GaN-based mode reconfigurable Doherty power amplifier

Abstract

The invention relates to a Doherty power amplifier with a reconfigurable mode, which belongs to the technical field of microwave circuits and comprises a power divider, a carrier power amplifier module, a peak power amplifier module and a combining impedance. According to the Doherty power amplifier, under the condition that a matching circuit is not changed, by exchanging the grid bias of the two transistors, the Doherty power amplifier achieves the function that the working frequency band is reconfigurable, and therefore the amplifier can work at multiple frequency bands. In addition, an output matching circuit of the amplifier is changed by utilizing a PIN switch SMP1345-079, so that the working frequency band bandwidth of the amplifier is increased. The power amplifier disclosed by the invention works in two modes, the working frequency bands of the first mode are 2.5-2.9 GHz and 3.3-3.7 GHz, and the working frequency band of the second mode is 2.8-3.4 GHz. According to the Doherty power amplifier, the reciprocal gate is adopted to be biased between two modes of different frequency bands to be switched, the proposed Doherty power amplifier can cover various frequency bands of 5G of operators, and therefore a promising solution is provided for 5G in broadband services.

Description

Technical Field

[0001] The present invention belongs to the field of microwave radio frequency communications, and specifically relates to a radio frequency power amplifier, and in particular to a GaN-based mode reconfigurable Doherty power amplifier. Background Art

[0002] With the rapid development of the information age, various communication needs continue to emerge, and corresponding communication systems have also emerged, such as GSM (Global System for Mobile Communications), 3G (third generation mobile communication system), 4G (fourth generation mobile communication system), 5G (fifth generation mobile communication system), etc. Communication systems are updated and iterated with the development of technology, and the requirements for RF front-end devices are also changing with each passing day. RF power amplifiers are key components of RF communication front ends. 5G communication has the characteristics of complex modulation, large bandwidth and high signal peak-to-average ratio, which puts higher requirements on the bandwidth and efficiency of power amplifiers. The Doherty power amplifier using load modulation technology has excellent characteristics of high back-off efficiency and good linearity. Due to the advantages of small space occupation and low power consumption, multi-band RF power amplifiers have received widespread attention in recent years. The earliest multi-frequency amplifiers were mainly achieved by installing multiple amplifiers in different frequency bands and using single-pole multi-throw switches or using a specially designed broadband load network to cover the entire frequency band. With the miniaturization and cost reduction of devices, the high cost, excessive size and low working efficiency of the former are increasingly difficult to meet the requirements of related industries: while the latter is quite difficult to obtain high efficiency within a broadband range.

[0003] In view of the difficulties existing in the current technology, it is necessary to conduct research to realize a simple mode switching to replace the traditional multi-band Doherty power amplifier, and on this basis propose a mode reconfigurable Doherty power amplifier while ensuring the back-off efficiency, and enable it to work in the 5G frequency band. Summary of the invention

[0004] In order to overcome the technical defects existing in the prior art, the present invention proposes a mode-reconfigurable Doherty power amplifier and a design method thereof, which achieves the purpose of exchanging the functions of the two power amplifiers by simply exchanging the gate bias of the two transistors, thereby realizing two Doherty power amplifier modes of different frequency bands, and finally using a single load modulation network in the DPA to achieve wide bandwidth. At the same time, when switching modes, the working state of the PIN switch is adjusted to improve the matching of the circuit, thereby improving the back-off efficiency, saturation efficiency and bandwidth of the Doherty power amplifier.

[0005] In order to solve the technical problems existing in the prior art, the technical solution of the present invention is as follows:

[0006] A mode-reconfigurable Doherty power amplifier comprises a power divider, a carrier power amplification module, a peak power amplification module, an impedance inverter, and a combined output matching network.

[0007] The power divider has an input end connected to the radio frequency signal output end, and an output end connected to the input ends of the carrier power amplifier module and the peak power amplifier module respectively.

[0008] The carrier power amplifier module includes a carrier input matching / bias network, a carrier power amplifier, a carrier output matching / bias network and an impedance inverter.

[0009] The peak power amplifier module includes an impedance inverter, a peak input matching / bias network, a peak power amplifier and a peak output matching / bias network.

[0010] The input bias network gate bias circuit is connected in parallel between the gate of the GaN power amplifier transistor and the stability circuit.

[0011] The output bias network is a drain bias circuit, which is connected in parallel between the output filter matching circuit and the output end of the GaN power amplifier transistor.

[0012] As a preferred technical solution, the gate bias of the two transistors is used to exchange the functions of the two power amplifiers, thereby realizing two Doherty power amplifier modes in different frequency bands.

[0013] As a preferred technical solution, the circuit matching is improved by adjusting the working state of the PIN switch when switching modes, thereby improving the back-off efficiency, saturation efficiency and bandwidth of the Doherty power amplifier.

[0014] As a preferred technical solution, the combined output matching network is formed by using multiple sections of step microstrip lines connected in series to expand the output bandwidth of the combined output matching network to a certain extent.

