U.S. patent application number 11/419770 was filed with the patent office on 2007-11-29 for mobile wireless communications device with reduced interfering rf energy into rf metal shield secured on circuit board.
This patent application is currently assigned to Research In Motion Limited. Invention is credited to Michael Corrigan, Liviu George, Robert Grant, Perry Jarmuszewski, Lizhong Zhu.
Application Number | 20070273602 11/419770 |
Document ID | / |
Family ID | 38749050 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070273602 |
Kind Code |
A1 |
Zhu; Lizhong ; et
al. |
November 29, 2007 |
MOBILE WIRELESS COMMUNICATIONS DEVICE WITH REDUCED INTERFERING RF
ENERGY INTO RF METAL SHIELD SECURED ON CIRCUIT BOARD
Abstract
A mobile wireless communications device includes a housing and
circuit board carried by the housing and having RF circuitry
comprising at least one RF component and plurality of other
components mounted on the circuit board. An RF metal shield is
secured to the circuit board and surrounds and isolates the at
least one RF component and plurality of other components within the
RF metal shield. An RF absorber is positioned adjacent an area of
the RF component that radiates energy to aid in reducing energy
radiated from the RF component into the RF metal shield.
Inventors: |
Zhu; Lizhong; (Waterloo,
CA) ; Corrigan; Michael; (Waterloo, CA) ;
Grant; Robert; (Listowel, CA) ; George; Liviu;
(Mississauga, CA) ; Jarmuszewski; Perry;
(Waterloo, CA) |
Correspondence
Address: |
ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST P.A.
1401 CITRUS CENTER 255 SOUTH ORANGE AVENUE
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
Research In Motion Limited
Waterloo
CA
|
Family ID: |
38749050 |
Appl. No.: |
11/419770 |
Filed: |
May 23, 2006 |
Current U.S.
Class: |
343/841 ;
343/702 |
Current CPC
Class: |
H04B 1/3838 20130101;
H05K 1/0243 20130101; H01Q 17/00 20130101; Y10T 29/49002 20150115;
H01Q 1/526 20130101; Y10T 29/49018 20150115; H05K 9/0039 20130101;
H01Q 1/243 20130101 |
Class at
Publication: |
343/841 ;
343/702 |
International
Class: |
H01Q 1/52 20060101
H01Q001/52 |
Claims
1. A mobile wireless communications device, comprising: a housing;
a circuit board carried by the housing and having RF circuitry
comprising at least one RF component and plurality of other
components mounted on said circuit board; an RF metal shield
secured to said circuit board and surrounding and isolating said at
least one RF component and plurality of other components within
said RF metal shield, said RF metal shield having an RF absorber
positioned adjacent an area of the RF component that radiates
energy to aid in reducing energy radiated from the RF component
into the RF metal shield and causing electromagnetic coupling or
interference with other portions of said RF component or other
components within said RF metal shield, wherein said RF metal
shield has an opening at an area of the RF component that radiates
energy and said RF absorber comprises an RF absorbing material
positioned at the opening of the RF metal shield.
2. (canceled)
3. A mobile wireless communications device according to claim 1,
wherein said RF absorbing material comprises a ferrite
material.
4. A mobile wireless communications device according to claim 3,
wherein said RF absorbing material comprises a planar sheet.
5. A mobile wireless communications device according to claim 4,
and further comprising an adhesive tape securing to said RF metal
shield said planar sheet that forms said RF absorbing material.
6. A mobile wireless communications device according to claim 1,
wherein said RF absorber is formed as a longitudinal slot
positioned over the area of the RF component that radiates
energy.
7. A mobile wireless communications device according to claim 1,
wherein said at least one RF component comprises an RF chip
set.
8. A mobile wireless communications device according to claim 7,
wherein said RF chip set comprises a transceiver chip set.
9. A mobile wireless communications device according to claim 8,
wherein said chip set comprises a transmitter chip, receiver chip
and local oscillator chip.
10. A mobile wireless communications device according to claim 9,
wherein said RF absorber is positioned adjacent said transmitter
chip.
11. A mobile wireless communications device according to claim 1,
wherein said RF circuitry is operative for generating Global System
for Mobile (GSM) communications packet bursts.
