U.S. patent application number 10/334631 was filed with the patent office on 2003-05-29 for personal, self-programming, short-range transceiver system.
Invention is credited to Collins, John Austin, Dress, William Alexander, Dress, William Benjamin.
Application Number | 20030100331 10/334631 |
Document ID | / |
Family ID | 23679379 |
Filed Date | 2003-05-29 |
United States Patent
Application |
20030100331 |
Kind Code |
A1 |
Dress, William Alexander ;
et al. |
May 29, 2003 |
Personal, self-programming, short-range transceiver system
Abstract
A method for establishing a communication link between a
transmitter and a receiver for the purpose of relaying audio
material derived from an existing source to a user desiring to
remain unencumbered by the source apparatus comprises the steps of
placing: the receiver unit into physical contact with the
transmitter unit, powering up both transmitter and receiver units,
and waiting for an indication of process completion before setting
the receiver unit in place. The transmitter unit searches for a
free rf communication channel, initiates transmission of
user-chosen audio material over permitted broadcast bands, and
programs the receiver unit with information allowing it to receive
on the same channel. The receiver unit is lightweight, worn in the
outer canal of the ear or on the head in the conventional manner.
The entire programming and transmission process takes place
automatically without further user intervention. This method allows
multiple users in proximity to receive their individually chosen
source material or to enjoy a common transmission.
Inventors: |
Dress, William Alexander;
(Knoxville, TN) ; Dress, William Benjamin;
(Knoxville, TN) ; Collins, John Austin;
(Knoxville, TN) |
Correspondence
Address: |
GRAY, CARY, WARE & FREIDENRICH LLP
1221 SOUTH MOPAC EXPRESSWAY
SUITE 400
AUSTIN
TX
78746-6875
US
|
Family ID: |
23679379 |
Appl. No.: |
10/334631 |
Filed: |
December 31, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10334631 |
Dec 31, 2002 |
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09423574 |
Nov 10, 1999 |
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6519448 |
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09423574 |
Nov 10, 1999 |
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PCT/US98/20531 |
Sep 30, 1998 |
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Current U.S.
Class: |
455/550.1 ;
455/41.1 |
Current CPC
Class: |
H03J 1/0091
20130101 |
Class at
Publication: |
455/550 ;
455/41 |
International
Class: |
H04B 001/38 |
Claims
What is claimed is:
1. A receiver unit or system comprising: a means for receiving and
demodulating frequency-, phase-, pulse-, or amplitude-modulated rf
information; a means for decoding said information to baseband to
recover the encoded audio signal; a method of generating and
maintaining a local heterodyne frequency to accomplish said
decoding; a method of selecting the source of rf input signal from
either of two sources, said sources being an rf signal at from the
integral antenna or from an included input connector or contact; a
means for converting said audio signal to an acoustic transducer; a
means for incorporating the acoustic transducer within a earphone
housing; and a means for supplying necessary power to all
circuitry.
2. A base unit or transmitter system comprising: a means for
modulating a preselected rf carrier frequency by an audio input
signal, said means being either phase, frequency, pulse, or
amplitude modulation; a means for transmitting said modulated
carrier; a method of selecting said carrier frequency; a means for
generating said carrier frequency by means of a frequency
synthesizer, a means for monitoring and charging the earphone
batteries of claim 1; and a method of establishing the local
heterodyne frequency of claim 1.
3. The method of claim 2, wherein said selection method subdivides
the frequency band into a plurality of bands, one of which,
sufficiently free of interference, is chosen for transmission by
the apparatus of claim 2.
4. An apparatus of claim 3 wherein said subdivision is accomplished
by a swept, voltage-controlled oscillator, said sweep lasting a
predetermined duration or until such time as a suitable channel has
been located.
5. An apparatus of claim 3 wherein said subdivision is accomplished
by a digital frequency synthesizer commanded by incrementing a
digital counter integral to said digital frequency synthesizer,
said counter being incremented until a suitable channel has been
located.
6. An apparatus of claim 3 wherein said frequency band is chosen
based on the signal level present in a particular bandwidth range
said bandwidth range being selected by the method of claim 3, the
selected frequency being applied to a mixer that mixes said
selected frequency with the signal received by the antenna of the
apparatus of claim 2. The output of said mixer being filtered and
compared to a predetermined level. The criterion for selection of
said frequency band being that said output be lower than said
predetermined level.
