United States Patent [19]
`Mizikovsky
`
`llllllllllllllllllllllIllllllllllllllllllllllllIlllHllllllllllllllllllllll
`5,228,074
`Jul. 13, 1993
`
`US005228074A
`[11] Patent Number:
`[45] Date of Patent:
`
`[54] DUAL MODE CELLULAR TELEPHONE
`APPARATUS
`[75] Inventor: semyon Mizikovsky Union Ni
`’
`’
`
`[73] Asslgnee. lsltzggstlmsgoratom of America, Park
`
`[21] Appl' NO‘: 684’774
`[22] Filed:
`Apr. 15, 1991
`[51] lm. c1.5 .................... .. H04M 11/00- H040 7/00~
`’ H0413 U46
`[52] us. c1. ................................... .. 379/59; 455/331-
`455/88’
`[53] Field of Search ................. .. 379/59, 60;455/33.1,
`45/54‘ 1, 88
`
`[56]
`
`References Cited
`U_5_ PATENT DOCUMENTS
`
`211222112122
`4,921,464 5/1990 Ito et al.
`455/541
`5,029,233 7/1991 Metroka ..... ..
`455/541
`5.119.397 6/1992 Dahlin et al. .................... .. 455/33.1
`
`Primary Examiner—Curtis Kuntz
`Assistant Examiner—Vijay Shankar
`Attorney, Agent, or Firm-William S. Frommer; Alvin -
`S1nderbrand
`
`ABSTRACT
`[57]
`Dual mode cellular telephone apparatus for communi
`eating in analog or digital modes. A portable unit
`adapted to communicate substantially only in an analog
`m°de i? oPerable ‘0 transmit voice sigl‘als “Pplied from
`an_aud1‘o Input tola cellular base station and to couple
`"°‘Ce slgnals “caved mm a Cellular has‘? Static“ ‘O a“
`audio output. The portable unit, which is capable of
`Operating as a “and 31°“ device’ is connectable ‘0 ‘=1
`mobile unit adapted to communicate in both analog and
`digital modes with the cellular base station. When the
`units are connected, voice signals pass through the mo
`bile unit to and from the portable unit for communica
`tion with the base station. A control unit determines
`mm
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`3 dlgltal m°de~
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`20 Claims, 2 Drawing Sheets
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`1
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`APPLE 1008
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`US. Patent
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`July 13, 1993
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`Sheet 1 of 2
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`5,228,074
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`POWER
`SUPPLY
`k ,2
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`FIG‘. 3
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`2
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`US. Patent
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`July 13, 1993
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`Sheet 2 of 2
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`5,228,074
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`3
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`1
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`DUAL MODE CELLULAR TELEPHONE
`APPARATUS
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`5,228,074
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`information and data and need not be limited solely to
`voice communication.
`In the dual mode cellular standard, a mobile station is
`controlled to communicate in analog form in the event
`that the cellular system with which it is used does not
`exhibit digital communication capabilities, such as in
`exurban environments, or in the event that all of the_
`digital channels are being used but some analog chan
`nels nevertheless are available. At other times, the mo
`bile station is controlled to communicate in digital form.
`However, to provide dual analog/digital capabilities in
`a mobile unit generally means that additional circuitry
`must ‘be provided therein, resulting in large, relatively
`heavy, bulky apparatus. As a consequence, the dual
`mode mobile unit no longer is considered portable. That
`is, the unit no longer is of a size and weight conducive
`for hand-held operation.
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`15
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`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to cellular telephone apparatus
`and, more particularly, to dual mode cellular telephone
`apparatus capable of operating in both analog and digi
`tal modes wherein a portable unit connectable to a mo
`bile unit may communicate with a cellular base station
`in either mode.
`2. Description of the Prior Art
`Cellular telephone standards provide particular con
`ventions and formats by which voice signals are com
`municated between mobile stations and cellular base
`stations. Typically, communication is carried out in
`analog form, wherein analog voice signals are modu
`lated onto a carrier and transmitted either from a mobile
`station to a base station or from a base station to a mo
`bile station. As an example, frequency modulation has
`been used for such communication.
