Mobile device, load modulation power amplifier system, and method of amplification in a mobile device

Abstract

To provide load modulated power amplifiers and methods that can provide high efficiency over a wide dynamic range.SOLUTION: A load modulated power amplifier 10 includes: a power amplifier 5 that receives a radio frequency signal (RF input signal RFIN) at a reception input and provides an amplified radio frequency signal at an output; and a controllable load impedance 6 coupled to the output of the power amplifier 5. The controllable load impedance receives an envelope signal ENV that changes in relation to an envelope of the radio frequency signal. The envelope signal is operable to control an impedance of the controllable load impedance to modulate a load at the output of the power amplifier.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an electronic system, and more particularly to a radio frequency (RF) electronic device.

Background Art

[0002] In an RF communication system, a power amplifier is used to amplify an RF signal for the purpose of transmission via an antenna.

[0003] Examples of RF communication systems having one or more power amplifiers include, but are not limited to, cellular phones, tablets, base stations, network access points, customer premise equipment (CPE), laptops, and wearable electronic devices. For example, in a wireless device that communicates using a cellular standard, a wireless local area network (WLAN) standard, and / or any other suitable communication standard, a power amplifier can be used for the purpose of RF signal amplification. The RF signal can have a frequency in the range of about 400 MHz to about 7.125 GHz for frequency range 1 (FR1) of the 5th generation (5G) communication standard, or in the range of about 24.250 GHz to about 71.000 GHz for frequency range 2 (FR2) of the 5G communication standard, for example, in the range of about 30 kHz to 300 GHz.

Summary of the Invention

[0004] In certain embodiments, the present disclosure relates to a portable device. The portable device includes a transceiver configured to generate a radio frequency signal and an envelope signal that varies in relation to the envelope of the radio frequency signal, and a front-end system including a load-modulated power amplifier configured to amplify the radio frequency signal. The load-modulated power amplifier includes a power amplifier configured to receive the radio frequency signal at an input and provide an amplified radio frequency signal at an output, and a controllable load impedance coupled to the output of the power amplifier. The envelope signal is operable to control the impedance of the controllable load impedance to modulate the load at the output of the power amplifier.

[0005] In various embodiments, the transceiver includes a shaping circuit configured to shape the envelope signal based on calibration data. According to a certain number of embodiments, the shaping circuit is operable to provide a flat gain versus input power characteristic to the power amplifier.

[0006] In some embodiments, the controllable load impedance includes a controllable capacitor controlled by the envelope signal, an output balun having a first winding coupled to the output of the power amplifier and a second winding coupled to the controllable capacitor. According to a certain number of embodiments, the power amplifier includes an input balun and a pair of amplifiers coupled between the input balun and the output balun. According to various embodiments, the second winding includes a first terminal that outputs an amplified radio frequency signal and a second terminal coupled to the controllable capacitor. According to some embodiments, the controllable capacitor includes a bipolar transistor and a load capacitor coupled to the collector of the bipolar transistor, and the envelope signal is operable to control the base of the bipolar transistor. According to a certain number of embodiments, the controllable load impedance includes a series combination of an inductor and a controllable capacitor having a capacitance controlled by the envelope signal.

[0007] In various embodiments, the portable device further includes an antenna operable to transmit an amplified radio frequency signal.

[0008] In a given embodiment, the present disclosure relates to a load modulation power amplifier system. The load modulation power amplifier system includes a power amplifier configured to receive a radio frequency signal at an input and provide an amplified radio frequency signal at an output. The load modulation power amplifier system further includes a controllable load impedance coupled to the output of the power amplifier, the controllable load impedance being configured to receive an envelope signal that varies in relation to the envelope of the radio frequency signal. The envelope signal is operable to control the impedance of the controllable load impedance to modulate the load at the output of the power amplifier.

[0009] In some embodiments, the controllable load impedance includes a controllable capacitor controlled by an envelope signal, an output balun having a first winding coupled to the output of the power amplifier and a second winding coupled to the controllable capacitor. According to a certain number of embodiments, the power amplifier includes an input balun and a pair of amplifiers coupled between the input balun and the output balun. According to various embodiments, the second winding includes a first terminal that outputs an amplified radio frequency signal and a second terminal coupled to the controllable capacitor. According to some embodiments, the controllable capacitor includes a bipolar transistor and a load capacitor coupled to the collector of the bipolar transistor, and the envelope signal is operable to control the base of the bipolar transistor.

[0010] In various embodiments, the controllable load impedance includes a series combination of an inductor and a controllable capacitor having a capacitance controlled by an envelope signal.

