefore, the frequency of the output signal is f ₀ , 2
f ₀ and 3f ₀ (the fourth harmonic or higher harmonics can be ignored). The undesired second and third harmonic components are canceled by combining them with two sinusoidal components at frequencies 2f ₀ and 3f ₀ , of the same amplitude and inverted in phase. This is a distortion generation that can provide the second harmonic of frequency 2f ₀ and the third harmonic of frequency 3f ₀ with antiphase directly out of phase with respect to the base frequency f ₀ except that it is slightly attenuated. Requires vessel design. If such a distortion generator is placed in front of the non-linear element, it is called a predistortion circuit, otherwise it is called a postdistortion circuit.

As shown in FIG. 3, when the pre-distortion compensating circuit 30 is arranged in front of the nonlinear element 31 for receiving the input signal of the frequency f ₀ , the output of the pre-distortion compensating circuit 30 is As described earlier, there are three harmonics (frequency f ₀ , 2f ₀ and 3f ₀ ) including harmonics of frequencies 2f ₀ and 3f ₀ , whose phases are inverted. When these pass through the non-linear element 31, 2f generated by the non-linear element 31 due to two phase-inverted harmonics
The harmonic components of ₀ and 3f ₀ are canceled.

Further, as shown in FIG. 4, when the post-distortion compensating circuit 41 is arranged to receive the output from the non-linear element 40 which receives the input signal of the frequency f ₀ , the output of the non-linear element 40 2f ₀ and 3f ₀ are generated by the post-distortion compensation circuit 41.
Will be canceled by the two phase inverted 2f ₀ , 3f ₀ harmonics. As a result, the output of the post-distortion compensation circuit 41 includes only the fundamental frequency of the frequency f ₀ . A conventional post-distortion compensation circuit is disclosed in US Pat. 5,48
1,389.

In a multi-carrier system, the 2f ₀ harmonic relates to CSO and the 3f ₀ harmonic relates to CTB. The purpose of the distortion compensation circuit of the present invention is to cancel the CSO / CTB component in the transmitted RF signal.

In the distortion compensating circuit of the present invention, the transmission signal includes a first signal sent to a first path (main path) and a second signal.
And a second signal sent to the path. Assuming that the output of the first signal is X, the output of the second signal is a · X (0 <a
<1) can be expressed. This can be achieved by using a directional coupler that can split the input into two outputs at a preset rate.

In accordance with the present invention, a number of diodes are C
Used to configure SO / CTB generator. This CSO / CTB generator is a major component of the distortion compensation circuit of the present invention, and is used to reduce unwanted CSO / CTB in the transmitted signal.
Corrected CSO / CT used to cancel CTB component
Generate a B signal.

FIG. 5 shows a diode that is forward biased, and FIG. 6 shows a diode that is reverse biased. Diode current (I)-voltage (V)
It is well known in the field of electron optics that the characteristic is a non-linear exponential curve. The exponential relationship between induced current (I) and load voltage (V) in a forward-biased diode can be expanded into a Taylor series as follows.

I = b ₀ + b ₁ · V + b ₂ · V ² + b ₃ · V ³ +. . . . . . (1) Further, the exponential relation in the reverse bias diode can be expanded to the following Taylor series. Here, the odd-numbered terms are inverted.

I = b₀-B₁・ V + b_Two・ V^Two-B_Three・ V^Three+. . . . . . (2) where I is the induced current flowing through the diode, and V is the load voltage.
Pressure, and b₀, B₁, B _Two, B_ThreeIs the Taylor series coefficient
You.

In theory, a coupling device such as a balun may be used to combine the two currents of equations (1) and (2) to cancel out the odd numbered terms. Can be used. If the two diodes are properly biased, the actual result will be very close to the theoretical value. In this case, CSO is generated because the odd-numbered terms cancel out.

