U.S. patent application number 14/151786 was filed with the patent office on 2015-07-09 for methods and apparatus for envelope tracking system.
This patent application is currently assigned to MEDIATEK INC.. The applicant listed for this patent is MEDIATEK INC.. Invention is credited to Hao-Ping Hong, Sheng-Hong Yan.
Application Number | 20150194988 14/151786 |
Document ID | / |
Family ID | 53397249 |
Filed Date | 2015-07-09 |
United States Patent
Application |
20150194988 |
Kind Code |
A1 |
Yan; Sheng-Hong ; et
al. |
July 9, 2015 |
METHODS AND APPARATUS FOR ENVELOPE TRACKING SYSTEM
Abstract
A communication unit includes a radio frequency, RF, transmitter
having: a power amplifier, PA, module; and an envelope tracking
system operably coupled to the PA module and having a supply
modulator arranged to variably control a supply voltage for the PA
module in response to a number of input samples of an envelope
signal; wherein the envelope tracking system further includes at
least one slew rate module arranged to re-distribute a maximum slew
rate across the number of input samples in a provision of a
variable power supply to the PA module.
Inventors: |
Yan; Sheng-Hong; (Tainan
City, TW) ; Hong; Hao-Ping; (Hsinchu County,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDIATEK INC. |
Hsin-Chu |
|
TW |
|
|
Assignee: |
MEDIATEK INC.
Hsin-Chu
TW
|
Family ID: |
53397249 |
Appl. No.: |
14/151786 |
Filed: |
January 9, 2014 |
Current U.S.
Class: |
375/297 |
Current CPC
Class: |
H03F 2200/105 20130101;
H03F 2200/504 20130101; H04B 2001/0408 20130101; H03F 3/24
20130101; H04L 27/3411 20130101; H04B 1/0475 20130101; H03F
2200/465 20130101; H04B 2001/0416 20130101 |
International
Class: |
H04B 1/04 20060101
H04B001/04 |
Claims
1. A communication unit comprising: a radio frequency, RF,
transmitter comprising: a power amplifier, PA, module; and an
envelope tracking system operably coupled to the PA module and
comprising a supply modulator arranged to variably control a supply
voltage for the PA module in response to a number of input samples
of an envelope signal; wherein the envelope tracking system further
comprises at least one slew rate module arranged to re-distribute a
maximum slew rate across the number of input samples in a provision
of a variable power supply to the PA module, and the supply
modulator comprises at least one DC-DC converter operably coupled
to a linear amplifier arranged to generate the variable power
supply to the PA module, such that the at least one slew rate
module provides the re-distributed maximum slew rate across the
number of input samples of the envelope signal to the at least one
DC-DC converter.
2. (canceled)
3. A communication unit comprising: a radio frequency, RF,
transmitter comprising: a power amplifier, PA, module; and an
envelope tracking system operably coupled to the PA module and
comprising a supply modulator arranged to variably control a supply
voltage for the PA module in response to a number of input samples
of an envelope signal; wherein the envelope tracking system further
comprises at least one slew rate module arranged to re-distribute a
maximum slew rate across the number of input samples in a provision
of a variable power supply to the PA module by averaging and evenly
re-distributing a plurality of the number of input samples between
a minimum value to a maximum value.
4. A communication unit comprising: a radio frequency, RF,
transmitter comprising: a power amplifier, PA, module; and an
envelope tracking system operably coupled to the PA module and
comprising a supply modulator arranged to variably control a supply
voltage for the PA module in response to a number of input samples
of an envelope signal.sup.., wherein the envelope tracking system
further comprises at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module,
the supply modulator is a hybrid supply modulator comprising a
linear amplifier, and the at least one slew rate module is further
arranged to reduce a bandwidth of an envelope signal applied to the
linear amplifier with a re-distribution of a maximum slew rate
across the number of input samples.
5. A communication unit comprising: a radio frequency, RF,
transmitter comprising: a power amplifier, PA, module; and an
envelope tracking system operably coupled to the PA module and
comprising a supply modulator arranged to variably control a supply
voltage for the PA module in response to a number of input samples
of an envelope signal.sup.., wherein the envelope tracking system
further comprises at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module,
the supply modulator is at least one from a group of: a hybrid
supply modulator, a switching modulator, and the at least one slew
rate module is further arranged to reduce a bandwidth of an
envelope signal as an input of the supply modulator in a
re-distribution of a maximum slew rate across the number of input
samples.
6. The communication unit of claim 1 wherein the envelope tracking
system comprises an envelope detector arranged to detect an
envelope of an input signal and provide the detected envelope to at
least one envelope mapping module arranged to map the envelope of
the input signal to a supply voltage input to the at least one slew
rate module.
7. A communication unit comprising: a radio frequency, RF,
transmitter comprising: a power amplifier, PA, module; and an
envelope tracking system operably coupled to the PA module and
comprising a supply modulator arranged to variably control a supply
voltage for the PA module in response to a number of input samples
of an envelope signal.sup.., wherein the envelope tracking system
further comprises at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module;
the envelope tracking system comprises an envelope detector
arranged to detect an envelope of an input signal and provide the
detected envelope to at least one envelope mapping module arranged
to map the envelope of the input signal to a supply voltage input
to the at least one slew rate module; and the envelope tracking
system comprises at least two envelope mapping modules wherein: a
first envelope mapping module is arranged to map the envelope of
the input signal to provide a supply voltage for a linear amplifier
operably coupled to the at least one slew rate module; and a second
envelope mapping module is arranged to map the envelope of the
input signal to provide a supply voltage for the PA module.
8. The communication unit of claim 7 wherein the RF transmitter
further comprises a digital predistortion module arranged to
receive and predistort the input envelope signal, wherein the
second envelope mapping module is arranged to provide an input
envelope indication of the input envelope signal to the digital
predistortion module such that the digital predistortion module
distorts the input envelope signal based at least partly on the
input envelope indication of the input envelope signal.
9. The communication unit of claim 7 wherein the envelope tracking
system comprises at least two slew rate modules operably coupled to
the respective at least two envelope mapping modules wherein a
second slew rate module operably coupled between a second envelope
mapping module and the linear amplifier and arranged to provide a
slew rate adjusted representation of an input envelope indication
of the input envelope signal to the linear amplifier.
10. The communication unit of claim 9 wherein the RF transmitter
further comprises a digital predistortion module arranged to
receive and predistort the input envelope signal, wherein both a
first slew rate module and the second slew rate module are arranged
to provide a slew rate adjusted representation of the input
envelope indication of the input envelope signal to the digital
predistortion module such that the digital predistortion module
distorts the input envelope signal based at least partly on the
input envelope indications of the input envelope signal.
11. An integrated circuit for a communication unit comprising a
radio frequency, RF, transmitter comprising a power amplifier, PA,
module; wherein the integrated circuit comprises: an envelope
tracking system operably couplable to the PA module and comprising:
a supply modulator arranged to variably control a supply voltage
for the PA module in response to a number of input samples of an
envelope signal; and at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module;
wherein the supply modulator comprises at least one DC-DC converter
operably coupled to a linear amplifier arranged to generate the
variable power supply to the PA module, such that the at least one
slew rate module provides the re-distributed maximum slew rate
across the number of input samples of the envelope signal to the at
least one DC-DC converter.
12. A method of envelope tracking in a wireless communication unit
comprising a radio frequency, RF, transmitter having a power
amplifier, PA, module and an envelope tracking system comprising a
supply modulator, the method comprising: receiving an input signal
with an envelope that varies with time at an input of the RF
transmitter; detecting an envelope of the input signal; mapping the
detected envelope of the input signal to a power supply voltage to
be applied to the PA module to produce a voltage reference signal
sampling the detected voltage reference signal; re-distributing a
maximum slew rate across a plurality of input samples of the
detected voltage reference signal to provide an output sample
variably control a supply voltage for the PA module.
13. The method of claim 12, wherein sampling the detected voltage
reference signal comprises: processing a plurality of input
samples; and calculating a current slew rate of each input
sample.
