WO2023060549A1

WO2023060549A1 - Impedance matching circuit for complex load

Info

Publication number: WO2023060549A1
Application number: PCT/CN2021/124076
Authority: WO
Inventors: Mohamed Hesham Mohamed MOSTAFA; Nam HA-VAN; Prasad Kumara Sampath JAYATHURATHNAGE; Xuchen WANG; Grigorii PTITCYN; Mohammad Sajjad MIRMOOSA; Sergei Tretyakov
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2021-10-15
Filing date: 2021-10-15
Publication date: 2023-04-20

Abstract

A impedance matching circuit (100) is connected between the signal source (200) and the complex load (300) and comprises a resistive circuit (110) that is modulated by a modulation signal (Vmod) thereby modulating the resistive circuit (110) synchronously with a high frequency modulated broadband signal (VS) from the signal source (200). The modulation signal (Vmod) and the high frequency modulated broadband signal (VS) are based on a common low frequency baseband signal. Thereby, improved power transfer is possible with low signal distortion.

Description

IMPEDANCE MATCHING CIRCUIT FOR A COMPLEX LOAD

Technical Field

The invention relates to a circuit for impedance matching a signal source to a complex load. Furthermore, the invention also relates to a communication device comprising such a circuit for impedance matching.

Background

Impedance matching of a signal source to a complex load usually relates to designing the input impedance of the complex load and/or the output impedance of the signal source to maximize power transfer to the complex load, and hence to minimize signal reflection from the complex load. Further, impedance mismatch of a signal source to a complex load may also result in signal distortion.

For complex load, such as small resonant antennas, broadband impedance matching can be achieved using active non-Foster elements, e.g. negative capacitors. However, such components are prone to instabilities. A conventional solution of using time-modulated capacitors, e.g. varactors, to realize negative capacitors offers stable performance but requires high-frequency modulation of the varactors. This means modulating with the same frequency as the signal frequency. This is difficult or even not practically possible for microwave and millimeter-wave frequencies.

Summary

An objective of examples of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

Another objective of examples of the invention is to provide a solution which provides improved power transfer compared to conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous examples of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a circuit for impedance matching a signal source to a complex load, the impedance matching circuit comprising:

an input connected to a signal source, the input being configured to receive a high frequency modulated broadband signal from the signal source;

an output connected to the complex load, the output being configured to provide the high frequency modulated broadband signal to the complex load;

a resistive circuit connected between the input and the output; and

a control device connected to the resistive circuit, the control device being configured to provide a modulation signal to the resistive circuit thereby modulating the resistive circuit synchronously with the high frequency modulated broadband signal, wherein the modulation signal and the high frequency modulated broadband signal are based on a common low frequency baseband signal.

That the modulation signal and the high frequency modulated broadband signal are based on a common low frequency baseband signal may be understood such that they are derived or determined or generated from the same baseband signal.

The frequency of the modulation signal is much smaller than the frequency of the high frequency modulated broadband signal which implies that the modulation of the resistive circuit may be considered slow and hence practically feasible.

An advantage of the impedance matching circuit according to the first aspect is that the present solution offers, among other things, improved power transfer of signal power compared to conventional solutions. Further, signal distortion is reduced compared to conventional solutions due to the improved impedance matching.

Also, broadband matching and no issues with stability due to low-frequency modulation in the baseband frequency range. Thereby, the present impedance matching circuit makes it possible to pass broadband modulated signals through narrowband resonant circuits without distortion and parasitic reflections.

In an implementation form of a circuit according to the first aspect, the resistive circuit is time modulated.

In an implementation form of a circuit according to the first aspect, the modulation signal is based on a frequency spectrum of the high frequency modulated broadband signal.

In an implementation form of a circuit according to the first aspect, the modulation signal is based on the frequency spectrum of the high frequency modulated broadband signal and a reactance of the complex load.

In an implementation form of a circuit according to the first aspect, a spectrum of the modulation signal is based on one or more modulation amplitudes and one or more modulation phases.

An advantage with this implementation form is that the modulation signal easily can be controlled by controlling the modulation amplitudes and modulation phases of the modulation signal for impedance matching.

