KR20010100649A - Feedforward linear power amplifier using error feedback - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feedforward linearization technique having a function of removing an intermodulation distortion (IMD) component generated when amplifying a signal of a power amplifier of a wireless communication system.

The feature is that the error feedback technique is applied to the general feedforward method to maximize the mutual intermodulation distortion suppression characteristics. In a typical manner, additional circuits are added by attaching a predistorter in front of the main amplifier, but the present invention is possible without additional circuitry.

Accordingly, the linearizer of the present invention can increase system capacity and improve call quality by dramatically reducing adjacent channel interference due to intermodulation distortion in a wireless communication system having a wideband characteristic.

Description

Feedforward linear power amplifier using error feedback

The present invention relates to a feedforward linearization technique having a function of removing inter-modulation distortion (IMD) components generated when amplifying a signal of a power amplifier. IMD refers to an intermodulation distortion component generated by the interaction of two carriers while passing through a nonlinear element when two or more carriers are applied. The feedforward method improves the characteristics of the system by modifying the results by moving parts of the input to the output stage.

In general, since long-distance communication such as satellite communication and mobile communication cannot transmit a signal at one time, a relay station or a base station is amplified and transmitted again at a predetermined distance. The power amplifier used at this time is for supplying power to the load, and is divided into a low frequency power amplifier and a high frequency power amplifier. It is important that the power amplifier can supply power to the load efficiently with little distortion. The power amplifier described above is generally operated in a saturation region having non-linear characteristics to obtain the maximum output. In this case, however, when the multi-carriers are input to the power amplifier, the multi-carriers generate cross-modulation distortion components, and thus the performance of the amplifier is greatly degraded. It is very difficult to remove these intermodulation components using conventional filters, and these intermodulation components act as a kind of noise that greatly affects the call quality. In order to reduce the nonlinear characteristics of the power amplifier, a linearization method using a feedforward is used. However, this feedforward also satisfies the requirements of the domestic PCS (Personal Communication Services) base station power amplifier, but the power amplifier for Group Special Mobile or Global Service for Mobile Communication (GSM), the European standard for digital cellular cordless telephones. The requirements are not met. Therefore, in order to satisfy these requirements, a predistorter is attached in front of the main amplifier to fuse with the existing feedforward method to satisfy the requirements of the power amplifier for GSM. The predistorter is a device that improves the intermodulation signal at the output of the amplifier by generating the intermodulation signal of a reverse phase, and is called a predistorter because it is located in front of the amplifier.

In general, the feedforward linearizer extracts only the intermodulation components from the carrier and intermodulation signals obtained at the output of the power amplifier and combines them in reverse phase to the output of the amplifier to cancel the intermodulation signal, thereby performing a carrier to intermodulation ratio. : It aims to improve C / I). C / I represents the ratio of the power of the carrier wave and the power of the intermodulated signal. The predistorter also distorts the intermodulation signal at the output by distorting the preamplifier in front of the main amplifier to produce distortion components in addition to the main signal.

1 is a schematic diagram of a feedforward linearizer circuit having a conventional predistorter, and FIG. 4 shows signal waveforms in respective parts of the circuit.

The operating principle of the feedforward linearizer with the predistorter 120 is as follows.

Path RF _in -A, RF _in -A '

In FIG. 1, when two carriers are applied to the linearizer input RF _in , the carrier is divided by the Wilkinson power divider 110 into the same size as the main path A and the auxiliary path A ′. At this time, the signal waveform at each point A and A 'is as shown in FIG.

2.Path A-B

The carrier of the main path has intermodulation components as shown in FIG. 4 (b) while passing through the predistorter B ″. At this time, the intermodulation signal has a 180 ° phase difference from the carrier wave.

3.Path B``-B

The signal passing through the predistorter 120 (B ``) of the main path passes through the power amplifier 130 (B) and is intermodulated together with the amplification of the carrier as shown in FIG. 4C due to the nonlinear characteristic of the amplifier. The components come together. At this time, the magnitude of the intermodulation signal is smaller than the intermodulation signal passing through the original amplifier due to the predistorter 120.

