Doherty amplifier

Abstract

The present disclosure relates to a Doherty amplifier. The invention relates to a Doherty amplifier. The present disclosure also relates to a base station for mobile communication comprising such an amplifier. And the Doherty amplifier comprises a main amplifier, a peak value amplifier, a Doherty shunt and a Doherty combiner. The amplifier further includes a non-impedance transformation connection between the output of the main amplifier and the first input port of the Doherty combiner, and a first impedance transformation network disposed between the output of the peaking amplifier and the second input port of the Doherty combiner. The signal at the first input port of the Doherty combiner and the signal at the second port of the Doherty combiner have opposite phases. The Doherty combiner includes a second impedance transformation network between the first input port and the output port, and a third impedance transformation network between the second input port and the output port, where the Doherty combiner is configured to add the signal amplified by the main amplifier and the signal amplified by the first amplifier in phase at the output port.

Description

Technical Field

[0001] Aspects of the present disclosure relate to a Doherty amplifier. Aspects of the present disclosure also relate to a base station for mobile communication comprising such an amplifier. Background Art

[0002] Doherty amplifiers and digital pre-distortion amplifiers (DPA) are known in the prior art. The DPA includes a main amplifier and one or more peak amplifiers. The main amplifier is usually biased in class B, while the one or more peak amplifiers are biased in class C. The Doherty splitter is used to divide the input radio frequency (RF) signal into a main signal portion and one or more peak signal portions, and to provide these signal portions to the main amplifier and the one or more peak amplifiers, respectively. The signal amplified by the main amplifier and the signal amplified by the one or more peak amplifiers are combined in phase by the Doherty combiner.

[0003] One major advantage of using a DPA is improved efficiency during power back-off. This improved efficiency is achieved using load modulation. More specifically, during power back-off conditions, one or more peak amplifiers are turned off. As a result, the one or more peak amplifiers do not output current through the output of the DPA, so the voltage at the output will be lower than if current were output through the one or more peak amplifiers. The lower voltage can be converted into a smaller impedance.

[0004] The Doherty combiner of the DPA is configured to transform this impedance behavior. In other words, the lower impedance seen near the combining node is transformed into a higher impedance presented at the output of the main amplifier. Similarly, when one or more peaking amplifiers do output current through the output, the effective impedance rises and a lower impedance is presented at the output of the main amplifier.

[0005] Compared to the saturated operating mode where all amplifiers output power, using a higher impedance at power back-off enables better efficiency at power back-off. More specifically, the efficiency of the DPA typically exhibits a peak efficiency close to the saturated output power and at least one additional peak efficiency at power back-off relative to the input power. Multiple peaks at power back-off can be obtained by using multiple peak amplifiers.

[0006] There are two known DPA topologies, both of which are Figure 11A. In the known topology DPA 1A, the input signal is split by a Doherty splitter 10 and the corresponding signal parts are amplified by a main amplifier 20 and a peak amplifier 30. An impedance transformer in the form of a 90-degree transmission line with a characteristic impedance Z0 is arranged between the output of the main amplifier 20 and the combining node C. Here, the combining node C also forms the output of the DPA 1A. A load impedance ZL can be connected to the combining node C. At power back-off, a transmission line with an impedance Z1 and a transmission line with an impedance Z2 are used to present a high impedance to the combining node C, while under saturated power conditions, these transmission lines provide impedance matching.

[0007] DPA 1B uses a coupler 40 to combine the signal from the main amplifier 20 and the signal from the peaking amplifier 30. If the peaking amplifier 30 is turned off, a high impedance is seen when looking at the peaking amplifier 30. This high impedance is transformed by the 90 degree transmission line with characteristic impedance Z0 into an RF short circuit presented at one port of the coupler 40. When the peaking amplifier 30 is turned on, there is a phase difference between the signals entering at the two different input ports of the coupler 40. As a result, the impedance seen by the main amplifier 20 under power back-off conditions is higher than the impedance under saturated power conditions, thereby achieving improved efficiency under power back-off conditions.

