A method of determining an analog predistorter target compensation curve

Abstract

The application provides a method for determining an analog predistorter target compensation curve. In view of the fallacy existing in the prior art target compensation curve determination method, the application gives steps for determining the amplitude target compensation characteristic curve and the phase target compensation characteristic curve in the power domain at any frequency based on the analog predistortion compensation mechanism, corrects the error existing in the prior art method, and improves the linearization compensation effect of the analog predistorter.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electromagnetic field and microwave technology, in particular to a design simulation predistorter, and more particularly to a method for determining a target compensation curve of a simulation predistorter. BACKGROUND

[0002] In the information age of today's fast developing communication industry, information transmission distance and information transmission quality are two issues that people generally concern, both of which are closely related to the performance of radio frequency power amplifier. Radio frequency power amplifier is a device that converts direct current power into radio frequency power of the same frequency as the input signal, amplifies the input small signal to a sufficient power level to enable long distance transmission, and is widely used in satellite communication, mobile communication, radar detection, remote sensing and telemetry systems.

[0003] In view of the indicators of radio frequency power amplifier, in addition to the conventional output power and gain, efficiency and linearity are always the indicators that are focused on. Both of these two indicators are related to the nonlinear characteristics of radio frequency power amplifier, that is, when the input signal increases to a certain extent, the fundamental gain will decrease and new harmonic and intermodulation frequency components will be generated. The nonlinearity of the amplifier not only directly reduces its gain when the signal is large, but also reduces the signal quality in the band and causes interference to the adjacent channels due to the generation of intermodulation and harmonics, both of which reduce the efficiency of the amplifier.

[0004] Due to the rapid growth of various information transmission needs, the spectrum resource is becoming increasingly scarce. In order to improve the spectrum utilization, some high-efficiency modulation methods represented by OFDM are applied more and more widely, and these modulation methods usually have a large peak-to-average ratio. The signal with large dynamic range means that the probability of the amplifier entering the nonlinear region is greatly increased, and accordingly it brings greater challenges to control the intermodulation and adjacent channel interference, thus higher requirements are put forward for the linearity of the amplifier. Whether it is to improve the energy utilization efficiency or to improve the spectrum utilization, linearization technology is urgently needed to maximize the elimination of the nonlinearity of radio frequency power amplifier.

[0005] The common linearization technologies at present mainly include power backoff, feedforward technology, negative feedback technology, digital and analog predistortion technology. Among them, analog predistortion technology becomes an indispensable linearization technology because it is suitable for use in high frequency and wideband conditions. The working configuration of analog predistortion is as follows Figure 1As shown, an analog predistorter is connected in series with the input end of the associated amplifier. In the input power range, the predistorter generates a nonlinear characteristic that satisfies certain conditions in advance corresponding to the nonlinear characteristic of the associated amplifier, and the linearization of the overall input-output characteristic is realized after the predistorter is connected in series with the amplifier, i.e. the gain constancy and phase constancy are realized in the input power range. Therefore, the nonlinear characteristic of the associated amplifier determines the input-output characteristic that the predistorter needs to realize, i.e. the compensation characteristic of the predistorter. Conversely, when the analog predistorter is made, the amplitude compensation characteristic and the phase compensation characteristic need to be correctly determined according to the nonlinear characteristic of the associated amplifier in advance, so that a good linear compensation effect can be realized. SUMMARY

[0006] In order to realize a good linear compensation effect on the associated amplifier, the present application aims to provide a method for determining the target compensation curve of an analog predistorter.

