Pseudo-Doherty load modulation balanced amplifier

Abstract

The present application relates to a pseudo-Doherty load modulated balanced amplifier (PD-LMBA), and to a mobile communication base station comprising the PD-LMBA. The present application relates to a load modulated balanced amplifier (PD-LMBA) and to a mobile communication base station comprising the PD-LMBA. According to the invention, the PD-LMBA comprises a phase offset unit comprising at least one shunt series circuit connected to the ground, each shunt series circuit comprising an impedance transformer and a termination circuit arranged between the impedance transformer and the ground, the termination circuit is configured to present an RF short circuit to the impedance transformer at a first frequency within or near the frequency band, where the impedance transformer is configured to transform the RF short circuit to an RF open circuit at the first frequency. The phase offset unit further comprises at least one parallel resonant circuit arranged between the input and the output of the phase offset unit, where an impedance of the at least one parallel resonant circuit corresponds to an RF open circuit at a second frequency outside the frequency band. The first frequency is closer to a center frequency of the frequency band than the second frequency.

Description

Technical Field

[0001] The present application relates to a pseudo-Doherty load modulated balanced amplifier (PD-LMBA) and a mobile communication base station comprising the PD-LMBA. The present application particularly relates to a PD-LMBA configured to operate within a given frequency band, wherein the center frequency corresponding to the frequency band is in the range of 0.5 GHz to 8 GHz, wherein the bandwidth of the frequency band relative to the center frequency is in the range of 10% to 40%, and / or wherein the PD-LMBA is configured to output a maximum output power in the range of 10 mW to 500 W. These amplifiers can be used, for example, in industry, cellular networks, avionics, radar and medical technology. Background Art

[0002] The PD-LMBA is known in the prior art. The PD-LMBA includes a main splitter for splitting an input radio frequency (RF) signal into a first signal and a second signal. The PD-LMBA also includes a main amplifier for amplifying the first signal and a balanced amplifier for amplifying the second signal. The balanced amplifier includes a splitter for splitting the second signal into a first part and a second part of the second signal. The balanced amplifier also includes a first amplifier and a second amplifier, the first amplifier and the second amplifier being used to amplify the first part of the second signal and the second part of the second signal, respectively. The balanced amplifier also includes a combiner. The latter combiner is configured to combine the amplified first signal, the amplified first part of the second signal, and the amplified second part of the second signal into an output RF signal.

[0003] The first and second amplifiers of the balanced amplifier are usually biased in class C, while the main amplifier is biased in class A / B or class B. For an input RF signal with relatively low power, only the main amplifier will amplify the signal. For an input RF signal with relatively high power, both the main amplifier and the balanced amplifier will amplify the signal.

[0004] Compared to a conventional Doherty amplifier that includes a main amplifier and a peak amplifier, a PD-LMBA uses a balanced amplifier as a peak amplifier. In addition, in a PD-LMBA, the output of the main amplifier is connected to a port of a combiner that combines the amplified first part and the amplified second part of the second signal with the amplified first signal. The combiner is typically implemented using a hybrid coupler, the isolated port of which is connected to the output of the main amplifier. Therefore, the load modulation of the main amplifier by the balanced amplifier is less or different when compared to the load modulation in a conventional Doherty amplifier. Therefore, the term "pseudo-Doherty amplifier" is used to refer to this type of amplifier.

[0005] For PD-LMBAs and conventional Doherty amplifiers alike, it is important to combine the various signals so that there is little or no phase offset between the various signals at the point where the various signals are combined. In other words, at the output of the PD-LMBA or other locations where the various signals are combined and / or coexist, the phase offset between the amplified first signal and the amplified second signal should be n×360 degrees, where n is an integer equal to or greater than 0. In order to minimize the phase offset, the PD-LMBA and Doherty amplifiers typically include a phase offset unit, such as a transmission line, which can be arranged before and after the various amplifiers.

[0006] For example, a conventional Doherty amplifier may include a splitter that divides an input RF signal into a first portion and a second portion. The first portion is directly provided to a main amplifier, while the second portion is provided to a peak amplifier via a phase shift unit that provides a phase shift equal to 90 degrees. The amplified first portion and the amplified second portion of the input RF signal are combined at a combining node. The output of the main amplifier is connected to the combining node via an impedance transformer in the form of a quarter-wave transformer that produces a phase shift of 90 degrees. The output of the peak amplifier is directly connected to the combining node.

[0007] In the above example, the phase shifting unit arranged upstream of the peaking amplifier ensures that the amplified first part and the amplified second part of the RF input signal are combined in phase at the combining node. It should be noted that there are various other Doherty topologies. However, a similar phase shifting unit is used for each topology to reduce the phase shift between the amplified first part and the amplified second part of the RF input signal when these signals are combined at the combining node. Each phase shifting unit causes a phase delay in the signal on which it operates.

[0008] It is usually not possible to obtain zero phase offset over the entire frequency band of interest and for all powers of the RF input signal. For example, the electrical length of a transmission line varies with frequency. In addition, the phase offset applied by the amplifier varies with input power. Therefore, both Doherty amplifiers and PD-LMBAs are usually designed to achieve zero phase offset for a given frequency (usually the center frequency) and for a given input power or output power.

