Method for determining target compensation curve of analog predistorter

Abstract

The invention provides a method for determining a target compensation curve of an analog predistorter. Aiming at the mistake existing in the existing target compensation curve determination method, the invention provides a step of determining an amplitude target compensation characteristic curve and a phase target compensation characteristic curve in a power domain under any frequency based on a simulation pre-distortion compensation mechanism, so that the mistake existing in the existing method is corrected, and the accuracy of the target compensation curve determination method is improved. And the linearization compensation effect of the analog predistorter is improved.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic field and microwave technology, specifically to the design of an analog predistorter, and in particular to a method for determining a target compensation curve of an analog predistorter. Background Art

[0002] In today's information age with rapid development of the communication industry, information transmission distance and information transmission quality are two issues that people generally pay attention to. Both of these issues are closely related to the performance of RF power amplifiers. RF power amplifiers are devices that convert DC power into RF power with the same frequency as the input signal, amplify the input small signal to a sufficient power level, and enable long-distance transmission. They are widely used in satellite communications, mobile communications, radar detection, remote sensing and telemetry systems.

[0003] Regarding the indicators of RF power amplifiers, in addition to conventional output power and gain, efficiency and linearity have always been the focus of attention. Both indicators are related to the nonlinear characteristics of the RF power amplifier, that is, when the input signal increases to a certain extent, its fundamental gain will decrease and generate new harmonics and intermodulation frequency components. The nonlinearity of the amplifier not only directly reduces its gain when the signal is large, but also reduces the signal quality within the band due to the generation of intermodulation and harmonics, and interferes with adjacent channels. Both factors reduce the efficiency of the amplifier.

[0004] Due to the rapid growth of demand for various types of information transmission, spectrum resources are becoming increasingly scarce. In order to improve spectrum utilization, some efficient modulation methods represented by OFDM are becoming more and more widely used, and these modulation methods usually have large peak-to-average values. The signal with a large dynamic range means that the probability of the amplifier entering the nonlinear region is greatly increased, which correspondingly brings greater challenges to controlling intermodulation and adjacent channel interference, and thus puts forward higher requirements for the linearity of the amplifier. Whether it is to improve energy efficiency or improve spectrum utilization, linearization technology is urgently needed to eliminate the nonlinearity of RF power amplifiers to the maximum extent.

[0005] At present, the common linearization technologies mainly include power back-off, feedforward technology, negative feedback technology, digital and analog pre-distortion technology. Among them, analog pre-distortion technology has become an indispensable linearization technology because it is suitable for use under high-frequency and broadband conditions. The working configuration of the analog pre-distorter is as follows: Figure 1As shown, an analog predistorter is cascaded at the input end of the matching amplifier. In the input power range, corresponding to the nonlinearity of the matching amplifier, the predistorter pre-generates nonlinearity that meets specific conditions, and realizes the linearization of the overall input-output characteristics after being cascaded with the amplifier, that is, constant gain and constant phase are achieved within the input power range. Therefore, the nonlinear characteristics of the matching amplifier determine the input and output characteristics that the predistorter needs to achieve, that is, the compensation characteristics of the predistorter. Conversely, when making an analog predistorter, it is necessary to first correctly determine the amplitude compensation characteristics and phase compensation characteristics according to the nonlinear characteristics of the matching amplifier in order to achieve a good linear compensation effect. Summary of the invention

[0006] In order to achieve a good linear compensation effect for an accompanying amplifier, the present invention aims to provide a method for determining a target compensation curve of an analog predistorter.

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

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

[0009] 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 );

[0010] 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;

[0011] Step 4: As the linear input power interval, select several points within the linear input power interval on the X-axis of the reference coordinate system, and 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.

[0012] Step 5: The value is the horizontal axis, corresponding to The value is the vertical coordinate, and the resulting curve is the analog predistorter amplitude input and output power target compensation curve.