[0011] In a given embodiment, the present disclosure relates to a method of amplification in a portable device. The method includes generating a radio frequency signal and an envelope signal that varies in relation to the envelope of the radio frequency signal using a transceiver. The method further includes amplifying the radio frequency signal using a power amplifier, which includes receiving the radio frequency signal at the input of the power amplifier and providing an amplified radio frequency signal at the output of the power amplifier. The method further includes modulating the load of the power amplifier using the envelope signal to control the impedance of a controllable load impedance coupled to the output of the power amplifier.

[0012] In various embodiments, the method further includes calibrating the power amplifier by shaping the envelope signal based on calibration data. According to a certain number of embodiments, calibrating the power amplifier includes providing a flat gain versus input power characteristic.

[0013] In some embodiments, modulating the load of a power amplifier includes controlling the capacitance of a controllable capacitor coupled to an output balun. According to a number of embodiments, the method further includes applying an amplified radio frequency signal to a first winding of the output balun, and the controllable capacitor is coupled to a second winding of the output balun. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments of the present disclosure are described below through non-limiting examples with reference to the accompanying drawings.

[0015]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12A

Figure 12B

Figure 13

Best Mode for Carrying Out the Invention

[0016] The following detailed description of a given embodiment presents various descriptions of a particular embodiment. However, the innovation described herein can be embodied in many different ways, for example, as defined and covered by the claims. In this specification, drawings are referred to in which the same reference numerals indicate the same or functionally similar elements. It is understood that the elements shown in the drawings are not necessarily to scale. It is further understood that a given embodiment may include more elements than shown in the drawings and / or a subset of the elements shown in the drawings. Further, some embodiments may include any suitable combination of features from two or more of the drawings.

[0017] A load modulation power amplifier is provided herein. In a given embodiment, the load modulation power amplifier includes a power amplifier that amplifies a radio frequency (RF) input signal and a load impedance coupled to the output of the power amplifier. The load impedance is controlled based on the envelope of the RF input signal so as to provide load modulation to the output of the power amplifier. By providing load impedance modulation in this manner, high efficiency can be obtained over a wide dynamic range.

[0018] In a given implementation example, the load impedance includes an output balun, which includes a first winding and a second winding that are electromagnetically coupled to each other. Additionally, the output of the power amplifier is coupled to the first terminal of the first winding (or is configured in a push-pull configuration where the output is coupled to two terminals of the first winding), while the amplified RF signal is output from the first terminal of the second winding. The load impedance further includes a controllable capacitor coupled to the second terminal of the second winding. This controllable capacitor has a capacitance that is controlled by the envelope of the RF signal.

[0019] That is, load modulation can be performed by sweeping the impedance of the termination capacitor at the secondary port of the balun. In a given implementation example, the termination capacitor is controlled by an analog envelope control signal from a transceiver, which can be calibrated by achieving desired gain and / or efficiency characteristics such as isogain.

[0020] In a given implementation example, the load impedance includes a heterojunction bipolar transistor (HBT) switch having a collector coupled to a capacitor and a base controlled by an envelope signal. Additionally, the HBT switch operates as a variable resistor having a maximum load line achieved when the switch is open and a minimum load line achieved at the highest envelope voltage level when the switch is closed. In such a configuration, minimum loss is achieved at the maximum load line, which is beneficial for the modulation efficiency of high peak-to-average power ratio (PAPR) waveforms such as those used in 5G communication.

[0021] Compared to a power amplifier in which an envelope tracker controls the supply voltage of the power amplifier based on an envelope signal, a load modulation power amplifier has a load impedance controlled based on an envelope signal. By providing load modulation in this manner, a high-efficiency power amplifier is obtained that has lower complexity than an envelope tracking amplifier while leveraging a circuit for generating and calibrating the envelope signal for the desired performance.

[0022] For example, a load-modulated power amplifier can be powered by a high-efficiency DC / DC converter, such as a power management unit (PMU) that operates with an efficiency of 93% or more. Such a PMU can operate, for example, using average power tracking (APT) over 5.5V + 2.5 to 3.0V (wherein the power amplifier efficiency can be good at a high supply voltage due to the non-zero knee voltage). In contrast, an envelope tracking system has only about 80% efficiency at a supply voltage of approximately 2.5 to 3.0V (wherein the power amplifier efficiency can deteriorate at a low supply voltage due to the non-zero knee voltage). Here, the PMU is also referred to as a power management integrated circuit (PMIC).

[0023] A load-modulated power amplifier may be included in a variety of RF communication systems including, but not limited to, base stations, network access points, cellular phones, tablets, customer premise equipment (CPE), laptops, computers, wearable electronics, and / or other communication devices.

[0024] FIG. 1 is a schematic diagram of a load-modulated power amplifier 10 according to an embodiment. The load-modulated power amplifier 10 includes a power amplifier 5 and a controllable load impedance 6. The load-modulated power amplifier 10 amplifies an RF input signal RF IN to generate an RF output signal RF OUT .