In an implementation form of a circuit according to the first aspect, the high frequency modulated broadband signal comprises a plurality of frequency harmonics, and wherein the modulation signal is modulated at the plurality of frequencies harmonics of the low frequency baseband signal.

An advantage with this implementation form is that impedance matching is also possible for high frequency modulated broadband signals comprising a plurality of frequency harmonics.

In an implementation form of a circuit according to the first aspect, the high frequency modulated broadband signal comprises two frequency harmonics, and wherein the modulation signal is based on a frequency difference between the two frequency harmonics.

In an implementation form of a circuit according to the first aspect, the high frequency modulated broadband signal comprises a carrier frequency and two frequency harmonics, and wherein the modulation signal is based on a frequency difference between the carrier frequency and any of the two frequency harmonics.

In an implementation form of a circuit according to the first aspect, the control device is configured to

determine a value corresponding to a negative of a reactance of the complex load; and

determine the modulation signal based on a comparison between the value corresponding to the negative of the reactance of the complex load and a value corresponding to the reactance of the complex load.

Thereby, a closed loop system may be implemented in which the modulation signal can be adapted to the reactance of the complex load in real time. This means that the impedance matching can be further improved due to the feedback mechanism.

In an implementation form of a circuit according to the first aspect, the resistive circuit comprises a FET; and wherein

the input is connected to a drain of the FET,

the output is connected to a source of the of the FET, and

the control device is connected to a gate of the FET and configured to provide the modulation signal at the gate of the FET.

By using a FET as the resistive circuit a low complex solution is provided easy to implement and using low cost components. However, also other electrical components may be used to implement the resistive circuit such as operational amplifiers (Op-amps) , etc.

In an implementation form of a circuit according to the first aspect, the signal source is a power amplifier.

In an implementation form of a circuit according to the first aspect, the impedance matching circuit is a part of the power amplifier.

Thereby an integrated compact solution is provided.

In an implementation form of a circuit according to the first aspect, the complex load is an amplifier or an antenna.

In an implementation form of a circuit according to the first aspect, the antenna is configured for microwave frequencies or millimeter-wave frequencies.

In an implementation form of a circuit according to the first aspect, the high frequency modulated broadband signal is modulated according to a communication scheme.

Thereby, the circuit for impedance matching is well suited for use in wireless communication systems, such as 3GPP 5G also known as new radio (NR) .

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a communication device for a communication system, the communication device comprising

a power amplifier;

an antenna; and

a circuit according to any implementation form of the invention.

Further applications and advantages of the examples of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different examples of the invention, in which:

- Fig. 1 illustrates a circuit for impedance matching according to an example of the invention when the circuit is implemented as a standalone device;

- Fig. 2 illustrates a circuit for impedance matching according to an example of the invention when the circuit is integrated with the signal source;

- Fig. 3 shows a conceptual equivalent circuit for illustrative purpose;

- Fig. 4 shows a circuit for impedance matching implemented with a FET transistor as the resistive circuit according to an example of the invention;

- Fig. 5 illustrates a circuit for impedance matching integrated in a closed loop system according to an example of the invention; and

- Fig. 6 shows a communication device comprising a circuit for impedance matching according to an example of the invention.

Detailed Description

As aforementioned, correct impedance matching is important for efficient power transfer from a signal source to a complex load and also for reducing signal distortion in the system. It is therefore herein disclosed and exemplified to implement a resistive circuit coupled between a signal source and a complex load. The resistive circuit is modulated at the baseband of a high frequency modulated signal to emulate reactance of a complex load. Since the frequency of the modulation signal is much smaller than the frequency of the high frequency modulated broadband signal the modulation of the resistive circuit may be considered slow and hence practically feasible and with enhanced power transfer compared to conventional solutions.

Fig. 1 shows a circuit 100 for impedance matching according to an example of the invention when the disclosed circuit 100 is implemented as a standalone device in relation to the signal source 200 and the complex load 300, respectively. With reference to Fig. 1, the impedance matching circuit 100 comprises an input 102 which is connected to a signal source 200. The input 102 is configured to receive a high frequency modulated broadband signal V _S from the signal source 200 as shown in Fig. 1. In examples of the invention, the signal source 200 is a power amplifier.