[0013] Furthermore, the method further comprises:

[0014] Step 6: The value is the horizontal axis, corresponding to The vertical coordinate is plotted, and the resulting curve is the insertion loss-input power target compensation curve of the simulated predistorter.

[0015] In a second aspect, the present invention provides a method for determining a phase target compensation curve of an analog predistorter, comprising:

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

[0017] 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 ordinate in the linear input power range, which is the total insertion phase shift curve of the cascaded analog predistorter and the matching amplifier;

[0018] Step 3: Select several points within the linear input power range on the X-axis of the reference coordinate system, and for each selected point 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 matching 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 matching amplifier, which intersects at point t, and determine the length of line segment st

[0019] 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.

[0020] Beneficial effects of the present invention:

[0021] The method for determining the target compensation curve of the analog predistorter provided by the present invention corrects the errors of the existing methods for determining the target compensation curve. Taking the gain-input power target compensation curve as an example, the existing method only qualitatively "reflects" the gain characteristic curve of the matching amplifier in the horizontal direction. Since the series relationship between the analog predistorter and the matching amplifier is ignored, there are errors both qualitatively and quantitatively. The method of the present invention provides accurate quantitative results based on the connection relationship and compensation principle between the analog predistorter and the matching amplifier. In particular, the gain-input power curve not only limits its area (the area below the horizontal axis) in the gain dimension, but also provides the accurate value of the transition area in the input power dimension, correcting the errors of the existing methods. The determination of the amplitude target curve has achieved a transition from qualitative to quantitative, and the operation is more rigorous.

[0022] The method of the present invention can conveniently construct the amplitude target compensation curve and the phase target compensation curve of the analog predistorter. It only needs to obtain the input and output amplitude characteristic curve (composed of a number of discrete points) and the phase characteristic curve of the matching amplifier, and specify the required maximum linear output power and the overall maximum phase shift, 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 present invention, which has strong operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the working configuration of the analog predistorter;

[0024] Figure 2 A schematic flow chart of a method for determining an analog predistorter amplitude target compensation curve provided by an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of drawing the target compensation curve of the amplitude of the analog predistorter provided by the embodiment of the present invention: Curve ①: input and output amplitude characteristics of the matching amplifier; Curve ②: overall input and output characteristics after cascading the analog predistorter; Curve ③: insertion loss-input power compensation curve of the analog predistorter; Curve ④: input and output target compensation characteristics of the analog predistorter;

[0026] Figure 4 A schematic diagram of a flow chart of a method for determining a phase target compensation curve of an analog predistorter provided by an embodiment of the present invention;

[0027] Figure 5 Schematic diagram of the analog predistorter phase target compensation curve proposed in the present invention: Curve ①: input and output phase characteristics of the matching amplifier; Curve ②: total phase shift of the analog predistorter and the amplifier after cascading; Curve ③: analog predistorter phase compensation target curve. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0030] The present invention is based on the analog predistortion compensation mechanism, aims at the errors existing in the existing target compensation curve determination method, and aims at the application demand of improving the linearization compensation effect of the analog predistorter. A method for determining the amplitude target compensation curve and the phase target compensation curve of the analog predistorter is proposed.

[0031] Example 1

[0032] The embodiment of the present invention provides a method for determining an amplitude target compensation curve of an analog predistorter. In this 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. Both amplitude target compensation curves are drawn in Figure 3 Completed in. Figure 2 and Figure 3 As shown, the processes are as follows:

[0033] S101: Set the reference coordinate system, such as Figure 3 As shown, the input-output amplitude characteristic curve ① of the matching amplifier is drawn in the reference coordinate system;

[0034] Specifically, after determining the amplifier to be used, the input power is given and its output power is measured, so that several sets of measurement data can be obtained. Figure 3 In the coordinate system shown, the input-output amplitude characteristic curve of the amplifier can be plotted in dBm units①.

