U.S. patent application number 09/795835 was filed with the patent office on 2001-11-29 for power adapter having a speaker for an electronic device.
Invention is credited to Hickman, Scott N, Muranami, Masahiko.
Application Number | 20010046305 09/795835 |
Document ID | / |
Family ID | 25471184 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046305 |
Kind Code |
A1 |
Muranami, Masahiko ; et
al. |
November 29, 2001 |
Power adapter having a speaker for an electronic device
Abstract
A power adapter for an electronic device, such as a notebook
computer, includes a speaker to generate low audio frequencies,
such as below 150 Hz. The speaker can be mounted in a variety of
arrangements, i.e. closed-box, bass-reflex, or a more intricate
shape which adds resonance (poles and zeros) to the acoustic
filtering properties of the enclosure. An exemplary bass-reflex
mounting includes a driver with resonance at 140 Hz, a chamber size
of 7.74 in.sup.3 and a port determined by Thiele-Small equations.
This gives a low frequency response beginning at 70 Hz. This low
frequency component is combined in free space with the higher
frequency components emanating from the portable electronic
device's internal speaker(s). The audio signal connection can be
made when the AC adapter is connected to the notebook computer by
using two additional wires in the power cord. Since users generally
carry their AC adapters with them, they can enjoy full harmonic
sound without taking anything extra along. Alternatively, the AC
adapter and electronic device can contain additional circuitry to
provide wireless paths for either the power distribution path or
audio interface or both.
Inventors: |
Muranami, Masahiko; (San
Jose, CA) ; Hickman, Scott N; (Corvallis,
OR) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P.O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
25471184 |
Appl. No.: |
09/795835 |
Filed: |
February 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09795835 |
Feb 27, 2001 |
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08938264 |
Sep 26, 1997 |
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6233343 |
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Current U.S.
Class: |
381/77 ;
361/679.55; 381/124; 381/338 |
Current CPC
Class: |
H04R 1/028 20130101;
H04R 2205/021 20130101; G06F 1/1632 20130101 |
Class at
Publication: |
381/77 ; 381/124;
361/683; 381/338 |
International
Class: |
H04B 003/00; H05K
005/00; H04B 001/00 |
Claims
What is claimed is:
1. A power adapter, comprising: a first speaker coupled to an audio
inlet; and means for converting energy from a mains receptacle to a
power outlet.
2. The power adapter of claim 1, further comprising: a cavity that
encloses said first speaker to form a resonant chamber.
3. The power adapter of claim 2, further comprising: a vented port
in said cavity.
4. The power adapter of claim 1, further comprising: a second
speaker coupled to said audio inlet.
5. The power adapter of claim 4, further comprising: a cavity the
encloses said first speaker and said second speaker to form a
resonant chamber.
6. The power adapter of claim 5, further comprising: a vented
portion said cavity.
7. The power adapter of claim 1, wherein: said means for converting
energy comprises an AC to DC switching power supply.
8. The power adapter of claim 1, wherein: said means for converting
energy comprises an AC to AC inductive transformer.
9. An electronic system with enhanced audio, comprising: an
electronic device, comprising; an audio outlet; a power inlet; a
power adapter external to said electronic device, comprising; a
mains receptacle; a power outlet; an audio inlet; a speaker
connected to said audio inlet; means for converting energy from
said mains receptacle to said power outlet; means for coupling said
power outlet to said power inlet; and means for interfacing said
audio outlet to said audio inlet.
10. The electronic system of claim 9, wherein: said electronic
device is a portable computer.
11. The electronic system of claim 9, wherein: said electronic
device is a portable television.
12. The electronic system of claim 9, wherein: said means for
coupling comprises a plurality of wires.
13. The electronic system of claim 9, wherein: said means for
coupling comprises wireless electromagnetic coupling.
14. The electronic system of claim 9, wherein: said means for
interfacing comprises a plurality of wires.
15. The electronic system of claim 9, wherein: said means for
interfacing comprises an infrared transmitter and an infrared
receiver.
16. The electronic system of claim 9, wherein: said means for
converting energy comprises an AC to DC switching power supply.
17. The electronic system of claim 9, wherein: said means for
converting energy comprises an AC to AC inductive transformer.
