Broadband impedance matching network that combines low-pass broadband matching, second-harmonic reflection phase shift, and high-pass complex conjugate matching

Abstract

The operating bandwidth of a broadband RF amplifier (M1) is increased by using a low-pass type broadband impedance transformer (LPMN) instead of a broadband matching network in a multi-stage impedance matching network, for example, connected to the amplifier input, output, or both. The multi-stage impedance matching network includes three stages connected in series. The first stage is a low-pass type broadband impedance transformer (LMPN, LPMN1) that provides a broadband low-reflection fundamental impedance and a high reflection for the second harmonic. The second stage is a phase shifter that controls the phase of the second harmonic reflection coefficient. The third stage is a high-pass input matching circuit (MN, MN1) that transforms the complex conjugate device input impedance to a real impedance. The three-stage impedance matching network provides fundamental and harmonic frequency impedances for broadband operation and controllability of the second harmonic reflection coefficient phase, where the device performance is consistent across the expected bandwidth.

Description

[0001] Related Applications

[0002] This application is a continuation of U.S. Patent Application No. 16 / 193,884, filed on Nov. 16, 2018, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention generally relates to radio frequency (RF) circuits, and more particularly to a low-pass broadband impedance matching circuit for a broadband RF amplifier. Background Art

[0004] Radio frequency (RF) power amplifiers are an important part of wireless communication circuits. High-power RF amplifiers are particularly important in wireless communication networks, such as, for example, in base stations that provide wireless transmission over large geographic areas. To transmit larger amounts and more types of content (e.g., video), wireless communication operates over increasingly wider frequency bands.

[0005] Broadband power amplifiers have received significant attention in this regard. A broadband power amplifier can support high data rate communication over a wider bandwidth without the need for multiple amplifiers. Moreover, compared to using multiple power amplifiers for multiple frequency bands, the small form factor of a single broadband amplifier saves space and power, simplifies circuit layout and wiring, and is otherwise beneficial. However, the optimal input and output impedances of power devices such as high electron mobility transistors (HEMTs) must be matched to the system impedance, which is typically 50 Ω.

[0006] The impedance matching network is frequency selective and introduces impedance dispersion with respect to frequency, resulting in band-limited power amplifier operation. Moreover, the harmonic impedance presented to the device significantly affects device performance, and the dispersion can cause performance degradation at specific frequency ranges. Therefore, a relatively small impedance dispersion of the matching network with respect to frequency and the ability to match the optimal impedance variation range are desirable for broadband amplifier operation.

[0007] The "Background Art" section of this document is provided to place embodiments of the present invention in a technical and operational context to assist those skilled in the art in understanding its scope and utility. The statements herein are not admitted to be prior art merely because they are included in the "Background Art" section, unless expressly so stated. Summary of the Invention

[0008] A simplified summary of the present disclosure is presented below to provide a basic understanding to those skilled in the art. This summary is not an exhaustive review of the present disclosure and is not intended to identify key / important elements of the embodiments of the invention or to delineate the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that follows.

[0009] The performance of a broadband RF amplifier depends not only on the fundamental impedance, but also on the second harmonic impedance presented to the amplifier input. According to embodiments of the present invention described and claimed herein, the operating bandwidth of a broadband RF amplifier is improved by using a low-pass type broadband impedance transformer instead of a broadband matching network in a multi-stage impedance matching network connected to the amplifier input, for example. In an embodiment of the present invention, the impedance matching network includes three stages connected in series. The first stage is a low-pass type broadband impedance transformer that provides a broadband fundamental impedance and high reflection for the second harmonic. The second stage is a phase shifter transmission line (or a lumped version of a transmission line) that controls the position of the phase of the second harmonic reflection coefficient for broadband operation. The third stage is a high-pass input matching circuit that transforms the complex conjugate device input impedance into a real impedance while passing the higher harmonic components to the next stage. The three-stage impedance matching network provides the fundamental and harmonic frequency impedances for broadband operation, as well as controllability of the phase of the second harmonic reflection coefficient, where the device performance is consistent over the expected bandwidth and the broadband fundamental impedance.