[0009] Typically, a transmission line is used to implement the phase shifting unit. Applicants have found that for PD-LMBA, the use of a transmission line is often insufficient to achieve a satisfactory phase shift when observed within a given frequency band. This will be explained below.

[0010] Figure 1A curve marked with a circle is shown which describes the desired phase offset to be added to the second signal before splitting the second signal into the first and second parts so that the signals amplified by the main amplifier and the balanced amplifier combine in phase. For example, when using a 2 GHz signal, it is desired that the second signal be delayed by 60 degrees.

[0011] like Figure 1 As shown, the desired phase shift to be added to the second signal is frequency dependent. In the same figure is shown a curve marked with a cross, which indicates the phase delay that can be added to the second signal when a transmission line is used.

[0012] The phase delay Off_c in degrees at the center frequency fc achieved by a transmission line of length l degrees is determined by the following formula:

[0013]

[0014] Where λ is the wavelength and v ph is the phase velocity. The phase delay difference Off_h-Off_l added to the second signal using the same transmission line between two frequencies fh and fl is given by:

[0015]

[0016] Therefore, the difference in phase delay (ie, Off_h - Off_l) that can be achieved using the transmission line over a given frequency band fh - fl is fixed.

[0017] exist Figure 1 In the above example, (fh-fl) / fc=0.2, Off_c=-60, and Off h -Off l =-12. Figure 1 It can be seen that at low frequencies the phase delay added by the transmission line to the second signal is too high, while at high frequencies the phase delay added by the transmission line to the second signal is too low. In other words, the derivative of the phase delay added by the transmission line to the second signal with respect to the frequency of the signal is too low. Summary of the invention

[0018] The purpose of this application is to provide a PD-LMBA that solves the above problems.

[0019] According to the present application, this object is achieved using the PD-LMBA defined in claim 1, characterized in that the PD-LMBA further comprises a phase shift unit, which is arranged upstream of the first amplifier and the second amplifier and downstream of the main splitter. The phase shift unit comprises at least one shunt series circuit connected to ground, each shunt series circuit comprising an impedance transformer and a terminal circuit arranged between the impedance transformer and the ground, wherein the terminal circuit is configured to present an RF short circuit to the impedance transformer at a first frequency within or close to the frequency band. The impedance transformer is configured to transform the RF short circuit into an RF open circuit at the first frequency.

[0020] The phase shift unit further comprises at least one parallel resonant circuit arranged between the input and output of the phase shift unit, wherein an impedance of the at least one parallel resonant circuit corresponds to an RF open circuit at a second frequency, the second frequency being outside the frequency band.

[0021] According to the present invention, the first frequency is closer to the center frequency of the frequency band than the second frequency.

[0022] Typically, a phase shifting unit should provide little or no impedance transformation within the frequency band while introducing a phase delay that shows a steeper curve with frequency than a transmission line to at least approximate the desired phase shifting behavior. Applicants have discovered that these goals can be achieved simultaneously using a phase shifting unit as described above.

[0023] In the context of the present invention, when the impedance is large compared to the reference impedance, for example, the impedance is at least 200%, preferably 400% of the reference impedance, the impedance should be interpreted as an RF open circuit. Similarly, in the context of the present invention, when the impedance is small compared to the reference impedance, for example, the impedance is at most 25%, preferably at most 10% of the reference impedance, the impedance should be interpreted as an RF short circuit. In addition, the reference impedance can be an impedance between 25 ohms and 75 ohms, and is preferably equal to 50 ohms.

[0024] The impedance transformer of at least one shunt series circuit may include a quarter-wave transmission line or its equivalent. Where multiple shunt series circuits are used, each shunt series circuit presents an RF open circuit at its respective first frequency, which may be the same or different from the first frequencies of the other shunt series circuits. The at least one shunt series circuit of the present invention enables an RF open circuit to be achieved over a greater bandwidth than a parallel resonant circuit that would produce an RF open circuit at the same frequency.

[0025] The at least one shunt series circuit may include a first shunt series circuit connected between the input end of the phase shift unit and the ground, and a second shunt series circuit connected between the output end of the phase shift unit and the ground. In addition, the at least one parallel resonant circuit may include a first parallel resonant circuit connected between the input end and the output end of the phase shift unit. In this case, the first frequency of the first shunt series circuit is preferably different from the first frequency of the second shunt series circuit.

[0026] Further, at least one parallel resonant circuit may include a second parallel resonant circuit connected between the first parallel resonant circuit and the output end of the phase shift unit. The second parallel resonant circuit and the first parallel resonant circuit are connected at an intermediate node. In this case, at least one shunt series circuit may include a third shunt series circuit connected between the intermediate node and ground. In this embodiment, preferably, the first frequency of the third shunt series circuit is different from the first frequency of the first shunt series circuit, and is different from the first frequency of the second shunt series circuit. In addition, the second frequency of the first parallel resonant circuit is preferably different from the second frequency of the second parallel resonant circuit.

