KR20050079713A - Pre-distortion apparatus of power amplitude - Google Patents

Abstract

The present invention relates to a predistortion device of a power amplifier, comprising: a divider for distributing an input signal into a Q path signal and an I path signal; A Schottky diode is connected to two ports of the 90 ° hybrid coupler and the 90 ° hybrid coupler, respectively, and receives a Q path signal from the divider to change the Q path signal gain and 180 ° of the Q path signal phase. A first reflective intermodulation generator for outputting a first intermodulation signal through a shift within a range; A Schottky diode is connected to two ports of the 90 ° hybrid coupler and the 90 ° hybrid coupler, respectively, and receives an I path signal from the splitter to change the I path signal gain and 180 ° of the I path signal phase. A second reflective intermodulation generator for outputting a second intermodulation signal through a shift within a range; And a combiner that receives the first intermodulation signal and the second intermodulation signal, and combines and outputs the first intermodulation signal. Accordingly, a predistortion apparatus of a power amplifier capable of outputting a predistortion signal having various gain and phase characteristics is provided.

Description

Pre-distortion apparatus of power amplitude

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-distortion apparatus of power amplitude, and more particularly, to a characteristic impedance including a 90 ° hybrid coupler and a Schottky diode having a 90 ° phase shift of a signal input stage. Of the power amplifier which outputs the predistortion signal having various gain and phase characteristics by arranging the reflection type intermodulation generator and the in-phase coupler having a sudden phase shift of 180 ° in a Cartesian vector modulator structure. It relates to a predistortion device.

In a general communication system, a signal may be received at a remote receiving end only by transmitting electromagnetic waves at a high output from an antenna of a transmitting end. The power amplifier is a module that is located at the final stage of the communication system and amplifies the input signal with high power of desired level and transmits it to the antenna. It is mainly manufactured using transistors.

With the development of mobile communication, there is an increasing demand for power amplifiers having high linearity as well as high power amplifiers.

One of the most important characteristics of a power amplifier is inter-modulation distortion (IMD), which requires high-power power amplifiers to operate in the nonlinear region to achieve maximum output, but lowers the input power due to distortion to operate in the linear region. A back-off method is used. This approach requires a large number of transistors, which leads to increased volume, reduced power efficiency, heat dissipation, and the need to supply larger power supplies.

 Complementing the disadvantages of high output power amplifiers is the use of a linearized power amplifier (LPA) using a linearizer. There are many ways to linearize, but the most widely used methods are predistorter and feed-forward.

Predistorter improves intermodulation characteristics by pre-investigating the input / output characteristics of the power amplifier to be linearized and applying the opposite signal to the intermodulation signal to be generated in the power amplifier. The advantage is that it can be implemented as a configuration. On the other hand, the feed-forward method is a method of linearizing by subtracting the intermodulation component generated in the amplifier at the final output stage.

Among the above methods, the predistortion method is widely used as a linearization method which is inexpensive compared to performance and operates at a wider bandwidth. In contrast to the nonlinear distortion characteristics of the power amplifier, such a predistortion method results in an improvement in linearity when the input signal is distorted in advance and provided to the input of the power amplifier.

The nonlinear characteristics of the power amplifier include AM / AM (Amplitude Modulation to Amplitude Modulation) characteristics, which indicate a change in output signal power according to an increase in input signal power, and AM / PM (a change in phase of an output signal according to an increase in input signal power). Amplitude Modulation to Phase Modulation).

AM-AM and AM-PM characteristics of power amplifier are classified into four types as follows.

1) Gain compression and phase lag,

2) gain expansion and phase lag,

3) Gain compression and phase advance,

4) Gain expansion and phase advance.

In order to improve the AM-AM and AM-PM characteristics, a preamplifier of a power amplifier may be used. In the past, various power amplifier predistorters have been proposed to compensate for various gain and phase characteristics.

1 is a block diagram of a conventional reflection type power amplifier predistorter.

Referring to FIG. 1, a predistortion apparatus is provided that provides different gain and phase characteristics through electrically manual tuning.

In the block diagram of the reflective power amplifier predistorter of FIG. 1, the 90 ° hybrid coupler 101 divides the input signal RFin through the signal input terminal 110 into an in-phase component and a phase difference component of 90 °. .