In addition, the bias on the two diodes can be unbalanced, for example, by using resistors of different resistance values or by using leakage currents that make the induced currents flowing through the two diodes different. , The two currents of Equations (1) and (2) are combined such that only the second and third terms are left as generated CSO and generated CTB, respectively. Therefore, CSO and CTB
Are simultaneously generated in this way.

In the case of the second-order distortion compensating circuit of the present invention, odd-numbered harmonic components will be bounced off. This causes interference on the signal on the main path. This problem can be solved, for example, by using a high quality directional coupler, or by placing an amplifier in front of the CSO / CTB generator to achieve optimal separation.

The CSO / CTB generator 7 show a detailed circuit structure of the CSO / CTB generator to be used as main components of the distortion correction circuit of the present invention. The CSO / CTB generator includes a number of resistors R1, R
2, R3, R4, R5, R6, many capacitors C1,
C2, C3, a pair of diodes D1, D2, a current source 70
And a balun 71. The input signal is received at node A by the CSO / CTB generator. Diodes D1 and D2 provide CSO / CT for the input signal.
Used to generate B strain. Big CSO /
From the viewpoint that CTB distortion can be generated, it is preferable to use a Schottky diode as the diode. Current source 70 and resistors R1, R2, R3, R
4, R5 and R6 are arranged to function as bias means for providing optimum bias voltages to the diodes D1 and D2.

In this embodiment, two diodes (ie, D1 and D2) are used to create CSO / CTB distortion. However, the number of diodes may be one or two or more. Basically, C
As the number of diodes used for the SO / CTB generator increases, greater CSO / CTB distortion will be created. However, this will increase the unwanted insertion loss. Therefore, the trade-off between these factors should be chosen by the designer. In this embodiment, two diodes D1 and D2 are connected in series. The positive terminal of the diode D1 is connected to the positive input terminal of the balun 71 via a capacitor C2. On the other hand, the negative terminal of the diode D2 is connected to the negative input terminal of the balun 71 via the capacitor C3.

The balun 71 has the ability to generate the difference between the odd-numbered harmonics and the sum of the even-numbered harmonics and combine these differences and the sum into a single composite output.

If the resistors R1, R2, R3, R4, R5 and R6 are designed such that R1 = R2, R3 = R4, R5 = R6, the CSO / CTB generator of FIG.
It simply functions as a CSO strain generator without generating the B component.

On the other hand, resistors R1, R2, R3, R4, R5
If and R6 are designed such that R1 = R2, R3 = R4, R5 ≠ R6, diodes D1 and D2 will not be equivalent with respect to impedance. Thereby C
The amplitude of the CTB component at the output of the SO / CTB generator will be increased. Also, R1 ≠ R2, R3 = R4, R
If it is designed so that 5 = R6, the diode D1
Will not be equal in magnitude to the current flowing through diode D2. This is CSO / C
It will increase the amplitude of the CTB component at the output of the TB generator.

Equalizer The present invention can be used for a multi-carrier communication system in a wide band such as 45 MHz to 860 MHz. An equalizer is used so that the amplitude response of the CSO is substantially flattened over its band. FIG. 8 is a schematic diagram showing the function of the equalizer indicated by reference numeral 80.
The equalizer is used as an auxiliary component of the distortion compensation circuit of the present invention. Input C to equalizer 80
The SO (unequal amplitude response over its frequency band) passes through the equalizer 80 and is substantially smoothly flattened across that band. FIG. 9 shows an example of the equalizer 80. In addition, equalizers having various circuit configurations can be used.

FIGS. 10 and 11 show three embodiments of the distortion compensating circuit of the present invention constructed based on the above components.
This will be described below with reference to FIGS.

First Embodiment As shown in FIG. 10, a distortion compensation circuit according to a first embodiment of the present invention includes an input terminal 100 for receiving an input signal, and a first directivity disposed at the input terminal 100. Combiner 110
including. The directional coupler 110 functions as a split unit that splits an input signal into two, and sends the split signals to a first path and a second path, respectively. In this embodiment, the second signal is 10 dB less at the output than the first signal. The delay circuit 120 is arranged on the first path. On the other hand, the second path includes a CSO / CTB generator 140,
Voltage control attenuator 150, amplifier 160, equalizer 1
70 are continuously arranged in this order. Further, a coupling means such as a second directional coupler 130 is used to couple the output of the first path and the output of the second path.

