Dual-frequency power amplifier adopting analog pre-distortion technology

Abstract

The invention discloses a dual-frequency power amplifier adopting an analog pre-distortion technology, which comprises an analog pre-distortion linearization circuit used for generating a pre-distortion signal; the dual-frequency power amplifier is used for amplifying the pre-distortion signal; the analog predistortion linearization circuit comprises a Wilkinson power divider, a nonlinear generator, an electrically controlled attenuator, a phase shifter and a combiner; the Wilkinson power divider is used for dividing an input signal into two paths; the nonlinear generator is used for superposing the pre-distortion signals; the electrically controlled attenuator is used for controlling the attenuation amount of the signal; the phase shifter is used for controlling the capacitive reactance of the variable capacitance diode through voltage to change the phase; and the combiner is used for combining the two paths of signals into one path of signal. The invention provides a design method of an analog pre-distortion linearization circuit, which can provide a pre-distortion signal for a subsequent dual-frequency power amplifier, and provides a method for carrying out harmonic suppression and dual-frequency matching on the dual-frequency power amplifier.

Description

Technical Field

[0001] The invention belongs to the technical field of power amplifier design, and in particular relates to a dual-frequency power amplifier using analog predistortion technology. Background Art

[0002] Today's society has an increasing demand for multi-band, low-power and high-linearity power amplifiers for 5G communication systems. However, it is difficult for existing dual-band power amplifiers to take into account both efficiency and linear amplification. If power back-off technology is used, even if the linearity of the power amplifier can be improved, this will undoubtedly greatly reduce the efficiency of the power amplifier; if a harmonic suppression power amplifier, such as a Class F power amplifier, is used, although the efficiency can be improved, the linearity of the power amplifier is often very poor. Therefore, further exploration is needed to ensure that the power amplifier can work in dual bands while taking into account efficiency and linearity. Summary of the invention

[0003] The present invention proposes a dual-frequency power amplifier using analog pre-distortion technology to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above object, the present invention provides a dual-frequency power amplifier using analog predistortion technology, comprising:

[0005] An analog predistortion linearization circuit for generating a predistortion signal;

[0006] A dual-band power amplifier, used for amplifying the predistortion signal;

[0007] The analog predistortion linearization circuit includes a Wilkinson power divider, a nonlinear generator, an electrically adjustable attenuator, a phase shifter and a combiner;

[0008] The Wilkinson power divider is used to divide the input signal into two paths;

[0009] The nonlinear generator is used to superimpose the predistortion signal;

[0010] The electrically adjustable attenuator is used to control the attenuation of the signal;

[0011] The phase shifter is used to change the phase by controlling the capacitance of the varactor diode through voltage;

[0012] The combiner is used to combine two signals into one signal.

[0013] Preferably, the dual-band power amplifier comprises a transistor, an RC stabilization circuit, a gate and drain bias circuit, an input matching circuit and an output matching circuit;

[0014] The transistor is used to amplify the input signal;

[0015] The RC stabilization circuit is used to improve the stability of the circuit by filtering out high-frequency noise and oscillation;

[0016] The gate and drain bias circuit is used to provide bias voltage for the gate and drain of the transistor;

[0017] The input matching circuit is used to couple the input signal into the amplifier;

[0018] The output matching circuit is used for harmonic suppression by changing the characteristic impedance and electrical length of the transmission line.

[0019] Preferably, the working method of the analog predistortion linearization circuit includes:

[0020] The input signal is divided into two paths through the Wilkinson power divider, one of which is passed through a nonlinear generator to generate a predistortion signal, and the other is passed through an electrically adjustable attenuator and a phase shifter to cancel each other with the predistortion signal at a combiner to obtain the predistortion signal required by the dual-frequency power amplifier.

[0021] Preferably, the nonlinear generator is designed based on a 3dB directional coupler, and a pair of reverse Schottky diodes are respectively connected to the straight-through tube and the coupling end of the 3dB directional coupler to construct the nonlinear generator.