4. Path A'-B '

In the auxiliary path, the delay time generated when passing through the predistorter 120 and the main power amplifier 130 in the main path A-B is compensated by using the delay line 170 (B '). Delay lines are typically used to compensate for the delay in passing through a device, usually using coaxial cables or microstrip lines.

5. Paths B-D, B-C

In the main path, the output signal of the power amplifier 130 is transmitted through the directional coupler 140 to the delay line of the main path partly without loss (D), and part of the output path of the power amplifier 130 by the variable attenuator 145. A certain amount of attenuation is input to the Wilkinson power combiner 200 of the auxiliary path. At this time, the signal waveform input to the Wilkinson power combiner 200 is as shown in FIG.

6. Path B'-C '

The signal passing through the delay line 170 in the auxiliary path is the same as the carrier component inputted by the variable attenuator 180 and the phase converter 190 to the Wilkinson power combiner 200 in the main path, and the phase is 180 ° different. Let me go. Therefore, the signal input to the Wilkinson power combiner 200 from the auxiliary mirror is as shown in FIG.

7. Path C / C'-D '

When signals input to the Wilkinson power combiner 200 from the main path and the auxiliary path are combined, the carrier signal is removed as shown in FIG. 4 (f) and only the intermodulation signal remains.

8. Path D'-E '

Since the signal having only the intermodulation component from the Wilkinson coupler 200 of the auxiliary path is relatively smaller than the intermodulation signal of the main path, the signal is amplified as shown in FIG. 4 (g) using the error amplifier 210.

9. Path D-E

The output signal of the high power amplifier (D) having passed through the directional coupler 140 in the main path uses the delay line 150 to compensate for the delay time generated by the error amplifier 210 in the auxiliary path and thus the directional coupler 160. Is entered. At this time, the signal waveform does not change as shown in FIG.

10. Path E'-F

The signal passing through the error amplifier 210 in the auxiliary path is equal in magnitude to the signal input to the directional coupler 160 in the main path using the variable attenuator 220 and the phase shifter 230 so that the phase is 180 ° out of phase. To combine. Therefore, the signal input to the directional coupler 160 in the auxiliary path is as shown in Figure 4 (g).

11.Path E / F-RF _out

When signals input to the directional coupler 160 from the main path and the auxiliary path are combined, the intermodulation signal is removed as shown in FIG. 4 (h), and only the input carrier is amplified.

The feedforward linearizer having the conventional predistorter 120 has a disadvantage that the IMD characteristic improvement effect is good but an additional predistorter is required.

It is an object of the present invention to maximize the improvement of intermodulation signals by combining error feedback techniques in feedforward linearizers without additional bulky circuitry.

Another object of the present invention is to provide a feedforward linearizer suitable for a wireless communication system having broadband characteristics.

Still another object of the present invention is to satisfy overseas requirements even when applied to foreign wireless communication systems.

It is another object of the present invention to provide a feedforward linearizer for linearizing the characteristics of a high output power amplifier in a wireless communication system.

In order to achieve these objects, the linearizer of the present invention provides a technique for maximizing the amount of intermodulation improvement that is limited by the conventional feedforward method. By applying the intermodulation component that passed through the error amplifier in the conventional feed forward method to the input and output of the main amplifier at the same time, the intermodulation component of the main amplifier output is extremely suppressed, and the amount of improvement in the conventional circuit is far exceeded.

1 is a block diagram of a feedforward linear power amplifier having a predistorter according to the prior art.

2 is a block diagram of a linear power amplifier using error feedback in accordance with the present invention.

3 is a circuit diagram of a feedforward linear power amplifier using error feedback in accordance with the present invention.

4 is a signal waveform diagram of each portion of each of the linear power amplifier circuits of FIGS.

