Filter combiner and Doherty amplifier for Doherty amplifier

Abstract

A filter combiner (301) for a Doherty amplifier (302), comprising: a first port (303), a second port (305), a third port (307) and a fourth port (309); wherein the first port is connected to the second port via a first network (311), the first network being a low-pass filter; the first port is connected to the third port via a second network (312), the second network being a low-pass filter, the low-pass filter being configured to operate as a band-stop filter when a high impedance is loaded to an input end or an output end of the second network when the peak amplifier is turned off; the third port is connected to the fourth port via a third network (313), the third network being a low-pass filter, the low-pass filter being configured to operate as a band-stop filter when a high impedance is loaded to an input end or an output end of the second network when the peak amplifier is turned off; and the fourth port is connected to the second port via a fourth network (314), the fourth network being a low-pass filter.

Description

Technical Field

[0001] The present invention relates to a combiner for a Doherty amplifier, and more particularly, to a filter combiner for a Doherty amplifier and a Doherty amplifier. Background Art

[0002] Today, the Doherty amplifier design is a very important amplifier design and is used in many different applications. But probably the most important use is in mobile communications for amplification in the RF output stage. The basic idea of ​​the Doherty amplifier is to combine a carrier amplifier with a peaking amplifier for peak power, see Figure 1 The Doherty amplifier combines the power of two (and more recently, more) amplifiers, one is called the "carrier" amplifier and the second is called the "peaking" amplifier. In many Doherty amplifiers, the two amplifiers are biased differently, with the carrier amplifier operating in normal Class AB (providing gain at any power level) or Class B, and the peaking amplifier operating in Class C, with the peaking amplifier only conducting for half of the cycle. Doherty amplifiers offer many beneficial characteristics at backed-off power levels compared to balanced amplifiers, such as improved power-added efficiency.

[0003] The Doherty amplifier pair works as follows: On the input, a quadrature coupler is used to split the signal, which may not necessarily be equal separation. The input behavior is the same as a balanced amplifier and has the same characteristics, where if the reflection coefficients are equal in amplitude and phase, the mismatched amplifiers will have their reflection coefficients reduced and the reflected waves end up in the load, terminating the isolated port of the coupler.

[0004] At the output of the Doherty pair, the two signals are 90 degrees out of phase, but with the addition of the quarter-wavelength transmission line of the peaking amplifier, they are brought back into phase and reactance combined. At this point, the two signals are in parallel producing a Z0 / 2 impedance. This is stepped up to Z0 through the quarter-wave transformer. However, the amplifiers operate nonlinearly, which means that the output combiner becomes more complex. During operation, the response of one amplifier actively load-pulls the other. In order to size and design the Doherty amplifier, a nonlinear analysis must be performed.

[0005] In the combiner, the signal from the peaking amplifier and the signal from the carrier amplifier are brought back into phase and reactance combined. This usually requires a quarter-wavelength transmission line and other parts of the transmission line, see Figure 2 , and if the operating frequency is low, these transmission lines may be large and bulky. In addition, due to the use of transmission lines, this solution may be narrow-band.

[0006] It is therefore an object of the present invention to provide a combiner which reduces the usage of transmission lines for its operation.

[0007] Several attempts have been made in the art to design such a combiner with varying degrees of success. In the following, such known attempts will be discussed.

[0008] An output combiner is disclosed in US 9071211 B1. However, this solution uses transmission lines for the main amplifier and for the peak amplifier, which may result in a design that is difficult to integrate due to the physical size of the transmission lines if lower frequencies are used. The combiner utilizes a combination of lumped elements (such as inductors, capacitors and transmission lines) to achieve the desired reactive coupling.

[0009] Therefore, there is still room for improvement in order to realize a small and efficient improved Doherty combiner. Summary of the invention

[0010] According to the invention, the above object is achieved by a filter combiner having the features defined in claim 1 .

