A linear three-way doherty power amplifier based on synthetic network compensation and a design method thereof

Abstract

The application discloses a linear three-way Doherty power amplifier based on a synthesis network compensation and a design method thereof, wherein a three-way Doherty synthesis network is composed of three transmission lines with electrical lengths of and respectively. The application establishes an analytical relationship between the amplitude-amplitude response and the amplitude-phase response of the three-way Doherty combining network and and by theoretically analyzing the transmission coefficient of the three-way Doherty combining network; a multi-objective collaborative optimization criterion is proposed; the gain curve and the phase curve of a transistor in a full working interval are extracted; the residual amplitude error sequence and the residual phase error sequence after the cascade superposition of the inherent distortion of the transistor and the compensation magnitude of the combiner are calculated; the optimal is determined by minimizing the weighted objective function of the residual errors, so that the combiner generates the amplitude and phase responses complementary to the nonlinear distortion of the transistor, and the linearization of the overall amplifier is realized. The application significantly improves the linearity while ensuring the 9-12 dB deep power backoff efficiency, and is independent of digital pre-distortion, and is suitable for 4G / 5G / 6G base stations and high peak-to-average ratio signal amplification scenarios.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, specifically relating to a high-efficiency, high-linearity three-channel Doherty power amplifier, and particularly a linearized enhanced three-channel Doherty power amplifier that compensates for transistor AM-AM and AM-PM distortions by utilizing the nonlinear characteristics generated by the combiner itself. Background Technology

[0002] With the continuous development of modern wireless communication systems (such as 4G / 5G / 6G), the peak-to-average power ratio (PAPR) of modulated signals continues to increase (typically 6-10 dB). Doherty power amplifiers (DPAs) have become core components of base stations and terminal transmitters because they can maintain high efficiency in the output back-off (OBO) region. However, the efficiency improvement of DPAs often comes at the cost of linearity: the active load modulation process and the non-ideal characteristics of transistors (such as gate voltage modulation, output capacitor nonlinearity, etc.) together lead to severe amplitude-amplitude (AM-AM) compression and amplitude-phase (AM-PM) distortion.

[0003] Existing linearization techniques mainly include digital predistortion (DPD), analog linearization circuits, and combiner parameter optimization. While DPD offers excellent performance, it increases the overhead of feedback loops, ADC / DAC, and digital processing, leading to higher system cost and power consumption. In recent years, methods to achieve "DPD-free linearization" by adjusting the transmission line length of the Doherty combiner to produce an AM-AM / AM-PM response opposite to that of a transistor have been reported in two-channel DPAs. However, the effective OBO range of two-channel DPAs is typically only around 6dB, which is insufficient to meet the high-efficiency amplification requirements of high PAPR signals (>7dB).

[0004] Three-way Doherty power amplifiers (TW-DPAs) can extend high-efficiency OBO to 9–12 dB, but their linearization design is extremely complex. Existing TW-DPA linearization methods (such as non-uniform input drive and bias optimization) either have limited compensation capabilities or sacrifice significant back-off efficiency. Unlike two-way Doherty power amplifiers, which only require optimization of one transmission line electrical length parameter, the synthesis network of a three-way Doherty power amplifier includes two independent adjustable electrical length parameters. and Its parameter space is two-dimensional, which significantly increases the optimization difficulty. The mature linearization compensation method in two-way DPA cannot be directly extended to three-way structure. Therefore, there is an urgent need for a TW-DPA and its systematic design method that can achieve high linearity and high efficiency in the deep back-off region (9 dB OBO). Summary of the Invention

[0005] To address the technical problems of complex linearization design of existing three-channel Doherty power amplifiers and the inability to directly extend existing two-channel DPA linearization methods to three-channel structures, this invention provides a linear three-channel Doherty power amplifier and its design method based on synthetic network compensation. Through systematic theoretical analysis and parameter optimization, the nonlinear characteristics of the synthetic network itself are used to compensate for the AM-AM and AM-PM distortions of the transistors, significantly improving linearity while ensuring high efficiency in the high-power back-off range.

[0006] The technical solution of this invention is as follows:

[0007] On one hand, this invention proposes a linear three-channel Doherty power amplifier based on a synthesis network compensation, comprising: a main power amplifier, a first auxiliary power amplifier, a second auxiliary power amplifier, a three-channel Doherty synthesis network, a 1-to-3 power divider, a first phase compensation line, a second phase compensation line, and a post-matching network; the input terminal of the main power amplifier is directly connected to the first output terminal of the 1-to-3 power divider, the input terminal of the first auxiliary power amplifier is connected to the second output terminal of the 1-to-3 power divider through the first phase compensation line, and the input terminal of the second auxiliary power amplifier is connected to the third output terminal of the 1-to-3 power divider through the second phase compensation line; the output terminals of the main power amplifier, the first auxiliary power amplifier, and the second auxiliary power amplifier are respectively connected to the three input terminals of the three-channel Doherty synthesis network, and the output terminal of the three-channel Doherty synthesis network is connected to the post-matching network.