<Brief description of the main parts of the drawing>

110,310,510,620: Wilkinson power divider 120: predistorter

130,330,530: main power amplifier

140,160,320,340,380,520,540,560,600: Directional Coupler

150,170,370,550,590: delay line

145,180,220,350,400,570,630,650: Variable Attenuator

190,230,360,410,580,640,660: variable phase converter

200: Wilkinson power combiner 210,390,610: error amplifier

In the linear power amplifier using the error feedback according to the present invention, a power splitter for inputting two carriers and distributing them equally to the main path and the auxiliary path, and a power carrier distributed by the power divider A primary amplifier for outputting intermodulated and distorted signals together with amplification of a carrier wave, a first directional coupler for transferring a portion of the main amplifier output signal to an error loop without loss in a main path, and a power carrier distributed by the power divider A first variable attenuator for input and attenuation through the auxiliary path, and a phase of an output signal of the first variable attenuator on the auxiliary path to be 180 degrees out of phase with a phase of the carrier signal input to the first directional coupler on the main path A first variable phase shifter for a carrier signal that is 180 ° phase-converted by the first variable phase shifter A delay line for compensating a delay time corresponding to an operation time of the main amplifier on the main path, and combining a portion of an output signal of the delay line and an output signal of the first directional coupler with a 90 ° phase difference to generate a carrier signal. A second directional coupler for removing and leaving only the intermodulated signal, an error amplifier for inputting and amplifying the intermodulated signal input from the second directional coupler, a second for attenuating the intermodulated signal amplified by the error amplifier The power divider uses a variable attenuator, a second variable phase converter for inputting a mixed modulated signal attenuated from the second variable attenuator so that a 180 ° phase difference occurs, and a mixed modulated signal having a 180 ° phase difference through the second variable phase converter. And a third directional coupler for inputting to the main amplifier by combining with the output signal of the main path side of the main amplifier. Achieved.

The error feedback method is a method of improving the intermodulation signal by extracting only the intermodulation signal from the output of the amplifier and applying the intermodulation signal to the input terminal of the amplifier.

According to the present invention, when the output signal of the third directional coupler is input to the main amplifier, the main amplifier removes intermodulation components and amplifies and outputs only a carrier wave. The power divider includes Wilkinson power. It is characterized by the use of distributors.

The gain and magnitude of the combined signal when combining the first and second directional couplers are equal to the gain and magnitude of the main amplifier so that an additional attenuation means such as a variable attenuator is not required even if the input signal changes. It is characteristic.

In addition, the feedforward linear power amplifier using the error feedback according to the present invention includes: a first power splitter for inputting two carriers and distributing them equally to the main path and the auxiliary path, and to the first power splitter. A main amplifier for inputting the power carriers distributed by the carrier and outputting the intermodulated distorted signal together with the amplification of the carrier; a first directional coupler for transferring a part of the main amplifier output signal to the error loop without loss in the main path; A first variable attenuator for inputting and attenuating power carriers distributed by a power divider through an auxiliary path, and a carrier signal inputting a phase of an output signal of the first variable attenuator on an auxiliary path to the first directional coupler on a main path A first variable phase converter for converting the phase to be 180 degrees out of phase, by the first variable phase converter A first delay line for compensating a delay time corresponding to an operation time of a main amplifier on the main path with respect to a 180 ° phase-converted carrier signal, a part of an output signal of the first directional coupler having a predetermined coupling degree, and A second directional coupler for coupling the output signal of the first delay line to remove the carrier signal and leaving only the intermodulated signal, an error amplifier for inputting and amplifying the intermodulated signal input from the second directional coupler, the error amplifier A second power divider for distributing the intermodulated signal amplified by the third variable, a third variable attenuator for inputting and attenuating a portion of the intermodulated signal distributed by the second power divider, attenuated by the third variable attenuator A third phase shifter for shifting the phase of the intermodulation signal by 180 °, the output signal of the third phase shifter and the second edge shifter; A fourth directional coupler for coupling the output signal of the line to remove the intermodulation component and outputting only the amplified carrier component, a second variable attenuator for attenuating the intermodulated signal amplified by the error amplifier, and the second variable attenuator A second variable phase converter for inputting an attenuated mixed modulated signal from the second variable phase converter and a mixed modulated signal having a 180 ° phase difference through the second variable phase converter to output the main path side output signal of the first power divider And a third directional coupler for coupling to the main amplifier.

In this case, the main amplifier inputting the output signal of the third directional coupler removes the intermodulation signal and amplifies only the carrier wave, and the amplified signal is output from the third variable phase converter by the fourth directional coupler. Merged with the intermodulation component of the phase, the intermodulation component is completely removed.