[0008] As can be observed, DPA 1B does not have an impedance transformer arranged between coupler 40 and main amplifier 20. Since these elements are usually implemented using 90 degree transmission lines, they tend to reduce the bandwidth of the amplifier. For this reason, DPA 1B presents an interesting topology from a bandwidth point of view. However, at the same time, implementing coupler 40 may take up a large area, especially for relatively low frequencies (e.g., 1 GHz). Summary of the invention

[0009] According to one aspect of the present disclosure, a Doherty amplifier is provided, which provides a bandwidth improvement that consumes less area. The Doherty amplifier includes a main amplifier, a peak amplifier, and a Doherty splitter, the Doherty splitter being configured to divide an input signal into a main signal portion and a peak signal portion, and to provide the main signal portion and the peak signal portion to the main amplifier and the peak amplifier, respectively. The Doherty amplifier also includes a Doherty combiner, which has a first input port, a second input port, and an output port. In addition, the Doherty amplifier includes a non-impedance transformation connector located between the output end of the main amplifier and the first input port, and a first impedance transformation network arranged between the output end of the peak amplifier and the second input port. The Doherty splitter, the non-impedance transformation connector, and the first impedance transformation network are configured so that the signal at the first input port of the Doherty combiner and the signal at the second port of the Doherty combiner have opposite phases.

[0010] The Doherty combiner includes: a second impedance transformation network located between the first input port and the output port, and a third impedance transformation network located between the second input port and the output port, wherein the Doherty combiner is configured to add the signal amplified by the main amplifier and the signal amplified by the first amplifier in phase at the output port.

[0011] Applicants have discovered that by ensuring a difference of at least about 180 degrees at the multiple input ports of a Doherty combiner, bandwidth improvements can be obtained even when implementing the Doherty combiner using less circuit board space.

[0012] The second impedance transformation network may include a transmission line or transmission line assembly having a first electrical length at the operating frequency. The third impedance transformation network may include a transmission line or transmission line assembly having a second electrical length at the operating frequency. The first electrical length and the second electrical length may differ by approximately 180 degrees at the operating frequency.

[0013] One of the second impedance transformation network and the third impedance transformation network may include a quarter wavelength transmission line, and the other of the second impedance transformation network and the third impedance transformation network may include a quarter wavelength transmission line in series with a half wavelength transmission line.

[0014] Additionally or alternatively, the Doherty combiner may further include a half-wavelength transmission line between the first input end and the second input end of the Doherty combiner, wherein the central region of the half-wavelength transmission line is RF grounded. For example, at or near the operating frequency, the electrical length between each of the first input port and the second input port of the Doherty combiner and the central region may be equal to 90 degrees. In this way, the impedance at each of the first input port and the second input port looking toward the central region through the half-wavelength transmission line corresponds to an RF open circuit, which is caused by the impedance transformation achieved by the quarter-wave band between the central region and the first input port and the second input port.

[0015] The quarter-wavelength transmission line and the half-wavelength transmission line of the second impedance transformation network and the third impedance transformation network can form a ring coupler together. The ring coupler has four ports arranged in a ring. The electrical distances between these ports (shown in brackets) correspond to p1->p2 (90), p2->p3 (90), p3->p4 (90), p4->p1 (270). In this example, port p2 can be grounded, ports p1 and p3 can be used as input ports of the Doherty combiner, and port p4 can be used as an output port.

[0016] Since the central region is RF grounded, the central region can be used to bias the main amplifier and the peak amplifier. For example, the Doherty amplifier can include a bias circuit for providing bias signals to the main amplifier and the peak amplifier, wherein the bias circuit is connected to the central region of a half-wavelength transmission line arranged between the first input terminal and the second input terminal of the Doherty combiner.

[0017] The characteristic impedances of all transmission lines of the second impedance transformation network and the third impedance transformation network may be equal to the same characteristic impedance. More specifically, all transmission lines of the second impedance transformation network and the third impedance transformation network may have the same transmission line type, and these transmission lines may have the same size except for the length.

[0018] The first impedance transformation network may include: a first impedance matching network connected to the output end of the peak amplifier, a first quarter-wavelength transmission line, and a second quarter-wavelength transmission line, wherein the first quarter-wavelength transmission line is arranged between the first impedance matching network and the second quarter-wavelength transmission line. At or near the operating frequency, the combined electrical length of the first impedance transformation network may correspond to 270 degrees.

[0019] The peak amplifier may include a peak power transistor having an intrinsic drain, wherein the first impedance matching network is connected between the intrinsic drain of the peak power transistor and the quarter wavelength transmission line.

[0020] The non-impedance transformation connection may include: a second impedance matching network connected to the output terminal of the main amplifier, and a first quarter-wavelength transmission line. At or near the operating frequency, the combined electrical length of the non-impedance transformation network may correspond to 180 degrees.

[0021] The main amplifier may include a first power transistor having an intrinsic drain. In this case, the second impedance matching network may be connected between the intrinsic drain of the main power transistor and the quarter-wavelength transmission line.