The delay circuit 120 is connected to the CSO /
CTB generator 140, voltage controlled attenuator 150, amplifier 1
60, used to delay the first signal by a time exactly equal to the delay time by the second signal passing through equalizer 170. Thus, the two output signals from the respective paths are synchronously encountered by the second directional coupler 130.

On the second path, the second signal is first CS
It is sent to O / CTB generator 140. The circuit structure of the CSO / CTB generator 140 is shown in FIG. In this embodiment, CSO / CTB generator 140 generates RSO to provide CTB to the output of CSO / CTB generator 140.
1 = R2, R3 = R4, R5 ≠ R6 or R1 ≠ R
2, R3 = R4, R5 = R6. Thus, CSO / CTB generator 140 includes both CSO and CTB in its output.

As shown in FIG. 10, the output of CSO / CTB generator 140 is subsequently sent to voltage controlled attenuator 150. The voltage-controlled attenuator 150 is a circuit composed of four pin (PIN) diodes, and attenuates its input with an adjustable attenuation ratio by changing the magnitude of the control voltage input to the voltage-controlled attenuator 150. Can be. In particular, the voltage-controlled attenuator 150 includes the CSO / CTB generator 1
It is used to control the amplitude of the 40 outputs to an optimal level.

The output of voltage controlled attenuator 150 is then amplified by amplifier 160. The output of amplifier 160 is sent to equalizer 170. Equalizer 170
Has the ability to correct for unwanted amplitude or phase characteristics of the output of amplifier 160. In this embodiment, the equalizer 170 flattens the amplitude responses of all the frequency components in the 45 MHz to 860 MHz band substantially smoothly. Thereafter, the output of the equalizer 170 is sent to the minus input terminal of the second directional coupler 130. The plus input terminal of the coupler 130 is connected to the delay circuit 12 on the first path.
Receive a delayed version of the first signal from zero. As a result, the second directional coupler 130 functions as a coupler that outputs the difference between the output on the first path and the output on the second path,
The undesired signal at the output of the first path is
Compensated CSO / CTB component of the output of the path is canceled. Therefore, the output of the second directional coupler 130 is a compensated version of the input signal. Second Embodiment FIG. 11 is a schematic diagram showing a second embodiment of the distortion compensation circuit according to the present invention. In this figure, components having the same structure and function as those of the first embodiment of FIG. 10 are denoted by the same reference numerals, and the description thereof will not be repeated here.

This embodiment differs from the first embodiment in the following points. That is, in the first embodiment, C
Although the SO / CTB generator 140, the voltage-controlled attenuator 150, the amplifier 160, and the equalizer 170 are arranged in this order, in the second embodiment, as shown in FIG.
0, CSO / CTB generator 140, voltage controlled attenuator 15
0 and the equalizer 170 are arranged in this order. CS
The arrangement of the amplifier 160 in front of the O / CTB generator 140 depends on the CSO / CT from the CSO / CTB generator 140.
It has the advantage of increasing the B output.

Since the odd-numbered components of the input to CSO / CTB generator 140 are bounced off and cause interference to the signal passing on the main path, the optimal separation
ation) should be applied. The placement of the amplifying garment 160 in front of the CSO / CTB generator 140 provides the additional benefit of suppressing bouncing CTBs due to the separation by the amplifier 160. However, amplifier 1
60 should be properly coordinated with the attenuating means so that the non-linear characteristics of the amplifier 160 do not distort the received signal. Third Embodiment FIG. 12 is a schematic diagram showing a third embodiment of the distortion compensation circuit according to the present invention. In this figure, the same drawing numbers are used for components having the same structure and function as those of the previous embodiment, and the description thereof will not be repeated here.

