CN112054978A - Double-branch analog predistortion system - Google Patents
Double-branch analog predistortion system Download PDFInfo
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- CN112054978A CN112054978A CN202010794348.8A CN202010794348A CN112054978A CN 112054978 A CN112054978 A CN 112054978A CN 202010794348 A CN202010794348 A CN 202010794348A CN 112054978 A CN112054978 A CN 112054978A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
- H04L25/40—Transmitting circuits; Receiving circuits
- H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
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- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3241—Modifications of amplifiers to reduce non-linear distortion using predistortion circuits
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Abstract
The invention provides a double-branch analog predistortion system, which comprises a dielectric substrate, a coupler 1, a nonlinear generator 2 and a coupler 2. The coupler 1 divides the radio frequency signal into two parts and outputs the two parts to the nonlinear generator 1 and the nonlinear generator 2 respectively. The nonlinear generator 1 utilizes nonlinearity of a field effect transistor to perform predistortion on a first radio frequency output signal to obtain a distorted signal 1, and the nonlinear generator 2 utilizes nonlinearity of a Schottky diode to perform predistortion on a second radio frequency output signal to obtain a distorted signal 2. And the distortion signal 1 and the distortion signal 2 are combined by the coupler 2 to obtain an analog predistortion output signal. The invention utilizes the double-branch structure to complement the distortion characteristic advantages of the Schottky diode and the field effect transistor, and improves the predistortion precision of the whole analog predistortion system. The circuit is simple in structure, only two paths of control voltages need to be adjusted during actual operation, and the circuit has the characteristics of low power consumption and low cost.
Description
Technical Field
The invention relates to a predistortion system, in particular to an analog predistortion system with a double-branch structure for a 5G small base station.
Background
The arrival of 5G will introduce nr (new radio) new air interface and new network architecture. The 5G small base station scheme can be used for improving network performance indexes such as peak rate, time delay and capacity. The large-scale small base station technology puts higher requirements on the aspects of power consumption, stability, cost and the like of the whole system.
The power amplifier is a core component of a 5G small base station communication system. Since the dynamic range of a general Power amplifier is limited, a signal with a large Peak to Average Power Ratio (PAPR) easily enters a nonlinear region of the Power amplifier, and while the output Power of the Power amplifier is continuously increased, the nonlinear distortion of the PA is increased, thereby causing obvious spectrum spreading interference and in-band signal distortion, and finally causing the performance of the whole wireless communication system to be seriously reduced. In order to ensure that the power amplifier can obtain higher output power and better linearity at the same time, thereby ensuring efficient and stable operation of the 5G small cell, a certain linearization measure is usually adopted to improve the nonlinear distortion of the power amplifier.
Predistortion systems are currently the main means to improve power amplifier nonlinearity. Predistortion systems are mainly classified into digital predistortion systems and analog predistortion systems. The analog predistortion system automatically adjusts the control voltage of the analog predistortion system by observing the signal of the output end of the power amplifier after predistortion according to the signal, so that the signal of the output end of the power amplifier after predistortion meets the requirement, and therefore the adjustment of predistortion parameters can be realized. Compared with a digital predistortion system, the analog predistortion system has lower cost, simple predistortion operation process and wide application.
The traditional analog predistortion system has simple structure, small volume and low power consumption, but has limited improvement amount on the nonlinearity of the power amplifier and larger limitation in practical application. The nonlinear devices used in the mainstream analog predistortion systems are generally schottky diodes or field effect transistors. The analog predistortion system based on the Schottky diode can effectively improve the output power and efficiency of a power amplifier aiming at the amplitude and the phase of a signal, and therefore, the analog predistortion system is also the mainstream application direction of modern communication. However, the analog predistortion system based on the schottky diode has a weak improvement effect on the broadband signal, and researches show that the analog predistortion system has a remarkable effect on third-order intermodulation, but is very easy to show a deterioration condition on a higher-order distortion component, and when the analog predistortion system is used for the currently most widely used broadband modulation signal, the predistortion precision is very poor, so that the application field of the analog predistortion system is greatly limited. The field effect transistor-based analog predistortion system is excellent in performance when distortion of broadband signals is improved, and researches show that the analog predistortion has a remarkable effect on improving distortion components of high-order signals, but the effect is weaker in improving next third-order intermodulation distortion. At present, in order to enhance the predistortion accuracy of an analog predistortion system, the circuit structure is usually designed, so that the whole system is complex and huge, the cost is increased, and in addition, the operation process becomes abnormally complex because a plurality of paths of control voltages need to be adjusted in the actual operation.
Disclosure of Invention
The invention aims to provide a double-branch analog predistortion system which is improved based on the existing analog predistortion structure, and solves the problems that in the prior art, a distortion system based on a Schottky diode is poor in predistortion precision of a high-order distortion component and a distortion system based on a field effect transistor is poor in third-order intermodulation distortion effect by utilizing a simple circuit structure.