12. A mobile wireless communications device, comprising: a housing;
a circuit board carried by the housing and having a RF circuitry
comprising a plurality of RF components including an RF transceiver
multi-chip module mounted on said circuit board; a RF metal shield
secured to said circuit board and surrounding and isolating said RF
components and RF transceiver multi-chip module within said RF
metal shield, said RF metal shield comprising a planar top surface
and having an opening at the top surface in a position where said
RF transceiver multi-chip module radiates energy, and an RF
absorbing material positioned at the opening to aid in reducing
radiation emitted from the RF transceiver multi-chip module into
the RF metal shield and causing electromagnetic coupling or
interference with other portions of said RF transceiver multi-chip
module or other RF components enclosed by said RF metal shield.
13. A mobile wireless communications device according to claim 12,
wherein said RF absorbing material comprises a ferrite
material.
14. A mobile wireless communications device according to claim 13,
wherein said RF absorbing material comprises a planar sheet.
15. A mobile wireless communications device according to claim 14,
and further comprising an adhesive tape securing said planar sheet
forming said RF absorbing material to said RF metal shield.
16. A mobile wireless communications device according to claim 12,
wherein said RF circuitry is operative for generating Global System
for Mobile (GSM) communications packet bursts.
17. A method for making a mobile wireless communications device,
which comprises: providing a housing, a circuit board carried by
the housing, radio frequency (RF) circuitry including at least one
RF component and other components carried by the circuit board, and
a RF metal shield secured to said circuit board and surrounding and
isolating said at least one RF component and other components
within said RF metal shield; reducing energy radiated from a
portion of an RF component into the RF metal shield to reduce the
electromagnetic coupling or interference with other portions of
said RF component or other components enclosed by said RF metal
shield by positioning an RF absorber adjacent the area of the RF
component that radiates energy; and forming a slot within the RF
metal shield over the portion of the at least one RF component that
radiates energy.
18. A method according to claim 17, which further comprises forming
the at least one RF component as an RF chip set.
19. (canceled)
20. A method according to claim 17, which further comprises forming
an opening in the RF metal shield and positioning an RF absorbing
material at the opening to form the RF absorber.
21. A method according to claim 20, which further comprises forming
the RF absorbing material as a ferrite material.
22. A mobile wireless communications device, comprising: a housing;
a circuit board carried by the housing and having RF circuitry
comprising at least one RF component and plurality of other
components mounted on said circuit board; an RF metal shield
secured to said circuit board and surrounding and isolating said at
least one RF component and plurality of other components within
said RF metal shield, said RF metal shield having an RF absorber
positioned adjacent an area of the RF component that radiates
energy to aid in reducing energy radiated from the RF component
into the RF metal shield and causing electromagnetic coupling or
interference with other portions of said RF component or other
components within said RF metal shield, wherein said RF absorber is
formed as a longitudinal slot positioned over the area of the RF
component that radiates energy.
23. A method for making a mobile wireless communications device,
which comprises: providing a housing, a circuit board carried by
the housing, radio frequency (RF) circuitry including at least one
RF component and other components carried by the circuit board, and
a RF metal shield secured to said circuit board and surrounding and
isolating said at least one RF component and other components
within said RF metal shield; reducing energy radiated from a
portion of an RF component into the RF metal shield to reduce the
electromagnetic coupling or interference with other portions of
said RF component or other components enclosed by said RF metal
shield by positioning an RF absorber adjacent the area of the RF
component that radiates energy; and forming an opening in the RF
metal shield and positioning an RF absorbing material at the
opening to form the RF absorber.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of communications
devices, and more particularly, to mobile wireless communications
devices and related methods.
BACKGROUND OF THE INVENTION
[0002] Cellular communication systems continue to grow in
popularity and have become an integral part of both personal and
business communications. Cellular telephones allow users to place
and receive phone calls most anywhere they travel. Moreover, as
cellular telephone technology is increased, so too has the
functionality of cellular devices. For example, many cellular
devices now incorporate Personal Digital Assistant (PDA) features
such as calendars, address books, task lists, calculators, memo and
writing programs, etc. These multi-function devices usually allow
users to wirelessly send and receive electronic mail (email)
messages and access the internet via a cellular network and/or a
wireless local area network (WLAN), for example.
[0003] As the functionality of cellular communications devices
continues to increase, so too does demand for smaller devices that
are easier and more convenient for users to carry. As any circuit
boards and electronic components thereon are reduced in size and
placed closer together, including antenna and microphone
components, various electronic components can pick up conductive
energy and create interference within the system.
