U.S. patent application number 14/929974 was filed with the patent office on 2016-02-25 for energy-efficient personal audio device output stage with signal polarity-dependent power supply update rate.
The applicant listed for this patent is Cirrus Logic, Inc.. Invention is credited to John L. Melanson, Bharath Kumar Thandri.
Application Number | 20160056777 14/929974 |
Document ID | / |
Family ID | 54708410 |
Filed Date | 2016-02-25 |
United States Patent
Application |
20160056777 |
Kind Code |
A1 |
Thandri; Bharath Kumar ; et
al. |
February 25, 2016 |
ENERGY-EFFICIENT PERSONAL AUDIO DEVICE OUTPUT STAGE WITH SIGNAL
POLARITY-DEPENDENT POWER SUPPLY UPDATE RATE
Abstract
A charge pump power supply may comprise a plurality of
capacitors and a switching circuit for switching the capacitors to
provide a first voltage or a second voltage in accordance with the
select input. The charge pump power supply may have a signal
polarity input for indicating a polarity of an output audio signal.
Switches for switching one or more capacitors providing a first
polarity voltage in a then-current operating mode may be configured
to switch at a greater frequency than switches for switching one or
more capacitors providing a second polarity voltage responsive to
the signal polarity input indicating a positive polarity of the
output audio signal. Switches for switching one or more capacitors
providing the first polarity voltage in a then-current operating
mode are configured to switch at a lesser frequency than switches
for switching one or more capacitors providing the second polarity
voltage responsive to the signal polarity input indicating a
negative polarity of the output audio signal.
Inventors: |
Thandri; Bharath Kumar;
(Austin, TX) ; Melanson; John L.; (Austin,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cirrus Logic, Inc. |
Austin |
TX |
US |
|
|
Family ID: |
54708410 |
Appl. No.: |
14/929974 |
Filed: |
November 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14067485 |
Oct 30, 2013 |
9209757 |
|
|
14929974 |
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Current U.S.
Class: |
330/251 |
Current CPC
Class: |
H03F 3/183 20130101;
H02M 3/07 20130101; H02M 2003/071 20130101; H02M 2003/072 20130101;
H03F 2200/03 20130101; H03F 3/217 20130101; H03F 1/0211 20130101;
H03F 3/185 20130101; H03F 1/0227 20130101; H03F 2200/102
20130101 |
International
Class: |
H03F 3/183 20060101
H03F003/183; H03F 3/217 20060101 H03F003/217; H02M 3/07 20060101
H02M003/07; H03F 1/02 20060101 H03F001/02 |
Claims
1. An audio amplifier circuit for providing an output signal to an
audio transducer, the audio amplifier circuit comprising: a power
amplifier having an audio input for receiving an audio input
signal, an audio output for providing the output signal, and a
power supply input; and a charge pump power supply for providing a
power supply voltage to the power supply input, wherein the power
supply voltage has a first polarity voltage relative to a
common-mode voltage and a second polarity voltage relative to the
common-mode voltage such that the power supply voltage equals a
difference between the first polarity voltage and the second
polarity voltage, wherein: the charge pump power supply has a
signal polarity input for indicating a polarity of the output
signal; and switches for switching one or more capacitors providing
the first polarity voltage are configured to switch in a first
sequence such that electrical charge is transferred from the one or
more capacitors providing the first polarity voltage at a greater
rate than a rate of transfer of electrical charge from the one or
more capacitors providing the second polarity voltage.
2. The audio amplifier circuit of claim 1, further comprising a
control circuit for generating the signal polarity input based on
the polarity of the output signal.
3. The audio amplifier circuit of claim 2, wherein the control
circuit determines the polarity of the output signal based on a
sign bit of a digital audio input signal.
4. The audio amplifier circuit of claim 2, wherein: the power
amplifier further comprises at least one driving device for
generating the output signal based on the audio input signal; and
the control circuit determines the polarity of the output signal
based on a ratio of load current to quiescent current in the at
least one driving device.
5. The audio amplifier circuit of claim 2, wherein: the charge pump
power supply further comprises an input for receiving a source
voltage; and the control circuit determines the polarity of the
output signal based on a voltage difference between the power
supply voltage and the source voltage.
6. (canceled)
7. The audio amplifier circuit of claim 1, wherein: responsive to a
magnitude of a difference between the output signal and the first
polarity voltage being less than a predetermined threshold, the
charge pump power supply operates the switches for switching one or
more capacitors providing the first polarity voltage at a first
frequency; and responsive to the magnitude of the difference
between the output signal and the first polarity voltage being
greater than the predetermined threshold, the charge pump power
supply operates the switches for switching one or more capacitors
providing the first polarity voltage at a second frequency less
than the first frequency.
8. The audio amplifier circuit of claim 1, wherein: responsive to a
magnitude of a difference between the output signal and the second
polarity voltage being less than a predetermined threshold, the
charge pump power supply operates the switches for switching one or
more capacitors providing the second polarity voltage at a first
frequency; and responsive to the magnitude of the difference
between the output signal and the second polarity voltage being
greater than the predetermined threshold, the charge pump power
supply operates the switches for switching one or more capacitors
providing the second polarity voltage at a second frequency less
than the first frequency.
9. The audio amplifier circuit of claim 1, wherein: the power
amplifier includes at least one switching device for generating a
first polarity of the output signal and at least one switching
device for generating a second polarity of the output signal based
on the audio input signal; responsive to the signal polarity input
indicating a positive polarity of the output signal, the at least
one switching device for providing the first polarity voltage
operates at a first current; and responsive to the signal polarity
input indicating a negative polarity of the output signal, the at
least one switching device for providing the first polarity voltage
operates at a second current less than the first current.