14. The method of claim 12, further comprising: repeating sampling
the detected voltage reference signal; and re-distributing the
maximum slew rate across a number of input samples of the detected
voltage reference signal to variably control a supply voltage for
the PA module.
15. The method of claim 12, wherein re-distributing a maximum slew
rate across a plurality of input samples of the detected voltage
reference signal comprises averaging a plurality of the number of
input samples between a minimum value to a maximum value.
16. The method of claim 12, further comprising providing a slew
rate adjusted representation of an input envelope indication of the
input envelope signal to a linear amplifier of a supply
modulator.
17. The method of claim 12, further comprising: mapping an envelope
of the input signal by a first envelope mapping module to provide a
supply voltage for a linear amplifier operably coupled to at least
one slew rate module; and mapping the envelope of the input signal
by a second envelope mapping module to provide a supply voltage for
the PA module.
18. The method of claim 12, further comprising: providing an input
envelope indication of the input envelope signal to a digital
predistortion module; and distorting the input envelope signal
based at least partly on the input envelope indication of the input
envelope signal.
19. The method of claim 18, further comprising: providing at least
one slew rate adjusted representation of at least one input
envelope indication of the input envelope signal to the digital
predistortion module; and distorting the input envelope signal
based at least partly on the at least one input envelope
indications of the input envelope signal.
20. A non-transitory computer program product comprising executable
program code for envelope tracking in a wireless communication unit
comprising a radio frequency, RF, transmitter, the executable
program code operable for, when executed at a communication unit,
performing the method of claim 12.
21. An integrated circuit for a communication unit comprising a
radio frequency, RF, transmitter comprising a power amplifier, PA,
module; wherein the integrated circuit comprises: an envelope
tracking system operably couplable to the PA module and comprising:
a supply modulator arranged to variably control a supply voltage
for the PA module in response to a number of input samples of an
envelope signal; and at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module
by averaging and evenly re-distributing a plurality of the number
of input samples between a minimum value to a maximum value.
22. An integrated circuit for a communication unit comprising a
radio frequency, RF, transmitter comprising a power amplifier, PA,
module; wherein the integrated circuit comprises: an envelope
tracking system operably couplable to the PA module and comprising:
a supply modulator arranged to variably control a supply voltage
for the PA module in response to a number of input samples of an
envelope signal; and at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module;
wherein the supply modulator is a hybrid supply modulator
comprising a linear amplifier, and the at least one slew rate
module is further arranged to reduce a bandwidth of an envelope
signal applied to the linear amplifier with a re-distribution of a
maximum slew rate across the number of input samples.
23. An integrated circuit for a communication unit comprising a
radio frequency, RF, transmitter comprising a power amplifier, PA,
module; wherein the integrated circuit comprises: an envelope
tracking system operably couplable to the PA module and comprising:
a supply modulator arranged to variably control a supply voltage
for the PA module in response to a number of input samples of an
envelope signal; and at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module;
wherein the supply modulator is at least one from a group of: a
hybrid supply modulator, a switching modulator, and the at least
one slew rate module is further arranged to reduce a bandwidth of
an envelope signal as an input of the supply modulator in a
re-distribution of a maximum slew rate across the number of input
samples.
24. An integrated circuit for a communication unit comprising a
radio frequency, RF, transmitter comprising a power amplifier, PA,
module; wherein the integrated circuit comprises: an envelope
tracking system operably couplable to the PA module and comprising:
a supply modulator arranged to variably control a supply voltage
for the PA module in response to a number of input samples of an
envelope signal; and at least one slew rate module arranged to
re-distribute a maximum slew rate across the number of input
samples in a provision of a variable power supply to the PA module;
wherein the envelope tracking system comprises an envelope detector
arranged to detect an envelope of an input signal and provide the
detected envelope to at least one envelope mapping module arranged
to map the envelope of the input signal to a supply voltage input
to the at least one slew rate module; and the envelope tracking
system comprises at least two envelope mapping modules wherein: a
first envelope mapping module is arranged to map the envelope of
the input signal to provide a supply voltage for a linear amplifier
operably coupled to the at least one slew rate module; and a second
envelope mapping module is arranged to map the envelope of the
input signal to provide a supply voltage for the PA module.
Description
BACKGROUND
[0001] 1. Field of the invention
[0002] The field of this invention relates to methods and apparatus
for an envelope tracking system, and in particular to methods and
apparatus for improving an efficiency of an envelope tracking
system for a power amplifier module, for example within a radio
frequency (RF) transmitter module of a wireless communication
unit.
[0003] 2. Background of the Invention
[0004] A primary focus and application of the present invention is
the field of radio frequency (RF) power amplifiers capable of use
in wireless telecommunication applications. Continuing pressure on
the limited spectrum available for radio communication systems is
forcing the development of spectrally-efficient linear modulation
schemes. Since the envelopes of a number of these linear modulation
schemes fluctuate, these result in the average power delivered to
the antenna being significantly lower than the maximum power,
leading to poor efficiency of the power amplifier. Specifically, in
this field, there has been a significant amount of research effort
in developing high efficiency topologies capable of providing high
performances in the `back-off` (linear) region of the power
amplifier.
[0005] Linear modulation schemes require linear amplification of
the modulated signal in order to minimise undesired out-of-band
emissions from spectral re-growth. However, the active devices used
within a typical RF amplifying device are inherently non-linear by
nature. Only when a small portion of the consumed DC power is
transformed into RF power, can the transfer function of the
amplifying device be approximated by a straight line, i.e. as in an
ideal linear amplifier case. This mode of operation provides a low
efficiency of DC to RF power conversion, which is unacceptable for
portable (subscriber) wireless communication units. Furthermore,
the low efficiency is also recognised as being problematic for the
base stations.
[0006] Additionally, the emphasis in portable (subscriber)
equipment is to increase battery life. To achieve both linearity
and efficiency, so called linearisation techniques are used to
improve the linearity of the more efficient amplifier classes, for
example class `AB`, `B` or `C` amplifiers. A number and variety of
linearising techniques exist, which are often used in designing
linear transmitters, such as Cartesian Feedback, Feed-forward, and
Adaptive Pre-distortion.
[0007] Voltages at the output of the linear, e.g. Class AB,
amplifier are typically set by the requirements of the final RF
power amplifier (PA) device. Generally, the minimum voltage of the
PA is significantly larger than that required by the output devices
of the Class AB amplifier. Hence, they are not the most efficient
of amplification techniques. The efficiency of the transmitter
(primarily the PA) is determined by the voltage across the output
devices, as well as any excess voltage across any pull-down device
components due to the minimum supply voltage (Vmin) requirement of
the PA.
[0008] In order to increase the bit rate used in transmit uplink
communication channels, larger constellation modulation schemes,
with an amplitude modulation (AM) component are being investigated
and, indeed, becoming required. These modulation schemes, such as
sixteen-bit quadrature amplitude modulation (16-QAM), require
linear PAs and are associated with high `crest` factors (i.e. a
degree of fluctuation) of the modulation envelope waveform. This is
in contrast to the previously often-used constant envelope
modulation schemes and can result in significant reduction in power
efficiency and linearity. To help overcome such efficiency and
linearity issues a number of solutions have been proposed.
[0009] One known technique, as illustrated in the block diagram 100
of FIG. 1, relates to controlling the supply voltage 120 provided
to the power amplifier 140. The illustrated technique is known as
average power tracking (APT). With APT, an average power level 105
of the transmitted signal is determined and applied to an APT-Vpa
mapping module 110 that determines a supply voltage (Vpa) 120 to be
applied to the PA 140 based on the determined average power level.
This signal is then applied to a DC-DC converter 115 and the
resultant (output) voltage is applied to the PA 140 as its supply
voltage (Vpa) 120. This technique is known to provide high
efficiency, but the speed of signal tracking is limited. Hence,
DC-DC converters are typically used in average power tracking (APT)
designs to accommodate signal tracking. One known problem with this
technique is that APT operates with less efficiency at the higher
output power levels when the peak to average power ratio (PAPR)
back-off is large, which is predominantly the case for more complex
modulation schemes.