The purpose of the invention is realized by the following technical scheme:
the double-branch analog predistortion system comprises a dielectric substrate, a first coupler, a first nonlinear generator, a second nonlinear generator and a second coupler; wherein said first coupler, said first nonlinear generator, said second nonlinear generator and said second coupler are disposed on the upper surface of the dielectric substrate; said first non-linear generator and said second non-linear generator being connected in parallel, said first non-linear generator comprising a field effect transistor and said second non-linear generator comprising a schottky diode; the first coupler divides an input radio frequency signal into a first radio frequency output signal and a second radio frequency output signal and then respectively outputs the first radio frequency output signal and the second radio frequency output signal to the first nonlinear generator and the second nonlinear generator; the first nonlinear generator utilizes nonlinearity generated by the field effect transistor to carry out predistortion on the first radio frequency output signal to obtain a first distortion signal; the second nonlinear generator utilizes nonlinearity generated by the Schottky diode to pre-distort the second radio frequency output signal to obtain a second distortion signal; and the first distortion signal and the second distortion signal are respectively input into the second coupler through the first input end and the second input end of the second coupler to be combined, so that an analog predistortion output signal is obtained.
Further, the first nonlinear generator further comprises a first bias circuit, a second bias circuit, a first direct current power supply, a second direct current power supply, a first coupling microstrip circuit, a second coupling microstrip circuit, a first matching microstrip line and a second matching microstrip line; one end of the first coupling microstrip circuit inputs the first radio frequency output signal, and the other end of the first coupling microstrip circuit is connected with the radio frequency input end of the first bias circuit; the radio frequency output end of the first bias circuit is connected with the grid electrode of the field effect transistor through the first matching microstrip line; the direct current input end of the first bias circuit is connected with the anode of the first direct current power supply; the negative electrode of the first direct current power supply is grounded; the source electrode of the field effect transistor is grounded, and the drain electrode of the field effect transistor is connected with the radio frequency input end of the second bias circuit through the second matching microstrip line; the radio frequency output end of the second bias circuit is connected with one end of the second coupling microstrip circuit, and the direct current input end of the second bias circuit is connected with the anode of the second direct current power supply; the negative electrode of the second direct current power supply is grounded; the other end of the second coupling microstrip circuit is used as the output end of the first nonlinear generator and is connected to the first input end of the second coupler.
Furthermore, the second nonlinear generator further comprises a third bias circuit, a third direct-current power supply, a third coupling microstrip circuit, a fourth coupling microstrip circuit, a third matching microstrip line and a fourth matching microstrip line; one end of the third coupling microstrip circuit inputs the second radio frequency output signal, and the other end of the third coupling microstrip circuit is connected with the anode of the Schottky diode and the radio frequency input end of the third bias circuit through a third matching microstrip line; the cathode of the Schottky diode is grounded; the radio frequency output end of the third bias circuit is connected with one end of a fourth coupling microstrip circuit through a fourth matching microstrip line; the direct current input end of the third bias circuit is connected with the anode of the third direct current power supply; the negative electrode of the third direct current power supply is grounded; the other end of the fourth coupling microstrip circuit is used as the output end of the second nonlinear generator and is connected to the second input end of the second coupler.
Furthermore, the first bias circuit, the second bias circuit and the third bias circuit are the same bias circuit, and the bias circuit comprises a first T-shaped junction, a first rectangular microstrip line, a second rectangular microstrip line, a third rectangular microstrip line, a fourth rectangular microstrip line, a first fan-shaped microstrip line and a second fan-shaped microstrip line; the first port of the first T-shaped junction is the radio frequency input end of the bias circuit, and the second port of the first T-shaped junction is the radio frequency output end of the bias circuit; one end of the third rectangular microstrip line is used as a direct current input end of the bias circuit, and direct current voltage sequentially passes through the third rectangular microstrip line, the second rectangular microstrip line and the first rectangular microstrip line and then is input to a third port of the first T-shaped junction; the first fan-shaped microstrip line and the second fan-shaped microstrip line are symmetrically connected to two sides of the fourth rectangular microstrip line.
Furthermore, the first rectangular microstrip line is a quarter-wavelength microstrip line; the first fan-shaped microstrip line and the second fan-shaped microstrip line are quarter fan-shaped open-loop microstrip lines.
Further, the first coupler and the second coupler are 3dB bridges with the same structure; the 3dB bridge comprises a fifth rectangular microstrip line, a sixth rectangular microstrip line, a seventh rectangular microstrip line, an eighth rectangular microstrip line, a ninth rectangular microstrip line, a tenth rectangular microstrip line, an eleventh rectangular microstrip line, a twelfth rectangular microstrip line, a second T-shaped junction, a third T-shaped junction, a fourth T-shaped junction and a fifth T-shaped junction; one end of the fifth rectangular microstrip line is the input end of the 3dB bridge, and the other end of the fifth rectangular microstrip line is connected with the first port of the second T-shaped junction; a second port of the second T-shaped junction is connected to a first port of the third T-shaped junction through the eighth rectangular microstrip line, and a third port of the second T-shaped junction is connected to a third port of the fourth T-shaped junction through the seventh rectangular microstrip line; the second port of the third T-shaped junction is connected with one end of the eleventh rectangular microstrip line, and the other end of the eleventh rectangular microstrip line is a straight-through end of the 3dB bridge; the third port of the third T-shaped junction is connected to the third port of the fifth T-shaped junction through the tenth rectangular microstrip line; one end of the sixth rectangular microstrip line is an isolation end of the 3dB bridge, and the other end of the sixth rectangular microstrip line is connected with the first port of the fourth T-shaped junction; the second port of the fourth T-shaped junction is connected to the first port of the fifth T-shaped junction through the ninth rectangular microstrip line; the second port of the fifth T-shaped junction is connected with one end of the twelfth rectangular microstrip line; the other end of the twelfth rectangular microstrip line is a coupling end of the 3dB bridge.