7. A method of commanding or programming the apparatus of claim 1
to cause said apparatus to start receiving on the frequency band
selected by the apparatus of claim 2.
8. An apparatus of claim 7 for causing a command signal from the
apparatus of claim 2 to the apparatus of claim 1 and information
describing the carrier frequency from the apparatus of claim 2 to
the apparatus of claim 1 by means of a common contacts between said
apparatuses, said command signal being a logic level and said
descriptive information being a sample of the output of the carrier
frequency generated by the frequency synthesizer of claim 2.
9. An apparatus of claim 8, said command signal being a logic level
of sufficient duration and said descriptive information being a
binary code describing said carrier frequency, the length of said
descriptive information presented to the apparatus of claim 1 being
determined by the duration of said logic level.
10. A method of claim 9 wherein the length of said descriptive
information is determined by the trailing edge of said command
signal logic level.
11. An apparatus of claim 1 wherein said local heterodyne frequency
is maintained by a phase-locked loop subsequent to transmission
from the apparatus of claim 2 established by the command level of
claim 8.
12. An apparatus of claim 1 wherein said local heterodyne frequency
is maintained by a digitally controlled frequency synthesizer that
receives its code from the apparatus of claim 9.
13. A method of claim 2 wherein any apparatus of claim 1 may be
frequency locked to any representative apparatus of claim 2 once
said apparatus is transmitting.
14. The apparatus of claim 1, wherein said electronics are
manufactured with surface-mount technologies using monolithic
integrated, discrete-component circuits, effecting a micro-receiver
suitable for miniature earphones.
15. The apparatus of claim 2, wherein said audio source is
contained within the apparatus of claim 2 rather than being an
auxiliary or external source.
16 The apparatus of claim 15, wherein said contained audio source
is a microphone with associated level control components.
17. The apparatus of claim 2, wherein said apparatus is
incorporated into or contained within other electronics devices
that provide source material for transmission.
18. An apparatus of claim 1, wherein said electronics are digital
in nature, making use of any of the common digital methods of
demodulation and decoding as customary in spread-spectrum devices,
said methods being any of time-division multiple access,
code-division multiple access, or frequency-division multiple
access.
19. An apparatus of claim 2, wherein said electronics are digital
in nature, making use of any of the common digital methods of
modulation and encoding as customary in spread-spectrum devices,
said methods being any of time-division multiple access,
code-division multiple access, or frequency-division multiple
access.
20. The apparatus of claim 1, wherein said earphones are mounted
externally to the ear and either attached to the ear by independent
loop contrivances or attached together with said attachment wire or
frame being worn over the head in the usual manner of
earphones.
21. An apparatus of claim 1, wherein said receiver unit presents
its demodulated audio signal to a connector rather than to an
acoustic transducer, making said audio signal available for use by
other electro-acoustic devices.
Description
TECHNICAL FIELD
[0001] The technical field of the invention is that of a consumer
electronics device based on wireless transmission of information.
The range of transmissions is purely local (i.e., short distances
up to thirty meters, more or less) and designed to provide a
personal transmission channel from a nearby audio source such as a
tape recorder, record player, compact-disk player, radio set, and
so forth. The transmitter and receiver technology operate in the
standard radio-frequency bands such as the US 88 Megahertz (MHz) to
108 MHz FM band or in the unregulated low-power bands where
standard frequency- and phase-modulation techniques are employed or
in the very-low frequency band where pulse-modulation techniques
are common.
BACKGROUND ART
[0002] The field of consumer audio electronics comprises a wide
variety of personal listening devices--from hand-held and wearable
radios and communicators to potable devices for retrieving audio
information stored in many forms such as cassette-tape media and
compact-disk media of various types. There also exist various
earphone devices auxiliary to or integral with many of these
personal entertainment devices. The vast majority of these personal
listening or entertainment devices require that the sound storage
and playback unit, i.e., the sound source that produces an
electrical signal in the audio range, be carried along with the
user. A majority of these latter devices that are equipped with
personal earphone units send an electrical signal from the playback
device to the earphone device via a cable or wire, potentially
encumbering the user or providing an easily noticed indicator that
the user is engaged in some sort of entertainment activity via an
audio source. Of course, there are a large number of such
commercial devices, ranging from those trade-marked to those fully
patent-protected, that are easily recognizable in the marketplace.
