# Patent

## Title
Multi-broadband Doherty power amplifier

## Abstract

Radio frequency (RF) amplification devices are disclosed that include Doherty amplification circuits and methods of operating the same. In one embodiment, a Doherty amplification circuit includes a main carrier RF amplifier, a peaking RF amplifier, and a periodic quadrature coupler. To provide Doherty amplification, the peaking RF amplifier is configured to be deactivated while an RF signal is below a threshold level and is configured to be activated while the RF signal is above the threshold level. The periodic quadrature coupler is configured to combine a first RF split signal from the main carrier RF amplifier and a second RF split signal from the peaking RF amplifier into the RF signal, such that the RF signal is output from an output port while the peaking RF amplifier is activated. The periodic quadrature coupler allows the Doherty amplification circuit to provide broadband amplification in various RF communication bands.

## Background
RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 61/839,072, filed on Jun. 25, 2013, the disclosure of which is hereby incorporated herein by reference in its entirety.
This application is also related to U.S. patent application Ser. No. 14/103,089, filed on Dec. 11, 2013 and entitled “DOHERTY POWER AMPLIFIER WITH TUNABLE IMPEDANCE LOAD,” the disclosure of which is hereby incorporated herein by reference in its entirety.


FIELD OF THE DISCLOSURE
This disclosure relates generally to radio frequency (RF) amplification devices.
BACKGROUND
In radio frequency (RF) applications, a conventional Doherty amplification circuit typically includes a main carrier RF amplifier coupled in parallel with a peaking RF amplifier. At low power levels, the main carrier RF amplifier in the conventional Doherty amplification circuit is activated and biased for linear operation, while the peaking RF amplifier is deactivated. The peaking RF amplifier is activated once an RF signal reaches a particular signal level, which is generally at or near a compression point of the main carrier RF amplifier. To increase power efficiency, quarter wave transmission line transformers or quarter wave transmission line inverters are often employed in conventional Doherty amplification circuits in order to provide the appropriate impedance transformations while the peaking RF amplifier is activated and deactivated. Unfortunately, quarter wave transmission line transformers/inverters have narrowband characteristics and thus do not allow for broadband operation. Furthermore, at the higher frequencies, the quarter wave transmission line transformers/inverters in these conventional Doherty amplification circuits degrade the power efficiency of the Doherty amplification circuit at backed-off power levels. Generally, this is due to the narrowband characteristics of the quarter wave transmission line transformers/inverters and, in addition, to the inability of the quarter wave transmission line transformers/inverters to correct for parasitic effects in the peaking RF amplifier at higher frequencies.
Accordingly, RF circuit designs that improve bandwidth performance and/or the power efficiency of the Doherty amplification circuit are needed.
SUMMARY
Radio frequency (RF) amplification devices, along with methods of operating the same, are disclosed that include Doherty amplification circuits configured to amplify an RF signal. In one embodiment, an RF amplification device includes a Doherty amplification circuit configured to amplify an RF signal. The Doherty amplification circuit includes a main carrier RF amplifier, a peaking RF amplifier, and a periodic quadrature coupler. To provide Doherty amplification, the peaking RF amplifier is configured to be deactivated while the RF signal is below a threshold level and is configured to be activated while the RF signal is above the threshold level. The periodic quadrature coupler has an output port and is configured to combine a first RF split signal from the main carrier RF amplifier and a second RF split signal from the peaking RF amplifier into the RF signal such that the RF signal is output from the output port after amplification by the Doherty amplification circuit while the peaking RF amplifier is activated. The periodic quadrature coupler allows the Doherty amplification circuit to provide broadband amplification in various RF communication bands.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.



BRIEF DESCRIPTION OF THE DRAWING FIGURES
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
FIG. 1 illustrates an exemplary radio frequency (RF) amplification device having a Doherty amplification circuit and a control circuit, wherein the Doherty amplification circuit includes a first periodic quadrature coupler that receives an RF signal; a main carrier RF amplifier; a peaking RF amplifier; and a second periodic quadrature coupler having an isolation port and a tunable impedance load coupled to the isolation port and configured to provide a tunable impedance to invoke Doherty amplification operation.
FIG. 2 illustrates one embodiment of a Lange coupler, which may be provided as an embodiment of the first periodic quadrature coupler and/or the second periodic quadrature coupler shown in FIG. 1.
FIG. 3 illustrates one embodiment of a transfer function of the Lange coupler shown in FIG. 2.
FIG. 4 illustrates one embodiment of a phase response of the transfer function provided by the Lange coupler shown in FIG. 2.
FIG. 5 illustrates one embodiment of the RF amplification device shown in FIG. 1, wherein the control circuit is configured to detect RF power in the Doherty amplification circuit at an output port provided by the second quadrature coupler.
FIG. 6 illustrates another embodiment of the RF amplification device shown in FIG. 1, wherein the control circuit is configured to detect RF power in the Doherty amplification circuit at an input port provided by the first quadrature coupler.
FIG. 7 illustrates yet another embodiment of the RF amplification device shown in FIG. 1, wherein the control circuit is configured to detect RF power in the Doherty amplification circuit from a supply current provided to the peaking RF amplifier.
FIG. 8 illustrates one embodiment of the tunable impedance load shown in FIG. 1, where the embodiment of the tunable impedance load shown in FIG. 8 is purely resistive.
FIG. 9 is a graph illustrating power curves that describe power added efficiency (PAE) as a function of output power in the RF amplification device shown in FIG. 5 using the tunable impedance load shown in FIG. 8, wherein each of the power curves demonstrates PAE versus output power for a different pairing of a carrier frequency of the RF signal and a tunable impedance of tunable impedance load where the carrier frequency/tunable impedance pairings correspond to (700 MHz, Znorm×6 (Znorm is a characteristic amplifier impedance of the Doherty amplification circuit)), (850 MHz, Znorm×8), (1000 MHz, Znorm×20), and (850 MHz, Znorm). Note that the optimum termination impedance is larger than Znorm to invoke Doherty amplification operation under backed-off power conditions and may be different at various frequencies across a band.
FIG. 10 is a graph illustrating power curves that describe PAE as a function of output power in the RF amplification device shown in FIG. 5 using the tunable impedance load shown in FIG. 8, wherein each of the power curves demonstrates PAE versus output power for a different pairing of a carrier frequency of the RF signal and a tunable impedance of tunable impedance load where the carrier frequency/tunable impedance pairings correspond to (2.6 GHz, Znorm×50), (2.4 GHz, Znorm×20), (2.2 GHz, Znorm×10), and (2.4 GHz, Znorm). Note that the optimum termination impedance is larger than Znorm to invoke Doherty amplification operation under backed-off power conditions and may be different at various frequencies across a band.
FIG. 11 is a graph illustrating power curves that describe PAE as a function of output power in the RF amplification device shown in FIG. 5 using the tunable impedance load shown in FIG. 8, wherein each of the power curves demonstrates PAE versus output power for a different pairing of a carrier frequency of the RF signal and a tunable impedance of tunable impedance load where the carrier frequency/tunable impedance pairings correspond to (850 MHz, Znorm) and (850 MHz, high impedance).
FIG. 12 is a graph illustrating power curves that describe PAE as a function of output power in the RF amplification device shown in FIG. 5 using the tunable impedance load shown in FIG. 8, wherein each of the power curves demonstrates PAE versus output power for a different pairing of a carrier frequency of the RF signal and a tunable impedance of tunable impedance load where the carrier frequency/tunable impedance pairings correspond to (2.4 GHz, Znorm) and (2.4 GHz, high impedance).
FIG. 13 illustrates another embodiment of the tunable impedance load shown in FIG. 1, where the embodiment of the tunable impedance load shown in FIG. 13 is resistive and inductive.
FIG. 14 illustrates still another embodiment of the tunable impedance load shown in FIG. 1, where the embodiment of the tunable impedance load shown in FIG. 14 is resistive, inductive, and capacitive so as to form resonant tanks.
FIG. 15 illustrates yet another embodiment of the tunable impedance load shown in FIG. 1, where the embodiment of the tunable impedance load shown in FIG. 15 is resistive and inductive, like the embodiment in FIG. 13, but includes inductors with varying physical sizes.