`Conventionally, a mobile station refers to a cellular
`telephone transmitter/receiver that moves from point
`to point. Typically, mobile stations are disposed in vehi
`cles, such as automobiles, boats, etc., and rely upon the
`vehicle source of power to energize the electronics
`included in the mobile station. I-Ieretofore, the construc
`tion of the transmit/receive/processing circuitry, the
`size of the usual radio antenna used therewith and the
`reliance on an external source of power have made it
`difficult to implement a mobile station in truly portable
`dimensions. Recently, however, advances in electronic
`miniaturization and improvements in circuit perfor
`mance have resulted in the introduction of portable, or
`hand-held, mobile units.
`A typical portable mobile unit includes a battery,
`such as a rechargeable battery, for supplying electrical
`energy, a microphone’ for converting audible signals to
`electrical voice signals, processing, transmitting and
`receiving circuitry to enable the analog transmission
`and reception of voice signals, a loudspeaker for con
`verting received voice signals to audible sounds and an
`antenna, such as a low gain antenna, by which analog
`voice signals may be communicated between the porta
`ble unit and a typical cellular base station. The portable
`unit also includes displays to apprise the user of differ
`ent modes of operation, a keypad by which the user may
`effect a telephone call to a desired party via the cellular
`communication system, and other ancillary or auxiliary
`elements. If the battery is of the rechargeable type,
`suitable external contacts may be provided on the porta
`ble unit to facilitate charging of the battery without
`removal thereof from the unit.
`To enhance cellular telephone systems and add capa
`bilities not heretofore exhibited by analog systems, par
`ticularly in geographic areas wherein cellular communi~
`cation traffic is heavy and dense, a dual mode cellular
`standard, identi?ed as the TIA IS-54 standard, has been
`introduced. This dual mode standard permits voice
`signals to be transmitted either in analog form, as be
`fore, or in digital form. The application of digital tech
`niques to voice communication improves the quality
`and ?delity of the transmitted voice signals and in
`creases the number of users which may access the cellu
`lar system simultaneously. In addition, the cellular com
`munication system may be used to communicate other
`
`OBJECTS AND SUMMARY OF THE
`INVENTION
`Therefore, it is an object of the present invention to
`provide dual mode cellular telephone apparatus which
`enjoys the advantages derived from a dual mode cellu
`lar standard, such as TIA IS-54, yet provides the user
`with the portability he has come to expect from analog
`cellular telephone equipment.
`Another object of this invention is to provide dual
`mode cellular telephone apparatus wherein digital com
`munication circuitry, which is inherently heavy and
`bulky, may be located in a vehicle and a portable unit
`which is relatively small, lightweight and admits of
`hand-held operation, is connectable to the digital com
`munication circuitry and admits of either stand alone
`operation or interaction with that digital communica
`tion circuitry.
`A further object of this invention is to provide dual
`mode cellular telephone apparatus of the aforemen
`tioned type operable in an analog mode as a portable
`hand-held, self-contained unit, and operable as a user
`interface when connected to a mobile-based unit having
`digital communications electronics therein.
`Various other objects, advantages and features of the
`present invention will become readily apparent from
`the ensuing detailed description, and the novel features
`will be particularly pointed out in the appended claims.
`In accordance with this invention, dual mode cellular
`telephone apparatus is provided for communicating in
`analog or digital modes. As used herein, communication
`in an analog mode is intended to refer to conventional
`analog modulation of voice signals, such as analog FM
`modulation. Communication in a digital mode is in
`tended to refer to a digital format and convention de
`?ned by a cellular standard, such as the TIA IS-54
`standard. The present invention is not concerned per se
`with the digital processing of voice or data signals,
`which is described in the aforementioned standard and,
`therefore, further description herein is not provided. It
`will be appreciated, however, that the digital processing
`includes VSELP voice coding, delay interval compen
`sation, channel coding, error correction, etc., all as
`described in greater detail in the aforementioned stan
`dard. Furthermore, it will be appreciated that a voice
`signal refers to a voice frequency signal and may repre
`sent speech information or other data that has been
`converted or modulated to voice frequency.