[0022] The Doherty amplifier may further include a printed circuit board PCB, wherein the Doherty combiner is implemented on the PCB. The first quarter-wavelength transmission line and the second quarter-wavelength transmission line of the first impedance transformation network may be implemented on the PCB, wherein the first impedance matching network is partially implemented on the PCB. Additionally or alternatively, the quarter-wavelength transmission line of the non-impedance transformation connector may be implemented on the PCB, wherein the second impedance matching network is partially implemented on the PCB.

[0023] The main amplifier and the peak amplifier can be provided as packaged devices, wherein the main amplifier and the peak amplifier are preferably provided in a single package. For example, the main amplifier and the peak amplifier can each include a laterally diffused metal-oxide-semiconductor (LDMOS), a power transistor, or a field effect power transistor based on gallium nitride. The semiconductor chips corresponding to these power transistors can be installed in a lead frame package, for example. In this case, the first impedance matching network can be partially formed by a bonding wire extending between a drain pad of the power transistor of the peak amplifier and a corresponding pin of the peak amplifier package. Similarly, the second impedance matching network can be partially formed by a bonding wire extending between a drain pad of the power transistor of the main amplifier and a corresponding pin of the main amplifier package.

[0024] According to a second aspect of the present disclosure, there is provided a base station for mobile communication, the base station comprising a Doherty amplifier as defined above. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Next, various aspects of the present disclosure will be described in more detail by referring to the accompanying drawings, wherein the same reference numerals will be used to represent the same or similar components, and in which:

[0026] Figure 1 Two known topologies for DPA are shown;

[0027] Figure 2A general embodiment of a DPA according to the present disclosure is shown;

[0028] Figure 3 A first specific embodiment of a DPA using a ring coupler according to the present disclosure is shown;

[0029] Figure 4 A first specific embodiment of a DPA using a transmission line according to the present disclosure is shown;

[0030] Figure 5 Another specific embodiment of a DPA using a ring coupler according to the present disclosure is shown;

[0031] Figure 6 The performance of a DPA according to the present disclosure compared to a known DPA is shown. DETAILED DESCRIPTION

[0032] Figure 2 A general embodiment of a DPA 100 according to the present disclosure is shown. The DPA 100 includes a splitter 110 for splitting an input signal, a main amplifier 120 , a peak amplifier 130 , a non-impedance transformation network 150 , a first impedance transformation network 160 , and a Doherty combiner 140 .

[0033] The main amplifier 120 and the peak amplifier 130 may be matched devices. For example, the main amplifier 120 and the peak amplifier 130 may each be matched with the impedance Zm for outputting saturated power.

[0034] The Doherty combiner 140 includes a second impedance transformation network 141 arranged between ports p1 and p3, and a third impedance transformation network 142 arranged between ports p2 and p3. The output end (corresponding to port p3) of the DPA 100 is connected to a load impedance ZL. The load impedance may correspond to an impedance matching network (e.g., a quarter-wavelength transmission line) and a real load (e.g., 50 ohms) connected in series.

[0035] In the context of the present disclosure, the transformation network has an electrical length of (2n+1)×90 degrees at or near an operating frequency, where n is an integer different from zero.

[0036] According to the present disclosure, the signals at ports p1 and p2 have opposite phases. More specifically, there is a phase difference of about 180 degrees between these signals at or near the operating frequency. To achieve a 180 degree phase shift, the splitter 110 can add a 90 degree delay to the signal provided to the peak amplifier 130 relative to the signal provided to the main amplifier 120.

[0037] When the power is backed off, the peak amplifier 130 will be turned off. Since the electrical length between the output of the peak amplifier 130 and port p3 is a multiple of 180 degrees, no or little impedance transformation occurs, and a high impedance can be seen when looking at the peak amplifier 130 at port p3. In addition, under these conditions, less current will be output through port p3 than under saturated power conditions. The effective impedance seen toward port p3 (for example, downstream of the second impedance transformation network 141) will be less than the effective impedance under saturated power conditions. Due to the combination of the non-impedance transformation connection 150 and the second impedance transformation network 141, this lower impedance will be transformed into a higher impedance seen at the output of the main amplifier 150. Therefore, high efficiency can be obtained when the power is backed off.

[0038] Figure 6 shows the DPA 100 with Figure 1 1A and the known DPA 100. The left graph shows the efficiency as a function of frequency (in GHz) under back-off (BO) and saturated power (SAT) conditions. The right graph shows the output power (in dBm) as a function of frequency (in GHz). As shown, DPA 100 provides a larger bandwidth than DPA 1A.

