# Patent

## Title
Communications based adjustments of a parallel amplifier power supply

## Abstract

A parallel amplifier and a parallel amplifier power supply are disclosed. The parallel amplifier power supply provides a parallel amplifier power supply signal, which is adjustable on a communications slot-to-communications slot basis. During envelope tracking, the parallel amplifier regulates an envelope power supply voltage based on the parallel amplifier power supply signal.

## Background
RELATED APPLICATIONS
This application claims the benefit of U.S. provisional patent application No. 61/756,248, filed Jan. 24, 2013, the disclosure of which is incorporated herein by reference in its entirety.
This application is related to U.S. patent application Ser. No. 14/163,229 entitled COMMUNICATIONS BASED ADJUSTMENTS OF AN OFFSET CAPACITIVE VOLTAGE by Khlat et al, filed Jan. 24, 2014, which is incorporated herein by reference in its entirety.


FIELD OF THE DISCLOSURE
Embodiments of the present disclosure relate to switching power supplies, analog power supplies, and radio frequency (RF) power amplifiers, any or all of which may be used in RF communication systems.
BACKGROUND
As wireless communications technologies evolve, wireless communications systems become increasingly sophisticated. As such, wireless communications protocols continue to expand and change to take advantage of the technological evolution. As a result, to maximize flexibility, many wireless communications devices must be capable of supporting any number of wireless communications protocols, each of which may have certain performance requirements, such as specific out-of-band emissions requirements, linearity requirements, or the like. Further, portable wireless communications devices are typically battery powered and need to be relatively small, and have low cost. As such, to minimize size, cost, and power consumption, RF circuitry in such a device needs to be as simple, small, and efficient as is practical. Thus, there is a need for RF circuitry in a communications device that is low cost, small, simple, and efficient.
SUMMARY
A parallel amplifier and a parallel amplifier power supply are disclosed according to one embodiment of the present disclosure. The parallel amplifier power supply provides a parallel amplifier power supply signal, which is adjustable on a communications slot-to-communications slot basis. During envelope tracking, the parallel amplifier regulates an envelope power supply voltage based on the parallel amplifier power supply signal.
In one embodiment of the present disclosure, an envelope tracking power supply includes an envelope tracking power supply output, the parallel amplifier, the parallel amplifier power supply, switching circuitry, an offset capacitive element, and a first inductive element. The envelope tracking power supply provides an envelope power supply voltage to an RF power amplifier via an envelope tracking power supply output. As such, during envelope tracking, the envelope power supply voltage at least partially envelope tracks an RF transmit signal from the RF power amplifier. By adjusting the parallel amplifier power supply signal on a communications slot-to-communications slot basis, efficiency of the envelope tracking power supply may be optimized.
Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings 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 shows an RF communications system according to one embodiment of the RF communications system.
FIG. 2 shows the RF communications system according to an alternate embodiment of the RF communications system.
FIG. 3 shows details of an envelope tracking power supply illustrated in FIG. 1 according to one embodiment of the envelope tracking power supply.
FIG. 4 shows details of the envelope tracking power supply illustrated in FIG. 1 according to an alternate embodiment of the envelope tracking power supply.
FIG. 5 shows details of the envelope tracking power supply illustrated in FIG. 1 according to an additional embodiment of the envelope tracking power supply.
FIG. 6 is a graph illustrating communications slots associated with the RF communications system shown in FIG. 1 according to one embodiment of the RF communications system.
FIG. 7 is a graph illustrating an RF transmit signal and an envelope power supply voltage shown in FIGS. 1 and 4, respectively, according to one embodiment of the RF transmit signal and the envelope power supply voltage.
FIGS. 8A and 8B are graphs illustrating the envelope power supply voltage shown in FIG. 4 according to alternate embodiments, respectively, of the envelope power supply voltage.
FIGS. 9A, 9B, and 9C show details of three different embodiments, respectively, of the parallel amplifier power supply illustrated in FIG. 4.
FIG. 10 shows details of the envelope tracking power supply illustrated in FIG. 1 according to another embodiment of the envelope tracking power supply.
FIG. 11 shows details of the envelope tracking power supply illustrated in FIG. 1 according to a further embodiment of the envelope tracking power supply.