This embodiment differs from the first embodiment in the following points. That is, the third path is provided by using the third directional coupler 180 at the input end of the second path. As shown in FIG. 12, the third directional coupler 180 has its plus port connected to the start of the second path,
The minus port is arranged so as to be connected to the start of the third path. This arrangement is the CSO / CTB generator 1
The bounce signal from 40 is directed to the third path. Further, a fourth directional coupler 190 is used to combine the output of the third path and the output of the second path. CSO / CT
B generator 140, voltage controlled attenuator 150, amplifier 16
0, equalizers 170 are arranged in the same order as the second path of the first embodiment. In the third path, a delay circuit 181, an amplifier 182, a voltage controlled attenuator 183, and an equalizer 184 are arranged in this order.

In this embodiment, the CSO / C on the second path
The TB generator 140 calculates (R1 = R2, R3 = R4, R5 =
It is set to generate only CSO (by setting it to R6). Thereby, the CTB component of the second partial signal is output from the CSO / CTB generator 140 to the third directional coupler 1.
It is bounced back to 80 and then sent by the third directional coupler 180 to the third path.

In the third path, the rebound CTB is first delayed by the delay circuit 181 so that the final output of the third path is synchronized with the output of the second path. Delay circuit 1
The output of 81 is amplified by amplifier 182 to an optimum amplitude. Thereafter, the output of amplifier 182 passes through voltage controlled attenuator 183, and the output of voltage controlled attenuator 183 is equalized by equalizer 184 with respect to the amplitude response in that band. The CSO output from the second path and the CTB output from the third path are combined by a fourth directional coupler 190. Thereafter, the output of the fourth directional coupler 190 is combined with the output of the first path by the second directional coupler 130 based on the method described above.

Although the present invention has been described based on the preferred embodiments, the scope of the present invention is not limited to these embodiments. Rather, they should be construed to cover various modifications and similar arrangements. Therefore, the scope of the present invention should be determined based on the broad interpretation including such modifications and similar arrangements.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a series of harmonic components generated in a sinusoidal RF or microwave signal by passing the signal through a non-linear (optical or electrical) element.

FIG. 2 is a schematic diagram of a conventional distortion compensation circuit for compensating for CSO / CTB distortion in an input signal.

FIG. 3 is a schematic diagram showing the principle of a pre-distortion compensating circuit capable of canceling harmonic components generated by a non-linear element.

FIG. 4 is a schematic diagram showing the principle of a post-distortion compensation circuit having the ability to cancel harmonic components generated by a non-linear element.

FIG. 5 is a schematic diagram of a forward bias diode.

FIG. 6 is a schematic diagram of a reverse bias diode.

FIG. 7 is a schematic circuit diagram of a CSO / CTB generator used as a component of the distortion compensation circuit of the present invention.

FIG. 8 is a schematic diagram showing the function of an equalizer used as a component of the distortion compensation circuit of the present invention.

FIG. 9 is a schematic circuit diagram of an equalizer.

FIG. 10 is a schematic diagram of a first embodiment of a distortion compensation circuit according to the present invention.

FIG. 11 is a schematic diagram of a second embodiment of the distortion compensation circuit according to the present invention.

FIG. 12 is a schematic diagram of a third embodiment of the distortion compensation circuit according to the present invention.

[Explanation of symbols]

 Reference Signs List 100 input terminal 110 first directional coupler 120 delay circuit 130 second directional coupler 140 CSO / CTB generator 150 voltage-controlled attenuator 160 amplifier 170 equalizer

Claims (11)