`The apparatus of the present invention includes a
`portable unit for communicating substantially only in an
`analog mode and operable to transmit voice signals
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`supplied from an audio input, such as a microphone, to
`a cellular base station and to couple voice signals re
`ceived from a cellular base station to an audio output,
`such as a speaker. A mobile unit, such as a unit intended
`to be disposed in a vehicle (eg. an automobile, a boat, a
`train or other means of conveyance), is adapted to com
`municate in both analog and digital modes with a cellu
`lar base station. The mobile unit is connectable to the
`portable unit, and a controller is responsive to the con
`nection of these units for transmitting voice signals from
`the audio input of the portable unit to the cellular base
`station via the mobile unit and for coupling voice sig
`nals received in analog or digital mode from the cellular
`base station to the audio output of the portable unit via
`the mobile unit. The particular mode which is adopted
`is determined by the cellular base station, as by the
`transmission of suitable control signals to the controller.
`As one aspect of this invention, the portable unit is
`usable as a stand alone device to communicate in an
`analog mode with the cellular base station and the mo
`bile unit is operable either in an analog mode or a digital
`mode. When the portable unit is connected to the mo
`bile unit, the transmitting and receiving circuitry in the
`portable unit, such as the RF circuitry included therein,
`is not used. Rather, RF circuitry provided in the mobile
`unit is used to receive voice signals from and to transmit
`voice signals to the base station, However, the usual
`analog modulator and demodulator provided in the
`portable unit are used when the mobile unit operates in
`its analog mode but not when the mobile unit operates
`in its digital mode.
`In one embodiment of this invention, controllable
`switching devices are provided to select portions of the
`portable unit and portions of the mobile unit for com
`municating with the base station during analog or digi
`tal modes.
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`5,228,074
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`other functions ‘conventionally performed by keypads
`and manually operable switches normally provided in
`typical cellular telephone handsets.
`For illustrative purposes, portable unit 1 is shown
`with a display 4, conventional to cellular telephone
`apparatus, and a low gain antenna 11. The antenna per»
`mits RF communication in an analog mode between the
`portable unit and a cellular base station. The portable
`unit also includes a microphone 40, to convert audible
`speech signals into electrical voice signals for transmis
`sion from the portable unit to the cellular base station,
`and a speaker 45 to convert electrical voice signals
`which are received from a cellular base station into
`audible sounds that are perceived by the user.
`Thus, by operating keypad 3, speaking into micro
`phone 40 and listening to speaker 45, the user of porta
`ble unit 1 may communicate in an analog mode with a
`remote base station.
`Mobile unit 5 is schematically illustrated as including
`an adapter 7 and a digital communications unit (DCU)
`8. Adapter 7 is provided with a set of contacts 6 adapted
`to mate with a similar set of contacts 2 provided on
`portable unit 1. As will be described below in connec
`tion with FIG. 3, when mobile unit 5 receives portable
`unit 1, matching contacts 2 and 6 enable the power
`supply normally used to energize the mobile unit now to
`power the portable unit. For example, a vehicle battery
`9 to which mobile unit 5 is connected may be used to
`supply power to portable unit 1. Adapter 7 thus may
`include power supply circuitry for energizing the cir
`cuits included in the portable unit. Alternatively,
`adapter 7 may be con?gured in a shape similar to that of
`the battery provided in the portable unit, whereupon
`the user may replace that battery With the adapter
`when the portable unit is received by mobile unit 5. The
`matching contacts 2 and 6 also enable a central control
`unit included in mobile unit 5 to sense when the portable
`unit is received by the mobile unit. The functions car
`ried out when the connection of these two units is
`sensed will be described below.
`Digital communications unit 8 includes the digital
`circuitry and a microprocessor for providing digital
`processing of voice and data signals consistent with, for
`example, dual mode cellular standard TIA 18-54. As
`mentioned above, such signal processing is known to
`those of ordinary skill in the art, forms no part of the
`present invention per se and, in the interest of brevity, is
`not described further herein. To the extent that a brief
`description of such signal processing may be useful in
`appreciating the present invention, such description is
`provided below in conjunction with FIG. 2.