[0008] In a further preferred embodiment, the first auxiliary power amplifier is identical to the second auxiliary power amplifier, and the optimal load impedance of all three sub-amplifiers is... ,in This indicates the optimal load impedance value for the transistor to achieve maximum output power and peak efficiency under target bias conditions.

[0009] A further preferred embodiment is that the three-way Doherty synthesis network consists of an electrical length of The first transmission line TL1 has an electrical length of The second transmission line TL2 and its electrical length are It consists of the third transmission line TL3; among which, The transmission phase length of the first transmission line TL1, The transmission phase lengths of the second transmission line TL2 and the third transmission line TL3 are used to control the AM-AM distortion and AM-PM distortion characteristics of the synthesized network.

[0010] In a further preferred embodiment, the characteristic impedances of the first transmission line TL1, the second transmission line TL2, and the third transmission line TL3 are all... .

[0011] In a further preferred embodiment, the output terminal of the main power amplifier is connected to the input terminal of the first transmission line TL1 in the three-channel Doherty synthesis network, the output terminal of the first auxiliary power amplifier is connected to the input terminal of the second transmission line TL2 in the three-channel Doherty synthesis network, and the output terminal of the second auxiliary power amplifier is connected to the input terminal of the third transmission line TL3 in the three-channel Doherty synthesis network.

[0012] In a further preferred embodiment, the outputs of the first transmission line TL1, the second transmission line TL2, and the third transmission line TL3 in the three-way Doherty synthesis network are connected together to form a synthesis node, which is then connected to the input of the post-matching network.

[0013] In a further preferred embodiment, the post-matching network matches the standard 50-ohm impedance to the synthesized impedance. ,in .

[0014] In a further preferred embodiment, the power distribution ratio of the 1:1:1 power divider is 1:1:1, achieving equal power distribution.

[0015] A further preferred embodiment is that the electrical length in the three-way Doherty synthesis network... and The combined network is configured such that the AM-AM and AM-PM responses of the combined network are complementary to the nonlinear distortion characteristics of the transistors in the main power amplifier, the first auxiliary power amplifier, and the second auxiliary power amplifier; wherein, the complementarity means that, at any input power level, the amplitude distortion generated by the combiner is opposite in sign and matches the absolute value of the amplitude distortion generated by the transistor; the phase distortion generated by the combiner is opposite in sign and matches the absolute value of the phase distortion generated by the transistor; the opposite sign indicates that: when the transistor exhibits gain compression, the combiner exhibits gain expansion, and when the transistor exhibits gain expansion, the combiner exhibits gain compression; when the transistor exhibits phase lag, the combiner exhibits phase lead, and when the transistor exhibits phase lead, the combiner exhibits phase lag.

[0016] A further preferred embodiment is that the electrical length and Transmission coefficient via combiner The analytical expression of the input signal amplitude and its application in normalized input signal amplitude to The amplitude and phase changes within the range are used to determine this; where... Main power amplifier output current With full-amplitude current The ratio, that is The combiner transmission coefficient Defined as the output voltage of the combiner With the main power amplifier output current The ratio, that is It is used to characterize the power transfer characteristics and nonlinear behavior of the combiner from the main power amplifier port to the combined output.

[0017] On the other hand, this invention also proposes a design method for a linear three-channel Doherty power amplifier based on synthetic network compensation, comprising the following steps:

[0018] Step 1: Determine the optimal load impedance of the transistor and combined impedance ,in ;

[0019] Step 2: Extract the gain curve of the transistor under the target bias. and phase curve ,by Using a reference point, calculate the relative amplitude distortion of the transistor. and relative phase distortion The AM-AM distortion characteristic curves and AM-PM distortion characteristic curves of transistors; among them, and These represent the transistor's normalized current amplitude. Gain and phase at the point;

[0020] Step 3: Establish the transmission coefficient of the combining network The mathematical model is used to obtain the AM-AM response curve and AM-PM response curve of the combiner. , The analytical relationships of change;

[0021] Step 4: Calculate the different values ​​according to the following formula. and Combiner amplitude distortion Combiner phase distortion :

[0022]

[0023]

[0024] in, This refers to the normalized current amplitude, specifically the output current of the main power amplifier. With full-amplitude current The ratio, that is ; Indicates that the combiner is from the low power region to saturation point The amplitude distortion, Indicates that the combiner is from the low power region to saturation point Phase distortion; Represents the transmission coefficient The modulus, Represents the transmission coefficient The phase angle;