Furthermore, the first coupling microstrip circuit, the second coupling microstrip circuit, the third coupling microstrip circuit and the fourth coupling microstrip circuit are the same coupling microstrip circuit; the coupling microstrip circuit comprises a thirteenth rectangular microstrip line, a fourteenth rectangular microstrip line, a fifteenth rectangular microstrip line and a sixteenth rectangular microstrip line; one end of the thirteenth rectangular microstrip line is the input end of the coupling microstrip circuit, and the other end of the thirteenth rectangular microstrip line is connected with one end of the fifteenth rectangular microstrip line; the sixteenth rectangular microstrip line is positioned below the fifteenth rectangular microstrip line, and a gap is formed between the sixteenth rectangular microstrip line and the fifteenth rectangular microstrip line; the other end of the sixteenth rectangular microstrip line is connected with one end of the fourteenth rectangular microstrip line, and the other end of the fourteenth rectangular microstrip line is used as the output end of the coupling microstrip circuit.
Further, a gap between the fifteenth rectangular microstrip line and the sixteenth rectangular microstrip line is 0.13 mm.
The double-branch simulation predistortion system of the invention utilizes the double-branch structure to complement the distortion characteristic advantages of the Schottky diode and the field effect transistor, thereby improving the predistortion precision of the whole simulation predistortion system. The circuit is simple in structure, only two paths of control voltages need to be adjusted during actual operation, and the circuit has the characteristics of low power consumption and low cost.
Drawings
FIG. 1 is a diagram of a two-branch analog predistortion system of the present invention;
FIG. 2 is a bias circuit diagram of the present invention;
FIG. 3 is a graph of the bias circuit simulation results of the present invention;
FIG. 4 is a circuit diagram of a coupler of the present invention;
FIG. 5 is a graph of coupler simulation results of the present invention;
FIG. 6 is a circuit diagram of a coupling microstrip of the present invention;
FIG. 7 is a simulation diagram of a coupled microstrip circuit of the present invention;
FIG. 8 is a comparison graph of the results of actual measurement according to the present invention.
Detailed Description
The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.
The embodiments of the present disclosure are described below with specific examples, and other advantages and effects of the present disclosure will be readily apparent to those skilled in the art from the disclosure in the specification. It is to be understood that the described embodiments are merely illustrative of some, and not restrictive, of the embodiments of the disclosure. The disclosure may be embodied or carried out in various other specific embodiments, and various modifications and changes may be made in the details within the description without departing from the spirit of the disclosure. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.
The two-branch analog predistortion system of the invention, as shown in fig. 1, comprises a dielectric substrate, a coupler 1, a nonlinear generator 2 and a coupler 2. Wherein the coupler 1, the nonlinear generator 2 and the coupler 2 are disposed on the upper surface of the dielectric substrate. The coupler 1 has an input, a first output and a second output. The coupler 2 has a first input, a second input and an output. The non-linear generator 1 and the non-linear generator 2 form a parallel two-branch structure. The input of the non-linear generator 1 is connected to the first output of the coupler 1, and the input of the non-linear generator 2 is connected to the second output of the coupler 1. The output terminal of the non-linear generator 1 is connected to the first input terminal of the coupler 2, and the output terminal of the non-linear generator 2 is connected to the second input terminal of the coupler 2. The non-linearity generator 1 comprises a field effect transistor and uses the non-linearity generated by the field effect transistor itself for pre-distortion. The non-linear generator 2 comprises a schottky diode and uses the non-linearity generated by the schottky diode itself for predistortion.
When a radio frequency signal is input into the double-branch analog predistortion system, the coupler 1 divides the radio frequency signal into two parts and outputs the two parts to the nonlinear generator 1 and the nonlinear generator 2 through a first output end and a second output end of the coupler 1 respectively. The nonlinear generator 1 and the nonlinear generator 2 perform predistortion processing on input radio frequency signals in an amplitude expansion mode to generate a distorted signal 1 and a distorted signal 2 respectively, and the distorted signal 1 and the distorted signal 2 are input to the coupler 2 through a first input end and a second input end of the coupler 2 respectively to perform combined processing to obtain an analog predistortion output signal RFout.