The circuit 100 further comprises an output 104 connected to the complex load 300. The output 104 is configured to provide the high frequency modulated broadband signal V _S to the complex load 300. In examples of the invention, the complex load 300 is an antenna or an amplifier.

The circuit 100 further comprises a resistive circuit 110 which is connected between the input 102 and the output 104 of the circuit 100. The circuit 100 further comprises a control device 120 which is connected to the resistive circuit 110. The control device 120 is configured to provide a modulation signal V _mod to the resistive circuit 110 thereby modulating the resistive circuit 110 synchronously with the high frequency modulated broadband signal V _S. The modulation signal V _mod and the high frequency modulated broadband signal V _S are based on a common low frequency baseband signal.

That the control device 120 is configured to provide a modulation signal V _mod to the resistive circuit 110 thereby modulating the resistive circuit 110 synchronously with the high frequency modulated broadband signal V _S can be understood as the following. Since the resistive circuit 110 is synchronously modulated with the high frequency modulated broadband signal V _S the impedance characteristics of the resistive circuit 110 will be adapted to the high frequency modulated broadband signal V _S when the high frequency modulated broadband signal V _S passes through or via the circuit 100. This implies that the circuit 100 will impedance match the signal source 200 and the complex load 300 in real time. In this respect, it may also be understood that the resistive circuit 110 is, in examples of the invention, time modulated by the control device 120. Hence, the output resistance of a signal source 200 that feeds an antenna, or any other complex load, is made time varying. For a given load, the time modulation is determined by the input signal spectrum, which means that the modulation signal V _mod is based on a frequency spectrum of the high frequency modulated broadband signal V _S in examples of the invention.

The present solution is therefore based on time modulation of the internal resistance of the signal source 200 by an external bias that can be controlled by, or derived from, a common baseband signal. This can e.g. be realized either by adding a time-varying resistive circuit in series with the signal source 200 or by modulating the signal source 200 itself in an integrated solution which includes the signal source 200 and the present circuit 100 in a common single device. By using a time-varied resistive circuit to emulate reactance and match resonant complex loads improved power transfer and reduced signal distortion is achieved.

Fig. 2 shows a circuit 100 for impedance matching according to an example of the invention when the circuit 100 as aforementioned is integrated in the signal source 200. This example therefore differs from the example in Fig. 1 in that the impedance matching circuit 100 in Fig. 1 is a standalone device and not part of or integrated in the power amplifier as in Fig. 2. However, the general principles and technical consideration are common for the two exemplary cases of Fig. 1 and 2.

Fig. 3 shows a conceptual equivalent circuit of a complex load 300, in this case an antenna, connected to a signal source 200 with a modulated resistive circuit 110 connected in series with the signal source 200 for illustrative purpose. The resistive circuit 110 is modelled as a constant resistance connected in series with a time varying resistance. Generally, an antenna is perfectly matched to a signal source when the load impedance is conjugate matched to the signal source. In other words, this is the case when there is maximum power transfer from the signal source to the antenna. In the disclosed case, the internal impedance of the signal source is real-valued. As the circuit model of an antenna includes a capacitor and an inductor in series, their reactive impedances cancel each other only at the resonance frequency, which means that the maximum power transfer condition can be met only at the resonance frequency. As a result, if we can have a maximum transfer of power from the signal source to the antenna at multiple frequencies or continuous spectrum, this is a significant improvement of the antenna performance.

The proposed solution herein makes it possible to add a virtual impedance that may be fully controlled at any frequencies. As a result, instead of meeting the condition of maximum power transfer only at the resonance frequency, designed reactive impedances at different frequencies can be added so that all of them meet the impedance matching condition, which assures the maximum power transfer at all input frequencies. In this case, all the power supplied by the signal source is radiated by the antenna, except the power dissipated in the source resistance and the ohmic resistance of the antenna. By properly modulating the resistive circuit 110, for all frequency harmonics of the input signal, the resonant load will look like a fixed resistor.