[0025] The load-modulated power amplifier 10 receives an envelope signal ENV that varies in relation to the envelope of the RF input signal RF IN . The envelope signal ENV is used to control the impedance of the controllable load impedance 6. For example, in this embodiment, the controllable load impedance 6 includes a series combination of an inductor 8 and a controllable capacitor 7, and the envelope signal ENV is used to control the capacitance of the controllable capacitor 7. Despite depicting an example of a controllable load impedance, the teachings herein are applicable to other implementations of the controllable load impedance.

[0026] FIG. 2 is a schematic diagram of a load modulation power amplifier 20 according to another embodiment. The load modulation power amplifier 20 in FIG. 2 is the same as the load modulation power amplifier 10 in FIG. 1, except that the load modulation power amplifier 20 in FIG. 2 includes a controllable load impedance 16 with a different implementation.

[0027] Specifically, the controllable load impedance 16 includes a balun 18 and a controllable capacitor 7. The output of the power amplifier 5 drives the first winding of the balun 18. Additionally, the first terminal of the second winding of the balun 18 outputs the RF output signal RF OUT while the second terminal of the second winding is coupled to the controllable capacitor 7. The controllable capacitor 7 is controlled by the envelope signal ENV.

[0028] By changing the value of the controllable capacitor 7, a part of the inductance of the second winding is effectively resonated, thereby effectively changing the turns ratio of the balun 18.

[0029] FIG. 3 is a schematic diagram of a load modulation power amplifier system 40 according to an embodiment. The load modulation power amplifier system 40 includes a load modulation power amplifier 25, a band switching and tuning circuit 26, and an antenna 3.

[0030] In the illustrated embodiment, the load modulation power amplifier 25 includes a driver amplifier 31, an input balun 32, a first output amplifier 33, a second output amplifier 34, and a controllable load impedance 16 including an output balun 18 and a controllable capacitor 7.

[0031] The load modulation power amplifier 25 is implemented as a push - pull amplifier in this embodiment. Additionally, the output of the first output amplifier 33 is connected to the first terminal of the first winding of the balun 18, while the output of the second output amplifier 34 is connected to the second terminal of the first winding of the balun 18.

[0032] Figure 4A is a schematic diagram of a load - modulated power amplifier system 110 of another embodiment. The load - modulated power amplifier system 110 includes an output balun 18, a power amplifier die 101, a switch die 102, an envelope generator die 103, and a driver die 104. The power amplifier die 101 includes a driver amplifier 31, an input balun 32, a first output amplifier 33, a second output amplifier 34, and a controllable capacitor 7. The switch die 102 includes a capacitor 107 and a switch 108. Further, the envelope generator die 103 includes a shaping circuit 105 that shapes the differential envelope signal ENV DIFF given to the driver die 104. The driver die 104 includes an amplifier 106 that receives the differential envelope signal ENV DIFF and outputs an envelope control signal ENV that controls the controllable capacitor 7.

[0033] The load - modulated power amplifier system 110 can operate by system - level calibration that aligns and shapes the envelope control signal for the controllable capacitor 7 with respect to the RF input signal amplified by the push - pull amplifier.

[0034] Figure 4B is a schematic diagram of a load - modulated power amplifier system 120 of another embodiment. The load - modulated power amplifier system 120 includes an output balun 18, a power amplifier die 111, a switch die 112, an envelope generator die 103, and a driver die 104.

[0035] The load - modulated power amplifier system 120 in Figure 4B is similar to the load - modulated power amplifier system 110 in Figure 4A, but differs in that it shows an implementation example where the controllable capacitor 7 is present on the switch die 112. Since the switch die 112 is typically implemented using a silicon - on - insulator (SOI) process and the power amplifier die 111 is implemented using a compound semiconductor process (e.g., GaAs), placing the controllable capacitor 7 on the switch die 112 helps to obtain a capacitor with a high quality factor (Q - value).

[0036] FIG. 5A is a schematic diagram of a controllable capacitor 210 of an embodiment for a load modulation power amplifier. The controllable capacitor 210 includes a bipolar transistor 201 (e.g., a heterojunction bipolar transistor or HBT), a base resistor 202, a base capacitor 203, and a load capacitor 204. The base of the bipolar transistor 201 is controlled by an envelope signal ENV (received from an envelope tracker via the base resistor 202), while the emitter of the bipolar transistor 201 is grounded. The load capacitor 204 is coupled between the collector of the bipolar transistor 201 and a load terminal LD that provides a load to the power amplifier (e.g., by serving as a termination capacitor for an output balun driven by the power amplifier). The base capacitor 203 is connected between the base of the bipolar transistor 201 and ground.