[0022] Preferably, the structure of the 3dB directional coupler includes:

[0023] A rectangular opening is provided at the center of the bottom layer of the microstrip coupling line;

[0024] A layer of square metal is arranged in the middle of the rectangular opening, and serpentine gaps and small rectangular gaps are opened on the square metal;

[0025] It is connected to the top microstrip line through a metal through-hole to change the coupling capacitance between the bottom microstrip gaps during odd-mode excitation and even-mode excitation.

[0026] Preferably, the output matching circuit includes a harmonic suppression circuit and a fundamental wave matching circuit;

[0027] The harmonic suppression circuit is used to reduce irrelevant harmonic components;

[0028] The fundamental wave matching circuit is used for performing impedance matching of the fundamental wave signal at the output end of the amplifier.

[0029] Preferably, the harmonic suppression circuit constructs a third harmonic control network and a second harmonic control network through transmission lines.

[0030] Preferably, the fundamental wave matching circuit is a π-shaped circuit.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] The present invention combines analog pre-distortion technology with a harmonic suppression dual-frequency power amplifier. The working principle of the analog pre-distortion technology is to load a nonlinear generating circuit with amplitude compensation and phase compensation in front of the power amplifier, so that the input signal generates a nonlinear signal before entering the power amplifier, so as to offset the amplitude and phase distortion of the power amplifier; then, the output matching of the dual-frequency power amplifier is designed, and the harmonics of the microstrip branches are suppressed to achieve the purpose of improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1 It is a schematic diagram of a dual-frequency power amplifier using analog pre-distortion technology according to an embodiment of the present invention;

[0035] Figure 2 It is a schematic diagram of an analog predistortion linearization circuit according to an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of a 3dB directional coupler structure based on a defective ground structure according to an embodiment of the present invention, wherein (a) is a coupling line diagram of the upper surface, and (b) is a groove diagram of the bottom surface;

[0037] Figure 4 It is a simulation diagram of the S parameters of the coupler according to the embodiment of the present invention;

[0038] Figure 5 A phase simulation diagram of the through end and the coupled end of the coupler according to an embodiment of the present invention;

[0039] Figure 6 3.45 GHz attenuation simulation results of an embodiment of the present invention, wherein (a) is a gain expansion diagram and (b) is a phase compression diagram;

[0040] Figure 7 4.85 GHz attenuation simulation results of an embodiment of the present invention, wherein (a) is a gain expansion diagram and (b) is a phase compression diagram;

[0041] Figure 8 A schematic diagram of dual-frequency output matching according to an embodiment of the present invention;

[0042] Fig. 9 A distribution diagram of the position of the impedance of the dual-frequency output matching circuit according to an embodiment of the present invention on a Smith chart;

[0043] Fig.10 A schematic diagram of a dual-band power amplifier according to an embodiment of the present invention;

[0044] Fig.11 is a curve showing gain compression versus output power according to an embodiment of the present invention;

[0045] Fig.12 FIG. 4 is a curve showing a change in power added efficiency versus frequency according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0047] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0048] Embodiment 1

[0049] like Figure 1 As shown, this embodiment provides a dual-band power amplifier using analog predistortion technology, including:

[0050] An analog predistortion linearization circuit for generating a predistortion signal;

[0051] A dual-band power amplifier for amplifying the predistorted signal;

[0052] The analog predistortion linearization circuit includes a Wilkinson power divider, a nonlinear generator, an electrically adjustable attenuator, a phase shifter and a combiner;

[0053] The Wilkinson power divider is used to split the input signal into two paths;

[0054] The nonlinear generator is used to superimpose the predistortion signal;

[0055] The electrically adjustable attenuator is used to control the attenuation of the signal;

[0056] Phase shifters are used to change the phase by controlling the capacitance of a varactor diode via voltage;

[0057] A combiner is used to combine two signals into one signal.

[0058] The dual-band power amplifier includes a transistor, an RC stabilization circuit, a gate and drain bias circuit, an input matching circuit and an output matching circuit;

[0059] Transistors are used to amplify input signals;

[0060] RC stabilization circuits are used to improve the stability of circuits by filtering out high frequency noise and oscillations;

[0061] The gate and drain bias circuit is used to provide bias voltage for the gate and drain of the transistor;

[0062] The input matching circuit is used to couple the input signal into the amplifier;

[0063] Output matching circuits are used to suppress harmonics by changing the characteristic impedance and electrical length of the transmission line.