10. The audio amplifier circuit of claim 1, wherein: the power
amplifier includes at least one switching device for generating a
first polarity of the output signal and at least one switching
device for generating a second polarity of the output signal based
on the audio input signal; responsive to the signal polarity input
indicating a negative polarity of the output signal, the at least
one switching device for providing the second polarity voltage
operates at a first current; and responsive to the signal polarity
input indicating a positive polarity of the output signal, the at
least one switching device for providing the second polarity
voltage operates at a second current less than the first
current.
11. The audio circuit of claim 1, wherein the power supply voltage
is a single-ended voltage referenced to a ground voltage in which
the common-mode voltage is equal to one-half of a maximum power
supply voltage and the second polarity voltage has a minimum equal
to the ground voltage.
12. The audio circuit of claim 1, wherein the power supply voltage
is a differential voltage in which the common-mode voltage is equal
to a mean of a maximum first polarity voltage and a minimum second
polarity voltage.
13. A method for providing an output signal to an audio transducer,
comprising: providing by a charge pump power supply a power supply
voltage to a power supply input of a power amplifier having an
audio input for receiving an audio input signal and an audio output
for providing the output signal, wherein: the power supply voltage
has a first polarity voltage relative to a common-mode voltage and
a second polarity voltage relative to the common-mode voltage such
that the power supply voltage equals a difference between the first
polarity voltage and the second polarity voltage, wherein: the
charge pump comprises a plurality of capacitors and a switching
circuit for switching the capacitors to provide the first voltage
or the second voltage in accordance with the select input; and the
charge pump power supply has a signal polarity input for indicating
a polarity of the output signal; and switching switches for
switching one or more capacitors providing the first polarity
voltage in a first sequence such that electrical charge is
transferred from the one or more capacitors providing the first
polarity voltage at a greater rate than a rate of transfer of
electrical charge from the one or more capacitors providing the
second polarity voltage.
14. The method of claim 13, further comprising generating the
signal polarity input based on the polarity of the output
signal.
15. The method of claim 14, further comprising determining the
polarity of the output signal based on a sign bit of a digital
audio input signal.
16. The method of claim 14, wherein: the power amplifier further
comprises at least one driving device for generating the output
signal based on the audio input signal; and determining the
polarity of the output signal further comprises determining the
polarity based on a ratio of load current to quiescent current in
the at least one driving device.
17. The method of claim 14, wherein: the charge pump power supply
further comprises an input for receiving a source voltage; and
determining the polarity of the output signal further comprises
determining the polarity based on a voltage difference between the
power supply voltage and the source voltage.
18. (canceled)
19. The method of claim 13, further comprising: responsive to a
magnitude of a difference between the output signal and the first
polarity voltage being less than a predetermined threshold,
operating the switches for switching one or more capacitors
providing the first polarity voltage at a first frequency; and
responsive to the magnitude of the difference between the output
signal and the first polarity voltage being greater than the
predetermined threshold, operating the switches for switching one
or more capacitors providing the first polarity voltage at the
second frequency less than a first frequency.
20. The method of claim 13, further comprising: responsive to a
magnitude of a difference between the output signal and the second
polarity voltage being less than a predetermined threshold,
operating the switches for switching one or more capacitors
providing the second polarity voltage at a first frequency; and
responsive to the magnitude of the difference between the output
signal and the second polarity voltage being greater than the
predetermined threshold, operating the switches for switching one
or more capacitors providing the second polarity voltage at the
second frequency less than a first frequency.
21. The method of claim 13, further comprising: responsive to the
signal polarity input indicating a positive polarity of the output
signal, operating the at least one switching device for providing
the first polarity voltage at a first current; and responsive to
the signal polarity input indicating a negative polarity of the
output signal, operating the at least one switching device for
providing the first polarity voltage at a second current less than
the first current.
22. The method of claim 13, further comprising: responsive to the
signal polarity input indicating a negative polarity of the output
signal, operating the at least one switching device for providing
the second polarity voltage at a first current; and responsive to
the signal polarity input indicating a positive polarity of the
output signal, operating the at least one switching device for
providing the second polarity voltage at a second current less than
the first current.
23. The method of claim 13, wherein the power supply voltage is a
single-ended voltage referenced to a ground voltage in which the
common-mode voltage is equal to one-half of a maximum power supply
voltage and the second polarity voltage has a minimum equal to the
ground voltage.
24. The method of claim 13, wherein the power supply voltage is a
differential voltage in which the common-mode voltage is equal to a
mean of a maximum first polarity voltage and a minimum second
polarity voltage.
25. The method of claim 13, further comprising switching switches
for switching one or more capacitors providing the first polarity
voltage in the first sequence responsive to the signal polarity
input indicating a positive polarity of the output signal.
26. The method of claim 13, further comprising switching the
switches for switching the one or more capacitors providing the
first polarity voltage in a second sequence such that electrical
charge is transferred from the one or more capacitors providing the
first polarity voltage at a lesser rate than the rate of transfer
of electrical charge from the one or more capacitors providing the
second polarity voltage.
27. The method of claim 16, further comprising: switching the
switches for switching the one or more capacitors providing the
first polarity voltage in the first sequence responsive to the
signal polarity input indicating a positive polarity of the output
signal; and switching the switches for switching the one or more
capacitors providing the first polarity voltage in the second
sequence responsive to the signal polarity input indicating a
negative polarity of the output signal.
28. The audio amplifier circuit of claim 1, wherein the switches
for switching one or more capacitors providing the first polarity
voltage are configured to switch in the first sequence responsive
to the signal polarity input indicating a positive polarity of the
output signal.