It is to be noted that the field of such devices, comprising the
bulk of the prior art, is too large to enumerate in this document.
The following discussion will be restricted to devices that are
more clearly and particularly focused in the field of the present
invention.
[0003] A commonly encountered device is a fully functional FM or AM
radio built into a set of wearable headphones. The advantages are
complete portability, wearability, and tuneability over the full
broadcast bands, including stereo reception for the FM band. For
example U.S. Pat. No. 4,930,148 describes a headband radiophone
containing a receiver-transmitter to reciprocally transmit or
receive signals. Another example is furnished by U.S. Pat. No.
5,095,382 which describes a wireless headphone designed to
reciprocally transmit and receive signals by means of an infrared
beam of light.
[0004] There are also several types of wireless headphones on the
market primarily designed to allow the user to listen to audio
sources such as television or a home-music or entertainment center
without disturbing others. The wireless nature of said devices
allows the user freedom to move about within the restricted range
of the transmissions without being encumbered by wires or cables
precisely as in the present invention. These wireless headsets are
meant for use in restricted areas usually confined to a few rooms
in or near a dwelling and do not provide capacity for a plurality
of channels for multiple users. The latter capability is achieved
by purchasing multiple units. As each device comes with its own
pre-assigned channel, these devices are not suitable for group
activities. The present invention would fulfill the stated purposes
of these existing devices yet not be burdened with the
aforementioned restrictions and limitations. In particular, the
present invention allows multiple independent users in the same
proximity by means of its self-programming function, and it allows
multiple users to share in the same locally broadcast material
without requiring multiple base units or transmitters.
[0005] Closer to the present invention is U.S. Pat. No. 5,677,964,
which describes a transmitter-receiver system wherein the
transmitter unit is installed in an audio equipment and the
receiver unit is installed in an earphone. A goal here is to allow
the user to listen to information transmitted from the audio
equipment without interfering with others in the vicinity or having
exposed wires or cables between the audio equipment and the
listener.
[0006] An invention likewise close to the present invention in the
area of miniaturization by describing a device fitting within the
outer canal of the ear, is U.S. Pat. No. 5,734,976 which describes
a micro-receiver for receiving a high-frequency frequency- or
phase-modulated signal and is based on single integrated circuits
in BiCMOS technology integrating the necessary amplifiers,
oscillators, modulators, demodulators, filters and audio
amplifier.
[0007] The description of U.S. Pat. No. 5,677,964 includes a
transmitter partially fulfilling the role of the "base unit"
described in the present invention. That of U.S. Pat. No. 5,734,976
is primarily concerned with a prosthetic hearing-aid device, yet
certainly meets one of the desired goals of the present invention
in being small, lightweight, unobtrusive, and capable of being worn
in the outer canal of the ear and containing the required receiver
circuitry and power supply. Neither of these descriptions considers
a base unit that automatically selects the first available
frequency band for transmissions, or a base unit that automatically
programs the receiver unit to receive transmissions on said
frequency band, or a base unit that is functionally as portable as
the receiver unit. The second description also implies that the
associated transmitter unit is to be worn by the user as
necessitated by utility of prosthetic hearing-aid devices.
Combining the essential ideas present in these two existing
inventions approaches, but does not reach, the functionality and
convenience of the proposed invention.
DISCLOSURE OF INVENTION
[0008] The idea of the invention is to provide a private and
unobtrusive means for a user to listen to a local (nearby) source
of music or other audio entertainment or information on a
dynamically selected channel that is simple to establish and does
not interfere with possibly many other users at the same location.
Logically and physically, the invention comprises two distinct
modules: (1) a receiver or earphone and (2) a transmitter or base
unit It is thus the intention of the invention to provide a
wireless connection between the earphones and base unit, allowing
the user to move freely about, unencumbered by cables or wires,
within the limited range of the base unit's transmissions. It is a
primary intention of this invention to allow multiple users in the
same location either to listen to independent sources of
entertainment or information or, if desired, to share such sources
with others possessing similar receiver units (earphones).
Furthermore, it is the intention of the invention that the receiver
unit be small, compact, lightweight, and unobtrusive both visually
and kinesthetically.
[0009] The first module consists of a lightweight, wireless,
radio-frequency receiver or receiver pair (for stereo sources)
mounted in lightweight headphone or head set or earphones.