One of the input signals passing through the 90 ° hybrid coupler 101 is applied to the open line line 105, and all the signals applied here reflect the linear components having the phase change amount of the open line line 105, 120). The other of the input signal passing through the 90 ° hybrid coupler 101 is applied to the Schottky diode 102 via the matching circuit 103 and the parallel capacitor 104 to generate a nonlinear component. Most of the power reaching the Schottky diode 102 enters the signal output terminal 120. In this way, the signal reflected by the open line line 105 and the Schottky diode 102 is combined at the 90 ° hybrid coupler 101 and output to the signal output terminal 120.

As such, in the 90 ° hybrid coupler 101, a predistortion signal is obtained through a combination of signals reflected from two ports. Here, the amount of phase change necessary to generate the predistortion signal is obtained by adjusting the length of the open line line 105.

However, the electrical manual tuning method shown in FIG. 1 has a problem in that it shows a certain limit in obtaining a predistortion signal for various gains and phases of a power amplifier. That is, since the nonlinear characteristic of the power amplifier tends to change according to the output power, there is a limit in accurately obtaining the predistortion signal. According to FIG. 1, when the nonlinear characteristic of the power amplifier is changed, the matching circuit 103 correspondingly. There is a problem that must be adjusted.

2 is a block diagram of a conventional Cartesian type power amplifier predistorter.

Referring to FIG. 2, the input signal PDin at the signal input terminal 230 of the Cartesian type power amplifier predistorter has two equal magnitudes in the 90 degree hybrid coupler 201 and has a 90 ° angle. The signals are separated into phase difference signals. The separated signals are input to biased dual-gate FETs 210 and 220, respectively, with nonlinear operation. The signals input to the dual-gate FM 210 and 220 are output to the in-phase combiner 202 and combined. The in-phase combiner 202 combines the input signals and outputs the predistorted output signal PDout to the signal output terminal 240. Non-linearity in the two dual-gate FM 210, 220 can be controlled by adjusting the DC bias (bias B, bias A) of each of the dual-gate FM 210, 220. According to FIG. 2, theoretically, two gain and phase characteristics may be obtained.

However, the conventional Cartesian type power amplifier predistorter shown in FIG. 2 has a problem of providing only two gain and phase characteristics because of the phase shift limitation of the presented arrangement. The limitation of the phase shift here is that the phase shift depends on the element (dual-gate FM) selected in the structure as shown in FIG. If the phase shift is reduced by the characteristics of the selected device, the range for improving the intermodulation signal is reduced.

The present invention has been proposed to solve the above problems, and includes a 90 ° hybrid coupler having a phase shift of 90 ° at a signal input stage and a reflective horn having a sudden phase shift of 180 ° near a characteristic impedance including a Schottky diode. It is an object of the present invention to provide a power amplifier predistortion apparatus in which a modulation generator and an in-phase combiner are arranged in a Cartesian vector modulator structure to output a predistortion signal having various gain and phase characteristics.

In addition, when the predistortion device for the nonlinearity compensation of the power amplifier is implemented, the present invention is a method by the electric manual tuning of the conventional predistortion device according to the nonlinear characteristics of the power amplifier, the amount of phase change according to the selected device This can generate predistortion signals regardless of how they occur. In the predistortion apparatus of the present invention, the bias voltage of the reflective intermodulation generators is adjusted to obtain four different gain and phase characteristics, thereby providing an optimum gain and phase characteristic for nonlinear compensation of a power amplifier. Its purpose is to.

A preferred embodiment of the predistortion device of the power amplifier of the present invention will be described in detail with reference to the accompanying drawings.

The apparatus of the present invention for achieving the above object comprises: a divider for distributing an input signal into a Q path signal and an I path signal; A Schottky diode is connected to two ports of the 90 ° hybrid coupler and the 90 ° hybrid coupler, respectively, and receives a Q path signal from the splitter to change the Q path signal gain and the Q path signal phase. A first reflective intermodulation generator for outputting a first intermodulation signal through a shift within a 180 ° range; A Schottky diode is connected to two ports of the 90 ° hybrid coupler and the 90 ° hybrid coupler, respectively, and receives an I path signal from the splitter to change the I path signal gain and the I path signal phase. A second reflective intermodulation generator for outputting a second intermodulation signal through a shift within a 180 ° range; And a predistorter of the power amplifier including a combiner configured to receive the first intermodulation signal and the second intermodulation signal, and combine and output the first intermodulation signal.