29. The audio amplifier circuit of claim 1, wherein the switches
for switching the one or more capacitors providing the first
polarity voltage are configured to switch in a second sequence such
that electrical charge is transferred from the one or more
capacitors providing the first polarity voltage at a lesser rate
than the rate of transfer of electrical charge from the one or more
capacitors providing the second polarity voltage.
30. The audio amplifier circuit of claim 29, wherein: the switches
for switching the one or more capacitors providing the first
polarity voltage are configured to switch in the first sequence
responsive to the signal polarity input indicating a positive
polarity of the output signal; and the switches for switching the
one or more capacitors providing the first polarity voltage are
configured to switch in the second sequence responsive to the
signal polarity input indicating a negative polarity of the output
signal.
31. An audio amplifier circuit for providing an output signal to an
audio transducer, the audio amplifier circuit comprising: a power
amplifier having an audio input for receiving an audio input
signal, an audio output for providing the output signal, and a
power supply input; and a charge pump power supply for providing a
power supply voltage to the power supply input, wherein the power
supply voltage has a first terminal with a first polarity voltage
relative to a common-mode voltage and a second terminal with a
second polarity voltage relative to the common-mode voltage such
that the power supply voltage equals a difference between the first
polarity voltage and the second polarity voltage, wherein: the
charge pump comprises a plurality of capacitors and a switching
circuit comprising a plurality of switches for switching the
capacitors to provide the power supply voltage; switches for
switching one or more capacitors providing the first polarity
voltage to the first terminal are configured to switch with a first
switching sequence and at a first frequency based on a first
current drawn by the power amplifier from the first terminal; and
switches for switching one or more capacitors providing the second
polarity voltage to the second terminal are configured to switch
with a second switching sequence and at a second frequency based on
a second current drawn by the power amplifier from the second
terminal.
32. The audio amplifier circuit of claim 31, wherein: the charge
pump power supply has a signal polarity input for indicating a
polarity of the output signal; and the charge pump power supply is
configured to output a first polarity voltage and a second polarity
voltage such that: when the polarity of the output signal is of a
first polarity, a magnitude of difference between the first
polarity voltage and the common-mode voltage is greater than a
magnitude of difference between the second polarity voltage and the
common-mode voltage; and when the polarity of the output signal is
of a second polarity, a magnitude of difference between the first
polarity voltage and the common-mode voltage is lesser than a
magnitude of difference between the second polarity voltage and the
common-mode voltage.
33. A method for providing an output signal to an audio transducer,
comprising: providing by a charge pump power supply a power supply
voltage to a power supply input of a power amplifier having an
audio input for receiving an audio input signal and an audio output
for providing the output signal, wherein the power supply voltage
has a first polarity voltage relative to a common-mode voltage and
a second polarity voltage relative to the common-mode voltage such
that the power supply voltage equals a difference between the first
polarity voltage and the second polarity voltage, and wherein the
charge pump comprises a plurality of capacitors and a switching
circuit comprising a plurality of switches for switching the
capacitors to provide the power supply voltage; switching switches
for switching one or more capacitors providing the first polarity
voltage with a first switching sequence and at a first frequency
based on a first current drawn by the power amplifier from the
first terminal; and switching switches for switching one or more
capacitors providing the first polarity voltage with a second
switching sequence and at a second frequency based on a second
current drawn by the power amplifier from the second terminal.
34. The method of claim 33, wherein the charge pump power supply
has a signal polarity input for indicating a polarity of the output
signal and further comprising outputting the first polarity voltage
and the second polarity voltage by the charge pump power supply
such that: when the polarity of the output signal is of a first
polarity, a magnitude of difference between the first polarity
voltage and the common-mode voltage is greater than a magnitude of
difference between the second polarity voltage and the common-mode
voltage; and when the polarity of the output signal is of a second
polarity, a magnitude of difference between the first polarity
voltage and the common-mode voltage is lesser than a magnitude of
difference between the second polarity voltage and the common-mode
voltage.
Description
FIELD OF DISCLOSURE
[0001] The present disclosure relates in general to circuits for
personal audio devices such as wireless telephones and media
players, and more specifically, to systems and methods for
conserving energy in a personal audio device output stage by
controlling an output stage power supply based on a polarity of an
audio signal.
BACKGROUND
[0002] Personal audio devices, including wireless telephones, such
as mobile/cellular telephones, cordless telephones, mp3 players,
and other consumer audio devices, are in widespread use. Such
personal audio devices may include circuitry for driving a pair of
headphones or one or more speakers. Such circuitry often includes a
power amplifier for driving an audio output signal to headphones or
speakers, and the power amplifier may often be the primary consumer
of power in a personal audio device, and thus, may have the
greatest effect on the battery life of the personal audio device.
In devices having a linear power amplifier for the output stage,
power is wasted during low signal level outputs, because the
voltage drop across the active output transistor plus the output
voltage will be equal to the constant power supply rail voltage.
Therefore, amplifier topologies such as Class-G and Class-H are
desirable for reducing the voltage drop across the output
transistor(s) and thereby reducing the power wasted in dissipation
by the output transistor(s). In such topologies, power consumption
is reduced by employing a power supply, typically a charge pump
power supply, which has selectable modes of operation based on an
amplitude of an audio output signal of the power amplifier, wherein
each of the selectable modes provides a different bi-polar supply
voltage across power supply rails of the power amplifier.