"Earphones" in the following description is understood to refer to
any convenient ear-external or internal device consistent with the
contained receiver units. The earphones may be either externally
worn or internally fitted to be placed in the outer canal of the
ear, as the user desires. Furthermore, the earphone receiver units
are "self-programed" as described below. This latter feature
ensures simplicity of operation and ease of use while maintaining
flexibility of multiple devices operating in the same local area
while minimizing inter-unit interference.
[0010] The second module, the transmitter or base unit, has four
functions: (1) to select automatically a clear transmission channel
for said transmission, (2) to program or lock the earphones to
receive exclusively on said automatically preselected channel, (3)
to modulate an appropriate radio frequency on said channel by the
chosen audio-level input for low-power transmission to the
earphones, and (4) to provide power to the earphones by way of
charging their contained batteries. The base unit is likewise
small, lightweight, and portable, being just large enough to
contain (1) the scanning circuitry, (2) the programming circuitry,
(3) the transmitter circuitry, (4) the battery-charging circuitry,
(5) minimal controls and indicators, (6) appropriate signal
connectors, and (7) a battery or other type of power supply.
[0011] In a typical situation, the user switches both the earphones
and the base unit to the "on" position as indicated by small
light-emitting diode indicators and then inserts the earphones into
specially designed receptacles located in the base unit. The
power-on action initiates charging of the earphone batteries should
they require it. This power-on action also initiates a "scan"
function comprising a sequence of events that (1) effectively
searches for an "open" channel, (2) locks a frequency synthesizer
or phase-locked loop to the frequency of the first open channel
thus located, and (3) sends a "lock" command via contacts located
in the receptacles to a frequency synthesizer or phase-locked loop
in each of the earphones. At the end of this "auto-programming"
sequence, (4) a "ready" indicator or signal indicates that the user
may now remove the earphones and place them in position for
listening, moving about the area as desired, within the limited
range of the base-unit's transmitter, receiving the audio
information from the source connected to the base unit via the
standard process of demodulation, amplification, and presentation
of the electrical signal thus obtained to the earphones'
electrical-acoustic transducers.
[0012] Other users of similar devices located within the same
transmission range, or even in overlapping transmission areas of
the first device, will not find an open channel at the same
frequency chosen by the unit just program or any active
prior-activated units as well. Any base unit attempting to program
its own earphones will scan for the first clear channel, starting
at one end of the selected spectrum, ensuring that no user will
interfere with any other and no strong, established broadcasts will
interfere with a user's auto-selected channel. The number of
channels available in any area depends on the broadcast band chosen
and the bandwidth (plus guard band) for each device. As an example,
assume parameters consistent with the standard US FM broadcast band
of 88 to 108 MHz and 100 KHz bands, there would be "room" for
perhaps 200 independent users, not accounting for any strong
commercial FM broadcasts, which would reduce this number by at
least one unit for each such strong station.
[0013] If other users of an identical device within the same
transmission range wished to listen on a common channel and hence
to the same audio source as provided via transmission by any given
base unit, they would simply place their compatible earphones into
the receptacles of said base unit and depress a secondary "program"
or "lock" control button. Such action would lock their earphones to
the preselected channel of the chosen unit. In this manner,
multiple users can listen to the same source, allowing for class or
shared-listening activity.
[0014] Due to its compact nature, the earphone electronics are
fabricated with surface-mount methods using standard integrated
circuits and monolithic lumped components. Discrete components are
used in the circuit where necessary to establish externally
selected frequency ranges as well as other functions such as
passive filters. Both receiver and transmitter units are separately
powered, with the receiver earphones having a battery power supply,
and the base unit either a battery or other means of power.
[0015] The key features of the invention are summarized as its
ability to avoid interference with commercial broadcasts due to the
auto-scan feature; to be compliant with communication authorities'
rules of low power and short range in certain restricted bands; to
its "foolproof" use based on minimal controls and no adjustments;
to provide wireless operation; to contain rechargeable or
replaceable batteries in base unit; to contain rechargeable and/or
replaceable batteries in earphones; to restrict the physical
dimensions of the base unit into a small, compact, lightweight, and
easily transportable and detachable module independent from any
particular source of program material; and to provide the user with
the earphones that are ultra-light weight and/or fit in outer ear
or mounted on a lightweight, supporting frame.
