Reducing effects of RF mixer-based artifact using pre-distortion of an envelope power supply signal

A radio frequency (RF) power amplifier (PA) and an envelope tracking power supply are disclosed. The RF PA receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which at least partially envelope tracks the RF transmit signal, such that the RF input signal has an RF mixer-based artifact. The envelope tracking power supply provides the envelope power supply signal, which includes mixer-based artifact pre-distortion to at least partially remove effects of the RF mixer-based artifact from the RF transmit signal.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate to switching power supplies, radio frequency (RF) power amplifiers, and RF system control circuitry, all of which may be used in RF communication systems.

BACKGROUND

RF emissions from RF transmit signals in cellular communications systems must be low enough to prevent RF receive problems in the cellular communications system and to prevent interference in non-cellular communications systems. Such RF emissions may be called RF spectral emissions since these emissions typically fall outside of a desired RF spectrum. RF spectral emissions may have a number of sources. For example, an RF transmit signal may originate from a complex RF modulator, which may include one or more RF mixers. As such, RF mixers may introduce RF mixer-based artifact into the RF transmit signal, thereby causing RF spectral emissions. Thus, there is a need to reduce effects of RF mixer-based artifact.

SUMMARY

Embodiments of the present disclosure relate to a radio frequency (RF) power amplifier (PA) and an envelope tracking power supply. The RF PA receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which at least partially envelope tracks the RF transmit signal, such that the RF input signal has an RF mixer-based artifact. The envelope tracking power supply provides the envelope power supply signal, which includes mixer-based artifact pre-distortion to at least partially remove effects of the RF mixer-based artifact from the RF transmit signal.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to an RF power amplifier (PA) and an envelope tracking power supply. The RF PA receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which at least partially envelope tracks the RF transmit signal, such that the RF input signal has an RF mixer-based artifact. The envelope tracking power supply provides the envelope power supply signal, which includes mixer-based artifact pre-distortion to at least partially remove effects of the RF mixer-based artifact from the RF transmit signal.

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 transmitter control circuitry22, an RF PA24, an envelope tracking power supply26, and PA bias circuitry28.

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 transmitter control circuitry22. 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 supply26. In one embodiment of the DC power source20, the DC power source20is a battery.

The transmitter control circuitry22is coupled to the envelope tracking power supply26and to the PA bias circuitry28. The envelope tracking power supply26provides an envelope power supply signal EPS to the RF PA24based on the envelope power supply control signal VRMP. The DC source signal VDC provides power to the envelope tracking power supply26. 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. Further, in one embodiment of the envelope tracking power supply26, the RF input signal RFI has an RF mixer-based artifact and the envelope power supply signal EPS at least partially envelope tracks the RF transmit signal RFT. Further, the envelope power supply signal EPS includes mixer-based artifact pre-distortion to at least partially remove effects of the RF mixer-based artifact from the RF transmit signal RFT.

The RF front-end circuitry16receives, processes, and transmits the RF transmit signal RFT via the RF antenna18. In one embodiment of the RF transmitter circuitry12, the transmitter control circuitry22configures the RF transmitter circuitry12based on the transmitter configuration signal PACS. The PA bias circuitry28provides a PA bias signal PAB to the RF PA24. In this regard, the PA bias circuitry28biases the RF PA24via the PA bias signal PAB. In one embodiment of the PA bias circuitry28, the PA bias circuitry28biases the RF PA24based on the transmitter configuration signal PACS. In one embodiment of the RF communications system10, the RF communications system10simultaneously receives and transmits the RF receive signal RFR and the RF transmit signal RFT, respectively. As such, the RF receive signal RFR and the RF transmit signal RFT are full-duplex RF signals.

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, at least one RF amplifier, 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.

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 interface30, which is coupled between the transmitter control circuitry22and a digital communications bus32. The digital communications bus32is 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 transmitter control circuitry22via the digital communications bus32and the digital communications interface30.

FIG. 3shows details of the envelope tracking power supply26illustrated inFIG. 1according to one embodiment of the envelope tracking power supply26. The envelope tracking power supply26includes power supply control circuitry34, a parallel amplifier36, and a switching supply38. The power supply control circuitry34controls the parallel amplifier36and the switching supply38. The parallel amplifier36and the switching supply38provide the envelope power supply signal EPS, such that the parallel amplifier36partially provides the envelope power supply signal EPS and the switching supply38partially provides the envelope power supply signal EPS. The switching supply38may provide power more efficiently than the parallel amplifier36. However, the parallel amplifier36may provide the envelope power supply signal EPS more accurately than the switching supply38. As such, the parallel amplifier36regulates a voltage of the envelope power supply signal EPS based on the setpoint of the envelope power supply signal EPS, and the switching supply38operates to drive an output current from the parallel amplifier36toward zero to maximize efficiency. In this regard, the parallel amplifier36behaves like a voltage source and the switching supply38behaves like a current source.