[0010] One embodiment relates to a broadband radio frequency (RF) amplifier circuit configured to amplify an RF signal received from a source over an RF band including a fundamental band. The RF amplifier circuit includes an amplification circuit. The RF amplifier circuit further includes a multi-stage broadband impedance matching circuit at the input of the amplification circuit. The multi-stage broadband impedance matching circuit includes a low-pass broadband impedance matching network that presents a low input reflection to the RF source at the fundamental band and a high input reflection to the RF source at the second harmonic of the fundamental band. The multi-stage broadband impedance matching circuit further includes a phase shift circuit configured to pass the RF signal at the fundamental band and shift the phase of the RF signal at the second harmonic of the fundamental band. The multi-stage broadband impedance matching circuit further includes an impedance matching circuit configured to transform the complex conjugate amplification circuit input impedance into a real impedance.

[0011] Another embodiment relates to a broadband radio frequency (RF) amplifier circuit configured to amplify an RF signal over an RF band including a fundamental band and output the amplified RF signal. The RF amplifier circuit includes an amplification circuit and a multi-stage broadband impedance matching circuit at the output of the amplification circuit. The multi-stage broadband impedance matching circuit includes: an impedance matching circuit connected to the output of the amplification circuit and configured to transform the complex conjugate amplification circuit input impedance into a real impedance; a phase shift circuit configured to pass the amplified RF signal at the fundamental band and shift the phase of the amplified RF signal at the second harmonic of the fundamental band; and a low-pass broadband impedance matching network that presents a low input reflection at the fundamental band and a high input reflection at the second harmonic of the fundamental band.

[0012] Another embodiment relates to a multi-stage broadband impedance matching circuit for a broadband radio frequency (RF) amplifier. The multi-stage broadband impedance matching circuit includes a low-pass broadband impedance matching network that presents a low input reflection to the RF source at the fundamental band and a high input reflection to the RF source at the second harmonic of the fundamental band. The multi-stage broadband impedance matching circuit further includes a phase shift circuit configured to pass the RF signal at the fundamental band and shift the phase of the RF signal at the second harmonic of the fundamental band. The multi-stage broadband impedance matching circuit further includes an impedance matching circuit configured to transform the complex conjugate amplifier input impedance into a real impedance.

[0013] Yet another embodiment relates to a method of operating a broadband radio frequency (RF) amplifier. An RF signal to be amplified is received from a source. The RF signal covers a fundamental band. A low input reflection is presented to the source at the fundamental band and a high input reflection is presented at the second harmonic of the fundamental band. The fundamental band is passed and the phase of the second harmonic of the fundamental band is shifted. The complex conjugate RF amplifier impedance is transformed into a real impedance. The RF signal is amplified.

[0014] Still yet another embodiment relates to a method of operating a broadband radio frequency (RF) amplifier. An RF signal is amplified. The complex conjugate RF amplifier output impedance is transformed into a real impedance. The fundamental band of the amplified RF signal is passed and the phase of the second harmonic of the fundamental band of the amplified RF signal is shifted. A low input reflection at the fundamental band and a high input reflection at the second harmonic of the fundamental band are presented to a circuit or component receiving the amplified RF signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. However, the invention should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers always refer to like elements.

[0016] Figure 1A is a block diagram of an amplifier and an impedance matching network;

[0017] Figure 1B is a Smith chart plotting the phase of the second harmonic reflection coefficient;

[0018] Figure 1C is a graph of drain efficiency as a function of the source second harmonic reflection coefficient in a first frequency range;

[0019] Figure 2A is a block diagram of a multi-stage impedance matching network utilizing a broadband matching network BMN;

[0020] Figure 2B isFigure 2A Schematic diagram of a multi-stage impedance matching network;

[0021] Figure 2C It depicts a phase shifter as a lumped element Figure 2A Schematic diagram of a multi-stage impedance matching network;

[0022] Figure 3A Block diagram of a multi-stage impedance matching network using a low-pass broadband matching network LPMN;

[0023] Figure 3B It depicts a LPMN as a lumped element, a phase shifter as a transmission line, and a matching network as a shunt inductor Figure 3A Schematic diagram of a multi-stage impedance matching network;