[0003] While such topologies are more energy efficient than
predecessor topologies, such topologies may still waste power. For
example, when an audio output signal is of a positive polarity,
load current to the audio output is typically delivered only from a
positive supply rail of the power amplifier, and a quiescent power
may be wasted in maintaining a voltage on the negative supply rail
by the power supply. Similarly, when an audio output signal is of a
negative polarity, load current to the audio output is typically
delivered only from a negative supply rail of the power amplifier,
and a quiescent power may be wasted in maintaining a voltage on the
positive supply rail by the power supply.
[0004] Therefore, it would be desirable to provide a power
amplifier circuit for a consumer audio device that has improved
efficiency and reduced power dissipation, while maintaining a
specified full-signal output level capability.
SUMMARY
[0005] In accordance with the teachings of the present disclosure,
the disadvantages and problems associated with existing approaches
to driving audio output signals may be reduced or eliminated.
[0006] In accordance with embodiments of the present disclosure, an
audio amplifier circuit for providing an output signal to an audio
transducer may include a power amplifier and a charge pump power
supply. The power amplifier may have an audio input for receiving
an audio input signal, an audio output for providing the output
signal, and a power supply input. The charge pump power supply may
provide a power supply voltage to the power supply input, wherein
the power supply voltage has a first polarity voltage relative to a
common-mode voltage and a second polarity voltage relative to the
common-mode voltage such that the power supply voltage equals a
difference between the first polarity voltage and the second
polarity voltage. The charge pump power supply may have a select
input for selecting an operating mode of the power supply. In a
first operating mode, the power supply voltage may be equal to a
first voltage, and in a second operating mode the power supply
voltage may be substantially equal to a rational fraction of the
first voltage. The charge pump power supply may comprise a
plurality of capacitors and a switching circuit for switching the
capacitors to provide the first voltage or the second voltage in
accordance with the select input. The charge pump power supply may
have a signal polarity input for indicating a polarity of the
output signal. Switches for switching one or more capacitors
providing the first polarity voltage in a then-current operating
mode are configured to switch at a greater frequency than switches
for switching one or more capacitors providing the second polarity
voltage responsive to the signal polarity input indicating a
positive polarity of the output signal. Switches for switching one
or more capacitors providing the first polarity voltage in a
then-current operating mode are configured to switch at a lesser
frequency than switches for switching one or more capacitors
providing the second polarity voltage responsive to the signal
polarity input indicating a negative polarity of the output
signal.
[0007] In accordance with these and other embodiments of the
present disclosure, a method for providing an output signal to an
audio transducer may include providing by a charge pump power
supply a power supply voltage to a power supply input of a power
amplifier having an audio input for receiving an audio input signal
and an audio output for providing the output signal. The power
supply voltage may have a first polarity voltage relative to a
common-mode voltage and a second polarity voltage relative to the
common-mode voltage such that the power supply voltage equals a
difference between the first polarity voltage and the second
polarity voltage, wherein the common-mode voltage is equal to a
mean of a maximum first polarity voltage and a minimum second
polarity voltage. The charge pump power supply may have a select
input for selecting an operating mode of the power supply. In a
first operating mode, the power supply voltage may be equal to a
first voltage, and in a second operating mode the power supply
voltage may be substantially equal to a rational fraction of the
first voltage. The charge pump power supply may comprise a
plurality of capacitors and a switching circuit for switching the
capacitors to provide the first voltage or the second voltage in
accordance with the select input. The charge pump power supply may
have a signal polarity input for indicating a polarity of the
output signal. The method may also include operating switches for
switching one or more capacitors providing the first polarity
voltage in a particular operating mode at a greater frequency than
switches for switching one or more capacitors providing the second
polarity voltage responsive to the signal polarity input indicating
a positive polarity of the output signal. The method may further
include operating switches for switching one or more capacitors
providing the first polarity voltage in the particular operating
mode at a lesser frequency than switches for switching one or more
capacitors providing the second polarity voltage responsive to the
signal polarity input indicating a negative polarity of the output
signal.
[0008] Technical advantages of the present disclosure may be
readily apparent to one skilled in the art from the figures,
description and claims included herein. The objects and advantages
of the embodiments will be realized and achieved at least by the
elements, features, and combinations particularly pointed out in
the claims.
[0009] It is to be understood that both the foregoing general
description and the following detailed description are examples and
explanatory and are not restrictive of the claims set forth in this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
[0011] FIG. 1 is an illustration of an example personal audio
device, in accordance with embodiments of the present
disclosure;
[0012] FIG. 2 is a block diagram of selected components of an
example audio integrated circuit of a personal audio device, in
accordance with embodiments of the present disclosure;
[0013] FIG. 3 is a schematic diagram depicting an example
charge-pump power supply, in accordance with embodiments of the
present disclosure;
[0014] FIGS. 4A-4D are schematic diagrams depicting individual
charge-pump clock phases for operating modes of the charge-pump
power supply circuit depicted in FIG. 3, in accordance with
embodiments of the present disclosure; and
[0015] FIGS. 5A-5D are schematic diagrams depicting individual
charge-pump clock phases for operating modes of the charge-pump
power supply circuit depicted in FIG. 3, in accordance with
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0016] FIG. 1 is an illustration of an example personal audio
device 1, in accordance with embodiments of the present disclosure.
FIG. 1 depicts personal audio device 1 coupled to a headset 3 in
the form of a pair of earbud speakers 8A and 8B. Headset 3 depicted
in FIG. 1 is merely an example, and it is understood that personal
audio device 1 may be used in connection with a variety of audio
transducers, including without limitation, headphones, earbuds,
in-ear earphones, and external speakers. A plug 4 may provide for
connection of headset 3 to an electrical terminal of personal audio
device 1. Personal audio device 1 may provide a display to a user
and receive user input using a touch screen 2, or alternatively, a
standard LCD may be combined with various buttons, sliders, and/or
dials disposed on the face and/or sides of personal audio device 1.