[0010] Another known supply voltage technique 200 is envelope
tracking (ET), illustrated in FIG. 2, which relates to modulating
the radio frequency (RF) power amplifier (PA) supply voltage (Vpa)
220 to match (e.g. track) the envelope of the radio frequency
waveform being transmitted by the RF PA 240. Typically, ET systems
control the RF PA supply voltage 220 in order to improve PA
efficiency through selecting a lower supply voltage dependent upon
an instantaneous envelope of the input signal. ET systems are often
also designed to improve linearity by selecting a RF PA supply
voltage 220 dependent upon a constant PA amplification gain. A
digital (quadrature) input signal 202 is input to an RF transmitter
230, whose output provides an input power level 235 to the RF PA
240. Concurrently, the digital (quadrature) input signal 202 is
applied to an envelope detector 204 arranged to determine a
real-time envelope of the signal to be transmitted (e.g. radiated)
. The determined real-time envelope signal output from the envelope
detector 204 is input to an envelope mapping function 210, which is
arranged to determine a suitable PA supply voltage (Vpa) 220 to be
applied to the PA 240 in order to substantially match the
instantaneous real-time envelope of the signal to be transmitted.
The output from the envelope mapping function 210 is input to a
delay control function 212 that aligns, in time, the PA supply
voltage (Vpa) 220 to the signal being passed through RF transmitter
230. The output from the delay control function 212 is input to a
supply modulator 214 that provides the PA supply voltage (Vpa) 220
to be applied to the PA 240.
[0011] With ET, the instantaneous PA supply voltage (Vpa) 220 of
the wireless transmitter is caused to approximately track the
instantaneous envelope (ENV) of the transmitted RF signal. Thus,
since the power dissipation in the PA 240 is proportional to the
difference between its supply voltage and output voltage, ET may
provide an increase in PA efficiency, reduced heat dissipation,
improved linearity and increased maximum output power 225, whilst
allowing the PA to produce the intended RF output. However, the
total system efficiency is affected by supply modulator efficiency
that is related to the supply modulator design, supply voltage
range, bandwidth and PA loading, which typically results in ET
modulator efficiency not being high enough for most applications.
The envelope mapping function 210 between ENV and Vpa is critical
for optimum performance (efficiency, gain, and adjacent channel
power (ACP)). Also critical to system performance is timing
alignment between the RF signal and Vpa at the PA.
[0012] A yet further known technique 300 is to combine envelope
tracking (ET) with digital pre-distortion (DPD), as illustrated in
FIG. 3. Here, control/manipulation of the input waveform/signal in
the digital domain is performed in order to compensate for PA
nonlinearity (AM-to-AM and AM-to-PM) effects, thereby improving PA
output linearity based on prior information or measured data of the
PA system. Again, a digital (quadrature) input signal 302 is input
to an RF transmitter 330 via a digital pre-distortion (DPD)
function 326, whose output provides an input power level 335 to the
RF PA 340. Concurrently, the digital (quadrature) input signal 302
is applied to an envelope detector 304 arranged to determine a
real-time envelope of the signal to be transmitted (e.g. radiated).
The determined real-time envelope signal output from the envelope
detector 304 is input to an envelope mapping function 310, which is
arranged to determine a suitable control voltage (Vdc) 320 to be
applied to the PA 340
[0013] In this manner, envelope-tracking can be combined with
digital pre-distortion (DPD) on the RF signal to improve adjacent
channel protection (ACP) robustness. However, since the ET system
is often a multichip implementation involving function blocks in
digital baseband (BB), analogue BB, RF transceiver, power
management and PA, consistent ET system performance cannot easily
be guaranteed across all devices by hardware.
[0014] The overall transmitter efficiency is, in large part,
dependent upon the efficiency of both the PA and the supply
modulator path. In particular, the inventors have recognised that
the efficiency usually decreases as the input signal bandwidth
increases.
[0015] A number of other modulator designs are known. For example,
a linear regulator/modulator design may be used, whereas although
signal tracking is fast it is known to suffer from poor efficiency.
As a result of the poor efficiency, it is rarely, if ever, used for
ET applications. Another example is a hybrid modulator, which
comprises a switching modulator and linear amplifier. In hybrid
modulators, most of the envelope energy is delivered by the
switching modulator, whilst the wide bandwidth of the envelope
signal is supported by linear amplifier. However, the linear
amplifier needs to accommodate large envelope bandwidths and also
suppress switching noise. These requirements have an adverse impact
on the hybrid modulator efficiency.
[0016] A paper titled `Slew-rate limited envelopes for driving
envelope tracking amplifiers` (by Gabriel Montoro, et al. and
published by the Dept of Signal Theory and Communications by the
Universitat Politecnica de Catalunya in Barcelona, Spain),
describes a technique that sets a maximum value for a slew-rate
limiter in an ET path, but has been identified as introducing some
delays and out-of-band emissions of the supply modulator under
varying load conditions.
[0017] A yet further paper titled `A DSP structure authorizing
reduced-bandwidth DC/DC Converters for Dynamic Supply of RF Power
Amplifiers in Wideband Applications` (by Albert Cesari, et al. and
published by the Groupe Integration de Systemes de Gestion de
l'Energie in Toulouse, France), describes a technique that tracks a
peak of an original envelope signal, but has been identified as
also introducing some delays and creating poor out-of-band
emissions of the supply modulator due to use of a DC/DC converter
input step signal.
[0018] Thus, there is a need for a more efficient and cost
effective solution to the problem of improving the overall
transmitter efficiency, and in particular the supply modulation
efficiency.
SUMMARY
[0019] Accordingly, the invention seeks to mitigate, alleviate or
eliminate one or more of the above mentioned disadvantages singly
or in any combination.
[0020] Aspects of the invention provide a communication unit, an
integrated circuit and a method of envelope tracking in a wireless
communication unit.
[0021] According to a first aspect of the invention, there is
provided a communication unit comprising a radio frequency, RF,
transmitter comprising: a power amplifier, PA, module; and an
envelope tracking system operably coupled to the PA module and
comprising a supply modulator arranged to variably control a supply
voltage for the PA module in response to a number of input samples
of an envelope signal. The envelope tracking system further
comprises at least one slew rate module arranged to re-distribute a
maximum slew rate across the number of input samples in a provision
of a variable power supply to the PA module.
[0022] In this manner, the at least one slew rate module
re-distributes a maximum slew rate across the number of input
samples and consequently avoids a step input to the supply
modulator that would cause out-of-band emissions, particularly
under varying load conditions. Consequently, a more efficient and
cost effective solution to the problem of improving the overall
transmitter efficiency is improved, and in particular the supply
modulation efficiency.
[0023] In an optional example embodiment, the supply modulator may
comprise at least one DC-DC converter operably coupled to a linear
amplifier arranged to generate the variable power supply to the PA
module, such that the at least one slew rate module may provide the
re-distributed maximum slew rate across the number of input samples
of the envelope signal to the at least one DC-DC converter. In this
manner, the at least one slew rate module re-distributes a maximum
slew rate across the number of input samples and consequently
avoids a step input to a DC-DC converter or a linear amplifier in
the supply modulator that would cause out-of-band emissions,
particularly under varying load conditions.
[0024] In an optional example embodiment, the at least one slew
rate module maybe arranged to re-distribute the maximum slew rate
across the number of input samples by averaging a plurality of the
number of input samples between a minimum value to a maximum value.
In this manner, a simple and evenly distribution of the slew rate
may be achieved.
[0025] In an optional example embodiment, the supply modulator is a
hybrid supply modulator comprising a linear amplifier and the at
least one slew rate module is further arranged to reduce a
bandwidth of an envelope signal applied to the linear amplifier
with the re-distribution of a maximum slew rate across the number
of input samples. In this manner, by reducing a bandwidth of
signals applied to the linear amplifier, there maybe a reduced
out-of-band emission level output from the linear amplifier, and/or
increased power headroom in the linear amplifier performance. This
may allow less expensive and/or lower performance linear amplifiers
to be used.