FIG. 4shows details of RF system control circuitry14illustrated inFIG. 1according to one embodiment of the RF system control circuitry14. The RF system control circuitry14illustrated inFIG. 4is similar to the RF system control circuitry14illustrated inFIG. 1, except the RF system control circuitry14illustrated inFIG. 4includes a complex RF modulator40and envelope signal processing circuitry42. The complex RF modulator40provides the RF input signal RFI to the RF PA24. As such, the complex RF modulator40is external to the RF transmitter circuitry12.

The envelope signal processing circuitry42provides the envelope power supply control signal VRMP to the transmitter control circuitry22. As such, the envelope power supply signal EPS and the mixer-based artifact pre-distortion are both based on the envelope power supply control signal VRMP. In general, the envelope power supply signal EPS is based on the envelope signal processing circuitry42. In one embodiment of the RF communications system10, the RF communications system10receives the RF receive signal RFR, such that the effects of the RF mixer-based artifact include receiver de-sensitization of the RF communications system10.

FIG. 5shows details of the RF system control circuitry14illustrated inFIG. 4according to an alternate embodiment of the RF system control circuitry14. The RF system control circuitry14illustrated inFIG. 5includes the complex RF modulator40and the envelope signal processing circuitry42. The complex RF modulator40includes a modulation vector generator44, a modulation vector processor46, a complex digital-to-analog converter (DAC)48, and RF mixing circuitry50. The envelope signal processing circuitry42includes a mixer-based vector pre-distortion processor52, an envelope vector processor54, and an envelope DAC56. The envelope vector processor54includes at least one look-up-table (LUT)58. In an alternate embodiment of the envelope vector processor54, the LUT58is omitted.

The modulation vector generator44provides modulation vectors MV to the modulation vector processor46and to the mixer-based vector pre-distortion processor52. The modulation vectors MV are representative of modulation of the RF input signal RFI. The modulation vector processor46processes the modulation vectors MV to provide complex digital modulation signals DMS to the complex DAC48In this regard, the modulation vector processor46may control gain, control signal delay, apply amplitude pre-distortion, apply phase pre-distortion, the like, or any combination thereof. The complex DAC48performs a DAC conversion of the complex digital modulation signals DMS to provide complex analog modulation signals AMS to the RF mixing circuitry50. The RF mixing circuitry50modulates at least one RF carrier signal using the complex analog modulation signals AMS to provide the RF input signal RFI.

The mixer-based vector pre-distortion processor52receives a gain control signal GCS, which is used to control a magnitude of the envelope power supply signal EPS (FIG. 4). Since the RF input signal RFI has the RF mixer-based artifact, the modulation vectors MV are used to create the mixer-based artifact pre-distortion. In this regard, the mixer-based vector pre-distortion processor52combines and pre-processes the modulation vectors MV and the gain control signal GCS to provide pre-processed modulation vectors PMV to the envelope vector processor54.

The envelope vector processor54processes the pre-processed modulation vectors PMV to provide a digital envelope control signal DEC. As such, the envelope vector processor54may process the pre-processed modulation vectors PMV, as needed, may operate in conjunction with the modulation vector processor46as needed, or both. In this regard, the envelope vector processor54may use the at least one LUT58, as needed, to provide the digital envelope control signal DEC. The envelope vector processor54may control gain, may control signal delay, the like, or any combination thereof. In one embodiment of the envelope vector processor54, the mixer-based artifact pre-distortion is based on the at least one LUT58.

The envelope DAC56receives and performs a DAC conversion of the digital envelope control signal DEC to provide the envelope power supply control signal VRMP. In one embodiment of the envelope power supply control signal VRMP, the envelope power supply control signal VRMP is a single-ended signal. In an alternate embodiment of the envelope power supply control signal VRMP, the envelope power supply control signal VRMP is a differential signal. In an alternate embodiment of the envelope signal processing circuitry42, the envelope DAC56is omitted, such that the envelope power supply control signal VRMP is provided via the digital communications bus32(FIG. 2).

FIG. 6shows details of the complex RF modulator40illustrated inFIG. 5according to an alternate embodiment of the complex RF modulator40. The complex RF modulator40illustrated inFIG. 6is a quadrature RF modulator. The complex RF modulator40illustrated inFIG. 6is similar to the complex RF modulator40illustrated inFIG. 5, except in the complex RF modulator40illustrated inFIG. 6, the complex DAC48includes an in-phase DAC60and a quadrature-phase DAC62, and the RF mixing circuitry50includes a local oscillator64, an in-phase mixer66, a quadrature-phase mixer68, and an RF combiner70. The RF mixing circuitry50illustrated inFIG. 6is quadrature RF mixing circuitry. Further, the modulation vectors MV include an in-phase modulation vector IMand a quadrature-phase modulation vector QM, the complex digital modulation signals DMS includes an in-phase digital modulation signal IDand a quadrature-phase digital modulation signal QD, and the complex analog modulation signals AMS include an in-phase modulation signal IS and a quadrature-phase modulation signal QS.