[0007] In the first aspect, the present application provides a method for determining the amplitude target compensation curve of an analog predistorter, comprising:

[0008] Step 1: setting a reference coordinate system, and drawing the input-output amplitude characteristic curve of the associated amplifier in the reference coordinate system;

[0009] Step 2: selecting the maximum power value P Max-out of the nonlinear output to be linearized on the input-output amplitude characteristic curve, and the horizontal coordinate of the corresponding point M is the upper limit value P Max-in of the linear input power range of the analog predistorter, i.e. M(P Max-in , P Max-out );

[0010] Step 3: determining the lower limit value P of the linear input power range of the analog predistorter, and determining a point M Connecting the point P and the point M obtains the overall input-output characteristic curve of the analog predistorter connected in series;

[0011] Step 4: taking P as the linear input power range, selecting a plurality of points located in the linear input power range on the X-axis of the reference coordinate system, and for each selected point P , drawing a line segment perpendicular to the X-axis from the point i to the overall input-output characteristic curve of the analog predistorter connected in series, and intersecting at the point j; drawing a line segment parallel to the X-axis from the point j to the input-output amplitude characteristic curve of the associated amplifier, and intersecting at the point s, and obtaining the horizontal coordinate P

[0012] Step 5: taking each P value as the horizontal coordinate, and taking the corresponding P value as the vertical coordinate, and drawing the obtained curve, which is the amplitude input-output power target compensation curve of the analog predistorter.

[0013] Further, the method further comprises:

[0014] Step 6: taking each value as the abscissa, and taking the corresponding value as the ordinate, the obtained curve is the pre-distortion insertion loss-input power target compensation curve of the analog pre-distortion device.

[0015] In a second aspect, the application provides a method for determining a phase-input power target compensation curve of an analog pre-distortion device, comprising:

[0016] Step 1: setting a reference coordinate system, and drawing a phase-input power characteristic curve of an amplifier in the reference coordinate system;

[0017] Step 2: determining a linear input power interval of the analog pre-distortion device, selecting an angle value on the phase-input power characteristic curve of the amplifier, and drawing a curve parallel to the X-axis of the reference coordinate system in the linear input power interval with the angle value as the ordinate, which is the total insertion phase shift curve of the analog pre-distortion device and the amplifier after being cascaded;

[0018] Step 3: selecting a plurality of points on the X-axis of the reference coordinate system in the linear input power interval, and for each selected point drawing a line segment from the point i to the total insertion phase shift curve of the analog pre-distortion device and the amplifier after being cascaded, which is perpendicular to the X-axis, and intersects at point j; drawing a line segment from the point j to the left side, which is parallel to the X-axis, and intersects at point s; drawing a line segment from the point s to the phase-input power characteristic curve of the amplifier, which is perpendicular to the X-axis, and intersects at point t; and determining the length of the line segment st

[0019] Step 4: taking each value as the abscissa, and taking the corresponding value as the ordinate, the obtained curve is the phase-input power target compensation curve of the analog pre-distortion device.

[0020] The application has the following beneficial effects:

[0021] The method for determining the target compensation curve of the analog predistorter provided by the application corrects the fallacy of the existing method for determining the target compensation curve. Taking the gain-input power target compensation curve as an example, the existing method only qualitatively "folds" the gain characteristic curve of the amplifier along the horizontal direction. Since the connection relationship between the analog predistorter and the amplifier is ignored, the fallacy exists in both qualitative and quantitative aspects. The method provided by the application gives accurate quantitative results based on the connection relationship between the analog predistorter and the amplifier and the compensation principle. Especially for the gain-input power curve, not only is the region where the curve is located (the region below the horizontal axis) defined in the gain dimension, but also the accurate value of the transition region is given in the input power dimension, which corrects the fallacy of the existing method. The determination of the amplitude target curve realizes the transition from qualitative to quantitative, and the operation is more rigorous.