DETAILED DESCRIPTION
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
FIG. 1 illustrates one embodiment of a radio frequency (RF) amplification device 10 having a Doherty amplification circuit 12 and a control circuit 14. As explained in further detail below, the control circuit 14 is operably associated with the Doherty amplification circuit 12 in order to improve the power performance and the Doherty characteristics of the Doherty amplification circuit 12. For instance, the control circuit 14 may be used in for the Doherty amplification circuit 12 to obtain improved power efficiency at backed-off power levels by increasing the impedance presented to an output of a main carrier RF amplifier by increasing an impedance at a termination port. Additionally, the control circuit 14 can also be used to improve the bandwidth performance of the Doherty amplification circuit 12 and thus allow the Doherty amplification circuit 12 to provide broadband amplification.
The Doherty amplification circuit 12 is configured to amplify an RF signal 16. To amplify the RF signal 16, the Doherty amplification circuit 12 includes a main carrier RF amplifier 18 and a peaking RF amplifier 20. While a signal level of the RF signal 16 is below a threshold level, the peaking RF amplifier 20 is deactivated and the main carrier RF amplifier 18 provides all of the amplification to the RF signal 16. The RF signal 16 may be any type of RF signal depending on the type of communication device (e.g., smartphone, tablet, laptop, base station, etc.) in which the Doherty amplification circuit 12 is provided and the amplification operation being provided by the Doherty amplification circuit 12. The main carrier RF amplifier 18 is configured to amplify the RF signal 16 in accordance with a main amplifier gain of the main carrier RF amplifier 18. So long as the main carrier RF amplifier 18 is within a linear operating range (i.e., not saturated and below a compression point), the peaking RF amplifier 20 is deactivated.
The specific characteristics of the Doherty amplification circuit 12 may vary in accordance with the communication device and technological environment in which the Doherty amplification circuit 12 is employed and, in addition, the performance parameters relevant to the operation of the Doherty amplification circuit 12 for the particular application(s) of the Doherty amplification circuit 12 within the communication device (or prospective communication device(s)) and the technological environment (or prospective technological environment(s)). It should be noted that the RF amplification device 10 may be configured for operation in any suitable communication device and technological environment. Thus, the RF signal 16 may be any type of RF signal.
More specifically, the RF amplification device 10 shown in FIG. 1 can be manufactured to meet the requirements of a wide variety of multiplexing schemes and RF communication standards. For example, the RF signal 16 may be an uplink signal transmitted to base stations and/or a downlink signal transmitted from base stations. Furthermore, the RF signal 16 may be encoded in accordance with any type of multiplexing scheme and/or RF communication standard. For example, the RF signal 16 may be multiplexed using time division multiplexing (TDM), frequency division multiplexing (FDM), space division multiplexing (SDM), code division multiple access (CDMA) multiplexing, orthogonal frequency division multiple access (OFDMA) multiplexing, and/or the like. Additionally, the RF amplification device 10 may be configured to provide duplexing for various RF communication standards. For example, the RF amplification device 10 may be configured to provide amplification for the RF signal 16 if the RF signal 16 is formatted in accordance with 2G Global System for Mobile Communications (GSM) standards, 3G standards, 4G Long Term Evolution (LTE) standards, and/or the like. Furthermore, the RF amplification device 10 may provide duplexing for one or more specifications within these RF communication standards, along with their RF communication bands. For instance, the RF signal 16 may be formatted in accordance with RF communication bands defined by specifications of the 2G GSM standard, such as a Digital Communication System (DCS) specification, a Personal Communications Service (PCS) specification, a GSM-850 specification, and a GSM-900 specification; specifications within the 3G standard, such as an Enhanced Data Rates for GSM Evolution (EDGE)-850 specification, an EDGE-950 specification, an EDGE-1800 specification, and an EDGE-1900 specification; and specifications within the 4G LTE standard, such as a Mobile Device Management (MDM) specification, a High Speed Packet Access (HSPA) specification, a Multiple-Input and Multiple-Output (MIMO) specification, and/or the like.
Note that relational terminology such as “substantially,” “approximately,” and/or the like should be interpreted objectively in accordance with the communication device and technological environment in which the RF amplification device 10 is employed and, in addition, the performance parameters relevant to the operation of the RF amplification device 10 for the particular application of the RF amplification device 10 within the communication device (or at least one prospective communication device) and the technological environment (or at least one prospective technological environment).
In this embodiment, the RF signal 16 may be an RF uplink signal for uplink to a base station from a mobile communication device (e.g., smartphone, tablet, laptop, etc.). The RF amplification device 10 may be within the mobile communication device and the mobile communication device may be using the Doherty amplification circuit 12 to amplify the RF signal 16 for transmission by an antenna (not shown). Alternatively, the RF amplification device 10 may be within the base station. Thus, the base station may be using the Doherty amplification circuit 12 for amplification upon reception of the RF signal 16 from the mobile communication device. In another embodiment, the RF signal 16 may be an RF downlink signal for downlink to the mobile communication device (e.g., smartphone, tablet, laptop, etc.) from the base station. In this case, the mobile communication device may be using the Doherty amplification circuit 12 to amplify the RF signal 16 after reception from the base station. Alternatively, the base station may be using the Doherty amplification circuit 12 to amplify the RF signal 16 for transmission by an antenna (not shown) to the mobile communication device.
Referring again to the Doherty amplification circuit 12 shown in FIG. 1, the output impedance of the peaking RF amplifier 20 is very high and the peaking RF amplifier 20 appears like an open circuit with respect to the main carrier RF amplifier 18 while the main carrier RF amplifier 18 is activated and the peaking RF amplifier 20 is deactivated. However, the peaking RF amplifier 20 is configured to activate in response to the signal level of the RF signal 16 reaching a threshold level. The Doherty amplification circuit 12 is configured such that the main carrier RF amplifier 18 remains activated while the peaking RF amplifier 20 is activated. In some embodiments, the main carrier RF amplifier 18 may be held at or near its peak power level (i.e., saturation). In general, this peak power level occurs just prior to the 1 dB compression point (i.e., a knee voltage) of the main carrier RF amplifier 18 and thus when the main carrier RF amplifier 18 is nearly saturated.
However, it should be noted that some embodiments of the RF amplification device 10 may hold the main carrier RF amplifier 18 at backed-off power levels while the peaking RF amplifier 20 is activated. If the RF amplification device 10 holds the main carrier RF amplifier 18 at backed-off power levels while the peaking RF amplifier 20 is activated, the control circuit 14 may be configured to reduce or prevent power-efficiency degradations in the Doherty amplification circuit 12 due to the main carrier RF amplifier 18 operating at power levels backed off from the 1 dB compression point by increasing an impedance presented at an output of the main carrier RF amplifier 18 by increasing an impedance presented at a termination port. This is typically desirable for modern communication systems.
As shown in FIG. 1, the main carrier RF amplifier 18 and the peaking RF amplifier 20 are operably associated by a first periodic quadrature coupler 22 and a second periodic quadrature coupler 24. With regard to the first periodic quadrature coupler 22, the first periodic quadrature coupler 22 includes a first port 26, a second port 28, a third port 30, and a fourth port 32. It should be noted that throughout this disclosure, the term “port” refers to any type of definable circuit location and/or structure that is operable to receive and/or transmit electromagnetic signals to or from an electronic component. For example, a port may be a terminal, a contact, a pad, a pin, a wire, a conductive bond, a node, a group of more than one of the aforementioned elements (e.g., terminals for a differential signal), and/or the like.
Throughout this disclosure, a “periodic quadrature coupler” (e.g., the first periodic quadrature coupler 22 and the second periodic quadrature coupler 24) is a quadrature coupler where passbands are repeated one or more times in a transfer function of the quadrature coupler. Thus, the term “periodic” is not referring to repetition in the time domain, but rather repetition of a frequency response in the frequency domain. For example, the first periodic quadrature coupler 22 may be configured to define a passband centered at a fundamental frequency and another passband centered at another frequency that is approximately equal to the fundamental frequency multiplied by an integer greater than one (1). Similarly, the second periodic quadrature coupler 24 may be configured to define a passband centered at a fundamental frequency and another passband centered at another frequency that is approximately equal to the fundamental frequency multiplied by an integer greater than one (1). In the embodiment shown in FIG. 1, the first periodic quadrature coupler 22 and the second periodic quadrature coupler 24 are configured to have approximately the same fundamental frequency. With regard to alternative exemplary embodiments, the fundamental frequency of the first periodic quadrature coupler 22 and the fundamental frequency of the second periodic quadrature coupler 24 may be significantly different. In one embodiment, the integer for both the first periodic quadrature coupler 22 and the second periodic quadrature coupler 24 is odd. For instance, the integer may be equal to three (3).
However, it should be noted that passbands may repeat more than once in the frequency domain. For example, the first periodic quadrature coupler 22 may be configured to define a set of passbands, wherein each of the passbands is centered approximately at the fundamental frequency of the first periodic quadrature coupler 22 multiplied by an integer in a set of integers. Similarly, the second periodic quadrature coupler 24 may be configured to define a set of passbands, wherein each of the passbands is centered approximately at the fundamental frequency of the second periodic quadrature coupler 24 multiplied by an integer in a set of integers. In one embodiment, the set of integers for both the first periodic quadrature coupler 22 and the second periodic quadrature coupler 24 is a set of odd integers (e.g., 1, 3, 5, etc.). With regard to the first periodic quadrature coupler 22, the first port 26 of the first periodic quadrature coupler 22 is operable to receive the RF signal 16. For example, the first port 26 may be coupled to receive the RF signal 16 from upstream RF circuitry (not shown) that is exogenous to the RF amplification device 10. Thus, a source impedance of the upstream RF circuitry may be presented to the Doherty amplification circuit 12 at the first port 26 of the first periodic quadrature coupler 22.
The second port 28 of the first periodic quadrature coupler 22 is an isolation port. In this embodiment, an impedance load 34 is coupled to the first periodic quadrature coupler 22 at the second port 28. The impedance load 34 thus serves as a termination impedance of the first periodic quadrature coupler 22.
As such, the second port 28 is isolated from the first port 26, the third port 30, and the fourth port 32. The third port 30 is coupled to an input terminal 36 of the main carrier RF amplifier 18 while the fourth port 32 is coupled to an input terminal 38 of the peaking RF amplifier 20. In this embodiment, a resistance and a reactance of the impedance load 34 is configured to be constant. As such, the impedance load 34 shown in FIG. 1 is not tunable. For example, the terminating impedance of the impedance load 34 may be approximately equal to 50Ω. Also, in some embodiments, the impedance may be purely resistive and constant such that the impedance load 34 has no reactance.
As mentioned above, the first periodic quadrature coupler 22 may be configured to define a first passband centered at a fundamental frequency and a second passband centered at a second frequency that is approximately equal to the fundamental frequency multiplied by an integer greater than one (1). For example, the integer may be equal to three (3). Thus, since the fundamental frequency is lower than the second frequency, the first passband has a frequency range that is lower than a frequency range of the second passband. With regard to the first passband centered at the fundamental frequency, the first periodic quadrature coupler 22 provides a 90-degree phase shift between the first port 26 and the third port 30 and a 90-degree phase shift between the second port 28 and the fourth port 32. However, with regard to the second passband, the first periodic quadrature coupler 22 provides a −90-degree phase shift between the first port 26 and the third port 30 and a −90-degree phase shift between the second port 28 and the fourth port 32. This is because of the periodic frequency response of the first periodic quadrature coupler 22. With regard to both the first passband and the second passband, a 0-degree phase shift may be provided between the first port 26 and the fourth port 32 and a 0-degree phase shift may be provided between the second port 28 and the third port 30.
With regard to the second periodic quadrature coupler 24, the second periodic quadrature coupler 24 may also be configured to define a first passband centered at a fundamental frequency and a second passband centered at a second frequency that is approximately equal to the fundamental frequency multiplied by an integer greater than one (1). For example, the integer may be equal to three (3). Thus, since the fundamental frequency is lower than the second frequency, the first passband has a frequency range that is lower than a frequency range of the second passband. With regard to the first passband centered at the fundamental frequency, the second periodic quadrature coupler 24 provides a 90-degree phase shift between the fifth port 40 and the eighth port 46 and a 90-degree phase shift between the sixth port 42 and the seventh port 44. However, with regard to the second passband, the second periodic quadrature coupler 24 provides a −90-degree phase shift between the fifth port 40 and the eighth port 46 and a −90-degree phase shift between the sixth port 42 and the seventh port 44. This is because of the periodic frequency response of the second periodic quadrature coupler 24. With regard to both the first passband and the second passband, a 0-degree phase shift may be provided between the fifth port 40 and the seventh port 44 and a 0-degree phase shift may be provided between the sixth port 42 and the eighth port 46. In this embodiment, the first passband of the first periodic quadrature coupler 22 and the first passband of the second periodic quadrature coupler 24 are approximately the same. Additionally, the second passband of the first periodic quadrature coupler 22 and the second passband of the second periodic quadrature coupler 24 are approximately the same.