[0027] The first frequency of the first shunt series circuit, the first frequency of the second shunt series circuit and the first frequency of the third shunt series circuit are preferably located in the frequency domain between the second frequency of the first parallel resonant circuit and the second frequency of the second parallel resonant circuit.

[0028] The PD-LMBA may also include a printed circuit board or a laminate substrate, wherein the main amplifier and the balanced amplifier are composed of one or more semiconductor dies on the printed circuit board or the laminate substrate, and the one or more semiconductor dies are in the form of a package or as discrete semiconductor dies, wherein the impedance transformer of at least one of the at least one shunt series circuit is implemented as a transmission line on the printed circuit board or the laminate substrate. In addition, the terminal circuit of at least one of the at least one shunt series circuit includes a surface mount device SMD capacitor, which is grounded through a via in the printed circuit board or the laminate substrate. Alternatively or additionally, at least one of the at least one parallel resonant circuit may include a transmission line arranged in parallel with the SMD capacitor on the printed circuit board or the laminate substrate.

[0029] The splitter of the balanced amplifier may include a first coupler having a first input port, a second input port, an output port, and an isolation port. The first input port may be connected to the output of the first amplifier, the second input port is connected to the output of the second amplifier, and the isolation port is connected to the output of the main amplifier. The output port may be configured to be connected to a load. In addition, each of the first input port, the second input port, the output port, and the isolation port has a corresponding reference impedance Z ref .

[0030] The reference impedance of each of the first input port, the second input port, the output port, and the isolation port may be the same.

[0031] The first coupler may include n stacked discrete couplers, each discrete coupler having a corresponding port impedance Z i , the corresponding port impedance is the same for all ports and is higher than Z ref , where n is an integer greater than 1, and where i represents the i-th discrete coupler, and i is an integer ranging from 1 to n, and where:

[0032]

[0033] Applicants have discovered that by stacking discrete couplers, a lower impedance Z ref This reduces the impedance transformation that needs to be achieved between each amplifier and the first coupler. In one embodiment, each coupler in the stack of discrete couplers is identical. Additionally or alternatively, for all i, Z i =Z 耦合器 Additionally or alternatively, Z ref can be in the range of 5 ohms to 30 ohms, and / or n can be equal to 2, 3 or 4, and / or Z 耦合器 Can be equal to 50 ohms.

[0034] It should be noted that the above-described stacked discrete couplers may be used in PD-LMBAs, such as those defined by the preamble of claim 1, which do not include a reference impedance Z associated with each port of the stack of discrete couplers. ref Additionally or alternatively, the reference impedances of corresponding ports of discrete couplers in a coupler stack may be the same, but the reference impedances of different ports of the same coupler may be different.

[0035] It should also be noted that the present application also relates to an electronic device comprising a printed circuit board or a laminate substrate and comprising n stacked discrete couplers as described above.

[0036] The corresponding ports of adjacent discrete couplers in a discrete coupler stack can be electrically connected, for example, using solder. Typically, discrete couplers are provided as substantially rectangular SMDs with electrical terminals at their corners. These terminals extend along the entire edge of the coupler. When the discrete couplers are stacked, these terminals are substantially aligned and can be interconnected using solder.

[0037] The PD-LMBA may also include a first impedance matching network disposed between the output terminal of the first amplifier and the first coupler. The first impedance matching network may be configured to provide a reference impedance Z associated with the first input port of the first coupler. ref , providing an impedance rise transformation in the direction from the first amplifier to the first coupler. Similarly, the PD-LMBA may include a second impedance matching network disposed between the output of the second amplifier and the first coupler and configured to provide a reference impedance Z associated with the second input port of the first coupler. ref , providing an impedance rise transformation in the direction from the second amplifier to the first coupler. The PD-LMBA may also include a third impedance matching network, which is arranged between the output of the main amplifier and the first coupler and is configured to provide a reference impedance Z associated with the isolated input port of the first coupler. ref , providing an impedance rising transformation in the direction from the main amplifier to the first coupler.

[0038] The PD-LMBA may also include a fourth impedance matching network disposed between the output port of the first coupler and the output end of the PD-LMBA, wherein the fourth impedance matching network is configured to provide an impedance rise transformation between a reference impedance associated with the output port of the first coupler and an impedance of a load to be connected to the output end of the PD-LMBA. For example, the load impedance may be equal to 50 ohms, and the reference impedance associated with the output port of the first coupler may be equal to 50 / 2 ohms, 50 / 3 ohms, or 50 / 4 ohms.

[0039] The splitter of the balanced amplifier may include a second coupler, wherein the second coupler includes an input port connected to the main splitter, a first output port connected to the input of the first amplifier, a second output port connected to the input of the second amplifier, and an isolation port connected to a default load. In addition, a phase shift unit may be connected between the input ports of the main splitter and the second coupler. Alternatively, the phase shift unit may include: a section arranged between the first output port of the second coupler and the input of the first amplifier, and a section arranged between the second output port of the second coupler and the input of the second amplifier. The phase delay achieved by the two sections should be the same. Additionally or alternatively, the PD-LMBA may also include: a fourth impedance matching network arranged between the first output port of the second coupler and the input of the first amplifier, and a fifth impedance matching network arranged between the second output port of the second coupler and the input of the second amplifier.