[0004] Many of the designs include an RF metal shield secured onto
the printed circuit board, and surrounding and isolating different
RF components, including transceiver chip sets such as multi-chip
modules, which are secured on the circuit board within the housing.
The RF metal shield encloses these components and chip sets. Some
of the RF components or chip sets radiate RF energy to other chips
or components that are in close proximity from electromagnetic
coupling through the RF metal shield. This type of electromagnetic
coupling (EMC) or electromagnetic interference (EMI) coupling
causes interference to the RF circuits, and degrades RF
performance, such as receiver sensitivity. Thus, the RF metal
shield that is supposed to shield the components from extraneous RF
energy can in and of itself create electromagnetic coupling
problems with different RF components that are supposed to be
shielded within the RF shield.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Other objects, features and advantages will become apparent
from the detailed description which follows when considered in
light of the accompanying drawings in which:
[0006] FIG. 1 is a schematic block diagram of an example of a
mobile wireless communications device configured as a handheld
device that can be used and illustrating basic internal components
thereof.
[0007] FIG. 2 is a front elevation view of the mobile wireless
communications device of FIG. 1.
[0008] FIG. 3 is a schematic block diagram showing basic functional
circuit components that can be used in the mobile wireless
communications device of FIGS. 1-2.
[0009] FIG. 4 is front elevational view of the mobile wireless
communications device having the front cover removed to illustrate
an example of RF circuitry, power amplifier, surface mounted
microphone and noise isolation components associated thereof.
[0010] FIG. 5 is a fragmentary, isometric drawing of a prior art RF
metal shield covering an RF transceiver on a printed circuit
board.
[0011] FIG. 6 is a fragmentary, isometric drawing of an RF metal
shield that includes an RF absorber formed as absorbing material
positioned at an opening of the RF metal shield to aid in reducing
RF energy radiated from an RF component such as part of an RF
transceiver chip set into the RF metal shield and causing
electromagnetic coupling or electromagnetic interference with other
portions of the RF components or chip set within the RF metal
shield.
[0012] FIG. 7 is a fragmentary side elevation drawing of the RF
metal shield and RF absorbing material positioned at an opening
within the RF metal shield and covering a portion of an RF
transceiver multi-chip module.
[0013] FIG. 8 is another embodiment showing the RF metal shield and
the RF absorber formed as a long and narrow slot on the RF metal
shield to reduce RF coupling.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Different embodiments will now be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments are shown. Many different forms can be set
forth and described embodiments should not be construed as limited
to the embodiments set forth herein. Rather, these embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope to those skilled in the art. Like
numbers refer to like elements throughout.
[0015] A mobile wireless communications device includes a housing
and circuit board carried by the housing and having RF circuitry
comprising at least one RF component, and a plurality of other
components mounted on the circuit board. An RF metal shield is
secured to the circuit board and surrounds and isolates the at
least one RF component and plurality of other components within the
RF metal shield. An RF absorber is positioned adjacent an area of
the RF component that radiates energy to aid in reducing any energy
radiated from the RF component into the RF metal shield. As a
result, the electromagnetic coupling or interference with other
portions of the RF component or other components within the RF
metal shield is reduced.
[0016] The RF shield, in one non-limiting example, has an opening
at an area of the RF component that radiates energy. The RF
absorber is formed as an RF absorbing material positioned at the
opening of the RF metal shield. This RF absorbing material could be
formed as a ferrite material, and preferably as a planar sheet that
could be secured by adhesive tape to the RF metal shield. The RF
absorber could also be formed as a longitudinal slot positioned
over the area of the RF component that radiates RF energy.
[0017] In another non-limiting example, the RF component can be
formed as an RF chip set and preferably as a transceiver chip set
that could be formed as a transmitter chip, receiver chip and local
oscillator chip. The RF absorber can be positioned adjacent the
transmitter chip. The RF circuitry could also be operative for
generating Global System for Mobile (GSM) communications packet
bursts. The RF circuitry could also include an RF transceiver,
multi-chip module and associated RF components.
[0018] A method aspect is also set forth.
[0019] A brief description will now proceed relative to FIGS. 1-3,
which disclose an example of a mobile wireless communications
device, for example, a handheld portable cellular radio, which can
incorporate the non-limiting examples of the various circuits.
