KR20020077974A - A small-sized predistortion linearizer using diode mixer for improving intermodulation distortion of broadband power amplifier - Google Patents

Abstract

PURPOSE: A compact predistortion linearizer by using a dynamic mixer for improving a modulation performance of a broadband power amplifier is provided to reduce a DC power loss and improve a change of modulation characteristics during a long time operation by employing a dynamic mixer as a modulation generator. CONSTITUTION: A compact predistortion linearizer by using a dynamic mixer for improving a modulation performance of a broadband power amplifier includes a first 90 degree hybrid coupler(210) for dividing a pair of carrier waves into a linear path and a nonlinear path, a variable phase shifter(220) for compensating a phase difference generated in the nonlinear path, a delay line(230) for compensating a delay time generated in the nonlinear path by inputting an output signal of the variable phase shifter(220), a mixer(260) for generating a modulation signal, an isolator(250) for preventing the modulation signal generated from the mixer(260) from entering back to the linear path, a variable attenuator(270) for modulating the size of the main signal and the modulation signal and a second 90 degree hybrid coupler for coupling the signal of the linear path through the delay line(230) with the signal of the nonlinear line through the variable attenuator(270). The predistortion linearizer employs a predistortion method having a predistorter composed of an inner carrier wave provided with the linear path and the nonlinear path for inputting a pair of carrier waves and an RF power amplifier(280) for outputting the carrier wave by removing the modulation signal generated by inputting the signal processed by the predistorter.

Description

A small-sized predistortion linearizer using diode mixer for improving intermodulation distortion of broadband power amplifier

The present invention provides a small pre-improvement method using a diode mixer to improve intermodulation components having characteristics opposite to those of power amplifiers to remove inter-modulation distortion (IMD) components generated during signal amplification of a broadband power amplifier. It relates to a distortion linearization technique.

High power amplifiers, which are used for wired and wireless communications and are essential for mobile and satellite communications, operate in a saturation region with nonlinear characteristics to produce maximum output. However, when the high power amplifier operates near the saturation region, the performance and performance of the amplifier are greatly degraded because the magnitude and phase of the output signal are distorted due to the nonlinear characteristics, thereby generating inter-modulation distortion components. Therefore, there is a problem in that the level of the input signal must be operated by several dB back-off or changed into a transistor having a large power capacity. In addition, inter-modulation components are very difficult to remove using a filter, which acts as a noise source of the entire system, causing a drop in transmission quality.

As a representative method for reducing such intermodulation components, a linearization technique using a feedforward method, a predistortion and a feedback method is widely used. However, in recent years, due to the demand for multi-carrier signal amplification at home and abroad, the cross-modulation of the power amplifier for base stations has become strict, so the dual-loop feedforward or feedforward combined with the feedforward method is combined. To achieve this performance.

FIG. 1 is a diagram illustrating a predistortion system, and FIG. 2 is a graph illustrating characteristics appearing in each section of FIG. 1. The theoretical operation of the predistortion system is as follows.

Path A-B:

The predistorter 10 makes the predistortion function β (V _i ) with respect to the input RF signal to be exactly opposite to the distortion component F (α) generated by the RF amplifier 20. The graph of β (V _i ) is shown in FIG. 2A.

Path B-C:

Characteristics in the RF amplifier 20 are as shown in the graph shown in FIG. 2B. From this, it can be seen that it has the characteristics exactly opposite to 2a.

Path C-RF _out :

When the opposite characteristics of the predistorter 10 and the RF amplifier 20 are combined at the RF output, the distortion component is compensated for, resulting in a linear representation of the input signal to the output signal. The results are shown in Figure 2c.

3 is a circuit diagram of a general predistortion linearizer, and FIG. 4 is a signal waveform diagram of each part of the circuit of FIG. 3. The operation principle of a general predistortion linearizer is as follows.

Route A-B, A-C:

In FIG. 3, when two carriers are applied to the predistorter at the input terminal RF _in , the carrier is divided into a linear path B and a nonlinear path C by a power divider 110. At this time, the signal waveform of the point A is as shown in Fig. 2 (a) and the signal waveforms of the points B and C is the signal as shown in Fig. 2 (a).

Path B-B ':

The linear path uses a phase shifter 120 and a delay line 130 to form an inter-modulation generator 150 and a variable atttenuator in a nonlinear path. To compensate more accurately the delay time generated by the 160 and the phase shifter 170. At this time, the signal waveform does not change as shown in FIG.