[0026] In an optional example embodiment, the supply modulator may
beat least one from a group of: a hybrid supply modulator, a
switching modulator, and wherein the at least one slew rate module
may be further arranged to reduce a bandwidth of an envelope signal
as an input of the supply modulator in a re-distribution of a
maximum slew rate across the number of input samples. In this
manner, a variety of supply modulator designs maybe used to benefit
from the concepts described herein.
[0027] In an optional example embodiment, the envelope tracking
system may comprise an envelope detector arranged to detect an
envelope of an input signal and provide the detected envelope to at
least one envelope mapping module arranged to map the envelope of
the input signal to a supply voltage input to the at least one slew
rate module. In this manner, the at least one slew rate module may
limit a slew rate of a mapped reference voltage to be applied to a
supply of the PA.
[0028] In an optional example embodiment, the envelope tracking
system may comprise at least two envelope mapping modules wherein a
first envelope mapping module may be arranged to map the envelope
of the input signal to provide a supply voltage fora linear
amplifier operably coupled to the at least one slew rate module;
and a second envelope mapping module is arranged to map the
envelope of the input signal to provide a supply voltage for the PA
module.
[0029] In an optional example embodiment, the RF transmitter
further comprises a digital predistortion module arranged to
receive and predistort the input envelope signal, wherein the
second envelope mapping module is arranged to provide an input
envelope indication of the input envelope signal to the digital
predistortion module such that the digital predistortion module
distorts the input envelope signal based at least partly on the
input envelope indication of the input envelope signal.
[0030] In an optional example embodiment, the envelope tracking
system comprises at least two slew rate modules operably coupled to
the respective at least two envelope mapping modules wherein a
second slew rate module operably coupled between a second envelope
mapping module and the linear amplifier and arranged to provide a
slew rate adjusted representation of an input envelope indication
of the input envelope signal to the linear amplifier.
[0031] In an optional example embodiment, the RF transmitter may
further comprise a digital predistortion module arranged to receive
and predistort the input envelope signal, wherein both a first slew
rate module and the second slew rate module are arranged to provide
a slew rate adjusted representation of the input envelope
indication of the input envelope signal to the digital
predistortion module such that the digital predistortion module
distorts the input envelope signal based at least partly on the
input envelope indications of the input envelope signal.
[0032] According to a second aspect of the invention, there is
provided an integrated circuit for a communication unit comprising
a radio frequency, RF, transmitter comprising a power amplifier,
PA, module. The integrated circuit comprises an envelope tracking
system operably couplable to the PA module and comprising: a supply
modulator arranged to variably control a supply voltage for the PA
module in response to a number of input samples of an envelope
signal; and at least one slew rate module arranged to re-distribute
a maximum slew rate across the number of input samples in a
provision of a variable power supply to the PA module.
[0033] According to a third aspect of the invention, there is
provided a method of envelope tracking in a wireless communication
unit comprising a radio frequency, RF, transmitter having a power
amplifier, PA, module and an envelope tracking system comprising a
supply modulator. The method comprises: receiving an input signal
with an envelope that varies with time at an input of the RF
transmitter; detecting an envelope of the input signal; mapping the
detected envelope of the inpuit signal to a power supply voltage to
be applied to the PA module to produce a voltage reference signal;
sampling the detected voltage reference signal; re-distributing a
maximum slew rate across a plurality of input samples of the
detected voltage reference signal to provide an output sample
variably control a supply voltage for the PA module.
[0034] In an optional example embodiment, sampling the detected
voltage reference signal comprises: processing a plurality of input
samples; and calculating a current slew rate of each input
sample.
[0035] In an optional example embodiment, the method may further
comprise repeating sampling the detected voltage reference signal;
and re-distributing the maximum slew rate across a number of input
samples of the detected voltage reference signal to variably
control a supply voltage for the PA module.
[0036] In an optional example embodiment, re-distributing a maximum
slew rate across a plurality of input samples of the detected
voltage reference signal comprises averaging a plurality of the
number of input samples between a minimum value to a maximum
value.
[0037] In an optional example embodiment, re-distributing a maximum
slew rate across a plurality of input samples of the detected
voltage reference signal comprises evenly distributing the maximum
slew rate across an output signal
[0038] According to a fourth aspect of the invention, there is
provided a non-transitory computer program product comprising
executable program code for envelope tracking in a wireless
communication unit comprising a radio frequency, RF, transmitter,
the executable program code operable for, when executed at a
communication unit, performing the method of the third aspect.
[0039] These and other aspects of the invention will be apparent
from, and elucidated with reference to, the embodiments described
hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] Further details, aspects and embodiments of the invention
will be described, by way of example only, with reference to the
drawings. In the drawings, like reference numbers are used to
identify like or functionally similar elements. Elements in the
figures are illustrated for simplicity and clarity and have not
necessarily been drawn to scale.
[0041] FIG. 1 illustrates a known block diagram architecture of an
average power tracking (APT) technique.
[0042] FIG. 2 illustrates a known block diagram architecture of
envelope tracking (ET) technique.
[0043] FIG. 3 illustrates a known block diagram architecture using
a combination of envelope tracking (ET) with digital pre-distortion
(DPD) .
[0044] FIG. 4 illustrates a simplified generic block diagram of an
example of a communication unit.
[0045] FIG. 5 illustrates a block diagram of a dynamic power
amplifier supply modulation circuit employing envelope tracking and
adapted in accordance with some examples of the invention,
[0046] FIG. 6 illustrates an example flowchart of a method of
controlling a power amplifier supply modulation circuit employing
envelope tracking, according to some examples of the invention.
[0047] FIG. 7 illustrates a further block diagram of a dynamic
power amplifier supply modulation circuit employing envelope
tracking and adapted in accordance with some examples of the
invention
[0048] FIG. 8 illustrates a yet further block diagram of a dynamic
power amplifier supply modulation circuit, according to some
examples of the invention.
[0049] FIG. 9 illustrates a simplified example of a typical
computing system that may be employed to implement signal
processing functionality in embodiments of the invention.
DETAILED DESCRIPTION
[0050] Examples of the invention will be described in terms of one
or more integrated circuits for use in a wireless communication
unit, such as user equipment in third generation partnership
project (3GPP.TM.) parlance. However, it will be appreciated by a
skilled artisan that the inventive concept herein described may be
embodied in any type of integrated circuit, wireless communication
unit or wireless transmitter that comprises or forms a part of an
envelope tracking system. Furthermore, because the illustrated
embodiments of the present invention may for the most part, be
implemented using electronic components and circuits known to those
skilled in the art, details will not be explained in any greater
extent than that considered necessary as illustrated below, for the
understanding and appreciation of the underlying concepts of the
present invention and in order not to obfuscate or distract from
the teachings of the present invention.
[0051] Examples of the invention will be described in terms of an
ET architecture that comprises a dynamic power amplifier supply
modulation circuit configured to reduce a slew rate and/or
bandwidth of an envelope signal or a voltage supply reference in
order to improve a supply modulator efficiency. In this manner, the
whole transmitter efficiency may be improved, since the whole
transmitter system efficiency is equal to a multiplication of the
supply modulator efficiency and PA efficiency. In one example, a
reduced bandwidth of the envelope signal may be applied at the
input of a switching modulator or hybrid modulator, in order to
increase its efficiency, for example to reduce switching loss
and/or a bandwidth requirement for analog circuits contained in the
transmitter. In one example, a reduced bandwidth of envelope signal
may be used as the supply voltage of a linear amplifier employing a
hybrid modulator in order to increase its efficiency, for example
to reduce a voltage headroom of the linear amplifier, thereby
increasing its operating efficiency.