[0022] The method provided by the application can conveniently construct the amplitude target compensation curve and the phase target compensation curve of the analog predistorter. Only the input-output amplitude characteristic curve (composed of a plurality of discrete points) and the phase characteristic curve of the amplifier are obtained, and the maximum linear output power and the overall maximum phase shift are specified, and then the amplitude target compensation curve and the phase target compensation curve can be conveniently and quickly given according to the steps of the application, which has strong operability. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A schematic diagram of the working configuration of the analog predistorter;

[0024] Figure 2 A flowchart of a method for determining the amplitude target compensation curve of the analog predistorter provided by the embodiment of the application;

[0025] Figure 3 A drawing for drawing the amplitude target compensation curve of the analog predistorter provided by the embodiment of the application: curve ①: input-output amplitude characteristic of the amplifier; curve ②: overall input-output characteristic after cascading the analog predistorter; curve ③: input-output target compensation characteristic of the analog predistorter;

[0026] Figure 4 A flowchart of a method for determining the phase target compensation curve of the analog predistorter provided by the embodiment of the application;

[0027] Figure 5 A drawing for drawing the phase target compensation curve of the analog predistorter provided by the application: curve ①: input-output phase characteristic of the amplifier; curve ②: total phase shift of the analog predistorter and the amplifier after cascading; curve ③: phase compensation target curve of the analog predistorter. DETAILED DESCRIPTION

[0028] In order to make the objects, technical solutions and advantages of the present application clearer, the following will clearly describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of the present application.

[0029] Corresponding to the AM-AM compression and AM-PM compression (or expansion) characteristics of the amplifier, the compensation characteristics to be achieved by the analog predistorter also correspondingly include amplitude compensation characteristics and phase compensation characteristics, which can be described by an amplitude target compensation characteristic curve and a phase target compensation characteristic curve respectively.

[0030] Based on the analog predistortion compensation mechanism, in view of the fallacy existing in the existing target compensation curve determination method and the application requirement of improving the linearization compensation effect of the analog predistorter, the present application provides a method for determining the amplitude target compensation curve and the phase target compensation curve of the analog predistorter.

[0031] Embodiment 1

[0032] The embodiment of the present application provides a method for determining the amplitude target compensation curve of the analog predistorter. In the embodiment, the amplitude target compensation curve includes two types: one is an input-output power target compensation curve, and the other is an insertion loss-input power target compensation curve. The drawing of the two types of amplitude target compensation curves is completed in Figure 3 . In combination with Figure 2 and Figure 3 , the processes are as follows:

[0033] S101: Set a reference coordinate system, as shown in Figure 3 , draw the input-output amplitude characteristic curve ① of the amplifier in the reference coordinate system;

[0034] Specifically, after determining the amplifier to be used, the input power is given, and the output power is measured, so that a plurality of sets of measurement data can be obtained. According to the measurement data, the input-output amplitude characteristic curve ① of the amplifier can be drawn in the coordinate system shown in Figure 3 in dBm units.

[0035] S102: As shown in Figure 3 , select the maximum power value P Max-out of the linearization output on the input-output amplitude characteristic curve ① according to the need, and the abscissa of the corresponding point M is the upper limit value P Max-in of the linear input power interval of the analog predistorter, that is, M(P Max-in , P Max-out );

[0036] S103: determining the lower limit value of the linear input power range of the analog predistorter and determining a point connecting the point P and the point M to obtain the overall input-output characteristic curve ② of the cascaded analog predistorter;

[0037] Specifically, the lower limit value of the linear input power range of the analog predistorter can be determined according to the minimum power level of the input signal of the matching amplifier

[0038] S104: taking as the linear input power range, selecting a plurality of points within the linear input power range on the X-axis of the reference coordinate system, and determining the horizontal coordinate of each selected point drawing a line segment from the point i to the overall input-output characteristic curve of the cascaded analog predistorter, which is perpendicular to the X-axis, and intersecting at the point j; drawing a line segment from the point j to the input-output amplitude characteristic curve of the matching amplifier, which is parallel to the X-axis, and intersecting at the point s, to obtain the horizontal coordinate of the point s

[0039] For example, as shown in the figure, any point A within the interval Figure 3 is selected on the X-axis of the reference coordinate system, and the horizontal coordinate of the point A is denoted as A line segment is drawn from the point A to the curve ②, which is perpendicular to the X-axis, and intersects at the point B; a line segment is drawn from the point B to the curve ①, which is parallel to the X-axis, and intersects at the point C; a perpendicular line is further drawn from the point C to the X-axis, and the foot of the perpendicular is the point D, and the horizontal coordinate of the point D is denoted as which is also the horizontal coordinate of the point C. In the above manner, for other points within the interval except the point A, the above process is repeated, and other corresponding to the values can be drawn within the interval .