[0011] The filter combiner for the Doherty amplifier according to the present invention includes: a first port, a second port and a third port, wherein the first port is configured to be connected to the output of the carrier amplifier and has an impedance of Z0; the second port is configured to be connected to the load and has an impedance of Z0·r / (1+r); the third port is configured to be connected to the peak amplifier and has an impedance of Z0·r / (1+r), wherein r is the power ratio of the carrier amplifier to the peak amplifier. The filter combiner also includes a fourth port configured to be connected to the output port of the Doherty amplifier and having an impedance of Z0. The first port is connected to the second port via a first network, wherein the first network is a low-pass filter. The first port is connected to the third port via a second network, wherein the second network is a low-pass filter, which is configured to operate as a band-stop filter when a high impedance is loaded to the input or output of the second network when the peak amplifier is turned off. The third port is connected to the fourth port via a third network, wherein the third network is a low-pass filter, which is configured to operate as a band-stop filter when a high impedance is loaded to the input or output of the second network when the peak amplifier is turned off. The fourth port is connected to the second port via a fourth network, wherein the fourth network is a low pass filter.

[0012] According to one embodiment, the first network, the second network, the third network and the fourth network comprise only lumped elements. In this way, the Doherty combiner becomes smaller as the number of bulky transmission line sections is reduced. Furthermore, this allows a combiner with wider bandwidth capabilities.

[0013] According to one embodiment, the high impedance is greater than 500 ohms.

[0014] According to one embodiment, the first network, the second network, the third network and the fourth network are π-type and / or T-type low-pass filters.

[0015] According to one embodiment, the first network, the second network, the third network and the fourth network are symmetric networks.

[0016] According to one embodiment, the first network, the second network and the third network form a first branch, and wherein the filter combiner comprises at least one further first branch, the at least one further first branch being cascade-coupled to the first branch via the fourth network and cascade-coupled to the fourth port of the filter combiner and cascade-coupled to the second port of the filter combiner. In this way, a broadband Doherty combiner can be designed.

[0017] The present invention also relates to a Doherty amplifier for telecommunications, comprising: an input port; a splitter having an input connected to the input port; a carrier amplifier having an input connected to an output of the splitter. The Doherty amplifier also includes a peaking amplifier having an input connected to the output of the splitter with a phase delay. The Doherty amplifier also includes a filter combiner according to any embodiment disclosed herein, and a first port of the filter combiner is connected to the output of the carrier amplifier, and a third port of the filter combiner is connected to the output of the peaking amplifier. Further, a load is connected to a second port of the filter combiner, and an output port is connected to a fourth port of the filter combiner.

[0018] Other advantages of the present invention will become apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0020] Figure 1 is a schematic block diagram of a prior art Doherty amplifier,

[0021] Figure 2 is a schematic block diagram of a prior art Doherty amplifier,

[0022] Figure 3 is a schematic block diagram of a Doherty amplifier with a combiner according to an embodiment of the present invention,

[0023] Figure 4 is a schematic block diagram of a Doherty amplifier with a combiner according to an embodiment of the present invention,

[0024] Figure 5 is a circuit diagram of a combiner according to an embodiment of the present invention,

[0025] Figure 6 is a circuit diagram of a combiner according to an embodiment of the present invention,

[0026] Figure 7 is a circuit diagram of a combiner according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] Reference now Figure 3 , which shows a Doherty amplifier for telecommunications, generally indicated as 302. The Doherty amplifier for telecommunications 302 includes: an input port 316; a splitter 317 having an input connected to the input port 316; a carrier amplifier 304 having an input connected to the output of the splitter 317; a peaking amplifier 308 having an input connected to the output of the splitter with a phase delay. The Doherty combiner 302 also includes a filter combiner 301 described below, wherein a first port 303 of the filter combiner 301 is connected to the output of the carrier amplifier 304, and a third port 307 of the filter combiner 301 is connected to the output of the peaking amplifier 308; a load 306 is connected to a second port 305 of the filter combiner 301; and an output port 310 is connected to a fourth port 309 of the filter combiner 301.