[0016] Although the primary conception and purpose of this
invention is to provide an auxiliary but extended capability for
standard sources of audio material in the sense that any source
device having the required "signal" or "audio" output connector
with compatible impedance characteristics can be connected to the
base unit described in this invention, there are numerous
variations possible based on the described invention besides the
mentioned uses of transmitting local audio to listeners not wishing
to be encumbered by wires or highly visible head pieces. These
variations may be differentiated, among other characteristics, by
various sources for the transmitted audio material. The preferred
embodiment presented herein should in no way restrict the present
invention to a particular configuration as regards usage.
[0017] A modification of the base unit could be made with a
built-in microphone or an input with an impedance-matching
amplifier and gain control designed for such a microphone. Such a
unit could be used to send verbal messages or any other sound based
on sound pressure waves to those with compatible earphones. For
example, a type of selective-broadcast communication only to users
having completed the "lock" process with the centrally chosen base
unit could be established, allowing only those users to receive
said communication, even though in a crowd or noisy location.
[0018] A modification of the base unit could be made to equip it
with a built-in radio receiver allowing the user to select a local
radio station for listening remotely from said radio receiver.
Otherwise and more generally stated, the standard types of sound
reproduction devices could incorporate the invention described here
rather than said invention serving said devices as an auxiliary. In
which case, the auto-scanning and self-programming functions would
be retained as essential to benefit from the innovations described
herein.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 depicts a particular representation of the base units
and illustrates how the earphones fit into the provided
receptacles.
[0020] FIG. 2 is a block diagram of a typical application
illustrating the logical relation of the audio source, base unit,
earphones, and the user following programming by the base unit.
[0021] FIG. 3 is a functional block diagram of the base unit
showing the logical relationships between the three functional
modules of scanner, transmitter, and programmer.
[0022] FIG. 4 shows details of the functional modules comprising
the base unit depicted in FIG. 3.
[0023] FIG. 5 is a functional block diagram of one of the
earphones; the other is identical except that it receives the
alternate stereo channel when applicable.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] A transmitter-receiver system in accordance with the present
invention is comprised of a transmitter unit (the "base unit") that
is either a separate module connected to an audio source by means
of a cable or suitable connector or integral to such a source, and
a receiver unit installed in an earphone or earphone pair
("earphones"). The inventive arrangements are directed to methods
and apparatuses for establishing a clear channel for the desired
transmission and for locking the receiver units to said clear
channel, ensuring that said transmitter and receiver units function
together as an integrated system. Secondary goals of lightweight
and unobtrusive earphones, the maintenance of sufficient energy for
the earphones, and wireless communications that includes
modulation, demodulation, methods of maintaining frequency
stability, amplification of rf and audio signals, and driving
appropriate electro-acoustic transducers are accomplished by
incorporating features and devices that are well known to those
familiar in the art
[0025] The present invention has been accomplished to provide a
transmitter-receiver system which eliminates the aforesaid problems
and simultaneously meets the particular objectives of effecting a
private and unobtrusive means of listening to a nearby source of
information, said means being simple to use yet having minimal
interference with other users of the same rf band in the same local
area. To this end, a wireless rf link between a self-programming,
transmitting base unit, and a receiver mounted in small,
lightweight earphones are described in detail. A particular
preferred means for effecting these goals is presented, along with
obvious and useful variations that extend the preferred means in
several nonessential ways.
[0026] A power source, typically a battery, together with its
necessary connections to each of the functional modules and devices
depicted is to be understood to be functionally present in all of
the figures, as is a suitable return path (earth or ground) for
returning current. to the power source, thus completing the
circuits as required.
[0027] Referring now to the drawings wherein like numbers refer to
like parts, FIG. 1 is a conceptual view showing the relationship
between the base unit 100 and the earphones 200 before and after
the programming operation and schematically indicating the process
of such programming. Other configurations are possible, so the
illustration of this particular configuration is not to be
restrictive for implementation or use of the invention. A
particular placement of the controls comprising power switch 102,
indicator lights 104 and 106, and audio-input connector 108 are
also shown. Control 112 allows manual programming of the earphones
200 once the programming operation is complete as indicated by
indicator light 104 changing state from flashing to steady. The
arrows indicate the process of inserting and removing the earphones
200 from their programming receptacles 110 in base unit 100.
Contacts 201, 203, and 207, located on earphones 200, have mating
contacts (not shown) in base unit 100 and allow communications
necessary for the programming activity to take place between these
two functional modules.