[0040] The main splitter may include a third coupler, wherein the third coupler includes an input port connected to the input end of the PD-LMBA, a first output port optionally connected to the input port of the second coupler through a phase shift unit, a second output port connected to the input end of the main amplifier, and an isolation port.

[0041] The above-mentioned first coupler, second coupler, and / or third coupler can each (optionally, independently of each other) include a coupler selected from the following items: a hybrid coupler, a Lange coupler, a directional coupler, a coupled line coupler, a stripline coupler, a branch line coupler, a waveguide coupler and a coaxial coupler.

[0042] The first amplifier, the second amplifier and the main amplifier may each include a power transistor, such as a silicon-based laterally diffused metal oxide semiconductor field effect transistor, or a gallium nitride-based field effect transistor. In a preferred embodiment, the first amplifier, the second amplifier and the third amplifier are implemented using the same type of power transistor and semiconductor material.

[0043] According to another aspect, the present invention provides a mobile communication base station comprising a PD-LMBA as defined above. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Next, the present invention will be described in more detail with reference to the accompanying drawings, in which:

[0045] Figure 1 shows the difference between the expected phase delay as a function of frequency for an exemplary PD-LMBA compared to the phase delay achievable using a transmission line;

[0046] Figure 2 An embodiment of a PD-LMBA according to the present invention is shown;

[0047] Figure 3 Shown in Figure 2 An embodiment of a phase shift unit used in a PD-LMBA;

[0048] FIG. 4A to FIG. 4C Shows Figure 2 Various performance parameters of the PD-LMBA; and

[0049] Figure 5 Shown in Figure 2 Example of a stacked discrete coupler used in the PD-LMBA. DETAILED DESCRIPTION

[0050] Figure 2An embodiment of a PD-LMBA according to the present invention is shown. The PD-LMBA 1 includes a main amplifier 10 and a balanced amplifier 20, wherein the balanced amplifier 20 includes a first amplifier 21 and a second amplifier 22. The main amplifier 10, the first amplifier 21 and the second amplifier 22 may be identical. However, the present invention is not limited thereto, and the amplifiers 10, 21, 22 may be implemented in the same or different semiconductor technologies. In addition, the saturated output powers of the amplifiers 10, 21, 22 may be the same or different, depending on the desired back-off behavior of the PD-LMBA 1. In the remainder of this article, it is assumed that the amplifiers 10, 21, 22 are identical and each amplifier is configured to output the same maximum output power, provided that the amplifiers have the same impedance at their output terminals. However, the main amplifier 10 is balanced in class AB or class B, while the amplifiers 21, 22 are biased in class C.

[0051] PD-LMBA1 receives an input RF signal at its input 2. Figure 1 , the input terminal 2 corresponds to or is connected to the input port p1 of the 90-degree hybrid coupler 30. The hybrid coupler 30 used as a main splitter further includes a first output port p4, a second output port p3, and an isolation port p2.

[0052] The signal received at the input port p1 (corresponding to and / or connected to the input terminal 2 of the PD-LMBA1) is distributed on the first output port p4 and the second output port p3. In addition, the signal output at the second output port p3 has a phase delay of substantially 90 degrees relative to the signal output at the first output port p4. Hereinafter, the signal output at the first output port p4 is referred to as the first signal, and the signal output at the second output port p3 is referred to as the second signal.

[0053] exist Figure 2 , the power is unevenly distributed on the first output port p4 and the second output port p3. More specifically, the power output to the first output port p4 corresponds to -4.77 dB, and the power output to the second output port p3 corresponds to -1.76 dB. This power distribution corresponds to a ratio of (2 / 3):(1 / 3). In addition, the isolation port p2 is connected to a terminal resistor 31 having an impedance corresponding to the reference impedance of the hybrid coupler 30, for example, 50 ohms.

[0054] The second signal is fed to a phase shifting unit 40 which imparts a predefined and frequency dependent phase delay to the second signal.The signal from the first output port p4 of the hybrid coupler 30 is fed to the main amplifier 10 via an impedance matching network 10A.

[0055] The output of the phase shift unit 40 is connected to a splitter in the form of a 90 degree hybrid coupler 23. The hybrid coupler 23 includes an input port p1, a first output port p4, a second output port p3 and an isolation port p2. Similar to the hybrid coupler 30, the isolation port p2 of the hybrid coupler 23 is connected to a terminal resistor 24, the impedance of which is equal to the reference impedance of the hybrid coupler 23, which may be 50 ohms.

[0056] The hybrid coupler 23 evenly distributes the second signal received at its input port p1 to the first output port p4 and the second output port p3. The signal output at the first output port p4 is referred to as the first part of the second signal, and the signal output at the second output port p3 is referred to as the second part of the second signal. In addition, the second part of the second signal has a phase delay of substantially 90 degrees relative to the first part of the second signal.

