KR20010008703A - Distortion Signal Compensation Device in Communication System - Google Patents

Abstract

PURPOSE: A distorted signal compensating device is provided to reduce a nonlinear distortion signal by controlling gain and phase characteristics of an RF(Radio Frequency) output amplifier by use of a delay path. CONSTITUTION: A distorted signal compensating device comprises a feed forward linearizer which consists of a variable attenuator(21), a variable phase shifter(22), the first to third delay lines(25,26,27), the first and second circuit parts(29,30) and a synchronizer(31). Linearization is realized by dividing a signal path into a main path and an error correction path. The main path uses the second delay line(26) for phase compensation, the error correction path uses the first delay line(25) for phase compensation and the third delay line(27) is used for phase control.

Description

Distortion Signal Compensation Device in Communication System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, and more particularly, to a distorted signal compensation device in a communication system that can reduce a nonlinear distortion signal by controlling gain and phase characteristics of an RF high power amplifier using a delay line provided in a base station receiver.

In general, various methods of linearization techniques and algorithms have been proposed to improve the nonlinearity of amplifiers in order to make RF high power amplifiers satisfying the standards related to the conventional digital mobile communication system.

Among them, typical linearization methods include a feed forward and a predistortion method.

Such various linearization methods will be described as follows.

First, a linearization method using a predistortion method.

This method is generally characterized by the spectral increase of high power amplifiers due to AM to AM (Amplitude Modulation) and AM to PM (PM) phase distortion, which are non-linearly changed in gain and phase according to the input signal. ) Is the main cause.

Therefore, when the gain and phase characteristics of the main amplifier input signal are distorted in a specific direction, the predistorter located in front of the main amplifier has the opposite characteristics, so that the characteristics of the entire amplifier are reversed. It is possible to obtain an output having improved nonlinearity by keeping the input signal almost the same.

Next, there is a feed forward method, which will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating an operation process of a conventional feedforward linearizer.

Referring to FIG. 1, the carrier applied to the input is separated with the same magnitude and phase as the main path and the auxiliary path.

In the main path, while the main amplifier 11 is amplified to a desired output level, intermodulation distortion signals are also generated.

When the carrier and the intermodulation distortion components are partially extracted from the output and applied to the subtractor 16, only the pure carrier is input to the subtractor in the auxiliary path, so only the intermodulated distortion signal is obtained for the signal output through the subtractor.

The intermodulation distortion signal components obtained by the subtractor 16 are coupled to the main path again through the variable attenuator 14, the variable phase shifter 15, and the error correction amplifier 17.

At this time, the variable attenuator 14 is for adjusting the level of the intermodulation distortion signal appearing in the main amplifier, and the variable phase shifter 15 is for adjusting the antiphase 180 ° when coupled to the main path again. .

Therefore, the magnitude of the intermodulation distortion signal coupled back to the main path is the same as the intermodulation distortion component generated by the main amplifier 11, and the phase is reversed, leaving only the pure carrier at the final output.

That is, the phases of the distorted signal components are 180 [deg.] To cancel each other out, leaving only the signal without distortion similar to the original input signal.

However, using the linearization method using the conventional feed forward method has the following disadvantages.

First, in order to remove the Inter Modulation Distortion derived from the signal output through the amplifier, the time delay and time delay of the time delay caused by passing through each main amplifier and the error amplifier are correct. It is necessary to obtain the antiphase (180 degrees) through the matching or accurate control of the variable attenuator and variable phase shifter, but the narrow bandwidth of the bandwidth and the control circuit are out of the operating range due to the time delay caused by the control of each of these components. There was a disadvantage that it was difficult to control.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, wherein a distortion compensation device in a communication system that reduces nonlinear distortion signals by controlling characteristics of gain and phase distortion of an RF high power amplifier using a delay line provided in a base station transmitter unit It is to provide. According to the present invention, the first control circuit portion for performing the strength and phase control function of the signal input to the main amplifier, and the intensity and phase change of the non-linear signal output from the error correction amplifier receiving the input signal A second control circuit section for fixing the value of? To a predetermined value; a delay line section for compensating the phase delay time of the error correction amplifier section by controlling the second control circuit section; and each of the first and second control circuit sections. It comprises a synchronization unit for matching the time delay between the automatic gain adjustment unit and the automatic phase adjustment units used.

Preferably, the delay line unit compensates the phase delay time of the error correction amplifier by adjusting the length of the delay line so that the phase of the input signal is changed in the dynamic region of the second control circuit unit.

The synchronization unit adjusts the length of the third delay line unit to synchronize the gain adjusting unit and the phase adjusting unit respectively provided in the first and second control circuits to perform real time control.

1 is a block diagram illustrating an operation process of a conventional feedforward linearizer.

2 is a block diagram illustrating the operation of an improved feed forward linearizer for distorted signal compensation according to the present invention;

Explanation of symbols on the main parts of the drawings

20: directional coupler 21: variable attenuator

22: variable phase displacement 23: main amplifier

24: subtractor 25: first delay line

26: second delay line 27: third delay line

28: error correction amplifier 29: first control circuit

30: second control circuit portion 31: synchronization portion

Hereinafter, a preferred embodiment according to the present invention will be described with reference to the accompanying drawings.

2 is a block diagram illustrating the operation of an improved feedforward linearizer for distorted signal compensation according to the present invention.