18. An electronic system with enhanced audio, comprising: an
electronic device, comprising; a power inlet; a power signal
coupled with said power inlet; an audio signal; a delta-sigma
modulator having said audio signal as an input and a modulated
signal as an output; means for superimposing said modulated signal
onto said power signal; a power adapter external to said electronic
device, comprising; a mains receptacle; a power outlet; means for
converting energy from said mains receptacle to said power outlet;
a superimposed signal received from said power outlet; a high pass
filter having said superimposed signal as an input and a filtered
digital signal as an output; a discriminator having said filtered
digital signal as an input and a recovered modulated signal as an
output; a low pass filter having said recovered modulated signal as
an input and a recovered audio signal as an output; a speaker
driven by said recovered audio signal; and means for coupling said
power outlet to said power inlet.
19. The electronic system of claim 18, wherein: said means for
coupling comprises a plurality of wires.
20. The electronic system of claim 18, wherein: said means for
coupling comprises wireless electromagnetic coupling.
21. The electronic system of claim 18, wherein said power adapter
further comprises: a cavity that encloses said speakers to form a
resonant chamber.
22. The electronic system of claim 21, wherein said power adapter
further comprises: a vented port in said cavity.
Description
BACKGROUND OF THE INVENTION
[0001] Electronic devices, such as notebook computers, are now
being designed to operate with multi-media features such as those
found in desktop units. In order for the user to have as enjoyable
an experience as with desktops, the sound emanating from the
notebook should present as full a harmonic content as the original
sound. Most notebooks today currently are limited to not having
frequencies generated below 150 Hz. Since most consumer audio
equipment supports a frequency range of 20 Hz to 20 kHz, the full
richness of the sound the user expects just is not present in
notebook computers.
[0002] Notebook computers are limited in generating this low
frequency content due to several factors. The first factor is that
the space limitation in the product restricts how large a speaker
may be used to replicate the sound. A second related factor is that
lower frequencies need to move a large mass of air to be heard and
there is little suitable volume in which to construct the air
chamber that a speaker needs. A third factor is that due to the
human ear's weak response to low frequency signals, more power is
required to generate a lower frequency signal with an equivalent
loudness compared to a signal greater than 150 Hz. More power
reduces the battery life of the notebook computer or requires more
expensive circuitry to implement than current designs.
[0003] Small electronic device makers such as notebook computer
manufacturers or small handheld television producers continually
fail to adequately provide a fill, rich harmonic sound in their
products.
SUMMARY OF THE INVENTION
[0004] A power adapter for an electronic device, such as a notebook
computer, includes a speaker to generate low audio frequencies,
such as below 150 Hz. The speaker can be mounted in a variety of
arrangements, i.e. closed-box, bass-reflex, or a more intricate
shape which adds resonance (poles and zeros) to the acoustic
filtering properties of the enclosure. An exemplary bass-reflex
mounting includes a driver with resonance at 140 Hz, a chamber size
of 7.74 in.sup.3 and a port determined by Thiele-Small equations.
This gives a low frequency response beginning at 70 Hz. This low
frequency component is combined in free space with the higher
frequency components emanating from the portable electronic
device's internal speaker(s). The audio signal connection can be
made when the AC adapter is connected to the notebook computer by
using two additional wires in the power cord. Since users generally
carry their AC adapters with them, they can enjoy full harmonic
sound without taking anything extra along. Alternatively, the AC
adapter and electronic device can contain additional circuitry to
provide wireless paths for either the power distribution path or
audio interface or both.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 shows an electronic device attached to the power
adapter of the preferred embodiment of the invention.
[0006] FIG. 2 shows another electronic device attached to the power
adapter of the preferred embodiment of the invention.
[0007] FIG. 3 shows the construction of the power adapter of the
preferred embodiment of the invention.
[0008] FIG. 4 shows the construction of the speaker element in the
preferred embodiment of the invention.
[0009] FIG. 5 is a frequency response graph showing the benefits of
the preferred embodiment of the invention over an alternative
embodiment.
[0010] FIG. 6 shows an alternative embodiment of the invention
using multiple speakers.
[0011] FIG. 7 shows the characteristics required of the speaker
port used in the preferred embodiment of the invention.
[0012] FIG. 8 is a block diagram showing the electronic device and
power adapter of the preferred embodiment of the invention.
[0013] FIG. 9 and FIG. 10 show an alternative embodiment of the
invention using wireless techniques.
[0014] FIG. 11 shows a block diagram of an alternative embodiment
of the invention using wireless techniques.
[0015] FIG. 12 shows a block diagram of an alternative embodiment
of the invention using superposition techniques.
DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS
[0016] FIG. 1 shows electronic device 12 as a notebook computer
having internal speakers 10 connected to power adapter 16 via
adapter cable 14. The power adapter 16 has mains receptacle 22
connected to AC mains via power cord 18. Inside power adapter 16 is
speaker 17 that supplies low frequency audio from electronic device
12.
[0017] FIG. 2 shows electronic device 12 as a portable handheld TV
that is connected to power adapter 16 through adapter cable 14.
Power adapter 16 has internal speaker 17 and mains receptacle 22.
Mains receptacle 22 is supplied mains AC power through power cord
18.
[0018] While electronic device 12 is shown above to be either a
notebook computer or a portable TV, those skilled in the art will
appreciate that electronic device 12 could be any small portable
device capable of generating sound and still fall within the spirit
and scope of the invention.
[0019] FIG. 3 shows power adapter 16 of the preferred embodiment in
more detail. A cut-away shows adapter circuitry 30 and a sample of
available air volume 42 in enclosure 44 of the adapter. Speaker 17
is preferably mounted on the top portion of power adapter 16 and
includes speaker port 48. Speaker port 48 has cross sectional area
36, diameter 34, and length 40, which create port volume 38,
enclosed within port wall 46. Adapter 16 connects to an electronic
device via adapter cable 14 that terminates in adapter plug 32.
External mains AC power is supplied to power adapter 16 through
mains receptacle 22.
[0020] FIG. 4A shows speaker 17 used in power adapter 16 of the
preferred embodiment of the invention in more detail. Speaker 17
consists of movable speaker cone 50 having area 54. Speaker 17 is
attached to adapter 16 using speaker flange 52. Speaker cone 50 has
a linear displacement movement 56 (FIG. 4B) that is related to the
sound it is reproducing and the environment in which it is
placed.
[0021] FIG. 5 is a graph comparing the low frequency response of a
speaker in two different implementations. Response of closed-box
adapter 62 has a very quick roll-off (6 dB per octave) below the
characteristic frequency f.sub.s of the speaker. Response of the
ported vent adapter 60 shows the relative increase in low frequency
response below f.sub.s, and the steeper roll-off (12 db per octive)
from using this technique.
[0022] FIG. 6 shows power adapter 16 in an alternate embodiment
that uses three speakers 17 (17A, 17B, 17C) in adapter enclosure 44
to get the desired bass response using speaker port 48 which has
port vent 36. FIG. 7 shows more detail of port vent 36 that has
length 40, cross-sectional area 36, and diameter 34. Port vent 36
is constructed such that it has wall thickness 46.
[0023] FIG. 8 is a block diagram of electronic device 12 and power
adapter 16 in the preferred embodiment of the invention. Adapter 16
has mains receptacle 22 that interfaces to energy converting
circuitry 66. The output of energy converting circuitry 66 is power
outlet 68. In the preferred embodiment, energy converting circuitry
66 converts a high voltage mains AC signal (e.g. 110 or 220 volts)
to a low voltage DC signal (e.g. 12 volts), although other types of
energy conversion could be used and still found within the spirit
and scope of the invention. Power outlet 68 is connected to power
inlet 76 on electronic device 12 via cable 14 and it supplies
energy to power supply 82, which may also receive energy from and
charge battery 80. Power supply 82 is used by other circuitry in
electronic device 12, including audio circuits 86. Audio circuits
86 generates an audio signal that optionally may be encoded in
audio circuit encoder 84 before being sent to audio outlet 78.
Adapter cable 14 is used to send the audio signal from audio outlet
78 to audio inlet 70 in power adapter 16. If the audio signal was
encoded, it is decoded in audio decoder 72 before being sent to
speaker 17. If additional bass boost is desired, the audio signal
may be amplified first using optional audio amplifier 74. Power
adapter 16 may have optional cavity 42 and optional port 48 that
can be used to increase the low frequency response of speaker 17
without resorting to audio amplifier 74, or it may be used in
combination with it.
[0024] FIG. 9 shows an alternate embodiment of the invention which
eliminates adapter cable 14, making it easier for the user to both
power electronic device 12 and have better low frequency audio,
using a wireless power adapter 88. The converted power can be
transmitted to the electronic device using an electromagnetic
coupled approach described in commonly assigned pending patent
application Ser. No. 08/759,693 which is incorporated herein by
reference. FIG. 10 shows how inductive charging field 64 couples
energy from power adapter 88 into electronic device 12. Electronic
device 12 generates the audio signal using an I/R beam 92 that is
received by power adapter 88 with I/R pickup 90. Power adapter 88
includes speaker(s) 17.
