Group delay calibration of RF envelope tracking

An RF communications system, which includes an RF power amplifier, an envelope tracking power supply, and supply control circuitry, is disclosed. The RF communications system operates in one of a normal operation mode and a calibration mode. During the calibration mode, the RF power amplifier receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which is provided by the envelope tracking power supply. Further, the supply control circuitry controls the envelope tracking power supply to cause a sharp transition of the envelope power supply signal when a setpoint of the envelope power supply signal transitions through a setpoint threshold of the envelope power supply signal.

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 communications 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

An RF communications system, which includes an RF power amplifier, an envelope tracking power supply, and supply control circuitry, is disclosed according to one embodiment of the present disclosure. The RF communications system operates in one of a normal operation mode and a calibration mode. During the calibration mode, the RF power amplifier receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which is provided by the envelope tracking power supply. Further, the supply control circuitry controls the envelope tracking power supply to cause a sharp transition of the envelope power supply signal when a setpoint of the envelope power supply signal transitions through a setpoint threshold of the envelope power supply signal.

By sharply transitioning the envelope power supply signal during the calibration mode, a delay mismatch between the envelope power supply signal and the RF input signal may be more accurately determined, thereby improving alignment of an envelope of the RF transmit signal with the envelope power supply signal during the normal operation mode. In one embodiment of the envelope power supply signal, a maximum rate of change of the envelope power supply signal during the sharp transition is greater than a maximum rate of change of the envelope power supply signal during the normal operation mode.

Certain emerging wireless communications protocols require increasingly larger modulation bandwidths of RF transmit signals. Such modulation bandwidths may impose increasingly tight alignment requirements between an RF transmit signal and an envelope power supply signal. Therefore, there is a need for calibration techniques to accurately align the envelope power supply signal with the RF transmit signal.

DETAILED DESCRIPTION

An RF communications system, which includes an RF power amplifier, an envelope tracking power supply, and supply control circuitry, is disclosed according to one embodiment of the present disclosure. The RF communications system operates in one of a normal operation mode and a calibration mode. During the calibration mode, the RF power amplifier receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which is provided by the envelope tracking power supply. Further, the supply control circuitry controls the envelope tracking power supply to cause a sharp transition of the envelope power supply signal when a setpoint of the envelope power supply signal transitions through a setpoint threshold of the envelope power supply signal.

By sharply transitioning the envelope power supply signal during the calibration mode, a delay mismatch between the envelope power supply signal and the RF input signal may be more accurately determined, thereby improving alignment of an envelope of the RF transmit signal with the envelope power supply signal during the normal operation mode. In one embodiment of the envelope power supply signal, a maximum rate of change of the envelope power supply signal during the sharp transition is greater than a maximum rate of change of the envelope power supply signal during the normal operation mode.

Certain emerging wireless communications protocols require increasingly larger modulation bandwidths of RF transmit signals. Such modulation bandwidths may impose increasingly tight alignment requirements between an RF transmit signal and an envelope power supply signal. Therefore, there is a need for calibration techniques to accurately align the envelope power supply signal with the RF transmit signal.

For example, with certain wireless local area network (WLAN) protocols, the RF transmit signal and the envelope power supply signal need to be aligned within 1.0 nanoseconds, or less. With certain multiple carrier long term evolution (LTE) protocols, the RF transmit signal and the envelope power supply signal need to be aligned within 0.5 nanoseconds, or less. With certain high frequency WLAN protocols, the RF transmit signal and the envelope power supply signal need to be aligned within 0.25 nanoseconds, or less.

FIG. 1shows an RF communications system10according to one embodiment of the RF communications system10. The RF communications system10includes RF transmitter circuitry12, RF system control circuitry14, RF front-end circuitry16, an RF antenna18, and a DC power source20. The RF transmitter circuitry12includes an envelope tracking integrated circuit (ETIC)22, an RF power amplifier (RF PA)24, and an RF feedback circuit26. The ETIC22includes supply control circuitry28and an envelope tracking power supply30. The RF system control circuitry14includes delay calibration data32.