Further, in a preferred embodiment provided in the present application, the nonlinear generator 1 further includes a bias circuit 1, a bias circuit 2, a DC power supply DC1, a DC power supply DC2, a coupling microstrip circuit 1, a coupling microstrip circuit 2, a matching microstrip line 1, and a matching microstrip line 2. The bias circuit 1 and the bias circuit 2 respectively have a radio frequency input terminal, a direct current input terminal and an output terminal. One end of the coupling microstrip circuit 1 is used as the input end of the nonlinear generator 1 to be connected with the first radio frequency output signal of the coupler 1, and the other end of the coupling microstrip circuit 1 is connected with the radio frequency input end of the bias circuit 1. The radio frequency output end of the bias circuit 1 is connected with the gate of the field effect transistor Q1 through the matching microstrip line 1. The DC input terminal of the bias circuit 1 is connected to the positive terminal of the DC power supply DC1, and the negative terminal of the DC power supply DC1 is grounded. The source of the field effect transistor Q1 is grounded, and the drain of the field effect transistor Q1 is connected to the radio frequency input terminal of the bias circuit 2 through the matching microstrip line 2. The radio frequency output end of the bias circuit 2 is connected with one end of the coupling microstrip circuit 2, and the direct current input end of the bias circuit 2 is connected with the positive pole of the direct current power supply DC 2. The negative pole of the direct current source DC2 is connected to ground, and the other end of the coupling microstrip circuit 2 is connected as an output of the non-linear generator 1 to a first input of the coupler 2.
The working principle of the nonlinear generator 1 is as follows: the coupling microstrip circuit 1 and the coupling microstrip circuit 2 are equivalent to capacitors, and play a role in conducting alternating current and isolating direct current, so that direct current voltage is prevented from flowing to RFin or RFout, and external devices are prevented from being damaged. Radio frequency signals (equivalent to alternating current signals) are transmitted to the grid electrode of the field effect transistor Q1 through the coupling microstrip circuit 1 and the matching microstrip line 1, and are output through the matching microstrip line 2 and the coupling microstrip circuit 2 after being pre-distorted due to the nonlinearity of the field effect transistor Q1. The bias circuit 1 and the bias circuit 2 play a role of isolating direct current and alternating current, and prevent the radio-frequency signals output by the coupling microstrip circuit 1 or the coupling microstrip circuit 2 from flowing to a direct-current power supply and damaging the direct-current power supply.
In the nonlinear generator 1, the gate voltage and the drain voltage of the field effect transistor Q1 are controlled to bias the field effect transistor to a nonlinear region, and a distortion signal having a characteristic opposite to the nonlinear distortion of the power amplifier is generated to compensate the nonlinear distortion of the power amplifier. The microstrip line 1 and 2 is a microwave transmission line formed by a single conductor strip supported on a dielectric substrate, and has two functions: firstly, high-frequency signals can be transmitted more effectively; secondly, a matching network is formed by the bias circuit and other solid devices, so that the radio frequency output end of the bias circuit 1 is well matched with the grid electrode of the field effect transistor Q1, or the drain electrode of the field effect transistor Q1 is well matched with the radio frequency input end of the bias circuit 2. In the preferred embodiment provided by the present invention, the impedance of the matching microstrip line 1 and the matching microstrip line 2 is 50 Ω. The field effect transistor Q1 generates different nonlinear signals by controlling the voltages output by the direct current power supplies DC1 and DC 2.
Further, in a preferred embodiment provided by the present application, the nonlinear generator 2 further includes a bias circuit 3, a DC power supply DC3, a coupling microstrip circuit 3, a coupling microstrip circuit 4, a matching microstrip line 3, and a matching microstrip line 4. The bias circuit 3 has a radio frequency input terminal, a direct current input terminal, and an output terminal. One end of the coupling microstrip circuit 3 is used as the input end of the nonlinear generator 2 to be connected with the second radio frequency output signal of the coupler 1, and the other end of the coupling microstrip circuit 3 is connected with the anode of the schottky diode D1 and the radio frequency input end of the bias circuit 3 through the matching microstrip line 3. The cathode of schottky diode D1 is grounded. The radio frequency output end of the bias circuit 3 is connected with one end of the coupling microstrip circuit 4 through the matching microstrip line 4. The DC input of the bias circuit 3 is connected to the positive terminal of a DC power supply DC 3. The negative terminal of the DC power supply DC3 is grounded. The other end of the coupling microstrip circuit 4 is connected as an output of the non-linear generator 2 to a second input of the coupler 2.
In the nonlinear generator 2, the bias voltage of the schottky diode is controlled to bias the schottky diode to a nonlinear region, and a distortion signal having a characteristic opposite to the nonlinear distortion of the power amplifier is generated to compensate the nonlinear distortion of the power amplifier. The voltage output by the DC power supply DC3 is controlled to generate different nonlinear signals for the schottky diode D1. The coupling microstrip circuit 3 and the coupling microstrip circuit 4 are equivalent to capacitors, and play a role of alternating current and direct current conduction and isolation, so that direct current voltage is prevented from flowing to RFin or RFout, and external devices are prevented from being damaged. The bias circuit 3 plays a role of isolating direct current and alternating current, and prevents the radio frequency signal output by the coupling microstrip circuit 3 or the coupling microstrip circuit 4 from flowing to the direct current power supply and damaging the direct current power supply.
The matching microstrip line 3 and the matching microstrip line 4 are microwave transmission lines each formed of a single conductor strip supported on a dielectric substrate, and have an impedance of 50 Ω. Its action is similar to that of the matching microstrip line 1 and matching microstrip line 2.