[0024] Figure 3C It depicts a part of a LPMN as a distributed element, a phase shifter as a transmission line, and a matching network as a shunt inductor Figure 3A Schematic diagram of a multi-stage impedance matching network;

[0025] Figure 3D It depicts a LPMN as a lumped element, a phase shifter as a lumped element, and a matching network as a shunt inductor Figure 3A Schematic diagram of a multi-stage impedance matching network;

[0026] Figure 3E It depicts a part of a LPMN as a distributed element, a phase shifter as a lumped element, and a matching network as a shunt inductor Figure 3A Schematic diagram of a multi-stage impedance matching network;

[0027] Figure 4A Block diagram of a broadband matching network BMN as a two-stage quarter-wavelength transmission line;

[0028] Figure 4B It shows Figure 4A Smith chart of the frequency response of the BMN in terms of the reflection coefficient;

[0029] Figure 4C It is Figure 4B Graph of the magnitudes of the reflection coefficient at the fundamental and second harmonic frequencies;

[0030] Figure 5A Block diagram of a broadband matching network BMN as a two-stage quarter-wavelength transmission line, where the phase shifter is implemented as a transmission line;

[0031] Figure 5B It shows Figure 5A Smith chart of the frequency response of the circuit in terms of the reflection coefficient;

[0032] Figure 5C is Figure 5B a graph of the magnitude of the reflection coefficient of

[0033] Figure 6A a block diagram of a multi - stage impedance matching network implemented as a broadband matching network BMN with a phase shifter and a shunt impedance matching circuit;

[0034] Figure 6B is a Smith chart showing Figure 6A the frequency response of the circuit of

[0035] Figure 7A in terms of the reflection coefficient in a first frequency range; Figure 4A a Smith chart showing the frequency response of the circuit of

[0036] Figure 7B is a Smith chart showing Figure 5A the frequency response of the circuit of

[0037] Figure 8A a graph of the drain efficiency as a function of the source second - harmonic reflection coefficient in a second frequency range;

[0038] Figure 8B is a Smith chart showing Figure 6A the frequency response of the circuit of

[0039] Figure 9A a block diagram of a multi - stage impedance matching network implemented as a low - pass type broadband matching network LPMN with a phase shifter;

[0040] Figure 9B is a Smith chart showing Figure 9A the frequency response of the LPMN of

[0041] Figure 9C is a Smith chart showing Figure 9A the frequency response of the circuit (LPMN + phase shifter) of

[0042] Figure 9D is Figure 6A a graph of the magnitude of the reflection coefficient of the circuit (BMN) of Figure 9A and the circuit (LPMN) of

[0043] Figure 10A is Figure 6A a plot of the simulation of the circuit of

[0044] Figure 10B is a Smith chart showing the frequency response in terms of reflection coefficient of the circuit of Figure 10A in the first frequency range;

[0045] Figure 10C is Figure 10A a graph of the simulated output power of the circuit of

[0046] Figure 10D is Figure 10A a graph of the simulated drain efficiency of the circuit of

[0047] Figure 11A is Figure 6A a simulation diagram of the circuit of

[0048] Figure 11B is a Smith chart showing the frequency response in terms of reflection coefficient of the circuit of Figure 11A in a second frequency range wider than the first frequency range;

[0049] Figure 11C is Figure 11A a graph of the simulated drain efficiency of the circuit of

[0050] Figure 12A is a simulation diagram of the circuit of Figure 9A using an LPMN implemented as lumped elements

[0051] Figure 12B is a Smith chart showing the frequency response in terms of reflection coefficient of the circuit of Figure 12A in the second frequency range;

[0052] Figure 12C is Figure 12A a graph of the simulated drain efficiency of the circuit of

[0053] Figure 13A is a simulation diagram of the circuit of Figure 9A using a part of an LPMN implemented as distributed elements

[0054] Figure 13B is a Smith chart showing the frequency response in terms of reflection coefficient of the circuit of Figure 13A in the second frequency range;

[0055] Figure 13C is Figure 13A a graph of the simulated drain efficiency of the circuit of

[0056] Figure 14It is a flowchart of a method for operating a broadband RF amplifier that has a multi-stage impedance matching network at its input, including a low-pass type broadband matching network LPMN;

[0057] Figure 15 It is a flowchart of a method for operating a broadband RF amplifier that has a multi-stage impedance matching network at its output, including a low-pass type broadband matching network LPMN. Detailed implementation

[0058] For simplicity and illustrative purposes, the present invention is described by mainly referring to exemplary embodiments of the present invention. In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that the present invention can be implemented without being limited to these specific details. In this specification, well-known methods and structures are not described in detail so as not to unnecessarily obscure the present invention.