[0025] Step 5: Perform multi-objective collaborative optimization in the two-dimensional parameter space:

[0026] First, based on the transistor gain curve extracted in the second step... and phase curve Calculate the transistor's normalized amplitude Relative amplitude distortion at the point and relative phase distortion :

[0027]

[0028]

[0029] Then, calculate the combiner in the corresponding Relative amplitude compensation at the location and relative phase compensation amount :

[0030]

[0031]

[0032] According to the superposition principle of cascaded networks, transistor distortion and combiner compensation are superimposed after cascading; because exist As the interval changes continuously, the error also increases. Changes occur as power changes, hence the data set is formed according to power order; calculations exist The concatenated residual amplitude error sequence corresponding to each discrete sampling point within the interval and residual phase error sequence :

[0033]

[0034]

[0035] Among them, residual error refers to the algebraic net value of the transistor's inherent distortion and the combiner's compensation at the corresponding power point, used to characterize the uncompensated residual at that power point; error sequence refers to... exist The sequence of residual error values ​​corresponding to multiple discrete sampling points arranged in power order within the interval is used to characterize the complete trajectory of residual error as power changes, distinguishing it from simply taking the saturation point. Evaluation method for a single value;

[0036] Finally, define the overall optimization objective function. for:

[0037]

[0038] in, for exist The number of discrete sampling points in the interval. and These are the amplitude error tolerance and phase error tolerance allowed by the system design specifications, respectively. and The weighting coefficients for amplitude error and phase error are respectively. Choose the objective function that optimizes the overall system. The optimal parameter combination is the one that minimizes the minimum value. and When the optimal parameter regions for amplitude compensation and phase compensation do not overlap, the weighting coefficients are adjusted for a compromise optimization, ensuring that the total AM-AM gain fluctuation after cascading is better than within a 9dB back-off range. Furthermore, the total AM-PM phase variability is better than ;

[0039] Step 6: Based on the calculated optimal... and Designing synthetic networks; this is a conventional technique in this field and will not be discussed in detail here.

[0040] Step 7: Use a synthesis network to complete the overall design of a linear three-channel Doherty power amplifier; this is a conventional technique in this field and will not be discussed in detail here.

[0041] A further preferred embodiment, the The preferred range is 70° to 110°, the The preferred range is 160° to 200°; the weighting coefficient The preferred range is 0.6 to 0.8. The preferred range is 0.2 to 0.4, in order to prioritize the compensation effect for phase distortion.

[0042] Beneficial effects

[0043] Compared with existing technologies, the linear three-channel Doherty power amplifier and its design method proposed in this invention have the following advantages:

[0044] First, this invention establishes the transmission coefficient of a three-way Doherty combining network through theoretical analysis. The analytical model is given, and the amplitude distortion of the combiner is presented. and phase distortion With two independent adjustable parameters and The quantitative relationship between them provides a systematic theoretical guide for the linearization design of the three-channel Doherty power amplifier, overcoming the shortcomings of traditional experience-based debugging methods.

[0045] Secondly, this invention achieves its goals through reasonable configuration. and This enables the synthesized network to generate AM-AM and AM-PM responses that complement the nonlinear distortion of the transistor, achieving both high linearity and high efficiency within a 9–12 dB power back-off range, thus meeting the amplification requirements of high PAPR modulation signals (>7 dB).

[0046] Third, compared with the digital predistortion (DPD) scheme, the present invention does not require additional feedback loops, ADC / DAC and digital signal processing units, which significantly reduces system cost, power consumption and implementation complexity.

[0047] Fourth, compared to a two-channel Doherty power amplifier, this invention extends the high-efficiency output back-off range from 6dB to 9-12dB, while simultaneously achieving this through two independently adjustable parameters. and The collaborative optimization achieves more flexible nonlinear compensation capabilities. Although the parameters of the synthesized network deviate from the ideal values ​​( , This will reduce drain efficiency to some extent, but the efficiency drop is limited (the efficiency drops by about 3-5 percentage points at the 9dB back-off point), achieving a good trade-off between linearity and efficiency within an acceptable range.

[0048] Fifth, the design method provided by this invention has good repeatability and universality, does not depend on the designer's experience, and can be widely applied to the design of three-channel Doherty power amplifiers with different frequency bands and power levels.