DETAILED DESCRIPTION
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, 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.
A parallel amplifier and a parallel amplifier power supply are disclosed according to one embodiment of the present disclosure. The parallel amplifier power supply provides a parallel amplifier power supply signal, which is adjustable on a communications slot-to-communications slot basis. During envelope tracking, the parallel amplifier regulates an envelope power supply voltage based on the parallel amplifier power supply signal.
In one embodiment of the present disclosure, an envelope tracking power supply includes an envelope tracking power supply output, the parallel amplifier, the parallel amplifier power supply, switching circuitry, an offset capacitive element, and a first inductive element. The envelope tracking power supply provides an envelope power supply voltage to an RF power amplifier via an envelope tracking power supply output. As such, during envelope tracking, the envelope power supply voltage at least partially envelope tracks an RF transmit signal from the RF power amplifier. By adjusting the parallel amplifier power supply signal on a communications slot-to-communications slot basis, efficiency of the envelope tracking power supply may be optimized.
FIG. 1 shows an RF communications system 10 according to one embodiment of the RF communications system 10. The RF communications system 10 includes RF transmitter circuitry 12, RF system control circuitry 14, RF front-end circuitry 16, an RF antenna 18, and a DC power source 20. The RF transmitter circuitry 12 includes transmitter control circuitry 22, an RF PA 24, an envelope tracking power supply 26, and PA bias circuitry 28.
In one embodiment of the RF communications system 10, the RF front-end circuitry 16 receives via the RF antenna 18, processes, and forwards an RF receive signal RFR to the RF system control circuitry 14. The RF system control circuitry 14 provides an envelope power supply control signal VRMP and a transmitter configuration signal PACS to the transmitter control circuitry 22. The RF system control circuitry 14 provides an RF input signal RFI to the RF PA 24. The DC power source 20 provides a DC source signal VDC to the envelope tracking power supply 26. The DC source signal VDC has a DC source voltage DCV. In one embodiment of the DC power source 20, the DC power source 20 is a battery.
The transmitter control circuitry 22 is coupled to the envelope tracking power supply 26 and to the PA bias circuitry 28. The envelope tracking power supply 26 provides an envelope power supply signal EPS to the RF PA 24 based on the envelope power supply control signal VRMP. The envelope power supply signal EPS has an envelope power supply voltage EPV. The DC source signal VDC provides power to the envelope tracking power supply 26. As such, the envelope power supply signal EPS is based on the DC source signal VDC. The envelope power supply control signal VRMP is representative of a setpoint of the envelope power supply signal EPS. The RF PA 24 receives and amplifies the RF input signal RFI to provide an RF transmit signal RFT using the envelope power supply signal EPS. The envelope power supply signal EPS provides power for amplification. The RF front-end circuitry 16 receives, processes, and transmits the RF transmit signal RFT via the RF antenna 18. In one embodiment of the RF transmitter circuitry 12, the transmitter control circuitry 22 configures the RF transmitter circuitry 12 based on the transmitter configuration signal PACS.
In this regard, in one embodiment of the RF communications system 10, the RF communications system 10 communicates with other RF communications systems (not shown) using multiple communications slots, which may include transmit communications slots, receive communications slots, simultaneous receive and transmit communications slots, or any combination thereof. Such communications slots may utilize the RF transmit signal RFT, the RF receive signal RFR, other RF signals (not shown), or any combination thereof. In one embodiment of an RF communications slot, the RF communications slot is a time period during which RF transmissions, RF receptions, or both, may occur. Adjacent RF communications slots may be separated by slot boundaries, in which RF transmissions, RF receptions, or both, may be prohibited. As a result, during the slot boundaries, the RF communications system 10 may prepare for RF transmissions, RF receptions, or both.
The PA bias circuitry 28 provides a PA bias signal PAB to the RF PA 24. In this regard, the PA bias circuitry 28 biases the RF PA 24 via the PA bias signal PAB. In one embodiment of the PA bias circuitry 28, the PA bias circuitry 28 biases the RF PA 24 based on the transmitter configuration signal PACS. In one embodiment of the RF front-end circuitry 16, the RF front-end circuitry 16 includes at least one RF switch, at least one RF amplifier, at least one RF filter, at least one RF duplexer, at least one RF diplexer, the like, or any combination thereof. In one embodiment of the RF system control circuitry 14, the RF system control circuitry 14 is RF transceiver circuitry, which may include an RF transceiver IC, baseband controller circuitry, the like, or any combination thereof.
FIG. 2 shows the RF communications system 10 according to an alternate embodiment of the RF communications system 10. The RF communications system 10 illustrated in FIG. 2 is similar to the RF communications system 10 illustrated in FIG. 1, except in the RF communications system 10 illustrated in FIG. 2, the RF transmitter circuitry 12 further includes a digital communications interface 30, which is coupled between the transmitter control circuitry 22 and a digital communications bus 32. The digital communications bus 32 is also coupled to the RF system control circuitry 14. As such, the RF system control circuitry 14 provides the envelope power supply control signal VRMP (FIG. 1) and the transmitter configuration signal PACS (FIG. 1) to the transmitter control circuitry 22 via the digital communications bus 32 and the digital communications interface 30.