As also shown in FIG. 1, personal audio device 1 may include an
audio integrated circuit (IC) 9 for generating an analog audio
signal for transmission to headset 3 and/or another audio
transducer or speaker.
[0017] FIG. 2 is a block diagram of selected components of an
example audio IC 9 of a personal audio device, in accordance with
embodiments of the present disclosure. As shown in FIG. 2, a
microcontroller core 18 may supply a digital audio input signal
DIG_IN to a digital-to-analog converter (DAC) 14, which may in turn
supply an analog audio input signal to a first amplifier stage A2
that may be operated from a fixed voltage power supply. In the
embodiments represented by FIG. 2, the input to DAC 14 may be a
digital audio source, but that is not a limitation of the present
disclosure, as the techniques of the present disclosure may be
applied to an audio amplifier having a purely analog signal path.
The signal at the output of first amplifier stage A2 may be
provided to an attenuator 16 that receives a volume control signal
and attenuates the signal accordingly. Attenuator 16 may be a
digital potentiometer having control provided from a
microcontroller or other digital control circuit responsive to a
user interface, volume knob encoder or program command, or
attenuator 16 may be an analog potentiometer that provides the
volume control signal as an output indication from a secondary deck
(separate potentiometer circuit coupled to the common shaft or
other mechanism). While an attenuator 16 is shown as the volume
control mechanism, it is understood that an equivalent volume
control may be provided by a programmable resistor or adjustable
gain in the feedback of amplifier A2 or another amplifier stage in
the signal path. A controller 27 may generate predriver signals
PDRV and NDRV based on the audio input signal V.sub.IN received
from attenuator 16, and a final power amplifier stage A1 may
amplify the predriver signals PDRV and NDRV to provide an audio
output signal V.sub.OUT, which may operate a speaker, headphone
transducer, and/or a line level signal output.
[0018] In some embodiments, the power supply voltage V.sub.SUPPLY
may comprise a single-ended voltage referenced to a ground voltage
having a common-mode voltage equal to one-half of a maximum power
supply voltage, and accordingly wherein the positive polarity
voltage has a maximum equal to the maximum power supply voltage and
the negative polarity voltage has a minimum equal to the ground
voltage. In other embodiments, the power supply voltage
V.sub.SUPPLY may comprise a differential voltage having a
common-mode voltage equal to a mean of a maximum positive polarity
voltage and a minimum negative polarity voltage. In both of these
embodiments, the audio output signal V.sub.OUT may be considered to
have a positive polarity when it is greater than the common-mode
voltage and to have a negative polarity when it is lesser than the
common-mode voltage. In embodiments in which V.sub.SUPPLY is a
single-ended supply having a quiescent voltage substantially
differing from ground, a capacitor may be utilized to couple the
output of amplifier A1 to a transducer or line level output.
[0019] A charge pump power supply 10 may provide the power supply
rail inputs of amplifier A1 and may receive a power supply input,
generally from a battery or other power supply, depicted as battery
terminal connections VBATT+ and VBATT-. A mode control circuit 12
may supply a mode select signal to charge pump power supply 10 that
selects an operating mode of charge pump power supply 10 as
described in greater detail elsewhere in this disclosure. Also,
output voltage V.sub.SUPPLY of charge pump power supply 10 may be
adjusted according to expected and/or actual audio signal levels at
the amplifier output according to the techniques disclosed
elsewhere in this disclosure.
[0020] When low signal levels exist and/or are expected at
amplifier output V.sub.OUT, the power efficiency of the audio
output stage may be improved by varying the supply voltage
V.sub.SUPPLY in conformity with the output signal V.sub.OUT or a
signal (e.g., volume control signal Volume, audio input signal
V.sub.IN) indicative of the output signal V.sub.OUT. In order to
determine the actual and/or expected signal amplitudes at the
output of amplifier A1, the volume control signal Volume, audio
output signal V.sub.OUT, and/or audio input signal V.sub.IN may be
supplied to mode control circuit 12 for controlling the
differential power supply V.sub.SUPPLY generated by charge pump
power supply 10, in conformity with the expected amplitude of the
output signal.
[0021] In addition, mode control circuit 12 may supply a polarity
signal to charge pump power supply 10 indicative of a polarity of
audio output signal V.sub.OUT. In some embodiments, mode control
circuit 12 may determine the polarity of audio output signal
V.sub.OUT based on a sign bit of digital audio input signal DIG_IN.
In other embodiments, mode control circuit 12 may determine the
polarity of audio output signal V.sub.OUT by comparing a load
current of a load coupled to the output of amplifier A1 to a
quiescent current through at least one driving device of amplifier
A1. In yet other embodiments, mode control circuit 12 may determine
the polarity of audio output signal V.sub.OUT based on a voltage
difference between supply voltage V.sub.SUPPLY and one or more of
battery voltage VBATT+ and VBATT-.