3 is a block diagram of a power amplifier predistortion apparatus using a Cartesian vector modulator structure according to an embodiment of the present invention.

Referring to FIG. 3, the predistortion device according to the embodiment of the present invention includes a signal input terminal 330, a 90 ° hybrid coupler 301, a reflective intermodulation generator 310, 320, and an in-phase coupler 304. And a signal output terminal 340.

In the predistortion linearization device configured as described above, phase shift is performed at the 90 ° hybrid coupler 301 and the reflective intermodulation generator 310 or 320 of the signal input terminal 330.

The hybrid coupler 301 of the signal input terminal 330 provides a phase shift so that the input signal Vin through the signal input terminal 330 is divided into an in-phase component and a phase difference component of 90 °.

In addition, the phase shift is also performed in the reflective intermodulation generators 310 and 320. This will be described.

The reflective intermodulation generator 310 consists of a 90 ° hybrid coupler 303 and a Schottky diode 307, 308. Reflective intermodulation generator 320 also includes a 90 ° hybrid coupler 302 and a Schottky diode 305 and 306.

Equivalent circuits corresponding to each of the Schottky diodes 305, 306, 307, and 308 have a resistance (as shown by reference numeral 350). ) And capacitor ( )

The load impedance of each of the Schottky diodes 307, 308, 305, and 306 is shown in Equation (1).

(One)

The load admittance of each of the Schottky diodes 305, 306, 307, and 308 is given by equation (2).

(2)

The reflection coefficients in the reflective intermodulation generators 310 and 320 are shown in Equation (3).

(3)

From here Is the inverse of the characteristic impedance. The reflection coefficients of Equation (3) are the gains to the reflection coefficients of the reflective intermodulation generators 310 and 320 of Equation (4) and the reflective intermodulation generators 310 and 320 of Equation (5). It can be expressed as the phase of the reflection coefficient of.

(4)

(5)

The phase shift characteristic is calculated through equation (5), which can be expressed as a diode resistance function.

In FIG. 4A, a sudden phase transition of 180 ° is shown to occur around the characteristic impedance. By changing the bias voltage applied to the Schottky diode, the resistance Rd is theoretically changed from infinity ohms (open) to zero ohms (short). According to the reflection coefficient formula of Equation (3), the gain has the largest attenuation at the resistance Rd at 50 ohms (θ), the phase is positive when the phase is greater than 50 ohms (θ), and 50 ohms ( If it is smaller than θ), it has a negative value and shows a phase change amount of 180 ° at 50 ohms. This change effect is used to change the polarity indication of the signal. The polarity selection of the signal causes the output signal of the embodiment of the present invention to appear in all quadrants as shown in Figure 4b. Thus, a preferred embodiment of the present invention may have a 360 ° phase shift without the implementation of complex circuits for phase shift.

The input signal Vin input through the signal input terminal 330 is transmitted to the 90 ° hybrid coupler 301. The signal output through the 90 ° hybrid coupler 301 is expressed as follows.

(6)

(7)

The signal (6) has an amplitude having a 3 dB attenuation in amplitude in the input signal, and the phase is transmitted to the Q path with a phase difference of 90 degrees. On the other hand, the signal (7) has an amplitude having a 3 dB attenuation in the amplitude of the input signal, and the phase is transmitted to the I path in phase.

Here, the 90 ° hybrid coupler 301 serves as a kind of power divider that equally distributes the input power as half power of each of the two outputs, that is, -3 dB coupler. The termination resistor 50θ at the signal input terminal 330 side serves as an isolation. The 90 ° hybrid coupler 301 is also commonly referred to as a 3 dB quadrature coupler or branch line coupler.

As described above, one of the separated input signals goes to the first reflective intermodulation generator 310 of the Q path and the other to the second reflective intermodulation generator 320 of the I path.

The reflection coefficients of the first reflective intermodulation generator 310 and the second reflective intermodulation generator 320 are considered to include nonlinearities of the Schottky diodes 307, 308, 305, and 306. .