[0039] Figure 3 A first specific embodiment of the DPA 100 is shown. More specifically, the DPA 200 includes a rat-race coupler 240 that implements the Doherty combiner 140 of the DPA 100. In addition, the non-impedance transformation network 150 is replaced by a via having an electrical length equal to n×360 degrees, where n is an integer, where n can be zero. The impedance transformation network 160 is implemented using a single 90-degree transmission line.

[0040] The electrical length between ports p1 and p3 is equal to 90 degrees, while the electrical length between ports p2 and p3 is equal to 270 degrees. Port p4 is RF grounded. When ports p1 and p4 and ports p1 and p2 are separated by an electrical length of 90 degrees, the RF short circuit will turn into an RF open circuit at ports p1 and p2. This aspect enables port p4 to be used as a bias access point. This Figure 5 , where capacitor C1 is used to realize RF grounding, and a bias circuit Vb is set to bias the peak amplifier 130 and the average amplifier 120. A direct current (DC) blocking capacitor C2 is used to block the DC signal from entering the load impedance ZL.

[0041] Figure 4A second specific embodiment of the DPA 100 is shown. More specifically, the DPA 300 includes a Doherty combiner 340 including a quarter-wavelength transmission line between ports p1 and p3, and a half-wavelength transmission line and a quarter-wavelength transmission line in series combination between ports p2 and p3. Similar to the ring coupler 240, the half-wavelength transmission line is arranged between ports p1 and p2, wherein the half-wavelength transmission line is RF-grounded at its central region.

[0042] Figure 5 Another specific embodiment of DPA 100 is shown, in which a ring coupler 240 is used. In this case, the non-impedance transformation network 450 includes an impedance matching network 4501 and a transmission line 4502. In addition, the main amplifier 120 and the peak amplifier 130 are arranged in a single package or mounted as separate packages on a printed circuit board PCB. The same PCB can be used to implement Figures 2 to 5 The annular coupler 240 and / or any other transmission line based component of the embodiment shown in FIG. The RF grounding of the annular coupler 240 or the central region of the half-wavelength transmission line 343 can be achieved using via technology or the like.

[0043] The main amplifier 120 can be formed using a semiconductor chip mounted in a lead frame package or other type of package. Typically, the drain of a power transistor implemented on a semiconductor chip is connected to a terminal of the package using some electrical connection (such as one or more bonding wires). These bonding wires and parasitic elements of other packages or devices can be part of an impedance matching network 4501. The impedance matching network typically also includes a portion of a transmission line implemented on a PCB, which can be partially used as a pad on which a terminal (such as a pin) of the package is mounted. The combination of the impedance matching network 4501 and the transmission line 4502 provides an electrical length equal to n×180 degrees at or near the operating frequency. In addition, in some embodiments, at or near the operating frequency, the impedance matching network 4501 and the transmission line 4502 both have an electrical length equal to or at least approximately 90 degrees.

[0044] Similarly, the peak amplifier 130 may be formed using a semiconductor chip mounted in a lead frame package or other types of packages. In addition, the first impedance transformation network 460 may include an impedance matching network 4601 and a pair of transmission lines 4602 , 4603 .

[0045] Impedance matching network 4601 may have a similar configuration as impedance matching network 4501. The combination of impedance matching network 4601 and transmission lines 4602, 4603 should provide an electrical length of (2n+1) x 90 degrees, where n is an integer of 1 or greater.

[0046] for Figure 3 , Figure 4 , Figure 5 In the illustrated embodiment, the transmission lines used in the Doherty combiners 140, 240, 340, whether as discrete lines or as part of a ring coupler, can have the same characteristic impedance. This impedance can correspond to sqrt(2) times ZL Under saturated power conditions, assuming a 1:1 power ratio between the main amplifier 120 and the peak amplifier 130, the effective impedance seen from the main branch and the peak branch at port p3 is equal to 2ZL. At port p1, this impedance is transformed by the second impedance transformation network to (sqrt(2)ZL)^2 / (2ZL)=ZL. The same impedance can be seen at port p2. In addition, the non-impedance transformation network 150 and the first impedance transformation network 160 ensure that the impedance is properly matched to the impedance required by the main amplifier 120 and the peak amplifier 130 to output saturated power.

[0047] Note that the example above assuming a power ratio of 1:1 is only an example. It is clear to those skilled in the art how various characteristic impedances must be selected to take into account different power ratios.

[0048] The above description presents details about embodiments according to aspects of the present disclosure. However, the present disclosure is not limited to these embodiments. Instead, various modifications are possible without departing from the scope of the present disclosure as defined by the appended claims and their equivalents.