FIGS. 1-3 are representative non-limiting examples of the many
different types of functional circuit components and their
interconnection.
[0020] Referring initially to FIGS. 1 and 2, an example of a mobile
wireless communications device 20, such as a handheld portable
cellular radio is first described. This device 20 illustratively
includes a housing 21 having an upper portion 46 and a lower
portion 47, and a dielectric substrate (i.e., circuit board) 67,
such as a conventional printed circuit board (PCB) substrate, for
example, carried by the housing. A housing cover (not shown in
detail) would typically cover the front portion of the housing. The
term circuit board 67 as used hereinafter can refer to any
dielectric substrate, PCB, ceramic substrate or other circuit
carrying structure for carrying signal circuits and electronic
components within the mobile wireless communications device 20. The
illustrated housing 21 is a static housing, for example, as opposed
to a flip or sliding housing which are used in many cellular
telephones. However, these and other housing configurations may
also be used.
[0021] Circuitry 48 is carried by the circuit board 67, such as a
microprocessor, memory, one or more wireless transceivers (e.g.,
cellular, WLAN, etc.), which includes RF circuitry, including audio
and power circuitry, including any keyboard circuitry. It should be
understood that keyboard circuitry could be on a separate keyboard,
etc., as will be appreciated by those skilled in the art. A battery
(not shown) is also preferably carried by the housing 21 for
supplying power to the circuitry 48. The term RF circuitry could
encompass the interoperable RF transceiver circuitry, power
circuitry and audio circuitry.
[0022] Furthermore, an audio output transducer 49 (e.g., a speaker)
is carried by an upper portion 46 of the housing 21 and connected
to the circuitry 48. One or more user input interface devices, such
as a keypad (keyboard) 23 (FIG. 2), is also preferably carried by
the housing 21 and connected to the circuitry 48. The term keypad
as used herein also refers to the term keyboard, indicating the
user input devices having lettered and/or numbered keys commonly
known and other embodiments, including multi-top or predictive
entry modes. Other examples of user input interface devices include
a scroll wheel 37 and a back button 36. Of course, it will be
appreciated that other user input interface devices (e.g., a stylus
or touch screen interface) may be used in other embodiments.
[0023] An antenna 45 is preferably positioned at the lower portion
47 in the housing and can be formed as a pattern of conductive
traces that make an antenna circuit, which physically forms the
antenna. It is connected to the circuitry 48 on the main circuit
board 67. In one non-limiting example, the antenna could be formed
on an antenna circuit board section that extends from the circuit
board at the lower portion of the housing. By placing the antenna
45 adjacent the lower portion 47 of the housing 21, the distance is
advantageously increased between the antenna and the user's head
when the phone is in use to aid in complying with applicable SAR
requirements. Also, a separate keyboard circuit board could be
used.
[0024] More particularly, a user will typically hold the upper
portion of the housing 21 very close to his head so that the audio
output transducer 49 is directly next to his ear. Yet, the lower
portion 47 of the housing 21 where an audio input transducer (i.e.,
microphone) is located need not be placed directly next to a user's
mouth, and can be held away from the user's mouth. That is, holding
the audio input transducer close to the user's mouth may not only
be uncomfortable for the user, but it may also distort the user's
voice in some circumstances. In addition, the placement of the
antenna 45 adjacent the lower portion 47 of the housing 21 also
advantageously spaces the antenna farther away from the user's
brain.
[0025] Another important benefit of placing the antenna 45 adjacent
the lower portion 47 of the housing 21 is that this may allow for
less impact on antenna performance due to blockage by a user's
hand. That is, users typically hold cellular phones toward the
middle to upper portion of the phone housing, and are therefore
more likely to put their hands over such an antenna than they are
an antenna mounted adjacent the lower portion 47 of the housing 21.
Accordingly, more reliable performance may be achieved from placing
the antenna 45 adjacent the lower portion 47 of the housing 21.
[0026] Still another benefit of this configuration is that it
provides more room for one or more auxiliary input/output (I/O)
devices 50 to be carried at the upper portion 46 of the housing.
Furthermore, by separating the antenna 45 from the auxiliary I/O
device(s) 50, this may allow for reduced interference
therebetween.
[0027] Some examples of auxiliary I/O devices 50 include a WLAN
(e.g., Bluetooth, IEEE 802.11) antenna for providing WLAN
communication capabilities, and/or a satellite positioning system
(e.g., GPS, Galileo, etc.) antenna for providing position location
capabilities, as will be appreciated by those skilled in the art.