[0025] FIG. 11 is a block diagram of power adapter 88 and
electronic device 12. Power adapter 88 has mains receptacle 22
which preferably couples AC power to power select charging circuit
98 which drives primary winding 106. The inductive energy in
inductive charging field 64 is transferred to power converter
pickup 100 via secondary winding 108 on electronic device 12 and
onto power supply 82 which may also receive power from and charge
battery 80. Power supply 82 provides power to the internal
circuitry of electronic device 12 including audio circuits 86. To
control charging of battery 80, status information from the battery
charger in power supply 80 should be communicated to power adapter
88. Multiplexing battery status with the audio signal performs this
communication. The audio signal is digitized in digitizer 104,
encoded and multiplexed in encoder 84 with status from the battery
charger in power supply 82 before being transmitted using I/R
transmitter 102. I/R beam 92 is captured by I/R receiver 90 and
reconverted into a digital signal via redigitizer 94. This digital
audio signal is then decoded in decoder 72. The battery status is
separated and sent to power select 98 circuit, and reconverted to
an analog signal in D/A converter 96. This audio signal is then
optionally amplified in amplifier 74 before reaching speaker
17.
[0026] FIG. 12 shows power adapter 16 having mains recepticle 22
that supplies energy converting circuitry 66 which outputs a power
signal. The power signal arrives at electronic device 12 where it
has a modulated audio signal superimposed in mixer 108. The audio
signal from electronic device 12 is converted in delta sigma
modulator 104. The superimposed power signal is also received in
power adapter 16. The modulated audio signal is separated in high
pas filter 110 and reconverted into a modulated signal in
discriminator 106. The audio signal is then recovered from the
modulated signal in low pass filter 102 and sent to speaker 17.
[0027] To enhance the bass response of speaker 17, speaker 17 can
be chosen such that its equivalent acoustical compliance V.sub.s is
approximately equal to the volume of air which remains in adapter
cavity 42 after subtracting the volume of the electrical components
from the adapter inner volume. This results in a "closed-box
subwoofer". Alternatively, the enclosure volume could be expanded
or reduced to match the V.sub.s of the speaker if limited in
choices of speaker selection. This approach will have a system
effective low frequency response that is dependent upon the
acoustical properties of the speaker and amplifier. Generally
speaking, the system's effective frequency response will be
slightly above the resonant characteristic frequency of the
speaker, f.sub.s, while designing to achieve a flat response.
[0028] A ported enclosure can further enhance the efficiency of the
speaker at low frequencies. This type of enclosure, bass-reflex,
achieves its efficiency by delaying the sound waves behind the
speaker such that they become in phase with the sound waves
emanating from the front of the speaker and thus the front and back
sound waves combine in-phase by superposition. If designed
properly, this approach allows the speaker to have an effective
lower frequency response in addition to twice the efficiency of the
closed box design. The design of the ported speaker enclosure,
however, is more complex than the closed-box subwoofer. Use of a
ported enclosure in a notebook computer system is shown in commonly
assigned U.S. Pat. No. 5,610,992, incorporated by reference herein.
To increase the efficiency of speaker 17 in power adapter 16, a
ported speaker approach can be used by designing with the equations
provided by N. Theile in his articles "Loudspeakers in Vented
Boxes:Part I", Journal of the Audio Engineering Society, vol. 19,
No. 5, pp. 382-392 (May 1971), and "Loudspeakers in Vented
Boxes:Part II", Journal of the Audio Engineering Society, vol. 19,
No. 6, pp. 471-483 (Jun. 1971) also incorporated by reference
herein.
[0029] There are two approaches that can be used. The first, an
interactive approach, is to determine what approximate volume of
air is present in an adapter cavity and then determine the speaker
parameters that are required to implement that solution, then
adjusting the size of the adapter cavity to match design. The
designated speaker can then be purchased if found in a catalog, or
custom ordered to specification. Another approach is to select a
desirable speaker (due to cost, availability, size, etc) from a
catalog and using its supplied parameters determine if the speaker
will match with the acoustical compliance of the adapter cavity. It
may be desirable to use more than one speaker to achieve the
required equivalent acoustical compliance match. Table 1 defines
the terms used in the design calculations that follow.