[0035] S102: Figure 3 As shown, according to the need, select the maximum power value P of the quasi-linear output on the input-output amplitude characteristic curve ① 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 );

[0036] S103: Determine the lower limit of the linear input power range of the analog predistorter And make sure Connect point P and point M to obtain the overall input-output characteristic curve of the cascaded analog predistorter②;

[0037] Specifically, the lower limit 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: As the linear input power interval, select several points within the linear input power interval on the X-axis of the reference coordinate system, and 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.

[0039] For example, Figure 3 As shown, select the region in the interval on the X-axis of the reference coordinate system. Any point A in Draw a line segment perpendicular to the X-axis from point A to curve ②, which intersects at point B; draw a line segment parallel to the X-axis from point B to curve ①, which intersects at point C; continue to draw a perpendicular line from point C to the X-axis, with the foot of the perpendicular being point D, and its coordinate is marked as is also the horizontal coordinate of point C. According to the above method, for the interval selected on the X-axis Repeat the above process for other points except A in the interval Others The corresponding value.

[0040] S105: The value is the horizontal axis, corresponding to The value is the vertical coordinate, and the resulting curve ④ is the analog predistorter amplitude input and output power target compensation curve.

[0041] S106: Each The value is the horizontal axis, corresponding to The vertical coordinate is plotted, and the resulting curve ③ is the insertion loss-input power target compensation curve of the simulated predistorter.

[0042] In order to verify the effectiveness of the method of the present invention, the present invention also carried out the following related experiments.

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

[0044] Table 1 Input and output amplitude and phase characteristics of the matching amplifier

[0045]

[0046] From the data in the table and curve ①, we determine that 30.05dBm corresponding to an input power of 2.5dBm is the maximum linear output power, which is represented by point M on curve ①. The above data is used as the initial condition for drawing the amplitude target compensation curve.

[0047] According to the method of drawing the amplitude target curve step S103, another point is taken on the left side of the X-axis at the input power of -37.5dBm, and its ordinate is -37.5+(30.05-2.5)=-9.55dBm. Thus, point P is obtained, and its coordinates are (-37.5,-9.55). Point P is connected with point M to obtain curve ②.

[0048] According to curve ① and curve ②, according to the method of step S104, a set of (i.e., predistorter output power), (i.e., the predistorter insertion loss value) and record it in Table 2.

[0049] Table 2 Simulation predistorter amplitude and phase target compensation data

[0050]

[0051] exist Figure 3 In Draw a curve ④ for the coordinates, with Draw curve ③ for the coordinates, and obtain the analog predistorter input and output amplitude target compensation curve and insertion loss-input power target compensation curve.

[0052] Validity verification: Based on the amplitude compensation data of the analog predistorter obtained by the method of the present invention, that is, the insertion loss and the gain data of the matching amplifier, the data of the two are multiplied in the linear input power range according to the cascade relationship between the two, and the relevant data are recorded in Table 3. It can be seen from the results of Table 3 that in the linear input power range (-37.5, 2.5), the total gain of the analog predistorter and the amplifier is constant, both of which are 27.55dB, thereby verifying the validity of the method of the present invention. It should be noted that the gain of the amplifier in Table 3 is based on the gain corresponding to the input power (predistorter output power, not predistorter input power) of the amplifier's own characteristics.

[0053] Table 3 Amplitude target compensation curve validity verification data

[0054]

[0055]

[0056] Example 2

[0057] The embodiment of the present invention provides a method for determining a phase target compensation curve of an analog predistorter. The phase target compensation curve is generally represented by a phase-input power curve. The phase target curve is drawn in Figure 5 Completed in. Figure 4 and Figure 5 As shown, the processes are as follows:

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

[0059] Specifically, after determining the amplifier to be used, given the input power, the phase shift is measured, and several sets of data can be obtained. Figure 5 In the coordinate system shown, the phase-input power characteristic curve of the amplifier used can be plotted in degrees (°) as the unit①.