Other examples of auxiliary I/O devices 50 include a second audio
output transducer (e.g., a speaker for speaker phone operation),
and a camera lens for providing digital camera capabilities, an
electrical device connector (e.g., USB, headphone, secure digital
(SD) or memory card, etc.).
[0028] It should be noted that the term "input/output" as used
herein for the auxiliary I/O device(s) 50 means that such devices
may have input and/or output capabilities, and they need not
provide both in all embodiments. That is, devices such as camera
lenses may only receive an optical input, for example, while a
headphone jack may only provide an audio output.
[0029] The device 20 further illustratively includes a display 22,
for example, a liquid crystal display (LCD) carried by the housing
21 and connected to the circuitry 48. A back button 36 and scroll
wheel 37 can also be connected to the circuitry 48 for allowing a
user to navigate menus, text, etc., as will be appreciated by those
skilled in the art. The scroll wheel 37 may also be referred to as
a "thumb wheel" or a "track wheel" in some instances. The keypad 23
illustratively includes a plurality of multi-symbol keys 24 each
having indicia of a plurality of respective symbols thereon. The
keypad 23 also illustratively includes an alternate function key
25, a next key 26, a space key 27, a shift key 28, a return (or
enter) key 29, and a backspace/delete key 30.
[0030] The next key 26 is also used to enter a "*" symbol upon
first pressing or actuating the alternate function key 25.
Similarly, the space key 27, shift key 28 and backspace key 30 are
used to enter a "0" and "#", respectively, upon first actuating the
alternate function key 25. The keypad 23 further illustratively
includes a send key 31, an end key 32, and a convenience (i.e.,
menu) key 39 for use in placing cellular telephone calls, as will
be appreciated by those skilled in the art.
[0031] Moreover, the symbols on each key 24 are arranged in top and
bottom rows. The symbols in the bottom rows are entered when a user
presses a key 24 without first pressing the alternate function key
25, while the top row symbols are entered by first pressing the
alternate function key. As seen in FIG. 2, the multi-symbol keys 24
are arranged in the first three rows on the keypad 23 below the
send and end keys 31, 32. Furthermore, the letter symbols on each
of the keys 24 are arranged to define a QWERTY layout. That is, the
letters on the keypad 23 are presented in a three-row format, with
the letters of each row being in the same order and relative
position as in a standard QWERTY keypad.
[0032] Each row of keys (including the fourth row of function keys
25-29) is arranged in five columns. The multi-symbol keys 24 in the
second, third, and fourth columns of the first, second, and third
rows have numeric indicia thereon (i.e., 1 through 9) accessible by
first actuating the alternate function key 25. Coupled with the
next, space, and shift keys 26, 27, 28, which respectively enter a
"*", "0", and "#" upon first actuating the alternate function key
25, as noted above, this set of keys defines a standard telephone
keypad layout, as would be found on a traditional touch-tone
telephone, as will be appreciated by those skilled in the art.
[0033] Accordingly, the mobile wireless communications device 20 as
described may advantageously be used not only as a traditional
cellular phone, but it may also be conveniently used for sending
and/or receiving data over a cellular or other network, such as
Internet and email data, for example. Of course, other keypad
configurations may also be used in other embodiments. Multi-tap or
predictive entry modes may be used for typing e-mails, etc. as will
be appreciated by those skilled in the art.
[0034] The antenna 45 is preferably formed as a multi-frequency
band antenna, which provides enhanced transmission and reception
characteristics over multiple operating frequencies. More
particularly, the antenna 45 is designed to provide high gain,
desired impedance matching, and meet applicable SAR requirements
over a relatively wide bandwidth and multiple cellular frequency
bands. By way of example, the antenna 45 preferably operates over
five bands, namely a 850 MHz Global System for Mobile
Communications (GSM) band, a 900 MHz GSM band, a DCS band, a PCS
band, and a WCDMA band (i.e., up to about 2100 MHz), although it
may be used for other bands/frequencies as well. To conserve space,
the antenna 45 may advantageously be implemented in three
dimensions although it may be implemented in two-dimensional or
planar embodiments as well.
