KR20010088150A - Feed-forward linearizer - Google Patents

Abstract

PURPOSE: A linearization apparatus for a feed-forward type is provided to maintain a stable linearization improvement characteristic by adding an adaptive controller. CONSTITUTION: A vector modulator(60) adjusts a level and a phase of an auxiliary path signal according to a control voltage. A main signal compensation combiner(70) outputs a cross modulation distortion component signal through a subtraction operation of an output of a main amplifier(20) and an output of the vector modulator(60). A detector(80) detects voltages of a plurality of terminals including an input and output terminal of the main signal compensation combiner(70). An adaptive controller(90) confirms a changed error from the voltages of the terminals detected by the detector(80) and outputs the control voltage according to the error. An adder(130) combines an adjusted auxiliary path signal with an inverse phase with the output of the main amplifier(20).

Description

Feed-forward linearizer {Feed-forward linearizer}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, and more particularly, to a feedforward linearization device for improving distortion due to nonlinear characteristics of a large power amplifier used in a wireless transmitter.

In general, an electrical signal amplifier is used to increase the power of an input electrical signal, and an amplifier that increases the signal strength only linearly without distorting the input signal is most ideal for increasing the power of an electrical signal. can do.

However, all signal amplifiers have a large number of active elements, and the nonlinear characteristics of these active elements cause distortion in the output of the signal amplifier.

In the case of an amplifier used in a communication system, if the strength of the input signal is small, there is no big problem in operating the amplifier in the linear region of the amplifier transfer function. However, most wireless transmitters operate the amplifier up to the nonlinear region of the amplifier transfer function in order to maximize the efficiency of signal transmission. The operation of the radio transmitter is not a problem for the performance of the entire device due to signal distortion in amplifying one carrier. However, in case of using a wireless transmitter that needs to amplify a large number of carriers, such as a mobile communication system or a personal mobile communication system, or employs a digital modulation scheme with high frequency efficiency, the intermodulation signal distortion (IMD) generated by the nonlinear characteristics of the signal amplifier (IMD) Intermodulation Distortion: The performance of an entire radio transmitter is severely affected.

In order to improve the intermodulation signal distortion (IMD) characteristics of the signal amplifier used in such a wireless transmitter, a class A amplifier having excellent linear characteristics should be used, and the strength of the input signal should be limited to sufficiently ensure the linearity of the amplifier. . However, this also causes a decrease in the efficiency of signal transmission of the radio transmitter, and the amplifier becomes very large because an amplifier with a high output must be manufactured to overcome the decrease in efficiency.

Recently, in order to solve the problems of low efficiency and high cost due to the nonlinear characteristics of the signal amplifier, various linearization circuits have been proposed. In recent years, a wireless communication system has a feed forwarding linearization technique and linear distortion. (Predistortion) linearization technique, Polar Envelope Correction linearization technique, and bias compensation linearization technique are used.

Among these linearization techniques, the feed forward linearization technique is briefly described. The signal input to the amplifier is divided into two paths to amplify the signal through one path and delay the signal through the other path. . Some of the signal amplified through one path is sampled and compared with the delayed signal through the other path, which separates the error signal between the sampled signal and the signal input to the amplifier due to the amplification. Done. This error signal is added to the input signal which is amplified and then amplified through the one path in reverse phase, thereby improving the distortion characteristic of the signal.

This feed-forward linearization technique is very effective to improve the distortion characteristics of the signal, but it is necessary to adjust the strength and phase of the error signal according to the degree of distortion generated by amplifying the input signal. .

1 is a block diagram showing the configuration of a general feedforward linearization apparatus according to the prior art.

In general, when a single frequency signal is input to a large power amplifier, amplitude to amplitude modulation (AM to AM; hereinafter abbreviated as AM-AM) distortion to amplitude modulation to phase modulation (AM to PM; hereinafter AM-PM) It is amplified by a signal having nonlinear characteristics such as distortion. This causes a decrease in output gain and phase delay.