[0040] S105: taking each value as the horizontal coordinate and taking the corresponding value as the vertical coordinate, the obtained curve ④ is the amplitude input-output power target compensation curve of the analog predistorter.

[0041] S106: taking each value as the horizontal coordinate and taking the corresponding as the vertical coordinate, the obtained curve ③ is the insertion loss-input power target compensation curve of the analog predistorter.

[0042] In order to verify the effectiveness of the method of the present application, the following related experiments are also performed.

[0043] ​The used power amplifier in this experiment is a C-band power amplifier with a gain of 34 dB, a saturated output power of 2 W (33 dBm) and a frequency of 6500 MHz. Its input-output power characteristics and gain data are shown in Table 1, and its input-output amplitude characteristic curve is shown as curve 1 in FIG. 1. The relevant data are obtained by using an E8257D signal source and a N9010B measuring device. Figure 3

[0044] Table 1 Input-output amplitude and phase characteristics of the used power amplifier

[0045]

[0046] According to the data in the table and curve 1, the input power of 2.5 dBm corresponds to a maximum linear output power of 30.05 dBm, which is represented by point M on curve 1. The above data are used as initial conditions for drawing the amplitude target compensation curve.

[0047] According to the method of step S103 of drawing the amplitude target curve, another point is taken at an input power of -37.5 dBm on the left side of the X-axis, and the ordinate is -37.5 + (30.05 - 2.5) = -9.55 dBm, thereby obtaining point P with coordinates (-37.5, -9.55). Curve 2 is obtained by connecting point P and point M.

[0048] According to curve 1 and curve 2, a set of (i.e., the output power of the pre-distorter), (i.e., the insertion loss value of the pre-distorter) can be obtained according to the method of step S104, and recorded in Table 2.

[0049] Table 2 Amplitude and phase target compensation data of the simulated pre-distorter

[0050]

[0051] In Figure 3 , curve 4 is drawn with as the coordinates, and curve 3 is drawn with as the coordinates, thereby obtaining the input-output amplitude target compensation curve and the insertion loss-input power target compensation curve of the simulated pre-distorter.

[0052] ​Effectiveness verification: based on the amplitude compensation data of the analog predistorter obtained by the method of the present application, i.e. the insertion loss and the gain data of the associated amplifier, according to the cascade relationship, the data of the two are multiplied in the linear input power interval, and the relevant data is recorded in Table 3. As can be seen from the results of Table 3, in the linear input power interval (-37.5, 2.5), the total gain of the analog predistorter and the amplifier is constant, which is 27.55 dB, thereby verifying the effectiveness of the method of the present application. It should be particularly pointed out that the gain of the amplifier in Table 3 is based on the gain of the amplifier itself at the corresponding input power (the output power of the predistorter, not the input power of the predistorter).

[0053] Table 3 amplitude target compensation curve effectiveness verification data

[0054]

[0055]

[0056] Example 2

[0057] The embodiment of the present application provides a method for determining the phase target compensation curve of an analog predistorter. The phase target compensation curve is generally represented by a phase-input power curve. The drawing of the phase target curve is completed in Figure 5 . In combination with Figure 4 and Figure 5 , the process is as follows:

[0058] S201: setting a reference coordinate system, and drawing a phase-input power characteristic curve of an associated amplifier in the reference coordinate system;

[0059] Specifically, after determining the associated amplifier, given the input power, the phase shift is measured, and a plurality of sets of data can be obtained. According to the measured data, the phase-input power characteristic curve of the associated amplifier can be drawn in the coordinate system shown in Figure 5 in degrees (°).