FIG. 3 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to one embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 includes power supply control circuitry 34, a parallel amplifier 36, and a switching supply 38. The power supply control circuitry 34 is coupled to the transmitter control circuitry 22, the parallel amplifier 36 is coupled to the power supply control circuitry 34, and the switching supply 38 is coupled to the power supply control circuitry 34. The transmitter control circuitry 22 may forward the envelope power supply control signal VRMP to the power supply control circuitry 34.
Since the envelope power supply control signal VRMP is representative of the setpoint of the envelope power supply signal EPS, the power supply control circuitry 34 controls the parallel amplifier 36 and the switching supply 38 based on the setpoint of the envelope power supply signal EPS. The parallel amplifier 36 and the switching supply 38 provide the envelope power supply signal EPS, such that the parallel amplifier 36 partially provides the envelope power supply signal EPS and the switching supply 38 partially provides the envelope power supply signal EPS. The switching supply 38 may provide power more efficiently than the parallel amplifier 36. However, the parallel amplifier 36 may provide the envelope power supply signal EPS more accurately than the switching supply 38. As such, the parallel amplifier 36 regulates the envelope power supply voltage EPV (FIGS. 1 and 7) based on the setpoint of the envelope power supply voltage EPV (FIGS. 1 and 7), and the switching supply 38 operates to drive an output current from the parallel amplifier 36 toward zero to maximize efficiency. In this regard, the parallel amplifier 36 behaves like a voltage source and the switching supply 38 behaves like a current source.
As previously mentioned, in one embodiment of the RF communications system 10, the RF PA 24 receives and amplifies the RF input signal RFI to provide the RF transmit signal RFT using the envelope power supply signal EPS, which provides power for amplification. In one embodiment of the RF input signal RFI, the RF input signal RFI is amplitude modulated. As such, the RF transmit signal RFT is also amplitude modulated, as illustrated in FIG. 7. Since the amplitude of the RF transmit signal RFT is modulated, the amplitude of the RF transmit signal RFT traverses within an envelope of the RF transmit signal RFT. For proper operation of the RF PA 24, the envelope power supply voltage EPV (FIGS. 1 and 7) must be high enough to accommodate the envelope of the RF transmit signal RFT. However, to increase efficiency in the RF PA 24, the envelope power supply voltage EPV (FIGS. 1 and 7) may at least partially track the envelope of the RF transmit signal RFT. This tracking by the envelope power supply voltage EPV is called envelope tracking.
In this regard, since the envelope power supply control signal VRMP is representative of the setpoint of the envelope power supply signal EPS, the envelope power supply control signal VRMP may be received and amplitude modulated to provide at least partial envelope tracking of the RF transmit signal RFT by causing the envelope power supply voltage EPV (FIGS. 1 and 7) to be amplitude modulated.
In a first embodiment of the envelope power supply control signal VRMP, a bandwidth of the envelope power supply control signal VRMP is greater than about 10 megahertz. In a second embodiment of the envelope power supply control signal VRMP, the bandwidth of the envelope power supply control signal VRMP is greater than about 20 megahertz. In a third embodiment of the envelope power supply control signal VRMP, the bandwidth of the envelope power supply control signal VRMP is greater than about 30 megahertz. In a fourth embodiment of the envelope power supply control signal VRMP, the bandwidth of the envelope power supply control signal VRMP is greater than about 40 megahertz. In a fifth embodiment of the envelope power supply control signal VRMP, the bandwidth of the envelope power supply control signal VRMP is greater than about 50 megahertz. In an alternate embodiment of the envelope power supply control signal VRMP, the bandwidth of the envelope power supply control signal VRMP is less than about 100 megahertz.
FIG. 4 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to an alternate embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 illustrated in FIG. 4 is similar to the envelope tracking power supply 26 illustrated in FIG. 3, except the envelope tracking power supply 26 illustrated in FIG. 4 further includes a parallel amplifier power supply 40, an offset capacitance voltage control loop 44, an offset capacitive element CA, a first filter capacitive element C1, and a second filter capacitive element C2. Additionally, the switching supply 38 includes switching circuitry 42 and a first inductive element L1. The envelope tracking power supply 26 has an envelope tracking power supply output PSO, such that the envelope power supply signal EPS is provided via the envelope tracking power supply output PSO. As previously mentioned, the envelope power supply signal EPS has the envelope power supply voltage EPV. The parallel amplifier 36 has a feedback input FBI and a parallel amplifier output PAO. The switching circuitry 42 has a switching circuitry output SSO.
In the embodiment shown, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the envelope tracking power supply output PSO. In general, the switching circuitry output SSO is coupled to the envelope tracking power supply output PSO via the first inductive element L1. As such, in other embodiments (not shown), the first inductive element L1 is coupled between the switching circuitry output SSO and the envelope tracking power supply output PSO using other intervening elements (not shown).
In the embodiment shown, the offset capacitive element CA is directly coupled between the parallel amplifier output PAO and the envelope tracking power supply output PSO. In general, the parallel amplifier output PAO is coupled to the envelope tracking power supply output PSO via the offset capacitive element CA. As such, in other embodiments (not shown), the offset capacitive element CA is coupled between the parallel amplifier output PAO and the envelope tracking power supply output PSO using other intervening elements (not shown).