1 TABLE 1 Term Definition V.sub.ab Volume of air in adapter cavity
used for acoustical design. V.sub.as Equivalent acoustical
compliance of speaker f.sub.3 -3 dB corner frequency of low
frequency roll-off representing the system response f.sub.s
Resonant characteristic frequency of speaker f.sub.b Resonant
frequency of adapter cavity, port and speaker defined as a resonant
system Q.sub.1s Total electrical, mechanical and acoustical Q of
speaker L.sub.v Length of vent in port S.sub.v Cross-sectional area
of vent in port V.sub.v Volume of vent in port V.sub.t Total volume
of adapter cavity and port vent, does not include components of
adapter X.sub.d Displacement of speaker cone C.sub.as Acoustical
compliance of speaker driver suspension C.sub.ab Acoustical
compliance of air in adapter enclosure Q.sub.t Total system Q (a
measure of acoustical dampening) S.sub.d Area of speaker driver
cone d Diameter of vent including wall thickness
[0030] For the first approach (see FIG. 3), to determine the ideal
custom speaker (FIG. 4) for a given cavity it is important to
determine the volume of open air 42 in the adapter. Typical
adapters use about one third of the volumetric space for the
circuitry 30 required to perform the energy conversion from the
mains power source to the transformed power source which meets the
voltage and current ratings of the portable electronic device. This
leaves approximately two thirds of the adapter volume that can be
used for lowering the dynamic range of the speaker. Assuming a
typical adapter such as the Hewlett-Packard F1044B, having a
physical size of 2.2 in by 1.2 in by 4.4 in or 11.6 in.sup.3 of
volume and approximately a V.sub.ab=7.74 in.sup.3
(11.6.times.0.67). Then from Thiel (May 1971) (Table I on page 388)
we chose that alignment which allows for a lower bass response than
the speaker alone which is number 9 (FIG. 5), a Chebyshev fourth
order design. The details provided from the table are 1 f 3 f s =
0.6 , 2 f 3 f b = 0.838 , Q ts = 0.557 , and V as V ab = 0.485
.
[0031] These details then give an equivalent acoustical compliance
of the speaker of V.sub.as=3.76 in.sup.3. Choosing the lowest
desired frequency of the system to be f.sub.3=70 Hz, then
f.sub.s=117 Hz, f.sub.b=117/0.838 or f.sub.b=140 Hz. The required
speaker parameters for the custom speaker are:
V.sub.as=3.76 in.sup.3, f.sub.s=117 Hz, Q.sub.ts=0.557.
[0032] Now we need to calculate the port dimensions required for
achieving the desired frequency response we have chosen. From Thiel
(May 1971), p. 391, equation 61 we can get the ratio of the length
of the port vent to the cross-sectional area of the vent; 3 L v S v
= 1.84 .times. 10 8 ( 2 f b ) 2 V b = 1.84 .times. 10 8 ( 2 140 ) 2
7.74 = 30.75 .
[0033] If we choose the port vent length to be approximately 4 in.
to fit within the enclosure, then S.sub.v=0.13 in.sup.2. To find
the end correction of the vent, equation 65 of Thiel (May 1971) is
used; 4 ( L v S v ) end = 0.823 S v = 0.823 0.13 = 2.28 ,
[0034] therefore;
L.sub.v=(30.75-2.28)x0.13=3.7 in.
[0035] The vent diameter can be found by adding the vent area and
the thickness (assume 0.062 in) of the vent wall; 5 d = 2 S v + 2 (
0.062 ) = 2 0.13 + 0.124 = 0.53 in .
[0036] The volume of the vent is then; 6 V v = d 2 L v 4 = ( ( 0.53
) ) 2 ( 3.7 ) 4 = 0.82 in 3 .
[0037] The adapter volume would then need to be increased to
accommodate this port volume. If we keep the width (2.2 in.) and
height (1.2 in.) constant and increase the length of the adapter by
7 0.82 in 3 2.2 in .times. 1.2 in = 0.31 in
[0038] to 4.71 in then the overall design is complete.
[0039] A different approach for implementation (see FIG. 6 and FIG.
7) would be to use standard speakers from a catalog and fit them
into an adapter housing which already exists. Assume a larger
standard adapter that is still a convenient size, that is 2.8 in by
1.5 in by 5.7 in or 24 in.sup.3. If the electronic components again
take up one third of the available volume, this leaves 16 in.sup.3
of volume in which to design the ported speaker enclosure. A
speaker with good low frequency characteristics is chosen from a
catalog such as the speaker model number Panasonic 5H-13371 with
the following specifications:
f.sub.s=239 Hz, V.sub.as=2.2 in.sup.3, Q.sub.ls=1.04, S.sub.d=0.7
in.sup.2.