[0028] FIG. 2 is a block diagram showing the unified operation of
the earphones 200 and the base unit 100. The earphones 200 have
already been programmed by the scanning function of the base unit
100 and are shown receiving the rf signal modulated by the audio
source, which may be any of a plurality of readily available
devices such as tape players, compact-disk players, and so forth.
The presence of the user is indicated by a sketch of a head in the
figure.
[0029] FIG. 3 is a block diagram of base unit 100 of FIG. 1. The
operation of this unit is described in functional order starting
with activation of the power-on switch 102, which supplies power
from battery 118 to all associated electronics via line 111, resets
all circuits and logic in base unit 100 to a standard initial
state, initiates the scanning and programming sequences, and causes
the "scan" indicator light 104 to flash, indicating that the
scanning sequence is in progress and that the unit has power. The
function of the three submodules are described here, while details
are deferred to a subsequent figure.
[0030] The scanner 120 comprises a scan controller 130, a channel
detector 150, a shared frequency synthesizer 170, a
transmit-receive switch 122 and indicator lights 104 and 106. Upon
power-on, the scan controller 130 examines the state of the
earphones 200 via line 113; if not turned on before insertion into
receptacles (110 of FIG. 1), warning light 106 is illuminated
indicating a procedural error to be corrected. The later criterion
being met or the error corrected, the scan controller 130 signals
the programmer 190 via line 117 and starts a frequency-sweep
sequence, sending coded information to the frequency synthesizer
170 via line 119, controlling the frequency-scanning sequence. The
channel detector 150 receives the synthesized frequency (local
oscillator frequency) from line 121 via the switch 122, which is
set to connect the frequency synthesizer 170 to the channel
detector 150 during the initialation sequence. The channel detector
150 then examines the signal from the antenna 114 via line 115
which signal is heterodyned with the synthesized frequency entrant
on line 121 in a manner familiar to those skilled in the art. The
transmit-receive switch 116 is likewise configured to connect the
antenna to the channel detector 150 during the initialization
sequence. The function of the channel detector 150 is to locate a
frequency subband where there is little or no carrier present. Such
a subband being located, the channel detector 150 signals the scan
controller 130 via line 123, whereupon scan controller 130 stops
commanding the frequency synthesizer 170 to advance, sends a signal
to the programmer 190 via line 125, changes the state of indicator
light "scan" 104 from flashing to continuously on, indicating that
the user may proceed to the next stage. Additionally, switches 116
and 122 are set to the alternate or "transmit" state via signals
(not shown) from the scan controller 130.
[0031] The programmer 190 comprises a battery charger 192 and a
one-shot circuit 194. Details concerning the action of the battery
charger 192 are known to those familiar with the art and are not
elaborated upon here. Upon receiving a start signal via line 117,
the battery charger examines the voltage level on each of the
batteries in the earphones 200 (FIG. 1) and supplies any current
needed to charge them to the operational point, said charging
operation taking place during the scan sequence; the charging
current is presented to the earphones via line 127 through contact
103. Contact 107 made to each earphone via connector block or
receptacle 110 transmits an enabling level from oneshot 194 via
line 129. Those skilled in the art recognize that oneshot 194 can
be made to emit a logic pulse of predetermined duration given a
leading- or trailing-edge trigger input as may be applied by the
scan controller 130 upon completion of its scan process or at the
discretion of the user via external control 112 via line 109.
Contact 101 in connector block 110 receives a sample of the
frequency of the located rf subband via line 124. Contact 105 in
connector block 110 provides a common ground to the earphones.
[0032] The transmitter 160 comprises the shared frequency
synthesizer 170, a modulator 180, and an rf amplifier 162. At the
end of the scan cycle as indicated by signals from the scan
controller 130, the switch 122 is configured so that the signal
from frequency synthesizer 170 is applied as the carrier frequency
to the modulator 180. The details of the phase and frequency
modulation as performed by modulator 180 are well known to those
skilled in the art and need not be described in detail. The
audio-in signal via connector 108 is used to modulate said carrier
frequency, whence the modulated carrier is amplified as necessary
by rf amplifier 162 and allowed to reach antenna 114 through switch
116, which has changed state via a signal (not shown) from scan
controller 130.