[0052] Referring first to FIG. 4, a block diagram of a wireless
communication unit (sometimes referred to as a mobile subscriber
unit (MS) in the context of cellular communications or a user
equipment (UE) in terms of a 3.sup.rd generation partnership
project (3GPP.TM. communication system) is shown, in accordance
with one example embodiment of the invention. The wireless
communication unit 400 contains an antenna 402 preferably coupled
to a duplex filter or antenna switch 404 that provides isolation
between receive and transmit chains within the wireless
communication unit 400.
[0053] The receiver chain 410, as known in the art, includes
receiver front-end circuitry 406 (effectively providing reception,
filtering and intermediate or base-band frequency conversion). The
front-end circuitry 406 is coupled to a signal processing function
408. An output from the signal processing function 408 is provided
to a suitable user interface, which may encompass a screen or flat
panel display. A controller 414 maintains overall subscriber unit
control and is coupled to the receiver front-end circuitry 406 and
the signal processing function 408 (generally realised by a digital
signal processor (DSP)). The controller 414 is also coupled to a
memory device 416 that selectively stores various operating
regimes, such as decoding/encoding functions, synchronisation
patterns, code sequences, and the like.
[0054] In accordance with examples of the invention, the memory
device 416 stores modulation data, and power supply data for use in
supply voltage control to track the envelope of the radio frequency
waveform to be output by the wireless communication unit 400.
Furthermore, a timer 418 is operably coupled to the controller 414
to control the timing of operations (transmission or reception of
time-dependent signals and in a transmit sense the time domain
variation of the PA supply voltage within the wireless
communication unit 400).
[0055] As regards the transmit chain 420, this essentially includes
the user interface, which may encompass a keypad or touch screen,
coupled in series via signal processing function 408 to
transmitter/modulation circuitry 422. The transmitter/modulation
circuitry 422 processes input signals for transmission and
modulates and up-converts these signals to a radio frequency (RF)
signal for amplifying in the power amplifier module or integrated
circuit 424. RF signals amplified by the PA module (or PA
integrated circuit) 424 are passed to the antenna 402. The
transmitter/modulation circuitry 422, power amplifier module 424
and PA supply voltage modulator 425 are each operationally
responsive to the controller 414, with the PA supply voltage
modulator 425 additionally responding to a reproduction of the
envelope modulated waveform from the transmitter/modulation
circuitry 422. In this manner, a PA supply voltage modulator 425 is
arranged to modulate the supply voltage to the PA 424 in accordance
with the envelope modulated waveform, thereby performing envelope
tracking modulation of the supply voltage provided to the PA
424.
[0056] The signal processor function in the transmit chain may be
implemented as distinct from the processor 408 in the receive chain
410. Alternatively, a single processor may be used to implement
processing of both transmit and receive signals, as shown in FIG.
4. Clearly, the various components within the wireless
communication unit 400 can be realised in discrete or integrated
component form, with an ultimate structure therefore being merely
an application-specific or design selection.
[0057] Furthermore, in accordance with examples of the invention,
the transmitter/modulation circuitry 422, together with power
amplifier 424, PA supply voltage modulator 425, memory device 416,
timer function 418 and controller 414 have been adapted to generate
a power supply to be applied to the PA 424. For example, a power
supply is generated that is suitable for a wideband linear power
amplifier, and configured to track the envelope waveform applied to
the PA 424.
[0058] Referring to FIG. 5, there is illustrated an example block
diagram of a dynamic power amplifier supply modulation circuit 500,
adapted in accordance with some examples of the invention. In one
example, the dynamic power amplifier supply modulation circuit 500
may be employed in the communication unit 400 of FIG. 4. The
example block diagram of a dynamic power amplifier supply
modulation circuit 500 supports ET as well as optionally supporting
digital pre-distortion (DPD).
[0059] The envelope tracking system comprises: an envelope detector
505 arranged to receive and detect an instantaneous envelope of the
input transmit signal 510, i.e. digital I/Q input signal 510, and
calculate an envelope value thereof, where supply modulator 520 is
operably coupled to a supply 535 of the PA module 555 and arranged
to variably control a supply voltage therefor.
[0060] Further, in this illustrated example, the envelope detector
505 may be operably coupled to a first envelope to reference
voltage (Vref) mapping module-1 515, which provides a mapping value
(Vref1) from the calculated envelope value of the digital I/Q input
signal 510, based on the detected envelope, to a supply voltage
modulator 520 (sometimes referred to as an ET modulator or supply
modulator). The mapping value (Vref1) is used to generate a supply
voltage of Linear Amp 570 to create a target output power level 540
from the PA 555. In this example, utilising envelope tracking to
control the output of the PA 555 may improve the efficiency of the
PA 555 and utilising envelope tracking to control the output of the
Linear Amp 570 may improve the efficiency of the Linear Amplifier
570.
[0061] In this illustrated example, a slew-rate reduction module
518 may be operably coupled between first envelope mapping module-1
515 and supply voltage modulator 520. Supply voltage modulator 520,
which in this example is a hybrid supply voltage modulator,
comprises a first DC-DC converter 522 arranged to receive the
slew-rate modified version (V1) of the first envelope to Vref
mapping value (Vref1).
[0062] The first DC-DC converter 522 then outputs a converted
voltage reference signal to linear amplifier 570. In this manner,
slew-rate reduction module 518 is able to control the supply
voltage of the linear amplifier 570. In one example, control of
slew-rate reduction module 518 may be performed by controller 414
of FIG. 4. In other examples, control of slew-rate reduction module
518 may be performed by any other signal processor or controller
module.
[0063] Linear amplifier 570 also receives a second envelope to
Vref2 mapping value (Vref2) output from a second envelope mapping
module-2 525, in order to generate the PA supply voltage, Vpa 535.
In accordance with some example embodiments, more accurate control
of Vpa 535 may improve PA efficiency by reducing the voltage
headroom of PA 555. In the same manner as first envelope to
reference voltage (Vref) mapping module-1 515, second envelope
mapping module-2 525 also receives the calculated envelope value
from envelope detector 505 and provides a mapping value direct to
linear amplifier 570. Notably, the RF transmitter 500 further
comprises a second envelope to supply mapping component 525
operably coupled to envelope detector 505 arranged to provide an
input (Vref2) to linear amplifier 570 of the supply modulator
520.
[0064] According to some example embodiments, the communication
unit comprises a radio frequency, RF, transmitter 500 comprising: a
transmit path comprising: a digital predistortion, DPD, module 560
arranged to receive and distort an input transmit signal, i.e.
digital I/Q input signal 510; and an RF transmit block 550 arranged
to receive the distorted transmit signal and to convert the
digitally predistorted signal to an analog form, amplify and
up-convert the distorted transmit signal and apply the amplified,
up-converted distorted transmit signal 530 to the PA module 555. In
some examples, DPD 560 may additionally receive a control signal
(not shown) in order to adjust the baseband (digital) signals to
compensate for AM-AM and AM-PM distortion that will be introduced
by PA 555. This is typically generated and routed back via a
coupler located between the PA 555 and an antenna (not shown) .
Notably, in accordance with some example embodiments of the
invention, the DPD 560 may also optionally receive a second input
signal (Vref2) from an output of the second envelope mapping
module-2 525. In this manner, improved PA linearity may be achieved
with the DPD receiving an indication of the instantaneous envelope
signal level. The digitally pre-distorted output signals from DPD
560 are input to RF transmitter module 550, which converts the
signals to analog form and up-converts the signal to an RF signal
for inputting to the PA 555. In some examples, RF transmitter
module 550 may further comprise a low pass filter, variable gain
amplifier, mixer and frequency synthesiser (not shown) . In one
example, calibration of a transmit chain of the RF transmitter
module 550 is performed in order to calibrate the PA 555 and
analogue transmit gain functions contained within RF transmitter
module 550.