The second periodic quadrature coupler 24 shown in FIG. 1 is also operably associated with the main carrier RF amplifier 18 and the peaking RF amplifier 20. The second periodic quadrature coupler 24 includes a fifth port 40, a sixth port 42, a seventh port 44, and an eighth port 46. The fifth port 40 of the second periodic quadrature coupler 24 is coupled to an output terminal 48 of the main carrier RF amplifier 18. Thus, the main carrier RF amplifier 18 is coupled between the third port 30 of the first periodic quadrature coupler 22 and the fifth port 40 of the second periodic quadrature coupler 24. The sixth port 42 is coupled to an output terminal 50 of the peaking RF amplifier 20. Thus, the peaking RF amplifier 20 is coupled between the fourth port 32 of the first periodic quadrature coupler 22 and the sixth port 42 of the second periodic quadrature coupler 24. An output impedance of the peaking RF amplifier 20 is thus presented at the sixth port 42 to the second periodic quadrature coupler 24 and an input impedance of the peaking RF amplifier 20 is presented to the first periodic quadrature coupler 22 at the fourth port 32.
The second periodic quadrature coupler 24 is operable to transmit the RF signal 16 at the seventh port 44 after the RF signal 16 has been amplified by the Doherty amplification circuit 12. The seventh port 44 of the second periodic quadrature coupler 24 is thus an output port of the Doherty amplification circuit 12. For example, the seventh port 44 may be coupled to transmit the RF signal 16 to downstream RF circuitry (not shown) that is exogenous to the RF amplification device 10. A load impedance of the downstream RF circuitry may thus be presented to the Doherty amplification circuit 12 at the seventh port 44 of the second periodic quadrature coupler 24.
The eighth port 46 of the second periodic quadrature coupler 24 is an isolation port. In this embodiment, a tunable impedance load 54 is coupled to the second periodic quadrature coupler 24 at the eighth port 46. The tunable impedance load 54 is configured to provide a tunable impedance, which is provided as a termination impedance of the second periodic quadrature coupler 24. Thus, the tunable impedance load 54 may have a variable resistance and/or a variable reactance. Since the tunable impedance may be set by the variable resistance and/or the variable reactance, adjusting the variable resistance and/or the variable reactance of the tunable impedance load 54 thereby adjusts the termination impedance of the second periodic quadrature coupler 24.
The control circuit 14 is configured to detect RF power in the Doherty amplification circuit 12. For example, in this embodiment, the control circuit 14 is configured to receive a feedback input 56 that indicates RF power in the Doherty amplification circuit 12. The feedback input 56 may include one or more feedback signals that indicate the RF power in the Doherty amplification circuit 12. The control circuit 14 may be analog, digital, or both, and thus may detect the RF power using analog techniques, digital techniques, and/or a mixture of both. When digital techniques are employed, digital-to-analog converters may be employed by the control circuit 14 such that the feedback input 56 can be converted into a digital reading related to RF power of the Doherty amplification circuit 12. If analog techniques are employed, the feedback input 56 may result in an analog response controlled by the characteristics of the feedback input 56 that indicate the RF power in the Doherty amplification circuit 12. Variations in topology and design for the control circuit 14 would be apparent to one of ordinary skill in the art provided one of ordinary skill in the art has a proper understanding of the control principles described in this disclosure. The control circuit 14 may thus also detect RF power in the Doherty amplification circuit 12 dynamically to employ Doherty amplification operation, as long as the Doherty amplification circuit 12 is providing amplification to the RF signal 16. In this manner, the control circuit 14 can respond dynamically to both exogenous and endogenous changes that result in modifications in the RF power of the Doherty amplification circuit 12.
The Doherty amplification circuit 12 has a characteristic amplifier impedance Znorm. The characteristic amplifier impedance Znorm is a source impedance of the Doherty amplification circuit 12. As seen from an input side of the second periodic quadrature coupler 24, the characteristic amplifier impedance Znorm is a source impedance presented at the fifth port 40 of the second periodic quadrature coupler 24 from the main carrier RF amplifier 18. The second periodic quadrature coupler 24 provides an impedance transformation to the characteristic amplifier impedance Znorm and the characteristic amplifier impedance Znorm presented from an output side of the second periodic quadrature coupler 24 at the seventh port 44 with the impedance transformation. Thus, the characteristic amplifier impedance Znorm is also presented as a source impedance at the seventh port 44, but with the impedance transformation provided by the second periodic quadrature coupler 24 relative to the input side at the fifth port 40.
A load impedance is presented at the output side of the second periodic quadrature coupler 24 at the seventh port 44. For example, the downstream RF circuitry may be coupled to the seventh port 44 to present the load impedance at the seventh port 44. At the seventh port 44, the load impedance is seen from the output side of the second periodic quadrature coupler 24. From the input side of the second periodic quadrature coupler 24, the second periodic quadrature coupler 24 provides an impedance transformation to the load impedance presented at the seventh port 44. From the input side, the load impedance is presented by the second periodic quadrature coupler 24 to the main carrier RF amplifier 18, but transformed relative to the output side of the second periodic quadrature coupler 24 in accordance with the impedance transformation provided by the second periodic quadrature coupler 24. In this embodiment, the second periodic quadrature coupler 24 presents the load impedance to the main carrier RF amplifier 18 at the fifth port 40.
To improve power efficiency, the control circuit 14 is configured to tune the tunable impedance load 54 dynamically as a function of the RF power detected in the Doherty amplification circuit 12 to employ Doherty amplification operation. This adjusts the impedance transformations provided by the second periodic quadrature coupler 24 to the source impedances and the load impedances described above. Thus, by tuning the tunable impedance load 54, the control circuit 14 can set the load impedance presented to the main carrier RF amplifier 18 by the second periodic quadrature coupler 24 at the fifth port 40 and the characteristic amplifier impedance Znorm presented at the seventh port 44 at or close to optimal values in different RF communication bands.
To provide Doherty amplification operation, the load impedance should approximately equal double the characteristic amplifier impedance Znorm while the peaking RF amplifier 20 is deactivated at the fifth port 40. Thus, when the main carrier RF amplifier 18 is approximately saturated and the peaking RF amplifier 20 is deactivated, the load impedance should equal approximately double the characteristic amplifier impedance Znorm at the fifth port 40. However, while the peaking RF amplifier 20 is activated, the load impedance seen by the main carrier RF amplifier 18 is decreased from approximately double the characteristic amplifier impedance Znorm to approximately the characteristic amplifier impedance Znorm. When both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are approximately at saturation, the load impedance seen by the main carrier RF amplifier 18 should be equal to the characteristic amplifier impedance Znorm.
The control circuit 14 may be configured to tune the tunable impedance of the tunable impedance load 54 dynamically so as to provide a Doherty amplification operation in different RF communication bands. As mentioned above, while the main carrier RF amplifier 18 is activated and the peaking RF amplifier 20 is being deactivated, the control circuit 14 is configured to tune the tunable impedance of the tunable impedance load 54 dynamically as the function of the RF power of the Doherty amplification circuit 12 such that the load impedance presented by the second periodic quadrature coupler 24 to the main carrier RF amplifier 18 at the fifth port 40 is approximately equal to double the characteristic amplifier impedance Znorm of the Doherty amplification circuit 12. For example, if the load impedance at the seventh port 44 is 50Ω, the control circuit 14 tunes the tunable impedance of the tunable impedance load 54 so that the main carrier RF amplifier 18 is presented a load impedance equal to 100Ω or double the characteristic amplifier impedance Znorm of the Doherty amplification circuit 12 at the fifth port 40. In this case, an impedance of the peaking RF amplifier 20 is very high and the peaking RF amplifier 20 appears like an open circuit with respect to the main carrier RF amplifier 18 and the seventh port 44.
The load impedance is maintained approximately equal to double the characteristic amplifier impedance Znorm of the Doherty amplification circuit 12 at the fifth port 40 until the main carrier RF amplifier 18 is approximately saturated and the peaking RF amplifier 20 is activated. While both the peaking RF amplifier 20 and the main carrier RF amplifier 18 are activated, the control circuit 14 is configured to tune the tunable impedance of the tunable impedance load 54 smaller such that the load impedance presented by the second periodic quadrature coupler 24 to the main carrier RF amplifier 18 at the fifth port 40 is decreased as the RF power of the Doherty amplification circuit 12 is increased. In other words, the main carrier RF amplifier 18 remains in saturation while the RF signal 16 is above the threshold level and the load impedance presented by the second periodic quadrature coupler 24 to the main carrier RF amplifier 18 at the fifth port 40 decreases as power to the peaking RF amplifier 20 is increased. The control circuit 14 tunes the tunable impedance load dynamically as the function of the RF power detected in the Doherty amplification circuit 12 such that the load impedance presented by the second periodic quadrature coupler 24 to the main carrier RF amplifier 18 has an impedance range from approximately double the characteristic amplifier impedance Znorm of the Doherty amplification circuit 12 to approximately the characteristic amplifier impedance Znorm of the Doherty amplification circuit 12. The load impedance presented at the fifth port 40 therefore varies from approximately 2*Znorm to Znorm as the RF power of the Doherty amplification circuit 12 is increased while the peaking RF amplifier 20 is activated. As such, the control circuit 14 is further configured to tune the tunable impedance of the tunable impedance load 54 dynamically as the function of the RF power of the Doherty amplification circuit 12 such that the load impedance presented by the second periodic quadrature coupler 24 to the main carrier RF amplifier 18 at the fifth port 40 is set approximately to the characteristic amplifier impedance Znorm when both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are approximately saturated.
To increase the power efficiency of the Doherty amplification circuit 12, the tunable impedance of the tunable impedance load 54 may have a variable real impedance (i.e., a variable resistance). Generally, the tunable impedance of the tunable impedance load 54 should be higher (i.e., by a factor of 5 or greater) than a real impedance of the load impedance presented at the seventh port 44 (i.e., the output port of the Doherty amplification circuit 12). Furthermore, to optimize the power efficiency in different RF communication bands, the tunable impedance of the tunable impedance load 54 may have different impedance levels at various frequencies for a given power level of the RF power and/or an imaginary impedance that compensates for non-ideal parasitic reactances of the output power load impedances of the peaking RF amplifier 20 and the main carrier RF amplifier 18 across a wide frequency band. The control circuit 14 is configured to dynamically vary the real impedance and/or the imaginary impedance of the tunable impedance provided by the tunable impedance load 54 to provide the Doherty amplification operation described above.
With regard to the control circuit 14 shown in FIG. 1, the control circuit 14 is configured to generate an impedance control output 58 that sets the tunable impedance of the tunable impedance load 54. The impedance control output 58 may include one or more control signals that are operable to set the variable resistance and/or the variable reactance of the tunable impedance load 54. The function implemented by the control circuit 14 may thus map the RF power detected in the Doherty amplification circuit 12 to permutations of the impedance control output 58. These permutations of the impedance control output 58 set the tunable impedance of the tunable impedance load 54 to different impedance levels. More specifically, different permutations of the impedance control output 58 can be selected by the control circuit 14 to adjust the variable resistance and/or variable reactance in the manner explained above. As such, the real impedance and/or the imaginary impedance of the tunable impedance provided by the tunable impedance load 54 are set by the control circuit 14 using the impedance control output 58. The function implemented by the control circuit 14 may thus ultimately map the RF power detected in the Doherty amplification circuit 12 to desired impedance levels for the tunable impedance provided by the tunable impedance load 54.
The tunable impedance load 54 may include networks of passive and/or active circuit components that are responsive to the impedance control output 58 such that the tunable impedance of the tunable impedance load 54 is set in accordance with the particular permutation of the impedance control output 58 provided by the control circuit 14. The control circuit 14 may be configured to generate the impedance control output 58 such that the permutations of the impedance control output 58 are (at least partially) discrete permutations and/or (at least partially) continuous permutations. This may depend on a particular topology of the tunable impedance load 54. For example, a non-saturated transistor (not shown) or a non-saturated network of transistors may be used so that the variable resistance and/or the variable reactance can be varied in a continuous manner based on the impedance control output 58. In this case, the impedance control output 58 may be at least partially analog. However, the tunable impedance load 54 may also be provided by an impedance matching network in which switches selectively connect passive circuit components (i.e., resistors, capacitors, and/or inductors) so that the tunable impedance of the tunable impedance load 54 varies discretely. In this case, the tunable impedance load 54 may switch the switches on and off in response to the particular and discrete permutation of the impedance control output 58 from the control circuit 14.
Additionally, the function implemented by the control circuit 14 may further depend on other variables besides the RF power detected. In this embodiment, the control circuit 14 is further configured to receive a control input 60, which may include one or more control signals. The control input 60 is configured to indicate at least one operational frequency characteristic of the RF signal 16. For example, an operational frequency characteristic of the RF signal 16 may be a carrier frequency of the RF signal 16 where the control input 60 may include one or more control signals identifying the carrier frequency. The function implemented by the control circuit 14 may thus not only depend on the RF power detected but also on the carrier frequency of the RF signal 16. Alternatively or additionally, another operational frequency characteristic of the RF signal 16 may be a frequency band of the RF signal 16. In one embodiment, to indicate the frequency band of the RF signal 16, the control input 60 may indicate an RF communication specification (see above) used to format the RF signal 16, and thus may ultimately indicate the frequency band in which the RF signal 16 operates.