[0059] Figure 1A Depicts an input matching network (MN) for a power device (M 1 ), such as a broadband RF amplifier. The device has a given input impedance (Z in ) at each harmonic frequency under its optimal operating conditions. In Figure 1A , 'n' represents the harmonic number, i.e., '1' is the fundamental component, '2' is the second harmonic, and so on. The symbol 'ω' represents the angular frequency involved in the design. The matching network transforms the system impedance (e.g., 50 Ω) into the complex conjugate of the device input impedance. However, the impedance transformation is usually satisfactory only within a limited frequency range. The implemented matching network presents a source impedance or a source reflection coefficient to the input of the device at each frequency including the harmonics. The reflection coefficient can be normalized to a certain reference impedance.

[0060] Figure 1B Is a Smith chart that depicts the phase of the second harmonic reflection coefficient when the RF source sweeps through various frequencies from 2.1 GHz to 2.7 GHz in 0.2 GHz steps. Figure 1CDepicts the efficiency performance variation with respect to the phase of the source second harmonic reflection coefficient presented to the device at various frequencies. It is assumed that the magnitude of the source reflection coefficient is constant, i.e., 0.95 normalized to 0.5 Ω. The RF amplifier output impedance matching network is fixed, and this disclosure focuses on the source impedance effect. However, those skilled in the art should readily recognize that the disclosed circuits and methods can also be applied to the output matching network without limitation. Apparently, the drain efficiency varies sharply with respect to the phase and frequency of the source second harmonic reflection coefficient. The characteristics of device M1 require an input matching network MN, whose frequency response presents a certain phase range with respect to the source reflection coefficient at the second harmonic frequency for broadband operation in order to obtain consistent performance with respect to frequency with minimal variation.

[0061] For this purpose, it is known to utilize a multi-stage impedance matching network at the RF amplifier input. As Figure 2A shown, the multi-stage impedance matching network includes a broadband matching network (BMN), a phase shifter, and an additional matching network (MN). As Figure 2B and 2C shown, the BMN can be implemented using a two-stage quarter-wavelength impedance transformer. The phase shifter can be implemented as a transmission line (as Figure 2B shown), or as a lumped element version of a transmission line with a specific cut-off frequency (as Figure 2C shown). The final impedance matching network MN is a high-pass type impedance matching network using a shunt inductor. The multi-stage impedance matching network of Figure 2 has a characteristic operating frequency range, and its performance degrades outside this frequency range.

[0062] According to an embodiment of the present invention, the multi-stage impedance matching network of Figure 2 is improved by using a low-pass type broadband matching network (LPMN) as Figure 3A shown instead of Figure 2A the broadband matching network BMN. In one embodiment, as Figure 3B shown, the low-pass type broadband matching network LPMN is implemented using lumped inductors and capacitors. In another embodiment, as Figure 3C shown, at least in some parts, distributed elements are used instead of lumped elements for implementation. Figure 3D Depicts the low-pass type broadband matching network LPMN, where the phase shifter is implemented as a lumped version of a transmission line. Figure 3E Depicts the low-pass type broadband matching network LPMN implemented using distributed elements in at least some parts, and the phase shifter implemented as a lumped element version of a transmission line with a specific cut-off frequency. In all four embodiments ( Figure 2B -E), the high-pass type impedance matching network MN is implemented using a shunt inductor.