In addition, when signals of various frequencies are input, intermodulation distortion components having different nonlinear propagation characteristics are generated in addition to an output signal having the same frequency as the input signal.

The signal (carrier) once input is separated into two paths, the main path and the auxiliary path, by the divider 1. The signals in each path have the same magnitude and phase.

The main path includes a main amplifier 2 (actually a large power amplifier), a coupler 3, and a first delay line 4, and the auxiliary path includes a second delay line 5 and a first attenuator 6. ), A first phase shifter 7, a subtractor 8, a second attenuator 9, a second phase shifter 10, and an error correction amplifier 11.

In the main path, the main amplifier 2 amplifies the signal to a desired output level. In this case, intermodulation distortion components are also generated. The input signal of the main amplifier 2 is non-linear in magnitude and phase.

Some of the output of the main amplifier 2 is extracted by a coupler 3, which is then applied to the next subtractor 8.

In the auxiliary path, a pure signal having no intermodulation distortion component is applied to the subtractor 8 while passing through the second delay line 5, the first attenuator 6, and the first phase shifter 7.

Subsequently, the subtractor 8 outputs only the intermodulation distortion component signal through a subtraction operation between the main path signal applied from the coupler 3 and the sub path signal applied from the first phase shifter 7.

The intermodulation distortion component signal output from the subtractor 8 passes through the second attenuator 9, the second phase shifter 10, and the error correcting amplifier 11, and the output of the error correcting amplifier 11 is again the first. It is added with the main path signal delayed by the delay line 4. Here, the second attenuator 9 is for adjusting the output of the subtractor 8 to the level of the intermodulation distortion component generated by the main amplifier 2, and the second phase shifter 10 is an auxiliary path signal as the main path signal. The auxiliary path signal is set to be in phase (180 °) with respect to the main path signal when summed with.

As such, the auxiliary path signal (inverse phase intermodulation distortion component) has the same magnitude as the intermodulation distortion component generated by the amplification of the main amplifier 2, and only its phase is reversed to be recombined with the main path signal. Therefore, only the pure signal (carrier) from which the intermodulation distortion component is finally removed is output.

The apparatus employing the conventional feed-forward linearization technique is very effective in improving the distortion characteristic of a signal. However, since the strength and phase of the error signal must be appropriately adjusted and amplified according to the degree of distortion generated by amplifying the input signal, it has a very complicated hardware structure compared to other linearization devices. In particular, it is very sensitive to external environmental changes such as temperature range, operating range change such as input power level change, and channel frequency change, so that the improvement of C / I ratio is very bad for such external environment change. As a result, the conventional feedforward linearization apparatus cannot maintain stable linearization improvement characteristics and is also limited in its application.

The object of the present invention was devised in view of the above point, and in particular, by adding an adaptive control circuit, it is possible to maintain stable linearization improvement characteristics against external environmental changes such as temperature change, operating range change, and channel frequency change. In order to provide a feedforward linearization apparatus.

A feature of the feedforward linearization device according to the present invention for achieving the above object is a divider for separating the input signal into the main path and the auxiliary path, and amplifying the main path signal separated by the main path by a predetermined level And a main amplifier for outputting the main amplifier, the vector modulator for adjusting the magnitude and phase of the auxiliary path signal separated by the auxiliary path according to a control voltage, the output and the vector modulator of the main amplifier extracted from the main path A main signal cancellation combiner for outputting an intermodulation distortion component signal through a subtraction operation of the output of the signal, and an input / output terminal of the main signal cancellation combiner; Determine the error changed from the terminal voltages of the offset coupler and before the control in the form of voltage according to the error An adaptive controller for outputting a signal and an auxiliary path signal adjusted to be out of phase with respect to the intermodulation distortion component signal which is output from the main signal canceling combiner and added to the output of the main amplifier, and outputs in combination with the output of the main amplifier. It consists of a summer.

Preferably, a first circuit block for determining the magnitude and phase of each of the main voltage canceling coupler detected by the detector by the adaptive controller, and the angle found in the first circuit block. And a second circuit block for outputting the control voltage converted from the terminal voltages using magnitude and phases.