In one embodiment of the RF communications system10, the RF front-end circuitry16receives via the RF antenna18, processes, and forwards an RF receive signal RFR to the RF system control circuitry14. The RF system control circuitry14provides an envelope power supply control signal VRMP and a transmitter configuration signal PACS to the supply control circuitry28. The RF system control circuitry14provides an RF input signal RFI to the RF PA24. The DC power source20provides a DC source signal VDC to the envelope tracking power supply30. The DC source signal VDC has a DC source voltage DCV. In one embodiment of the DC power source20, the DC power source20is a battery.

The supply control circuitry28is coupled to the envelope tracking power supply30. The envelope tracking power supply30provides an envelope power supply signal EPS to the RF PA24based 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 supply30. 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 PA24receives 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 circuitry16receives, processes, and transmits the RF transmit signal RFT via the RF antenna18.

In one embodiment of the RF feedback circuit26, the RF feedback circuit26receives the RF transmit signal RFT and provides an RF feedback signal RFF to the RF system control circuitry14based on the RF transmit signal RFT. In one embodiment of the RF feedback circuit26, the RF feedback circuit26comprises an RF detector, such that the RF feedback signal RFF is based on detecting the RF transmit signal RFT. In an alternate embodiment of the RF feedback circuit26, the RF feedback circuit26comprises an RF attenuator, such that the RF feedback signal RFF is based on attenuating the RF transmit signal RFT. In one embodiment of the RF transmitter circuitry12, the supply control circuitry28configures the RF transmitter circuitry12based on the transmitter configuration signal PACS.

In one embodiment of the RF front-end circuitry16, the RF front-end circuitry16includes 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 circuitry14, the RF system control circuitry14is RF transceiver circuitry, which may include an RF transceiver IC, baseband controller circuitry, the like, or any combination thereof.

In one embodiment of the RF communications system10, the RF communications system10operates in one of a normal operation mode and a calibration mode. In one embodiment of the RF system control circuitry14, during the normal operation mode and during the calibration mode, the RF system control circuitry14provides the RF input signal RFI and the envelope power supply control signal VRMP, such that the RF PA24receives and amplifies the RF input signal RFI to provide the RF transmit signal RFT using the envelope power supply signal EPS, which is based on the envelope power supply control signal VRMP.

In one embodiment of the RF communications system10, during the calibration mode, the RF system control circuitry14measures a delay mismatch between the envelope power supply signal EPS and the RF input signal RFI using the RF feedback signal RFF. As such, the RF feedback signal RFF is representative of the delay mismatch between the envelope power supply signal EPS and the RF input signal RFI. In one embodiment of the delay calibration data32, the delay calibration data32is based on the RF feedback signal RFF. In one embodiment of the RF system control circuitry14, during the calibration mode, the RF system control circuitry14provides the RF input signal RFI and the envelope power supply control signal VRMP, such that the RF PA24receives and amplifies the RF input signal RFI to provide the RF transmit signal RFT using the envelope power supply signal EPS, which is based on the envelope power supply control signal VRMP.

FIG. 2shows the RF communications system10according to an alternate embodiment of the RF communications system10. The RF communications system10illustrated inFIG. 2is similar to the RF communications system10illustrated inFIG. 1, except in the RF communications system10illustrated inFIG. 2; the RF transmitter circuitry12further includes a digital communications interface34, which is coupled between the supply control circuitry28and a digital communications bus36. The digital communications bus36is also coupled to the RF system control circuitry14. As such, the RF system control circuitry14provides the envelope power supply control signal VRMP (FIG. 1) and the transmitter configuration signal PACS (FIG. 1) to the supply control circuitry28via the digital communications bus36and the digital communications interface34.

FIG. 3is a graph illustrating the RF transmit signal RFT and the envelope power supply signal EPS shown inFIGS. 1 and 2, according to one embodiment of the RF transmit signal RFT and the envelope power supply signal EPS.FIG. 3is described based on the RF communications system10illustrated inFIGS. 1 and 2. In one embodiment of the RF communications system10, the delay calibration data32is based on a group delay mismatch between the RF transmit signal RFT and the envelope power supply signal EPS.