[0040] From Thiel (May 1971) we again chose alignment #9 on p. 388
and use the following definitions for a forth order Chebyshev port
design: 8 f 3 f s = 0.6 , f 3 f b = 0.838 , C as C a b = 0.485 , Q
i = 0.557 .
[0041] We can then determine the following specifications using
three speakers:
f.sub.3=0.6f.sub.s=0.6(239)=143 Hz
f.sub.b=f.sub.3/0.838=143/0.838=171 Hz
V.sub.ab=V.sub.as/0.485=2.2/0.485=4.54 in.sup.3
V.sub.ab.vertline.3speakers=13.6 in.sup.3
[0042] 9 L v S v = 1.84 .times. 10 8 ( 2 f b ) 2 V ab = 1.84
.times. 10 8 ( 2 ( 171 ) ) 2 13.6 = 11.7 in - 1
[0043] From Thiel (May 1971), we want the port area to be
approximately one fourth the area of the driver thus; 10 S v = 0.7
4 = .175 in 2
[0044] We now need to determine the blunt end correction factor; 11
( L v S v ) end = 0.823 S v = 0.823 0.175 = 1.97
[0045] To determine the length of the vent; 12 L v 3 = ( L v S v 3
- ( L v S v ) end ) S v = ( 11.7 - 1.97 ) 0.175 = 1.71 in .
[0046] Assuming that the vent wall thickness is 0.062 in. then the
port diameter is; 13 d = 2 Sv + 2 ( 0.062 ) = 2 0.175 + 0.124 = 0.6
in .
[0047] The volume of the port is then;
V.sub.v.vertline.3=.pi.(0.3).sup.21.71=0.483 in.sup.3.
[0048] The total volume of the adapter cavity and port vent is;
V.sub.t.vertline.3=V.sub.b.vertline.3+V.sub.v.vertline.3=13.6+0.483=14.4
in.sup.3.
[0049] Since the available adapter volume is 16 in.sup.3, blocking
off 1.6 in.sup.3 of volume to better match the ported speaker
design would optimize the response.
[0050] Energy converting circuitry 66 in the preferred embodiment
is an AC/DC switching power supply or an inductive transformer to
provide an AC/AC conversion. The AC/DC approach, while more
complicated, is preferred as it can have higher efficiency and
trans-locates the circuitry from the electronic device to the
adapter where generally lower cost components can be used due to
the additional space. The alternate AC/AC approach has a typical
frequency of the AC supply being 50 Hz or 60 Hz. These frequencies
are near the desired low frequency (e.g. 70 Hz) of speaker 17 and
thus there is some chance that intercoupling of the power frequency
can occur in a wired cable which provides both for power
distribution and audio interfacing. Using a DC signal can prevent
the power intercoupling; however, there may still be some
intercoupling due to transient loads required of the adapter from
the electronic device. Since these loads vary depending on the use
pattern of the electronic device, filtering them out can be
challenging. It is therefore desirable to prevent this coupling
from occuring in the first place. One alternative approach is to
encode the audio signal before the interface such that the encoding
reduces the intercoupling from the power distribution to the audio
signal.
[0051] An alternate embodiment contemplated has the audio signal
superimposed onto the power signal, thereby reducing the number of
conductors in the cable from adapter 16 to electronic device 12.
Additional circuitry is required in both electronic device 12 and
adapter 16 to perform the superposition and decomposition of the
signals. Additionally, the power supply inside electronic device 12
needs to be tolerant to the audio signal, which can act as a noise
source on the input power signal. In this embodiment, a delta-sigma
modulator 104 is used on the audio signal to highly oversample the
audio signal. This modulation converts the analog signal to a high
frequency digital signal where the quantization noise is shaped to
the higher frequency portion of the signal content. This highly
oversampled signal is at a much higher frequency (for a 1000 Hz and
below audio signal, approximately 100 Khz) than the power signal.
This signal is filtered out at adapter 16 using high pass filter
110 to eliminate the power signal. The filtered signal is then
passed through discriminator 106 to restore the digital signal and
the digital signal is filtered using digital or analog methods in
low pass filter 102 to restore the analog audio signal while
removing the shaped quantization noise.
* * * * *