In the embodiment shown, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the feedback input FBI. In general, the switching circuitry output SSO is coupled to the feedback input FBI via the first inductive element L1. As such, in other embodiments (not shown), the first inductive element L1 is coupled between the switching circuitry output SSO and the feedback input FBI using other intervening elements (not shown).
In one embodiment of the first filter capacitive element C1, the first filter capacitive element C1 is coupled between the envelope tracking power supply output PSO and a ground. In one embodiment of the second filter capacitive element C2, the second filter capacitive element C2 is coupled between an output from the parallel amplifier power supply 40 and the ground. The parallel amplifier power supply 40 provides a parallel amplifier power supply signal LPS to the parallel amplifier 36 via the output from the parallel amplifier power supply 40. The parallel amplifier power supply signal LPS has a parallel amplifier power supply voltage PSV.
The parallel amplifier 36 receives the parallel amplifier power supply signal LPS and regulates the envelope power supply voltage EPV via the parallel amplifier output PAO based on the setpoint of the envelope power supply voltage EPV using the parallel amplifier power supply signal LPS. As such, the parallel amplifier power supply signal LPS provides power for amplification. In this regard, since the parallel amplifier 36 receives the envelope power supply voltage EPV via the feedback input FBI, the parallel amplifier 36 drives the envelope power supply voltage EPV toward the setpoint of the envelope power supply voltage EPV. In one embodiment of the parallel amplifier 36, during envelope tracking, the parallel amplifier 36 provides the envelope power supply voltage EPV to the RF PA 24 via the envelope tracking power supply output PSO, such that the envelope power supply voltage EPV at least partially tracks the RF transmit signal RFT from the RF PA 24.
In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply signal LPS is adjustable on a communications slot-to-communications slot basis. As such, during at least one communications slot 46 (FIG. 6), the parallel amplifier power supply signal LPS is regulated to be about constant. Further, between communications slots 46, 48 (FIG. 6), the parallel amplifier power supply signal LPS may be changed.
An output voltage swing at the parallel amplifier output PAO of the parallel amplifier 36 is approximately between a source headroom voltage SRC (not shown) below the parallel amplifier power supply voltage PSV and a sink headroom voltage SNK (not shown) above the ground. However, during envelope tracking, the envelope power supply voltage EPV may traverse between an expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and an expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV. Since the parallel amplifier 36 drives the envelope power supply voltage EPV toward the setpoint of the envelope power supply voltage EPV, the parallel amplifier 36 and the offset capacitive element CA must be able to drive between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV. However, the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV may be significantly above ground.
In this regard, without the offset capacitive element CA, the parallel amplifier 36 would need an output voltage swing between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV. When the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV is significantly above the ground, the voltage drop between the parallel amplifier output PAO and the ground is large, thereby degrading efficiency. However, by using the offset capacitive element CA, the voltage swing between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV may be shifted down at the parallel amplifier output PAO.
In this regard, to maximize efficiency, the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV at the envelope tracking power supply output PSO would be shifted down to the sink headroom voltage SNK (not shown) above ground at the parallel amplifier output PAO, and the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV at the envelope tracking power supply output PSO would be shifted down to the source headroom voltage SRC (not shown) below the parallel amplifier power supply voltage PSV.
In one embodiment of the offset capacitance voltage control loop 44, the offset capacitive element CA has an offset capacitive voltage OSV, which is regulated by the offset capacitance voltage control loop 44. In one embodiment of the offset capacitance voltage control loop 44, the offset capacitive voltage OSV is adjustable on a communications slot-to-communications slot basis. As such, during at least one communications slot 46 (FIG. 6), the offset capacitive voltage OSV is regulated to be about constant. Further, between communications slots 46, 48 (FIG. 6), the offset capacitive voltage OSV may be changed. Further, in one embodiment of the offset capacitance voltage control loop 44, during at least one communications slot 46 (FIG. 6), the offset capacitive voltage OSV is further regulated, such that an average DC current through the offset capacitive element CA is equal to about zero.
If the offset capacitive voltage OSV is too large, then the parallel amplifier 36 will be unable to drive the parallel amplifier output PAO low enough to provide the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV at the parallel amplifier output PAO. Therefore, in one embodiment of the offset capacitance voltage control loop 44, the offset capacitance voltage control loop 44 regulates the offset capacitive voltage OSV, such that the offset capacitive voltage OSV is less than or equal to a difference between the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV and the sink headroom voltage SNK (not shown). In one embodiment of the sink headroom voltage SNK (not shown), the sink headroom voltage SNK (not shown) is equal to about 0.2 volts. If the expected minimum 54 (FIG. 7) of the envelope power supply voltage EPV is represented as EMN, the above requirement is shown in EQ. 1, below.