In further examples of the invention, the modulation signal V _mod is based on the frequency spectrum of the high frequency modulated broadband signal V _S and a reactance of the complex load 300. Hence, the reactance is also considered in this example of the invention. The reactance is the imaginary part of an impendence and together with the real part, i.e. resistance, impedance describes how the complex load will respond to the signal source. In the antenna case, the reactance comes from the timing of the wave reflected from the end points of the antenna. At a certain antenna length, the reflections align such that voltage and current are in phase at the feed point terminals, which means that the reactance is zero and the antenna is said to be resonant.

When the high frequency modulated broadband signal V _S comprises a plurality of frequency harmonics, the modulation signal V _mod may be modulated at the plurality of frequencies harmonics of the low frequency baseband signal. In this respect the spectrum of the modulation signal V _mod can be controlled based on the parameters: modulation amplitude m and modulation phase

The modulation parameters m and

may be selected so that the additional virtual reactance or additional emulated reactance induced at the frequencies of the high frequency modulated broadband signal V _S compensate the load reactance at these frequencies. For example, for a high frequency modulated broadband signal V _S that comprises two frequency harmonics, the resistive circuit 110 may be modulated at the difference frequency. In other words, when the high frequency modulated broadband signal V _S comprises two frequency harmonics ω _-1, ω ₁, the modulation signal V _mod is based on a frequency difference between the two frequency harmonics, i.e. ω _-1, ω ₁.

By expanding the above general reasoning, when the high frequency modulated broadband signal V _S also comprises a carrier frequency ω _C in addition to two frequency harmonics ω _-1, ω ₁, the modulation signal V _mod can be determined and generated based on a frequency difference between the carrier frequency ω _C and any of the two frequency harmonics ω _-1, ω ₁.

Consider Eq. 1 which gives an expression of the high frequency modulated broadband signal V _S that may also be denoted voltage source:

V _S (t) = a _-1 cos (ω _-1t+θ _-1) +a ₁cos (ω ₁t+θ ₁) Eq. 1

in which a _n is the amplitude, ω _n represent the angular frequency, θ _n represent the phase, and where n is an index.

Further, consider Eq. 2 which models the time varying resistance R (t) seen at the input 102:

in which R ₀ is the static resistance, m is the modulation amplitude, Δω is the modulation frequency that is equal to the difference frequency between ω _-1, ω ₁, and

denotes the modulation phase. The static resistance R ₀ is the total static resistance between in the closed circuit in Fig. 3, so R (t) can be understood as the real part of the input impedance at 102 in Fig. 1.

For the example for two input frequency harmonics, assuming the resonant frequency of the antenna is equal to

the additional induced impedance at the input frequencies ω _-1 and ω ₁ are given by,

is tuned to compensate the antenna reactance at this frequency. The first term in Eq. 3 expresses the additional induced impedance.

The same conclusion can be made for an amplitude-modulated (AM) signal. If the AM high frequency modulated broadband signal V _AM to the complex load is given by the expression:

V _AM (t) = cos (ω _ct) [a _c+2 a _scos (ω _mt) ] =a _scos (ω _-1) +a _ccos (ω _ct) +a _scos (ω ₁) Eq. 4

where a _c is the amplitude of the carrier and a _s is the amplitude of the baseband signal.

Then, the time varying resistance may be modulated in the same way as previously in Eq. 2, i.e.:

but with the difference that the modulation frequency Δω in this case is equal to the difference between the carrier frequency ω _c and ω ₁ or ω _-1, which is equal to ω _m.

By selecting proper modulation phase, the induced impedance

brought at the side-harmonic frequencies by modulation are given by:

where

denotes the additional virtual reactance added by the modulation as the induced impedance is imaginary. Note that the impedance at every frequency is calculated by dividing the voltage as a function of frequency by the current as a function of frequency. Then, the term proportional to the modulation amplitude m is considered to be the impedance induced by modulation.