[0037] The bipolar transistor 201 operates as a variable resistor having a maximum load line achieved when the envelope signal ENV is low and a minimum load line achieved when the envelope signal ENV is high. The lowest loss is achieved at the maximum load line. This is beneficial for the modified efficiency of high PAPR waveforms.

[0038] FIG. 5B is a schematic diagram of a controllable capacitor 220 of an embodiment for a load modulation power amplifier. The controllable capacitor 220 includes a plurality of controllable capacitor cells 211a, 211b, 211c, …, 211n connected in parallel with each other between a load terminal LD (which provides a load to the power amplifier) and ground.

[0039] As shown in FIG. 5B, the controllable capacitor cell 211a includes a bipolar transistor 201a, a base resistor 202a, a base capacitor 203a, a load capacitor 204a, a clamp diode 205a, and a clamp resistor 206a. The base of the bipolar transistor 201a is controlled by an envelope signal ENV received via the base resistor 202a, while the emitter of the bipolar transistor 201a is grounded. The load capacitor 204a is coupled between the collector of the bipolar transistor 201a and the load terminal LD. The base capacitor 203a is connected between the base of the bipolar transistor 201a and ground. Additionally, the clamp diode 205a and the clamp resistor 206a are connected in series between the base of the bipolar transistor 201a and ground. The capacitor 203a is parallel to the series connection of the clamp diode 205a and the clamp resistor 206a.

[0040] Continuing to refer to FIG. 5B, the controllable capacitor cell 211b includes a bipolar transistor 201b, a base resistor 202b, a base capacitor 203b, a load capacitor 204b, a clamp diode 205b, a clamp resistor 206b, a diode bias resistor 207b, and a Schottky diode 208b1. Additionally, the controllable capacitor cell 211c includes a bipolar transistor 201c, a base resistor 202c, a base capacitor 203c, a load capacitor 204c, a clamp diode 205c, a clamp resistor 206c, a diode bias resistor 207c, and Schottky diodes 208c1 and 208c2. Further, the controllable capacitor cell 211n includes a bipolar transistor 201n, a base resistor 202n, a base capacitor 203n, a load capacitor 204n, a clamp diode 205n, a clamp resistor 206n, a diode bias resistor 207n, and Schottky diodes 208n1, 208n2, …, 208nm.

[0041] Although four controllable capacitor cells are depicted, any number of controllable capacitor cells may be included. As shown in FIG. 5B, additional controllable capacitor cells each include an additional Schottky diode compared to the preceding controllable capacitor.

[0042] FIG. 6 is an example of a Smith chart of collector impedance versus control voltage for a load-modulated power amplifier. In this example, when the envelope control voltage (VCTRL) varies from 0.7 V to 2.1 V, a change exceeding a 2x change (doubling) in load impedance is achieved.

[0043] FIG. 7 is a graph of an example of a gain versus output power plot for a load-modulated power amplifier.

[0044] FIG. 8 is a graph of an example of a power-added efficiency (PAE) versus output power plot for a load-modulated power amplifier.

[0045] Referring to FIGS. 7 and 8, the graphs relate to one implementation example of a two-stage push-pull power amplifier having a 0.3 dB balance loss.

[0046] A waterfall curve is depicted with exemplary values shown for achieving isogain using envelope calibration (e.g., by selecting shaping values in an envelope shaping circuit).

[0047] FIG. 9 is a graph of an example of a gain versus output power plot for a load-modulated power amplifier.

[0048] FIG. 10 is a graph of another example of a PAE versus output power plot for a load-modulated power amplifier.

[0049] Referring to FIGS. 9 and 10, in this example, an extremely flat PAE is achieved over a 6 dB dynamic range.

[0050] FIG. 11 is a schematic diagram of a mobile device 800 in one embodiment. The mobile device 800 includes a baseband system 801, a transceiver 802, a front-end system 803, an antenna 804, a power management system 805, a memory 806, a user interface 807, and a battery 808.

[0051] The mobile device 800 can be used to communicate using a variety of communication technologies including, but not limited to, 2G, 3G, 4G (LTE, LTE-Advanced, and LTE-Advanced Pro), 5GNR, WLAN (e.g., WiFi), WPAN (e.g., Bluetooth® and ZigBee®), WMAN (e.g., WiMax), and / or GPS technology.

[0052] The transceiver 802 generates RF signals for transmission and processes incoming RF signals received from the antenna 804. It will be understood that the various functions associated with the transmission and reception of RF signals can be accomplished by one or more components collectively represented as the transceiver 802 in FIG. 11. In one example, separate components (e.g., separate circuits or dies) may be provided to handle a given type of RF signal.