Furthermore, the control circuit 14 may be operable in a detect mode and in a non-detect mode. In the detect mode, the control circuit 14 is configured to detect the RF power in the Doherty amplification circuit 12, as described above. However, in the non-detect mode, the control input 60 may further indicate the RF power of the Doherty amplification circuit 12. For example, the RF power may be at a known a priori given power setting for transmission or reception of the RF signal 16. In this manner, the control circuit 14 may be configured to store a look-up table (in a non-transient computer-readable medium) and implement the look-up table to invoke Doherty amplification operation, which indicates the permutation of the impedance control output 58 given the RF power and/or the operating frequency of the Doherty amplification circuit 12 that is indicated by the control input 60. As such, the control circuit 14 is also configured to tune the tunable impedance of the tunable impedance load 54 in accordance with the RF power and/or operating frequency of the Doherty amplification circuit 12 indicated by the control input 60.
Thus, in both the detect mode and the non-detect mode, the control circuit 14 may be configured to tune the tunable impedance of the tunable impedance load 54 dynamically based on the RF power of the Doherty amplification circuit 12 and the operational frequency characteristic(s) of the RF signal 16. This is advantageous, since the characteristic amplifier impedance Znorm presented at the fifth port 40 generally may vary based on the operational frequency characteristic(s) of the RF signal 16. Furthermore, the source impedance presented by the upstream RF circuitry (not shown) at the first port 26 and the load impedance presented by the downstream RF circuitry (not shown) at the seventh port 44 also vary based on the operational frequency characteristic(s) of the RF signal 16. Finally, the imaginary impedance of the tunable impedance provided by the tunable impedance load 54 varies depending on the operational frequency characteristic(s) of the RF signal 16. As such, since the function implemented by the control circuit 14 is both the function of the RF power of the Doherty amplification circuit 12 and of the operational frequency characteristic(s) of the RF signal 16, the control circuit 14 can provide the Doherty amplification operation in different RF communication bands. The RF amplification device 10 is thus configured for broadband operation. Note that other relevant quantities, such as temperature and biasing levels, may be indicated by the feedback input 56 and/or the control input 60. The function implemented by the control circuit 14 may further depend on these other relevant quantities so that the control circuit 14 can determine how the control circuit 14 tunes the tunable impedance load 54 based on a wider range of operational conditions.
As mentioned above, the Doherty amplification circuit 12 is configured to maintain the peaking RF amplifier 20 deactivated until the RF signal level of the RF signal 16 reaches the threshold level. Different embodiments of the Doherty amplification circuit 12 can be provided where the main carrier RF amplifier 18 is simply a higher class of amplifier than the peaking RF amplifier 20. In this embodiment, the main carrier RF amplifier 18 is a Class A amplifier while the peaking RF amplifier is a Class C amplifier. The Doherty amplification circuit 12 shown in FIG. 1 is configured to activate the peaking RF amplifier 20 when the main carrier RF amplifier 18 is below saturation. However, in alternative embodiments, the peaking RF amplifier 20 may be activated before the main carrier RF amplifier 18 is saturated or at least prior to the main carrier RF amplifier 18 becoming fully saturated. For example, the peaking RF amplifier 20 may be configured to be activated before the main carrier RF amplifier 18 reaches saturation if the main carrier RF amplifier 18 is a Class A amplifier and the peaking RF amplifier 20 is a Class AB amplifier. In some applications, this helps linearize the Doherty amplification circuit 12 and increases power efficiency.
Since different classes of amplifier may be provided for both the main carrier RF amplifier 18 and the peaking RF amplifier 20 in the Doherty amplification circuit 12, the peaking RF amplifier 20 may or may not be off when the peaking RF amplifier 20 is deactivated. This may depend on the class of the peaking RF amplifier 20. More specifically, the peaking RF amplifier 20 being activated and deactivated refers to whether the peaking RF amplifier 20 is providing amplification or not providing amplification. Depending on the class of amplifiers being used for the main carrier RF amplifier 18 and the peaking RF amplifier 20, the peaking RF amplifier 20 may not be off when the peaking RF amplifier 20 is deactivated. For example, if the peaking RF amplifier 20 is the Class C amplifier described above, the peaking RF amplifier 20 may not be truly off during operation, but may be deactivated because the peaking RF amplifier 20 is not providing amplification. In contrast, if the peaking RF amplifier 20 is a Class B amplifier, the peaking RF amplifier 20 may be turned off in order to deactivate the peaking RF amplifier 20. Thus, how the peaking RF amplifier 20 is activated and deactivated may depend on a particular implementation of the Doherty amplification circuit 12.
With regard to the Doherty amplification circuit 12 shown in FIG. 1, the first periodic quadrature coupler 22 is configured such that the first port 26 is phase-aligned with the fourth port 32 and such that the second port 28 is phase-aligned with the third port 30. In addition, the first periodic quadrature coupler 22 is configured such that the first port 26 has a quadrature phase shift with respect to the third port 30, and such that the second port 28 (i.e., the isolation port of the first periodic quadrature coupler 22) has a quadrature phase shift with respect to the fourth port 32. While the peaking RF amplifier 20 is deactivated, the input impedance of the peaking RF amplifier 20 essentially appears like an open circuit. As such, in this case, the RF signal 16 is not split, but is passed to the third port 30 and an input terminal 36 of the main carrier RF amplifier 18. Accordingly, the first periodic quadrature coupler 22 is configured to provide the RF signal 16 such that there is a quadrature phase difference between the RF signal 16 at the first port 26 and the third port 30 while the peaking RF amplifier 20 is deactivated. The main carrier RF amplifier 18 is then configured to amplify the RF signal 16 and output the RF signal 16 from the output terminal 48. In this manner, the RF signal 16 is provided to the second periodic quadrature coupler 24 at the fifth port 40.
The second periodic quadrature coupler 24 is configured to receive the RF signal 16 at the fifth port 40 while the peaking RF amplifier 20 is deactivated. The second periodic quadrature coupler 24 is configured such that the fifth port 40 is phase-aligned with the seventh port 44 (i.e., the output port of the Doherty amplification circuit 12) and such that the sixth port 42 is phase-aligned with the eighth port 46. In addition, the second periodic quadrature coupler 24 is configured such that the fifth port 40 has a quadrature phase shift with respect to the eighth port 46 (i.e., the isolation port of the second periodic quadrature coupler 24) and the sixth port 42 has a quadrature phase shift with respect to the seventh port 44. While the peaking RF amplifier 20 is deactivated, the output impedance of the peaking RF amplifier 20 essentially appears like an open circuit. However, since the fifth port 40 has the quadrature phase shift with respect to the eighth port 46 (i.e., the isolation port of the second periodic quadrature coupler 24) and since the first periodic quadrature coupler 22 provided the quadrature phase shift to the RF signal 16 at the third port 30, the tunable impedance appears very high (ideally, infinite) at the eighth port 46. The RF signal 16 is again not split. Instead, the second periodic quadrature coupler 24 is configured to pass the RF signal 16 to the seventh port 44 while the peaking RF amplifier 20 is deactivated. As such, the Doherty amplification circuit 12 is configured to output the RF signal 16 from the seventh port 44 to downstream RF circuitry (not shown) once the main carrier RF amplifier 18 has amplified the RF signal 16. Consequently, the total amplification gain of the Doherty amplification circuit 12 is set entirely by the amplification gain of the main carrier RF amplifier 18 while the peaking RF amplifier 20 is deactivated.
The peaking RF amplifier 20 is activated when the signal level of the RF signal 16 is reaches or is above the threshold voltage at the first port 26 (i.e., the input port of the Doherty amplification circuit 12). While the peaking RF amplifier 20 is activated, the input impedance of the peaking RF amplifier 20 decreases inversely with respect to the RF signal level of the RF signal 16. As such, in this case, the RF signal 16 is split, but is passed to the third port 30 and the input terminal 36 of the main carrier RF amplifier 18. Accordingly, the first periodic quadrature coupler 22 is configured to provide the RF signal 16 such that there is a quadrature phase difference between the RF signal 16 at the first port 26 and the third port 30 while the peaking RF amplifier 20 is deactivated. The main carrier RF amplifier 18 is then configured to amplify the RF signal 16 and output the RF signal 16 from the output terminal 48. In this manner, the RF signal 16 is provided to the second periodic quadrature coupler 24 at the fifth port 40.
The second periodic quadrature coupler 24 is configured to receive the RF signal 16 at the fifth port 40 while the peaking RF amplifier 20 is deactivated. The second periodic quadrature coupler 24 is configured such that the fifth port 40 is phase-aligned with the seventh port 44 (i.e., the output port of the Doherty amplification circuit 12) and such that the sixth port 42 is phase-aligned with the eighth port 46. In addition, the second periodic quadrature coupler 24 is configured such that the fifth port 40 has a quadrature phase shift with respect to the eighth port 46 (i.e., the isolation port of the second periodic quadrature coupler 24) and the sixth port 42 has a quadrature phase shift with respect to the seventh port 44.
While the peaking RF amplifier 20 is deactivated, the output impedance of the peaking RF amplifier 20 essentially appears like an open circuit. However, since the fifth port 40 has the quadrature phase shift with respect to the eighth port 46 (i.e., the isolation port of the second periodic quadrature coupler 24) and since the first periodic quadrature coupler 22 provided the quadrature phase shift to the RF signal 16 at the third port 30, the tunable impedance appears very high (ideally, infinite) at the eighth port 46. The RF signal 16 is again not split. Instead, the second periodic quadrature coupler 24 is configured to pass the RF signal 16 to the seventh port 44 while the peaking RF amplifier 20 is deactivated. As such, the Doherty amplification circuit 12 is configured to output the RF signal 16 from the seventh port 44 to downstream RF circuitry (not shown) once the main carrier RF amplifier 18 has amplified the RF signal 16. Consequently, the total amplification gain of the Doherty amplification circuit 12 from the first port 26 (i.e., the input port of the Doherty amplification circuit 12) to the seventh port 44 (i.e., the output port of the Doherty amplification circuit 12) is set entirely by the amplification gain of the main carrier RF amplifier 18 while the peaking RF amplifier 20 is deactivated.
The Doherty amplification circuit 12 is configured such that the peaking RF amplifier 20 is activated when the RF signal level of the RF signal 16 is at or above the threshold level. While the main carrier RF amplifier 18 is activated and the peaking RF amplifier 20 is activated, the first periodic quadrature coupler 22 is configured to split the RF signal 16 into a first RF split signal 62 and a second RF split signal 64. As explained above, the first periodic quadrature coupler 22 is configured to receive the RF signal 16 at the first port 26. The first periodic quadrature coupler 22 provides the quadrature phase shift from the first port 26 to the fourth port 32, and thus, the first RF split signal 62 is received by the main carrier RF amplifier 18 at the input terminal 36 with a quadrature phase shift while both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are activated. The first port 26 of the first periodic quadrature coupler 22 is also phase-aligned with the fourth port 32. As such, the second RF split signal 64 is phase-aligned with the RF signal 16 at the first port 26. Consequently, the first RF split signal 62 at the third port 30 and the second RF split signal 64 at the fourth port 32 have a quadrature phase difference with respect to one another.
In this case, the main carrier RF amplifier 18 is (or is nearly) saturated, and thus the input impedance of the main carrier RF amplifier 18 increases as the RF signal level of the RF signal 16 increases. On the other hand, the input impedance of the peaking RF amplifier 20 decreases as the RF signal level of the RF signal 16 increases above the threshold level. As such, a proportion of an amount of power of the RF signal 16 in the second RF split signal 64 relative to an amount of power of the RF signal 16 in the first RF split signal 62 increases as the RF signal level of the RF signal 16 at the first port 26 increases relative to the threshold level. The inverse of this relationship is also true, and therefore the proportion decreases as the RF signal level of the RF signal 16 decreases relative to the threshold level at the first port 26 while both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are activated.
Additionally, while both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are activated, the main carrier RF amplifier 18 is configured to amplify the first RF split signal 62 in accordance with the amplification gain of the main carrier RF amplifier 18 and output the first RF split signal 62 from the output terminal 48. The second periodic quadrature coupler 24 is configured to receive the first RF split signal 62 from the main carrier RF amplifier 18 at the fifth port 40. The peaking RF amplifier 20 is configured to receive the second RF split signal 64 at an input terminal 38. While both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are activated, the peaking RF amplifier 20 is configured to amplify the second RF split signal 64 in accordance with the amplification gain of the peaking RF amplifier 20 and output the second RF split signal 64 from the output terminal 50. The second periodic quadrature coupler 24 is configured to receive the second RF split signal 64 from the peaking RF amplifier 20 at the sixth port 42.
The second periodic quadrature coupler 24 is configured to combine the first RF split signal 62 and the second RF split signal 64 back into the RF signal 16 after the first RF split signal 62 and the second RF split signal 64 are amplified by the main carrier RF amplifier 18 and the peaking RF amplifier 20, respectively. More specifically, the first periodic quadrature coupler 22 is configured such that the first RF split signal 62 passes to the seventh port 44 just like the RF signal 16 when the peaking RF amplifier 20 is deactivated.
Similarly since the sixth port 42 has a quadrature phase shift with respect to the seventh port 44 (i.e., the isolation port of the second periodic quadrature coupler 24) and since the first periodic quadrature coupler 22 provides no phase shift to the second RF split signal 64 at the fourth port 32 with respect to the first port 26, the second RF split signal 64 thus passes to the seventh port 44. Furthermore, the first RF split signal 62 and the second RF split signal 64 become phase-aligned at the seventh port 44 because the second periodic quadrature coupler 24 is configured to provide the quadrature phase shift to the second RF split signal 64 between the sixth port 42 and the seventh port 44. As such, the second periodic quadrature coupler 24 combines the first RF split signal 62 and the second RF split signal 64 into the RF signal 16 at the seventh port 44 once the Doherty amplification circuit 12 has amplified the RF signal 16. Consequently, the total amplification gain of the Doherty amplification circuit 12 from the first port 26 (i.e., the input port of the Doherty amplification circuit 12) to the seventh port 44 (i.e., the output port of the Doherty amplification circuit 12) is set in accordance with the amplification gain of the main carrier RF amplifier 18, the amplification gain of the peaking RF amplifier 20, and the proportion of the RF signal 16 provided in the first RF split signal 62 at the third port 30 relative to the second RF split signal 64 at the fourth port 32 while both the main carrier RF amplifier 18 and the peaking RF amplifier 20 are activated.