[0035] The mobile wireless communications device shown in FIGS. 1
and 2 can incorporate e-mail and messaging accounts and provide
different functions such as composing e-mail, PIN messages, and SMS
messages. The device can manage messages through an appropriate
menu that can be retrieved by choosing a messages icon. An address
book function could add contacts, allow management of an address
book, set address book options and manage SIN card phone books. A
phone menu could allow for the making and answering of phone calls
using different phone features, managing phone call logs, setting
phone options, and viewing phone information. A browser application
could permit the browsing of web pages, configuring a browser,
adding bookmarks, and changing browser options. Other applications
could include a task, memo pad, calculator, alarm and games, as
well as handheld options with various references.
[0036] A calendar icon can be chosen for entering a calendar
program that can be used for establishing and managing events such
as meetings or appointments. The calendar program could be any type
of messaging or appointment/meeting program that allows an
organizer to establish an event, for example, an appointment or
meeting.
[0037] A non-limiting example of various functional components that
can be used in the exemplary mobile wireless communications device
20 of FIGS. 1 and 2 is further described in the example below with
reference to FIG. 3. The device 20 illustratively includes a
housing 120, a keypad 140 and an output device 160. The output
device 160 shown is preferably a display, which is preferably a
full graphic LCD. Other types of output devices may alternatively
be used. A processing device 180 is contained within the housing
120 and is coupled between the keypad 140 and the display 160. The
processing device 180 controls the operation of the display 160, as
well as the overall operation of the mobile device 20, in response
to actuation of keys on the keypad 140 by the user.
[0038] The housing 120 may be elongated vertically, or may take on
other sizes and shapes (including clamshell housing structures).
The keypad may include a mode selection key, or other hardware or
software for switching between text entry and telephony entry.
[0039] In addition to the processing device 180, other parts of the
mobile device 20 are shown schematically in FIG. 3. These include a
communications subsystem 101; a short-range communications
subsystem 102; the keypad 140 and the display 160, along with other
input/output devices 106, 108, 110 and 112; as well as memory
devices 116, 118 and various other device subsystems 121. The
mobile device 20 is preferably a two-way RF communications device
having voice and data communications capabilities. In addition, the
mobile device 20 preferably has the capability to communicate with
other computer systems via the Internet.
[0040] Operating system software executed by the processing device
180 is preferably stored in a persistent store, such as the flash
memory 116, but may be stored in other types of memory devices,
such as a read only memory (ROM) or similar storage element. In
addition, system software, specific device applications, or parts
thereof, may be temporarily loaded into a volatile store, such as
the random access memory (RAM) 118. Communications signals received
by the mobile device may also be stored in the RAM 118.
[0041] The processing device 180, in addition to its operating
system functions, enables execution of software applications
130A-130N on the device 20. A predetermined set of applications
that control basic device operations, such as data and voice
communications 130A and 130B, may be installed on the device 20
during manufacture. In addition, a personal information manager
(PIM) application may be installed during manufacture. The PIM is
preferably capable of organizing and managing data items, such as
e-mail, calendar events, voice mails, appointments, and task items.
The PIM application is also preferably capable of sending and
receiving data items via a wireless network 141. Preferably, the
PIM data items are seamlessly integrated, synchronized and updated
via the wireless network 141 with the device user's corresponding
data items stored or associated with a host computer system.
[0042] Communication functions, including data and voice
communications, are performed through the communications subsystem
101, and possibly through the short-range communications subsystem.
The communications subsystem 101 includes a receiver 150, a
transmitter 152, and one or more antennae 154 and 156. In addition,
the communications subsystem 101 also includes a processing module,
such as a digital signal processor (DSP) 158, and local oscillators
(LOs) 161. The specific design and implementation of the
communications subsystem 101 is dependent upon the communications
network in which the mobile device 20 is intended to operate. For
example, the mobile device 20 may include a communications
subsystem 101 designed to operate with the Mobitex.TM., Data
TAC.TM. or General Packet Radio Service (GPRS) mobile data
communications networks, and also designed to operate with any of a
variety of voice communications networks, such as AMPS, TDMA, CDMA,
PCS, GSM, etc. Other types of data and voice networks, both
separate and integrated, may also be utilized with the mobile
device 20.
[0043] Network access requirements vary depending upon the type of
communication system. For example, in the Mobitex and DataTAC
networks, mobile devices are registered on the network using a
unique personal identification number or PIN associated with each
device. In GPRS networks, however, network access is associated
with a subscriber or user of a device. A GPRS device therefore
requires a subscriber identity module, commonly referred to as a
SIM card, in order to operate on a GPRS network.