[0053] The front-end system 803 assists in conditioning the signals transmitted to and / or received from the antenna 804. In the illustrated embodiment, the front-end system 803 includes an antenna tuning circuit 810, a plurality of power amplifiers (PAs) 801, a plurality of low-noise amplifiers (LNAs) 812, a plurality of filters 813, a plurality of switches 814, and a signal splitting / combining circuit 815. However, other implementations are possible.

[0054] For example, the front-end system 803 can provide a certain number of functions including, but not limited to, amplification of the transmission signal, amplification of the reception signal, filtering of the signal, switching between different bands, switching between different power modes, switching between the transmission mode and the reception mode, duplexing of the signal, multiplexing of the signal (e.g., diplexing or triplexing), or some combination thereof.

[0055] At least one of the plurality of power amplifiers 811 is implemented as a load modulation power amplifier according to the teachings herein. Despite showing a communication system in one embodiment where the mobile device 800 can implement one or more load modulation power amplifiers, the teachings herein are applicable to a wide range of systems. Thus, other implementations are also possible.

[0056] In a given implementation, the mobile device 800 supports carrier aggregation, so flexibility is obtained to increase the peak data rate. Since carrier aggregation can be used for both frequency division duplexing (FDD) and time division duplexing (TDD), it may be used to aggregate (aggregate) multiple carriers or channels. Carrier aggregation includes continuous aggregation in which continuous carriers within the same operating frequency band are aggregated. Carrier aggregation may be discontinuous and may include carriers with separated frequencies within the same band or different bands.

[0057] The plurality of antennas 804 can include antennas used for a wide variety of types of communication. For example, the antenna 804 can include antennas for transmission and / or reception of signals associated with a wide variety of frequencies and communication standards.

[0058] In a given implementation example, the antenna 804 supports MIMO communication and / or switched diversity communication. For example, MIMO communication uses multiple antennas to communicate multiple data streams via a single radio frequency channel. MIMO communication benefits from spatial multiplexing (multiplexing) of the radio environment, resulting in a high signal-to-noise ratio, improved coding, and / or signal interference reduction. Switched diversity refers to communication in which a specific antenna operating at a specific time is selected. For example, a switch can be used to select a specific antenna from a group of antennas based on various factors such as observed bit error rate and / or signal strength indicator.

[0059] The mobile device 800 can operate with beamforming in a given implementation example. For example, the front-end system 803 can include an amplifier with a controllable gain and a phase shifter with a controllable phase to provide beamforming and directivity for transmitting and / or receiving signals using the antenna 804. For example, in the context of signal transmission, the amplitude and phase of the transmission signal applied to the antenna 804 are controlled so that the signals radiated from the antenna 804 are combined using constructive and destructive interference, and an aggregated transmission signal is generated that exhibits qualities such as a strong signal intensity propagating in a given direction. In the context of signal reception, the amplitude and phase are controlled so that more signal energy is received when the signal arrives at the antenna 804 from a specific direction. In a given implementation example, the antenna 804 includes one or more arrays of antenna elements to enhance beamforming.

[0060] The baseband system 801 is coupled to a user interface 807 that facilitates the processing of various user inputs / outputs (I / O) such as voice and data. The baseband system 801 provides a digital representation of the transmission signal to a transceiver 802, which processes it to generate an RF signal for transmission. The baseband system 801 also processes the digital representation of the received signal provided by the transceiver 802. As shown in FIG. 11, the baseband system 801 is coupled to a memory 806 to facilitate the operation of the portable device 800.

[0061] The memory 806 can be used for a variety of purposes such as storing data and / or instructions to facilitate the operation of the portable device 800 and / or to provide for the storage of user information.

[0062] The power management system 805 provides a number of power management functions for the portable device 800. In a given implementation, the power management system 805 includes a PA supply control circuit that controls the supply voltage of a plurality of power amplifiers 811. For example, the power management system 805 may be configured to vary the supply voltage provided to one or more of the plurality of power amplifiers 811 to improve efficiency such as power added efficiency (PAE).

[0063] As shown in FIG. 11, the power management system 805 receives a battery voltage from a battery 808. The battery 808 may be any suitable battery including, for example, a lithium ion battery for use in the portable device 800.

[0064] FIG. 12A is a schematic diagram of a package module 900 of one embodiment. FIG. 12B is a schematic diagram of a cross section of the package module 900 taken along line 12B-12B of FIG. 12A.

[0065] The package module 900 includes a radio frequency component 901, a semiconductor die 902, a surface mount device 903, wire bonds 908, a package substrate 920, and an encapsulation structure 940. The package substrate 920 includes pads 906 formed from conductors disposed therein. Additionally, the semiconductor die 902 includes pins or pads 904, and the wire bonds 908 are used to connect the pads 904 of the die 902 to the pads 906 of the package substrate 920.