[0057] The first part of the second signal is fed to the first amplifier 21 through the impedance matching network 25, which matches the reference impedance of the first output port p4 of the hybrid coupler 23 with the input impedance of the first amplifier 21. Similarly, the second part of the second signal is fed to the second amplifier 22 through the impedance matching network 26, which matches the reference impedance of the second output port p3 of the hybrid coupler 23 with the input impedance of the second amplifier 22.

[0058] The first amplifier 21 and the second amplifier 22 are connected to the respective ports of the combiner 29, and the combiner 29 is implemented using a 90-degree hybrid coupler. More specifically, the output terminal of the first amplifier 21 is connected to the first input port p1 of the hybrid coupler 29 through an impedance matching network 27, and the output terminal of the second amplifier 22 is connected to the second input port p2 of the hybrid coupler 29 through an impedance matching network 28. The output port p4 of the hybrid coupler 29 is connected to the load 60 through an impedance transformer 50, and the load 60 is connected to the output terminal 3 of the PD-LMBA1. The impedance transformer 50 can be implemented using a quarter-wave transformer. The isolation port p3 of the hybrid coupler 29 is connected to the output terminal of the main amplifier 10 through an impedance matching network 11. It should be noted that the signal received at the first input port p1 of the hybrid coupler 29 is coupled to the output port p4 of the hybrid coupler with a delay of substantially 90 degrees relative to the signal received at the second input port p2 of the hybrid coupler 29.

[0059] It should be noted that the same 90 degree hybrid coupler can be used to implement the splitters 23, 30 and the combiner 29. In addition, various types of couplers can be used to implement the splitters 23, 30 and the combiner 29. For example, the splitters 23, 30 and the combiner 29 can each independently include a coupler selected from the following items: a Lange coupler, a directional coupler, a coupled line coupler, a stripline coupler, a branch line coupler, a waveguide coupler, and a coaxial coupler.

[0060] The splitters 23, 30 and combiners 29 may be characterized using a reference impedance for each port. The reference impedance corresponds to the impedance that must be connected to a given port to prevent reflections at the interface between the port and the impedance. Typically, the reference impedance for each port is the same.

[0061] The impedance matching networks 11, 25, 26, 27, 28 provide impedance matching between the respective ports of the splitter 23 or combiner 29 to which one end of the impedance matching network is connected and the components to which the other end of the impedance matching network is connected. Each impedance matching network 11, 25, 26, 27, 28 may be implemented, for example, using one or more quarter-wavelength transmission lines or their lumped equivalents.

[0062] The impedance matching network 25 provides impedance matching between the reference impedance at the first output port p4 of the hybrid coupler 23 and the input impedance of the first amplifier 21, the impedance matching network 26 provides impedance matching between the reference impedance at the second output port p3 of the hybrid coupler 23 and the input impedance of the second amplifier 22, the impedance matching network 27 provides impedance matching between the reference impedance at the first input port p1 of the hybrid coupler 29 and the target output impedance of the first amplifier 21, the impedance matching network 28 provides impedance matching between the reference impedance at the second input port p2 of the hybrid coupler 29 and the target output impedance of the second amplifier 22, and the impedance matching network 11 provides impedance matching between the reference impedance at the isolation port p3 of the hybrid coupler 29 and the target output impedance of the main amplifier 10. The various target impedances correspond to impedances that should be presented to the amplifiers 11, 21, 22 so that the amplifiers output a predetermined output power. As an example, the target impedance of the main amplifier 10 may be equal to 2×Ropt, and the target impedances of the first amplifier 21 and the second amplifier 22 may be equal to Ropt, where Ropt corresponds to an impedance that should be presented to one of the amplifiers 10, 21, 22 so that the amplifier can output a saturated output power. These target impedances will be different when the maximum saturated power ratio of the amplifiers 10, 21, 22 deviates from 1:1:1.

[0063] The amplified first and second parts of the second signal and the amplified first signal should be added in phase by combiner 29. However, the total phase delays encountered by the various signals may be different. To account for the various phase delays, phase shifting unit 40 should impart a phase delay to the second signal.

[0064] exist Figure 2 In the embodiment, the phase shift unit 40 is arranged between the main splitter 30 and the splitter 23 of the balanced amplifier 20. However, the phase shift unit may also include a first part arranged between the splitter 23 and the first amplifier 21, and a second part arranged between the splitter 23 and the second amplifier 22. Typically, the phase shift imparted by these parts will be substantially the same and equal to the phase shift imparted by Figure 2 The phase delay is imparted by the phase shift unit 40 in FIG.

[0065] It should be noted that the phase delay imparted by the phase offset unit 40 depends not only on the frequency but also on the power of the RF input signal. Therefore, a trade-off must be made between power and frequency to obtain the desired performance of the PD-LMBA1. In the following, the frequency-dependent phase delay imparted by the phase offset unit 40 will be referred to as the desired phase delay behavior. Figure 1 An example of the expected phase delay behavior for a generic PD-LMBA is shown in . As mentioned previously, the expected phase delay behavior shows a stronger frequency dependence than the phase delay achievable using a transmission line segment.