OSV<=EMN−SNK.  EQ. 1:

Additionally, the parallel amplifier power supply 40 must make sure that the parallel amplifier power supply voltage PSV is high enough to provide the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV. In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply 40 provides the parallel amplifier power supply voltage PSV, such that the parallel amplifier power supply voltage PSV is greater than or equal to a sum of the source headroom voltage SRC (not shown) and a difference between the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV and the offset capacitive voltage OSV. In one embodiment of the source headroom voltage SRC (not shown), the source headroom voltage SRC (not shown) is equal to about 0.1 volts. If the expected maximum 52 (FIG. 7) of the envelope power supply voltage EPV is represented as EMX, the above requirement is shown in EQ. 2, below.

PSV>=SRC+EMX−OSV.  EQ. 2:

In this regard, in one embodiment of the envelope tracking power supply 26, the offset capacitive voltage OSV is regulated to minimize a voltage drop between the parallel amplifier output PAO and the ground when the parallel amplifier 36 is sinking current. Further, in one embodiment of the envelope tracking power supply 26, the parallel amplifier power supply voltage PSV is regulated to minimize a voltage drop between the parallel amplifier output PAO and the parallel amplifier power supply 40 when the parallel amplifier 36 is sourcing current. Minimizing these voltage drops improves the efficiency of the envelope tracking power supply 26
In one embodiment of the switching supply 38, the switching supply 38 operates to drive an output current from the parallel amplifier 36 toward zero to maximize efficiency. The power supply control circuitry 34 is coupled to each of the parallel amplifier 36, the parallel amplifier power supply 40, the switching circuitry 42, and the offset capacitance voltage control loop 44. As such, in one embodiment of the power supply control circuitry 34, the power supply control circuitry 34 provides information and receives information from any or all of the parallel amplifier 36, the parallel amplifier power supply 40, the switching circuitry 42, and the offset capacitance voltage control loop 44, as needed.
The switching supply 38 and the parallel amplifier power supply 40 receive the DC source signal VDC from the DC power source 20 (FIG. 1). The parallel amplifier power supply 40 provides the parallel amplifier power supply signal LPS based on the DC source signal VDC. The power supply control circuitry 34 provides a parallel amplifier power supply select signal LPSS to the parallel amplifier power supply 40. The parallel amplifier power supply 40 selects one of a group of parallel amplifier supply voltages based on the parallel amplifier power supply select signal LPSS. The parallel amplifier power supply 40 provides the parallel amplifier power supply voltage PSV as the selected one of the group of parallel amplifier supply voltages.
FIG. 5 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to an additional embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 illustrated in FIG. 5 is similar to the envelope tracking power supply 26 illustrated in FIG. 4, except the switching supply 38 illustrated in FIG. 5 further includes a second inductive element L2. Further, in the envelope tracking power supply 26 illustrated in FIG. 4, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the envelope tracking power supply output PSO. However, in the envelope tracking power supply 26 illustrated in FIG. 5, the first inductive element L1 and the second inductive element L2 are coupled in series between the switching circuitry output SSO and the envelope tracking power supply output PSO. As such, the first inductive element L1 is directly coupled between the switching circuitry output SSO and the feedback input FBI, and the second inductive element L2 is directly coupled between the feedback input FBI and the envelope tracking power supply output PSO.
In one embodiment of the envelope tracking power supply 26, the series combination of the first inductive element L1 and the second inductive element L2 form a voltage divider, which provides a phase-shifted signal to the feedback input FBI. The voltage divider may compensate for bandwidth limitations in the parallel amplifier 36, thereby providing improved regulation of the envelope power supply voltage EPV. The first inductive element L1 has a first inductance and the second inductive element L2 has a second inductance.
In a first embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than ten. In a second embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than 100. In a third embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than 500. In a fourth embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is greater than 1000. In a fifth embodiment of the first inductive element L1 and the second inductive element L2, a ratio of the first inductance divided by the second inductance is less than 5000.
FIG. 6 is a graph illustrating multiple communications slots 46, 48 associated with the RF communications system 10 shown in FIG. 1 according to one embodiment of the RF communications system 10. In one embodiment of the RF communications system 10, the RF communications system 10 communicates with other RF communications systems (not shown) using the multiple communications slots 46, 48, which may include transmit communications slots, receive communications slots, simultaneous receive and transmit communications slots, or any combination thereof. The multiple communications slots 46, 48 may utilize the RF transmit signal RFT, the RF receive signal RFR, other RF signals (not shown), or any combination thereof.
The multiple communications slots 46, 48 include a communications slot 46 and an adjacent communications slot 48. In one embodiment of the communications slot 46, the communications slot 46 is a time period during which RF transmissions, RF receptions, or both, may occur. In one embodiment of the communications slot 46 and the adjacent communications slot 48, a slot boundary 50 is between the communications slot 46 and the adjacent communications slot 48. In one embodiment of the slot boundary 50, RF transmissions, RF receptions, or both, may be prohibited. As a result, during the slot boundary 50, the RF communications system 10 may prepare for RF transmissions, RF receptions, or both.
In one embodiment of the parallel amplifier power supply 40, the parallel amplifier power supply signal LPS may be adjusted during the slot boundary 50 and is prohibited from being adjusted during the communications slot 46 and during the adjacent communications slot 48. In this regard, the parallel amplifier power supply signal LPS is adjustable on a communications slot-to-communications slot basis. Further, in one embodiment of the offset capacitance voltage control loop 44, the offset capacitive voltage OSV may be adjusted during the slot boundary 50 and is prohibited from being adjusted during the communications slot 46 and during the adjacent communications slot 48. In this regard, the offset capacitive voltage OSV is adjustable on a communications slot-to-communications slot basis.