[0066] The semiconductor die 902 includes a load modulation power amplifier 945 that may be implemented according to any of the embodiments herein.

[0067] The packaging substrate 920 is configured to receive a plurality of components such as the radio frequency component 901, which includes, for example, surface mount capacitors and / or inductors, the semiconductor die 902, and the surface mount device 903. In one implementation example, the radio frequency component 901 includes an integrated passive device (IPD).

[0068] As shown in FIG. 12B, the package module 900 includes a plurality of contact pads 932. The plurality of contact pads 932 are disposed on the side of the package module 900 opposite the side used to attach the semiconductor die 902. Configuring the package module 900 in this manner may assist in connecting the package module 900 to a circuit board such as a phone board of a portable device. Examples of the contact pads 932 can be configured to provide radio frequency signals, bias signals, and / or power (e.g., power supply voltage and ground) to the semiconductor die 902 and / or other components. As shown in FIG. 12B, the electrical connection between the contact pads 932 and the semiconductor die 902 can be facilitated by a connection 933 through the package substrate 920. The connection 933 can represent an electrical path formed to pass through the package substrate 920, such as a connection associated with vias and conductors of a multilayer package substrate.

[0069] In some embodiments, the package module 900 may also include one or more package structures, such as to provide protection and / or facilitate handling. Such package structures may include an overmold or encapsulation structure 940 formed over a package substrate 920 on which components and dies are disposed.

[0070] It will be appreciated that although the package module 900 is depicted in the context of wirebond-based electrical connections, one or more features of the present disclosure can also be implemented in other package configurations, such as a flip-chip configuration, for example.

[0071] FIG. 13 is a schematic diagram of one embodiment of a communication system 1130 that transmits RF signals. The communication system 1130 includes a baseband processor 1107, a signal delay circuit 1108, a digital predistortion (DPD) circuit 1109, an I / Q modulator 1110, an observation receiver 1111, an intermodulation detection circuit 1112, a power amplifier 1113, a directional coupler 1114, a duplexing and switching circuit 1115, an antenna 1116, an envelope delay circuit 1121, a coordinate rotation digital computation (CORDIC) circuit 1122, a shaping circuit 1123, a digital / analog converter 1124, and a reconstruction filter 1125.

[0072] The communication system 1130 of FIG. 13 shows an example of an RF system that includes a load modulation power amplifier according to the teachings herein. However, load modulation power amplifiers can be used in a wide variety of RF systems.

[0073] The baseband processor 1107 operates to generate I and Q signals corresponding to the signal components of a sine wave or a sine signal of a desired amplitude, frequency, and phase. For example, the I signal is used to represent the in-phase component of the sine wave, and the Q signal is used to represent the quadrature phase component of the sine wave, thereby providing an equivalent representation of the sine wave. In a given implementation example, the I and Q signals are provided to the I / Q modulator 1110 in digital form. The baseband processor 1107 may be any suitable processor configured to process baseband signals. For example, the baseband processor 1107 may include a digital signal processor, a microprocessor, a programmable core, or any combination thereof.

[0074] The signal delay circuit 1108 provides adjustable delays to the I and Q signals to assist in controlling the relative alignment between the envelope signal and the RF signal RF IN The amount of delay provided by the signal delay circuit 1108 is controlled based on the amount of intermodulation detected by the intermodulation detection circuit 1112.

[0075] The DPD circuit 1109 operates to provide digital shaping to the delayed I and Q signals from the signal delay circuit 1108 to generate digitally pre-distorted (DPD) I and Q signals. In the illustrated embodiment, the pre-distortion provided by the DPD circuit 1109 is controlled based on the amount of intermodulation detected by the intermodulation detection circuit 1112. The DPD circuit 1109 serves to reduce the distortion of the power amplifier 1113 and / or increase the efficiency of the power amplifier 1113.

[0076] The I / Q modulator 1110 receives the digitally pre-distorted I and Q signals, and these signals are the RF signal RF INIt is processed to generate. For example, the I / Q modulator 1110 includes a DAC configured to convert the digitally pre-distorted I signal and Q signal into an analog format, a mixer that up-converts the analog I signal and Q signal to a radio frequency, and a signal combiner that combines the up-converted I signal and Q signal into an RF signal suitable for amplification by the power amplifier 1113. In a given implementation example, the I / Q modulator 1110 may include one or more filters configured to filter the frequency components of the processed signal.