[0033] FIG. 4a shows the details of the scan controller 130. Upon
receiving power via line 111 from the power-on switch (102 FIG. 3),
AND gate 134 senses the state of the unit's power. The state of
earphones 200 (FIG. 1) is sensed via line 113 by comparator 136
whose output, indicating "on" state for the earphones 200 (FIG. 1),
is also applied to AND gate 134. Reference 132 in an internally set
parameter chosen according to design parameters. The complementary
state of the comparator 136 is sent to buffer amplifier 138 which
connects to "fault" indicator light 106 should the earphones 200
(FIG. 1) be in the power-off state. The AND gate 134 passes the
"start" logic level obtained from the power line via line 111 when
power is on in both the base unit 100 (FIG. 1) and earphones 200
(FIG. 1). Power-on switch 102 (FIG. 3), via line 111, also applies
power (via the V.sub.CC connections common to all modules) to
multivibrator 140 to send a flashing signal to buffer 142 and
thence to indicator light 104 indicating that a scan is in
progress. The logic level from AND gate 134 triggers oneshot 144
which emits a logic pulse or level of duration of approximately 1
second, predetermined by the time-constant capacitor (not shown).
This level is applied to integrator 146 and thence to
sample-and-follow 148. The output of sample-and-follow 148 follows
the input from the integrator 146 until it receives a "sample"
command. Said output is sent to the frequency synthesizer 170 (FIG.
3) via line 119. Once a clear channel is located as determined by
the channel detector 150 (FIG. 3), line 123 is activated by said
channel detector. A high logic level on line 129, buffered by
amplifier 149, causes sample-and-follow 148 to sample and transfer
a digitally coded version of its input voltage to its internal
digital memory, effectively maintaining said voltage level for
subsequent presentation to the frequency synthesizer 170 (FIG. 3).
The particular details of how said sample-and-follow accomplishes
its function are known to those familiar with the art. Said logic
level on line 129 also halts multivibrator 140, leaving it in a
"high" state so that indicator light 104 is now steadily
illuminated indicating an end to the scan process and communicating
the "ready" state to the user.
[0034] Referring now to FIG. 4b, which depicts the details of the
channel detector 150, an rf signal from the antenna 114 (FIG. 3)
enters via line 115 and is filtered in band-pass filter 151 which
is set broad enough to encompass the frequency band of interest
over which the transmitted information might appear, depending on
the particular operating band pre-chosen for the device. Said
signal thence passing to rf amplifier 152 and to mixer 154 wherein
said antenna signal is heterodyned with the frequency signal from
frequency synthesizer 170 (FIG. 3) via line 126 after being
buffered by amplifier 153. The heterodyned signal, now at baseband
of the frequency from said frequency synthesizer, is passed through
low-pass filter 155. Filtered by integrator 157 to remove ripples,
the slowly varying, nearly DC signal is presented to comparator
158. Said comparator compares the input signal to a preset voltage
reference level 159. When said signal falls below a said reference
value, the comparator communicates this information as a voltage
level via line 123.
[0035] FIG. 4c shows the details of the frequency synthesizer 170
which comprises a voltage-controlled oscillator 172 and a band-pass
filter 174 in this embodiment. Line 119 conveys the ramp signal
produced by integrator 146 (FIG. 4a) via sample-and-follow 148
(FIG. 4a), causing the voltage-controlled oscillator 172 to slowly
increase its frequency from the lower end of the preselected
frequency band to the upper end of said band. Said increase in
frequency is presented to the channel detector 150 via lines 121
and 126 (FIG. 3) causing said channel detector to scan the
frequency band of interest until the input to said
voltage-controlled oscillator no longer changes.
[0036] A block diagram of the earphone circuitry 200 is shown in
FIG. 5. Said circuitry comprises a complete rf receiver system 220,
that receives its signal to be selected and demodulated in the
manner known to those familiar with the art, via line 209. In the
programming mode, which is controlled by the scan controller 130
(FIG. 3) via contact 207, the transmit-receive switch 210 connects
contact 201 to the said receiver via line 209. Said
transmit-receive switch is placed in the aforementioned position by
powering up said earphones by closing switch 204, which allows the
internal battery 206 to be connected to the V.sub.CC line that
powers all modules present in said earphones. Once the base unit
100 (FIG. 1) has selected an appropriate frequency for
transmissions, input to latch 208 rises via contact 207 having
received a voltage level from one-shot 194 (FIG. 3) in programmer
190 (FIG. 3) via line 129 (FIG. 3). The falling edge of said
voltage level triggers latch 208 which commands switch 210 to
disconnect line from contact 201 and connect antenna 214 to
receiver 220 via line 209. At this point, the receiver is receiving
and decoding the transmitted material encoded by the transmitter
160 (FIG. 3). The decoded audio signal is presented to audio
amplifier 212 via line 211. Receiver 220 also produces an automatic
gain control signal in a manner familiar to those skilled in the
art, presenting said signal via line 213 to said audio amplifier
for the purpose of controlling the gain of said amplifier should
the signal at the antenna 214 weaken or strengthen due to the user
moving too far from or too close to the base unit 100 (FIG. 1).