[0063] Briefly discuss having Figure 2AThe operation of a known multi-stage impedance matching network of a broadband matching network BMN is used to place the low-pass type broadband matching network LPMN of the present invention in context. Generally, due to the large device periphery, RF power amplifiers have low input and output optimum impedances. The first stage of the multi-stage impedance matching network uses a two-stage broadband impedance matching circuit BMN as shown in Figure 4A to transform the 50 Ω system impedance to a low impedance. The reflection coefficient seen from the low impedance port is plotted on the Smith chart in Figure 4B . Due to the broadband impedance transformer, the fundamental frequency response is well concentrated. In Figure 4C , the magnitude of the reflection coefficient is plotted versus frequency, where the fundamental frequency is concentrated at 2.4 GHz and the second harmonic frequency is concentrated at approximately 4.8 GHz. As shown in this figure, the reflection coefficient is very low in the fundamental frequency band and approaches 0 at 2.4 GHz. On the other hand, the reflection coefficient at the second harmonic frequency (ZS2H) centered at 4.7 GHz is very high. This is because the quarter-wavelength transformer has a half-wavelength at the second harmonic frequency, thus maintaining the 50 Ω system impedance in this frequency band. Due to the low input impedance of the amplifier, the frequency response is highly reflective.

[0064] Figure 5A The circuit shown in adds a phase shifter to the output of the broadband matching network BMN. The phase shifter has the same characteristic impedance as the low impedance port of the BMN (i.e., it is impedance matched). Therefore, it has broadband characteristics at the fundamental frequency band while it shifts the second harmonic frequency band, as shown by the reflection coefficient in Figure 5B . By adjusting the electrical length of the phase shifter, the phase of the second harmonic source reflection coefficient can be determined while maintaining the same magnitude. Figure 5C depicts the magnitude of the reflection coefficient versus frequency and is very similar to the plot in Figure 4C . As shown in Figure 2B and 2C , the phase shifter can be implemented using a transmission line or a lumped version of a transmission line.

[0065] Figure 6A An additional matching network MN is added, which is implemented as a shunt inductor to match the complex conjugate of the RF amplifier input impedance. In the case of varying load conditions, the complex conjugate of the amplifier input impedance at different power levels is shown as circles in Figure 6B and is denoted as Zin * . The fundamental frequency band response seen from the amplifier is shown as a dashed line near these circles. The second harmonic frequency band response is labeled as ZS2H. By changing the electrical length of the phase line, the phase of the second harmonic reflection coefficient can be placed in the high performance region of Figure 1C as desired.

[0066] Depending on the values of the matching network elements, the phase of the second harmonic reflection coefficient can lie within a specific frequency range. For example, the frequency responses of FIGS. 4, 5, and 6 are plotted from 2.1 GHz to 2.7 GHz. However, when the design frequency is extended to a wider bandwidth from 1.8 - 2.7 GHz, the frequency response of the network is more dispersed, as Figure 7A shown in (BMN) and 7B (BMN + phase shifter). Figure 8B The phase of the second harmonic reflection coefficient of the multi-stage impedance matching network presented to the amplifier is plotted over this extended frequency range. These are outside the Figure 8A high performance region.

[0067] The present inventors have found that using a low-pass type broadband multi-stage matching network (LPMN) (such as Figure 9A shown) exhibits less dispersion when amplifying a wider frequency band. Figure 9B The frequency response of the low-pass type broadband matching network alone, looking into the amplifier input, is depicted in. The low-pass type broadband matching network LPMN provides low reflection at the fundamental frequency band, as Figure 9B shown by the line labeled ZS1H in. As shown by the line labeled ZS2H, the low-pass type broadband matching network LPMN provides high reflection at the second harmonic frequency band. Compared to the BMN (see Figure 7A ), the second harmonic reflection phase has less dispersion at higher magnitudes, which can result in higher performance. Figure 9C The frequency response of the LPMN together with the phase shifter is depicted in, which also plots the response of the prior art BMN circuit ( Figure 6A ) for comparison.

[0068] Figure 9D The magnitude of the reflection coefficient of the LPMN and the phase shifter is depicted. The fundamental frequency response exhibits two local minima at 2.0 and 2.6 GHz and has a maximum value of less than 0.2 at 1.8 GHz and 2.7 GHz. The reflection coefficient at the second harmonic is very high, close to or at 1.0, spanning a range from approximately 4 - 5.4 GHz. For comparison, Figure 6A the reflection coefficient of the BMN circuit of is also plotted. These range from 0.8 to 0.9 over the second harmonic frequency band (dashed line). These graphs show lower dispersion for the higher reflection magnitude of the LPMN circuit over the BMN, which translates to higher performance broadband operation.