In general, when the Schottky diodes 307, 308, 305, and 306 are applied with a constant voltage and input power, the Schottky diodes 307, 308, 306, and 306 operate nonlinearly at some point. Is a diode that is easy to achieve the opposite characteristic. The first bias voltage VQ and the second bias voltage VI biased with respect to each of the first reflective intermodulation generator 310 and the second reflective intermodulation generator 320 have a desired gain and phase characteristic. Is applied to obtain. The applied first bias voltage VQ and the second bias voltage VI are configured to be adjustable.

The output signals from the first reflective intermodulation generator 310 and the second reflective intermodulation generator 320 are diodes 307, 308, ((2) as shown in equations (8) and (9) below. 305, and the reflection coefficient with the nonlinearity of 306.

(8)

(9)

From here, Wow Are the reflection coefficients of the Q path and the I path, respectively.

The output signal in the Q path and the output signal in the I path are combined in an in-phase combiner 304. In the in-phase combiner 304, equation (8) corresponding to the input signal * reflection coefficient of the first intermodulation generator 310 in the Q path and the input signal * reflection of the second intermodulation generator 320 in the I path. The equation (9) corresponding to the coefficient is combined and output to the signal output terminal 340. Here, the predistortion signal is generated when the Q path signal and the I path signal are combined in the in-phase coupler 304.

Here, the 90 ° hybrid coupler 301, the first reflective intermodulation generator 310, the second reflective intermodulation generator 320, and the in-phase combiner 304 are connected in a Cartesian vector modulator structure. You can see that.

By combining the signal of the I path with the signal of the Q path, the output signal Vout output through the output terminal 340 is expressed by Equation (10).

10

Dividing the whole term by the first term on the right side in Eq. (10) yields a normalized predistortion linearizer signal as shown in Eq. (11).

(11)

Equation (11) may be represented in a polar form as in Equation (12).

(12)

(12) It can be represented by. θ is the phase of the Q path relative to the phase of the I path and can be seen as the phase difference of the combined signal at the output of the predistorter. Therefore, the overall signal phase shift can be viewed as the phase difference θ.

The main operation of the analog predistortion device of the embodiment of the present invention is that the phase shift and gain change of 360 ° can be obtained at the signal output terminal 340 through the sum of the signals output through the Q path and the I path.

The operating principle of the embodiment of the present invention is as follows. The 90 ° phase difference current and in-phase current are applied to the Schottky diodes 307, 308, 305, and 306. The 90 ° phase difference current and in-phase current flow through the Schottky diodes 307, 308, 305, and 306 to generate a 90 ° phase difference resistance and in phase resistance. The 90 [deg.] Phase current and in-phase current are each completely separated and each current change is also possible for the desired phase shift value and gain change value. Phase shift provides a first bias voltage VQ and a second bias voltage VI for each of the first reflective intermodulation generator 310 and the second reflective intermodulation generator 320 providing nonlinear gain and phase characteristics. Is controlled by

5A is a diagram illustrating the output vector diagram in FIG. 3 under a fixed input power condition, showing a signal vector combination of a Q path and an I path of an embodiment of the present invention. Here, the signal of the I path is regarded as the reference signal. The gain of the I path is 1 and the phase is 0. The gain of the Q path is r and the phase is θ. Under a fixed output, the gain and phase characteristics according to one embodiment of the present invention for the phase shift of the entire signal can be calculated. In FIG. 5A, using the cosine law, the gain and phase characteristics are calculated by the following equations (13) and (14).

(13)

(14)

The slope of the gain and phase at a particular point can be calculated using the partial derivative because of two variables. Therefore, the gain and phase inclination characteristics are as shown in Eqs. (15) and (16), respectively.

(15)

(16)

Using equations (15) and (16), the gain and phase slope characteristics can be calculated, and the results can be presented for the overall signal phase shift.

FIG. 5B is a graph illustrating gain and phase slope characteristics of FIG. 3 when the Q path signal has a gain of 0.1. FIG. Here, the gain of the Q path signal is fixed at 0.1.

Referring to FIG. 5B, it can be seen that there may be four types of gain and phase characteristics under a fixed input power.

1) Region I with negative gain slope and positive phase slope has the characteristics of gain compression and phase advance.

2) Region II with negative gain slope and negative phase slope has the characteristics of gain compression and phase delay.