[0064] The working method of the analog predistortion linearization circuit includes:

[0065] The input signal is divided into two paths through the Wilkinson power divider. One of the signals is passed through a nonlinear generator to generate a predistortion signal, and the other signal is passed through an electrically adjustable attenuator and a phase shifter to cancel each other with the predistortion signal at the combiner to obtain the predistortion signal required by the dual-band power amplifier.

[0066] The specific structure of the dual-band power amplifier is as follows:

[0067] The dual-band power amplifier designed in this embodiment is mainly divided into two parts, the first part is an analog pre-distortion linearization circuit, and the second part is a dual-band power amplifier. First, a signal is input and passed through a Wilkinson power divider to divide it into two signals. The signal of the lower branch generates a pre-distortion signal after passing through a nonlinear generator. The signal of the upper branch is offset by the baseband signal of the nonlinear signal at the combiner under the action of an electrically adjustable attenuator and a phase shifter, and only the pre-distortion signal required by the dual-band power amplifier is retained. Finally, the pre-distortion signal is driven by the power amplifier to adjust the output power, so that the dual-band power amplifier obtains the required input power, completing the analog pre-distortion process.

[0068] Figure 2 This is the schematic diagram of the analog predistortion linearization circuit of the present invention. The circuit is mainly composed of a Wilkinson power divider, an attenuator, a phase shifter and a nonlinear generator.

[0069] Both the phase shifter and the nonlinear generator are designed based on a 3dB directional coupler. Figure 3 The invention discloses a 3dB directional coupler based on a defective ground structure.

[0070] like Figure 3 As shown, a rectangular opening with a length of L2 and a width of W2 is opened at the center of the bottom layer of the microstrip coupling line. In the middle of the rectangular opening, a layer of square metal with a length of W3 is added directly below the coupling line, and a serpentine gap with a width of Wg and four small rectangular gaps are opened on the square metal. Finally, it is connected to the top microstrip line through a metal through-hole with a radius of R. This method changes the coupling capacitance between the bottom microstrip gaps during odd-mode excitation and even-mode excitation, which can not only enhance the coupling degree but also reduce the processing difficulty of the coupler.

[0071] like Figure 3 As shown, the length of the microstrip coupling line is L, and the operating frequency band of the coupler can be changed by adjusting its length.

[0072] like Figure 3 As shown in the figure, a serpentine gap with a width of Wg and four small rectangular gaps are opened on the square metal below the microstrip line, and finally connected to the top microstrip line through a metal through-hole with a radius of R. In this way, the purpose of expanding the spacing s of the microstrip coupling lines can be achieved, which not only enhances the coupling degree but also reduces the processing difficulty of the coupler.

[0073] like Figure 3 As shown, four rectangular slots with a width of W1 and a length of L1 are opened on the left and right sides of the microstrip coupling line. Through this method, two resonance points can be generated, which can be superimposed on each other to expand the working bandwidth of the coupler.

[0074] like Figure 3 As shown, four rectangular branches with a width of a and a length of b are added on the left and right sides of the microstrip coupling line. This method is equivalent to adding a filter capacitor, which can make the fluctuation of the scattering parameters S21 and S31 smoother.

[0075] like Figure 4 As shown, the coupling degree of the coupler designed by the invention is 3.2dB±0.2dB in the two frequency bands of 3.3-3.6GHz and 4.8-4.9GHz, and the return loss and isolation are both greater than 16dB. It can be used in the design of nonlinear generators and phase shifters.

[0076] like Figure 5 As shown, the phase difference between the straight-through pipe and the coupled end of the coupler is approximately 90°.

[0077] like Figure 2 As shown in the figure, a pair of reverse Schottky diodes are connected to the coupler through-tube and the coupled end respectively to construct a nonlinear generator. Since the through-end and the coupled end have a 90° phase difference and the two ports are well isolated, the standing wave of the circuit can be reduced. Through this reflective structure, the reverse Schottky diode pair can superimpose the pre-distortion signal, and then adjust the phase compression and gain expansion of the nonlinear generator by adjusting the size of Vg.