[0069] For the BMN, the magnitude of the reflection coefficient at the second harmonic frequency range is mainly determined by the difference between the system impedance and the low impedance. In contrast, for the LPMN, the magnitude of the reflection coefficient at the second harmonic frequency range is determined by the order of the low-pass type broadband matching network and its losses.

[0070] Embodiments of the present invention are simulated using a commercial non - linear simulator that uses harmonic - balance simulation with non - linear device models. In the same frequency range, the performance of the multi - stage impedance - matching network using LPMN is compared with the performance of the multi - stage impedance - matching network using BMN. First, as Figure 10A shown, an impedance - matching network with BMN is applied to a non - linear model with class - B bias. The input power and load are scanned with respect to frequency in a first frequency range from 2.1 GHz to 2.7 GHz. Figure 10B The fundamental - wave device input impedance (Zin1H) presented to the device and the source second - harmonic impedance (dots, labeled ZS2H) are plotted. The simulated output power is plotted with respect to frequency in Figure 10C while the drain efficiency is plotted in Figure 10D .

[0071] Then, for the Figure 11A circuit, the simulation is extended to a second frequency range of 1.8 - 2.7 GHz (i.e., wider than the first frequency range). Figure 11B The fundamental - wave (Zin1H) and second - harmonic (ZS2H) impedances are plotted, which clearly shows a wider spread compared to Figure 10B . As a result, the drain efficiency plotted in Figure 11C shows fluctuations (as expected; see Figure 8A ).

[0072] Next, in the second frequency range (1.8 - 2.7 GHz), the multi - stage impedance - matching network of the present invention using LPMN implemented with lumped inductors and capacitors as shown in Figure 12A is simulated. As shown in Figure 12B , the fundamental - wave (Zin1H) impedance is similar to those in Figure 11A , but the second - harmonic reflection coefficient (dots, labeled ZS2H) shows less frequency dispersion. Additionally, the drain efficiency plotted in Figure 12C shows less fluctuation with respect to frequency than the drain efficiency depicted in Figure 11C .

[0073] In one embodiment, as shown in Figure 13A , the low - pass type broadband matching network LPMN is implemented using distributed elements in at least some parts. This design is also simulated. It shows performance similar to that of the Figure 12A lumped - element embodiment, as shown in the Smith chart of Figure 13B and the drain - efficiency - versus - frequency graph of Figure 13C . Thus, the low - pass type broadband matching network LPMN can be implemented using lumped or distributed elements or various combinations.

[0074] Figure 14Describes method 100 for operating a broadband RF amplifier. The RF amplifier includes a multi-stage impedance matching network at its input, including a low-pass type broadband matching network LPMN. Although described in discrete, sequential steps, those skilled in the art will recognize that method 100 is continuously executed as long as the broadband RF amplifier is in operation. An RF signal to be amplified is received from a source such as a processing circuit like a DSP or a base station of a wireless communication network by the multi-stage impedance matching network (block 102). The RF signal covers the baseband. The low input reflection at the baseband and the high input reflection at the second harmonic of the baseband are presented back to the source by the LPMN (block 104). The baseband is passed to the amplifier, and the phase of the second harmonic of the baseband is shifted by a phase shifter (block 106). For example, the second harmonic can be shifted to operate in an efficient region, as depicted in Figure 1C or 8A. The complex conjugate RF amplifier impedance is transformed to a real impedance by a final matching network (block 108). Then, the RF signal is amplified by the RF amplifier. As shown in FIGS. 12 and 13, using the LPMN in the multi-stage impedance matching network results in superior performance over a wider frequency bandwidth compared to prior art amplifier circuits.

[0075] Although embodiments of the present invention have been described herein with respect to a multi-stage impedance matching network deployed at the input of an amplifier, the multi-stage impedance matching network of the present invention (including the low-pass type broadband matching network) can also be advantageously used to match the impedance at the output of an amplifier. In this case, the order of the three components will be the reverse order or “mirror image” of the above circuit. In particular, in an effective multi-stage impedance matching network applied to the output of an amplifier, the impedance matching circuit will be connected to the amplifier output. The phase shift circuit will be connected to the matching network. Finally, the low-pass type broadband matching network will be connected to the phase shift circuit. In both cases (i.e., input and output), the phase shift circuit is inserted between the low-pass type broadband matching network connected to the system and the impedance matching circuit connected to the amplifier.