In this regard, during the normal operation mode, the RF system control circuitry14uses the delay calibration data32to approximately align an envelope38of the RF transmit signal RFT with the envelope power supply signal EPS as illustrated inFIG. 3. As such, the RF system control circuitry14may make timing adjustments to the RF input signal RFI, the envelope power supply control signal VRMP, or both.

FIGS. 4A and 4Bare graphs illustrating the envelope power supply control signal VRMP and the envelope power supply signal EPS shown inFIG. 1during the normal operation mode, according to one embodiment of the envelope power supply control signal VRMP and the envelope power supply signal EPS, respectively.FIGS. 4A and 4Bare described based on the RF communications system10illustrated inFIG. 1. The envelope power supply control signal VRMP is representative of a setpoint of the envelope power supply signal EPS. As such, the envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 4A and 4Bare about phase-aligned with one another. Any group delay in the illustrated embodiments between the envelope power supply control signal VRMP and the envelope power supply signal EPS are not shown. The envelope power supply signal EPS shown inFIG. 4Bfollows the envelope power supply control signal VRMP illustrated inFIG. 4A. Further the envelope power supply signal EPS shown inFIG. 4Bis similar to the envelope power supply signal EPS shown inFIG. 3.

The envelope power supply control signal VRMP has a control magnitude40, which correlates with a setpoint magnitude42of the envelope power supply signal EPS. Further, during the normal operation mode, the envelope power supply signal EPS has a normal envelope peak44.

FIGS. 5A and 5Bare graphs illustrating the envelope power supply control signal VRMP and the envelope power supply signal EPS shown inFIG. 1during the calibration mode, according to one embodiment of the envelope power supply control signal VRMP and the envelope power supply signal EPS, respectively.FIGS. 5A and 5Bare described based on the RF communications system10illustrated inFIG. 1. The envelope power supply control signal VRMP is representative of the setpoint of the envelope power supply signal EPS. As such, the envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 5A and 5Bare about phase-aligned with one another. Any group delay in the illustrated embodiments between the envelope power supply control signal VRMP and the envelope power supply signal EPS are not shown. The envelope power supply signal EPS shown inFIG. 5Bis based on the envelope power supply control signal VRMP illustrated inFIG. 5A.

A shape of the envelope power supply control signal VRMP illustrated inFIG. 5Ais a rough square-wave with sloped transitions. This shape may provide easier detection of delay mismatch between the RF transmit signal RFT and the envelope power supply signal EPS by the RF feedback circuit26. Due to bandwidth limitations in the envelope tracking power supply30, a shape of the envelope power supply signal EPS illustrated inFIG. 5Bhas rounded corners. The envelope power supply control signal VRMP has the control magnitude40, which correlates with a setpoint threshold46of the envelope power supply signal EPS. During the calibration mode, the envelope power supply signal EPS has a calibration envelope peak48.

In one embodiment of the envelope power supply signal EPS, a maximum value of the normal envelope peak44(FIG. 4B) is about equal to a maximum value of the calibration envelope peak48. In one embodiment of the RF communications system10, during the calibration mode, the calibration envelope peak48has the maximum value of the calibration envelope peak48. In a first embodiment of the envelope power supply signal EPS, the maximum value of the calibration envelope peak48is equal to about 4.5 volts. In a second embodiment of the envelope power supply signal EPS, the maximum value of the calibration envelope peak48is between about 5 volts and 6 volts. In a third embodiment of the envelope power supply signal EPS, the maximum value of the calibration envelope peak48is between about 4 volts and 5 volts. In a fourth embodiment of the envelope power supply signal EPS, the maximum value of the calibration envelope peak48is between about 3 volts and 4 volts.

FIGS. 6A and 6Bare graphs illustrating the envelope power supply control signal VRMP and the envelope power supply signal EPS shown inFIG. 1during the calibration mode, according to an alternate embodiment of the envelope power supply control signal VRMP and the envelope power supply signal EPS, respectively.FIGS. 6A and 6Bare described based on the RF communications system10illustrated inFIG. 1.

The envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 6A and 6B, respectively, are similar to the envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 5A and 5B, respectively, except a shape of the envelope power supply signal EPS illustrated inFIG. 6Bis modified significantly.

In one embodiment of the supply control circuitry28, during the calibration mode, when the setpoint of the envelope power supply signal EPS, which is based on the envelope power supply control signal VRMP as illustrated inFIG. 6A, transitions from below a setpoint threshold46to above the setpoint threshold46, the supply control circuitry28causes a sharp transition52of the envelope power supply signal EPS from a target magnitude50of the setpoint of the envelope power supply signal EPS to the setpoint of the envelope power supply signal EPS, as illustrated inFIG. 6B. As such, the target magnitude50is less than the setpoint threshold46.

In one embodiment of the supply control circuitry28, during the calibration mode, the supply control circuitry28controls the envelope tracking power supply30, such that when the setpoint of the envelope power supply signal EPS transitions from above the setpoint threshold46to below the setpoint threshold46, the supply control circuitry28causes a sharp transition52of the envelope power supply signal EPS to the target magnitude50.

In general, in one embodiment of the supply control circuitry28, during the calibration mode, the supply control circuitry28controls the envelope tracking power supply30, such that when the setpoint of the envelope power supply signal EPS transitions through the setpoint threshold46, the supply control circuitry28causes the sharp transition52of the envelope power supply signal EPS. In one embodiment of the envelope power supply signal EPS, a maximum rate of change of the envelope power supply signal EPS during the sharp transition52is greater than a maximum rate of change of the envelope power supply signal EPS during the normal operation mode.

In a first embodiment of the setpoint threshold46, the setpoint threshold46is greater than about fifty percent of an amplitude of the envelope power supply signal EPS. In a second embodiment of the setpoint threshold46, the setpoint threshold46is greater than about sixty percent of the amplitude of the envelope power supply signal EPS. In a third embodiment of the setpoint threshold46, the setpoint threshold46is greater than about seventy percent of the amplitude of the envelope power supply signal EPS. In a fourth embodiment of the setpoint threshold46, the setpoint threshold46is greater than about eighty percent of the amplitude of the envelope power supply signal EPS. In one embodiment of the setpoint threshold46, selection of the setpoint threshold46is based on providing sufficient sensitivity of a delay mismatch between the envelope power supply signal EPS and the RF input signal RFI.

In a first embodiment of the target magnitude50, the target magnitude50is less than about 500 millivolts. In a second embodiment of the target magnitude50, the target magnitude50is less than about 400 millivolts. In a third embodiment of the target magnitude50, the target magnitude50is less than about 300 millivolts. In a fourth embodiment of the target magnitude50, the target magnitude50is less than about 200 millivolts. In a fifth embodiment of the target magnitude50, the target magnitude50is less than about 100 millivolts. In one embodiment of the target magnitude50, selection of the target magnitude50is based on providing sufficient sensitivity of a delay mismatch between the envelope power supply signal EPS and the RF input signal RFI.

FIG. 7is a graph illustrating feedback sensitivity of the RF feedback circuit26to delay mismatch between the RF transmit signal RFT and the envelope power supply signal EPS according to one embodiment of the RF feedback circuit26.FIG. 7is described based on the RF communications system10illustrated inFIG. 1. As the delay mismatch between the RF transmit signal RFT and the envelope power supply signal EPS increases in a positive direction, the feedback sensitivity of the RF feedback circuit26increases in a negative direction until the feedback sensitivity reaches a maximum negative sensitivity peak. Similarly, as the delay mismatch between the RF transmit signal RFT and the envelope power supply signal EPS increases in a negative direction, the feedback sensitivity of the RF feedback circuit26increases in a positive direction until the feedback sensitivity reaches a maximum positive sensitivity peak. As a result, in one embodiment of the RF communications system10, during the calibration mode, timing between the RF transmit signal RFT and the envelope power supply signal EPS are deliberately mismatched to increase delay mismatch sensitivity between the RF transmit signal RFT and the envelope power supply signal EPS, thereby improving characterization of the delay mismatch between the envelope power supply signal EPS and the RF input signal RFI, which may provide improved alignment of the envelope of the RF transmit signal RFT with the envelope power supply signal EPS during the normal operation mode.