[0060] S202: 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 ordinate in the linear input power range, which is the total insertion phase shift curve of the cascaded analog predistorter and the matching amplifier②;

[0061] Specifically, in the manner of the above-mentioned embodiment 1, based on the measurement data of the matching amplifier, the amplitude target curve of the analog predistorter can be firstly drawn to determine the input and output amplitude characteristics (i.e., insertion loss-input power characteristics) of the analog predistorter, and its linear input power range can be determined.

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

[0063] S203: Select a number of points within the linear input power interval on the X-axis of the reference coordinate system, and for each selected point 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 matching 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 matching amplifier, which intersects at point t, and determine the length of line segment st

[0064] For example, select any point A on the X-axis of the reference coordinate system that is within the linear input power range, and its horizontal coordinate is marked as Draw a line segment perpendicular to the X-axis from point A to curve ②, intersecting at point B; draw a line segment parallel to the X-axis from point B to the left, with the end point of the line segment at point C; continue to draw a perpendicular line from point C to the X-axis, intersecting curve ① at point D, and determine the length of line segment CD It can be understood that the length of line segment BC is the input power value of the analog predistorter. Insertion loss value.

[0065] S204: Each The value is the horizontal axis, corresponding to The value is the vertical coordinate, and the resulting curve ③ is the phase-input power target compensation curve of the analog predistorter.

[0066] Specifically, a perpendicular line is drawn upward from point A to the X-axis, and the length of the perpendicular line segment is equal to the length of line segment CD, and its end point is recorded as point E. Other points other than A are selected in the linear input power interval, and the processes of steps S203 and S204 are repeated to obtain other points in the linear input power interval. and the corresponding E i Point. The value is the horizontal axis, with the corresponding E i The vertical coordinate of the point (i.e. ) points are plotted and curves are drawn. The obtained curve ③ is the phase-input power target compensation curve of the analog pre-distorter.

[0067] In order to verify the effectiveness of the method of the present invention, the present invention also carried out the following related experiments.

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

[0069] From the data in Table 1, we determine that 30.05dBm corresponding to an input power of 2.5dBm is the maximum linear output power, and (-30, 2.5) is taken as the linear input power range of the analog predistorter. Here, we take 350° as an example and draw a horizontal line ②.

[0070] according to Figure 5 In the middle curve ① and curve ②, according to the method of drawing the phase target compensation curve step S203 and step S204, a set of points E can be obtained. i , and mark its vertical coordinates in Table 2. Connect each E i Click to Figure 5 The phase-input power target curve ③ is drawn in the figure.

[0071] Validity verification: Based on the phase compensation data of the simulated predistorter obtained by the method of the present invention, that is, the insertion phase shift and the insertion phase shift of the matching amplifier, the data of the two are multiplied in the linear input power range according to the cascade relationship between the two, and the relevant data are recorded in Table 4. It can be seen from the results of Table 4 that in the linear input power range (-37.5, 2.5), the total insertion phase shift of the simulated predistorter and the amplifier is constant, both of which are 350°, thereby verifying the validity of the method of the present invention. It should be noted that the insertion phase shift of the amplifier in the table is based on the insertion phase shift corresponding to the input power (predistorter output power, not predistorter input power) of the amplifier's own characteristics.

[0072] Table 4 Phase target compensation curve validity verification data

[0073]

[0074]

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

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

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 an 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, select several points within the linear input power interval on the X-axis of the reference coordinate system, and for each selected point Draw a line segment perpendicular to the X-axis from point i to the overall input-output characteristic curve of the cascaded analog predistorter, which intersects at point j; draw a line segment parallel to the X-axis from point i 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 analog predistorter amplitude input and output power target compensation curve.

2. The method for determining an analog predistorter amplitude target compensation curve according to claim 1, characterized in that: Also includes: Step 6: The value is the horizontal axis, corresponding to The vertical coordinate is plotted, and the resulting curve is 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 ordinate 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 within the linear input power range on the X-axis of the reference coordinate system, and for each selected point 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 matching 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 matching 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.

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