[0076] Figure 15 Describes method 200 for operating a broadband RF amplifier that has a multi-stage impedance matching network at its output, including a low-pass type broadband matching network LPMN. Although described in discrete, sequential steps, those skilled in the art will recognize that method 200 can be continuously executed as long as the broadband RF amplifier is in operation. The RF signal is amplified (block 202). The complex conjugate RF amplifier output impedance is transformed to a real impedance by a matching network (block 204). The baseband of the amplified RF signal is passed through, and the phase of the second harmonic of the baseband is shifted by a phase shifter (block 206). The low input reflection at the baseband and the high input reflection at the second harmonic of the baseband are presented by the LPMN to downstream components or circuits (block 208).

[0077] Embodiments of the present invention present many advantages over the prior art. As described above, for the prior art broadband matching network BMN, the magnitude of the reflection coefficient in the second harmonic frequency range is mainly determined by the difference between the system impedance and the low impedance. In the case of an embodiment of the low-pass broadband matching network LPMN of the present invention, the magnitude of the reflection coefficient in the second harmonic frequency range is determined by the order of the low-pass type broadband matching network and its losses. Through proper design of the LPMN, superior reflection of the second harmonic component of the broadband RF signal is achieved, resulting in improved performance of the RF amplifier.

[0078] Of course, without departing from the essential characteristics of the present invention, the present invention may be implemented in other ways different from those specifically set forth herein. This embodiment should be considered illustrative rather than restrictive in all respects, and all changes within the meaning and scope of equivalence of the appended claims are included therein.

Claims

1. A broadband radio frequency (RF) amplifier circuit configured to amplify an RF signal received from a source across an RF band including a baseband, the broadband RF amplifier circuit comprises: an amplifier circuit; and a multi-stage broadband impedance matching circuit at an input of the amplifier circuit and comprising: a low-pass broadband impedance matching network that presents a low input reflection to the RF source at the baseband and a high input reflection to the RF source at the second harmonic of the baseband; a phase shift circuit configured to pass the RF signal at the baseband and shift the phase of the RF signal at the second harmonic of the baseband; and an impedance matching circuit configured to transform a complex conjugate amplifier circuit input impedance into a real impedance.

2. The RF amplifier circuit according to claim 1, wherein the low-pass broadband impedance matching network transforms a 50Ω system impedance into a characteristic impedance of the phase shift circuit.

3. The RF amplifier circuit according to claim 1, wherein the phase shift circuit is connected between the low-pass broadband impedance matching network and the impedance matching circuit.

4. The RF amplifier circuit according to claim 1, wherein the low-pass broadband impedance matching network at least partially comprises distributed inductance and capacitance.

5. The RF amplifier circuit according to claim 1, wherein the low-pass broadband impedance matching network at least partially comprises lumped inductors and capacitors.

6. The RF amplifier circuit according to claim 1, wherein the phase shift circuit comprises a transmission line.

7. The RF amplifier circuit according to claim 1, wherein the phase shift circuit comprises a lumped element version of a transmission line having a predetermined cut-off frequency.

8. The RF amplifier circuit according to claim 1, wherein the impedance matching circuit is a high-pass impedance matching circuit.

9. The RF amplifier circuit according to claim 8, wherein the high-pass impedance matching circuit comprises a shunt inductor.

10. The RF amplifier circuit according to claim 1, further comprising a multi-stage broadband impedance matching circuit at an output of the amplifier circuit, and it comprises: an impedance matching circuit connected to the output of the amplifier circuit and configured to transform a complex conjugate amplifier circuit input impedance into a real impedance; a phase shift circuit configured to pass the amplified RF signal at the baseband and shift the phase of the amplified RF signal at the second harmonic of the baseband; and a low-pass broadband impedance matching network that presents a low input reflection at the baseband and a high input reflection at the second harmonic of the baseband.