[0060] S202: determining a linear input power interval of the analog predistorter, selecting an angle value on the side of the phase-input power characteristic curve of the associated amplifier, and drawing a curve parallel to the X-axis of the reference coordinate system with the angle value as the ordinate in the linear input power interval, which is the total insertion phase shift curve of the analog predistorter and the associated amplifier after cascade.

[0061] Specifically, according to the method in the above-mentioned embodiment 1, according to the measurement data of the associated amplifier, the amplitude target curve of the analog predistorter is first drawn, the input-output amplitude characteristic (i.e. the insertion loss-input power characteristic) of the analog predistorter is determined, and the linear input power interval is determined.

[0062] It can be understood that the selected angle value is the total insertion phase shift of the analog predistorter and the associated amplifier, which is usually determined according to the group delay value in the frequency domain.

[0063] S203: selecting a plurality of points in the linear input power interval on the X axis of the reference coordinate system, and determining the phase value of the associated amplifier at each selected point drawing a line segment from the point i to the total insertion phase shift curve of the analog predistorter and the associated amplifier perpendicularly to the X axis, intersecting at the point j; drawing a line segment from the point j to the left side parallel to the X axis, intersecting at the point s; drawing a line segment from the point s to the phase-input power characteristic curve of the associated amplifier perpendicularly to the X axis, intersecting at the point t; and determining the length of the line segment st

[0064] For example, any point A in the linear input power interval is selected on the X axis of the reference coordinate system, and the abscissa is marked as drawing a line segment from the point A to the curve ② perpendicularly to the X axis, intersecting at the point B; drawing a line segment from the point B to the left side parallel to the X axis, and the terminal point of the line segment is the point C; continuing to draw a perpendicular line from the point C to the X axis, intersecting the curve ① at the point D, and determining the length of the line segment CD It can be understood that the length of the line segment BC is the insertion loss value of the analog predistorter at the input power value .

[0065] S204: taking each value as the abscissa and taking the corresponding value as the ordinate, and drawing the obtained curve ③, which is the phase-input power target compensation curve of the analog predistorter.

[0066] Specifically, a perpendicular line of the X axis is drawn from the point A upwards, the length of the perpendicular line segment is equal to the length of the line segment CD, and the terminal point is marked as the point E. Other points are selected in the linear input power interval except for the point A, and the steps S203 and S204 are repeated, so that other and the corresponding E i points can be drawn in the linear input power interval. Taking each value as the abscissa and taking the ordinate of the corresponding E i point (i.e. ) as the ordinate, the curve is drawn by dotting and drawing, and the obtained curve ③ is the phase-input power target compensation curve of the analog predistorter.

[0067] In order to verify the effectiveness of the method of the present application, the following related experiments are also performed.

[0068] The associated amplifier used in the experiment is the same as that in Embodiment 1, which is still a C-band power amplifier with a microwave power amplifier gain of 34 dB, a saturated output power of 2 W (33 dBm), and a frequency of 6500 MHz. The phase-input power characteristic and gain data are shown in Table 1, and the phase-input power characteristic curve is shown in FIG. 2.Figure 5 The curve 1 is shown in the figure. The relevant data is obtained by 3672D microwave network analyzer, E8257D signal source and N9010B measurement.

[0069] According to the data in table 1, the corresponding 30.05dBm is determined as the maximum linear output power when the input power is 2.5dBm, and (-30, 2.5) is taken as the linear input power range of the analog predistorter. Here, 350° is taken as an example, and the horizontal straight line 2 is drawn.

[0070] According to the data in table 1, the corresponding 30.05dBm is determined as the maximum linear output power when the input power is 2.5dBm, and (-30, 2.5) is taken as the linear input power range of the analog predistorter. Here, 350° is taken as an example, and the horizontal straight line 2 is drawn. Figure 5 According to the curve 1 and the curve 2, a group of points E i is obtained according to the phase target compensation curve drawing steps S203 and S204, and the ordinate of each point E i is marked in table 2. Connecting each point E Figure 5 , the phase-input power target curve 3 can be drawn in the figure.