1 is a block diagram showing the configuration of a general feedforward linearization device according to the prior art.

Figure 2 is a block diagram showing the configuration of a feedforward linearization apparatus according to the present invention.

3 is an internal circuit diagram of a main signal canceling coupler according to the present invention;

4 is a detailed internal circuit diagram of the adaptive controller according to the present invention.

* Description of the symbols for the main parts of the drawings *

10: divider 20: main amplifier

30 coupler 40 first delay line

50: second delay line 60: vector modulator

70: main signal cancel coupler 80: detector

90: adaptive controller 100: variable attenuator

110: variable phase shifter 120: error amplifier

130: summer

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

2 is a block diagram showing the configuration of a feedforward linearization apparatus according to the present invention.

Referring to FIG. 2, a signal (carrier) input to a feedforward linearization apparatus according to the present invention is divided into two paths, a main path and an auxiliary path, by a divider 10. The signals in each path have the same magnitude and phase.

In the main path, there is a main amplifier 20 (actually a large power amplifier), a coupler 30, and a first delay line 40 as in the prior art. The auxiliary path includes a second delay line 50, a vector modulator 60, and a main signal cancel coupler 70, a variable attenuator 100 for varying the intensity of the signal, and a variable for varying the phase of the signal. There is a phase shifter 110 and an error correction amplifier 120.

In particular, in the present invention, a loop from the main signal canceling coupler 70 to the vector modulator 60 is formed, and the detector 80 and the adaptive controller 90 exist in the loop.

In the main path, the main amplifier 20 amplifies the signal to a desired output level. In this case, intermodulation distortion components are also generated. The input signal of the main amplifier 20 is non-linear in magnitude and phase.

A portion of the output of the main amplifier 20 is extracted by a coupler 30, which is then applied to the next main signal cancellation coupler 70.

In the auxiliary path, a pure signal having no intermodulation distortion component is applied to the main signal canceling coupler 70 while passing through the second delay line 50 and the vector modulator 60 which changes the signal magnitude and phase to the control range.

Thereafter, the main signal canceling coupler 70 outputs only the intermodulation distortion component signal through a subtraction operation between the main path signal applied from the coupler 30 and the auxiliary path signal applied from the vector modulator 60. An internal circuit of the main signal cancel coupler 70 is illustrated in FIG. 3.

At this time, the detector 80 detects the voltage at each terminal according to the respective power P1, P2, P3, P4 from the four terminals of the main signal canceling coupler 70 shown in FIG. Authorize. This is in case the external environment change such as temperature change, operating range change and channel frequency change occurs and affects the auxiliary path. Of course, if there is no change as described above, it can be linearized with the same operation as before. .

The adaptive controller 90 finds out the changed error from the applied voltages and applies this error signal to the vector modulator 60 as a control voltage in the form of voltage.

The vector modulator 60 adjusts its control range by the applied control voltage. In other words, the vector modulator 60 adjusts its output by changing the input power (magnitude) and frequency (phase) with the applied control voltage. do. By doing so, the magnitude and phase of the intermodulation distortion component signal output from the main signal canceling combiner 70 are compensated.

The auxiliary path signal (intermodulation distortion component signal) whose magnitude and phase are compensated in response to the change in the external environment is changed by the variable attenuator 100, and the phase is changed by the variable phase shifter 110. Finally, the error correction amplifier 120 is passed through.

Thereafter, the output of the error correction amplifier 120 is summed with the main path signal delayed by the first delay line 40 again. Here, the variable attenuator 100 is for adjusting the output of the main signal canceling coupler 70 to the level of the intermodulation distortion component generated by the main amplifier 20. The variable phase shifter 110 has an auxiliary path signal as the main path. When added to the signal, the auxiliary path signal is set to be exactly in phase (180 °) with respect to the main path signal.