(57) [Claims] A distortion compensating circuit for a broadband optical fiber communication system, comprising: a first signal transmitted to a first path and a second signal transmitted to a second path; Split means for splitting into two signals; CSO / CTB arranged in the second path for receiving the second signal and selectively generating a compensated CSO / CTB output
Generation means; and C generated at the end of the first and second paths and generated in the optical fiber communication system.
Combining means for combining the compensated CSO / CTB output from the CSO / CTB generating means with a first signal to offset SO / CTB distortion. 2. The splitting means is a directional coupler having an input port connected to receive an input signal and a pair of output ports respectively connected to the first and second paths. The distortion compensation circuit according to claim 1, wherein 3. The coupling means includes a positive input port connected to a terminal part of the first path, a positive input port connected to a terminal part of the second path, and an output of the CSO / CTB generating means on a second path. A directional coupler having a minus input port capable of inverting the phase and an output port for outputting the difference between the first signal from the first path and the output of the CSO / CTB generating means from the second path; 3. The distortion compensation circuit according to claim 1, wherein 4. The distortion compensating circuit according to claim 1, wherein said second path includes the following configuration.
A voltage-controlled attenuator for receiving the output of the TB generating means and for selectively adjusting the attenuation ratio of the output of the CSO / CTB generating means; an amplifier for receiving and amplifying the output of the attenuator;
And an equalizer that receives the output of the amplifier and equalizes the amplitude response of the amplifier output over its band. 5. A delay circuit for delaying said first signal by a time substantially equal to a delay time of a second signal passing through said CSO / CTB generating means, a voltage controlled attenuator, an amplifier and said equalizer. The distortion compensation circuit according to claim 4, wherein the distortion compensation circuit is provided on the first path. 6. The distortion compensating circuit according to claim 5, wherein said second path includes the following configuration: said distortion compensating circuit is arranged in front of said CSO / CTB generating means for receiving a second signal from said splitting means. An amplifier for amplifying the received second signal, an output of the amplifier being input to CSO / CTB generating means; receiving an output of the CSO / CTB generating means, and adjusting an attenuation ratio of an output of the CSO / CTB generating means. And an equalizer that receives the output of the attenuator and equalizes the amplitude response of the output from the attenuator over its band. 7. The amplifier, CSO / CTB generating means,
A voltage controlled attenuator and a delay circuit for delaying the first signal by a time substantially equal to a delay time of a second signal passing through the equalizer are provided on the first path. Item 6. A distortion compensation circuit. 8. A distortion compensation circuit according to claim 1, comprising: a directional coupler coupled to a start of said second path to form a third path; The combiner has the ability to send a bounce signal from the CSO / CTB generation means to the third path, and when the CSO / CTB generation means is set to generate only CSO, the bounce signal is CTB; Combined CSO from the second path and CTB from the third path to generate an output located at the end of the second and third paths and indicating the sum of the CSO from the second path and the CTB from the third path CSO to do
/ CTB coupling means. 9. A distortion compensating circuit, wherein the third path includes the following configuration: receiving a rebound CTB from the directional coupler, and outputting a final output from the third path to a second path.
A delay circuit for delaying the CTB by a delay time so as to synchronize the output of the path with the CSO / CTB coupling means; an amplifier for receiving an output from the delay circuit and amplifying an output of the delay circuit; an output of the amplifier And a voltage controlled attenuator for adjusting the attenuation ratio of the output of the amplifier; and an equalizer for receiving the output of the attenuator and equalizing the amplitude response of the output from the attenuator. 10. The distortion compensation circuit according to claim 1, wherein said CSO / CTB generating means includes the following configuration: an input port for receiving said second signal; a first diode and a second diode. At least one pair of diodes connected in series, the negative terminal of the first diode is connected to the positive terminal of the second diode, and the negative terminal of the first diode and the positive terminal of the second diode are both the input terminals. Bias means for applying a bias to each of the first and second diodes; and a positive input terminal connected to the positive terminal of the first diode and a negative terminal connected to the negative terminal of the second diode. A balanced-unbalanced converter having an input end, the output of the balanced-unbalanced converter being the CSO / C
Used as an output of the TB generation means. 11. The semiconductor device according to claim 1, wherein each of the first and second diodes is a Schottky diode.
Zero distortion compensation circuit.