In one embodiment of the offset capacitance voltage control loop 44, to quickly adjust the offset capacitive voltage OSV and since the offset capacitive voltage OSV may be adjusted during the slot boundary 50, a bandwidth of the offset capacitance voltage control loop 44 during the slot boundary 50 is higher than the bandwidth of the offset capacitance voltage control loop 44 during the communications slots 46, 48.
FIG. 7 is a graph illustrating the RF transmit signal RFT and the envelope power supply voltage EPV shown in FIGS. 1 and 4, respectively, according to one embodiment of the RF transmit signal RFT and the envelope power supply voltage EPV. Further, FIGS. 8A and 8B are graphs illustrating the envelope power supply voltage EPV shown in FIG. 4 according to alternate embodiments of the envelope power supply voltage EPV. In one embodiment of the envelope tracking power supply 26, the envelope tracking power supply 26 operates in one of an envelope tracking mode and an average power tracking mode. Selection of the one of an envelope tracking mode and an average power tracking mode may be made by the RF system control circuitry 14, the transmitter control circuitry 22, or the power supply control circuitry 34.
During envelope tracking, the envelope tracking power supply 26 operates in the envelope tracking mode. As such, during the envelope tracking mode, the envelope tracking power supply 26 provides the envelope power supply voltage EPV to the RF PA 24 via the envelope tracking power supply output PSO, such that the envelope power supply voltage EPV at least partially tracks the RF transmit signal RFT from the RF PA 24, shown in FIG. 7. In this regard, the RF transmit signal RFT is amplitude modulated and the envelope power supply voltage EPV at least partially follows an envelope of the RF transmit signal RFT, as shown. The envelope power supply voltage EPV has the expected maximum 52 and the expected minimum 54, as shown in FIG. 7.
In one embodiment of the envelope power supply voltage EPV and the RF transmit signal RFT, the expected maximum 52 of the envelope power supply voltage EPV is high enough to accommodate the envelope of the RF transmit signal RFT without causing significant distortion of the RF transmit signal RFT. In an alternate embodiment of the envelope power supply voltage EPV and the RF transmit signal RFT, the expected maximum 52 of the envelope power supply voltage EPV is low enough to cause clipping (not shown) of the envelope of the RF transmit signal RFT, thereby causing some distortion of the RF transmit signal RFT. However, if the distortion of the RF transmit signal RFT is small enough to allow compliance with communications standards, the clipping may be acceptable.
During average power tracking, the envelope tracking power supply 26 operates in the average power tracking mode. As such, during the average power tracking mode, the envelope tracking power supply 26 provides the envelope power supply voltage EPV to the RF PA 24 via the envelope tracking power supply output PSO, such that during a communications slot 46 (FIG. 6), the envelope power supply voltage EPV is about constant, as shown in FIGS. 8A and 8B.
In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, the envelope power supply voltage EPV is above a voltage threshold 56, as shown in FIG. 8A. In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, the envelope power supply voltage EPV is below the voltage threshold 56, as shown in FIG. 8B.
FIGS. 9A, 9B, and 9C show details of three different embodiments, respectively, of the parallel amplifier power supply 40 illustrated in FIG. 4. In general, the parallel amplifier power supply 40 receives the parallel amplifier power supply select signal LPSS and the DC source signal VDC and provides the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS and the DC source signal VDC. The parallel amplifier power supply signal LPS has the parallel amplifier power supply voltage PSV, which is a selected one of the group of parallel amplifier supply voltages.
FIG. 9A shows a first embodiment of the parallel amplifier power supply 40. The parallel amplifier power supply 40 has a charge pump 58 and a multiplexer 60. The charge pump 58 receives the parallel amplifier power supply select signal LPSS and the DC source signal VDC and provides an output voltage from the charge pump 58 to the multiplexer 60 if the DC source voltage DCV (FIG. 1) is not the selected one of the group of parallel amplifier supply voltages, such that the output voltage from the charge pump 58 is based on the parallel amplifier power supply select signal LPSS and the DC source signal VDC. The multiplexer 60 receives the parallel amplifier power supply select signal LPSS, the DC source signal VDC, and the output voltage from the charge pump 58 and forwards either the DC source signal VDC or the output voltage from the charge pump 58 to provide the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS. In this regard the selected one of the group of parallel amplifier supply voltages is either the forwarded DC source voltage DCV or the forwarded output voltage from the charge pump 58.
In an alternate embodiment of the parallel amplifier power supply 40, the multiplexer 60 is omitted, such that the charge pump 58 provides the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS and the DC source signal VDC. As such, the parallel amplifier power supply voltage PSV is the selected one of the group of parallel amplifier supply voltages.
FIG. 9B shows a second embodiment of the parallel amplifier power supply 40. The parallel amplifier power supply 40 has a two flying capacitor-based charge pump 62, a first flying capacitive element CF1, a second flying capacitive element CF2, and the multiplexer 60. The first flying capacitive element CF1 and the second flying capacitive element CF2 are coupled to the two flying capacitor-based charge pump 62, which charges and discharges each of the first flying capacitive element CF1 and the second flying capacitive element CF2 as needed to provide a selected output voltage.
The two flying capacitor-based charge pump 62 receives the parallel amplifier power supply select signal LPSS and the DC source signal VDC and provides an output voltage from the two flying capacitor-based charge pump 62 to the multiplexer 60 if the DC source voltage DCV (FIG. 1) is not the selected one of the group of parallel amplifier supply voltages, such that the output voltage from the two flying capacitor-based charge pump 62 is based on the parallel amplifier power supply select signal LPSS and the DC source signal VDC. The multiplexer 60 receives the parallel amplifier power supply select signal LPSS, the DC source signal VDC, and the output voltage from the two flying capacitor-based charge pump 62 and forwards either the DC source signal VDC or the output voltage from the two flying capacitor-based charge pump 62 to provide the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS. In this regard the selected one of the group of parallel amplifier supply voltages is either the forwarded DC source voltage DCV or the forwarded output voltage from the two flying capacitor-based charge pump 62.
FIG. 9C shows a third embodiment of the parallel amplifier power supply 40. The parallel amplifier power supply 40 has an inductor-based charge pump 64, a charge pump inductive element LC, and the multiplexer 60. The charge pump inductive element LC is coupled between the inductor-based charge pump 64 and the multiplexer 60.