As such, the auxiliary path signal (the intermodulation distortion component of the inverse phase) has the same magnitude as the intermodulation distortion component generated by the amplification of the main amplifier 20, and only its phase is reversed to be combined with the main path signal again. Therefore, only the pure signal (carrier) from which the intermodulation distortion component is finally removed is output.

Next, the main signal canceling coupler 70 will be described in more detail.

3 is an internal circuit diagram of the main signal cancel coupler 70 according to the present invention. As mentioned above, the main signal cancel coupler 70 has four terminals.

Referring to FIG. 3, when the signal magnitudes of the first terminal are A and B, respectively, and the phase θ is 0 ° in the main signal canceling coupler 70, the signal magnitude A ₂ of the second terminal and its The phase is shown in Equation 1 below.

In Equation 1, "δA" is a magnitude error, and "δφ" is a phase error.

In addition, the signal of the third terminal is represented by the following equation (2).

(only, )

The output of the main signal canceling coupler 70 output from the last fourth terminal is as shown in Equation 3 below.

(only, )

The powers P1, P2, P3, and P4 of the terminals of the next main signal cancel coupler 70 are represented by Equation 4.

)

From the above equations, the adaptive controller 90 finds out the changed error signal as shown in Equation 5 below.

Error signal phase (β) = P1 + P2 + 2P3

As a result, the voltage for the error signal detected by the detector 80 is expressed by the following Equation 6.

According to the error signal, the control voltage applied to the vector modulator 60 is expressed by Equation 7 below.

In Equation 7, C ₁ and C ₂ are coefficients determined by the amplification degree of the main amplifier 20.

The following relates to the structure of the adaptive controller 90, which is shown in FIG.

4 is a detailed internal circuit diagram of the adaptive controller 90 according to the present invention. The adaptive controller 90 receives the four terminal voltages of the main signal canceling coupler 70 from the detector 80 and the magnitudes of the voltages. The circuit is divided into a first circuit block 91 for finding a phase and a second circuit block 92 for converting the four terminal voltages into control voltages using the magnitude and phase of the found voltage. At this time, of course, if the error signal is added to the four terminal voltages, the control voltage will be as shown in Equation 7 above.

The control voltage converted by the adaptive controller 90 is applied to the vector modulator 60, and the vector modulator 60 changes its input power and frequency after adjusting its control range with this control voltage.

As described above, the effects of using the feedforward linearization apparatus according to the present invention are as follows.

In the present invention, by further using an adaptive controller which is an adaptive control circuit to an existing feedforward linearization device, the linearization improvement characteristic is more stable against external environment changes such as temperature change, operating range change and channel frequency change. Can be maintained.

As a result, the feedforward linearization apparatus of the present invention can maintain a more stable linearization improvement characteristics, and thus has a wider operating range than in the past, which has been limited to a small operating range or a narrow band even in its application. Is applicable.

Claims (2)

A divider for dividing an input signal into a main path and an auxiliary path, and a main amplifier for amplifying and outputting the main path signal separated by the main path by a predetermined level, A vector modulator for controlling the magnitude and phase of the auxiliary path signal separated by the auxiliary path according to a control voltage; A main signal cancellation combiner for outputting a intermodulation distortion component signal through a subtraction operation of the output of the main amplifier extracted from the main path and the output of the vector modulator; A detector for detecting a voltage of a plurality of terminals including an input / output terminal of the main signal canceling coupler; An adaptive controller which detects a change in the terminal voltages of the main signal canceling coupler detected by the detector and outputs the control voltage in the form of a voltage according to the error; And an adder configured to combine the output of the main amplifier with the output of the main amplifier by outputting from the main signal canceling combiner and adjusted to be out of phase with respect to the intermodulation distortion component signal added to the output of the main amplifier. Feedforward linearization device. The method of claim 1, wherein the adaptive controller, A first circuit block for finding the magnitude and phase of each of the terminal voltages of the main signal canceling coupler detected by the detector; And a second circuit block configured to output the control voltage converted from the terminal voltages using respective magnitudes and phases found in the first circuit block.