[0049] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0050] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0051] Figure 1 This is a block diagram of the linear three-channel Doherty power amplifier in this invention;

[0052] Figure 2 This is a simplified structural diagram of the linear three-channel Doherty power amplifier in this invention;

[0053] Figure 3 Different in this invention and Combiner amplitude distortion under parameter combinations and phase distortion Contour distribution map;

[0054] Figure 4 Different in this invention Below, the normalized AM-AM and AM-PM responses of the combiner;

[0055] Figure 5 For the purposes of this invention Below, the efficiency response of a linear three-way Doherty power amplifier;

[0056] Figure 6 This is a simulation model diagram of a linear three-channel Doherty power amplifier in an embodiment of the present invention;

[0057] Figure 7 The AM-AM response of the simulation model of the linear three-channel Doherty power amplifier in this embodiment of the invention;

[0058] Figure 8 The AM-PM response of the simulation model of the linear three-channel Doherty power amplifier in this embodiment of the invention;

[0059] Figure 9 This is the efficiency response of the simulation model of the linear three-channel Doherty power amplifier in the embodiment of the present invention. Detailed Implementation

[0060] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and should not be construed as limiting the invention.

[0061] (a) Explanation of symbols

[0062] To facilitate understanding of the technical solution of this invention, the mathematical symbols used in the derivation of specific embodiments are explained uniformly below:

[0063] The optimal load impedance value for the transistor to achieve maximum output power and peak efficiency under target bias conditions;

[0064] The input impedance of the post-matching network at the output of the three-way Doherty combining network (at the combining node);

[0065] Characteristic impedance of the first transmission line TL1;

[0066] Characteristic impedances of the second transmission line TL2 and the third transmission line TL3;

[0067] The electrical transmission length of the first transmission line TL1 is the first independently adjustable design parameter in this invention.

[0068] The electrical transmission lengths of the second transmission line TL2 and the third transmission line TL3 are the second independently adjustable design parameter in this invention.

[0069] : The maximum output current of the main power amplifier, that is, the full-scale output current of the transistor in saturation state;

[0070] The output current of the main power amplifier varies with the input power, ranging from 0 to... ;

[0071] : Output current of the first auxiliary power amplifier;

[0072] : Output current of the second auxiliary power amplifier;

[0073] Normalized current amplitude, ranging from 0 to 1, when When the auxiliary power amplifier is off; when At that time, the auxiliary power amplifier starts to conduct;

[0074] : Voltage at the output port of the main power amplifier;

[0075] The voltage at the output port of the auxiliary power amplifier in a symmetrical design. This also indicates the output port voltage of the first auxiliary power amplifier and the second auxiliary power amplifier;

[0076] The current flowing through the first transmission line TL1 into the combining node;

[0077] The current flowing through the second transmission line TL2 or the third transmission line TL3 into the combining node is equal in the two auxiliary branches in a symmetrical design.

[0078] The output voltage at the combining node, i.e., the output port voltage of the combiner;

[0079] The transmission coefficient of the combiner (combining network) is used to characterize the transmission characteristics of the combiner from the main power amplifier port to the combined output.

[0080] Transmission coefficient The modulus value characterizes the amplitude transmission characteristics of the combiner;

[0081] Transmission coefficient The phase angle characterizes the phase transmission characteristics of the combiner;

[0082] The amplitude distortion of the combiner indicates the change in power from the low-power region. to saturation point The change in gain;

[0083] Phase distortion of the combiner indicates the amount of phase distortion that occurs when the combiner transitions from the low-power region. to saturation point The amount of phase change;

[0084] Transistor normalized amplitude Gain at the location;

[0085] Transistor normalized amplitude Phase at;

[0086] Transistors in Relative amplitude distortion at the location;

[0087] Transistors in The relative phase at the location;

[0088] Combiner in The relative amplitude compensation amount at the location;

[0089] Combiner in The relative phase compensation amount at the location;

[0090] After cascading transistors and combiners, Residual amplitude error at the location;

[0091] After cascading transistors and combiners, Residual phase error at the location;

[0092] : Optimize the weighting coefficients of the magnitude error term in the objective function;

[0093] : Optimize the weighting coefficients of the phase error term in the objective function;

[0094] Normalized amplitude In the interval The number of discrete sampling points within;

[0095] The overall optimization objective function is the weighted average of the squared residual amplitude error and the residual phase error.

[0096] (II) Theoretical Analysis

[0097] Figure 1 The basic block diagram of the three-channel Doherty amplifier is shown, while its simplified schematic diagram is as follows: Figure 2 As shown in the simplified schematic, the main power amplifier, the first auxiliary power amplifier, and the second auxiliary power amplifier are powered by three current sources. , , The substitutions can be represented as follows:

[0098] (1)

[0099] (2)

[0100] in, The maximum output current (full-scale current) of the main power amplifier. Main power amplifier output current With full-amplitude current The ratio, that is .when When both auxiliary power amplifiers are in the off state (biased to Class C, gate voltage below the turn-on threshold), the output current is zero; when At this time, the two auxiliary power amplifiers begin to conduct, and their output current increases linearly with the increase of input power. When full current is reached The phase term in formula (2) The first and second phase compensation lines are used to ensure that the output signals of the main power amplifier and the two auxiliary power amplifiers are superimposed in phase at the synthesis node. It should be noted that formula (2) is a theoretical model under ideal conditions. In actual design, due to the influence of transistor manufacturing tolerances, parasitic parameters (such as output capacitance, package inductance, etc.) and layout differences, the two auxiliary power amplifiers cannot be completely identical. The phase compensation lines need to be fine-tuned through simulation optimization and debugging.