Following amplification, the decoded audio signal is converted to
sound-pressure waves by the electro-acoustic transducer 215,
whereupon the user may listen to said audio signal while moving
about the area.
[0037] In the preferred embodiment, receiver 220 is a simple
phase-locked loop (PLL) well known to those skilled in the art.
Said PLL is augmented in a manner likewise well known to provide a
signal proportional to the strength of said carrier frequency for
use as an automatic gain control in addition to the demodulated
frequency- or phase-modulated carrier that is subsequently
amplified and converted to the desired acoustic signal. The
operation of said recover as regards the particulars of the present
invention is described in the paragraph above.
[0038] An alternate configuration that is more reliable in
frequency locking and holding, but requires additional circuitry,
is briefly described here. The alternate method relies on digital
synthesis of frequency in the base unit 100 and communication of a
digital code for said frequency to the earphones 200. This is
accomplished by modifying the scan controller 130 as follows.
Replace oneshot 144, integrator 146, and sample-and-hold 148 by an
oscillator running at a rate of approximately 256 Hz and a
monostable to produce a train of pulses that are presented to
digital frequency synthesizer 170 via line 119. Upon receiving a
pulse, said frequency synthesizer advances by approximately 50 KHz
more or less, presenting said frequency to the channel detector
150, which functions as above. Upon selection of a suitable
frequency band, channel detector 150 signals scan controller 130 as
above via line 123. Said signal halts said oscillator, effectively
maintaining the current digital count held by the digital frequency
synthesizer 170. Said digital frequency synthesizer is then clocked
by a signal from scan controller 130 via a line not shown to
command said digital frequency synthesizer to present the coded
word locked in its internal scalar/counter as a parallel 8-bit
digital word to a parallel-to-serial converter in the scan
controller 130. The serial code is subsequently sent to contact 101
during the logic level strobe from said scan controller via line
129. On the earphone side, via contact 201, the serial code is
converted to a parallel digital 8-bit word by a serial-to-parallel
converter (not shown) and read into the digital frequency
synthesizer (not shown) contained as a part of receiver 220 of said
earphones 200.
INDUSTRIAL APPLICABILITY
[0039] The present invention is aimed at the consumer entertainment
area where individual users desire privacy or wish not to disturb
near-by persons, desire freedom from constricting and unsightly
wires, and desire to be unencumbered by a the source of sound
entertainment or information attached to their person. The
invention is useful to anyone already in possession of a primary
sound source exemplified by but not restricted to a cassette tape
player, a commercial-band fm or am radio, a compact-disk player, a
television set, or any form of local sound monitor incorporating a
microphone or other means of producing electro-acoustic information
or entertainment. As an add-on or auxiliary device to be used in
conjunction with the aforementioned sound sources, possession of a
device based on the present invention becomes a desirable goal. As
a system incorporated into presently available primary sources of
entertainment or information such as listed above by way of
example, the present invention would materially extend the
capability of such primary sources and hence increase the
usefulness of said sources beyond that of said sources not
incorporating the present invention.
[0040] Additionally, group activities such as museum tours wherein
each group member's earphones are tuned to the same base unit would
also be an appropriate and desirable application. There are s
systems currently available that meet this requirement, but once
manufactured as a consumer entertainment device, adaptation of the
present invention to group usage would be much more cost effective
than such presently available systems. This group-usage
functionality is incorporated into the present invention by
intention of design as described above.
[0041] By a simple modification, the receiver unit can be made to
present its audio signal to a connector rather than to acoustic
transducers. Such signal being available as a source of information
for self-powered speakers containing appropriate audio amplifiers.
This modification allows, for example, a remote, indoor sound
source to service outdoor speakers, while maintaining the
convenience of automatic channel selection.
* * * * *