[0066] Figure 3 An embodiment of a phase shifting unit 400 is shown, with which a desired phase shifting behavior can be achieved to a greater extent than with a transmission line segment.

[0067] The phase shift unit 400 includes three shunt series circuits S1, S2, S3, each of which is grounded. The phase shift unit 400 also includes two parallel resonant circuits P1, P2.

[0068] Each series circuit S1, S2, S3 includes an impedance transformer in the form of a quarter-wave transmission line 404, 405, 406, which is connected in series with a capacitor and grounded. The transmission line is implemented on a printed circuit board, and the capacitor is a surface mounted device (SMD) mounted on the printed circuit board. Here, each SMD capacitor is simulated by a capacitor C1, C2, C3. In addition, an inductor L1, L2, L3 is used to simulate the inductance associated with the ground connection, such as the inductance of a via in the printed circuit board.

[0069] The main amplifier 10, the first amplifier 21 and the second amplifier 22 may correspond to semiconductor dies or packaged devices arranged on a printed circuit board. The splitters 23, 30 and the combiner 29 may be implemented using SMD couplers arranged on a printed circuit board. The impedance matching network 25, 26, 27, 28, 11 may be implemented using transmission line segments on a printed circuit board, and the terminal resistors 24, 31 may be implemented using SMD resistors arranged on a printed circuit board. As an example, the main amplifier 10, the first amplifier 21 and / or the second amplifier 22 may be implemented using a field effect transistor based on gallium nitride, or a silicon based laterally diffused metal-oxide-semiconductor (LDMOS) transistor.

[0070] For each segment, the quarter-wavelength transmission line converts the RF short circuit created by capacitors C1 , C2 , C3 to an RF open circuit at a respective first frequency that is within or near the frequency band in which the PD-LMBA1 is configured to operate. Figure 4A The S11 parameter measured at the input terminal 401 is shown. As shown, S11 shows three minimum values ​​M1, M2, M3 that can be associated with the shunt series circuits S1, S2, S3, respectively. Note that if the inductance associated with the ground connection of the SMD capacitor together with the capacitance of the SMD capacitor is not sufficient to cause resonance within the frequency band, the length of the transmission line can be extended beyond the length of a quarter wavelength. The additional inductance will reduce the frequency of the series resonance.

[0071] Since the RF short circuit is transformed into an RF open circuit within the frequency band, the shunt series circuits S1 , S2 , and S3 have almost no effect on the overall impedance transformation of the phase shift unit 400 .

[0072] The parallel resonant circuits P1, P2 each include a transmission line segment, the input and output of which are connected using an SMD capacitor. The SMD capacitor has a given inductance, which causes a series resonance at a relatively high frequency. For frequencies closer to the operating frequency band, the parallel connection of the SMD capacitor and the transmission line segment will introduce a parallel resonance configured to be outside the operating frequency band. At this parallel resonance, there is almost no signal transmission between the input 401 and the output 402 of the phase shift unit 400. These resonant frequencies can be Figure 4B (showing the magnitude of the S21 parameter of the phase shift unit 400) and Figure 4C (The corresponding phase of S21 is shown). More specifically, the minimum values ​​M4 and M5 associated with the parallel resonant circuits P1, P2 can be identified in S21.

[0073] The applicant has found that the combination of at least one parallel resonant circuit P1, P2 and at least one shunt series circuit S1, S2, S3 allows a suitable phase delay to be imparted to the second signal while ensuring impedance matching between the second output port p3 of the splitter 30 and the input port P1 of the splitter 23. This is particularly true if the phase shift unit 400 includes one or more sections connected in series, each section including an input, an output, a shunt series network connected to the input, and a parallel resonant circuit arranged between the input and the output, wherein for each pair of adjacent sections, the input of one section is connected to the output of the other section. The input of the first section of the one or more sections forms the input of the phase shift unit, and the output of the last section of the one or more sections forms the output of the phase shift unit. In this case, the output of the last section is connected to the shunt series circuit. For example, in Figure 3 In the embodiment, the circuits S1 and P1 form a first section, and the circuits S2 and P2 form a second section. The output terminal 402 is connected to the shunt series circuit S3.

[0074] In order to obtain broadband performance, it is important that the impedance ratio between the output impedance presented at the output of the main amplifier 10 and the reference impedance of the hybrid coupler 29 is not too large. The same is true for the impedance ratio between the output impedance presented at the output of the first amplifier 21 and the second amplifier 22 and the reference impedance of the hybrid coupler 29. In particular, for high power applications, the impedance presented at the output of the amplifiers 10, 21, 22 is relatively low. In order to address the need to increase the bandwidth of the PD-LMBA while still providing a compact solution, the present invention proposes stacked discrete couplers. These couplers are preferably symmetrical so that the reference impedance at all ports of a given coupler is the same. However, the reference impedance may be different between stacked couplers.