[0101] The three sub-amplifiers are connected to the first, second, and third transmission lines of the combining network, respectively. The characteristic impedance of the first transmission line TL1 is... The characteristic impedances of the second transmission line TL2 and the third transmission line TL3 are: All are optimal load impedances ,Right now:

[0102] (3)

[0103] Load impedance at the synthesis node for:

[0104] (4)

[0105] The derivation of formula (4) is based on the principle of three-way equal power combining: in the three-way Doherty power amplifier, all three sub-amplifiers operate at the optimal load impedance. At this point, the three currents at the synthesizing node are superimposed in phase, and the total current is three times the single-channel current. Under the condition of maintaining the same output voltage amplitude, the equivalent load impedance presented by the synthesizing node is reduced to one-third of the optimal impedance of a single channel. This impedance is obtained from a standard 50Ω load transformation through a post-matching network (output matching network).

[0106] According to transmission line theory, the ABCD matrices of the first transmission line TL1, the second transmission line TL2, and the third transmission line TL3 in the composite network are as follows:

[0107] (5)

[0108] (6)

[0109] Therefore, in a simplified schematic, the relationship between port voltage and current can be expressed as:

[0110] (7)

[0111] (8)

[0112] in, The voltage at the output port of the main power amplifier. The current flowing into the main transmission line TL1 is negative (the sign is negative to conform to the port current direction definition of the ABCD matrix, i.e., the current flows into the network in the positive direction). To assist the output port voltage of the power amplifier, This refers to the current flowing into auxiliary transmission lines TL2 or TL3; This represents the voltage at the synthesis node; and These are the currents flowing through transmission lines TL1 and TL2 (or TL3) to the combining node.

[0113] according to Figure 2 It can be seen that the current at the synthesis node satisfies Kirchhoff's current law:

[0114] (9)

[0115] The left side of equation (9) represents the sum of the currents flowing into the combining node from the three transmission lines, and the right side represents the current flowing through the combining node to the load. The total outflowing current. The coefficient "2" in the formula indicates that the two auxiliary branches are identical, with each branch providing current. .

[0116] From equations (7) and (8), the relationship between the voltage and current across the transmission line can be further expressed as:

[0117] (10)

[0118] (11)

[0119] Simplifying the second equation regarding current in formulas (10) and (11), we obtain the expression for the current flowing into the combining node from the transmission line:

[0120] (12)

[0121] Substituting formula (12) into formula (9) yields the composite node voltage. The parsing expression:

[0122] (13)

[0123] Here, the transmission coefficient of the synthesizer is defined as Its definition

[0124] (14)

[0125] This transmission coefficient This represents the voltage transfer characteristics of the combiner from the main power amplifier port to the combined output. Because... Follow The amplitude-amplitude (AM-AM) and amplitude-phase (AM-PM) response characteristics of the combiner change with variations in the input power level, directly reflecting the nonlinear behavior of the combiner.

[0126] (15)

[0127] (16)

[0128] In formula (15), This represents the power gain of the combiner, minus its value in... The gain value at the reference point is the relative gain change of the combiner as the input power changes, which is the AM-AM distortion. In formula (16), This represents the transmission phase angle of the combiner, minus its value at the time of transmission. The phase angle value at the reference point is the relative phase change of the combiner as the input power changes, which is the AM-PM distortion.

[0129] From the low-power region to the saturation point, the total amplitude distortion and total phase distortion of the combiner are defined as follows:

[0130] (17)

[0131] (18)

[0132] in, This indicates that the combiner starts from the low power reference point ( (i.e., when the auxiliary amplifier is just turned on) to saturation point ( , which is the total gain change when all power amplifiers reach full output, with positive values ​​indicating gain expansion and negative values ​​indicating gain compression; This represents the total phase change of the combiner from the low-power reference point to the saturation point. A positive value indicates phase lead, and a negative value indicates phase lag.