[0071] Effectiveness verification: the phase compensation data of the analog predistorter obtained based on the method of the present application, namely the insertion phase shift and the insertion phase shift of the amplifier, are multiplied according to the cascade relationship of the two in the linear input power range, and the relevant data is counted in table 4. It can be seen from the results in table 4 that the total insertion phase shift of the analog predistorter and the amplifier is constant in the linear input power range (-37.5, 2.5), and is 350°. Thus, the effectiveness of the method of the present application is verified. It should be particularly pointed out that the insertion phase shift of the amplifier in the table is based on the insertion phase shift of the amplifier itself at the corresponding input power (the output power of the predistorter, not the input power of the predistorter).

[0072] Table 4: data for verifying the effectiveness of the phase target compensation curve

[0073]

[0074]

[0075] The method of the present application gives the steps for determining the amplitude target compensation characteristic curve and the phase target compensation characteristic curve in the power domain at any frequency, corrects the errors in the existing methods, and improves the linearization compensation effect of the analog predistorter.

[0076] Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining an analog predistorter amplitude target compensation curve, characterized in that: include: Step 1: Setting a reference coordinate system, and drawing the input-output amplitude characteristic curve of the amplifier in the reference coordinate system; Step 2: Select the maximum power value P of the quasi-linearized output on the input-output amplitude characteristic curve Max-out The corresponding point M, the horizontal coordinate of point M is the upper limit value P of the linear input power range of the analog predistorter Max-in , that is, M(P Max-in , P Max-out ); Step 3: Determine the lower limit of the linear input power range of the analog predistorter And make sure Connecting point P and point M, the overall input-output characteristic curve of the cascaded analog predistorter is obtained; Step 4: As the linear input power interval, several points located within the linear input power interval are selected on the X-axis of the reference coordinate system. For each selected point Draw a line segment perpendicular to the X-axis from point i to the overall input-output characteristic curve after the cascaded analog predistorter, which intersects at point j; draw a line segment parallel to the X-axis from point j to the input-output amplitude characteristic curve of the matching amplifier, which intersects at point s, and obtain the horizontal coordinate of point s. Step 5: The value is the horizontal axis, corresponding to The value is the vertical coordinate, and the resulting curve is the target compensation curve of the analog predistorter amplitude input and output power.

2. The method for determining an analog predistorter amplitude target compensation curve according to claim 1, wherein: Also includes: Step 6: The value is the horizontal axis, corresponding to The vertical axis is the curve obtained by drawing the insertion loss-input power target compensation curve of the simulated predistorter.

3. A method for determining a phase target compensation curve of an analog predistorter, characterized in that: include: Step 1: Setting a reference coordinate system, and drawing a phase-input power characteristic curve of the amplifier in the reference coordinate system; Step 2: Determine the linear input power range of the analog predistorter, select an angle value on the upper side of the phase-input power characteristic curve of the matching amplifier, and draw a curve parallel to the X-axis of the reference coordinate system with the angle value as the vertical coordinate in the linear input power range, which is the total insertion phase shift curve of the cascaded analog predistorter and the matching amplifier; Step 3: Select several points on the X-axis of the reference coordinate system that are within the linear input power range. Draw a line segment perpendicular to the X-axis from point i to the total insertion phase shift curve of the cascaded analog predistorter and the accompanying amplifier, which intersects at point j; draw a line segment parallel to the X-axis from point j to the left, which intersects at point s; draw a line segment perpendicular to the X-axis from point s to the phase-input power characteristic curve of the accompanying amplifier, which intersects at point t, and determine the length of line segment st Step 4: The value is the horizontal axis, corresponding to The value is the vertical axis, and the resulting curve is the phase-input power target compensation curve of the analog predistorter.

Images