[0077] The envelope delay circuit 1121 delays the I signal and Q signal from the baseband processor 1107. Additionally, the CORDIC circuit 1122 processes the delayed I signal and Q signal to generate a digital envelope signal representative of the envelope of the RF signal RF IN Although FIG. 13 shows one implementation example using the CORDIC circuit 1122, the envelope signal can also be obtained in other ways.

[0078] The shaping circuit 1123 operates to shape the digital envelope signal to enhance the performance of the communication system 1130. In a given implementation example, the shaping circuit 1123 includes a shaping table that maps each level of the digital envelope signal to a corresponding shaped envelope signal level. Envelope shaping can help control the linearity, distortion, and / or efficiency of the power amplifier 1113.

[0079] In the illustrated embodiment, the shaped envelope signal is a digital signal converted to an analog envelope signal by the DAC 1124. Additionally, the analog envelope signal is filtered by the reconstruction filter 1125 to generate an envelope signal suitable for modulating the load of the power amplifier 1113. In a given implementation example, the reconstruction filter 1125 includes a low-pass filter.

[0080] Continuing to refer to FIG. 13, the power amplifier 1113 receives the RF signal RF from the I / Q modulator 1110 and amplifies the RF signal RF IN to obtain the amplified RF signal RF OUTIn this example, it is supplied to antenna 1116 via a duplexing and switching circuit 1115.

[0081] By arranging the directional coupler 1114 between the output of the power amplifier 1113 and the input of the duplexing and switching circuit 1115, measurement of the output power of the power amplifier 1113 without including the insertion loss of the duplexing and switching circuit 1115 is allowed. The output signal detected from the directional coupler 1114 is supplied to the observation receiver 1111. The observation receiver 1111 may include a mixer that generates a down-converted I signal and Q signal, and a DAC that generates an I observation signal and a Q observation signal from the down-converted signal.

[0082] The intermodulation detection circuit 1112 determines the intermodulation product of the I observation signal and Q observation signal and the I signal and Q signal from the baseband processor 1107. Additionally, the intermodulation detection circuit 1112 controls the predistortion provided by the DPD circuit 1109 and / or the delay of the signal delay circuit 1108, and controls the relative alignment between the envelope signal and the RF signal RF IN In a predetermined implementation example, the intermodulation detection circuit 1112 also plays a role in controlling the shaping provided by the shaping circuit 1123.

[0083] By including the feedback path from the output of the power amplifier 1113 and the baseband, the I signal and Q signal can be dynamically adjusted to optimize the operation of the communication system 1130. For example, by configuring the communication system 1130 in this manner, power control, compensation for transmitter failures, and / or execution of DPD can be assisted.

[0084] Although shown as a single stage, the power amplifier 1113 may include one or more stages. Further, the teachings herein are also applicable to communication systems including multiple power amplifiers.

[0085] End

[0086] Unless the context clearly dictates otherwise, throughout the specification and claims, terms such as "comprising," "including," etc. shall be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, i.e., in the sense of "including but not limited to." The term "coupled" as generally used herein refers to the possibility that two or more elements can be either directly connected or connected via one or more intermediate elements. Similarly, the term "connected" as generally used herein also refers to the possibility that two or more elements can be either directly connected or connected via one or more intermediate elements. Additionally, as used in this application, the terms "herein," "above," "below," and terms of similar meaning refer to the entire application and not to any specific portion thereof. Where context permits, the terms in the above detailed description using singular or plural numbers may also include the plural or singular numbers, respectively. The terms "or" and "or alternatively" referring to a list of two or more items cover all of the following interpretations of the term, i.e., any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0087] Furthermore, unless specifically recited or understood otherwise within the context in which it is used, conditional language such as, among others, "may," "can," "able to," "might," "for example," "such as," etc. as used herein generally does not intend that a given embodiment includes a given feature, element, and / or state while other embodiments do not. That is, such conditional language is not generally intended to imply that a feature, element, and / or state exists in any way that is necessary for one or more embodiments or that one or more embodiments necessarily include the logic for determining whether these features, elements, and / or states are included or not, with or without the author's input or prompt, or whether they should be performed in any particular embodiment.

[0088] The above description of the embodiments of the present invention is not intended to be exhaustive or to limit the invention to the exact form disclosed. Specific embodiments and examples of the present invention have been described above for illustrative purposes, but as will be recognized by those skilled in the art, various equivalent modifications are possible within the scope of the present invention. For example, while a process or block is presented in a given order, alternative embodiments can execute a routine having steps in a different order or use a system having blocks, and some processes or blocks can be deleted, moved, added, subdivided, combined, and / or modified. These processes or blocks can each be implemented in various different manners. Also, while a process or block may be shown as being executed serially, these processes or blocks may instead be executed in parallel or at different times.

[0089] The teachings of the present invention provided herein can be applied to other systems that are not necessarily the systems described above. The elements and operations of the various embodiments described above may be combined to provide further embodiments.