Hence, by properly selecting the modulation amplitude m and phase

the induced impedance can be engineered. This is an intriguing possibility to engineer effective reactance at desired frequencies without adding additional reactive components in the system. Indeed, by modulating the resistance in the circuit 100, power loss and gain can be controlled. Even more interesting, the reactive response of the circuit 100 can be adjusted.

Fig. 4 shows an example of the invention when the resistive circuit 110 is implemented using a field effect transistor (FET) . Hence, the FET can represent the time-modulated resistance by connecting the circuit as illustrated in Fig. 4. The input 102 of the circuit 100 is connected to a drain D of the FET T. The output 104 is connected to a source S of the FET T. Finally, the control device 120 is connected to a gate G of the FET T and configured to provide the modulation signal V _mod at the gate G of the FET T. Thereby, the gate G is time modulated by the modulation signal V _mod.

It is also noted in Fig. 4 that the signal source 200 and the antenna 300 are connected to a common ground, i.e. Ground 1, while the control device 120 is connected to another separate ground, i.e. Ground 2. Ground 1 and Ground 2 are isolated from each other. Further, a bias circuit 130 is connected to the gate G of the FET T and the function of the bias circuit 130 is to create a voltage supply to turn on the FET T. The bias circuit 130 also has a common ground with the control device 120, i.e. Ground 2. It is to be noted that other electrical components and circuits may be used for implementing the resistive circuit 110, e.g. by using an operational amplifier.

Fig. 5 illustrates a closed loop impedance matching system 500 in which a circuit 100 according to an example of the invention is employed. It is envisaged that in principle it is possible to measure the antenna reactance dynamically during operation of the antenna 300, and hence adjust the modulation of the resistive circuit 100 accordingly to variable antenna conditions. Thereby, e.g. the effects of user proximity, etc., can be compensated when time modulating the resistive circuit 110. Hence, a self-matched and self-adapted antenna system is provided in which the determination and generation of the modulation signal V _mod is continuously and dynamically updated and adapted to shifting antenna conditions. The impedance matching will adapt to shifting conditions for improved performance.

The general concept of the closed loop system 500 with feedback is that the control device 120 is configured to determine a value corresponding to a negative of a reactance of the complex load 300. The value may be a representation of the negative of a reactance of the complex load 300.

For obtaining the value corresponding to a negative of a reactance the control device 120 may emulate the negative of the reactance thereby creating/generating a virtual reactance that is equal to the negative of the reactance of the load 300 so that the two cancel each out and hence impedance matching is achieved. The control device 120 can therefore determine the modulation signal V _mod based on a comparison between the value corresponding to the negative of the reactance of the complex load 300 and a value corresponding to the reactance of the complex load 300.

With reference to Fig. 5, a radio frequency (RF) generator 430 is connected to a signal modulator 440. A baseband signal (BS) is also provided to the modulator 430. The input signal in the form of a low-frequency signal may be denoted a baseband signal. The baseband signal can e.g. be voice or music, and the frequencies of the baseband signal may be in the range of 1-10 kHz. In case of amplitude modulation with a single tone, this is the modulation signal V _mod. For more complex modulations, the modulation signal V _mod needs to be modified but the frequency of the modulation signal V _mod remains in the low-frequency baseband.

A local oscillator of the RF generator 430 generates a high-frequency carrier, e.g. 2-5 GHz for wireless communications. This is a simple harmonic oscillation that does not contain any information in contrast to the baseband signal. The baseband signal and the local oscillator output from the RF generator 430 are mixed in the modulator 440 and provided to the power amplifier 200. As a result, a high frequency modulated broadband signal V _S is generated that contains the information of the baseband signal that is to be transmitted in a radio channel over an air interface. The baseband signal is also provided to the circuit 100 for impendence matching. Hence, the modulation signal V _mod and the high frequency modulated broadband signal V _S are based on a common low frequency baseband signal.

The high frequency modulated broadband signal V _S and the modulation signal V _mod are synchronized since they are based on the common low frequency baseband signal. This may be expressed as that the high frequency modulated broadband signal V _S and the modulation signal V _mod are formed from the same baseband input and therefore coherent. Hence, the modulation signal V _mod can be considered as a baseband representation of the high frequency modulated broadband signal V _S. The modulation signal V _mod may either be the same baseband signal or a reshaped version of the baseband signal. The use of the baseband signal for modulating the resistive circuit 110 can be particularly important for the antenna matching application as the baseband can provide the information to be transmitted with the antenna.

