Amplitude and phase independently adjustable analog predistorter suitable for SSPA
Technical Field
The invention relates to an amplitude and phase independently adjustable analog predistorter suitable for an SSPA.
Background
With the development of modern wireless communication technology, in order to cope with the rapid increase of the number of user terminals and communication data traffic, a complex digital modulation scheme like quadrature amplitude modulation (64-QAM) and a multi-carrier transmission technology of Orthogonal Frequency Division Multiplexing (OFDM) are widely applied in modern wireless communication systems. The application of these techniques significantly improves spectral efficiency, but allows a higher Peak to Average Power Ratio (PAPR, hereinafter referred to as Peak-to-Average Ratio) for the transmitted signal. Signals with high peak-to-average ratio can more easily cause the power amplifier to enter a saturation working area to generate nonlinear distortion, so that the power amplifier needs to have higher linearity. At present, the mainstream high-power amplifier is a solid-state power amplifier (SSPA) and a traveling wave tube power amplifier (TWTA). Linearization techniques have been developed to improve the linearity index of amplifiers. The most common linearization techniques at present include: feedforward technique, negative feedback technique, predistortion technique, etc. The analog predistortion technology circuit has the advantages of simple structure, low cost, high working frequency band and easy integration, and is widely applied to engineering practice.
The analog predistortion technique is a linearization technique for performing pre-compensation on a target power amplifier curve. The analog predistorter is divided into a series transmission type, a parallel transmission type, a bridge reflection type and a two-way type structure according to different circuit structures, and a Schottky barrier diode is mostly adopted as a nonlinear signal generating device to generate a curve with the characteristic opposite to that of a target power amplifier so as to realize the linearization of the power amplifier.
Currently, analog predistorters are mainly classified into four types: series transmission, parallel transmission, bridge reflection and two-way structures. The transmission type analog predistorter has a simple structure, and mainly generates a predistortion curve which is complementary with the nonlinear characteristic of a power amplifier on a main transmission line by connecting nonlinear devices in series or in parallel; the bridge reflection type adopts a 3dB bridge structure, nonlinear devices are loaded at the through and coupling ports of the bridge, and the required transmission characteristics are generated by utilizing the synthesis of two paths of reflection signals; the two-way analog predistorter is based on the theory of vector synthesis of two-way signals, and generally adopts a phase shifter and an attenuator to form a linear branch, utilizes a nonlinear device to form a nonlinear branch, and generates the required transmission characteristic through the vector synthesis of two-way signals.
The currently applied analog predistorter has few adjustable parameters and poor circuit adjustability. In addition, the traditional predistorter has strong correlation between amplitude and phase distortion characteristics, and any state of a circuit is changed, so that the amplitude and phase characteristics are changed. When the power amplifier is actually used, the predistortion circuit is often difficult to ensure that amplitude and phase compensation meet the linearization requirement of a target power amplifier, so that the linearization effect is poor, and even the situation such as deterioration occurs.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a reflection type structure which adopts two paths of asymmetry, so that the adjustable parameters of the analog predistorter are more; the analog predistorter has the advantages of independent adjustment of amplitude and phase of a predistortion compensation curve, high adjustability, simple structure and the like, and is suitable for SSPA.
The purpose of the invention is realized by the following technical scheme: the analog predistorter with independently adjustable amplitude and phase suitable for the SSPA comprises a 3dB 90-degree electric bridge, a nonlinear reflection branch, a linear reflection branch, a first direct current bias circuit and a second direct current bias circuit;
the nonlinear reflection branch comprises a first Schottky barrier diode and a second Schottky barrier diode which are connected in parallel in an opposite direction, and the linear reflection branch comprises a variable capacitance diode;
an input signal of the radio frequency signal input port is divided into two paths of signals through a 3dB 90-degree electric bridge and is respectively output from the through port and the coupling port; the output signal of the through port is loaded on the anode of the first Schottky barrier diode and the cathode of the second Schottky barrier diode respectively after passing through the first blocking capacitor, and the anode of the first Schottky barrier diode and the cathode of the second Schottky barrier diode are also connected with the first direct current bias circuit respectively; the output of the coupling port is loaded to the negative electrode of the variable capacitance diode after passing through a second blocking capacitor, and the negative electrode of the variable capacitance diode is also connected with a second direct current bias circuit;
the reflected signals generated by the nonlinear reflection branch and the linear reflection branch are synthesized at an isolation port with 3dB90 degrees and output through a radio frequency signal output port.