[0044] When required network registration or activation procedures
have been completed, the mobile device 20 may send and receive
communications signals over the communication network 141. Signals
received from the communications network 141 by the antenna 154 are
routed to the receiver 150, which provides for signal
amplification, frequency down conversion, filtering, channel
selection, etc., and may also provide analog to digital conversion.
Analog-to-digital conversion of the received signal allows the DSP
158 to perform more complex communications functions, such as
demodulation and decoding. In a similar manner, signals to be
transmitted to the network 141 are processed (e.g., modulated and
encoded) by the DSP 158 and are then provided to the transmitter
152 for digital to analog conversion, frequency up conversion,
filtering, amplification and transmission to the communication
network 141 (or networks) via the antenna 156.
[0045] In addition to processing communications signals, the DSP
158 provides for control of the receiver 150 and the transmitter
152. For example, gains applied to communications signals in the
receiver 150 and transmitter 152 may be adaptively controlled
through automatic gain control algorithms implemented in the DSP
158.
[0046] In a data communications mode, a received signal, such as a
text message or web page download, is processed by the
communications subsystem 101 and is input to the processing device
180. The received signal is then further processed by the
processing device 180 for an output to the display 160, or
alternatively to some other auxiliary I/O device 106. A device user
may also compose data items, such as e-mail messages, using the
keypad 140 and/or some other auxiliary I/O device 106, such as a
touchpad, a rocker switch, a thumb-wheel, or some other type of
input device. The composed data items may then be transmitted over
the communications network 141 via the communications subsystem
101.
[0047] In a voice communications mode, overall operation of the
device is substantially similar to the data communications mode,
except that received signals are output to a speaker 110, and
signals for transmission are generated by a microphone 112.
Alternative voice or audio I/O subsystems, such as a voice message
recording subsystem, may also be implemented on the device 20. In
addition, the display 160 may also be utilized in voice
communications mode, for example to display the identity of a
calling party, the duration of a voice call, or other voice call
related information.
[0048] Any short-range communications subsystem enables
communication between the mobile device 20 and other proximate
systems or devices, which need not necessarily be similar devices.
For example, the short-range communications subsystem may include
an infrared device and associated circuits and components, or a
Bluetooth.TM. communications module to provide for communication
with similarly-enabled systems and devices.
[0049] FIG. 4 is an example of a circuit layout on part of the
circuit board 67 that can be included within the mobile wireless
communications device 20 of FIGS. 1-3, and showing a front cover
removed from a housing to illustrate a surface mounted microphone
200 and its circuitry and associated noise isolation components as
will be explained in greater detail below. The circuit board 67
includes radio frequency (RF) circuitry, for example, cellular
telephone communications circuitry, which is mounted in first and
second isolation RF metal shields or "cans" 210,212, as often
called by those skilled in the art, forming a compartment on the
circuit board, each which receive the RF circuitry and other
components, which typically are RF components. Each can 210,212
forms a radio frequency isolation compartment and typically
includes sides and a top, such as a portion of the top 210a shown
remaining on can 210. The first can 210 includes a transceiver chip
set 220, for example, a transmitter chip, receiver chip, and local
oscillator chip as non-limiting examples with those chips labeled
A, B and C. The chip set could, in non-limiting examples, be formed
as an RF transceiver multi-chip module. Other illustrated
components could include the various resistors, capacitors,
amplifiers, regulators and other circuit components common to those
devices, but not explained in detail.
[0050] Located outside first and second isolation cans 210,212, but
mounted on the circuit board 67, is a liquid crystal display (LCD)
connector 230 and a keyboard connector 232, as well as associated
circuit components 234. These components 230, 232 and 234 can be
configured in different configurations besides the configuration
illustrated in the non-limiting example of FIG. 4. The compartment
within the second isolation can 212 includes a power amplifier 236
and switch diplexer 238. Other components 240 are mounted within
the compartment and form the resistors, capacitors, transistors,
and inductors necessary to drive the audio and power circuits for
the microphone, power amplifier and other circuits.
[0051] To provide microphone isolation, a radio frequency isolation
shield 250, formed in the illustrated non-limiting example as a
third isolation "can" 250, is positioned at a corner of the second
"can" 212, and forms another isolation compartment at this corner.