[0090] Although certain embodiments of the present invention have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the disclosure. In fact, the novel methods and systems described herein may be embodied in a variety of other forms, and various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. The appended claims and their equivalents are intended to cover such forms or modifications as fall within the scope and spirit of the disclosure.

Claims

1. A portable device, comprising: a transceiver configured to generate a radio frequency signal and an envelope signal that varies in relation to the envelope of the radio frequency signal; a front-end system including a load-modulated power amplifier configured to amplify the radio frequency signal; wherein the load-modulated power amplifier includes a power amplifier configured to receive the radio frequency signal at an input and provide an amplified radio frequency signal at an output; a controllable load impedance coupled to the output of the power amplifier; wherein the envelope signal is operable to control the impedance of the controllable load impedance to modulate the load at the output of the power amplifier; the controllable load impedance includes a controllable capacitor controlled by the envelope signal; an output balun having a first winding coupled to the output of the power amplifier and a second winding coupled to the controllable capacitor; a portable device.

2. The portable device according to claim 1, wherein the transceiver includes a shaping circuit configured to shape the envelope signal based on calibration data.

3. The portable device according to claim 2, wherein the shaping circuit is operable to provide a flat gain versus input power characteristic to the power amplifier.

4. The power amplifier includes an input balun; a pair of amplifiers coupled between the input balun and the output balun; The portable device according to claim 1.

5. The second winding of the output balun includes a first terminal for outputting the amplified radio frequency signal; a second terminal coupled to the controllable capacitor; The portable device according to claim 1.

6. The controllable capacitor includes a bipolar transistor; a load capacitor coupled to the collector of the bipolar transistor; wherein the envelope signal is operable to control the base of the bipolar transistor.

7. The portable device according to claim 1, further including an antenna operable to transmit the amplified radio frequency signal.

8. The portable device according to claim 1, further including a band switch having an input electrically connected to the second winding of the output balun.

9. The portable device according to claim 8, wherein the second winding of the output balun is electrically connected between the input of the band switch and the controllable capacitor.

10. A load-modulated power amplifier system, A power amplifier configured to receive a radio frequency signal at an input and provide an amplified radio frequency signal at an output, a controllable load impedance coupled to the output of the power amplifier, and the controllable load impedance is configured to receive an envelope signal that varies in relation to the envelope of the radio frequency signal, the envelope signal is operable to control the impedance of the controllable load impedance to modulate the load at the output of the power amplifier, the controllable load impedance includes a controllable capacitor controlled by the envelope signal, and an output balun having a first winding coupled to the output of the power amplifier and a second winding coupled to the controllable capacitor, a load modulation power amplifier system. **Claim 11** The power amplifier includes an input balun, and a pair of amplifiers coupled between the input balun and the output balun, The load modulation power amplifier system of claim 10. **Claim 12** The second winding includes a first terminal that outputs the amplified radio frequency signal, and a second terminal coupled to the controllable capacitor, The load modulation power amplifier system of claim 10. **Claim 13** The controllable capacitor includes a bipolar transistor, and a load capacitor coupled to the collector of the bipolar transistor, and the envelope signal is operable to control the base of the bipolar transistor, The load modulation power amplifier system of claim 10. **Claim 14** A method of amplification in a portable device, comprising: generating, using a transceiver, a radio frequency signal and an envelope signal that varies in relation to the envelope of the radio frequency signal; amplifying the radio frequency signal using a power amplifier, including receiving the radio frequency signal at an input of the power amplifier and providing an amplified radio frequency signal at an output of the power amplifier; modulating the load of the power amplifier using the envelope signal to control the impedance of a controllable load impedance coupled to the output of the power amplifier, wherein modulating the load of the power amplifier includes controlling the capacitance of a controllable capacitor coupled to an output balun. **Claim 15** The method of claim 14, further comprising calibrating the power amplifier by shaping the envelope signal based on calibration data.

16. The method of claim 15, wherein calibrating the power amplifier includes providing a flat gain versus input power characteristic.

17. Further comprising applying the amplified radio frequency signal to the first winding of the output balun, The method of claim 14, wherein the controllable capacitor is coupled to the second winding of the output balun.

18. The power amplifier includes an input balun, a pair of amplifiers coupled between the input balun and the output balun and The method of claim 17, further comprising applying the amplified radio frequency signal from the pair of amplifiers to the first winding of the output balun.

19. The controllable capacitor includes a bipolar transistor, a load capacitor coupled to the collector of the bipolar transistor and The method of claim 14, further comprising controlling the base of the bipolar transistor using the envelope signal.

20. The method of claim 14, further comprising transmitting the amplified radio frequency signal using an antenna.

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