The in-phase DAC60receives and DAC converts the in-phase digital modulation signal IDto provide the in-phase modulation signal IS. The quadrature-phase DAC62receives and DAC converts the quadrature-phase digital modulation signal QDto provide the quadrature-phase modulation signal QS. The local oscillator64provides an in-phase local oscillator signal ILO to the in-phase mixer66. The local oscillator64provides a quadrature-phase local oscillator signal QLO to the quadrature-phase mixer68. The in-phase local oscillator signal ILO and the quadrature-phase local oscillator signal QLO are both RF signals. In one embodiment of the in-phase local oscillator signal ILO and the quadrature-phase local oscillator signal QLO, the in-phase local oscillator signal ILO and the quadrature-phase local oscillator signal QLO are phase-shifted from one another by about 90 degrees.

The in-phase mixer66mixes the in-phase modulation signal IS and the in-phase local oscillator signal ILO to provide an in-phase RF signal IRF to the RF combiner70. The quadrature-phase mixer68mixes the quadrature-phase modulation signal QS and the quadrature-phase local oscillator signal QLO to provide a quadrature-phase RF signal QRF to the RF combiner70. The RF combiner70combines the in-phase RF signal IRF and the quadrature-phase RF signal QRF to provide the RF input signal RFI.

In this regard, the in-phase mixer66and the quadrature-phase mixer68form a quadrature RF mixer. As such, in one embodiment of the complex RF modulator40, the complex RF modulator40includes the quadrature RF mixer, such that the RF input signal RFI and the RF mixer-based artifact are both based on the quadrature RF mixer. In one embodiment of the complex RF modulator40, the RF mixer-based artifact is based on a DC offset of the quadrature RF mixer. In one embodiment of the complex RF modulator40, the RF mixer-based artifact includes intermodulation content100(FIG. 9) produced by the quadrature RF mixer. In one embodiment of the complex RF modulator40, desired frequency content90(FIG. 8) of the RF input signal RFI and the RF mixer-based artifact are both based on the quadrature RF mixer.

In one embodiment of the RF system control circuitry14, the modulation vectors MV are represented as quadrature vectors, as shown in EQ. 1 below.
MV=IM+jQMEQ. 1:

However, the quadrature RF mixer may produce both the desired frequency content90(FIG. 8) and an image92(FIG. 8) of the desired frequency content90(FIG. 8). The image92(FIG. 8) may be represented as image vectors IV, which are the complex conjugate of the modulation vectors MV, as shown in EQ. 2 below.
IV=IM−jQMEQ. 2:

A complex image correction factor CF is shown in EQ. 3 below.
CF=AI*ejφI,  EQ. 3:

where AIis an amplitude portion of the correction factor CF and φI is a phase portion of the correction factor CF. As such, in one embodiment of the RF system control circuitry14, pre-distorted vectors PV are based on adding a corrected version of the image vectors IV to the modulation vectors MV, as shown in EQ. 4 below.
PV=MV+(IV*CF)=(IM+jQM)+(IM−jQM)*AI*ejφI.  EQ. 4:

FIG. 7shows details of the complex RF modulator40illustrated inFIG. 5according to another embodiment of the complex RF modulator40. The complex RF modulator40illustrated inFIG. 7is a polar RF modulator. The complex RF modulator40illustrated inFIG. 7is similar to the complex RF modulator40illustrated inFIG. 6, except in the complex RF modulator40illustrated inFIG. 7, the RF mixing circuitry50is polar RF mixing circuitry instead of quadrature RF mixing circuitry. As such, the modulation vectors MV are polar modulation vectors instead of quadrature modulation vectors.

In this regard, an amplitude modulation vector AMand a phase modulation vector φMreplace the in-phase modulation vector IMand the quadrature-phase modulation vector QM, respectively. A digital amplitude modulation signal ADand a digital phase modulation signal φDreplace the in-phase digital modulation signal IDand the quadrature-phase digital modulation signal QD, respectively. An amplitude modulation signal AS and a phase modulation signal φS replace the in-phase modulation signal IS and the quadrature-phase modulation signal QS, respectively.

The RF mixing circuitry50includes the local oscillator64and an RF mixer72. The local oscillator64receives the phase modulation signal φS and provides a phase-modulated local oscillator signal LOP based on the phase modulation signal φS. As such, a phase of the phase-modulated local oscillator signal LOP is based on the phase modulation signal φS. The RF mixer72receives the phase-modulated local oscillator signal LOP and the amplitude modulation signal AS. As such, the RF mixer72mixes the amplitude modulation signal AS and the phase-modulated local oscillator signal LOP to provide the RF input signal RFI.