[0065] The output of the linear amplifier 570 is arranged to
generate supply (Vpa) 535 of the PA module 555, with a suitable DC
level shift introduced by summing junction 572 that also receives
an input from second DC-DC converter 575. Second DC-DC converter
575 receives a DC level shift value (V3) from DSP 580 based on a
transmit power control (TPC) signal and provides an adjustment
value between linear amplifier output voltage and VPA 535. The DC
level shift value (V3) from DSP 580 is the DC component of Vpa 535,
which is calculated by DSP 580 with information from a transmit
power control (TPC) module (not shown), based on, say, a specific
standard, such as 3GPP.TM.. In accordance with example embodiments
of the invention, slew-rate reduction module 518 is arranged to
provide an even and therefore reduced re-distribution of a maximum
slew rate and bandwidth of the signal envelope (first envelope to
Vref mapping value (Vref1)), in order to improve the efficiency of
supply modulator 520. For example, the output signal (V1) from
slew-rate reduction module 518 may improve an efficiency of
(hybrid) supply modulator 520 by reducing a voltage headroom of
linear amplifier 570. Furthermore, the first envelope tracking path
that produces V1 may be operated at a much lower sampling rate than
the second envelope tracking path (resulting in Vref2) in order to
conserve more power.
[0066] In order to best appreciate the operation of the slew-rate
reduction module 518, let us consider an input sequence of: [0 0 0
0 0 3]. An output sequence from a known supply modulator, following
this input sequence would be: [0 0 0 1 2 3]. As illustrated, the
slew rate is not evenly distributed across the sampled input
signal, thereby leading to potential problems of overload or
under-load.
[0067] However, in contrast to the known prior art, employing the
slew-rate reduction module 518 according to example embodiments of
the invention, the output sequence of FIG. 5 is: [0.6 1.2 1.8 2.4
3.0]. In this manner, the slew rate is now evenly distributed and
manageable, thereby preventing overload or under-load problems.
[0068] Referring now to FIG. 6, there is illustrated an example
flowchart 600 for controlling a power amplifier supply modulation
circuit employing envelope tracking according to some example
embodiments of the invention. The flowchart commences at 602 and
transitions to 603 where an input signal is received and a
plurality of samples of the input signal are processed. At 604, for
example, the slew-rate reduction module 518 of FIG. 5 may take N
input samples
vpa.sub.i(n-N+m), m=0 . . . N-1) [1]
for each output sample [2] provided by, say, first envelope to
reference voltage (Vref) mapping module-1 515 of FIG. 5:
vpa.sub.o(n-N) [2]
[0069] For this example, Vpa.sub.i is Vref1 and Vpa.sub.o is V1 of
FIG. 5.
[0070] At 606, slew-rate reduction module 518 may then be arranged
to calculate a current slew rate of each input sample [1], for
example according to [3]:
SR ( 1 ) = [ .upsilon. pa i ( n - N ) - .upsilon. pa o ( n - N - 1
) ] / 1 SR ( 2 ) = [ .upsilon. pa i ( n - N + 1 ) - .upsilon. pa o
( n - N - 1 ) ] / 2 SR ( 3 ) = [ .upsilon. pa i ( n - N + 2 ) -
.upsilon. pa o ( n - N - 1 ) ] / 3 SR ( N ) = [ .upsilon. pa i ( n
- N + N - 1 ) - .upsilon. pa o ( n - N - 1 ) ] / N [ 3 ]
##EQU00001##
[0071] At 608, and based thereon, slew-rate reduction module 518
may then be arranged to influence a current output single by evenly
re-distributing a maximum slew rate of a plurality of input samples
across the output single, for example according to [4]:
vpa.sub.o(n-N)=vpa.sub.o(n-N-1)+max[S(1), S(2), S(3), . . . ,
S(B)]. [4]
[0072] In one example, at 610, the slew-rate reduction module 518
may then repeat this process for the next and subsequent output
sample (s) [2] until the transmission is complete, when the process
ends at 612.
[0073] In this manner, the slew rate of the signal envelope (first
envelope to Vref mapping value (Vref1)) may be evenly distributed
and manageable. Hence, in some examples, overload or under-load of
the signal envelope may be avoided. Furthermore, the slew-rate
modified version (V1) of the first envelope signal may be better
able to track the peak of the original envelope signal. In
addition, both the bandwidth and slew rate of the first envelope
signal can be reduced. Such a solution to the aforementioned
problem is notably low in complexity.
[0074] Referring to FIG. 7, there is illustrated an example block
diagram of a further dynamic power amplifier supply modulation
circuit 700, adapted in accordance with some examples of the
invention. In one example, the dynamic power amplifier supply
modulation circuit 700 may be employed in the communication unit
400 of FIG. 4 . The example block diagram of a dynamic power
amplifier supply modulation circuit 700 supports ET, as well as
optionally supporting digital pre-distortion (DPD) . The
illustrated example of FIG. 7 has many features in common with FIG.
5, and, thus, only additional aspects will be discussed in
detail.
[0075] In some examples, the further dynamic power amplifier supply
modulation circuit 700 may comprise an envelope detector module 705
operable to receive a digital I/Q input signal 710 and calculate an
envelope value from the digital I/Q signal 710. In this illustrated
example, the envelope detector 705 is operably coupled to a single
(when compared to FIG. 5) envelope to reference voltage (Vref)
mapping module-2 715, which may provide a mapping value based on
the detected envelope to an input signal (V2) to supply voltage
modulator 720, in order to generate a PA supply voltage (Vpa) 735,
thereby to create a target output power level 740 from the PA 755.
In this example, utilising envelope tracking to control the output
of the PA 555 may improve the efficiency of the PA 555, for example
by reducing a voltage headroom used (e.g. voltage range to be
supported) by the PA 555.
[0076] In this illustrated example, a (second) slew-rate reduction
module 718 may be operably coupled between (second) envelope
mapping module-2 715 and supply voltage modulator 720. Supply
voltage modulator 720, which in this example may be either a hybrid
supply voltage modulator or a switching supply voltage modulator
and may comprise a (second) DC-DC converter (not shown), is
arranged to receive the slew-rate modified version (V2) of the
first envelope to Vref mapping value (Vref2).
[0077] By careful control of the (second) slew-rate reduction
module 718 and signals or values output therefrom, the slew-rate
modified version (V2) of the first envelope to Vref mapping value
(Vref2) may improve an efficiency of a hybrid modulator version of
the supply modulator 720, for example by reducing a bandwidth and
slew rate of V2 and therefore reducing one or more performance
requirement(s) placed on a linear amplifier of hybrid modulator.
Alternatively, by careful control of the (second) slew-rate
reduction module 718, the slew-rate modified version (V2) of the
first envelope to Vref mapping value (Vref2) may improve an
efficiency performance of a switching modulator version of the
supply modulator 720, by reducing a bandwidth and slew rate of V2
and therefore reducing one or more performance requirement(s)
placed on the switching modulator. Thus, in this manner, (second)
slew-rate reduction module 718 may be configured to reduce a slew
rate and/or a signal bandwidth of the ET signal (Vref2) output from
second envelope mapping module-1 715. In one example, control of
slew-rate reduction module 718 maybe performed by controller 414 of
FIG. 4. In other examples, control of slew-rate reduction module
718 may be performed by any other signal processor or controller
module.
[0078] In order to address the linearity requirements of the
transmitter, digital I/Q input signal 710 may also be input to DPD
760. DPD 760 receives and adjusts the digital I/Q signal 710 to
compensate for AM-AM and AM-PM distortion that will be introduced
by PA 755. Notably, in accordance with some example embodiments of
the invention, the DPD 760 also optionally receives a second input
signal (V2) from an output of the (second) slew-rate reduction
module 718, dependent upon the envelope-to-reference voltage
(Vref2) mapping value. In this manner, improved PA linearity may be
achieved with the DPD additionally receiving an indication of the
instantaneous envelope signal level, as adjusted by slew-rate
reduction module 718. The digitally pre-distorted output signals
from DPD 760 are input to RF transmitter module 750, which converts
the signals to analog form and up-converts the signal to an RF
signal for inputting to the PA 755. In some examples, RF
transmitter module 750 may further comprise a low pass filter,
variable gain amplifier, mixer and frequency synthesiser (not
shown).