Further, in a preferred embodiment provided herein, the bias circuit 1, the bias circuit 2 and the bias circuit 3 are the same. Taking the bias circuit 1 as an example for explanation, the bias circuit 1 includes a first T-junction Tee1, a first rectangular microstrip line TL1, a second rectangular microstrip line TL2, a third rectangular microstrip line TL3, a fourth rectangular microstrip line TL4, a first fan-shaped microstrip line Stub1, and a second fan-shaped microstrip line Stub 2. The first rectangular microstrip line is a quarter-wavelength microstrip line and has an impedance of 100 Ω. The first fan-shaped microstrip line and the second fan-shaped microstrip line are both quarter fan-shaped annular open-circuit microstrip lines, and the impedance is 50 omega. The first T-junction Tee1 has a first port, a second port, and a third port. The first port of the first T-shaped junction is the radio frequency input end of the bias circuit 1, the second port of the first T-shaped junction is the radio frequency output end of the bias circuit 1, and the third port of the first T-shaped junction is connected with the front end of the first rectangular microstrip line. The rear end of the first rectangular microstrip line is connected with the front end of the fourth rectangular microstrip line, the first fan-shaped microstrip line is positioned on the left side of the fourth rectangular microstrip line, and the second fan-shaped microstrip line is positioned on the right side of the fourth rectangular microstrip line. The first fan-shaped microstrip line and the second fan-shaped microstrip line are symmetrical left and right relative to the fourth rectangular microstrip line. The inner circle surface of the first fan-shaped microstrip line is connected with the left end of the fourth rectangular microstrip line, and the inner circle surface of the second fan-shaped microstrip line is connected with the right end of the fourth rectangular microstrip line. The rear end of the fourth rectangular microstrip line is connected with the front end of the second rectangular microstrip line, and the rear end of the second rectangular microstrip line is connected with the front end of the third rectangular microstrip line. The rear end of the third rectangular microstrip line is the direct current input end of the bias circuit 1. The structure of the bias circuit 2 is the same as that of the bias circuit 1. The bias circuit 1 adopts a fan-shaped open circuit structure, and can effectively prevent the direct current bias circuit from influencing the impedance characteristics of each part of the alternating current circuit. Wherein the first rectangular microstrip line takes the form of a quarter-wavelength microstrip line with an impedance of 100 omega. Since the main path signal line and the bias circuit 1 are connected in parallel, when the impedance of the bias circuit 1 is sufficiently large, the influence of the bias circuit 1 on the main path signal is small. The first rectangular microstrip line is used for equivalent inductance, and the effect of direct current resistance alternating current is achieved. Two quarter-fan annular open-circuit microstrip lines (a first fan-shaped microstrip line and a second fan-shaped microstrip line) with the impedance of 50 omega are adopted to be equivalent to a capacitor, clutter can be effectively removed, and the stability of the circuit is improved. And this bias circuit 1 adopts the form of pure microstrip line to form the distributed parameter circuit, has abandoned the risk that these lumped components and parts of capacitance inductance can produce the parasitic parameter, especially under the situation that the lumped component of ultrahigh frequency has already been inapplicable, the circuit formed by pure microstrip line can be more stable more practical. The bias circuit mainly has the functions of electrifying direct current and blocking alternating current signals so as to prevent the alternating current signals from entering a direct current power supply to damage an instrument.
In the embodiment of the present invention, the length of the first rectangular microstrip line in the left-right direction is 0.26mm, and the length in the front-rear direction is 13.56 mm. The length of the second rectangular microstrip line along the left-right direction is 0.26mm, and the length along the front-back direction is 3 mm. The length of the third rectangular microstrip line in the left-right direction is 1.11mm, and the length in the front-back direction is 6 mm. The length of the fourth rectangular microstrip line in the left-right direction is 1.11mm, and the length in the front-back direction is 0.5 mm. The central angles of the first fan-shaped microstrip line and the second fan-shaped microstrip line are both 60 degrees, the outer diameters of the first fan-shaped microstrip line and the second fan-shaped microstrip line are both 9.75mm, and the inner diameters of the first fan-shaped microstrip line and the second fan-shaped microstrip line are both 0.64 mm. The above dimensions should not be taken as limiting the invention.
Further, in a preferred embodiment provided by the present application, the coupler 1 and the coupler 2 are 3dB bridges having the same structure. The 3dB bridge comprises a fifth rectangular microstrip line TL5, a sixth rectangular microstrip line TL6, a seventh rectangular microstrip line TL7, an eighth rectangular microstrip line TL8, a ninth rectangular microstrip line TL9, a tenth rectangular microstrip line TL10, an eleventh rectangular microstrip line TL11, a twelfth rectangular microstrip line TL12, a second T-shaped junction Tee2, a third T-shaped junction Tee3, a fourth T-shaped junction Tee4 and a fifth T-shaped junction Tee 5. The second, third, fourth and fifth T-junctions have first, second and third ports, respectively. One end of the fifth rectangular microstrip line is the input/output end of the 3dB bridge, and the other end of the fifth rectangular microstrip line is connected with the first port of the second T-shaped junction. The second port of the second T-shaped junction is connected with one end of the eighth rectangular microstrip line, and the third port of the second T-shaped junction is connected with one end of the seventh rectangular microstrip line. The other end of the eighth rectangular microstrip line is connected with the first port of the third T-shaped junction. And a second port of the third T-shaped junction is connected with one end of an eleventh rectangular microstrip line, and the other end of the eleventh rectangular microstrip line is a straight-through end of the 3dB bridge. And a third port of the third T-shaped junction is connected with one end of the tenth rectangular microstrip line. One end of the sixth rectangular microstrip line is an isolation end of the 3dB bridge, and the other end of the sixth rectangular microstrip line is connected with the first port of the fourth T-shaped junction. And a second port of the fourth T-shaped junction is connected with one end of the ninth rectangular microstrip line, and a third port of the fourth T-shaped junction is connected with the other end of the seventh rectangular microstrip line. The other end of the ninth rectangular microstrip line is connected with a first port of a fifth T-shaped junction, and a second port of the fifth T-shaped junction is connected with one end of the twelfth rectangular microstrip line. The other end of the twelfth rectangular microstrip line is a coupling end of the 3dB bridge. And a third port of the fifth T-shaped junction is connected with the other end of the tenth rectangular microstrip line.