The inductor-based charge pump 64 receives the parallel amplifier power supply select signal LPSS and the DC source signal VDC and provides an output voltage from the charge pump inductive element LC to the multiplexer 60 if the DC source voltage DCV (FIG. 1) is not the selected one of the group of parallel amplifier supply voltages, such that the output voltage from the charge pump inductive element LC is based on the parallel amplifier power supply select signal LPSS and the DC source signal VDC. The multiplexer 60 receives the parallel amplifier power supply select signal LPSS, the DC source signal VDC, and the output voltage from the charge pump inductive element LC and forwards either the DC source signal VDC or the output voltage from the charge pump inductive element LC to provide the parallel amplifier power supply signal LPS based on the parallel amplifier power supply select signal LPSS. In this regard the selected one of the group of parallel amplifier supply voltages is either the forwarded DC source voltage DCV or the forwarded output voltage from the charge pump inductive element LC.
FIG. 10 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to another embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 illustrated in FIG. 10 is similar to the envelope tracking power supply 26 shown in FIG. 4, except the envelope tracking power supply 26 illustrated in FIG. 10 further includes a first switching element 66 and a second switching element 68, and the offset capacitance voltage control loop 44 is not shown for clarity. The first switching element 66 is coupled between the parallel amplifier output PAO and the ground. The second switching element 68 is coupled between the envelope tracking power supply output PSO and the output from the parallel amplifier power supply 40.
During the envelope tracking mode, the first switching element 66 is in an OPEN state and the second switching element 68 is in an OPEN state. Further, the parallel amplifier 36 is enabled, the switching circuitry 42 is enabled, and the parallel amplifier power supply 40 is enabled.
In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, when the envelope power supply voltage EPV is above the voltage threshold 56 (FIG. 8A), the first switching element 66 is in a CLOSED state, the second switching element 68 is in the OPEN state, the parallel amplifier 36 is disabled, the parallel amplifier power supply 40 is disabled, and the switching circuitry 42 is enabled. Since the envelope power supply voltage EPV is constant and above the voltage threshold 56 (FIG. 8A), the parallel amplifier 36 and the parallel amplifier power supply 40 are not needed to vary the envelope power supply voltage EPV. Therefore, the switching circuitry 42 may provide the envelope power supply voltage EPV with high efficiency. Further, with the first switching element 66 in the CLOSED state, one end of the offset capacitive element CA is coupled to ground for stability.
In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, when the envelope power supply voltage EPV is below the voltage threshold 56 (FIG. 8A), the first switching element 66 is in the CLOSED state, the second switching element 68 is in a CLOSED state, the parallel amplifier 36 is disabled, the parallel amplifier power supply 40 is enabled, and the switching circuitry 42 is disabled. Since the envelope power supply voltage EPV is constant and below the voltage threshold 56 (FIG. 8A), the parallel amplifier 36 is not needed to vary the envelope power supply voltage EPV. Further, the parallel amplifier power supply 40 may provide the envelope power supply voltage EPV with higher efficiency than the switching circuitry 42.
FIG. 11 shows details of the envelope tracking power supply 26 illustrated in FIG. 1 according to a further embodiment of the envelope tracking power supply 26. The envelope tracking power supply 26 illustrated in FIG. 11 is similar to the envelope tracking power supply 26 shown in FIG. 10, except in the envelope tracking power supply 26 illustrated in FIG. 10, the PA bias signal PAB is based on the parallel amplifier power supply signal LPS.
In one embodiment of the envelope tracking power supply 26, during the envelope tracking mode, the first switching element 66 is in the OPEN state and the second switching element 68 is in the OPEN state. Further, the parallel amplifier 36 is enabled, the switching circuitry 42 is enabled, and the parallel amplifier power supply 40 is enabled, such that the PA bias signal PAB is based on the parallel amplifier power supply signal LPS.
In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, when the envelope power supply voltage EPV is above the voltage threshold 56 (FIG. 8A), the first switching element 66 is in a CLOSED state, the second switching element 68 is in the OPEN state, the parallel amplifier 36 is disabled, the parallel amplifier power supply 40 is enabled, and the switching circuitry 42 is enabled. Since the envelope power supply voltage EPV is constant and above the voltage threshold 56 (FIG. 8A), the parallel amplifier 36 and the parallel amplifier power supply 40 are not needed to vary the envelope power supply voltage EPV. However, the parallel amplifier power supply 40 must be enabled to provide the PA bias signal PAB. Further, the switching circuitry 42 may provide the envelope power supply voltage EPV with high efficiency. With the first switching element 66 in the CLOSED state, one end of the offset capacitive element CA is coupled to ground for stability.
In one embodiment of the envelope tracking power supply 26, during the average power tracking mode, when the envelope power supply voltage EPV is below the voltage threshold 56 (FIG. 8A), the first switching element 66 is in the CLOSED state, the second switching element 68 is in the CLOSED state, the parallel amplifier 36 is disabled, the parallel amplifier power supply 40 is enabled, and the switching circuitry 42 is disabled. Since the envelope power supply voltage EPV is constant and below the voltage threshold 56 (FIG. 8A), the parallel amplifier 36 is not needed to vary the envelope power supply voltage EPV. Further, the parallel amplifier power supply 40 may provide the envelope power supply voltage EPV with higher efficiency than the switching circuitry 42. Also, the PA bias signal PAB is based on the parallel amplifier power supply signal LPS.
Those skilled in the art will recognize improvements and modifications to the 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. An envelope tracking power supply having an envelope tracking power supply output and comprising:
a parallel amplifier power supply configured to provide a parallel amplifier power supply signal, which is configured to be adjustable on a communications slot-to-communications slot basis;
a parallel amplifier having a parallel amplifier output, which during envelope tracking, is configured to regulate an envelope power supply voltage based on the parallel amplifier power supply signal; and
switching circuitry having a switching circuitry output, wherein:
an offset capacitive element is directly coupled between the parallel amplifier output and the envelope tracking power supply output; and
a first inductive element is coupled between the switching circuitry output and the envelope tracking power supply output.