[0015] The beneficial effects of the present invention are as follows: the present invention is not only easy to implement, but also can effectively improve the bandwidth, reduce the overall cost, and can be well applied to the fifth generation mobile communication system by changing the mode of the Doherty power amplifier through the reciprocal gate voltage.

[0016] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0018] Figure 1 A mode reconfigurable Doherty power amplifier;

[0019] Figure 2 A conceptual diagram of a mode-reconfigurable Doherty power amplifier;

[0020] Figure 3 A conceptual diagram of the efficiency of a Doherty power amplifier with reconfigurable modes;

[0021] Figure 4 Using generalized output matching networks for a mode reconfigurable Doherty power amplifier carrier and peak amplifier;

[0022] Figure 5 A topological structure diagram of a mode-reconfigurable Doherty power amplifier in the present invention;

[0023] Figure 6 It is the efficiency and output power simulation result diagram of the present invention;

[0024] Figure 7 is a graph showing the relationship between output power and efficiency of the present invention; DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0026] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0027] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] like Figure 1 As shown, the present invention provides a mode reconfigurable Doherty power amplifier, which includes a power divider, a carrier power amplifier module, a peak power amplifier module, an impedance inverter, and a combined output matching network. The total input end is connected in parallel to the carrier power amplifier module and the peak power amplifier module through the power divider, and the carrier power amplifier module and the peak power amplifier module are combined and output through the combined output matching network.

[0029] like Figure 2 As shown in the figure, the conceptual diagram of the mode reconfigurable Doherty power amplifier is shown. The core idea is to simply switch the gate voltage V of two identical transistors without changing the circuit. gs-1 and V gs-2 , to achieve Doherty characteristics in different frequency bands and different modes. Figure 2 As shown, in Mode 1, transistor 1 (T1) is biased in AB mode with V gs-1 As a carrier amplifier, transistor 2 (T2) is biased in C mode to V gs-2 As a peaking amplifier. In mode 2, the matching network is the same, but the gate biases of T1 and T2 are swapped, thus swapping the carrier and peaking amplifiers, i.e., T1 becomes the peaking amplifier and T2 becomes the carrier amplifier. The frequency response of the load modulation network in different modes is different. With proper design, in mode 1, the power amplifier can cover the middle frequency band, while in mode 2, it can cover the remaining two frequency bands at both ends, such as Figure 3 The combined frequency band of the Doherty power amplifiers shown will be very wide.

[0030] like Figure 4As shown in the figure, the generalized output matching network (OMN) is used for the carrier and peaking amplifiers, where the two transistors are represented by current sources (CG). To simplify the analysis, we assume that the parasitic and packaging parameters of the transistors can be fully incorporated into the OMN. For this schematic, the two proposed modes are defined as follows: in mode 1, CG1 is biased in class AB mode as a carrier device and CG2 is biased in class C mode as a peaking device, while in mode 2, CG1 becomes a peaking device and CG2 becomes a carrier device. It is assumed that the OMN can achieve Z within the design frequency band. T to Z T The ABCD matrix of lossless OMN can be described as formula (1):

[0031]

[0032] Where Z T Set to R opt , which is the optimal load impedance for the Class B power amplifier. Therefore, the voltage-current relationship between the current source (CG) and the combination node can be expressed as formula (2)

[0033]

[0034] From formula (2), the current of the current source can be obtained as:

[0035] I M =V MT ·(jsinθ M / Z T )+cosθ M I MT #(3)

[0036] At the same time, the voltage at the combined node is:

[0037] V MT =(I MT1 +I MT2 )·Z L #(4)

[0038] In formula (4), Z L is the combined load of the two branches, equal to Z T / 2.

[0039] Symmetrical Doherty operation needs to satisfy the equal phase merging condition at the merging node when saturated, and the following current relationship must be met:

[0040] I MT2，sat =I MT1，sat #(5)

[0041] Through formulas (3) to (5), we can get:

[0042]

[0043] Therefore, no matter in mode 1 or mode 2, the currents generated by CG1 and CG2 should satisfy the following relationship:

[0044]

[0045] It can be seen from equation (7) that by adding a phase compensation network with a phase shift of (θM1-θM2) at the input of CG1, both mode 1 and mode 2 can meet the conditions of equal combination at saturation.

[0046] When the equal phase combination condition in equation (5) is met, the load impedance at the combination node can be calculated as:

[0047] Z MT1，sat =Z MT2，sat =Z T #(8)

[0048] Z M The matching impedance at can be expressed as:

[0049]

[0050] Where Z MT is the load impedance of each amplifier branch before the combining point. Substituting (1) into (9) we get:

[0051]

[0052] Where Z M1 and Z M2 is the matching impedance of OMN.

[0053] Substituting formula (8) into formula (10) and formula (11), we can get:

[0054] Z M1，sat =Z M2，sat =Z T #(12)

[0055] This means that the required impedance for both the carrier branch and the peaking branch is equal to R opt Match, satisfying the conditions for Doherty saturation.