It should be noted that while the tunable impedance load 54 is coupled to the eighth port 46 in the embodiment shown in FIG. 1, this may or may not be the case in other embodiments. For example, in a first alternative embodiment, the tunable impedance load 54 is coupled to the second port 28 of the first periodic quadrature coupler 22, while the impedance load 34 is coupled to the eighth port 46 of the second periodic quadrature coupler 24. In this case, the control circuit 14 would thus control the tunable impedance of the tunable impedance load 54 in the same manner described above, except that with regard to tuning the tunable impedance of the tunable impedance load 54, the load impedance should be switched with the output impedance of the upstream RF circuitry at the first port 26 (i.e., the other exogenous connection port). In a second alternative embodiment, the tunable impedance load 54 is still coupled to the eighth port 46, but another tunable impedance load that is similar to the tunable impedance load 54 is coupled to the second port 28. In this case, the control circuit 14 would simultaneously tune the tunable impedance load 54, as described above for the RF amplification device 10 shown in FIG. 1, and tune a tunable impedance of the other tunable impedance load at the second port 28 in the same manner as the tunable impedance load 54 in the first alternative embodiment.
Referring again to the RF amplification device 10 shown in FIG. 1, the RF amplification device 10 is formed as an integrated circuit (IC) on a semiconductor substrate 66. The semiconductor substrate 66 has a substrate body 68 formed from a wafer and/or doped layers of a suitable semiconductor material. For example, the semiconductor material may be Silicon (Si), Silicon Germanium (SiGe), Gallium Arsenide (GaAs), Indium Phosphorus (InP), and/or the like. Typical dopants that may be utilized to dope the semiconductor layers are Gallium (Ga), Arsenic (As), Silicon (Si), Tellurium (Te), Zinc (Zn), Sulfur (S), Boron (B), Phosphorus (P), Aluminum Gallium Arsenide (AlGaAs), Indium Gallium Arsenide (InGaAs), and/or the like. Furthermore, metallic layers may be formed on a top, within, and/or on a bottom of the substrate body 68 to provide terminals, traces, contact pads, coils, connections, passive impedance elements, active semiconductor components, and/or the like. Also, any type of suitable semiconductor technology may be used to provide the topology of the semiconductor substrate 66. For example, the semiconductor technology of the semiconductor substrate 66 may be Complementary Metal-On-Oxide Semiconductor (CMOS) technology, BiComplementary Metal-On-Oxide Semiconductor (BiCMOS) technology, Silicon-On-Insulator (SOI) technology, and/or the like. In this embodiment, the semiconductor technology is SOI, and thus the semiconductor material of the substrate body 68 is Si.
FIG. 2 illustrates an embodiment of a Lange coupler LC. The Lange coupler LC is an exemplary embodiment of a periodic quadrature coupler. As such, the first periodic quadrature coupler 22 (shown in FIG. 1) and/or the second periodic quadrature coupler 24 (shown in FIG. 1) may be provided as the Lange coupler LC. Alternative embodiments may be provided simply as coupled transmission lines, a branch line coupler, or any other suitable type of quadrature coupler that provides periodicity in its frequency response. As shown in FIG. 2, the Lange coupler LC includes a port P1, a port P2, a port P3, and a port P4. With regard to the first periodic quadrature coupler 22 shown in FIG. 1, the port P1, the port P2, the port P3, and the port P4 correspond to the first port 26, the second port 28, the third port 30, and the fourth port 32, respectively. Additionally, with regard to the second periodic quadrature coupler 24 shown in FIG. 1, the port P1, the port P2, the port P3, and the port P4 correspond to the fifth port 40, the sixth port 42, the seventh port 44, and the eighth port 46, respectively. The Lange coupler LC shown in FIG. 2 has periodic frequency performance at low and high bands (e.g., the first passbands and the second passbands of the first periodic quadrature coupler 22 and the second periodic quadrature coupler 24 shown in FIG. 1). Impedances of the Lange coupler LC may be configured differently depending on the fundamental frequency, power parameters, and other operational conditions. The Lange coupler LC also includes a plurality of interdigitated fingers ID. The interdigitated fingers ID are closely spaced transmission lines, such as microstrip lines. A length L of the interdigitated fingers ID sets a fundamental frequency of the Lange coupler LC. For example, the length L may be approximately equal to a quarter wavelength of the fundamental frequency.
With regard to a first passband centered approximately at the fundamental frequency, the Lange coupler LC is configured to provide a 90-degree phase shift between the port P1 and the port P3, and between the port P2 and the port P4. However, because of the periodic frequency response of the Lange coupler LC, the Lange coupler LC provides a −90-degree phase shift between the port P1 and the port P3 and between the port P2 and the port P4 with regard to a second passband centered at an integer multiple of the fundamental frequency. Furthermore, at the second and higher passband, a 3 dB amplitude split is provided. However, this does not disrupt the Doherty operation of the Doherty amplification circuit 12 shown in FIG. 1. Moreover, the Lange coupler LC extends the capability of the Doherty amplification circuit 12 to operate as a multi-band amplification circuit.
FIG. 3 illustrates one embodiment of a transfer function TF of the Lange coupler LC shown in FIG. 2. More specifically, FIG. 3 illustrates an S(2,1) response of the Lange coupler LC and an S(4,1) response of the Lange Coupler LC. The S(2,1) response illustrates that the Lange Coupler LC is configured to provide a first passband PB1 at a fundamental frequency fF. In this embodiment, the fundamental frequency fF is approximately 850 MHz. The S(2,1) response and the S(4,1) response also illustrate the periodic frequency response characteristics of the Lange coupler LC. As shown in FIG. 3, the Lange coupler LC also defines a second passband PB2 centered at a second frequency fH. In this embodiment, the second frequency fH is approximately 2.4 GHz, which is approximately equal to 3 times the fundamental frequency fF. In this embodiment, the Lange coupler LC also has a 3 dB power dividing/combining performance at 850 MHz and 2.4 GHz, which is illustrated by the intersections of the S(4,1) response and the S(2,1) response. As such, the RF amplification device 10 (shown in FIG. 1) may utilize the periodic frequency response characteristics of the Lange coupler LC to produce multi-band Doherty amplification operations.
FIG. 4 illustrates one embodiment of a phase response PR of the transfer function TF provided by the Lange coupler LC shown in FIG. 2. As shown in FIG. 4, the phase response PR of the Lange coupler LC (shown in FIG. 2) at the fundamental frequency fF is 180 degrees out of phase with the phase response PR at the second frequency fH. In order to provide multi-band Doherty amplification operation using the Lange coupler LC as the second periodic quadrature coupler 24 (shown in FIG. 1), the Lange coupler LC may also be provided as the first periodic quadrature coupler 22 in order to track a phase inversion of the second passband PB2 (shown in FIG. 32) and therefore help preserve the Doherty amplification operation of the Doherty amplification circuit 12 shown in FIG. 1. As mentioned above, an embodiment of the Doherty amplification circuit 12 shown in FIG. 1 may provide the second periodic quadrature coupler 24 (shown in FIG. 1) as an embodiment of the Lange coupler LC and the first periodic quadrature coupler 22 as an embodiment of the Lange coupler LC. This embodiment of the Doherty amplification circuit 12 has excellent Doherty performance at both 850 MHz and 2.4 GHz.
As demonstrated by the transfer function TF shown in FIGS. 3 and 4, the Lange coupler LC shown in FIG. 2 can provide broader bandwidth than a typical quarter-wave transformer. For example, with regard to the passband PB1 (shown in FIG. 3), the Lange coupler LC shown in FIG. 2 has an allowable quadrature phase bandwidth performance from 500 MHz to 1.1 GHz. In contrast, the quarter-wave transformer may have an allowable quadrature phase bandwidth performance from 800 MHz to 900 MHz. The Lange coupler LC shown in FIG. 2 therefore provides 6 times (100 MHz×6) the quadrature phase bandwidth than the quarter-wave transformer.
FIG. 5 illustrates an exemplary RF amplification device 10(1), which is one embodiment of the RF amplification device 10 shown in FIG. 1. The RF amplification device 10(1) includes a Doherty amplification circuit 12(1) and a control circuit 14(1). The Doherty amplification circuit 12(1) is one embodiment of the Doherty amplification circuit 12 shown in FIG. 1. Thus, the Doherty amplification circuit 12(1) includes a main carrier RF amplifier 18(1), a peaking RF amplifier 20(1), a first periodic quadrature coupler 22(1), and a second periodic quadrature coupler 24(1).
The main carrier RF amplifier 18(1) is one embodiment of the main carrier RF amplifier 18 described above with respect to FIG. 1, and thus operates in the same manner as the main carrier RF amplifier 18 described above. The main carrier RF amplifier 18(1) thus includes the input terminal 36 and the output terminal 48. In this embodiment, the main carrier RF amplifier 18(1) is a Class A amplifier built using one or more field effect transistors (FETs). The main carrier RF amplifier 18(1) is configured to receive a supply voltage VS in order to power amplification by the main carrier RF amplifier 18(1). As such, a supply current ID1 is generated from the supply voltage VS within the main carrier RF amplifier 18(1) while the main carrier RF amplifier 18(1) is activated.
The peaking RF amplifier 20(1) is one embodiment of the peaking RF amplifier 20 described above with respect to FIG. 1, and thus operates in the same manner as the peaking RF amplifier 20 described above. The peaking RF amplifier 20(1) thus includes the input terminal 38 and the output terminal 50. In this embodiment, the peaking RF amplifier 20(1) is a Class C amplifier built using one or more FETs. The peaking RF amplifier 20(1) is also configured to receive the supply voltage VS in order to power amplification by the peaking RF amplifier 20(1). As such, a supply current ID2 is generated by the supply voltage VS within the peaking RF amplifier 20(1), where a supply current level of the supply current ID2 depends on harmonic characteristics of the Doherty amplification circuit 12(1), both while the peaking RF amplifier 20(1) is activated and while the peaking RF amplifier 20(1) is deactivated.
The first periodic quadrature coupler 22(1) is one embodiment of the first periodic quadrature coupler 22 described above with respect to FIG. 1, and thus operates in the same manner as the first periodic quadrature coupler 22 described above. The first periodic quadrature coupler 22(1) thus includes the first port 26, the second port 28, the third port 30, and the fourth port 32. Also, the RF signal 16 is received at the first port 26, the impedance load 34 is coupled to the second port 28, the input terminal 36 is coupled to the third port 30, and the input terminal 38 is coupled to the fourth port 32. In this embodiment, the first periodic quadrature coupler 22(1) is a Lange coupler.
The second periodic quadrature coupler 24(1) is one embodiment of the second periodic quadrature coupler 24 described above with respect to FIG. 1, and thus operates in the same manner as the second periodic quadrature coupler 24 described above. The second periodic quadrature coupler 24(1) thus includes the fifth port 40, the sixth port 42, the seventh port 44, and the eighth port 46. Also, the output terminal 48 is coupled to the fifth port 40, the output terminal 50 is coupled to the sixth port 42, the RF signal 16 is output from the seventh port 44, and the tunable impedance load 54 is coupled to the eighth port 46. In this embodiment, the second periodic quadrature coupler 24(1) is also a Lange coupler.
The control circuit 14(1) is one embodiment of the control circuit 14 described above with respect to FIG. 1, and thus operates in the same manner as the control circuit 14 described above. The control circuit 14(1) is configured to generate the impedance control output 58 in the same manner described above to tune the tunable impedance of the tunable impedance load 54 as the function of the RF power detected in the Doherty amplification circuit 12(1). However, in this embodiment, the control circuit 14(1) is coupled to the seventh port 44 (i.e., the output port of the Doherty amplification circuit 12(1)) to detect RF power in the Doherty amplification circuit 12(1). More specifically, the control circuit 14(1) is coupled to the seventh port 44 in order to receive a feedback signal 56(1).
The feedback signal 56(1) is one embodiment of the feedback input 56 described above with respect to FIG. 1, and the feedback signal 56(1) has a feedback signal level that indicates the RF power of the Doherty amplification circuit 12(1). More specifically, the feedback signal level (e.g., feedback voltage level, feedback current level, etc.) of the feedback signal 56(1) is set in accordance with the RF signal level (e.g., RF voltage level, RF current level, etc.) of the RF signal 16 after the Doherty amplification circuit 12(1) has amplified the RF signal 16. The RF signal level (e.g., RF voltage level, RF current level, etc.) of the RF signal 16 is related to the RF power by the Doherty amplification circuit 12(1), since the RF signal level of the RF signal 16 at the seventh port 44 depends on an amount of power provided by the Doherty amplification circuit 12(1). Since the feedback signal level of the feedback signal 56(1) is set in accordance with the RF signal level of the RF signal 16 at the seventh port 44, the feedback signal level of the feedback signal 56(1) indicates the RF power of the Doherty amplification circuit 12(1). By detecting the feedback signal level of the feedback signal 56(1), the control circuit 14(1) is configured to detect the RF power of the Doherty amplification circuit 12(1). The control circuit 14(1) is also configured to receive the control input 60 described above with respect to FIG. 1. The function implemented by the control circuit 14(1) thus maps the feedback signal level of the feedback signal 56(1) and the operational frequency characteristic(s) indicated by the control input 60 to permutations of the impedance control output 58. The control circuit 14(1) is thus configured to dynamically tune the tunable impedance of the tunable impedance load 54 with the impedance control output 58 as described above with respect to the control circuit 14 shown in FIG. 1.
FIG. 6 illustrates another exemplary RF amplification device 10(2), which is another embodiment of the RF amplification device 10 shown in FIG. 1. The RF amplification device 10(2) includes the Doherty amplification circuit 12(1) described above with respect to FIG. 5. However, the RF amplification device 10(2) includes another embodiment of a control circuit 14(2). The control circuit 14(2) is another embodiment of the control circuit 14 described above with respect to FIG. 1, and thus operates in the same manner as the control circuit 14 described above. The control circuit 14(2) is configured to generate the impedance control output 58 in the same manner described above to tune the tunable impedance of the tunable impedance load 54 as the function of the RF power detected in the Doherty amplification circuit 12(1). However, in this embodiment, the control circuit 14(2) is coupled to the first port 26 (i.e., the input port of the Doherty amplification circuit 12(1)) to detect the RF power in the Doherty amplification circuit 12(1). More specifically, the control circuit 14(2) is coupled to the first port 26 in order to receive a feedback signal 56(2).