Path C-C ':

The signal passing through the power divider 110 in the nonlinear path generates the intermodulation component to be input to the RF amplifier 180 by the intermodulation generator 150 and adjusts the variable attenuator 160 and the phase shifter 170. By adjusting the components and amplitude and phase of the linear path by 180 ° difference to be combined with the linear path. At this time, the signal waveform is as shown in FIG.

Path B '/ C'-D:

When the signals in the linear path and the non-linear path are combined by the power combiner 140, the RF amplifier 180 generates an inter-modulated signal in which the main signal and the phase are inverted by 180 ° as shown in FIG. 2 (c). Enter the input of.

Path D-E:

The signal generated by the combination of the linear path and the nonlinear path as shown in FIG. 2 (c) enters the input of the RF amplifier 180 and is reversed from the intermodulation signal generated by the RF amplifier 180, thereby eliminating only the pure carrier signal. Comes out. At this time, the signal is as shown in FIG.

Such a conventional predistortion linearizer has an IMD characteristic improvement effect, but is generally bulky by the power distribution / combiner 110, 140 and 180 ° phase converters 120, 170, and the intermodulation generator 150. ) Consumes a lot of DC power, reducing the overall efficiency of the linearizer. In addition, long-term operation causes a change in the IMD characteristics, reducing the overall performance of the linearizer.

In addition, conventionally, a diode or RF amplifier is mainly used as the intermodulation generator 150, and DC power consumption is high. When using a mixer, there is an inconvenience in applying a signal to the LO port.

An object of the present invention is to provide a predistortion linear power amplifier that can reduce the DC power loss by using a diode mixer as a intermodulation generator, and can improve the problems caused by intermodulation characteristics changes occurring during long time operation.

Another object of the present invention is to improve the performance in a wide bandwidth by setting up a wide bandwidth intermodulation generator terminated by 50 kHz when using an existing intermodulation generator as a mixer.

Another object of the present invention is to use a 90 ° hybrid coupler in the distribution and combination of the linear and non-linear path, and to isolate the problem of isolation between the linear and non-linear paths when using the 90 ° hybrid coupler in the non-linear path isolator (Isolator And to provide a small predistorter linearizer with good intermodulation performance over broadband.

Another object of the present invention is to insert a linearizer at the front of the power amplifier to accurately compensate for the distortion characteristics of the main amplifier.

Another object of the present invention is to input a distortion component having a characteristic opposite to that generated in the power amplifier in advance, and to cancel the intermodulation signal generated in the power amplifier, so that the carrier to inter-modulation ratio of the amplifier To reduce the size of the entire linearizer by improving the C / I) and enabling the compact insertion of the predistorter into the high output amplifier.

Other objects and advantages of the present invention will become more apparent from the following detailed description of the invention and the accompanying drawings.

1 is a block diagram of a predistortion system.

2 is a characteristic curve of each section of FIG.

3 is a block diagram of a general predistortion linearizer.

4 is a signal waveform diagram of each part of FIG. 3;

5 is a block diagram of a small predistortion linearizer using a mixer according to the present invention.

6 is a signal waveform diagram of each part of FIG. 5;

<Brief description of the main parts of the drawings>

10: predistorter 20,180,280: RF power amplifier

100,200: predistortion linear power amplifier 110: power divider

120,170: phase shifter 130,230: delay line

140: power combiner 150: intermodulation generator

160,270: variable attenuator 210,240: hybrid coupler

220: variable phase shifter 250: isolator

260: mixer

<Example>

A preferred embodiment of the predistortion linear broadband power amplifier according to the present invention is a predistortor which inputs two carriers and whose carrier transmission path is composed of a linear path and a nonlinear path and processed by the predistorter. It is provided with an RF power amplifier for inputting the signal to remove the intermodulation signal generated by the RF power amplifier to amplify and output only the pure carrier.