Further, the first dc bias circuit includes a first rf choke inductor, a schottky barrier diode bias resistor, and a schottky barrier diode dc bias voltage, which are connected in sequence, and the first rf choke inductor is connected to an anode of the first schottky barrier diode and a cathode of the second schottky barrier diode, respectively.
Further, the second direct current bias circuit comprises a second radio frequency choke inductor, a variable capacitance diode bias resistor and a variable capacitance diode direct current bias voltage which are sequentially connected, and the second radio frequency choke inductor is connected with the negative electrode of the variable capacitance diode.
The invention has the beneficial effects that: the invention provides an analog predistorter structure with independently adjustable amplitude and phase suitable for SSPA, which can realize relatively independent change of amplitude and phase compensation quantity of the predistorter by changing the bias state of a circuit. The Schottky barrier diode is used as a nonlinear signal generating device, so that the circuit structure becomes simpler; the signal is equally divided into two paths through a 3dB 90-degree electric bridge; one branch adopts a reverse parallel Schottky barrier diode to generate a nonlinear distorted reflected signal; the other branch adopts a variable capacitance diode to generate a linear reflection signal; the reflected signals of the two branches are subjected to vector synthesis at the isolation end of the bridge, and the function of relatively independently controlling the amplitude and the phase compensation quantity of the synthesized vector signals can be realized by adjusting the bias states of the two branches. Compared with the traditional reflection type circuit structure, the two paths of asymmetric reflection type structures are adopted, so that more adjustable parameters of the analog predistorter are provided; the two branches adopt a separate power supply mode, so that the adjustability of the whole circuit is improved. The integral analog predistorter structure has the advantages of independent adjustment of amplitude and phase of a predistortion compensation curve, high adjustability, simple structure and the like.
Drawings
Fig. 1 is a schematic structural diagram of an analog predistorter with independently adjustable amplitude and phase for SSPA of the present invention;
fig. 2 is a simulation result of the amplitude and phase compensation curve of the analog predistorter of the present embodiment;
wherein, 1-radio frequency signal input port; 2-a radio frequency signal output port; 3-3dB 90 degree bridge; 4-a first blocking capacitor; 5-a second blocking capacitor; 6-a first radio frequency choke inductance; 7-a second radio frequency choke inductance; 8-Schottky barrier diode bias resistance; 9-varactor bias resistance; 10-schottky barrier diode dc bias voltage; 11-varactor dc bias voltage; 12-a first schottky barrier diode; 13-a second schottky barrier diode; 14-varactor.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in fig. 1, the analog predistorter with independently adjustable amplitude and phase for SSPA of the present invention includes a 3dB90 ° bridge 3, a nonlinear reflection branch, a linear reflection branch, a first dc bias circuit and a second dc bias circuit;
the nonlinear reflection branch comprises a first Schottky barrier diode 12 and a second Schottky barrier diode 13 which are connected in parallel in an opposite direction, and the linear reflection branch comprises a variable capacitance diode 14;
an input signal of a radio frequency signal input port 1 is divided into two paths of signals through a 3dB 90-degree electric bridge 3, and the two paths of signals are respectively output from a through port and a coupling port; the output signal of the through port is loaded on the positive pole of the first Schottky barrier diode 12 and the negative pole of the second Schottky barrier diode 13 respectively after passing through the first blocking capacitor 4, and the positive pole of the first Schottky barrier diode 12 and the negative pole of the second Schottky barrier diode 13 are also connected with the first direct current bias circuit respectively; the output of the coupling port is loaded to the cathode of the variable capacitance diode 14 through the second blocking capacitor 5, and the cathode of the variable capacitance diode is also connected with a second direct current bias circuit;
the reflected signals generated by the nonlinear reflection branch and the linear reflection branch are combined at an isolation port with 3dB90 degrees and output through a radio frequency signal output port 2.