[0022] In these and other embodiments, currents generated by
switching devices of amplifier A1 may be controlled based on the
polarity of audio output signal V.sub.OUT. For example, power
amplifier A1 may include at least one switching device for
generating the positive polarity voltage of audio output signal
V.sub.OUT and at least one switching device for generating the
negative polarity voltage of audio output signal V.sub.OUT based on
the audio input signal. As mentioned above, audio IC 9 may include
a controller 27 configured to generate predriver signals PDRV and
NDRV based on the audio input signal V.sub.IN received from
attenuator 16. Predriver signal PDRV may drive the at least one
switching device for generating the positive polarity voltage of
audio output signal V.sub.OUT and predriver signal NDRV may drive
the at least one switching device for generating the negative
polarity voltage of audio output signal V.sub.OUT. Responsive to a
positive polarity of audio output signal V.sub.OUT (as indicated by
the polarity signal generated by mode control circuit 12 or another
component of audio IC 9), controller 27 may generate predriver
signals PDRV and NDRV such that the at least one switching device
for providing the positive polarity voltage operates at a first
current and responsive to a negative polarity of audio output
signal V.sub.OUT, the at least one switching device for providing
the positive polarity voltage operates at a second current less
than the first current. Similarly, responsive to a negative
polarity of audio output signal V.sub.OUT, controller 27 may
generate predriver signals PDRV and NDRV such that the at least one
switching device for providing the negative polarity voltage
operates at a first current and responsive to a positive polarity
of audio output signal V.sub.OUT, the at least one switching device
for providing the negative polarity voltage operates at a second
current less than the first current. Accordingly, audio IC 9 may
utilize output signal polarity information to provide reduction in
power consumption of a charge pump power supply, as compared with
traditional approaches.
[0023] Referring now to FIG. 3 and additionally with reference to
FIGS. 4A-4D, details of an example charge pump power supply 10 are
depicted, in accordance with embodiments of the present disclosure.
When a first operating mode (Mode 1) of charge pump power supply 10
is selected, as may be indicated by the MODE SELECT signal set in
the logical high ("1") state, switch S8 may close, and the voltage
VBATT+ may be applied directly to the positive polarity terminal
(OUT+) of charge pump power supply 10. FIGS. 4A and 4B show an
equivalent circuit arrangement for Mode 1 in first and second clock
phases, respectively, omitting open switches and inactive circuit
components. Switches S1, S2 and S4 are open and not activated in
the first operating mode, as logical AND gates AND10 and AND11
disable the control signals to switches S1, S2 and S4, and the
inverted Mode Select signal provided by inverter I10 is in a
logical low ("0") state. For a single-ended (unipolar) power
supply, capacitors C12-C13, switches S3, S6, and S7 may be omitted.
As illustrated in FIGS. 4A and 4B, in Mode 1, the positive power
supply voltage at the positive polarity terminal is supplied
directly from the positive input terminal VBATT+.
[0024] To produce the negative output supply voltage in mode 1, the
input voltage provided between input terminals VBATT+ and VBATT- is
inverted by a voltage inverter. In phase one (.phi..sub.1) of Mode
1, switches S3 and S6 may be closed, which may charge capacitor C12
by connection across input terminals VBATT+ and VBATT-, as
illustrated in FIG. 4A. In phase two (.phi..sub.2) of mode 1,
switch S3 and switch S6 may open and switch S5 and switch S7 may
close, which may reverse the terminal of capacitor C12 applied to
the VBATT- input terminal. Switch S7 may apply the terminal of
capacitor C12 that was applied to the VBATT- input terminal in
phase one, to the negative polarity terminal (OUT-), as further
illustrated by FIG. 4B. The switching action described above
provides a negative voltage at the negative polarity terminal with
respect to the VBATT- terminal that is substantially equal to the
magnitude of the voltage between the positive polarity terminal and
the VBATT- terminal, which acts as the reference midpoint voltage
(ground) at the junction between output capacitors C11 and C13.
[0025] In a second operating mode (Mode 2), which may be active
when the MODE SELECT signal is in the logical low ("0") state,
switch S8 may be opened. In phase one (.phi..sub.1) of Mode 2,
switches S1 and S4 may be closed, which may apply capacitor C10 in
series with output capacitor C11 across the VBATT+ and VBATT-
terminals, as further illustrated in FIG. 4C. In phase two
(.phi..sub.2) of Mode 2, switches S1 and S4 may be opened and
switches S2 and S5 may be closed, which may couple capacitor C10 in
parallel with capacitor C11 as further illustrated in FIG. 4D.
Because the second phase of mode 2 equalizes the voltage on
capacitors C10 and C11, the stable operating point of the circuit
may be such that the input voltage between the VBATT+ and VBATT-
terminals will be split equally during the charging phase,
irrespective of the relative capacitance of C10 and C11. Thus the
voltage at the positive polarity output terminal in Mode 2 will be
half of the voltage across the VBATT+ and VBATT- terminals. Other
ratios can be constructed by switching more capacitors in series
with capacitors C10 and C11 during phase one, and connecting them
all in parallel during phase two. For example, a voltage of one
third of the input battery voltage may be produced by using three
capacitors connected alternatively in series across the battery
terminals and parallel between the positive polarity terminal and
the VBATT- terminal.
[0026] The negative supply in the second operating mode (Mode 2)
may be provided in a manner similar to that of the first operating
mode and the connections of capacitor C12 are shown in FIG. 4B and
FIG. 4D, as being the same. However, as illustrated in FIG. 4C,
because switch S8 is open in the second operating mode, during
phase one of Mode 2, capacitor C12 is charged from the positive
polarity terminal rather than the VBATT+ terminal as was shown in
FIG. 4A for Mode 1. Switch S4 may perform the operation of
connecting capacitor C12 to the positive polarity terminal, as
illustrated in FIG. 4C, along with the above-described operation of
applying capacitor C10 in series with capacitor C11 in phase one
for the positive power supply and therefore the relative phases
between the voltage inverter supplying the negative polarity
terminal voltage and the circuit supplying the positive polarity
terminal voltage must be maintained in the depicted configuration.