The predistorter is a linearizer coupled to the front end of the RF power amplifier to linearize the RF power amplifier, and includes a first 90 ° hybrid coupler and a linear path for dividing the input two carriers into a linear path and a nonlinear path. A variable phase shifter that compensates for a phase difference occurring in a nonlinear path by inputting a carrier divided by the first 90 ° hybrid coupler, and an output signal of the variable phase shifter to compensate for a delay time that occurs in a nonlinear path Isolators for inputting carriers divided by the first 90 ° hybrid coupler in delay lines, mixers and nonlinear paths to generate intermodulation signals, and for preventing intermodulation signals generated in the mixers from being reinjected into the linear paths. ), Input the intermodulation signal generated by the mixer and the main signal It comprises a variable attenuator and a 2 90 ° hybrid coupler for coupling the non-linear path through the side signal path side linear signal and the variable attenuator via the delay line for adjusting the size of the modulation signal components.

In this embodiment, it is desirable to couple a resistor of a predetermined magnitude to the LO signal input terminal of the mixer to compensate for the power amplifier characteristics in the nonlinear path.

In addition, the predetermined magnitude of resistance is preferably 50 kΩ.

The signal waveform of the linear path and the nonlinear path has a phase difference of 90 ° by the first 90 ° hybrid coupler, and the intermodulation signal input to the RF amplifier is a signal whose phase is inverted by 180 °.

At this time, the mixer is a diode mixer, it is preferable to use a high output power amplifier as the RF power amplifier.

In addition, the predistorter is preferably mounted on a feedforward linear device, and the predistorter is an IMT-2000 satellite communication base station, an IMT-2000 repeater, a PCS mobile communication base station, a PCS repeater, a GSM mobile communication base station, a GSM repeater, or a ground. Increase the channel capacity of wireless communication systems including microwave radio systems, mobile communication base stations for cellular phones and repeaters for cellular phones.

Preferably, the linearizer inputs a distortion component having characteristics opposite to those generated in the RF power amplifier, and the linearizer is inserted into the RF power amplifier.

Hereinafter, the configuration and operation principle of the present invention will be described in detail with reference to the accompanying drawings. FIG. 5 is a circuit diagram of a predistortion linearizer using a mixer according to the present invention, and FIG. 6 is a signal waveform diagram of each part of FIG. 5. The operation principle of the linearizer of the predistortion method using the mixer of the present invention is as follows.

Path RF _in -A, RF _in -A ':

In FIG. 5, when two carriers are applied to the input terminal RF _in of the linearizer, the carrier is divided into a linear path A and a nonlinear path A ′ by a 90 ° hybrid coupler 210. At this time, the signal waveform of the points A and A 'becomes a signal as shown in FIG. 6 (a) having a 90 ° difference due to the 90 ° hybrid coupler 210 in phase.

Path A-B:

The linear path is input to the 90 ° hybrid coupler 240 by using the variable phase converter 220 and the delay line 230 to compensate for the phase difference and the delay time that may occur in the nonlinear path. At this time, the signal waveform is as shown in FIG.

Path A'-B ':

As a method of compensating the power amplifier characteristics in the nonlinear path, a mixer 260 that couples 50 kHz to the LO signal input is used. The isolator 250 is used to prevent the intermodulation signal generated by the mixer 260 from being re-injected in a linear path when the 90 ° hybrid coupler 210 is used. At this time, the signal waveform is as shown in FIG.

Path B'-B '':

The variable attenuator 270 in the nonlinear path was used to adjust the magnitude of the main signal and intermodulation component input to the main power amplifier 280. At this time, the signal waveform is as shown in FIG.

Path B / B ''-C:

The signals inputted to the 90 ° hybrid coupler 240 in the linear path and the nonlinear path are combined so that the intermodulated signal 180 ° inverted in phase with the main signal enters the input terminal of the main power amplifier 280. The signal waveform at this time is as shown in FIG.

Path C-D:

The signals generated by the combination of the linear path and the nonlinear path are input to the main power amplifier 280 to remove the intermodulation signal generated by the main power amplifier 280, and only pure carriers are amplified. At this time, the signal is as shown in FIG.

The present invention can be variously modified and can take various forms and only the specific embodiments thereof are described in the detailed description of the invention. It is to be understood, however, that the present invention is not limited to the specific forms mentioned in the detailed description of the invention, but rather includes all modifications, equivalents, and substitutions within the spirit and scope of the invention as defined by the appended claims. It should be understood to do.

The present invention is a small predistortion linearizer using a diode mixer to improve the linearization performance of a high output power amplifier. Using a diode mixer as the intermodulation generator reduces the DC power loss and combines this predistorter with the front end of the power amplifier to be linearized to improve intermodulation performance.