3) Region III with positive gain slope and positive phase slope has the characteristics of gain expansion and phase advance.

4) Region IV with positive gain slope and negative phase slope is characterized by gain expansion and phase delay.

FIG. 5C is a graph illustrating gain slope characteristics of FIG. 3 according to gain and phase shift of a normalized Q path signal, and FIG. 5D illustrates phase slope characteristics of FIG. 3 according to gain and phase shift of a normalized Q path signal. It is a graph.

5C and 5D are graphs showing gain slope characteristics and phase slope characteristics of a normalized Q path signal, and show that the gain and phase characteristics may be respectively present in all quadrants.

6A is a graph of gain compression and phase delay characteristics measured under certain conditions in FIG. 3, FIG. 6B is a graph of gain expansion and phase delay characteristics measured under certain conditions in FIG. 3, and FIG. A graph of gain compression and phase advance characteristics measured under conditions, FIG. 6D is a graph of gain extension and phase advance characteristics measured under certain conditions in FIG. 3.

Referring to FIG. 3, the first bias voltage VQ and the second bias voltage VI are bias voltages applied to each of the first reflective intermodulation generator 310 and the second reflective intermodulation generator 320. Indicates.

6A illustrates gain compression and phase delay characteristics measured according to an embodiment of the present invention under test conditions of first bias voltage (VQ) = 307.9 mV and second bias voltage (VI) = 0.0 mV.

These gain and phase characteristics are suitable for power amplifiers with gain expansion and phase advance characteristics at large output back-offs, such as class AB and class B power amplifiers.

FIG. 6B illustrates gain expansion and phase delay characteristics measured according to an embodiment of the present invention under test conditions of first bias voltage VQ = 450.6 mV and second bias voltage VI = 297.6 mV.

This gain and phase characteristic is well suited for power amplifiers with gain compression and phase advance characteristics near low output back-off or P1dB.

FIG. 6C illustrates the gain compression and phase advance characteristics measured according to an embodiment of the present invention under test conditions of first bias voltage VQ = 0.0 mV and second bias voltage VI = 326.8 mV.

These gain and phase characteristics are suitable for power amplifiers with gain expansion and phase delay characteristics at large output back-offs, such as class AB and class B power amplifiers.

FIG. 6D illustrates the gain expansion and phase advance characteristics measured according to an embodiment of the present invention under test conditions of first bias voltage VQ = 323.7 mV and second bias voltage VI = 450.1 mV.

This gain and phase characteristic is well suited for power amplifiers with gain compression and phase delay characteristics near low output back-off or P1dB.

6A to 6D, the gain and phase characteristics measured in four forms can be obtained by adjusting two bias voltages as in the gain and phase characteristics calculated at a fixed input power as shown in FIG. 5B. It can be seen that.

Furthermore, if the predistorter of the power amplifier of the present invention is configured by adding the feed-forward power amplifier, the linearity may be better than that of the conventional feed-forward power amplifier used in the mobile communication repeater or the base station.

The analog predistortion linearization device of the present invention is not limited to the above-described embodiments, and may be variously modified and implemented within the range permitted by the technical idea of the present invention.

As described above, the present invention relates to a predistortion device of a power amplifier, and has the following effects.

First, the predistorter of the power amplifier is obtained by combining the nonlinear components generated by the intermodulation generator with the 180 ° phase shift of the input hybrid coupler and the sudden phase shift of 180 ° using the Schottky diode in the in-phase coupler. There are effects of obtaining four different gain and phase characteristics by using the 360 ° phase shift characteristic.

Second, according to the predistortion device of the power amplifier of the present invention, since it is applicable to the nonlinear characteristics of various power amplifiers, it is possible to replace the predistortion device that can be used only for a specific power amplifier like the conventional power amplifier predistortion device. There is.

Third, the predistorter of the power amplifier can be widely used in a situation where a simpler and smaller communication system and a reduction in manufacturing cost are required.

Fourth, the pre-distortion device of the power amplifier improves the nonlinear characteristics of the power amplifier to minimize the influence of adjacent channels, thereby improving the call quality of the mobile communication system and increasing the subscriber capacity.