FIGS. 8A and 8Bare graphs illustrating the envelope power supply control signal VRMP and the envelope power supply signal EPS shown inFIG. 1during the calibration mode, according to an additional embodiment of the envelope power supply control signal VRMP and the envelope power supply signal EPS, respectively.FIGS. 8A and 8Bare described based on the RF communications system10illustrated inFIG. 1. The envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 8A and 8Bare similar to the envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 6A and 6B, respectively, except during the calibration mode, the envelope power supply signal EPS illustrated inFIG. 8Bis delayed from the envelope power supply control signal VRMP illustrated inFIG. 8Aby a positive delay54. In one embodiment of the envelope power supply control signal VRMP and the RF input signal RFI, during the calibration mode, the envelope power supply control signal VRMP and the RF input signal RFI are about phase-aligned with one another. Therefore, during the calibration mode, the envelope power supply signal EPS is delayed from the RF input signal RFI by the positive delay54. In one embodiment of the positive delay54, the positive delay54is based on the maximum positive sensitivity peak illustrated inFIG. 7. In one embodiment of the positive delay54, the positive delay54is based on the transmitter configuration signal PACS.

FIGS. 9A and 9Bare graphs illustrating the envelope power supply control signal VRMP and the envelope power supply signal EPS shown inFIG. 1during the calibration mode, according to another embodiment of the envelope power supply control signal VRMP and the envelope power supply signal EPS, respectively.FIGS. 9A and 9Bare described based on the RF communications system10illustrated inFIG. 1. The envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 9A and 9Bare similar to the envelope power supply control signal VRMP and the envelope power supply signal EPS illustrated inFIGS. 6A and 6B, respectively, except during the calibration mode, the envelope power supply signal EPS illustrated inFIG. 9Bis delayed from the envelope power supply control signal VRMP illustrated inFIG. 9Aby a negative delay56. In one embodiment of the envelope power supply control signal VRMP and the RF input signal RFI, during the calibration mode, the envelope power supply control signal VRMP and the RF input signal RFI are about phase-aligned with one another. Therefore, during the calibration mode, the envelope power supply signal EPS is delayed from the RF input signal RFI by the negative delay56. In one embodiment of the negative delay56, the negative delay56is based on the maximum negative sensitivity peak illustrated inFIG. 7. In one embodiment of the negative delay56, the negative delay56is based on the transmitter configuration signal PACS.

In one embodiment of the RF communications system10illustrated inFIGS. 1 and 2, any combination of the positive delay54(FIGS. 8A and 8B), the negative delay56(FIGS. 9A and 9B), and the sharp transition52(FIG. 6B) may be used to provide sufficient sensitivity of a delay mismatch between the envelope power supply signal EPS and the RF input signal RFI. In a first exemplary embodiment of the RF communications system10, by using either the positive delay54(FIGS. 8A and 8B) or the negative delay56(FIGS. 9A and 9B), the feedback sensitivity of the RF feedback circuit26is on the order of about 0.2 decibels/nanosecond, which may allow the RF communications system10to align the envelope power supply signal EPS and the RF input signal RFI during the normal operation mode within about 0.5 nanoseconds.

In a second exemplary embodiment of the RF communications system10, by using both the positive delay54(FIGS. 8A and 8B) and the negative delay56(FIGS. 9A and 9B), the effective feedback sensitivity of the RF feedback circuit26is on the order of about 0.4 decibels/nanosecond, which may allow the RF communications system10to align the envelope power supply signal EPS and the RF input signal RFI during the normal operation mode within about 0.25 nanoseconds.