Claims

1. A Doherty amplifier (100, 200, 300, 400), comprising: Main amplifier (120); A peak amplifier (130); A Doherty splitter (110) configured to split an input signal into a main signal portion and a peak signal portion, and provide the main signal portion and the peak signal portion to the main amplifier and the peak amplifier respectively; A Doherty combiner (140, 240, 340) having a first input port (p1), a second input port (p2) and an output port (p3); A non-impedance transformation connector (150, 450) located between the output end of the main amplifier and the first input port; as well as A first impedance transformation network (160, 460) arranged between the output end of the peak amplifier and the second input port; The Doherty splitter, the non-impedance transformation connector and the first impedance transformation network are configured so that a signal at the first input port of the Doherty combiner and a signal at the second port of the Doherty combiner have opposite phases; The Doherty combiner comprises: a second impedance transformation network (141, 341) located between the first input port and the output port, and a third impedance transformation network (142, 342) located between the second input port and the output port, wherein the Doherty combiner is configured to add the signal amplified by the main amplifier and the signal amplified by the first amplifier in phase at the output port.

2. The Doherty amplifier according to claim 1, wherein: The second impedance transformation network includes a transmission line or a transmission line component having a first electrical length at an operating frequency, and wherein the third impedance transformation network includes a transmission line or a transmission line component having a second electrical length at the operating frequency, wherein the first electrical length and the second electrical length differ by approximately 180 degrees at the operating frequency.

3. The Doherty amplifier according to claim 2, wherein: One of the second impedance transformation network (341) and the third impedance transformation network comprises a quarter-wavelength transmission line, and wherein the other of the second impedance transformation network and the third impedance transformation network (342) comprises a quarter-wavelength transmission line (3421) connected in series with a half-wavelength transmission line (3422).

4. The Doherty amplifier according to claim 3, wherein: The Doherty combiner (340) further comprises a half-wavelength transmission line (343) located between the first input end and the second input end of the Doherty combiner, wherein a central region of the second half-wavelength transmission line is RF grounded.

5. The Doherty amplifier according to claim 4, wherein: The quarter-wavelength transmission line and the half-wavelength transmission line of the second impedance transformation network and the third impedance transformation network jointly form a ring coupler (240).

6. The series Doherty amplifier according to claim 4, wherein: The Doherty amplifier further comprises a bias circuit (Vb) for providing bias signals to the main amplifier and the peak amplifier, wherein the bias circuit is connected to a central region of a half-wavelength transmission line arranged between the first input terminal and the second input terminal of the Doherty combiner.

7. The Doherty amplifier according to claim 6, wherein: The characteristic impedances of all transmission lines of the second impedance transformation network and the third impedance transformation network are equal to the same characteristic impedance.

8. The Doherty amplifier according to claim 1, wherein: The first impedance transformation network (460) comprises: a first impedance matching network (4601) connected to the output end of the peak amplifier, a first quarter-wavelength transmission line (4602) and a second quarter-wavelength transmission line (4602), wherein the first quarter-wavelength transmission line is arranged between the first impedance matching network and the second quarter-wavelength transmission line.

9. The Doherty amplifier according to claim 8, wherein: The peak amplifier includes a peak power transistor having an intrinsic drain, wherein the first impedance matching network is connected between the intrinsic drain of the peak power transistor and the quarter-wavelength transmission line.

10. The Doherty amplifier according to claim 1, wherein: The non-impedance transformation connection element (450) comprises: a second impedance matching network (4501) connected to the output end of the main amplifier, and a quarter-wavelength transmission line (4502).

11. The Doherty amplifier according to claim 10, wherein: The main amplifier comprises a main power transistor having an intrinsic drain, wherein the second impedance matching network is connected between the intrinsic drain of the main power transistor and the quarter-wavelength transmission line.

12. The Doherty amplifier according to claim 1, further comprising a printed circuit board PCB, wherein: The Doherty combiner is implemented on the PCB.

13. The Doherty amplifier according to claim 12 and claim 8, wherein: The first quarter-wavelength transmission line and the second quarter-wavelength transmission line of the first impedance transformation network are implemented on the PCB, and wherein the first impedance matching network is partially implemented on the PCB.

14. The cascade Doherty amplifier according to claim 12 and claim 10, wherein: The quarter-wavelength transmission line of the non-impedance transforming connection is implemented on the PCB, and wherein the second impedance matching network is partially implemented on the PCB.

15. The cascade Doherty amplifier according to claim 1, wherein: The main amplifier and the peak amplifier are provided as packaged devices, wherein the main amplifier and the peak amplifier are preferably provided in a single package.

16. A base station for mobile communications comprising a Doherty amplifier as defined in any preceding claim.

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