[0133] (III) Parameter Selection and Design Methods

[0134] Using formulas (17) and (18), Figure 3 Depicting different and Combiner amplitude distortion under parameter combinations and phase distortion The contour map. For example... Figure 3 As shown, when , At this time, the combiner exhibits ideal linear amplitude and phase response ( , ); and when , At this time, the combiner will introduce a specific nonlinear response. For example, such as... Figure 3 As shown in (a), when At this time, the combiner exhibits AM-AM characteristics with gain expansion (…). This can be used to compensate for gain compression in the saturation region of a three-channel Doherty amplifier. Furthermore, such as... Figure 3 As shown in (b), when At this time, the combiner exhibits phase-leading AM-PM characteristics ( ); and when When this occurs, it exhibits phase-lag AM-PM characteristics ( These AM-PM responses can be used to compensate for the inherent phase distortion of the three-channel Dohety amplifier.

[0135] However, the contour plots derived from formulas (17) and (18) alone are insufficient to resolve the multi-objective conflict caused by the coupling of amplitude and phase responses in the two-dimensional parameter space. Therefore, this invention further proposes a multi-objective cooperative optimization criterion:

[0136] First, extract the transistor throughout its entire operating range ( Gain curve from 1 / 3 to 1) and phase curve Instead of extracting only the single distortion value at the saturation point. The relative amplitude distortion of the transistor is referenced to a reference point. and relative phase distortion They are respectively:

[0137] (19)

[0138] (20)

[0139] This constitutes the AM-AM distortion characteristic curve. This constitutes the AM-PM distortion characteristic curve.

[0140] Secondly, in and A two-dimensional traversal scan is performed within the range of values. For each set of parameters, the combiner is calculated using formulas (14) to (16) in the corresponding... Relative amplitude compensation at the location and relative phase compensation amount :

[0141] (twenty one)

[0142] (twenty two)

[0143] According to the superposition principle of cascaded networks, transistor distortion and combiner compensation are superimposed after cascading. The residual amplitude error and residual phase error after cascading are respectively:

[0144] (twenty three)

[0145] (twenty four)

[0146] like and This indicates that the distortion at that power point is completely canceled out, and the cascaded system exhibits ideal linear characteristics.

[0147] because exist As the interval changes continuously, the error also increases. Changes occur with variations, therefore, intervals can be taken at equal or unequal intervals within the interval. For each discrete sampling point, the error value is calculated and arranged in ascending order of power to form a sequence. This sequence completely describes the trajectory of error as power changes, compared to simply taking the saturation point. Compared to evaluation methods that focus only on the endpoints and may ignore residual errors at intermediate power points, this invention ensures global linearity across the entire 9dB backoff range.

[0148] For the entire work area within Given discrete points, define the overall optimization objective function. The mean of the weighted sum of squares of the residual amplitude error and residual phase error after normalization:

[0149] (25)

[0150] in, and These are the amplitude error tolerance and phase error tolerance allowed by the system design specifications, respectively. In this embodiment, the preferred tolerance is... and By introducing the above-mentioned normalization benchmark, the amplitude error and phase error have unified dimensions and physical comparability in the objective function. and The weighting coefficients for amplitude error and phase error are respectively. By minimizing the objective function Choose the one that minimizes the overall residual error. As the optimal combination of parameters.

[0151] When the optimal parameter regions for amplitude compensation and phase compensation do not overlap, it indicates a conflict between the two in the current two-dimensional parameter space. In this case, a compromise can be reached by increasing the weight coefficients of key indicators based on the system's specific linearity requirements. Considering that AM-PM distortion in Doherty power amplifiers is generally more difficult to correct than AM-AM distortion using external digital predistortion (DPD), and that phase distortion has a more significant impact on adjacent channel leakage ratio (ACLR), this embodiment prioritizes ensuring the compensation accuracy of phase distortion and sets... The preferred range is 0.6 to 0.8. The preferred range is 0.2 to 0.4. Through the above weighted optimization, even if the amplitude and phase cannot simultaneously reach the theoretical optimum, the system can still ensure that the cascaded total AM-AM gain fluctuation is better than that within the entire 9dB back-off range. Furthermore, the total AM-PM phase variability is better than This allows for the achievement of optimal linearization in engineering practice.

[0152] Using formulas (15) and (16), Figure 4 Showing different Below are the normalized AM-AM and AM-PM responses of the three-channel Doherty power amplifier combiner as a function of the normalized output. Since the combiner parameters are adjusted to compensate for the nonlinear response of the transistors, the drain efficiency of the three-channel Doherty power amplifier is also affected. Using formulas (10) and (11)... and Different The drain efficiency of the lower three channels of the Doherty power amplifier varies with the normalized output response. For example... Figure 5 As shown, the drain efficiency at the pullback point will increase with... The increase in linearity has decreased, but the decrease is limited, indicating that the present invention can achieve a significant improvement in linearity while maintaining high backoff efficiency.