In addition, the length of the delay line in the linear path, which is a disadvantage of the conventional predistortion method, is reduced, and the effect of the change of the intermodulation characteristics in the long time operation is replaced by the mixer. In other words, the linearizer of the present invention is inserted into the front end of the high output power amplifier in small size to improve the intermodulation component, and the predistorter using the diode mixer is maximized by applying the feed mixer to the feed forward method.

In addition, by using 90 ° hybrid coupler for input and output, the variable phase shifter, which occupy a large volume, is eliminated. By reducing the delay line of the linear path, the size of the overall predistorter can be reduced to achieve wideband intermodulation characteristics. .

In addition, when the small predistorter linearizer using the mixer of the present invention is applied together with the high output power amplifier and the feedforward linearizer, the amount of intermodulation improvement can be maximized.

If the linearizer of the present invention is applied to various wireless communication systems such as IMT-2000, which will be commercialized based on the present satellite communication base station and repeater, PCS and GSM mobile communication base station and repeater, terrestrial microwave radio, the channel capacity of the system is increased, It will have many advantages such as DC power consumption, low cost and miniaturization, which will provide many subscribers with high quality service and increased reliability for wireless communication.

Claims (13)

A predistorter for inputting two carriers and having an internal carrier transmission path composed of a linear path and a nonlinear path; And A predistortion linear power amplifier comprising an RF power amplifier which inputs a signal processed by the predistorter, removes intermodulation signals generated therein, and amplifies and outputs only a pure carrier wave. The predistorter is a linearizer coupled to the front end of the RF power amplifier to linearize the RF power amplifier, A first 90 ° hybrid coupler for dividing the input two carriers into a linear path and a nonlinear path; A variable phase shifter configured to compensate the phase difference occurring in the nonlinear path by inputting a carrier divided by the first 90 ° hybrid coupler in a linear path; A delay line configured to input an output signal of the variable phase shifter to compensate a delay time occurring in the nonlinear path; A mixer for generating intermodulation signals; An isolator for inputting a carrier divided by the first 90 [deg.] Hybrid coupler in a nonlinear path and preventing the intermodulation signal generated by the mixer from being reinjected into the linear path; A variable attenuator for inputting the intermodulation signal generated by the mixer to adjust the magnitude of the main signal and the intermodulation signal component; And And a second 90 [deg.] Hybrid coupler for combining the linear path side signal through the delay line and the nonlinear path side signal through the variable attenuator. 2. The predistortion linear broadband power amplifier of claim 1, wherein a predetermined magnitude of resistor is coupled to the LO signal input terminal of the mixer to compensate for power amplifier characteristics in a nonlinear path. 3. The predistortion linear broadband power amplifier of claim 2, wherein the predetermined magnitude of resistance is 50 Hz. The predistortion linear broadband power amplifier of claim 1, wherein the signal waveforms of the linear path and the nonlinear path have a phase difference of 90 ° by the first 90 ° hybrid coupler. The predistortion linear broadband power amplifier of claim 1, wherein the intermodulation signal input to the RF amplifier is a signal in which a phase is inverted by 180 ° from a main signal. The predistortion linear broadband power amplifier of claim 1, wherein the mixer is a diode mixer. 2. The predistortion linear broadband power amplifier of claim 1, wherein the RF power amplifier is a high output power amplifier. 8. A predistortion linear broadband power amplifier as claimed in claim 1 or 7, wherein the predistorter is a feed forward linearizer. The predistortion linear broadband power amplifier of claim 1, wherein the predistorter increases the channel capacity of a wireless communication system. 10. The system of claim 9, wherein the wireless communication system includes an IMT-2000 satellite communication base station, an IMT-2000 repeater, a PCS mobile communication base station, a PCS repeater, a GSM mobile communication base station, a GSM repeater, a terrestrial microwave radio system, and a mobile communication base station for cellular phones. A predistortion linear broadband power amplifier, characterized by a repeater for cellular phones. The predistortion linear broadband power amplifier according to claim 1, wherein the distortion device is previously inputted with a distortion component having a property opposite to that generated by the RF power amplifier. The predistortion linear broadband power amplifier of claim 1, wherein the linearizer is inserted into the RF power amplifier. The predistortion linear broadband power amplifier of claim 1, wherein the linearizer is inserted into a feedforward linearizer.