The Wilkinson power divider is used as the first and second power dividers.

In addition, the gain and magnitude of the combined signal when combining the first and second directional couplers are equal to the gain and magnitude of the main amplifier so that an additional attenuation means such as a variable attenuator is not required even if the input signal changes. Is characteristic.

Hereinafter, the operation principle of the present invention will be described in detail with reference to the accompanying drawings. First, an embodiment of an error feedback linearizer according to the present invention will be described.

The error feedback linearizer of the present invention improves on the problems posed by the conventional feedback scheme. The main drawback of the conventional feedback method is the attenuation of the main signal. This error feedback scheme improves this problem. The amount of improvement in intermodulation signals is also superior to that of conventional feedback.

FIG. 2 is a circuit diagram of an error feedback type linearizer according to the present invention, and FIG. 4 is a signal waveform of each part of the circuit.

The operation of the error feedback type linearizer according to the present embodiment will be described as follows.

1) Path RFin -A, RFin -A '

In FIG. 3, when two carriers are applied to the input of the linearizer (RFin), the carrier is divided by the Wilkinson power divider 310 into the same size as the main path (A) and the auxiliary path (A '). At this time, the signal waveform at each point A and A 'is as shown in FIG.

2) Path A-B

As the carrier of the main path passes through the main power amplifier 330 (B), intermodulation components are generated together with the amplification of the carrier as shown in FIG. 4 (c) (intermodulation component-dotted line) due to the nonlinear characteristics of the amplifier. .

3) Path A'-B '

In the auxiliary path, the variable attenuator 350 and the variable phase shifter 360 have a 180 ° phase difference as shown in FIG.

4) Paths B-D, B-C

In the main path, the output signal of the main power amplifier 330 is passed through the directional coupler 340 in part without loss to the error loop (D), and part of the directional coupler 340 with a phase difference of 90 °. Is entered. At this time, the signal waveform input to the directional coupler 340 is as shown in FIG.

5) Path B'-C '

In the auxiliary path, a delay line 370 is used to compensate the operation time of the main power amplifier of the main path by using a delay line 370 in which the phase difference between the carrier component inputted to the directional coupler 380 and the phase is 180 °. The signal input to the directional coupler 380 is as shown in FIG.

6) Path C / C'-D '

When signals input to the directional coupler 380 from the main path and the auxiliary path are combined, the carrier signal is removed and only the intermodulation signal remains, as shown in FIG. 4 (f), and the intermodulation signal is amplified by the error amplifier 390. ..

7) Path D'-E '

The signal having only the amplified intermodulation component of the auxiliary path is fed back with a 180 ° phase difference through the variable attenuator 400 and the variable phase shifter 410 and applied to the input terminal of the main amplifier 330 as shown in FIG. do.

8) Path E` / A-A

The carrier wave and the fed back error signal in the main path are combined by the directional coupler 320 at the input terminal of the main amplifier 330 as shown in FIG. 4 (b).

9) Path A'-D-RFout

When a signal as shown in FIG. 4 (b) is applied to the main amplifier 330, the intermodulation component is removed from the output of the main amplifier 330 as shown in FIG.

Now, the operation of the feedforward linearizer using the error feedback technique according to the present invention will be described separately by path. In this example, intermodulation components are extremely removed without additional circuitry such as a predistorter.

FIG. 3 shows a circuit diagram of a feedforward linearizer using an error feedback technique according to the present invention, and FIG. 4 shows signal waveforms in each part of the circuit.

The operation principle of the feedforward linearizer using the error feedback technique is as follows.

1) Path RFin -A, RFin-A '

In FIG. 5, when two carriers are applied to the input of the linearizer (RFin), the carrier is divided by the Wilkinson power divider 510 into the same size as the main path A and the auxiliary path A '. At this time, the signal waveform at each point A and A 'is as shown in FIG.

2) Path A-B

The carrier of the main path passes through the main power amplifier 530 (B) and due to the nonlinear characteristic of the power amplifier, intermodulation components are generated together with the amplification of the carrier as shown in FIG. 4C (intermodulation component-dotted line). do.