Furthermore, when the predistortion device of the power amplifier of the present invention is configured by adding the feed-forward power amplifier, it is possible to obtain better linearity than the conventional feed-forward power amplifier used in a mobile communication repeater or a base station.

1 is a block diagram of a conventional reflection type power amplifier predistorter;

2 is a block diagram of a conventional Cartesian type power amplifier predistorter;

3 is a block diagram of a power amplifier predistortion apparatus using a Cartesian vector modulator structure according to an embodiment of the present invention;

4A is a graph showing a phase shift characteristic according to Schottky diode resistance displacement of the reflective intermodulation generator in FIG. 3, and FIG. 4B is a diagram showing that the output signal diagram in FIG. 3 exists in all quadrants.

FIG. 5A is a diagram illustrating the output signal diagram of FIG. 3 under a fixed input power condition. FIG. 5B is a graph illustrating slope and gain characteristics of the gain and phase of FIG. 3 when the gain of the Q path is 0.1. FIG. 5C is a normalized Q path. 3 is a graph illustrating gain slope characteristics of FIG. 3 according to gain and phase shift of a signal, and FIG. 5D is a graph illustrating phase slope characteristics of FIG. 3 according to gain and phase shift of a normalized Q path signal,

6A is a graph of gain compression and phase delay characteristics measured under certain conditions in FIG. 3, FIG. 6B is a graph of gain expansion and phase delay characteristics measured under certain conditions in FIG. 3, and FIG. A graph of gain compression and phase advance characteristics measured under conditions, FIG. 6D is a graph of gain extension and phase advance characteristics measured under certain conditions in FIG. 3.

<Explanation of symbols for the main parts of the drawings>

101, 201, 301, 302, 303: 90 ° Hybrid coupler,

102, 305, 306, 307, 308: Schottky diode,

103: matching circuit,

104: parallel capacitor,

105: open-circuited line,

202, 304: In-phase combiner,

210, 220: dual-gate FET,

310: first reflection IM generator,

320: second reflection IM generator,

110, 230, 330: signal input terminal,

120, 240, 340: signal output stage,

350: equivalent circuit of a Schottky diode.

Claims (7)

A divider for distributing an input signal into a Q path signal and an I path signal; A Schottky diode is connected to two ports of the 90 ° hybrid coupler and the 90 ° hybrid coupler, respectively, and receives a Q path signal from the splitter to change the Q path signal gain and the Q path signal phase. A first reflective intermodulation generator for outputting a first intermodulation signal through a shift within a 180 ° range; A Schottky diode is connected to two ports of the 90 ° hybrid coupler and the 90 ° hybrid coupler, respectively, and receives an I path signal from the splitter to change the I path signal gain and the I path signal phase. A second reflective intermodulation generator for outputting a second intermodulation signal through a shift within a 180 ° range; And Predistortion device of the power amplifier consisting of a combiner for receiving the first intermodulation signal and the second intermodulation signal to be coupled to each other and output. The method of claim 1, The splitter predistorter of the power amplifier, characterized in that consisting of a 90-degree hybrid coupler. The method of claim 1, The first intermodulation signal is a signal obtained by multiplying the reflection coefficient of the first reflection type intermodulation generator by the Q path signal, And the second intermodulation signal is a signal obtained by multiplying the reflection coefficient of the second reflection type modulation module by the I path signal. The method of claim 1, The predistorter of the power amplifier, characterized in that the combiner is made of an in-phase coupler. The method according to any one of claims 1 to 4, Applying a first bias voltage (VQ) to the first reflective intermodulation generator for shifting the Q path signal gain and shifting within a 180 ° range of the Q path signal phase; Pre-distortion of the power amplifier, characterized in that for applying the second bias voltage (VI) to the second reflection type intermodulation generator for the change in the I path signal gain and the shift within the 180 ° range of the I path signal phase Device. The method of claim 5, The first bias voltage VQ and the second bias voltage VI are adjustable. Four kinds of gain compression and phase advance, gain compression and phase delay, gain extension and phase advance, and gain extension and phase delay according to the adjustment of the first bias voltage VQ and the second bias voltage VI A power amplifier predistortion device having a gain characteristic and a phase characteristic. The method of claim 1, And said divider, said first reflective intermodulation generator, said second reflective intermodulation generator, and said combiner are connected in a Cartesian vector modulator structure.