Since the original input is a low-frequency baseband signal, the modulation signal V _mod will be in the same baseband range, e.g. 1-10 kHz. In an example, if the carrier frequency is 2.5 GHz then the high frequency modulated broadband signal V _S will occupy the frequency band of 5.5 GHz plus/minus the baseband bandwidth 10 kHz.

Furthermore, a current probe 410 is arranged at the antenna 300 and is connected to the control device 120 of the circuit 100 via a first feedback line 450. The control device 120 obtains measurements about the current spectra at the antenna 300 from the current probe 410. Further, a voltage probe 420 is arranged at the connection between the modulator 440 and the amplifier 200 and is also connected to the control device 120 via a second feedback line 460. The control device 120 obtains measurements about the voltage/signal spectrum of the modulated signal previous to amplification from the voltage probe 420. By comparing and analyzing the current spectra with the voltage/signal spectrum the circuit 100 emulates the negative of the reactance of the antenna 300. The emulation of a reactance can be better understood from the transmission line theory. In case of a transmission line terminated by a time-varying resistance, there will be reflections, and by controlling the modulation, it is possible to control these reflections. Then, when the termination has a reactive component, the modulation is designed so that the reflections resulting from the modulation cancel out with the reflections resulting from the reactive components. Thereby, providing reflectionless termination that receives the incident power perfectly. The effect of the modulated resistive termination is similar to the effect of a termination composed from both resistive and reactive components, so we can consider the modulated resistive termination as being equivalent to a static termination that has both resistive and reactive components. In the case when the load is an antenna, and the negative of the reactance of the antenna needs to be canceled by the emulated reactance, the modulation signal can be adapted to the present reactance of the antenna, e.g. by tuning the previously mentioned modulation parameters. This procedure may be performed continuously and dynamically by the circuit 100 so as to guarantee high performance adaptions of impedance matching for excellent power transfer and low signal distortion in the closed loop system 500.

Moreover, Fig. 6 illustrates a communication device 400 according to an example of the invention. The communication device 400 comprises a power amplifier 200 which act as a signal source providing a high frequency modulated broadband signal V _S. The power amplifier 200 is connected to an antenna 300 via a circuit 100 for impedance matching according to an example of the invention. The circuit 100 may be a standalone device or integrated with the power amplifier and the latter example is shown in Fig. 6. The communication device 400 may also include a closed loop system 500 as disclosed in Fig. 5. This is however not shown.

The communication device 400 herein may be a mobile device such as a user equipment (UE) . The communication device houses at least one processor (not shown in Fig. 6) , at least one display device 412, and at least one communication means (not shown in Fig. 6) . The communication device further comprises input means e.g. in the form of a keyboard 414 communicatively connected to the display device 412. The communication device further comprises output means e.g. in the form of a speaker 416. The communication device 400 may be a mobile phone, a tablet PC, a mobile PC, a smart phone, a standalone mobile device, or any other suitable communication device. The communication device 400 hence has the capabilities and is configured for wireless communication in any suitable wireless communication network and system. Non-limiting examples of communication systems are 3GPP communication systems and WiFi systems.

Therefore, in examples of the invention, the high frequency modulated broadband signal V _S may be modulated according to a communication scheme that may be given by a communication standard. Non-limiting examples of such modulation schemes are amplitude modulation (AM) , frequency modulation (FM) , phase modulation (PM) , frequency-shift keying (FSK) , phase-shift keying (PSK) , amplitude-shift keying (ASK) , quadrature amplitude modulation (QAM) , orthogonal frequency division multiplexing (OFDM) , etc.