[0075] Figure 5 An example of stacked discrete couplers 29A, 29B is shown, which can be used as Figure 2 Hybrid coupler 29 in PD-LMBA. In the figure, the terminal regions T1 and T2 of ports p1 and p2 of couplers 29A and 29B are aligned. Terminal regions T1 and T2 are made of conductive materials such as one or more metals. A conductive connector that contacts regions T1 and T2 at the same time can be used to achieve a fixed and conductive connection between couplers 29A and 29B. An example of such a conductive connector is formed by solder or conductive glue.

[0076] To arrange a stack of discrete couplers, the first coupler 29A may first be mounted to pads 61 on a printed circuit board 60. Note that the printed circuit board 60 is the same as the printed circuit board described above (ie, the printed circuit board on which the amplifiers 10, 21, 22 are mounted).

[0077] To mount the coupler 29A, solder is used to connect the terminal regions of the coupler (e.g., regions T1 and T2) to the corresponding pads 61. As a next step, the Figure 5 The manner shown places coupler 29B on top of coupler 29A. After this alignment, the corresponding terminal areas can be connected using solder or the like.

[0078] Applicants have discovered that the combination of stacked couplers behaves as a coupler with a lower reference impedance for each port. For example, if the stack includes two couplers with reference impedances Z1 and Z2, the combination of these two couplers will have a reference impedance equal to Z1Z2 / (Z1+Z2) for each port.

[0079] In the above, the present invention has been described using detailed embodiments of the present invention. However, the present invention is not limited to these embodiments. On the contrary, various modifications are possible as long as they do not depart from the scope of the present invention defined by the attached claims and their equivalents.

Claims

1. A pseudo-Doherty load modulated balanced amplifier (PD-LMBA) (1), the PD-LMBA being configured to operate within a given frequency band and comprising: A main splitter (30) for splitting an input radio frequency (RF) signal into a first signal and a second signal; A main amplifier (10), configured to amplify the first signal; A balanced amplifier (20), used for amplifying the second signal, the balanced amplifier comprising: A splitter (23) for dividing the second signal into a first part and a second part of the second signal; a first amplifier (21) and a second amplifier (22), for amplifying a first part of the second signal and a second part of the second signal, respectively; and Combiner (29); wherein the combiner is configured to combine the amplified first signal, the amplified first portion of the second signal, and the amplified second portion of the second signal into an output RF signal; The PD-LMBA further comprises a phase shift unit (40, 400), which is arranged upstream of the first amplifier and the second amplifier and downstream of the main splitter, wherein the phase shift unit comprises: at least one shunt series circuit (S1, S2, S3) connected to ground, each shunt series circuit comprising an impedance transformer and a terminal circuit arranged between the impedance transformer and ground, wherein the terminal circuit is configured to present an RF short circuit to the impedance transformer at a first frequency, the first frequency being within or close to the frequency band, wherein the impedance transformer is configured to transform the RF short circuit into an RF open circuit at the first frequency; and at least one parallel resonant circuit (P1, P2), the at least one parallel resonant circuit being arranged between an input terminal (401) and an output terminal (402) of the phase shift unit, wherein an impedance of the at least one parallel resonant circuit corresponds to an RF open circuit at a second frequency, the second frequency being outside the frequency band; The first frequency is closer to the center frequency of the frequency band than the second frequency.

2. The PD-LMBA according to claim 1, wherein: The impedance transformer of at least one shunt series circuit comprises a quarter wavelength transmission line (404, 405, 406) or its equivalent.

3. The PD-LMBA according to claim 1, wherein: The at least one shunt series circuit comprises: a first shunt series circuit (S1) connected between an input end (401) of the phase shift unit and ground, and a second shunt series circuit (S3) connected between an output end of the phase shift unit and ground, and wherein the at least one parallel resonant circuit comprises a first parallel resonant circuit (P1) connected between an input end and an output end of the phase shift unit; The first frequency of the first shunt series circuit is different from the first frequency of the second shunt series circuit.

4. The PD-LMBA according to claim 3, wherein: The at least one parallel resonant circuit comprises: a second parallel resonant circuit (P2) connected between the first parallel resonant circuit and an output terminal of the phase shift unit, wherein the second parallel resonant circuit and the first parallel resonant circuit are connected at an intermediate node (403), wherein the at least one shunt series circuit comprises a third shunt series circuit (S2) connected between the intermediate node and ground; wherein the first frequency of the third shunt series circuit is different from the first frequency of the first shunt series circuit, and is different from the first frequency of the second shunt series circuit; and The second frequency of the first parallel resonant circuit is different from the second frequency of the second parallel resonant circuit.

5. The PD-LMBA according to claim 4, wherein: The first frequency of the first shunt series circuit, the first frequency of the second shunt series circuit and the first frequency of the third shunt series circuit are located between the second frequency of the first parallel resonant circuit and the second frequency of the second parallel resonant circuit in the frequency domain.

6. The PD-LMBA according to claim 1, wherein: The PD-LMBA comprises a printed circuit board (60) or a laminate substrate, the main amplifier and the balanced amplifier are composed of one or more semiconductor dies on the printed circuit board or the laminate substrate, the one or more semiconductor dies are in the form of a package or as discrete semiconductor dies, and wherein the impedance transformer of at least one of the at least one shunt series circuit is implemented as a transmission line on the printed circuit board or the laminate substrate.