[0153] Based on the above theoretical analysis, this embodiment designs a linear three-channel Doherty power amplifier operating at 1.9 GHz. The active devices used in both the main and auxiliary power amplifiers are CG2H40010F transistors. The substrate used is a Rogers 4350B with a thickness of 20 mil and a dielectric constant of 3.66. In this design, the gate bias voltage of the main power amplifier is -2.9 V (Class AB bias, quiescent current approximately 5%-10% of full-amplitude current), and the gate bias voltage of the two auxiliary power amplifiers is -4.3 V (Class C bias, quiescent current zero). This bias condition allows the auxiliary power amplifiers to... The transistors begin conducting at a certain time. The drain supply voltage for all transistors is set to 28V. Under this bias condition, the optimal load impedance is obtained through load pull testing. The impedance is 20Ω, therefore the combined impedance is... Can be set to In actual engineering, 7Ω is used.

[0154] To verify the linearization enhancement effect of the proposed method, a traditional three-channel Doherty power amplifier was constructed using an ideal synthesis network as a comparison benchmark, such as... Figure 6 As shown. At the input end, the input matching network (IMN) of the carrier and peak power amplifiers is designed based on the source pull result to achieve optimal power and efficiency matching. Simultaneously, during the IMN design, each sub-amplifier's gate is connected in series with a gate stabilizing resistor or in parallel with an RC stabilizing branch. Specific values ​​are determined through small-signal S-parameter simulation to ensure that the transistor's stability factor K > 1 across the entire operating frequency band and in the low-frequency range, and to satisfy the Rolleiflex condition, avoiding occasional oscillations caused by drastic impedance changes under Class C bias. A phase tuning line is used to align the phase difference between the main and auxiliary power amplifiers, ensuring that the three output signals are superimposed in phase at the combining node. In the ideal combining network, , (Derived as Case-I). The combiner of Case-I produces ideal linear AM-AM and AM-PM responses. Under these conditions, the overall AM-AM and AM-PM responses of the three-channel Doherty power amplifier are entirely determined by the nonlinear characteristics of the active transistors. The normalized AM-AM and AM-PM responses of the three-channel Doherty power amplifier based on the Case-I combining network are as follows: Figure 7 and Figure 8 As shown in the figures, these curves indicate that the three-channel Doherty power amplifier exhibits significant amplitude and phase distortion.

[0155] To compensate for amplitude and phase distortion of active devices, the characteristic parameters of the combiner are determined using the aforementioned multi-objective cooperative optimization criterion. In this embodiment, the measured gain curves of the transistors are extracted. and phase curve Then, the relative amplitude distortion is calculated. and relative phase distortion Set the number of sampling points. Weighting coefficient , The focus is on compensating for phase distortion. Combined with... Figure 3 The contour lines are scanned in two dimensions and traversed. Between 70° and 110°, For all combinations within the range of 160° to 200°, calculate the objective function value for each set of parameters according to formula (25). Ultimately, the choice made Minimum parameter and To construct synthetic networks (Case-II), such as Figure 6 As shown. After applying the Case-II synthesis network, the normalized AM-AM and AM-PM responses of the three Doherty power amplifiers were also plotted. Figure 7 and Figure 8 As can be seen from these curves, using the Case-II combining network, the three-channel Doherty power amplifier exhibits near-linear AM-AM and AM-PM responses throughout the operating range. This indicates that the distortion of the active transistors is compensated by the passive combiner. In other words, the passive combining network exhibits nonlinear characteristics opposite to the inherent distortion of the transistors. Ultimately, the entire three-channel Doherty power amplifier exhibits flat AM-AM and AM-PM responses.

[0156] Furthermore, the simulated drain efficiency of the three-channel Doherty power amplifier using Case-I and Case-II combiners is as follows: Figure 9 As shown in the figure, while linearity was improved using the Case-II combiner, the drain efficiency of the three Doherty power amplifiers decreased. However, the efficiency decrease was limited (the efficiency dropped by about 3-5 percentage points at the 9dB back-off point from about 55% in Case-I to about 50%-52% in Case-II), indicating that the linearization enhancement combiner can effectively introduce nonlinearity compensation while maintaining high back-off efficiency.

[0157] In practical design, due to the influence of transistor parasitic parameters (such as output capacitance, package inductance, etc.) and non-ideal PCB layout, the theoretically calculated... and Iterative optimization requires combining full-circuit electromagnetic simulation. Specifically, this can be achieved after initial determination... and Then, the AM-AM and AM-PM responses of the overall amplifier are extracted through harmonic balance simulation. If the residual distortion exceeds the specification requirements, fine-tuning is performed. and The simulation is repeated until the linearity criterion is met. This iterative optimization process typically converges within 2-3 rounds.