In a third exemplary embodiment of the RF communications system10, by using a combination of the positive delay54(FIGS. 8A and 8B), the negative delay56(FIGS. 9A and 9B), and the sharp transition52(FIG. 6B), the effective feedback sensitivity of the RF feedback circuit26is on the order of about 1.0 decibels/nanosecond, which may allow the RF communications system10to align the envelope power supply signal EPS and the RF input signal RFI during the normal operation mode within about 0.1 nanoseconds.

FIGS. 10A and 10Bare graphs illustrating transition times of the envelope power supply signal EPS during the sharp transition52from the target magnitude50to the setpoint threshold46and during the sharp transition52from the setpoint threshold46to the target magnitude50, respectively, according to one embodiment of the envelope power supply signal EPS illustrated inFIGS. 6B, 8B, and 9B.

FIG. 10Aillustrates a transition time58of the sharp transition52of the envelope power supply signal EPS from the target magnitude50to the setpoint threshold46. The transition time58is defined as the time needed for the envelope power supply signal EPS to traverse from ten percent of the sharp transition52to ninety percent of the sharp transition52.FIG. 10Billustrates the transition time58of the sharp transition52of the envelope power supply signal EPS from the setpoint threshold46to the target magnitude50. The transition time58is defined as the time needed for the envelope power supply signal EPS to traverse from ninety percent of the sharp transition52to ten percent of the sharp transition52.

In a first embodiment of the transition time58, the transition time58is less than about one-seventh divided by a normal operation mode bandwidth of the envelope power supply signal EPS. In a second embodiment of the transition time58, the transition time58is less than about one-tenth divided by the normal operation mode bandwidth of the envelope power supply signal EPS. In a third embodiment of the transition time58, the transition time58is less than about one-twentieth divided by the normal operation mode bandwidth of the envelope power supply signal EPS. In a fourth embodiment of the transition time58, the transition time58is less than about one-fiftieth divided by the normal operation mode bandwidth of the envelope power supply signal EPS. In a fifth embodiment of the transition time58, the transition time58is less than about one-hundredth divided by the normal operation mode bandwidth of the envelope power supply signal EPS. In a sixth embodiment of the transition time58, the transition time58is less than about two-hundredth divided by the normal operation mode bandwidth of the envelope power supply signal EPS.

FIG. 11illustrates a process for calibrating the RF communications system10illustrated inFIGS. 1 and 2according to one embodiment of the RF communications system10. The calibration process begins by providing an RF power amplifier24, an RF feedback circuit26, an envelope tracking power supply30, and an supply control circuitry28(Step100). The calibration process proceeds by operating in the calibration mode (Step102). The calibration process is furthered by providing an RF input signal RFI, an envelope power supply signal EPS, and an RF feedback signal RFF (Step104).

The calibration process continues by receiving and amplifying the RF input signal RFI to provide an RF transmit signal RFT using the envelope power supply signal EPS (Step106). The process advances by controlling the envelope tracking power supply30to cause a sharp transition52(FIG. 6B) of the envelope power supply signal EPS when a setpoint of the envelope power supply signal EPS transitions through a setpoint threshold46of the envelope power supply signal EPS (Step108).

The calibration process proceeds by applying a positive delay54(FIGS. 8A and 8B) to the envelope power supply signal EPS (Step110). The calibration process is furthered by measuring a positive feedback sensitivity of the RF feedback circuit26using the RF feedback signal RFF (Step112).

The calibration process proceeds by applying a negative delay56(FIGS. 9A and 9B) to the envelope power supply signal EPS (Step114). The calibration process is furthered by measuring a negative feedback sensitivity of the RF feedback circuit26using the RF feedback signal RFF (Step116).

In one embodiment of the RF communications system10, the delay calibration data32is based on both the positive feedback sensitivity and the negative feedback sensitivity. In an alternate embodiment of the RF communications system10, Steps114and116are omitted, such that the delay calibration data32is based on the positive feedback sensitivity. In an additional embodiment of the RF communications system10, Steps110and112are omitted, such that the delay calibration data32is based on the negative feedback sensitivity.