Otherwise, eight switches may be utilized and the common connection
between capacitor C10 and C12 broken. The additional switch may be
provided between capacitor C12 and the positive polarity terminal,
and would be active in Mode 2, phase 1. It is also possible to
further reduce the number of switches from seven to six, by
removing switch S3 and controlling switch S4 with the unqualified
(.phi..sub.1) signal. However, the inclusion of switch S3 may
reduce the impedance of the power supply path in the first
operating mode, which may be the highest voltage/current operating
mode. Therefore, it may generally be advantageous to include switch
S3 in the circuit.
[0027] In some embodiments, switches of the switching circuit
integral to charge pump power supply 10 may be operated at a
particular frequency based on a magnitude of audio output signal
V.sub.OUT. Turning again to FIG. 2, audio IC 9 may include an
envelope detector 20 and a clock generator 22. Envelope detector 20
may comprise any system, device, or apparatus configured to detect
when digital audio input signal DIG_IN (or another signal
indicative of audio output signal V.sub.OUT) is within a
predetermined threshold of its maximum or minimum full-range
magnitude, and generate a signal PEAK_DETECT when such signal
indicative of audio output signal V.sub.OUT is within such
threshold. Clock generator 22 may be any system, device, or
apparatus (e.g., phase-locked loop, delay-locked loop, etc.)
configured to generate one or more periodic clock signals (e.g.,
signals CLK and CLK2). In some embodiments, the clock signal CLK
generated by clock generator 22 may be of a first frequency when
signal PEAK_DETECT is asserted and a second frequency lesser than
the first frequency when signal PEAK_DETECT is not asserted. Thus,
where magnitude of audio output signal V.sub.OUT approaches either
of the positive polarity voltage or negative polarity voltage of
V.sub.SUPPLY (as indicated by the signal PEAK_DETECT which is
generated from digital audio input signal DIG_IN or another signal
indicative of audio output signal V.sub.OUT), switches for
switching one or more capacitors providing the particular polarity
of supply voltage V.sub.SUPPLY may switch at a greater frequency
relative to that in which the magnitude of audio output signal
V.sub.OUT is not near either of the positive polarity voltage or
negative polarity voltage of supply voltage V.sub.SUPPLY. Thus,
responsive to a magnitude of a difference between audio output
signal V.sub.OUT and the positive polarity voltage of supply
voltage V.sub.SUPPLY being less than a predetermined threshold,
charge pump power supply 10 may operate the switches for switching
one or more capacitors providing the positive polarity voltage of
supply voltage V.sub.SUPPLY at a first frequency, and responsive to
the magnitude of difference between audio output signal V.sub.OUT
and the positive polarity voltage of supply voltage V.sub.SUPPLY
being greater than the predetermined threshold, charge pump power
supply 10 may operate the switches for switching one or more
capacitors providing the positive polarity voltage of supply
voltage V.sub.SUPPLY at a second frequency less than the first
frequency. Similarly, responsive to a magnitude of a difference
between audio output signal V.sub.OUT and the negative polarity
voltage of supply voltage V.sub.SUPPLY being less than a
predetermined threshold, charge pump power supply 10 may operate
switches for switching one or more capacitors providing the
negative polarity voltage of supply voltage V.sub.SUPPLY at a first
frequency, and responsive to the magnitude of the difference
between audio output signal V.sub.OUT and the negative polarity
voltage of supply voltage V.sub.SUPPLY being greater than the
predetermined threshold, charge pump power supply 10 may operate
the switches for switching one or more capacitors providing the
negative polarity voltage of supply voltage V.sub.SUPPLY at a
second frequency less than a first frequency. Accordingly, audio IC
9 may utilize output signal magnitude information to provide
reduction in power consumption of a charge pump power supply, as
compared with traditional approaches.
[0028] As described in greater detail elsewhere in this disclosure,
charge pump power supply 10 may include a plurality of capacitors
and a switching circuit for switching the capacitors to provide
supply voltage V.sub.SUPPLY in accordance with the select input. In
addition, switches of the switching circuit may be operated based
on the polarity of audio output signal V.sub.OUT. For example,
responsive to the signal polarity signal indicating a positive
polarity of the output signal, switches for switching one or more
capacitors providing a positive polarity of supply voltage
V.sub.SUPPLY in a particular operating mode of charge pump power
supply 10 may be configured to switch at a greater frequency than
switches for switching one or more capacitors providing a negative
polarity of supply voltage V.sub.SUPPLY in the particular operating
mode. Conversely, responsive to the signal polarity signal
indicating a negative polarity of the output signal, switches for
switching one or more capacitors providing the negative polarity of
supply voltage V.sub.SUPPLY in the particular operating mode of
charge pump power supply 10 may be configured to switch at a
greater frequency than switches for switching one or more
capacitors providing the positive polarity of supply voltage
V.sub.SUPPLY in the particular operating mode. To further
illustrate, as shown in FIG. 3, two or more clock signals
comprising signals CLK and CLK2, may be provided to charge pump
power supply 10, wherein the frequency of CLK may be greater than
that of CLK2. Thus, in Mode 1 described above, when audio output
signal V.sub.OUT has a positive polarity, switch S8 may be clocked
by signal CLK and switches S3, S6, S5, and S7 may be clocked by
signal CLK2, and when audio output signal V.sub.OUT has a negative
polarity, switch S8 may be clocked by signal CLK2 and switches S3,
S6, S5, and S7 may be clocked by signal CLK. Similarly, in Mode 2
described above, when audio output signal V.sub.OUT has a positive
polarity, switches S1, S2, and S4 may be clocked by signal CLK and
switches S6, S5, and S7 may be clocked by signal CLK2, and when
audio output signal V.sub.OUT has a negative polarity, switches S2
and S4 may be clocked by signal CLK2 and switches S1, S6, S5, and
S7 may be clocked by signal CLK. In Mode 2, switch S1 may be
clocked by the higher-frequency clock CLK for either polarity of
audio output signal V.sub.OUT, as switch S1 is used to provide both
the positive polarity and negative polarity of power supply voltage
V.sub.SUPPLY in Mode 2. Accordingly, audio IC 9 may utilize output
signal polarity information to provide reduction in power
consumption of a charge pump power supply, as compared with
traditional approaches.
