FILTER COMBINER FOR A DOHERTY AMPLIFIER, AND A DOHERTY AMPLIFIER

Abstract

A filter combiner for a Doherty amplifier includes a first port with an impedance of Z0 configured to be connected to an output of a carrier amplifier; a second port with an impedance of Z0.Math.r/(1+r) configured to be connected to a load; a third port with an impedance of Z0.Math.r/(1+r) configured to be connected to a peak amplifier, wherein r is a power ratio for the carrier amplifier to the peak amplifier; and a fourth port with an impedance of Z0 configured to be connected to an output port of the Doherty amplifier. The first port is connected to the second port via a first network that is a lowpass filter and to the third port via a second network that is a lowpass filter which is configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The third port is connected to the fourth port via a third network that is a lowpass filter configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The fourth port is connected to the second port via a fourth network that is a lowpass filter.

Claims

1. A filter combiner for a Doherty amplifier, wherein the filter combiner comprises: a first port with an impedance of Z0 configured to be connected to an output of a carrier amplifier; a second port with an impedance of Z0.Math.r/(1+r) configured to be connected to a load; a third port with an impedance of Z0.Math.r/(1+r) configured to be connected to a peak amplifier, wherein r is a power ratio for the carrier amplifier to the peak amplifier; a fourth port with an impedance of Z0 configured to be connected to an output port of the Doherty amplifier; wherein the first port is connected to the second port via a first network, wherein the first network is a lowpass filter; wherein the first port is connected to the third port via a second network, wherein the second network is a lowpass filter which is configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off; wherein the third port is connected to the fourth port via a third network 4, wherein the third network is a lowpass filter configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off; wherein the fourth port is connected to the second port via a fourth network, wherein the fourth network is a lowpass filter.

2. A filter combiner according to claim 1, wherein the first network, the second network, the third network, and the fourth network only comprises lumped elements.

3. A filter combiner according to claim 1, wherein the high impedance is above 500 ohm.

4. A filter combiner according to claim 1, wherein the first, second, third, and the fourth network are π-type, or T-type, low pass filters.

5. A filter combiner according to claim 1, wherein the first network, the second network, the third network, and the fourth network are symmetrical networks.

6. The filter combiner according to claim 1, wherein the first network, the second network and the third network forms a first branch, and wherein the filter combiner comprises at least one further first branch cascade coupled to the first branch and to the fourth port of the filter combiner and to the second port of the filter combiner via said fourth network.

7. A Doherty amplifier for telecommunication, comprising: an input port; a splitter with an input connected to the input port; a carrier amplifier with an input connected to an output of the splitter; a peak amplifier with an input connected to an output of the splitter with a phase delay; and characterized by comprising a filter combiner according to claim 1; wherein the first port of the filter combiner is connected to an output of the carrier amplifier, and the third port of the filter combiner is connected to an output of the peak amplifier; a load is connected to the second port of the filter combiner; and an output port connected to the fourth port of the filter combiner.

Description

LIST OF DRAWINGS

[0019] Embodiments of the invention will now be described in detail with regard to the annexed drawings, in which:

[0020] FIG. 1 is a schematic block diagram of a prior-art Doherty amplifier,

[0021] FIG. 2 is schematic block diagram of a prior-art Doherty amplifier,

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

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

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

[0025] FIG. 6 is circuit diagram for a combiner according to an embodiment of the present invention, and

[0026] FIG. 7 is circuit diagram for a combiner according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0027] Reference is now made to FIG. 3 which shows a Doherty amplifier for telecommunication, generally designated 302. The Doherty amplifier 302 for telecommunication, comprises an input port 316; a splitter 317 with an input connected to the input port 316; a carrier amplifier 304 with an input connected to an output of the splitter 317; a peak amplifier 308 with an input connected to an output of the splitter with a phase delay. The Doherty combiner 302 further comprises a filter combiner 301 described herein below, wherein a first port 303 of the filter combiner 301 is connected to an output of the carrier amplifier 304, and a third port 307 of the filter combiner 301 is connected to an output of the peak amplifier 308; and a load 306 is connected to a second port 305 of the filter combiner 301; and an output port 310 connected to a fourth port 309 of the filter combiner 301.