The herein disclosed and described control device 120 may be any device having the suitable means, further devices and capabilities for performing and being part of the described examples of the invention. The control device 120 may be distributed or have a single location depending on application. The control device 120 may e.g. be a signal processing device comprising capabilities in the form of e.g., functions, means, units, elements, etc., for performing the solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

Especially, the processor (s) of the control device 120 may comprise, e.g., one or more instances of a Central Processing Unit (CPU) , a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC) , a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Finally, it should be understood that the invention is not limited to the examples described above, but also relates to and incorporates all examples within the scope of the appended independent claims.

Claims

A circuit (100) for impedance matching a signal source (200) to a complex load (300) , the impedance matching circuit (100) comprising:

an input (102) connected to a signal source (200) , the input (102) being configured to receive a high frequency modulated broadband signal (V _S) from the signal source (200) ;

an output (104) connected to the complex load (300) , the output (104) being configured to provide the high frequency modulated broadband signal (V _S) to the complex load (300) ;

a resistive circuit (110) connected between the input (102) and the output (104) ; and

a control device (120) connected to the resistive circuit (110) , the control device (120) being configured to provide a modulation signal (V _mod) to the resistive circuit (110) thereby modulating the resistive circuit (110) synchronously with the high frequency modulated broadband signal (V _S) , wherein the modulation signal (V _mod) and the high frequency modulated broadband signal (V _S) are based on a common low frequency baseband signal.
The circuit (100) according to claim 1, wherein the resistive circuit (110) is time modulated.
The circuit (100) according to claim 1 or 2, wherein the modulation signal (V _mod) is based on a frequency spectrum of the high frequency modulated broadband signal (V _S) .
The circuit (100) according to claim 3, wherein the modulation signal (V _mod) is based on the frequency spectrum of the high frequency modulated broadband signal (V _S) and a reactance of the complex load (300) .
The circuit (100) according to claim 3 or 4, wherein a spectrum of the modulation signal (V _mod) is based on one or more modulation amplitudes (m) and one or more modulation phases
The circuit (100) according to any one of claims 3 to 5, wherein the high frequency modulated broadband signal (V _S) comprises a plurality of frequency harmonics, and wherein the modulation signal (V _mod) is modulated at the plurality of frequencies harmonics of the low frequency baseband signal.
The circuit (100) according to claim 6, wherein the high frequency modulated broadband signal (V _S) comprises two frequency harmonics (ω _-1, ω ₁) , and wherein the modulation signal (V _mod) is based on a frequency difference between the two frequency harmonics (ω _-1, ω ₁) .
The circuit (100) according to claim 6, wherein the high frequency modulated broadband signal (V _S) comprises a carrier frequency (ω _C) and two frequency harmonics (ω _-1, ω ₁) , and wherein the modulation signal (V _mod) is based on a frequency difference between the carrier frequency (ω _C) and any of the two frequency harmonics (ω _-1, ω ₁) .
The circuit (100) according to any one of the preceding claims, wherein the control device (120) is configured to

determine a value corresponding to a negative of a reactance of the complex load (300) ; and

determine the modulation signal (V _mod) based on a comparison between the value corresponding to the negative of the reactance of the complex load (300) and a value corresponding to the reactance of the complex load (300) .
The circuit (100) according to any one of the preceding claims, wherein the resistive circuit (110) comprises a FET (T) ; and wherein

the input (102) is connected to a drain (D) of the FET (T) ,

the output (104) is connected to a source (S) of the of the FET (T) , and

the control device (120) is connected to a gate (G) of the FET (T) and configured to provide the modulation signal (V _mod) at the gate (G) of the FET (T) .
The circuit (100) according to any one of the preceding claims, wherein the signal source (200) is a power amplifier.
The circuit (100) according to claim 11, wherein the impedance matching circuit (100) is a part of the power amplifier.
The circuit (100) according to any one of the preceding claims, wherein the complex load (300) is an amplifier or an antenna.
The circuit (100) according to claim 13, wherein the antenna is configured for microwave frequencies or millimeter-wave frequencies.
The circuit (100) according to any one of the preceding claims, wherein the high frequency modulated broadband signal (V _S) is modulated according to a communication scheme.
A communication device (400) for a communication system (500) , the communication device (400) comprising

a power amplifier (200) ;

an antenna (300) ; and

a circuit (100) according to any one of the preceding claims.