[0029] Also as described elsewhere in this disclosure, based on the
polarity of audio output signal V.sub.OUT, charge pump power supply
10 may generate a positive polarity voltage of supply voltage
V.sub.SUPPLY of a particular magnitude relative to the common-mode
voltage of charge pump power supply 10 and a negative polarity
voltage of supply voltage V.sub.SUPPLY of a different magnitude
relative to the common-mode voltage. To illustrate, in particular
embodiments charge pump power supply 10 may operate in a first mode
("Mode A") in which it generates a maximum positive polarity
voltage of V.sub.MAX and a minimum negative polarity voltage of
-V.sub.MAX, and may operate in a second mode ("Mode B") in which it
generates a maximum positive polarity voltage of V.sub.MAX/2 and a
minimum negative polarity voltage of -V.sub.MAX/2. When charge pump
power supply 10 is operating in Mode A (in accordance with the mode
select signal), charge pump power supply 10 may generate a negative
polarity voltage of -V.sub.MAX and a positive polarity voltage of
V.sub.MAX/2 when the audio output signal V.sub.OUT has a negative
polarity, and thus have an equivalent circuit arrangement similar
or identical to that shown in FIG. 5A for phase one (.phi..sub.1)
of Mode A and an equivalent circuit arrangement similar or
identical to that shown in FIG. 5B for phase two (.phi..sub.2) of
Mode A. When charge pump power supply 10 is operating in Mode A (in
accordance with the mode select signal), charge pump power supply
10 may generate a positive polarity voltage of V.sub.MAX and a
negative polarity voltage of -V.sub.MAX/2 when the audio output
signal V.sub.OUT has a positive polarity, and thus may have an
equivalent circuit arrangement similar or identical to that shown
in FIG. 5C for phase one (.phi..sub.1) of Mode A and an equivalent
circuit arrangement similar or identical to that shown in FIG. 5D
for phase two (.phi..sub.2) of Mode A. With respect to FIGS. 5C and
5D, switches S9 and S10 and capacitor C14 are present which are not
depicted in FIG. 3. Thus, in embodiments where charge pump power
supply 10 operates in response to a polarity of audio output signal
V.sub.OUT, charge pump power supply depicted in FIG. 3 may be
modified to include switches S9 and S10 and capacitor C14.
[0030] When charge pump power supply 10 is operating in Mode B (in
accordance with the mode select signal), charge pump power supply
10 may generate a positive polarity voltage of V.sub.MAX/2 and a
negative polarity voltage of -V.sub.MAX/2 regardless of the
polarity of audio output signal V.sub.OUT, and thus may have an
equivalent circuit arrangement similar or identical to that shown
in FIG. 4C for phase one (.phi..sub.1) of Mode B and an equivalent
circuit arrangement similar or identical to that shown in FIG. 4D
for phase two (.phi..sub.2) of Mode B.
[0031] Accordingly, in the embodiments where charge pump power
supply 10 operates in response to a polarity of audio output signal
V.sub.OUT, when the polarity of audio output signal V.sub.OUT is
positive, a magnitude of a difference between the positive polarity
voltage and the common-mode voltage may be equal to a particular
mode-dependent voltage and a magnitude of a difference between the
negative polarity voltage and the common-mode voltage may be
substantially equal to a rational fraction of the particular
mode-dependent voltage, while when the polarity of audio output
signal V.sub.OUT is negative, a magnitude of a difference between
the negative polarity voltage and the common-mode voltage may be
equal to a particular mode-dependent voltage and a magnitude of a
difference between the positive polarity voltage and the
common-mode voltage may be substantially equal to a rational
fraction of the particular mode-dependent voltage. In such
embodiments, the various logic gates (e.g., AND gates) of charge
pump power supply 10 may be configured to provide for different
magnitude of voltages being supplied to the outputs of charge pump
power supply 10. Accordingly, audio IC 9 may utilize output signal
polarity information to provide reduction in power consumption of a
charge pump power supply, as compared with traditional
approaches.
[0032] This disclosure encompasses all changes, substitutions,
variations, alterations, and modifications to the exemplary
embodiments herein that a person having ordinary skill in the art
would comprehend. Similarly, where appropriate, the appended claims
encompass all changes, substitutions, variations, alterations, and
modifications to the exemplary embodiments herein that a person
having ordinary skill in the art would comprehend. Moreover,
reference in the appended claims to an apparatus or system or a
component of an apparatus or system being adapted to, arranged to,
capable of, configured to, enabled to, operable to, or operative to
perform a particular function encompasses that apparatus, system,
or component, whether or not it or that particular function is
activated, turned on, or unlocked, as long as that apparatus,
system, or component is so adapted, arranged, capable, configured,
enabled, operable, or operative.
[0033] All examples and conditional language recited herein are
intended for pedagogical objects to aid the reader in understanding
the invention and the concepts contributed by the inventor to
furthering the art, and are construed as being without limitation
to such specifically recited examples and conditions. Although
embodiments of the present inventions have been described in
detail, it should be understood that various changes,
substitutions, and alterations could be made hereto without
departing from the spirit and scope of the disclosure.
* * * * *