The working principle of the 3dB bridge is as follows:
the coupler circuit has two main functions, and can divide a signal into two parts when the signal is input, and the two parts are respectively input to the nonlinear generator 1 and the nonlinear generator 2. When the signals are output, two paths of signals output by the nonlinear generator 1 and the nonlinear generator 2 can be combined to form one path of signal output. When the 3dB bridge is used as the coupler 1, a radio frequency signal is input from the input/output terminal, and is output from the through terminal and the coupling terminal. When the 3dB bridge is used as the coupler 2, radio frequency signals are input from the through terminal and the coupling terminal and output from the input/output terminal. In practical use, the sixth rectangular microstrip line is grounded through a 50 Ω resistor, so that the port isolation is improved.
In this embodiment, the lengths of the fifth rectangular microstrip line, the sixth rectangular microstrip line, the eleventh rectangular microstrip line and the twelfth rectangular microstrip line are all 2mm, and the widths thereof are all 1.11 mm. The length of the eighth rectangular microstrip line and the length of the ninth rectangular microstrip line are both 11.57mm, and the width of the eighth rectangular microstrip line and the ninth rectangular microstrip line are both 1.88 mm. The widths of the seventh rectangular microstrip line and the tenth rectangular microstrip line are both 1.12mm, and the lengths of the seventh rectangular microstrip line and the tenth rectangular microstrip line are both 12.63 mm. The dimensions of the rectangular microstrip line should not be taken as limiting the invention.
Further, in a preferred embodiment provided by the present application, the coupling microstrip circuit 1, the coupling microstrip circuit 2, the coupling microstrip circuit 3, and the coupling microstrip circuit 4 are the same coupling microstrip circuit. The coupling microstrip circuit includes a thirteenth rectangular microstrip line Tee13, a fourteenth rectangular microstrip line Tee14, a fifteenth rectangular microstrip line Tee15, and a sixteenth rectangular microstrip line Tee 16. One end of a thirteenth rectangular microstrip line is an input end of the coupling microstrip circuit, the other end of the thirteenth rectangular microstrip line is connected with one end of the fifteenth rectangular microstrip line, the sixteenth rectangular microstrip line is located below the fifteenth rectangular microstrip line and parallel to the fifteenth rectangular microstrip line, the distance between the sixteenth rectangular microstrip line and the fifteenth rectangular microstrip line is 0.13mm, the other end of the sixteenth rectangular microstrip line is connected with one end of the fourteenth rectangular microstrip line, and the other end of the fourteenth rectangular microstrip line is used as an output end of the coupling microstrip circuit.
The working principle of the coupling microstrip circuit is as follows: and a video signal is input from one end of the thirteenth rectangular microstrip line, is coupled to the sixteenth rectangular microstrip line when passing through the fifteenth rectangular microstrip line, and is output after passing through the fourteenth rectangular microstrip line.
The coupling microstrip circuit mainly has the functions of communicating alternating current signals and blocking direct current so as to prevent direct current signals from entering a signal generator and a spectrum analyzer to damage an instrument.
In this embodiment, the length of each of the thirteenth rectangular microstrip line and the fourteenth rectangular microstrip line is 2mm, and the width thereof is 1.11 mm. The fifteenth rectangular microstrip line and the sixteenth rectangular microstrip line are both 14mm in length and 0.15mm in width. The gap between the fifteenth rectangular microstrip line and the sixteenth rectangular microstrip line is 0.13 mm. The dimensions of the rectangular microstrip line should not be taken as limiting the invention.
Fig. 8 is a graph comparing the measured results, wherein the abscissa is frequency and the ordinate is power spectral density. The curve with the triangular sign is the power spectral density curve without the predistortion system and the curve with the dots is the power spectral density curve with the two-branch analog predistortion system of the present invention added. It can be seen that when a 5G NR signal of 100MHz is inputted, the ACPR (Adjacent Channel Leakage Ratio) of the signal after the system is added to the analog predistortion system with the dual-branch structure can be improved a lot.