3) Path A'-B '

In the auxiliary path, the variable attenuator 570 and the variable phase shifter 580 have a 180 ° phase difference as shown in FIG.

4) Paths B-D, B-C

In the main path, the output signal of the main power amplifier 530 is transmitted without attenuation through the directional coupler 540 and a part thereof is input to the directional coupler 600 of the auxiliary path with the coupling degree of the coupler. At this time, the signal waveform input to the directional coupler 600 is as shown in Figure 4 (d).

5) Path B'-C '

The signal passing through the variable attenuator 570 and the variable phase shifter 580 in the auxiliary path is compensated for the operation time of the main power amplifier 530 using the delay line 590 to the directional coupler 600 of FIG. ) Is applied.

6) Path C / C'-D '

When the signals inputted to the directional coupler 600 from the main path and the auxiliary path are combined, the carrier signal is removed and only the intermodulation signal remains and amplified by the error amplifier 610 as shown in FIG.

7) Path D-E

The signal passing through the directional coupler 540 in the main path passes through the delay line 550 to compensate for the operation time of the error amplifier 610.

8) Path D'-E '

In the auxiliary path, the amplified intermodulation signal is divided by the Wilkinson power combiner 620, and the signal is divided by the variable attenuator 630 and the variable phase converter 640 as shown in FIG.

9) Path E / E'-RFout

The signal passing through the error amplifier 610 in the auxiliary path is equal in magnitude to the intermodulation component of the signal applied to the directional coupler 560 in the main path using the variable attenuator 630 and the phase shifter 640, and the phase is 180. Only the components of the amplified carrier combined by the difference are left.

10) Path D``-E``-F``

The signal having only the amplified intermodulation component of the auxiliary path is fed back with a 180 ° phase difference through the variable attenuator 650 and the variable phase shifter 660 to the input terminal of the main power amplifier 530 as shown in FIG. Is approved.

11) Path A ''-B-D-E-RFout

When a signal as shown in FIG. 4 (b) is applied to the main power amplifier 530, the intermodulation component is removed from the output of the main power amplifier 530 as shown in FIG. The signal from which the intermodulation component has been removed and is then removed is combined with the reverse phase intermodulation component at the directional coupler 560 at the output to completely remove the intermodulation component.

According to the present invention, unlike the feedforward linearizer having a predistorter in order to have a better performance in the feedforward method of a high output power amplifier used in a wireless communication system, that is, to obtain a low intermodulation distortion, an error feedback method is used as a feedforward method. Can be combined to achieve the best IMD improvement.

The linearizer of the present invention provides a method of reducing the neighbor channel interference by the horn modulation distortion characteristic in which the influence of adjacent channel interference due to intermodulation distortion of the transmission system in the wireless communication system greatly affects the capacity of the entire wireless communication system. You can increase capacity as much as possible and improve call quality. It can also meet the IMD requirements of any system.

The increase in power of the satellite repeater can additionally reduce the size of the earth station antenna.If the satellite repeater and earth station amplifier are replaced for low power, the amplifier and voltage supply can be made smaller, lighter, low DC power consumption, increased reliability, It has many advantages such as low cost.

In addition, it can be used not only for PCS base station and GSM base station but also for future IMT-2000 through the improvement of the maximum intermodulation distortion level.

Claims (11)