The feedback signal 56(2) is another embodiment of the feedback input 56 described above with respect to FIG. 1, and the feedback signal 56(2) has a feedback signal level that indicates the RF power of the Doherty amplification circuit 12(1). More specifically, the feedback signal level (e.g., feedback voltage level, feedback current level, etc.) of the feedback signal 56(2) is set in accordance with the RF signal level (e.g., RF voltage level, RF current level, etc.) of the RF signal 16 before the Doherty amplification circuit 12(1) has amplified the RF signal 16. The RF signal level (e.g., RF voltage level, RF current level, etc.) of the RF signal 16 is related to the RF power by the Doherty amplification circuit 12(1), since the RF signal level of the RF signal 16 at the first port 26 indicates an amount of power that the Doherty amplification circuit 12(1) will use to amplify the RF signal 16. Since the feedback signal level of the feedback signal 56(2) is set in accordance with the RF signal level of the RF signal 16 at the first port 26, the feedback signal level of the feedback signal 56(2) indicates the RF power of the Doherty amplification circuit 12(1). By detecting the feedback signal level of the feedback signal 56(2), the control circuit 14(2) is configured to detect the RF power of the Doherty amplification circuit 12(1). The control circuit 14(2) is also configured to receive the control input 60 described above with respect to FIG. 1. The function implemented by the control circuit 14(2) thus maps the feedback signal level of the feedback signal 56(2) and the operational frequency characteristic(s) indicated by the control input 60 to permutations of the impedance control output 58. The control circuit 14(2) is thus configured to dynamically tune the tunable impedance of the tunable impedance load 54 with the impedance control output 58 as described above with respect to the control circuit 14 shown in FIG. 1.
FIG. 7 illustrates another exemplary RF amplification device 10(3), which is another embodiment of the RF amplification device 10 shown in FIG. 1. The RF amplification device 10(3) also includes the Doherty amplification circuit 12(1) described above with respect to FIG. 5. However, the RF amplification device 10(3) includes another embodiment of a control circuit 14(3). The control circuit 14(3) is another embodiment of the control circuit 14 described above with respect to FIG. 1, and thus operates in the same manner as the control circuit 14 described above. The control circuit 14(3) is configured to generate the impedance control output 58 in the same manner described above to tune the tunable impedance of the tunable impedance load 54 as the function of the RF power detected in the Doherty amplification circuit 12(1). However, in this embodiment, the control circuit 14(3) is coupled to an internal node (not explicitly shown) of the peaking RF amplifier 20(1). More specifically, the control circuit 14(3) is coupled to the internal node in order to receive a feedback signal 56(3).
The feedback signal 56(3) is another embodiment of the feedback input 56 described above with respect to FIG. 1, and the feedback signal 56(3) has a feedback signal level that indicates the RF power of the Doherty amplification circuit 12(1). More specifically, the feedback signal level (e.g., feedback voltage level, feedback current level, etc.) of the feedback signal 56(3) is set in accordance with the supply current ID2 provided to the peaking RF amplifier 20(1). Since the peaking RF amplifier 20(1) is a Class C amplifier, a supply current level of the supply current ID2 is related to the RF power of the Doherty amplification circuit 12(1). The control circuit 14(3) is coupled to the peaking RF amplifier 20(1) such that a feedback signal level of the feedback signal 56(3) is set in accordance with the supply current level of the supply current ID2. The feedback signal level of the feedback signal 56(3) therefore indicates the RF power of the Doherty amplification circuit 12(1). By detecting the feedback signal level of the feedback signal 56(3), the control circuit 14(3) is configured to detect the RF power of the Doherty amplification circuit 12(1). The control circuit 14(3) is also configured to receive the control input 60 described above with respect to FIG. 1. The function implemented by the control circuit 14(3) thus maps the feedback signal level of the feedback signal 56(3) and the operational frequency characteristic(s) indicated by the control input 60 to permutations of the impedance control output 58. The control circuit 14(3) is thus configured to dynamically tune the tunable impedance of the tunable impedance load 54 with the impedance control output 58 as described above with respect to the control circuit 14 shown in FIG. 1.
FIG. 8 illustrates an exemplary tunable impedance load 54(1). The tunable impedance load 54(1) is one embodiment of the tunable impedance load 54 described above with respect to FIG. 1. The tunable impedance load 54(1) shown in FIG. 8 includes a plurality of selectable impedance branches (referred to generically as elements 72 and specifically as elements 72(1)-72(6)). The selectable impedance branches 72 are each coupled in parallel with respect to one another. An input terminal 74 of the tunable impedance load 54(1) may be coupled to the eighth port 46 (shown in FIGS. 1 and 5-7).
The selectable impedance branches include resistors (referred to generically as elements 76 and specifically as elements 76(1)-76(6)) and switches (referred to generically as elements 78 and specifically as elements 78(1)-78(6)). More specifically, the selectable impedance branch 72(1) includes a resistor 76(1) coupled in series with a switch 78(1). The selectable impedance branch 72(2) includes a resistor 76(2) coupled in series with a switch 78(2). Additionally, the selectable impedance branch 72(3) includes a resistor 76(3) coupled in series with a switch 78(3). Furthermore, the selectable impedance branch 72(4) includes a resistor 76(4) coupled in series with a switch 78(4). Also, the selectable impedance branch 72(5) includes a resistor 76(5) coupled in series with a switch 78(5). Finally, the selectable impedance branch 72(6) includes a resistor 76(6) coupled in series with a switch 78(6).
For each of the selectable impedance branches 72, the selectable impedance branch 72 is configured to be selected when the switch 78 in the selectable impedance branch 72 is closed, and to be deselected when the switch 78 in the selectable impedance branch 72 is open. Each of the resistors 76 may have a different resistance. The resistance of the resistor 76 of the selectable impedance branch 72 is presented at the input terminal 74 (and thus at the eighth port 46 shown in FIGS. 1 and 5-7) when the switch 78 in the selectable impedance branch 72 is closed. Otherwise, when the switch 78 in the selectable impedance branch 72 is open, the selectable impedance branch 72 appears as an open circuit. Each of the switches 78 shown in FIG. 8 may be any type of suitable switch. For example, the switches 78 may be provided as FETs and/or as microelectromechanical switches (MEMSs).
The switches 78 are opened and closed in response to an impedance control output 58(1), which is one embodiment of the impedance control output 58 described above with respect to FIGS. 1 and 5-7. In this embodiment, the impedance control output 58(1) includes a plurality of switch control signals (referred to generically as elements 80 and specifically as elements 80(1)-80(6)). Each of the switch control signals 80 is received by a corresponding one of the switches 78. For each of the switch control signals 80, the switch control signal 80 received by the switch 78. The switch 78 is activated when the switch control signal 80 is in a switch activation state and the switch 78 is deactivated when the switch control signal 80 is in a switch deactivation state. A switch control signal 80(1) provided in the impedance control output 58(1) is received by the switch 78(1). A switch control signal 80(2) provided in the impedance control output 58(1) is received by the switch 78(2). A switch control signal 80(3) provided in the impedance control output 58(1) is received by the switch 78(3). A switch control signal 80(4) provided in the impedance control output 58(1) is received by the switch 78(4). A switch control signal 80(5) provided in the impedance control output 58(1) is received by the switch 78(5). A switch control signal 80(6) provided in the impedance control output 58(1) is received by the switch 78(6). Permutations of the impedance control output 58(1) thus refer to particular combinations of the switch control signals 80 that are in the switch activation state and in the switch deactivation state.
Since the switches 78 are used to vary the tunable impedance presented at the input terminal 74, the tunable impedance load 54(1) discretely varies the tunable impedance. Furthermore, in this embodiment, the tunable impedance is purely resistive because each of the selectable impedance branches 72 only includes the resistors 76 and no reactive components.
FIG. 9 is a graph illustrating power curves 84, 86, 88, and 90 that describe power added efficiency (PAE) as a function of output power in the RF amplification device 10(1) shown in FIG. 5. Furthermore, to obtain the power curves 84, 86, 88, and 90, the tunable impedance load 54 (shown in FIG. 5) is provided as the tunable impedance load 54(1) shown in FIG. 8, and the impedance control output 58 (shown in FIG. 5) is provided as the impedance control output 58(1) (shown in FIG. 8). Note that the optimum termination impedance is larger than Znorm to invoke Doherty amplification operation under backed-off power conditions and may be different at various frequencies across a band.
The power curve 84 is provided by the RF amplification device 10(1). More specifically, the power curve 84 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 700 MHz and the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm×6 by the impedance control output 58(1) shown in FIG. 8.
The power curve 86 is provided by the RF amplification device 10(1). More specifically, the power curve 86 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 850 MHz and the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm×8 by the impedance control output 58(1) shown in FIG. 8. Again, Znorm is the normalized (conventional characteristic impedance, Zo) termination impedance of the second periodic quadrature coupler 24(1) (shown in FIG. 8) at the eighth port 46 (shown in FIG. 5).
The power curve 88 is provided by the RF amplification device 10(1). More specifically, the power curve 88 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 1000 MHz. Furthermore, the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm×20 by the impedance control output 58(1) shown in FIG. 8.
The power curve 90 is provided by the RF amplification device 10(1). More specifically, the power curve 90 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 850 MHz and the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm by the impedance control output 58(1) shown in FIG. 8.
The performance of the RF amplification device 10(1) (shown in FIG. 5) decreases frequency variation when the tunable impedance of the tunable impedance load 54(1) is set to Znorm×8. As such, the RF amplification device 10(1) demonstrates better overall bandwidth efficiency. When an operating frequency of the RF signal 16 is shifted by other factors, such as parasitics or system requirements, the performance of the amplifier can be degraded. The control circuit 14(1) shown in FIG. 5 may then be employed to adjust the tunable impedance load 54(1) to compensate for the effects of parasitics and other factors across power, frequency of operation, and other conditions. FIG. 9 thus shows that the RF amplification device 10(1) provides optimum efficiency at low subbands, medium subbands, and high subbands of the passband PB1 shown in FIG. 3.
FIG. 10 is a graph illustrating power curves 92, 94, 96, and 98 that describe PAE as a function of output power in the RF amplification device 10(1) shown in FIG. 5. Furthermore, to obtain the power curves 92, 94, 96, and 98, the tunable impedance load 54 (shown in FIG. 5) is provided as the tunable impedance load 54(1) shown in FIG. 8, and the impedance control output 58 (shown in FIG. 5) is provided as the impedance control output 58(1) (shown in FIG. 8). Note that the optimum termination impedance is larger than Znorm to invoke Doherty amplification operation under backed-off power conditions and may be different at various frequencies across a band.
The power curve 92 is provided by the RF amplification device 10(1). More specifically, the power curve 92 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 2.6 GHz and the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm×50 by the impedance control output 58(1) shown in FIG. 8.
The power curve 94 is provided by the RF amplification device 10(1). More specifically, the power curve 94 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 2.4 GHz and the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm×20 by the impedance control output 58(1) shown in FIG. 5. Again, Znorm is the normalized (conventional characteristic impedance, Zo) termination impedance of the second periodic quadrature coupler 24(1) (shown in FIG. 5) at the eighth port 46 (shown in FIG. 5).
The power curve 96 is provided by the RF amplification device 10(1). More specifically, the power curve 96 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 2.2 GHz. Furthermore, the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm×10 by the impedance control output 58(1) shown in FIG. 8.
The power curve 98 is provided by the RF amplification device 10(1). More specifically, the power curve 98 is provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 2.4 GHz and the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm by the impedance control output 58(1) shown in FIG. 8.
FIG. 10 shows the performance of the RF amplification device 10(1) (shown in FIG. 5) at various frequencies within the passband PB2 (shown in FIG. 3) which is centered at 2.4 GHz. The RF amplification device 10(1) shown in FIG. 5 demonstrates excellent performance at 2.4 GHz also. The control circuit 14(1) shown in FIG. 5 may therefore be employed to adjust the tunable impedance load 54(1) to compensate for the effects of parasitics and other factors across power, frequency of operation, and other conditions. FIG. 10 thus shows that the RF amplification device 10(1) provides optimum efficiency at low subbands, medium subbands, and high subbands of the passband PB2 shown in FIG. 3.
FIG. 11 is a graph illustrating power curves 100 and 102 that describe PAE as a function of output power in the RF amplification device 10(1) shown in FIG. 5. Furthermore, to obtain the power curves 100 and 102, the tunable impedance load 54 (shown in FIG. 5) is provided as the tunable impedance load 54(1) shown in FIG. 8, and the impedance control output 58 (shown in FIG. 5) is provided as the impedance control output 58(1) (shown in FIG. 8). Both the power curves 100 and 102 are provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 850 MHz. However, the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm with regard to the power curve 100 and is set to a higher impedance with respect to the power curve 102. The RF amplification device 10(1) shown in FIG. 5 is assumed to have been in accordance with a WIN_043 process. As shown by the power curve 100, the Doherty amplification operation of the RF amplification device 10(1) shown in FIG. 5 results in improved PAE at backed-off power levels.
FIG. 12 illustrates a graph illustrating power curves 104 and 106 that describe PAE as a function of output power in the RF amplification device 10(1) shown in FIG. 5. Furthermore, to obtain the power curves 104 and 106, the tunable impedance load 54 (shown in FIG. 5) is provided as the tunable impedance load 54(1) shown in FIG. 8, and the impedance control output 58 (shown in FIG. 5) is provided as the impedance control output 58(1) (shown in FIG. 8). Both the power curves 104 and 106 are provided by the RF amplification device 10(1) when a carrier frequency of the RF signal 16 (shown in FIG. 5) is approximately 2.4 MHz. However, the tunable impedance of the tunable impedance load 54(1) is set approximately equal to Znorm with regard to the power curve 104 and is set to a higher impedance with respect to the power curve 106. The RF amplification device 10(1) shown in FIG. 5 is assumed to have been in accordance with a WIN_043 process. As shown by the power curve 104, the Doherty amplification operation of the RF amplification device 10(1) shown in FIG. 5 results in improved PAE at backed-off power levels.