11. A broadband radio frequency (RF) amplifier circuit configured to amplify an RF signal across an RF band including a baseband, the broadband RF amplifier circuit comprises: an amplifier circuit; and a multi-stage broadband impedance matching circuit at an output of the amplifier circuit and comprising: an impedance matching circuit connected to the output of the amplifier circuit and configured to transform a complex conjugate amplifier circuit input impedance into a real impedance; A phase shift circuit configured to pass the amplified RF signal at the baseband and shift the phase of the amplified RF signal at the second harmonic of the baseband; and A low-pass broadband impedance matching network presenting low input reflection at the baseband and high input reflection at the second harmonic of the baseband.

12. The RF amplifier circuit according to claim 11, wherein, The RF amplifier circuit receives an RF signal from a source and further includes a multi-stage broadband impedance matching circuit at the input of the amplifier circuit, the multi-stage broadband impedance matching circuit including: A low-pass broadband impedance matching network presenting low input reflection to the RF source at the baseband and high input reflection to the RF source at the second harmonic of the baseband; A phase shift circuit configured to pass the RF signal at the baseband and shift the phase of the RF signal at the second harmonic of the baseband; and An impedance matching circuit configured to transform the complex conjugate amplifier circuit input impedance into a real impedance.

13. A multi-stage broadband impedance matching circuit for a broadband radio frequency (RF) amplifier operating across an RF band including a baseband, comprising: A low-pass broadband impedance matching network presenting low input reflection at the baseband and high input reflection at the second harmonic of the baseband; A phase shift circuit configured to pass the RF signal at the baseband and shift the phase of the RF signal at the second harmonic of the baseband; and An impedance matching circuit configured to transform the complex conjugate device impedance into a real impedance.

14. The impedance matching circuit according to claim 13, wherein, The low-pass broadband impedance matching network transforms a 50Ω system impedance into the characteristic impedance of the phase shift circuit.

15. The impedance matching circuit according to claim 13, wherein, The phase shift circuit is connected between the low-pass broadband impedance matching network and the impedance matching circuit.

16. The impedance matching circuit according to claim 13, wherein, The low-pass broadband impedance matching network at least partially includes distributed inductance and capacitance.

17. The impedance matching circuit according to claim 13, wherein, The low-pass broadband impedance matching network at least partially includes lumped inductors and capacitors.

18. The impedance matching circuit according to claim 13, wherein, The phase shift circuit includes a transmission line.

19. A method (100) of operating a broadband radio frequency (RF) amplifier, comprising: Receiving (102) an RF signal to be amplified from a source, the RF signal covering a baseband; Presenting (104) low input reflection at the baseband and high input reflection at the second harmonic of the baseband to the source; Passing (106) the baseband and shifting the phase of the second harmonic of the baseband; Transforming (108) the complex conjugate RF amplifier impedance into a real impedance; and Amplifying (110) the RF signal.

20. The method (100) according to claim 19, further comprising: Transforming the complex conjugate RF amplifier output impedance into a real impedance; Pass the fundamental band of the amplified RF signal and shift the phase of the second harmonic of the fundamental band of the amplified RF signal; and Present a low input reflection at the fundamental band and a high input reflection at the second harmonic of the fundamental band to a circuit or component receiving the amplified RF signal.

21. A method (200) of operating a broadband radio frequency (RF) amplifier, comprising: amplifying (202) an RF signal; transforming (204) the complex conjugate RF amplifier output impedance to a real impedance; passing (206) the fundamental band of the amplified RF signal and shifting the phase of the second harmonic of the fundamental band of the amplified RF signal; and presenting (208) a low input reflection at the fundamental band and a high input reflection at the second harmonic of the fundamental band to a circuit or component receiving the amplified RF signal.

22. The method (200) according to claim 21, further comprising: receiving from a source an RF signal to be amplified, the RF signal covering a fundamental band; presenting a low input reflection at the fundamental band and a high input reflection at the second harmonic of the fundamental band to the source; passing the fundamental band and shifting the phase of the second harmonic of the fundamental band; transforming the complex conjugate RF amplifier impedance to a real impedance; and amplifying the RF signal.

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