Compared with the traditional analog predistortion system, the invention integrates the advantages of the field effect transistor and the Schottky diode through two paths of nonlinear generators to form a more perfect predistortion signal to fit the nonlinear distortion of the power amplifier in the communication system. The predistortion precision of the whole system is higher, and the defect that the nonlinear improvement quantity of the power amplifier is insufficient by the traditional analog predistortion is overcome. Compared with the prior multi-path parallel analog predistortion system, the invention abandons a complex circuit structure, fully integrates the advantages of two analog predistortion by utilizing the most basic structure, perfectly achieves the predistortion effect and exceeds the traditional amplitude-phase adjustable parallel structure. In addition, the invention utilizes the nonlinearity generated by the Schottky diode and the field effect transistor, has the advantages of simple structure, small volume, low cost, easy operation and realization, high predistortion precision and the like, and can even act on 5G modulation signals which are widely applied at present to improve the performance of a future 5G communication system.
In the present invention, unless otherwise expressly specified or limited, the terms "connected," "connecting," and the like are to be construed broadly, e.g., as meaning as being electrically connected or communicable with each other; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the description of the present invention, it is to be understood that the terms "intermediate", "length", "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "radial", "circumferential", and the like, are used in the positional or positional relationship indicated in the drawings, which are based on the positional or positional relationship shown in the drawings, and are used merely for convenience of description and simplicity of description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus should not be construed as limiting the present invention.
The above description is for the purpose of illustrating embodiments of the invention and is not intended to limit the invention, and it will be apparent to those skilled in the art that any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the invention shall fall within the protection scope of the invention.
Claims (10)
1. The double-branch analog predistortion system is characterized by comprising a dielectric substrate, a first coupler, a first nonlinear generator, a second nonlinear generator and a second coupler; wherein said first coupler, said first nonlinear generator, said second nonlinear generator and said second coupler are disposed on the upper surface of the dielectric substrate; said first non-linear generator and said second non-linear generator being connected in parallel, said first non-linear generator comprising a field effect transistor and said second non-linear generator comprising a schottky diode; the first coupler divides an input radio frequency signal into a first radio frequency output signal and a second radio frequency output signal and then respectively outputs the first radio frequency output signal and the second radio frequency output signal to the first nonlinear generator and the second nonlinear generator; the first nonlinear generator utilizes nonlinearity generated by the field effect transistor to carry out predistortion on the first radio frequency output signal to obtain a first distortion signal; the second nonlinear generator utilizes nonlinearity generated by the Schottky diode to pre-distort the second radio frequency output signal to obtain a second distortion signal; and the first distortion signal and the second distortion signal are respectively input into the second coupler through the first input end and the second input end of the second coupler to be combined, so that an analog predistortion output signal is obtained.
2. The dual-branch analog predistortion system of claim 1, wherein the first nonlinear generator further comprises a first bias circuit, a second bias circuit, a first dc power supply, a second dc power supply, a first coupled microstrip circuit, a second coupled microstrip circuit, a first matched microstrip line and a second matched microstrip line; one end of the first coupling microstrip circuit inputs the first radio frequency output signal, and the other end of the first coupling microstrip circuit is connected with the radio frequency input end of the first bias circuit; the radio frequency output end of the first bias circuit is connected with the grid electrode of the field effect transistor through the first matching microstrip line; the direct current input end of the first bias circuit is connected with the anode of the first direct current power supply; the negative electrode of the first direct current power supply is grounded; the source electrode of the field effect transistor is grounded, and the drain electrode of the field effect transistor is connected with the radio frequency input end of the second bias circuit through the second matching microstrip line; the radio frequency output end of the second bias circuit is connected with one end of the second coupling microstrip circuit, and the direct current input end of the second bias circuit is connected with the anode of the second direct current power supply; the negative electrode of the second direct current power supply is grounded; the other end of the second coupling microstrip circuit is used as the output end of the first nonlinear generator and is connected to the first input end of the second coupler.
3. The dual-branch analog predistortion system of claim 1, wherein the second nonlinear generator further comprises a third bias circuit, a third dc power supply, a third coupling microstrip circuit, a fourth coupling microstrip circuit, a third matching microstrip line and a fourth matching microstrip line; one end of the third coupling microstrip circuit inputs the second radio frequency output signal, and the other end of the third coupling microstrip circuit is connected with the anode of the Schottky diode and the radio frequency input end of the third bias circuit through a third matching microstrip line; the cathode of the Schottky diode is grounded; the radio frequency output end of the third bias circuit is connected with one end of a fourth coupling microstrip circuit through a fourth matching microstrip line; the direct current input end of the third bias circuit is connected with the anode of the third direct current power supply; the negative electrode of the third direct current power supply is grounded; the other end of the fourth coupling microstrip circuit is used as the output end of the second nonlinear generator and is connected to the second input end of the second coupler.
4. The dual-branch analog predistortion system of claim 2, wherein the first and second bias circuits are the same bias circuit, and the bias circuit comprises a first T-junction, a first rectangular microstrip line, a second rectangular microstrip line, a third rectangular microstrip line, a fourth rectangular microstrip line, a first fan-shaped microstrip line and a second fan-shaped microstrip line; the first port of the first T-shaped junction is the radio frequency input end of the bias circuit, and the second port of the first T-shaped junction is the radio frequency output end of the bias circuit; one end of the third rectangular microstrip line is used as a direct current input end of the bias circuit, and direct current voltage sequentially passes through the third rectangular microstrip line, the second rectangular microstrip line and the first rectangular microstrip line and then is input to a third port of the first T-shaped junction; the first fan-shaped microstrip line and the second fan-shaped microstrip line are symmetrically connected to two sides of the fourth rectangular microstrip line.