[0078] like Figure 2 As shown, the attenuator of the present invention is powered by v1, and v2 controls the attenuation of the signal, thereby achieving the purpose of controlling the size of the upper branch signal.

[0079] like Figure 2 As shown, the phase shifter is a variable capacitance diode connected to the coupler through-tube and the coupling end, and the capacitance of the diode is controlled by the voltage Vc, so as to achieve the purpose of changing the phase.

[0080] Figure 6 and Figure 7 By changing the phase compression and gain expansion curves at two frequencies after the attenuation, it can be obtained that the predistortion linearization circuit has good phase compression and gain expansion capabilities, and the size of the phase compression and gain expansion can be controlled by controlling the attenuation.

[0081] The power amplifier structure is shown in the figure Figure 8 As shown, it mainly includes transistors, RC stabilization circuits, gate and drain bias circuits, and input / output matching circuits

[0082] Figure 8 The schematic diagram of the output matching circuit of the present invention includes two parts: a dual-frequency harmonic control circuit and a dual-frequency fundamental matching circuit. The dual-frequency harmonic control network is established by using a quarter-wavelength transmission line. We can perform harmonic suppression by changing the characteristic impedance and electrical length of the transmission line. The third harmonic control network is designed using transmission lines T1, T2 and T3, and T4, T5, T6 and T7 are used to design the second harmonic control network. At the same time, T7 can also be used as a drain bias circuit. By setting the characteristic impedance and electrical length of T1 to T7, the second harmonic in the two frequency bands is short-circuited and the third harmonic is open-circuited. The fundamental matching is then performed through the subsequent Π-shaped circuit to complete the design of the entire output matching.

[0083] like Figure 8 As shown, the center frequencies of the two frequency bands are f1 and f2 (f1 is less than f2), k = f2 / f1,

[0084] The three branches T1, T2 and T3 are used to control the third harmonic and make it reach the open circuit state, so we can get:

[0085]

[0086] The characteristic impedance is infinite in the open circuit state, so according to the above formula we can get Z1, θ1, θ2, and θ3.

[0087] T4, T5, T6 and T7 are used to design the second harmonic control network to achieve the purpose of short-circuiting the second harmonic. In order to short-circuit the second harmonic, θ6 = π / 4. At the same time, T7 also plays the role of the drain bias circuit. The other parameters are free parameters. By adjusting them on ADS, they can be used to further optimize the harmonic suppression effect.

[0088] like Figure 8 As shown, fundamental wave matching is achieved through a π-shaped circuit.

[0089] like Fig. 9The figure shows the position distribution of the impedance of the dual-frequency output matching circuit on the Smith chart. It can be seen that the second harmonic and third harmonic impedances in the two frequency bands are close to the edge of the Smith chart (generally the edge is the high efficiency area of ​​the second harmonic and third harmonic).

[0090] The schematic diagram of the dual-band power amplifier is as follows: Fig.10 shown.

[0091] Input matching network: The left side of the circuit starts with a 50Ω impedance, which represents the signal source impedance (usually 50Ω). This is followed by a series of transmission line segments whose length and width (in millimeters) are precisely designed to achieve a specific impedance transformation.

[0092] Transmission line segment: Each microstrip line segment is considered as an impedance transformer, and its length determines its electrical length, which affects its operating characteristics at a specific frequency. For example, a microstrip line with a length of 1 / 4 wavelength acts as an impedance transformer, transforming one impedance into another impedance.

[0093] Output matching network: It is used to match the conjugate impedance of the transistor output impedance to the load impedance (usually 50Ω), so as to achieve the purpose of maximum power transmission of the output signal.

[0094] Bias circuit: The function of the bias circuit is to provide a stable power supply voltage for the operation of the transistor. It also has a certain filtering capability to prevent the RF signal from flowing into the DC power supply and damaging it. There are two bias voltages (V G and V D ), V G is the gate voltage used to control the quiescent operating point of the transistor, V D is the drain voltage, which is used to provide DC power. Transistors are used in power amplifiers to amplify signals.