7. The PD-LMBA according to claim 6, wherein: The terminal circuit of at least one of the at least one shunt series circuit comprises a surface mounted device SMD capacitor (C1, C2, C3), which is preferably connected to ground through a via in the printed circuit board or laminate substrate.

8. The PD-LMBA according to claim 6, wherein: At least one of the at least one parallel resonant circuit comprises a transmission line arranged in parallel with an SMD capacitor (C4, C5) on the printed circuit board or laminate substrate.

9. The PD-LMBA according to claim 1, wherein: The combiner of the balanced amplifier comprises a first coupler (29), the first coupler having a first input port (p1), a second input port (p2), an output port (p3) and an isolation port (p4), wherein the first input port is connected to the output of the first amplifier, the second input port is connected to the output of the second amplifier, the isolation port is connected to the output of the main amplifier, and wherein the output port is configured to be connected to a load, each of the first input port, the second input port, the output port and the isolation port having a corresponding reference impedance Z ref .

10. The PD-LMBA according to claim 9, wherein: The reference impedance of each of the first input port, the second input port, the output port, and the isolated port is the same.

11. The PD-LMBA according to claim 10, wherein: The first coupler comprises n stacked discrete couplers (29A, 29B), each discrete coupler having a corresponding port impedance Z i , the corresponding port impedance is the same for all ports and is higher than Z ref , where n is an integer greater than 1, and where i represents the i-th discrete coupler, and i is an integer ranging from 1 to n, and where:

12. The PD-LMBA according to claim 11, wherein: For all i, Z i =Z 耦合器 .

13. The PD-LMBA according to claim 11, wherein: Z ref is in the range of 5 ohms to 30 ohms, and / or wherein, n is equal to 2, 3 or 4, and / or wherein Z 耦合器 Equivalent to 25 ohms, 50 ohms or 75 ohms.

14. The PD-LMBA according to claim 10, wherein: Corresponding ports of adjacent discrete couplers in the stack of discrete couplers are electrically connected, for example using solder.

15. The PD-LMBA of claim 9, further comprising: a first impedance matching network (27) disposed between the output terminal of the first amplifier and the first coupler and configured to provide a reference impedance Z associated with a first input port of the first coupler; ref , providing an impedance rise transformation in a direction from the first amplifier to the first coupler; a second impedance matching network (28) disposed between the output of the second amplifier and the first coupler and configured to provide a reference impedance Z associated with a second input port of the first coupler; ref , providing an impedance rise transformation in a direction from the second amplifier to the first coupler; a third impedance matching network (11), which is arranged between the output terminal of the main amplifier and the first coupler and is configured to provide a reference impedance Z associated with the isolated input port of the first coupler; ref , providing an impedance rising transformation in a direction from the main amplifier to the first coupler.

16. The PD-LMBA of claim 1, further comprising a fourth impedance matching network, the fourth impedance matching network being arranged between the output port of the first coupler and the output end of the PD-LMBA, wherein: The fourth impedance matching network is configured to ref An impedance rise transformation is provided between the impedance of a load to be connected to the output terminal of the PD-LMBA.

17. The PD-LMBA according to claim 1, wherein: The splitter of the balanced amplifier comprises a second coupler (23), wherein the second coupler comprises an input port (p1) connected to the main splitter, a first output port (p2) connected to the input end of the first amplifier, a second output port (p3) connected to the input end of the second amplifier, and an isolation port (p4), wherein the phase shift unit is connected between the input port of the main splitter and the second coupler; Wherein, the PD-LMBA further comprises: a fourth impedance matching network (25), the fourth impedance matching network being arranged between the first output port of the second coupler and the input end of the first amplifier; and A fifth impedance matching network (26) is arranged between the second output port of the second coupler and the input end of the second amplifier.

18. The PD-LMBA according to claim 1, wherein: The main splitter includes a third coupler, wherein the third coupler includes: an input port (p1) connected to the input end of the PD-LMBA, a first output port (p2) connected to the input port of the second coupler, the first output port is optionally connected to the input port of the second coupler through the phase shift unit, a second output port (p3) connected to the input end of the main amplifier, and an isolation port (p4).

19. The PD-LMBA according to claim 1, wherein: The first coupler, the second coupler and / or the third coupler include a coupler selected from the group consisting of a hybrid coupler, a Lange coupler, a directional coupler, a coupled-line coupler, a stripline coupler, a branch-line coupler, a waveguide coupler and a coaxial coupler; wherein the first amplifier, the second amplifier and the main amplifier each include a power transistor, such as a silicon-based laterally diffused metal oxide semiconductor field effect transistor, or a gallium nitride-based field effect transistor; wherein a center frequency corresponding to the frequency band is in the range of 0.5 GHz to 8 GHz, wherein a bandwidth of the frequency band relative to the center frequency is in the range of 10% to 40%, and / or wherein the PD-LMBA is configured to output a maximum output power in the range of 10 mW to 500 W.

20. A mobile communication base station comprising a PD-LMBA as defined in any one of the preceding claims.

Images