The first dc bias circuit is used to provide a bias state to an antiparallel diode composed of the first schottky barrier diode 12 and the second schottky barrier diode 13. The impedance of the reverse parallel schottky barrier diodes (the anode of the first schottky barrier diode 12 is connected to the cathode of the second schottky barrier diode 13, and the cathode of the first schottky barrier diode 12 is connected to the anode of the second schottky barrier diode 13) is related to the input power level and dc bias state of the rf signal. The first direct current bias circuit comprises a first radio frequency choke inductor 6, a Schottky barrier diode bias resistor 8 and a Schottky barrier diode direct current bias voltage 10 which are sequentially connected, wherein the first radio frequency choke inductor 6 is respectively connected with the anode of a first Schottky barrier diode 12 and the cathode of a second Schottky barrier diode 13; the distortion characteristic of the nonlinear signal generated by the anti-parallel diode pair composed of the first schottky barrier diode 12 and the second schottky barrier diode 13 can be adjusted by adjusting the bias voltage V1 of the first dc bias circuit.
The second direct current bias circuit is used for providing a bias state for the variable capacitance diode 14, the second direct current bias circuit comprises a second radio frequency choke inductor 7, a variable capacitance diode bias resistor 9 and a variable capacitance diode direct current bias voltage 11 which are sequentially connected, and the second radio frequency choke inductor 7 is connected with the negative electrode of the variable capacitance diode 14. The phase of the linear reflected signal generated by the first varactor diode 14 can be adjusted by adjusting the bias voltage V2 of the second dc bias circuit.
The cathode of the first schottky barrier diode 12 and the anode of the second schottky barrier diode 13, the anode of the varactor diode 14, the schottky barrier diode dc bias voltage 10, and the varactor diode dc bias voltage 11 are all grounded.
Finally, the nonlinear signal and the linear signal are synthesized at the isolation end through a 3dB 90-degree electric bridge 3, and a curve capable of compensating for the nonlinear characteristic of the SSPA is generated. The phase difference between the reflection coefficient of the nonlinear branch and the reflection coefficient of the linear branch is within a certain range by adjusting circuit parameters, and in this state: the amplitude compensation amount of the predistorter can be adjusted by independently adjusting the bias voltage V1 of the first direct current bias circuit; the independent adjustment of the bias voltage V2 of the second dc bias circuit can make the amplitude compensation amount of the predistorter almost constant when the phase compensation amount of the predistorter varies greatly, i.e. the effect of independently adjusting the amplitude and the phase of the predistorter for the SSPA can be achieved.
Fig. 2 is a simulation result of the amplitude and phase compensation curve of the analog predistorter of the present embodiment. When the voltage V2 is a constant value, the voltage V1 can adjust the gain expansion amount and the phase compression amount of the predistorter when the bias voltage V1 of the first dc bias circuit is tunable in the range of 39.75GHz and V2 is 0V; (b) at 39.75GHz, when V1 is 2.3V, the bias voltage V2 of the second dc bias circuit can tune the amplitude-phase characteristic curve, and it can be seen from the figure that, when the voltage V1 is a certain value, the voltage V2 can adjust the phase compression amount of the predistorter, while the gain expansion amount is almost kept unchanged, thereby realizing independent adjustment of amplitude and phase. The abscissa Pin in fig. 2 represents the input power in dBm; the ordinate Gain represents the Gain in dB; the ordinate Phase represents the Phase in degrees.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.