5. The dual-branch analog predistortion system of claim 4, wherein the first rectangular microstrip line is a quarter-wavelength microstrip line; the first fan-shaped microstrip line and the second fan-shaped microstrip line are quarter fan-shaped open-loop microstrip lines.
6. The dual-branch analog predistortion system of claim 3, wherein the third bias circuit comprises a first T-junction, a first rectangular microstrip, a second rectangular microstrip, a third rectangular microstrip, a fourth rectangular microstrip, a first fan-shaped microstrip and a second fan-shaped microstrip; the first port of the first T-shaped junction is the radio frequency input end of the third biasing circuit, and the second port of the first T-shaped junction is the radio frequency output end of the third biasing circuit; one end of the third rectangular microstrip line is used as a direct current input end of the third bias circuit, and direct current voltage sequentially passes through the third rectangular microstrip line, the second rectangular microstrip line and the first rectangular microstrip line and then is input to the third port of the first T-shaped junction; the first fan-shaped microstrip line and the second fan-shaped microstrip line are symmetrically connected to two sides of the fourth rectangular microstrip line.
7. The two-branch analog predistortion system of claim 1, wherein the first coupler and the second coupler are 3dB bridges of the same structure; the 3dB bridge comprises a fifth rectangular microstrip line, a sixth rectangular microstrip line, a seventh rectangular microstrip line, an eighth rectangular microstrip line, a ninth rectangular microstrip line, a tenth rectangular microstrip line, an eleventh rectangular microstrip line, a twelfth rectangular microstrip line, a second T-shaped junction, a third T-shaped junction, a fourth T-shaped junction and a fifth T-shaped junction; one end of the fifth rectangular microstrip line is the input end of the 3dB bridge, and the other end of the fifth rectangular microstrip line is connected with the first port of the second T-shaped junction; a second port of the second T-shaped junction is connected to a first port of the third T-shaped junction through the eighth rectangular microstrip line, and a third port of the second T-shaped junction is connected to a third port of the fourth T-shaped junction through the seventh rectangular microstrip line; the second port of the third T-shaped junction is connected with one end of the eleventh rectangular microstrip line, and the other end of the eleventh rectangular microstrip line is a straight-through end of the 3dB bridge; the third port of the third T-shaped junction is connected to the third port of the fifth T-shaped junction through the tenth rectangular microstrip line; one end of the sixth rectangular microstrip line is an isolation end of the 3dB bridge, and the other end of the sixth rectangular microstrip line is connected with the first port of the fourth T-shaped junction; the second port of the fourth T-shaped junction is connected to the first port of the fifth T-shaped junction through the ninth rectangular microstrip line; the second port of the fifth T-shaped junction is connected with one end of the twelfth rectangular microstrip line; the other end of the twelfth rectangular microstrip line is a coupling end of the 3dB bridge.
8. The dual-branch analog predistortion system of claim 2, wherein the first coupling microstrip circuit and the second coupling microstrip circuit are the same coupling microstrip circuit; the coupling microstrip circuit comprises a thirteenth rectangular microstrip line, a fourteenth rectangular microstrip line, a fifteenth rectangular microstrip line and a sixteenth rectangular microstrip line; one end of the thirteenth rectangular microstrip line is the input end of the coupling microstrip circuit, and the other end of the thirteenth rectangular microstrip line is connected with one end of the fifteenth rectangular microstrip line; the sixteenth rectangular microstrip line is positioned below the fifteenth rectangular microstrip line and is parallel to the fifteenth rectangular microstrip line, and a space is arranged between the sixteenth rectangular microstrip line and the fifteenth rectangular microstrip line; the other end of the sixteenth rectangular microstrip line is connected with one end of the fourteenth rectangular microstrip line, and the other end of the fourteenth rectangular microstrip line is used as the output end of the coupling microstrip circuit.
9. The dual-branch analog predistortion system of claim 3, wherein the third coupling microstrip circuit and the fourth coupling microstrip circuit are the same coupling microstrip circuit; the coupling microstrip circuit comprises a thirteenth rectangular microstrip line, a fourteenth rectangular microstrip line, a fifteenth rectangular microstrip line and a sixteenth rectangular microstrip line; one end of the thirteenth rectangular microstrip line is the input end of the coupling microstrip circuit, and the other end of the thirteenth rectangular microstrip line is connected with one end of the fifteenth rectangular microstrip line; the sixteenth rectangular microstrip line is positioned below the fifteenth rectangular microstrip line and is parallel to the fifteenth rectangular microstrip line, and a space is arranged between the sixteenth rectangular microstrip line and the fifteenth rectangular microstrip line; the other end of the sixteenth rectangular microstrip line is connected with one end of the fourteenth rectangular microstrip line, and the other end of the fourteenth rectangular microstrip line is used as the output end of the coupling microstrip circuit.
10. The dual-branch analog predistortion system of claim 8 or 9, wherein the gap between the fifteenth rectangular microstrip and the sixteenth rectangular microstrip is 0.13 mm.
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