[0056] In mode 1, only CG1 is working when the Doherty amplifier is backed off, and CG2 is not yet connected and is in an open circuit state. MT1,bo =Z L / / Z MO2,bo , where Z MO2,bo The output impedance of the CG2 branch can be expressed as:

[0057]

[0058] Substituting formula (13) into formula (10), we can get the back-off matching impedance Z of mode 1: M1,bo for:

[0059]

[0060] To meet the working conditions of Doherty amplifier, Z M1,bo Should be combined with 2R opt The phase of the OMN is frequency dependent. Assume the center frequency is θM1 = -90°, θM2 = -180°. If you use the normalized frequency to sweep θM1 and θM2, and watch Z M1,bo The relationship between normalized resistance and normalized frequency shows that DPA can work in a very wide frequency band.

[0061] In mode 2, CG2 becomes the carrier device and CG1 becomes the peak device. Since the proposed DPA adopts a symmetrical structure, formula (12) can still be satisfied in the saturation state. When backing off, the carrier branch becomes the CG2 branch and the CG1 branch is closed. Therefore, Z MT2,bo =Z L / / Z MO1,bo , where Z MO1,bo It can be expressed as:

[0062]

[0063] Substituting formula (15) into formula (11), the back-off matching impedance Z of mode 2 is M2,bo It can be calculated as:

[0064]

[0065] As mentioned before, in the proposed DPA, we only switch the bias without changing the circuit when moving from mode 1 to mode 2. Therefore, θM1 and θM2 remain unchanged.

[0066] If we again sweep θM1 and θM2 with the normalized frequency, we can see that Z M2,bo The relationship between normalized resistance and normalized frequency. Although the PA can no longer operate as a Doherty in the center frequency band, the output impedance can still be close to the optimal value in each sideband, so that Doherty operation can still be achieved.

[0067] like Figure 5As shown, the present invention discloses a mode-reconfigurable Doherty power amplifier, which includes a power divider, a carrier power amplifier module, a peak power amplifier module, and a combined impedance. By exchanging the gate bias of two transistors, the Doherty power amplifier can realize the function of reconfigurable working frequency band, so that the amplifier can work in multiple frequency bands. The matching of the circuit is also improved by the working state of the PIN switch, and the performance of the amplifier working frequency is optimized.

[0068] like Figure 6 As shown in FIG. 1 , it is a diagram of efficiency, output power and simulation results of a mode reconfigurable Doherty power amplifier. The result diagram shows that within 2.5-3.8 GHz, its output power is greater than 40 dBm and the drain efficiency is greater than 60%.

[0069] like Figure 7 As shown, it is a simulation result diagram of the relationship between output power and efficiency of a mode reconfigurable Doherty power amplifier. The result diagram shows that the efficiency of the 6dB back-off point within 2.5-3.8GHz is greater than 45%.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A GaN-based mode reconfigurable Doherty power amplifier, characterized in that: It includes power divider, carrier power module, peak power amplifier module, impedance inverter, and combined output matching network; The input end of the power divider is connected to the RF signal output end, and is divided into two outputs, which are respectively connected to the carrier loop and the peak loop; The carrier loop at least includes a carrier power amplifier module and an impedance inverter, and the carrier power amplifier module includes a carrier input matching / bias network, a stability module, a carrier power amplifier, and a carrier output matching / bias network; the peak loop at least includes an impedance inverter and a peak power amplifier module, and the peak power amplifier module includes a peak input matching / bias network, a peak power amplifier, and a peak output matching / bias network; The carrier loop and the peak loop are combined into an output, and connected to a load via a combined output matching network.

2. A GaN-based mode reconfigurable Doherty power amplifier according to claim 1, characterized in that: Without changing the matching circuit, the carrier power amplifier and the peak power amplifier in the Doherty power amplifier are exchanged by simply exchanging the gate bias of the transistor, and finally two DPA modes in different frequency bands are realized, so that a wide bandwidth can be achieved using a single load modulation network in the Doherty power amplifier.

3. The GaN-based mode reconfigurable Doherty power amplifier according to claim 1, characterized in that: The Doherty power amplifier has two different frequency band modes. Mode one is a dual-frequency mode with an operating frequency band of 2.5-2.9GHz and 3.3-3.7GHz; Mode two is an intermediate frequency mode with an operating frequency band of 2.8-3.4GHz.

4. The GaN-based mode reconfigurable Doherty power amplifier according to claim 1, characterized in that: The Doherty power amplifier improves circuit matching by adjusting the working state of the PIN switch when switching modes, thereby improving the performance of the Doherty power amplifier.

5. The GaN-based mode reconfigurable Doherty power amplifier according to claim 1, characterized in that: The Doherty power amplifier uses Rogers 4350 dielectric with a dielectric constant of 3.66 and a thickness of 0.508 mm. The Doherty power amplifier tube uses the CG2H40010F power tube of Digi-Key, which better realizes the performance of the Doherty power amplifier.

6. The GaN-based mode reconfigurable Doherty power amplifier according to claim 1, characterized in that: The output bias module is a drain bias circuit, which is connected in parallel between the output filter matching circuit and the output end of the GaN power amplifier transistor.

7. The GaN-based mode reconfigurable Doherty power amplifier according to claim 1, characterized in that: The input bias module is a gate bias circuit, which is connected in parallel between the gate of the GaN power amplifier transistor and the stability circuit.

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