Any combination of passive or active IC impedance components may be used to provide the tunable impedance. FIGS. 13 and 14 illustrate additional embodiments of the tunable impedance load 54 shown in FIGS. 1 and 5-7.
FIG. 13 illustrates another exemplary tunable impedance load 54(2). The tunable impedance load 54(2) is another embodiment of the tunable impedance load 54 described above with respect to FIG. 1. Like the tunable impedance load 54(1) shown in FIG. 8, the tunable impedance load 54(2) includes a plurality of selectable impedance branches (referred to generically as elements 108 and specifically as elements 108(1)-108(6)). The selectable impedance branches 108 are each coupled in parallel with respect to one another. An input terminal 110 of the tunable impedance load 54(2) may be coupled to the eighth port 46 (shown in FIGS. 1 and 5-7).
The selectable impedance branches include resistors (referred to generically as elements 112 and specifically as elements 112(1)-112(6)), switches (referred to generically as elements 114 and specifically as elements 114(1)-114(6)), and inductors (referred to generically as elements 116 and specifically as elements 116(1)-116(6)). More specifically, the selectable impedance branch 108(1) includes a resistor 112(1), a switch 114(1), and an inductor 116(1) coupled in series. The selectable impedance branch 108(2) includes a resistor 112(2), a switch 114(2), and an inductor 116(2) coupled in series. Additionally, the selectable impedance branch 108(3) includes a resistor 112(3), a switch 114(3), and an inductor 116(3) coupled in series. Furthermore, the selectable impedance branch 108(4) includes a resistor 112(4), a switch 114(4), and an inductor 116(4) coupled in series. Also, the selectable impedance branch 108(5) includes a resistor 112(5), a switch 114(5), and an inductor 116(5) coupled in series. Finally, the selectable impedance branch 108(6) includes a resistor 112(6), a switch 114(6), and an inductor 116(6) coupled in series.
For each of the selectable impedance branches 108, the selectable impedance branch 108 is configured to be selected when the switch 114 in the selectable impedance branch 108 is closed, and to be deselected when the switch 114 in the selectable impedance branch 108 is open. Each of the resistors 112 may have a different resistance and each of the inductors 116 may have a different inductance. The resistance of the resistor 112 and the inductance of the inductor 116 of the selectable impedance branch 108 is presented at the input terminal 110 (and thus at the eighth port 46 shown in FIGS. 1 and 5-7) when the switch 114 in the selectable impedance branch 108 is closed. Otherwise, when the switch 114 in the selectable impedance branch 108 is open, the selectable impedance branch 108 appears as an open circuit. Each of the switches 114 shown in FIG. 5 may be any type of suitable switch. For example, the switches 114 may be provided by as FETs and/or MEMs.
The switches 114 are opened and closed by an impedance control output 58(2). The impedance control output 58(2) is one embodiment of the impedance control output 58 described above with regard to FIGS. 1 and 5-7. In this embodiment, the impedance control output 58(2) includes a plurality of switch control signals (referred to generically as elements 118 and specifically as elements 118(1)-118(6)). Each of the switch control signals 118 is received by a corresponding one of the switches 114. For each of the switch control signals 118, the switch control signal 118 is received by the corresponding switch 114. The switch 78 is activated when the switch control signal 118 is in a switch activation state and the switch 78 is deactivated when the switch control signal 118 is in a switch deactivation state. A switch control signal 118(1) provided in the impedance control output 58(2) is received by the switch 114(1). A switch control signal 118(2) provided in the impedance control output 58(2) is received by the switch 114(2). A switch control signal 118(3) provided in the impedance control output 58(2) is received by the switch 114(3). A switch control signal 118(4) provided in the impedance control output 58(2) is received by the switch 114(4). A switch control signal 118(5) provided in the impedance control output 58(2) is received by the switch 114(5). A switch control signal 118(6) provided in the impedance control output 58(2) is received by the switch 114(6). Thus, in this embodiment, permutations of the impedance control output 58(2) refer to particular combinations of the switch control signals 118 that are in the switch activation state and in the switch deactivation state.
Since the switches 114 are used to vary the tunable impedance presented at the input terminal 110, the tunable impedance load 54(2) discretely varies the tunable impedance. Furthermore, in this embodiment, the tunable impedance is both resistive and reactive, since each of the selectable impedance branches 108 includes one of the resistors 112 and one of the inductors 116.
With regard to FIG. 14, FIG. 14 illustrates another embodiment of a tunable impedance load 54(4). The tunable impedance load 54(4) is another embodiment of the tunable impedance load 54 described above with respect to FIG. 1. The tunable impedance load 54(4) includes a plurality of selectable impedance branches (referred to generically as elements 120 and specifically as elements 120(1)-120(6)). The selectable impedance branches 120 are each coupled in parallel with respect to one another. An input terminal 122 of the tunable impedance load 54(4) may be coupled to the eighth port 46 (shown in FIGS. 1 and 5-7).
In this embodiment, the selectable impedance branches 120(1), 120(3), and 120(5) (referred to collectively as elements 120CAP) include capacitors (referred to generically as elements 124 and specifically as elements 124(1)-124(3)). In contrast, the selectable impedance branches 120(2), 120(4), and 120(6) (referred to collectively as elements 120RL) include resistors (referred to generically as elements 126 and specifically as elements 126(1)-126(3)) and inductors (referred to generically as elements 128 and specifically as elements 128(1)-128(3)). The selectable impedance branches 120 also include switches (referred to generically as elements 130 and specifically as elements 130(1)-130(6)).
More specifically, the selectable impedance branch 120(1) includes a capacitor 124(1) and a switch 130(1) coupled in series. The selectable impedance branch 120(2) includes a resistor 126(1), an inductor 128(1), and a switch 130(2) coupled in series. Additionally, the selectable impedance branch 120(3) includes a capacitor 124(2) and a switch 130(3) coupled in series. Furthermore, the selectable impedance branch 120(4) includes a resistor 126(2), an inductor 128(2), and a switch 130(4) coupled in series. Also, the selectable impedance branch 120(5) includes a capacitor 124(3) and a switch 130(5) coupled in series. Finally, the selectable impedance branch 120(6) includes a resistor 126(3), an inductor 128(3), and a switch 130(6) coupled in series.
For each of the selectable impedance branches 120, the selectable impedance branch 120 is configured to be selected when the switch 130 in the selectable impedance branch 120 is closed, and to be deselected when the switch 130 in the selectable impedance branch 120 is open. Each of the capacitors 124 may have a different capacitance, each of the resistors 126 may have a different resistance, and each of the inductors 128 may have a different inductance. The capacitance of the capacitor 124 of each of the selectable impedance branches 120CAP is presented at the input terminal 122 when the switch 130 in the selectable impedance branches 120CAP is closed. The resistance of the resistor 126 and the inductance of the inductor 128 of each of the selectable impedance branches 120RL is presented at the input terminal 122 (and thus the eighth port 46 shown in FIGS. 1 and 5-7) when the switch 130 in the selectable impedance branches 120RL is closed. Otherwise, when the switch 130 in the selectable impedance branches 120 is open, the selectable impedance branch 120 appears as an open circuit.
In this embodiment, different resonant impedance tanks may be presented at the input terminal 122 by selecting different combinations of the capacitors 124, the resistors 126, and the inductors 128. More specifically, different resonant impedance tanks may be presented at the input terminal 122 by selecting one or more of the selectable impedance branches 120CAP and by selecting one or more of the selectable impedance branches 120RL. In this manner, the tunable impedance of the tunable impedance load 54(4) can be provided with a high Q factor, which is advantageous in high frequency applications.
The switches 130 are opened and closed by an impedance control output 58(4). The impedance control output 58(4) is one embodiment of the impedance control output 58 described above with regard to FIGS. 1 and 5-7. In this embodiment, the impedance control output 58(4) includes a plurality of switch control signals (referred to generically as elements 131 and specifically as elements 131(1)-131(6)). Each of the switch control signals 131 is received by a corresponding one of the switches 130. For each of the switch control signals 131, the corresponding switch control signal 131 received by the switch 130 is activated when the switch control signal 131 is in a switch activation state and is deactivated when the switch control signal 131 is in a switch deactivation state. A switch control signal 131(1) provided in the impedance control output 58(4) is received by the switch 130(1). A switch control signal 131(2) provided in the impedance control output 58(4) is received by the switch 130(2). A switch control signal 131(3) provided in the impedance control output 58(4) is received by the switch 130(3). A switch control signal 131(4) provided in the impedance control output 58(4) is received by the switch 130(4). A switch control signal 131(5) provided in the impedance control output 58(4) is received by the switch 130(5). A switch control signal 131(6) provided in the impedance control output 58(4) is received by the switch 130(6). Thus, in this embodiment, permutations of the impedance control output 58(4) thus refer to particular combinations of the switch control signals 131 that are in the switch activation state and in the switch deactivation state.
Since the switches 131 are used to vary the tunable impedance presented at the input terminal 122, the tunable impedance load 54(4) discretely varies the tunable impedance. Furthermore, in this embodiment, the tunable impedance is both resistive and reactive since each of the selectable impedance branches 120RL include one of the resistors 126 and one of the inductors 128, and since each of the selectable impedance branches 120CAP includes one of the capacitors 124. In this manner, the tunable impedance of the tunable impedance load 54(4) is a complex impedance and thus includes a real impedance and an imaginary impedance.
FIG. 15 illustrates another embodiment of a tunable impedance load 54(3). The tunable impedance load 54(3) is another embodiment of the tunable impedance load 54 described above with respect to FIG. 1. The tunable impedance load 54(3) is similar to the tunable impedance load 54(2) shown in FIG. 13. Like the tunable impedance load 54(2) shown in FIG. 13, the tunable impedance load 54(3) includes a plurality of selectable impedance branches (referred to generically as elements 132 and specifically as elements 132(1)-132(6)). The selectable impedance branches 132 are each coupled in parallel with respect to one another. An input terminal 134 of the tunable impedance load 54(3) may be coupled to the eighth port 46 (shown in FIGS. 1 and 5-7).
The selectable impedance branches include resistors (referred to generically as elements 136 and specifically as elements 136(1)-136(6)), switches (referred to generically as elements 138 and specifically as elements 138(1)-138(6)), and inductors (referred to generically as elements 140 and specifically as elements 140(1)-140(6)). More specifically, the selectable impedance branch 132(1) includes a resistor 136(1), a switch 138(1), and an inductor 140(1) coupled in series. The selectable impedance branch 132(2) includes a resistor 136(2), a switch 138(2), and an inductor 140(2) coupled in series. Additionally, the selectable impedance branch 132(3) includes a resistor 136(3), a switch 138(3), and an inductor 140(3) coupled in series. Furthermore, the selectable impedance branch 132(4) includes a resistor 136(4), a switch 138(4), and an inductor 140(4) coupled in series. Also, the selectable impedance branch 132(5) includes a resistor 136(5), a switch 138(5), and an inductor 140(5) coupled in series. Finally, the selectable impedance branch 132(6) includes a resistor 136(6), a switch 138(6), and an inductor 140(6) coupled in series.
For each of the selectable impedance branches 132, the selectable impedance branch 132 is configured to be selected when the switch 138 in the selectable impedance branch 132 is closed, and to be deselected when the switch 138 in the selectable impedance branch 132 is open. Each of the resistors 136 may have a different resistance and each of the inductors 140 may have a different inductance. The resistance of the resistor 136 and the inductance of the inductor 140 of the selectable impedance branch 132 is presented at the input terminal 134 (and thus at the eighth port 46 shown in FIGS. 1 and 5-7) when the switch 138 in the selectable impedance branch 132 is closed. Otherwise, when the switch 138 in the selectable impedance branch 132 is open, the selectable impedance branch 132 appears as an open circuit. Each of the switches 138 shown in FIG. 15 may be any type of suitable switch. For example, the switches 138 may be provided by as FETs and/or MEMs.
The switches 138 are opened and closed by an impedance control output 58(3). The impedance control output 58(3) is one embodiment of the impedance control output 58 described above with regard to FIGS. 1 and 5-7. In this embodiment, the impedance control output 58(3) includes a plurality of switch control signals (referred to generically as elements 142 and specifically as elements 142(1)-142(6)). Each of the switch control signals 142 is received by a corresponding one of the switches 138. For each of the switch control signals 142, the corresponding switch control signal 142 received by the switch 138 is activated when the switch control signal 142 is in a switch activation state, and is deactivated when the switch control signal 142 is in a switch deactivation state. A switch control signal 142(1) provided in the impedance control output 58(3) is received by the switch 138(1). A switch control signal 142(2) provided in the impedance control output 58(3) is received by the switch 138(2). A switch control signal 142(3) provided in the impedance control output 58(3) is received by the switch 138(3). A switch control signal 142(4) provided in the impedance control output 58(3) is received by the switch 138(4). A switch control signal 142(5) provided in the impedance control output 58(3) is received by the switch 138(5). A switch control signal 142(6) provided in the impedance control output 58(3) is received by the switch 138(6). Thus, in this embodiment, permutations of the impedance control output 58(3) refer to particular combinations of the switch control signals 142 that are in the switch activation state and in the switch deactivation state.
Since the switches 138 are used to vary the tunable impedance presented at the input terminal 134, the tunable impedance load 54(2) discretely varies the tunable impedance. Furthermore, in this embodiment, the tunable impedance is both resistive and reactive, since each of the selectable impedance branches 132 includes one of the resistors 136 and one of the inductors 140. However, unlike the tunable impedance load 54(2) shown in FIG. 13, the inductors 140(4), 140(5), and 140(6) each have a much higher inductance than an inductance of each of the inductors 140(1), 140(2), and 140(3). Accordingly, the inductors 140(4), 140(5), and 140(6) may physically be significantly larger than the inductors 140(1), 140(2), and 140(3). This thus allows for the tunable impedance load 54(3) to be used in multi-band applications when certain RF communication specifications have stringent quality (Q) factor requirements.
Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