The shield is formed as a separate metallic housing secured to the
circuit board and surrounding the microphone, effectively covering,
i.e., shielding the entire microphone. Although a "can"
configuration formed as a metallic housing with top and sides and
is used for the RF shield, other configurations could be used. The
compartment formed by the isolation shield 250 receives a
microphone 200 formed preferably as a surface mounted microphone
integrated circuit chip 200 on the circuit board 67. As illustrated
in this non-limiting configuration, this places the microphone chip
adjacent to the bottom center of the device 20 where the sound hole
is typically located in the cover of a cellular phone or similar
mobile wireless communications device.
[0052] To reduce noise resulting from RF circuitry, the metal RF
shield or "can" forming an isolation shield includes a side and top
metal wall, i.e., forming a complete isolation shield surrounding
or covering the microphone 200 and its associated circuitry to
provide isolation from the RF circuitry. This isolation shield
provides the necessary isolation from the RF amplifiers and from
any energy radiated from the antenna.
[0053] Referring now to FIGS. 5, a circuit board 300, such as the
type explained relative to FIGS. 1-4, is shown and includes an RF
transceiver 302 mounted thereon, which could correspond to an RF
transceiver multi-chip module as explained before, and having
transmitter, receiver and local oscillator chips as explained
before. The RF transceiver 302 is covered by an RF metal shield 304
as explained before. In this prior art example, the entire RF
transceiver 302 is covered by the RF metal shield. In some
instances, the RF energy from one portion of the RF transceiver or
other RF component is generated into the RF metal shield and cause
electromagnetic coupling or interference with certain sections of
the RF transceiver or other RF components within the RF metal
shield.
[0054] In accordance with one non-limiting example, the RF metal
shield 308 shown in FIG. 6 has been modified to include an opening
310 positioned at that area or section of the RF transceiver or
other RF component that radiates RF energy. An RF absorber 312 is
formed as an RF absorbing material in this illustrated embodiment
and positioned at the opening, i.e., adjacent that area of the RF
component, such as the transceiver or chip that radiates RF energy,
to aid in reducing RF energy radiated from the component into the
RF metal shield and causing electromagnetic coupling or
interference with other portions of the RF component or chip within
the RF metal shield. This RF absorbing material 312 in the
illustrated embodiment is formed as a ferrite material, preferably
formed and as a planar sheet. Adhesive tape 314 can secure the RF
absorbing material 312 to the RF metal shield. Of course, the RF
transceiver is shown as one unit, such as an RF
transceiver/multi-chip module, but it could include the basic
transmitter chip, receiver chip and local oscillator chips labeled
A, B and C as shown in FIG. 7, which are shown positioned in a
multi-chip module and adjacent other RF and perhaps non-RF
components 320 that are within the confines of the RF metal
shield.
[0055] The RF absorbing material can be formed of different ferrite
materials and typically has an applicable frequency of about 0.1 to
about 3.0 GHz. An example of such RF absorbing material is the
microwave absorbing material sold under the designation EA20/EA21
by Murata Manufacturing Company, Ltd. The thickness in non-limiting
examples can range from about 0.05 millimeters to about 3.00
millimeters. The structure can be halogen free and have a flame
resistance and operating temperature range from about -40 to about
+120.degree. C. Adhesive tape can be used to secure the material to
an object, for example, the RF metal shield in this example. The
material can be formed from an Ni--Zn ferrite material in one
non-limiting example, and can have a specific gravity of about 3.4
(Typ) and a tensile strength of 3.0 MPa (min) and a surface
resistance of about 1.0.times.10.sup.11 (min), in non-limiting
examples. Flame resistance can be compatible to UL94V-O.
[0056] FIG. 8 shows another RF metal shield 330 in which the RF
absorber is formed as a longitudinally extending, but narrow slot
332 that is on the metal shield and positioned over that portion of
the RF component that emits the RF radiation to prevent RF coupling
as described before. In this specific instance, the longitudinal
slot is operable to break-up the RF energy from coupling into the
metal shield and onto other components, thus reducing the
undesirable electromagnetic interference and electromagnetic
coupling.
[0057] Many modifications and other embodiments of the invention
will come to the mind of one skilled in the art having the benefit
of the teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is understood that the invention
is not to be limited to the specific embodiments disclosed, and
that modifications and embodiments are intended to be included
within the scope of the appended claims.
* * * * *