[0158] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A linear three-channel Doherty power amplifier based on synthetic network compensation, characterized in that: include: The system comprises a main power amplifier, a first auxiliary power amplifier, a second auxiliary power amplifier, a three-channel Doherty synthesizer network, a 1-to-3 power divider, a first phase compensation line, a second phase compensation line, and a post-matching network. The input of the main power amplifier is directly connected to the first output of the 1-to-3 power divider. The input of the first auxiliary power amplifier is connected to the second output of the 1-to-3 power divider via the first phase compensation line. The input of the second auxiliary power amplifier is connected to the third output of the 1-to-3 power divider via the second phase compensation line. The outputs of the main power amplifier, the first auxiliary power amplifier, and the second auxiliary power amplifier are respectively connected to the three inputs of the three-channel Doherty synthesizer network. The output of the three-channel Doherty synthesizer network is connected to the post-matching network.

2. The linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The first auxiliary power amplifier is identical to the second auxiliary power amplifier, and the optimal load impedance of all three sub-amplifiers is... ,in This indicates the optimal load impedance value for the transistor to achieve maximum output power and peak efficiency under target bias conditions.

3. The linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The three-way Doherty synthesis network consists of an electrical length of The first transmission line TL1 has an electrical length of The second transmission line TL2 and its electrical length are It consists of the third transmission line TL3; among which, The transmission phase length of the first transmission line TL1, The transmission phase lengths of the second transmission line TL2 and the third transmission line TL3 are used to control the AM-AM distortion and AM-PM distortion characteristics of the synthesized network.

4. The linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 3, characterized in that: The characteristic impedances of the first transmission line TL1, the second transmission line TL2, and the third transmission line TL3 are all .

5. A linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The output of the main power amplifier is connected to the input of the first transmission line TL1 in the three-channel Doherty synthesis network, the output of the first auxiliary power amplifier is connected to the input of the second transmission line TL2 in the three-channel Doherty synthesis network, and the output of the second auxiliary power amplifier is connected to the input of the third transmission line TL3 in the three-channel Doherty synthesis network.

6. The linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The outputs of the first transmission line TL1, the second transmission line TL2, and the third transmission line TL3 in the three-way Doherty synthesis network are connected together to form a synthesis node, which is then connected to the input of the post-matching network.

7. A linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The post-matching network matches the standard 50-ohm impedance to the combined impedance. ,in .

8. A linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The electrical length in the three-way Doherty synthesis network and The synthesis network is configured such that the AM-AM and AM-PM responses of the synthesized network are complementary to the nonlinear distortion characteristics of the transistors in the main power amplifier, the first auxiliary power amplifier, and the second auxiliary power amplifier.

9. A linear three-channel Doherty power amplifier based on synthetic network compensation according to claim 1, characterized in that: The electrical length and Transmission coefficient via combiner The analytical expression of the input signal amplitude and its application in normalized input signal amplitude to The amplitude and phase changes within the range are used to determine this; where... ; It is used to characterize the power transfer characteristics and nonlinear behavior of the combiner from the main power amplifier port to the combined output.

10. A design method for a linear three-channel Doherty power amplifier based on synthetic network compensation as described in any one of claims 1 to 9, comprising the following steps: Step 1: Determine the optimal load impedance of the transistor and combined impedance ,in ; Step 2: Extract the gain curve of the transistor under the target bias. and phase curve ,by Using a reference point, calculate the relative amplitude distortion of the transistor. and relative phase distortion The AM-AM distortion characteristic curves and AM-PM distortion characteristic curves of transistors; among them, and These represent the transistor's normalized current amplitude. Gain and phase at the point; Step 3: Establish the transmission coefficient of the combining network The mathematical model is used to obtain the AM-AM response curve and AM-PM response curve of the combiner. , The analytical relationships of change; Step 4: Calculate the different values ​​according to the following formula. and Combiner amplitude distortion Combiner phase distortion : Step 5: Perform multi-objective collaborative optimization in the two-dimensional parameter space: First, based on the transistor gain curve extracted in the second step... and phase curve Calculate the transistor's normalized amplitude Relative amplitude distortion at the point and relative phase distortion : Then, calculate the combiner in the corresponding Relative amplitude compensation at the location and relative phase compensation amount : calculate exist The cascaded residual amplitude error at each discrete sampling point within the interval and residual phase error sequence : Finally, define the overall optimization objective function. for: in, for exist The number of discrete sampling points in the interval. and These are the amplitude error tolerance and phase error tolerance allowed by the system design specifications, respectively. and The weighting coefficients for amplitude error and phase error are respectively. Choose the objective function that optimizes the overall system. The optimal parameter combination is the one that minimizes the minimum value. and ; Step 6: Based on the calculated optimal... and Design a synthetic network; Step 7: Complete the overall design of the linear three-channel Doherty power amplifier.

Images