[0079] In accordance with example embodiments of the invention,
slew-rate reduction module 718 is arranged to provide an even
re-distribution (and therefore reduced) slew rate and bandwidth of
the signal envelope mapping value (first envelope to Vref mapping
value (Vref2)), in order to improve the efficiency of supply
modulator 720. For example, the output signal (V2) from slew-rate
reduction module 718 may improve an efficiency of (hybrid) supply
modulator 720 by reducing bandwidth and/or slew rate of (hybrid)
supply modulator 720.
[0080] Referring to FIG. 8, there is illustrated an example block
diagram of a dynamic power amplifier supply modulation circuit 800,
adapted in accordance with some examples of the invention. In one
example, the dynamic power amplifier supply modulation circuit 800
may be employed in the communication unit 400 of FIG. 4. According
to some example embodiments of the invention, the envelope tracking
system comprises an envelope detector 805 arranged to detect an
instantaneous envelope value of the input transmit digital I/Q
input signal 810. Further, in this illustrated example, an output
of the envelope detector 805 is operably coupled to a first
envelope to reference voltage (Vref) mapping module-1 815, which
provides a mapping value dependent upon the calculated envelope
value to a power amplifier supply voltage modulator 820. The first
envelope to supply mapping component 815 is arranged to set a
supply voltage level (V1) of a linear amplifier 870 of supply
modulator 820 based on a detected envelope, where supply modulator
820 is operably coupled to a supply 835 of the PA module 855 and
arranged to variably control a supply voltage therefor.
[0081] The example block diagram of a dynamic power amplifier
supply modulation circuit 800 supports ET as well as optionally
supporting digital pre-distortion (DPD) . In this example, power
amplifier supply voltage modulator 820 is a hybrid modulator
[0082] Additionally, in this illustrated example, the envelope
detector 805 is also operably coupled to a second envelope to
reference voltage (Vref) mapping module-2 825, which also provides
a mapping value dependent upon the calculated envelope value to the
power amplifier supply voltage modulator 820. In this example, the
two mapping values are provided to a linear amplifier 870, in order
to generate a PA supply voltage (Vpa) 835, which in turn creates a
target output power level 840 from the PA 855.
[0083] In this illustrated example, each of the mapping values are
input to respective slew rate reduction modules 818, 802, in order
to modify the mapping values according to a desired reduced slew
rate and/or reduced bandwidth of the signals (Vref1 and Vref2)
passing therethrough. Thus, a first slew-rate reduction module 818
may be operably coupled between first envelope mapping module-1 815
and supply voltage modulator 820. Supply voltage modulator 820,
which in this example is a hybrid supply voltage modulator,
comprises a first DC-DC converter 822 arranged to receive the first
slew-rate modified version (V1) of the first envelope to Vref
mapping value (Vref1). In this manner, slew-rate reduction module
818 is able to control the supply voltage of the Linear Amplifier
870, by control/manipulation of the first slew-rate modified
version (V1) of the first envelope to Vref mapping value (Vref1).
In one example, the first slew-rate modified version (V1) of the
first envelope to Vref mapping value (Vref1) may be able to improve
the operating efficiency of hybrid supply voltage modulator by
reducing a voltage headroom employed by the linear amplifier
870.
[0084] In this example, a second slew-rate reduction module 802 is
operably coupled between second envelope mapping module-2 825 and
supply voltage modulator 820. In this example, linear amplifier 870
also receives a slew-rate modified version (V2) of second
envelope-to-Vref2 mapping value (Vref2) output from the second
envelope mapping module-2 825, in order to generate the PA supply
voltage, Vpa 835. In accordance with some example embodiments, the
slew-rate modified version (V2) of second envelope-to-Vref2 mapping
value (Vref2) may improve the operating efficiency of the hybrid
supply modulator 820 by reducing an operating bandwidth and/or a
slew rate requirement of linear amplifier 870.
[0085] Thus, in accordance with example embodiments of the
invention, first slew-rate reduction module 818 and second
slew-rate reduction module 802 are both arranged to provide an even
(and therefore reduced) re-distribution of slew rate and bandwidth
of the first envelope to Vref mapping value (Vref1) and second
envelope to Vref mapping value (Vref2), in order to improve the
efficiency of supply modulator 820.
[0086] The output of the linear amplifier 870 is arranged to
generate supply (Vpa) 835 of the PA module 855, with a suitable DC
level shift introduced by summing junction 872 that also receives
an input from a second DC-DC converter 875. Second DC-DC converter
875 receives a DC level shift value (V3) from digital signal
processor (DSP) 880, based on a transmit power control (TPC)
signal, and provides an adjustment value between linear amplifier
output voltage and VPA 835. The DC level shift value (V3) from DSP
880 is the DC component of Vpa 835, which is calculated by DSP 880
with information from a transmit power control (TPC) module (not
shown), based on, say, a specific standard, such as 3GPP.TM..
[0087] In one example, the first slew-rate modified version (V1)
path can be operated at a much lower sampling rate than the second
slew-rate modified version (V2) path in order to save even more
power. In this manner, this example facilitates usage of less
expensive and lower performance DC-DC converters 822, 875 in hybrid
modulator 820
[0088] In order to address the linearity requirements of the
transmitter, digital I/Q input signal 810 may also be input to DPD
860. DPD 860 receives inputs to adjust the digital I/Q input signal
810 in order to compensate for amplitude modulation-to-amplitude
modulation (AM-AM) and amplitude modulation-to-phase modulation
(AM-PM) distortion that will be introduced by PA 855. Notably, in
accordance with some example embodiments of the invention, the DPD
860 may also optionally receive a second input signal (V1) from an
output of the (first) slew-rate reduction module 818, dependent
upon the envelope-to-reference voltage (Vref1) mapping value that
is output from the first envelope-to-Vref mapping module-1 818. As
mentioned, in one example, (first) slew-rate reduction module 818
is used to reduce the bandwidth and/or slew rate of the output
(Vref1) of first envelope mapping module-1 815 in order to improve
the efficiency of Linear Amplifier 870. As such, second input
signal (V1) output from (first) slew-rate reduction module 818 is
used to control the supply voltage of Linear Amplifier 870 and the
efficiency of Linear Amplifier 870 can be further improved by
reducing voltage headroom of Linear Amplifier 870 through first
envelope mapping module-1 815. However, in some instances, this may
cause some distortion on the output signal of the Linear Amplifier
870, and therefore Vpa 835 and hence PA output 840. Therefore,
providing the second input signal (V1) from an output of the
(first) slew-rate reduction module 818 to DPD 860 is useful in DPD
860 compensating for any such generated non-linearity.
[0089] Furthermore, in accordance with some example embodiments of
the invention, the DPD 860 may also optionally receive a third
input signal (V2) from an output of the (second) slew-rate
reduction module 802, dependent upon the envelope-to-reference
voltage (Vref2) mapping value output from the second
envelope-to-Vref mapping module-2 825. In one example, third input
signal (V2) may be used to control Vpa 835, and as such if the
bandwidth and/or slew rate of V2 is reduced, DPD 860 is provided
with a representation of third input signal (V2) to compensate for
the fact that the PA 855 is no longer operated at constant
gain.
[0090] Notably, in the example of FIG. 8, second input signal (V1)
and third input signal (V2) are advantageously independently
controlled and applied to DPD 860, as compared to the Vref signal
applied to DPD 560 in FIG. 5, thereby providing more flexibility
and control in the PA linearization process.
[0091] In this manner, improved PA linearity may be achieved with
the DPD receiving an indication of the instantaneous envelope
signal level. The digitally pre-distorted output signals from DPD
860 are input to RF transmitter module 850, which converts the
signals to analog form and up-converts the signal to an RF signal
for inputting to the PA 855. In some examples, RF transmitter
module 850 may further comprise a low pass filter, variable gain
amplifier, mixer and frequency synthesiser (not shown).
[0092] Referring now to FIG. 9, there is illustrated a typical
computing system 900 that may be employed to implement
software-controlled power control functionality in embodiments of
the invention that utilize envelope tracking and load control.