Referring to Figure 2, the feed forward linearizer proposed in the present invention (Feed Foward Linearizer) is a variable attenuator 21 for adjusting the signal size, a variable phase shifter 22 for adjusting the phase, a subtractor, separated into each path First, second and third delay lines 25, 26 and 27 for matching the time delay of the signal and first and second control circuit sections 29 and 30 for adjusting internal circuit elements, And a synchronizer 31 for synchronizing the time delays between the respective control circuits.

The circuit elements configured as described above are divided into two paths, a main path and an error correction path, to implement linearization for compensation of a distorted signal.

At this time, if the time delay of the two paths is different, the time delay can be adjusted by adjusting the phase with a phase shifter for one frequency. However, because the time delay is different in the two paths at other frequencies, the phase is changed and the bandwidth is increased. It is inevitable to shrink.

In order to prevent such a case, the present invention adopts a linearization method using a delay line.

In other words, by using a delay line, the input signal matches the time delay that occurs while passing through the circuit elements performing the operation control function in the linearizer, thereby narrowing the bandwidth caused by the phase difference caused by the time delay. It is to prevent.

Therefore, in the present invention, the second delay line 26 is used for the phase compensation for the main path, and the first delay line 25 is used for the phase compensation for the error correction path. The third delay line 27 was used for phase control.

The third delay line 27 additionally provided together with the first and second delay lines 25 and 26 used previously performs a main function for the compensation of the distorted signal component according to the present invention. An operation description thereof will be described in more detail with reference to the accompanying drawings.

Referring to FIG. 2, in order for the feedforward linearizer to operate properly, not only the time delay of the main path and the error correction path but also the gain of the error correction amplifier must be maintained at a constant value.

Therefore, although the second delay line 26 between the main signal sections B to D1 performs a linear operation as a passive element, the error correction amplifier 28 located in the auxiliary signal section compensates for this since it is an active element having a nonlinear output characteristic. You must do it.

For this purpose, an automatic control function of the signal strength and phase is required, which is performed by the third delay line 27 and the second control circuit unit 30 in the structure of the present invention.

The third delay line 27 is an error correction amplifier 28 so as to be changed in the dynamic range of the second control circuit unit 30 which automatically controls the phase of the subtractor 24 output signal. Compensates for the phase delay time.

In the conventional phase control, the signal is adjusted by controlling the auto gain controller (hereinafter referred to as AGC) / auto phase controller (hereinafter referred to as APC) by comparing the previous signal with the current signal. It is impossible to process in real time by the method, but there is some error, but in the present invention, accurate phase control is possible in real time by adjusting the length of the delay line.

As a whole, the synchronization of the automatic gain controllers 29a and 30a and the automatic phase controllers 29b and 30b used in the first control circuit unit 29, the second control circuit unit 30 and the second control circuit unit 30 is controlled. A synchronization unit 31 is further provided to allow for real-time control through linearization of the entire distorted signal.

Referring to the operation of the present invention having such a configuration in detail as follows.

First, the input signal is divided into two and input as a main path and an error correction path, respectively.

Each input signal performs the intensity and phase control functions of the main signal by the first control circuit unit 29 and controls the phase after the automation of the intensity control.

The intensity control is performed at the variable phase displacement point 22 so that both signals are in phase at a point including a subtractor 24 where a part of the input signal separated in the main signal section and a signal in the error correction path meet. Adjust the phase shifter by the signal.

In addition, the second control circuit unit 30 adjusts the non-linear intensity and phase change of the signal amplified by the error correction amplifier 28 to have a fixed value.

Therefore, the signal of the point between the directional coupler 30c of the third delay line 27 and the second control circuit unit 30 is used as a reference signal of the subtractor 24 in which the phase delay time is compensated in the third delay line 27. The phase shifter may be operated by the control signal of the second control circuit unit 30 with respect to the output signal phase and the output signal phase amplified by the error correction amplifier 28. Through this path, at the final stage, the intermodulation distortion (IMD) signals may be canceled with each other and only the main component, that is, the original signal, may be output.

That is, the circuit proposed in the present invention controls the error correction amplifier 28 using the third delay line 27 as described above to perform the function of the linearizer in real time for various input power levels. can do.

Therefore, the signal is combined by adjusting the phase difference exactly 180 degrees at the point of the second control circuit unit 30 without providing a separate detector circuit.

In addition, since the linear circuit does not use an active circuit to suppress the non-linearity of signal components in the error correction path (Error Correction Path (from the start point to the second control circuit section 30 section) used as a reference value, the signal distortion and The oscillation was prevented to improve the stability of the circuit.

According to the present invention as described above, by using a delay line as a condition for implementing a linearizer for reducing the distorted signal components of the high output amplifier by matching the time delay caused by the signal passing through the various elements in the linearizer, By preventing the narrowing of the band due to the mismatch of time delay and controlling the gain and phase characteristics of the error correction amplifier, it is possible to control in real time on the input signals having different magnitudes and phases in a wider band than the conventional method. .

Claims (2)

A first control circuit part performing a strength and phase control function of a signal input to the main amplifier part; A second control circuit unit for fixing the values of the intensity and phase change of the nonlinear signal output from the error correction amplifier receiving the input signal to a predetermined value; A delay line unit for controlling the second control circuit unit to compensate the phase delay time of the error correction amplifier unit; And a synchronization unit for synchronizing time delays between the automatic gain adjusting unit and the automatic phase adjusting units used in the first and second control circuit units, respectively. The phase correction unit of claim 1, wherein the delay line unit adjusts the length of the delay line so that the phase of the input signal is changed in the dynamic region of the second control circuit unit. Distorted signal compensation apparatus in a communication system, characterized in that the.