[0028] The filter combiner 301 comprises: a first port 303 with an impedance of Z.sub.0 configured to be connected to an output of a carrier amplifier 304, a second port 305 with an impedance of Z.sub.0.Math.r/(1+r) configured to be connected to a load 306, a third port 307 with an impedance of Z.sub.0.Math.r/(1+r) configured to be connected to a peak amplifier 308, wherein r is a power ratio for the carrier amplifier to the peaking amplifier; a fourth port 309 with an impedance of Z.sub.0 configured to be connected to an output port 310 of the Doherty amplifier 302. The first port is connected to the second port via a first network 311. The first network is a lowpass filter. The first port is connected to the third port via a second network 312. The second network is a lowpass filter which is configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The third port is connected to the fourth port via a third network 313. The third network is a lowpass filter configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance 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 lowpass filter.

[0029] RF design and especially microwave design used to be an art that relied heavily upon experience and manual tuning with ferrite blocks and carving the PCB with an utility knife. This manual work has today been replaced to a large extent with numerical simulations that incorporates both electromagnetic field simulations and circuit simulations. An important tool of such simulation packages is the optimizer in which a goal is set by the operator and the simulator adapts the circuit to achieve the goal.

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

[0031] Now with reference made to FIG. 3 a design process of the inventive filter combiner will be outlined. The filter combiner of the present invention may be designed by following the steps below: [0032] a) Design a traditional Doherty amplifier with the following impedances: [0033] First port 303 with the impedance of Z.sub.0. [0034] Second port 305 start with an initial reactive load value for the load 306. [0035] Third port 307 with an impedance of Z.sub.0.Math.r/(1+r). [0036] Fourth port 309 with an impedance of Z.sub.0. [0037] b) Fix the impedance values for the first port 303, the third port 307, and for the fourth port 309. Set up variables for the first network 311, second network 312, third network 313, and the fourth network 314. The variables may be the component values for the passive components of respective network as well as fixed Q values and a fixed operation frequency. Set up optimization goals which may be expressed as small signal S-parameters, and phase shift and group delay. [0038] c) Select a proper optimization strategy and perform the optimization such that the error between the goal and the current design is minimized. [0039] d) When the optimization goals are achieved the filter combiner design is fixed. [0040] e) Fine tune the load 306 until the designed Doherty amplifier has acceptable performance.

[0041] FIG. 4 shows a cascade coupled filter combiner according to an embodiment of the present invention in which the first network, second network and the third network forms a first branch (315), and wherein the filter combiner comprises at least one further first branch (401) cascade coupled to the first branch (315) and to the fourth port (309) of the filter combiner and to the second port (305) of the filter combiner via said fourth network (314).

[0042] Now with reference made to FIG. 3 again, first network 311, the second network 312, the third network 313, and the fourth network 314 only comprises lumped elements. The first network 311, second network 312, third network 313, and the fourth network 314 are π-type, and/or T-type, low pass filters. Furthermore, the first network 311, the second network 312, the third network 313, and the fourth network 314 are symmetrical networks. This is illustrated in FIG. 5 which shows a filter combiner 500 according to an embodiment of the present invention. This filter combiner 500 comprises a first port 1 connected to a second port 2 via an inductance L1. The first port 1 is also connected to a third port 3 via an inductance L4. The third port 3 is connected to a fourth port 4 via an inductance L3. The filter combiner also comprises two capacitors C1-C8 for each inductance L1-L4, wherein each inductance is provided a capacitor connected to a ground node at its input and output, respectively.

[0043] The filter combiner disclosed in FIG. 6, generally designated 600, differs from the filter combiner 500 in FIG. 5 in that the capacitors connected to the same nodes in the circuit are lumped together.

[0044] Finally, FIG. 7 discloses a filter combiner 700 in which the first port 1 is connected to the second port 2 via an inductance L1. Furthermore, 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. The common node between the capacitors C1 and C3 is connected to the common node between the capacitors C2 and C4 via an inductance L2. This embodiment of a filter combiner utilizes a small number of components and may be formed in a dense package.

[0045] The inventor has realized that by loading a lowpass filter with a varying load the low pass filter may function as a band stop filter for example. This insight may be used in many different circuits for a filter combiner without departing from the inventive idea. The embodiments shown in FIG. 5 to FIG. 7 are only examples of such filter combiners and many more examples may be found.

LIST OF ITEMS

[0046] filter combiner 301, 500, 600, 700 [0047] Doherty amplifier 302 [0048] first port 303,1 [0049] carrier amplifier 304 [0050] second port 305,2 [0051] load 306 [0052] third port 307,3 [0053] peak amplifier 308 [0054] fourth port 309,4 [0055] output port 310 [0056] first network 311 [0057] second network 312 [0058] third network 313 [0059] fourth network 314 [0060] first branch 315 [0061] input port 316 [0062] splitter 317 [0063] further first branch 401