[0028] The filter combiner 301 includes: a first port 303, a second port 305, a third port 307 and a fourth port 309; the first port 303 is configured to be connected to the output of the carrier amplifier 304 and has an impedance of Z0; the second port 305 is configured to be connected to the load 306 and has an impedance of Z0·r / (1+r); the third port 307 is configured to be connected to the peak amplifier 308 and has an impedance of Z0·r / (1+r); wherein r is the power ratio of the carrier amplifier to the peak amplifier; the fourth port 309 is configured to be connected to the output port 310 of the Doherty amplifier 302 and has an impedance of Z0. The first port is connected to the second port via a first network 311. The first network is a low-pass filter. The first port is connected to the third port via a second network 312. The second network is a low-pass filter, which is configured to operate as a band-stop filter when a high impedance is loaded to the input or output of the second network when the peak amplifier is turned off. The third port is connected to the fourth port via a third network 313. The third network is a low pass filter configured to operate as a band stop filter when a high impedance is loaded to the input or output of the second network when the peak amplifier is off. The fourth port is connected to the second port via a fourth network 314. The fourth network is a low pass filter.

[0029] RF design and especially microwave design used to be a technical field that relied heavily on experience and manual tuning with ferrite blocks and engraving PCBs with general-purpose knives. Today, this manual work has been largely replaced by numerical simulations that combine electromagnetic field simulations and circuit simulations. An important tool of such simulation packages is the optimizer, in which the goals are set by the operator and the simulator adapts the circuit to achieve the goals.

[0030] The design of a filter combiner according to the present invention relies heavily on the use of such an optimizer, and the process of designing such a combiner will be outlined herein.

[0031] Reference now Figure 3 , the design process of the filter combiner of the present invention will be summarized. The filter combiner of the present invention can be designed by the following steps:

[0032] a) Design a conventional Doherty amplifier with the following impedance:

[0033] The first port 303 has an impedance of Z0.

[0034] A second port 305 having an initial reactive load value for a load 306 .

[0035] The third port 307 has an impedance of Z0·r / (1+r).

[0036] The fourth port 309 has an impedance of Z0.

[0037] b) Fix the impedance values ​​of the first port 303, the third port 307 and the fourth port 309. Establish variables for the first network 311, the second network 312, the third network 313 and the fourth network 314. The variables may be component values ​​for the passive components of the respective networks as well as fixed Q values ​​and fixed operating frequencies.

[0038] An optimization goal is established, which can be expressed as small signal S parameters, as well as phase shift and group delay.

[0039] c) Select an appropriate optimization strategy and perform the optimization so that the error between the target and the current design is minimized.

[0040] d) When the optimization goal is achieved, the filter combiner design is fixed.

[0041] e) Fine tune the load 306 until the designed Doherty amplifier has acceptable performance.

[0042] Figure 4A cascade-coupled filter combiner according to an embodiment of the present invention is shown, wherein a first network, a second network and a third network form a first branch (315), and wherein the filter combiner comprises at least one further first branch (401), the at least one further first branch (401) being cascade-coupled to the first branch (315) via the fourth network (314) and cascade-coupled to a fourth port (309) of the filter combiner and cascade-coupled to a second port (305) of the filter combiner.

[0043] Now refer to it again Figure 3 , the first network 311, the second network 312, the third network 313 and the fourth network 314 only include lumped elements. The first network 311, the second network 312, the third network 313 and the fourth network 314 are π-type and / or T-type low-pass filters. In addition, the first network 311, the second network 312, the third network 313 and the fourth network 314 are symmetrical networks. This Figure 5 It is shown in Figure 5 A filter combiner 500 according to an embodiment of the present invention is shown. The filter combiner 500 comprises a first port 1 connected to a second port 2 via an inductor L1. The first port 1 is also connected to a third port 3 via an inductor L4. The third port 3 is connected to a fourth port 4 via an inductor L3. The filter combiner further comprises two capacitors C1-C8 for each inductor L1-L4, wherein each inductor is provided with capacitors connected to a ground node at its input and output ends, respectively.

[0044] Figure 6 The filter combiner generally designated 600 disclosed in Figure 5 The filter combiner 500 in FIG. 5 differs in that the capacitors connected to the same node in the circuit are lumped together.

[0045] at last, Figure 7 A filter combiner 700 is disclosed, wherein a first port 1 is connected to a second port 2 via an inductor L1. In addition, the first port 1 is connected to a third port 3 via two capacitors C1 and C3 connected in series. The second port 2 is connected to a fourth port 4 via two capacitors C2 and C4 connected in series. A common node between capacitors C1 and C3 is connected to a common node between capacitors C2 and C4 via an inductor L2. The described embodiments of the filter combiner utilize a small number of components and can be formed in a dense package.