[0095] Fig.11 The curve of gain compression versus output power after the overall circuit is cascaded. We can see that after adding the analog pre-distortion circuit in the two frequency bands of 3.45 / 4.85GHz, the gain compression drops from 2.5dB to less than 1dB at 40dBm output, and the gain flatness is significantly improved.

[0096] Fig.12 is a curve of power added efficiency changing with frequency. It can be seen from the figure that compared with the case where no analog pre-distortion circuit is added, the efficiency of the overall circuit is improved by 3% to 6%.

[0097] The advantages of the present invention are as follows: (1) A more detailed and vivid explanation of the working principle of a dual-band power amplifier using analog pre-distortion technology is provided; (2) The power amplifier can work in dual frequency bands while taking into account both efficiency and linearity. (3) A detailed design method is provided, which can be used not only in the 3.3-3.6 GHz and 4.8-4.9 GHz dual frequency bands, but also in the design of other frequency bands.

[0098] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A dual-band power amplifier using analog predistortion technology, characterized in that: include: An analog predistortion linearization circuit for generating a predistortion signal; A dual-band power amplifier, used for amplifying the predistortion signal; The analog predistortion linearization circuit includes a Wilkinson power divider, a nonlinear generator, an electrically adjustable attenuator, a phase shifter and a combiner; The Wilkinson power divider is used to divide the input signal into two paths; The nonlinear generator is used to superimpose the predistortion signal; The electrically adjustable attenuator is used to control the attenuation of the signal; The phase shifter is used to change the phase by controlling the capacitance of the varactor diode through voltage; The combiner is used to combine two signals into one signal.

2. The dual-band power amplifier according to claim 1, characterized in that: The dual-frequency power amplifier includes a transistor, an RC stabilization circuit, a gate and drain bias circuit, an input matching circuit and an output matching circuit; The transistor is used to amplify the input signal; The RC stabilization circuit is used to improve the stability of the circuit by filtering out high-frequency noise and oscillation; The gate and drain bias circuit is used to provide bias voltage for the gate and drain of the transistor; The input matching circuit is used to couple the input signal into the amplifier; The output matching circuit is used for harmonic suppression by changing the characteristic impedance and electrical length of the transmission line.

3. The dual-band power amplifier according to claim 1, characterized in that: The working method of the analog predistortion linearization circuit comprises: The input signal is divided into two paths through the Wilkinson power divider, one of which is passed through a nonlinear generator to generate a predistortion signal, and the other is passed through an electrically adjustable attenuator and a phase shifter to cancel each other with the predistortion signal at a combiner to obtain the predistortion signal required by the dual-frequency power amplifier.

4. The dual-band power amplifier according to claim 1, characterized in that: The nonlinear generator is designed based on a 3dB directional coupler, and a pair of reverse Schottky diodes are respectively connected to the straight-through tube and the coupling end of the 3dB directional coupler to construct the nonlinear generator.

5. The dual-band power amplifier according to claim 4, characterized in that: The structure of the 3dB directional coupler includes: A rectangular opening is provided at the center of the bottom layer of the microstrip coupling line; A layer of square metal is arranged in the middle of the rectangular opening, and serpentine gaps and small rectangular gaps are opened on the square metal; It is connected to the top microstrip line through a metal through-hole to change the coupling capacitance between the bottom microstrip gaps during odd-mode excitation and even-mode excitation.

6. The dual-band power amplifier according to claim 2, characterized in that: The output matching circuit includes a harmonic suppression circuit and a fundamental wave matching circuit; The harmonic suppression circuit is used to reduce irrelevant harmonic components; The fundamental wave matching circuit is used for performing impedance matching of the fundamental wave signal at the output end of the amplifier.

7. The dual-band power amplifier according to claim 6, characterized in that: The harmonic suppression circuit constructs a third harmonic control network and a second harmonic control network through transmission lines.

8. The dual-band power amplifier according to claim 6, characterized in that: The fundamental wave matching circuit is a π-shaped circuit.

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