FIG. 8is a graph illustrating a cellular communications band74associated with the RF communications system10illustrated inFIG. 4according to one embodiment of the RF communications system10. In one embodiment of the RF communications system10, the RF communications system10simultaneously receives and transmits the RF receive signal RFR (FIG. 4) and the RF transmit signal RFT (FIG. 4), respectively. As such, the RF receive signal RFR (FIG. 4) and the RF transmit signal RFT (FIG. 4) are full-duplex RF signals.

The cellular communications band74includes a transmit channel76and a receive channel78. The transmit channel76is associated with the RF transmit signal RFT (FIG. 4) and the receive channel78is associated with the RF receive signal RFR (FIG. 4). The transmit channel76has a transmit channel center frequency80and the receive channel78has a receive channel center frequency82. The transmit channel76has a transmit channel bandwidth84and the receive channel78has a receive channel bandwidth86. A duplex offset88is a difference between the transmit channel center frequency80and the receive channel center frequency82.

In one embodiment of the RF communications system10, while transmitting using certain RF communications protocols, such as some 3G and 4G protocols, the RF input signal RFI (FIG. 4) has a bandwidth that is significantly less than the transmit channel bandwidth84. In the embodiment illustrated inFIG. 8, the RF input signal RFI (FIG. 4) has a desired frequency content90, which has a fairly narrow bandwidth compared to the transmit channel bandwidth84and is toward an upper end of the transmit channel bandwidth84. However, the RF input signal RFI (FIG. 4) also includes an image92of the desired frequency content90. The image92has a fairly narrow bandwidth compared to the transmit channel bandwidth84and is toward a lower end of the transmit channel bandwidth84. The RF mixer-based artifact in the RF input signal RFI (FIG. 4) includes intermodulation content100(FIG. 9) produced by the quadrature RF mixer (FIG. 4). The intermodulation content100(FIG. 9) and non-linearity of the RF PA24(FIG. 4) combine to provide an image foldover94of the image92. While the image foldover94illustrated inFIG. 8does not fall within the receive channel78, a harmonic96of the image foldover94does fall within the receive channel78. As such, reception of the RF receive signal RFR (FIG. 4) may be compromised. To at least partially remove effects of the image foldover94, the envelope power supply signal EPS (FIG. 4) includes mixer-based artifact pre-distortion.

In the embodiment of the RF communications system10illustrated inFIG. 8, the receive channel center frequency82is greater than the transmit channel center frequency80. In an alternate embodiment of the RF communications system10(not shown), the receive channel center frequency82is less than the transmit channel center frequency80. In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), the image foldover94falls within the receive channel78. In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), the image foldover94falls within a non-cellular communications band98(FIG. 9). In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), a harmonic of the image foldover94falls within a non-cellular communications band98(FIG. 9). In one embodiment of the non-cellular communications band98(FIG. 9), the non-cellular communications band98(FIG. 9) is a Personal Handy-phone System (PHS) band.

In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), the RF mixer-based artifact includes the image92of the desired frequency content90of the RF input signal RFI (FIG. 4). In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), the image92of the desired frequency content90of the RF input signal RFI (FIG. 4) falls within the receive channel78. In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), the image92of the desired frequency content90of the RF input signal RFI (FIG. 4) falls within a non-cellular communications band98(FIG. 9). In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), a harmonic96of the image92of the desired frequency content90of the RF input signal RFI (FIG. 4) falls within the receive channel78. In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), a harmonic96of the image92of the desired frequency content90of the RF input signal RFI (FIG. 4) falls within a non-cellular communications band98(FIG. 9).

FIG. 9is a graph illustrating the cellular communications band74and a non-cellular communications band98associated with the RF communications system10illustrated inFIG. 4according to one embodiment of the RF communications system10. The cellular communications band74illustrated inFIG. 9is similar to the cellular communications band74illustrated inFIG. 8, except the cellular communications band74illustrated inFIG. 9does not show the receive channel78. Further, the desired frequency content90of the RF input signal RFI (FIG. 4) is toward a lower end of the transmit channel bandwidth84. The RF mixer-based artifact includes the intermodulation content100produced by the quadrature RF mixer (FIG. 6). The intermodulation content100and non-linearity of the RF PA24(FIG. 4) combine to provide a folding image102of the desired frequency content90of the RF input signal RFI (FIG. 4). The folding image102falls within the non-cellular communications band98. As such, the folding image102may interfere with operations within the non-cellular communications band98.

In one embodiment of the non-cellular communications band98, the non-cellular communications band98is a PHS band. In an alternate embodiment of the RF communications system10(FIG. 4) (not shown), the folding image102falls within the receive channel78(FIG. 8).