2. The envelope tracking power supply of claim 1 wherein the first inductive element is directly coupled between the switching circuitry output and the envelope tracking power supply output.

3. The envelope tracking power supply of claim 1 further comprising an offset capacitance voltage control loop, wherein the offset capacitive element has an offset capacitive voltage, which is configured to be adjusted using the offset capacitance voltage control loop.

4. The envelope tracking power supply of claim 1 wherein during at least one communications slot an average DC current through the offset capacitive element is equal to about zero.

5. The envelope tracking power supply of claim 1 wherein the envelope tracking power supply is configured to provide the envelope power supply voltage to a radio frequency power amplifier via the envelope tracking power supply output, such that during envelope tracking, the envelope power supply voltage at least partially envelope tracks a radio frequency transmit signal from the radio frequency power amplifier.

6. The envelope tracking power supply of claim 5 wherein for at least one communications slot, the parallel amplifier power supply signal is based on an expected maximum and an expected minimum of the envelope power supply voltage.

7. The envelope tracking power supply of claim 6 wherein the offset capacitive element has an offset capacitive voltage, such that during the at least one communications slot, the offset capacitive voltage is based on the expected minimum of the envelope power supply voltage.

8. The envelope tracking power supply of claim 7 wherein the parallel amplifier output has a sink headroom voltage, such that the offset capacitive voltage is less than or equal to a difference between the expected minimum of the envelope power supply voltage and the sink headroom voltage.

9. The envelope tracking power supply of claim 8 wherein the sink headroom voltage is equal to about 0.2 volts.

10. The envelope tracking power supply of claim 7 wherein the parallel amplifier power supply signal has a parallel amplifier power supply voltage, such that during the at least one communications slot, the parallel amplifier power supply voltage is based on a difference between the expected maximum of the envelope power supply voltage and the expected minimum of the envelope power supply voltage.

11. The envelope tracking power supply of claim 10 wherein the parallel amplifier output has a source headroom voltage, such that during the at least one communications slot, the parallel amplifier power supply voltage is greater than or equal to a sum of the source headroom voltage and a difference between the expected maximum of the envelope power supply voltage and the offset capacitive voltage.

12. The envelope tracking power supply of claim 11 wherein the expected maximum of the envelope power supply voltage is low enough to clip the radio frequency transmit signal from the radio frequency power amplifier.

13. The envelope tracking power supply of claim 5 wherein the parallel amplifier power supply is further configured to receive a DC source signal from a DC power source and provide the parallel amplifier power supply signal based on the DC source signal.

14. The envelope tracking power supply of claim 13 wherein the DC power source is a battery.

15. The envelope tracking power supply of claim 13 wherein the parallel amplifier power supply comprises a two flying capacitor-based charge pump.

16. The envelope tracking power supply of claim 13 wherein the parallel amplifier power supply comprises an inductor-based charge pump.

17. The envelope tracking power supply of claim 13 wherein:
the envelope tracking power supply is further configured to operate in one of an envelope tracking mode and an average power tracking mode;
during the envelope tracking mode, the envelope tracking power supply is further configured to provide the envelope power supply voltage to the radio frequency power amplifier via the envelope tracking power supply output, such that the envelope power supply voltage at least partially envelope tracks the radio frequency transmit signal from the radio frequency power amplifier; and
during the average power tracking mode, the envelope tracking power supply is further configured to provide the envelope power supply voltage to the radio frequency power amplifier via the envelope tracking power supply output, such that during a communications slot the envelope power supply voltage is about constant.

18. The envelope tracking power supply of claim 17 wherein during the envelope tracking mode:
the parallel amplifier is enabled;
the switching circuitry is enabled; and
the parallel amplifier power supply is enabled.

19. The envelope tracking power supply of claim 18 wherein the radio frequency power amplifier is configured to receive a power amplifier bias signal, which is based on the parallel amplifier power supply signal.

20. The envelope tracking power supply of claim 17 wherein during the average power tracking mode and when the envelope power supply voltage is above a voltage threshold:
the parallel amplifier is disabled;
the switching circuitry is enabled; and
the parallel amplifier power supply is enabled, such that the radio frequency power amplifier is configured to receive a power amplifier bias signal, which is based on the parallel amplifier power supply signal.

21. The envelope tracking power supply of claim 17 wherein during the average power tracking mode and when the envelope power supply voltage is above a voltage threshold:
the parallel amplifier is disabled;
the switching circuitry is enabled; and
the parallel amplifier power supply is disabled.

22. The envelope tracking power supply of claim 17 wherein during the average power tracking mode and when the envelope power supply voltage is below a voltage threshold:
the parallel amplifier is disabled;
the switching circuitry is disabled; and
the parallel amplifier power supply is enabled, such that the envelope power supply voltage is based on the parallel amplifier power supply signal.

23. The envelope tracking power supply of claim 22 wherein the radio frequency power amplifier is configured to receive a power amplifier bias signal, which is based on the parallel amplifier power supply signal.

24. The envelope tracking power supply of claim 5 wherein:
the parallel amplifier further has a feedback input;
the first inductive element is directly coupled between the switching circuitry output and the feedback input; and
a second inductive element is directly coupled between the feedback input and the envelope tracking power supply output.

25. The envelope tracking power supply of claim 24 wherein the first inductive element has a first inductance and the second inductive element has a second inductance, such that a ratio of the first inductance divided by the second inductance is greater than ten.

26. The envelope tracking power supply of claim 5 wherein a first filter capacitive element is coupled between the envelope tracking power supply output and a ground.

27. A method for providing and operating an envelope tracking power supply having an envelope tracking power supply output comprising:
providing a parallel amplifier power supply;
using the parallel amplifier power supply to provide a parallel amplifier power supply signal, which is configured to be adjustable on a communications slot-to-communications slot basis;
regulating an envelope power supply voltage based on the parallel amplifier power supply signal;
providing a parallel amplifier having a parallel amplifier output; and
providing switching circuitry having a switching circuitry output, wherein:
an offset capacitive element is directly coupled between the parallel amplifier output and the envelope tracking power supply output; and
a first inductive element is coupled between the switching circuitry output and the envelope tracking power supply output.