## Claims

1. A radio frequency (RF) amplification device comprising a Doherty amplification circuit configured to amplify an RF signal, wherein the Doherty amplification circuit comprises:
a main carrier RF amplifier;
a peaking RF amplifier configured to be deactivated while the RF signal is below a threshold level and configured to be activated while the RF signal is above the threshold level;
a periodic quadrature coupler having an output port configured to output the RF signal after amplification by the Doherty amplification circuit, wherein the periodic quadrature coupler is configured to combine a first RF split signal from the main carrier RF amplifier and a second RF split signal from the peaking RF amplifier into the RF signal such that the RF signal is output from the output port after amplification by the Doherty amplification circuit while the peaking RF amplifier is activated;
a tunable impedance load configured to provide a tunable impedance, and wherein the periodic quadrature coupler has an isolation port and the tunable impedance load is coupled to the isolation port of the periodic quadrature coupler; and
a control circuit configured to tune the tunable impedance of the tunable impedance load dynamically as a function of RF power to employ Doherty amplification operation, wherein the tunable impedance load is increased as the RF power is backed off to employ Doherty amplification operation.

2. The RF amplification device of claim 1 wherein the periodic quadrature coupler is a Lange coupler.

3. The RF amplification device of claim 1 wherein the periodic quadrature coupler is configured to define a first passband centered at a fundamental frequency and a second passband centered at a second frequency that is approximately equal to the fundamental frequency multiplied by an integer greater than one (1).

4. The RF amplification device of claim 3 wherein the integer is odd.

5. The RF amplification device of claim 3 wherein the integer is equal to three.

6. The RF amplification device of claim 1 wherein the periodic quadrature coupler is configured to define a set of passbands, wherein each of the passbands is centered approximately at a fundamental frequency multiplied by an integer in a set of integers.

7. The RF amplification device of claim 6 wherein the set of integers consists of a set of multiple odd integers.

8. The RF amplification device of claim 7 wherein:
the main carrier RF amplifier is a Class A amplifier; and
the peaking RF amplifier is a Class C amplifier.

9. The RF amplification device of claim 1 wherein the Doherty amplification circuit further comprises a second periodic quadrature coupler and wherein:
the main carrier RF amplifier is coupled between the periodic quadrature coupler and the second periodic quadrature coupler; and
the peaking RF amplifier is coupled between the periodic quadrature coupler and the second periodic quadrature coupler.

10. The RF amplification device of claim 1 wherein the main carrier RF amplifier is configured to be activated while the RF signal is below the threshold level and above the threshold level.

11. The RF amplification device of claim 1 wherein the Doherty amplification circuit further comprises a second periodic quadrature coupler and wherein:
the second periodic quadrature coupler comprises an input port configured to receive the RF signal for the Doherty amplification circuit;
the main carrier RF amplifier is coupled between the periodic quadrature coupler and the second periodic quadrature coupler; and
the peaking RF amplifier is coupled between the periodic quadrature coupler and the second periodic quadrature coupler.

12. The RF amplification device of claim 1 further comprising a second periodic quadrature coupler wherein:
the peaking RF amplifier is configured to be deactivated while the RF signal is below the threshold level and is configured to be activated while the RF signal is above the threshold level;
the main carrier RF amplifier is configured to be activated while the RF signal is below the threshold level and above the threshold level; and
the second periodic quadrature coupler is operably associated with the periodic quadrature coupler so as to pass the RF signal to the main carrier RF amplifier while the peaking RF amplifier is deactivated and split the RF signal into the first RF split signal and the second RF split signal while the peaking RF amplifier is activated, wherein the second periodic quadrature coupler is configured to pass the first RF split signal to the main carrier RF amplifier and pass the second RF split signal to the peaking RF amplifier while the peaking RF amplifier is activated.

13. The RF amplification device of claim 1 wherein the control circuit is further configured to:
detect the RF power in the Doherty amplification circuit; and
tune the tunable impedance of the tunable impedance load dynamically to invoke Doherty amplification operation as the function of the RF power detected of the Doherty amplification circuit.

14. The RF amplification device of claim 13 wherein the control circuit is further configured to receive a control input that indicates at least one operational frequency characteristic of the RF signal, and wherein the function of the RF power detected in the Doherty amplification circuit is further the function of the at least one operational frequency characteristic indicated by the control input.

15. The RF amplification device of claim 1 wherein the control circuit is coupled to the output port and is configured to detect the RF power of the Doherty amplification circuit by being configured to receive a feedback signal having a feedback signal level set in accordance with an RF signal level of the RF signal when the RF signal is output from the output port of the periodic quadrature coupler.

16. The RF amplification device of claim 1 wherein the Doherty amplification circuit further comprises a second periodic quadrature coupler and wherein:
the second periodic quadrature coupler comprises an input port configured to receive the RF signal for the Doherty amplification circuit; and
the control circuit is coupled to the input port and is configured to detect the RF power of the Doherty amplification circuit by being configured to receive a feedback signal having a feedback signal level set in accordance with an RF signal level of the RF signal at the input port of the second periodic quadrature coupler.

17. The RF amplification device of claim 1 wherein:
the peaking RF amplifier is configured to receive a supply voltage such that a supply current is generated by the supply voltage; and
the control circuit is coupled to the peaking RF amplifier and is configured to detect the RF power of the Doherty amplification circuit by being configured to receive a feedback signal having a feedback signal level set in accordance with a supply current level of the supply current.

18. The RF amplification device of claim 1 wherein the control circuit is further configured to:
receive a control input that indicates the RF power of the Doherty amplification circuit;
store a look-up table; and
tune the tunable impedance of the tunable impedance load dynamically as the function of the RF power of the Doherty amplification circuit indicated by the control input by being configured to implement the look-up table to invoke Doherty amplification operation.

19. The RF amplification device of claim 1 wherein the tunable impedance load is increased as the RF power is backed off to employ Doherty amplification operation.