[0046] The inventors have realised that by loading the low pass filter with a varying load, the low pass filter can be used as, for example, a band stop filter. This insight can be used in many different circuits for a filter combiner without departing from the inventive concept. Figures 5 to 7The embodiments shown in are only examples of such filter combiners and many more examples can be found.

[0047] Project List

[0048] Filter combiners 301, 500, 600, 700

[0049] Doherty Amplifier 302

[0050] First port 303,1

[0051] Carrier amplifier 304

[0052] Second port 305, 2

[0053] Load 306

[0054] The third port 307, 3

[0055] Peaking amplifier 308

[0056] Fourth port 309, 4

[0057] Output port 310

[0058] First Network 311

[0059] Second Network 312

[0060] Third Network 313

[0061] Fourth Network 314

[0062] First Branch 315

[0063] Input port 316

[0064] Separator 317

[0065] Another first branch 401 .

Claims

1. A Doherty amplifier (302) for telecommunications, comprising: InputPort(316); a separator (317), the separator (317) having an input end connected to the input port (316); a carrier amplifier (304) having an input connected to the output of the separator (317); a peak amplifier (308) having an input terminal connected to another output terminal of the splitter with a phase delay; The invention is characterized by comprising a filter combiner (301), wherein the filter combiner (301) comprises: A first port (303), the first port (303) having an impedance of Z0 and connected to an output end of the carrier amplifier (304); A second port (305) having an impedance of Z0⋅r / (1+r) and connected to a load (306); A third port (307) having an impedance of Z0⋅r / (1+r) and connected to the peak amplifier (308), wherein r is a power ratio of the carrier amplifier to the peak amplifier; a fourth port (309), the fourth port (309) having an impedance of Z0 and connected to an output port (310) of the Doherty amplifier (302); wherein the first port is connected to the second port via a first network (311), wherein the first network is a low pass filter; wherein the first port is connected to the third port via a second network (312), wherein the second network is a low pass filter and is configured to operate as a band stop filter when a high impedance is loaded to the input or the output of the second network when the peak amplifier is turned off; wherein the third port is connected to the fourth port via a third network (313), wherein the third network is a low pass filter and is configured to operate as a band stop filter when a high impedance is loaded to the input or the output of the second network when the peak amplifier is turned off; wherein the fourth port is connected to the second port via a fourth network (314), wherein the fourth network is a low-pass filter, the first network, the second network, the third network and the fourth network only include lumped elements and are π-type or T-type low-pass filters, and the first network, the second network, the third network and the fourth network are symmetric networks, In the filter combiner (301, 500), the first port (303, 1) is connected to the second port (2) via an inductor L1, the first port (303, 1) is further connected to the third port (307, 3) via an inductor L4, the third port (307, 3) is connected to the fourth port (309, 4) via an inductor L3, the second port (2) is connected to the fourth port (309, 4) via an inductor L2, each inductor is provided with capacitors connected to a ground node at its input and output ends, or In the filter combiner (301, 700), the first port (303, 1) is connected to the second port (305, 2) via an inductor L1, the first port (303, 1) is connected to the third port (307, 3) via two capacitors C1 and C3 connected in series, the second port (305, 2) is connected to the fourth port (4) via two capacitors C2 and C4 connected in series, the third port (307, 3) is connected to the fourth port (4) via an inductor L3, wherein a common node between the capacitors C1 and C3 is connected to a common node between the capacitors C2 and C4 via an inductor L2.

2. The Doherty amplifier (302) according to claim 1, characterized in that The high impedance is greater than 500 ohms.

3. The Doherty amplifier (302) according to any one of the preceding claims, characterized in that The first network, the second network and the third network form a first branch (315), and wherein the filter combiner comprises at least one further first branch (401), the at least one further first branch (401) being cascade-coupled to the first branch (315) via the fourth network (314) and to the fourth port (309) of the filter combiner and to the second port (305) of the filter combiner.

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