Computing systems of this type maybe used in wireless communication
units, such as base stations eNodeBs. Those skilled in the relevant
art will also recognize how to implement the invention using other
computer systems or architectures. For example, computing system
900 may represent, for example, a desktop, laptop or notebook
computer, hand-held computing device (PDA, cell phone, palmtop,
etc.), mainframe, server, client, or any other type of special or
general purpose computing device as may be desirable or appropriate
for a given application or environment. Computing system 900 can
include one or more processors, such as a processor 904. Processor
904 can be implemented using a general or special-purpose
processing engine such as, for example, a microprocessor,
microcontroller or other control logic. In this example, processor
904 is connected to a bus 902 or other communications medium.
[0093] Computing system 900 can also include a main memory 908,
such as random access memory (RAM) or other dynamic memory, for
storing information and instructions to be executed by processor
904. Main memory 908 also may be used for storing temporary
variables or other intermediate information during execution of
instructions to be executed by processor 904. Computing system 900
may likewise include a read only memory (ROM) or other static
storage device coupled to bus 902 for storing static information
and instructions for processor 904.
[0094] In some examples, computing system 900 may be operable to
implement various software programs to control a power amplifier
load modulation circuit in a calibration state and/or control a
power amplifier load modulation circuit in a transmission
state.
[0095] The computing system 900 may also include information
storage system 910, which may include, for example, a media drive
912 and a removable storage interface 920. The media drive 912 may
include a drive or other mechanism to support fixed or removable
storage media, such as a hard disk drive, a floppy disk drive, a
magnetic tape drive, an optical disk drive, a compact disc (CD) or
digital video drive (DVD) read or write drive (R or RW) , or other
removable or fixed media drive. Storage media 918 may include, for
example, a hard disk, floppy disk, magnetic tape, optical disk, CD
or DVD, or other fixed or removable medium that is read by and
written to by media drive 912. As these examples illustrate, the
storage media 918 may include a computer-readable storage medium
having particular computer software or data stored therein.
[0096] In alternative embodiments, information storage system 910
may include other similar components for allowing computer programs
or other instructions or data to be loaded into computing system
900. Such components may include, for example, a removable storage
unit 922 and an interface 920, such as a program cartridge and
cartridge interface, a removable memory (for example, a flash
memory or other removable memory module) and memory slot, and other
removable storage units 922 and interfaces 920 that allow software
and data to be transferred from the removable storage unit 918 to
computing system 900.
[0097] Computing system 900 can also include a communications
interface 324. Communications interface 924 can be used to allow
software and data to be transferred between computing system 900
and external devices. Examples of communications interface 924 can
include a modem, a network interface (such as an Ethernet or other
NIC card), a communications port (such as for example, a universal
serial bus (USB) port), a PCMCIA slot and card, etc. Software and
data transferred via communications interface 324 are in the form
of signals which can be electronic, electromagnetic, and optical or
other signals capable of being received by communications interface
924. These signals are provided to communications interface 924 via
a channel 928. This channel 928 may carry signals and may be
implemented using a wireless medium, wire or cable, fiber optics,
or other communications medium. Some examples of a channel include
a phone line, a cellular phone link, an RF link, a network
interface, a local or wide area network, and other communications
channels.
[0098] In some further alternative embodiments, part or all of
computing system 900 may be operably coupled through a real-time
communication network, for example the internet. Therefore, in some
cases, the architecture of computing system 900 maybe
geographically distributed over a network, with the means and
ability to run the distributed parts of computing system 900
simultaneously. In some further embodiments, computing system 900
may be operably coupled to one or more further computing systems
via a distributed computing network.
[0099] In this document, the terms `computer program product`,
`computer-readable medium` and the like may be used generally to
refer to media such as, for example, memory 908, storage device
918, or storage unit 922. These and other forms of
computer-readable media may store one or more instructions for use
by processor 904, to cause the processor to perform specified
operations. Such instructions, generally referred to as `computer
program code` (which may be grouped in the form of computer
programs or other groupings), when executed, enable the computing
system 900 to perform functions of embodiments of the present
invention. Note that the code may directly cause the processor to
perform specified operations, be compiled to do so, and/or be
combined with other software, hardware, and/or firmware elements
(e.g., libraries for performing standard functions) to do so.
[0100] In an embodiment where the elements are implemented using
software, the software may be stored in a computer-readable medium
and loaded into computing system 900 using, for example, removable
storage drive 922, drive 912 or communications interface 924. The
control logic (in this example, software instructions or computer
program code), when executed by the processor 904, causes the
processor 904 to perform the functions of the invention as
described herein.
[0101] In the foregoing specification, the invention has been
described with reference to specific examples of embodiments of the
invention. It will, however, be evident that various modifications
and changes may be made therein without departing from the broader
spirit and scope of the invention as set forth in the appended
claims.
[0102] Those skilled in the art will recognize that the boundaries
between logic blocks are merely illustrative and that alternative
embodiments may merge logic blocks or circuit elements or impose an
alternate decomposition of functionality upon various logic blocks
or circuit elements. Thus, it is to be understood that the
architectures depicted herein are merely exemplary, and that in
fact many other architectures can be implemented which achieve the
same functionality.
[0103] Any arrangement of components to achieve the same
functionality is effectively `associated` such that the desired
functionality is achieved. Hence, any two components herein
combined to achieve a particular functionality can be seen as
`associated with` each other such that the desired functionality is
achieved, irrespective of architectures or intermediary components.
Likewise, any two components so associated can also be viewed as
being `operably connected`, or `operably coupled`, to each other to
achieve the desired functionality.
[0104] Furthermore, those skilled in the art will recognize that
boundaries between the above described operations merely
illustrative. The multiple operations may be combined into a single
operation, a single operation may be distributed in additional
operations and operations may be executed at least partially
overlapping in time. Moreover, alternative embodiments may include
multiple instances of a particular operation, and the order of
operations may be altered in various other embodiments.
[0105] For example, in some example embodiments, it is envisaged
that the power controller and load controlled may be combined
within a single controller. Furthermore, in some example
embodiments, although the LUTs have been described individually,
thereby suggesting that they may comprise separate memory elements,
it is envisaged that a number or each may form a portion of a
single LUT or memory element .
[0106] Also for example, the various components/modules, or
portions thereof, may implemented as soft or code representations
of physical circuitry or of logical representations convertible
into physical circuitry, such as in a hardware description language
of any appropriate type.
[0107] Also, the invention is not limited to physical devices or
units implemented in non-programmable hardware but can also be
applied in programmable devices or units able to perform the
desired device functions by operating in accordance with suitable
program code, such as mainframes, minicomputers, servers,
workstations, personal computers, notepads, personal digital
assistants, electronic games, automotive and other embedded
systems, cell phones and various other wireless devices, commonly
denoted in this application as `computer systems`.
[0108] However, other modifications, variations and alternatives
are also possible. The specifications and drawings are,
accordingly, to be regarded in an illustrative rather than in a
restrictive sense.
[0109] In the claims, any reference signs placed between
parentheses shall not be construed as limiting the claim. The word
`comprising` does not exclude the presence of other elements or
steps then those listed in a claim. Furthermore, the terms `a` or
`an`, as used herein, are defined as one or more than one. Also,
the use of introductory phrases such as `at least one` and `one or
more` in the claims should not be construed to imply that the
introduction of another claim element by the indefinite articles
`a` or `an` limits any particular claim containing such introduced
claim element to inventions containing only one such element, even
when the same claim includes the introductory phrases `one or more`
or `at least one` and indefinite articles such as `a` or `an`. The
same holds true for the use of definite articles. Unless stated
otherwise, terms such as `first` and `second` are used to
arbitrarily distinguish between the elements such terms describe.
Thus, these terms are not necessarily intended to indicate temporal
or other prioritization of such elements. The mere fact that
certain measures are recited in mutually different claims does not
indicate that a combination of these measures cannot be used to
advantage.
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