A power splitter for inputting two carriers and distributing them equally in the primary path and the secondary path; A main amplifier for inputting a power carrier distributed by the power divider and outputting a cross-modulated and distorted signal together with amplifying a carrier; A first directional coupler for transferring a part of the main amplifier output signal in the main path to the error loop without loss; A first variable attenuator configured to input and attenuate power carriers distributed by the power divider through an auxiliary path; A first variable phase converter for converting a phase of an output signal of the first variable attenuator on the auxiliary path to be 180 degrees different from a phase of a carrier signal input to the first directional coupler on the main path; A delay line for compensating a delay time corresponding to an operation time of a main amplifier on the main path with respect to a carrier signal 180 ° phase-converted by the first variable phase converter; A second directional coupler for combining the output signal of the delay line and a part of the output signal of the first directional coupler with a 90 ° phase difference to remove the carrier signal and leave only the intermodulation signal; An error amplifier for inputting and amplifying the intermodulation signal input from the second directional coupler; A second variable attenuator for attenuating the intermodulated signal amplified by the error amplifier; A second variable phase converter for inputting the intermodulated signal attenuated from the second variable attenuator to cause a 180 ° phase difference; And And a third directional coupler for combining a mixed modulated signal having a 180 ° phase difference through the second variable phase converter with a main path side output signal of the power divider and inputting the mixed signal to the main amplifier. Power amplifier. The linear power amplifier according to claim 1, wherein when the output signal of the third directional coupler is input to the main amplifier, the main amplifier removes intermodulation components and amplifies and outputs only a carrier wave. The linear power amplifier of claim 1 or 2, wherein the power divider is a Wilkinson power divider. 4. The method of claim 3, wherein the gain and magnitude of the signal obtained by combining the two signals combined when the first and second directional couplers are combined is equal to the gain and magnitude of the main amplifier so that no additional attenuation means is required even if the input signal changes. Linear power amplifier using error feedback. 5. A linear power amplifier using error feedback as claimed in claim 4 wherein said additional attenuation means is a variable attenuator. A first power splitter for inputting two carriers and distributing them equally to the primary path and the secondary path; A main amplifier for inputting a power carrier distributed by the first power divider and outputting an intermodulated and distorted signal together with amplifying a carrier; A first directional coupler for transferring a part of the main amplifier output signal in the main path to the error loop without loss; A first variable attenuator for inputting and attenuating power carriers distributed by the first power divider through an auxiliary path; A first variable phase converter for converting a phase of an output signal of the first variable attenuator on the auxiliary path to be 180 degrees different from a phase of a carrier signal input to the first directional coupler on the main path; A first delay line for compensating a delay time corresponding to an operation time of a main amplifier on the main path with respect to a carrier signal 180 ° phase-converted by the first variable phase converter; A second directional coupler for coupling a portion of the output signal of the first directional coupler with a predetermined degree of coupling to remove the carrier signal and leaving only the intermodulation signal; An error amplifier for inputting and amplifying the intermodulation signal input from the second directional coupler; A second power divider for distributing the intermodulated signal amplified by the error amplifier; A third variable attenuator for inputting and attenuating a portion of the intermodulation signal distributed by the third power divider; A third phase shifter for shifting the phase of the intermodulated signal attenuated by the third variable attenuator 180 degrees; A fourth directional coupler for combining the output signal of the third phase shifter and the output signal of the second delay line to remove intermodulation components and to output only amplified carrier components; A second variable attenuator for attenuating the intermodulated signal amplified by the error amplifier; A second variable phase converter for inputting the intermodulated signal attenuated from the second variable attenuator to cause a 180 ° phase difference; And And a third directional coupler for coupling a mixed modulated signal having a 180 ° phase difference through the second variable phase converter with a main path side output signal of the first power divider to be input to the main amplifier. Feedforward linear power amplifier. 7. The feedforward linear power amplifier using error feedback according to claim 6, wherein the output signal of the second variable phase converter and the output signal of the second delay line are equal in magnitude and 180 degrees out of phase. 8. The apparatus of claim 6 or 7, wherein the main amplifier inputting the output signal of the third directional coupler removes the intermodulation signal and amplifies only the carrier wave and outputs the amplified signal by the fourth directional coupler. A feedforward linear power amplifier using error feedback, characterized in that the intermodulation component is summed up with the intermodulation component of the reverse phase output from the third variable phase converter. 10. The feedforward linear power amplifier of claim 8 wherein the first and second power dividers are Wilkinson power dividers. 10. The method of claim 9, wherein the gain and magnitude of the signal obtained by combining the two signals combined when the first and second directional couplers are combined is equal to the gain and magnitude of the main amplifier so that no additional attenuation means is required even if the input signal changes. A feedforward linear power amplifier using error feedback. 11. The feedforward linear power amplifier according to claim 10, wherein the additional attenuation means is a variable attenuator.