`As one advantageous feature of the present invention,
`digital communications unit 8 is not provided with
`audio input or audio output circuitry. Rather, when the
`portable unit and the mobile unit are connected, the
`audio input and audio output circuitry as well as the
`microphone and speaker of the portable unit are used
`with the digital communications unit to transmit voice
`signals to and receive voice signals from a cellular base
`station in digital mode. Accordingly, suitable switching
`devices are provided in digital communications unit 8 as
`well as in portable unit 1 to facilitate the interchange of
`voice and data signals between these units. As will be
`apparent, similar switches also may be provided in
`adapter 7; and if desired, the switches provided in the
`digital communications unit, to be described, may in
`stead be provided in the adapter.
`
`35
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`BRIEF DESCRIPTION OF THE DRAWINGS
`The following detailed description, given by way of
`example, will best be understood in conjunction with
`40
`the accompanying drawings in which:
`FIG. 1 is a schematic representation of dual mode
`cellular telephone apparatus in accordance with the
`present invention;
`FIG. 2 is a block diagram of portions of the portable
`analog unit and the mobile unit connectable therewith,
`in accordance with the present invention; and
`FIG. 3 is a schematic representation of the manner in
`which the portable unit is selectively energized when
`connected to and disconnected from the mobile unit.
`
`45
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`DETAILED DESCRIPTION OF CERTAIN
`PREFERRED EMBODIMENTS
`Referring now to the drawings, wherein like refer-.
`55
`ence numerals are used throughout, FIG. 1 is a sche
`matic representation of dual mode cellular telephone
`apparatus which incorporates the present invention.
`This apparatus is intended to be disposed in a mobile
`station 10 of the type normally used in a vehicle, such as
`an automobile, a boat, a train or other means of convey
`ance. Mobile station 10 is comprised of a portable unit 1
`that is physically and electrically connectable to a mo
`bile unit 5. Portable unit 1 includes analog modulating
`/demodulating circuitry and is adapted to operate as a
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`self-contained, stand alone unit by which a user may
`communicate with a cellular base station. Accordingly,
`the portable unit includes a keypad 3 which is operable
`to “dial” a desired telephone number and to carry out
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`Mobile unit 5 is coupled to a main antenna 25 from
`which voice signals are transmitted to and received
`from a cellular base station. It is appreciated that such
`voice signals may be transmitted either as analog signals
`or digital signals, compatible with the operation of the
`base station.
`In a typical environment, mobile unit 5 is disposed in
`an automobile. Preferably, the automobile battery (or
`other local power source) is used to supply electrical
`energy to the mobile unit. FIG. 1 illustrates the mobile
`unit connected to an automobile battery 9. As will be
`discussed below in conjunction with FIG. 3, when por
`table unit 1 is received by mobile unit 5, automobile
`battery 9 is used to energize the electrical circuitry
`included in the portable unit.
`In a preferred embodiment, a multi-conductor con
`nector 42 provided with suitable plugs or other con
`necting devices 43 and 44 at its opposite ends serves to
`electrically connect portable unit 1 with mobile unit 5.
`The multiple conducting elements included in connec
`tor 42 provide a suf?cient number of signal transmission
`paths between the units, as will be described. Alterna
`tively, and in place of connector 42, contacts 2 and 6
`may be provided with multiple, individual contacts to
`serve as the multiple signal paths between the portable
`and mobile units. For example, contacts 2 and 6 may be
`comprised of multiple pins and sockets, respectively.
`Before-describing portable unit 1 and mobile unit 5 in
`greater detail, a brief description of typical uses of these
`units now follows. Portable unit 1 preferably includes a
`battery and may be used separate and apart from mobile
`unit 5. In that event, connector 42 is disconnected from
`the portable unit and the portable unit is removed from
`adapter 7. The portable unit now may function as a
`separate, stand alone, hand-held cellular telephone de
`vice. The user may operate portable unit 1 in much the
`same way as typical cellular telephone devices are oper
`ated, whereby voice signals derived from microphone
`40 are modulated and transmitted in analog form to a
`cellular base station from low gain antenna 11. Like
`wise, voice signals that are modulated in analog form
`are received from the cellular base station via antenna
`11; and the modulated voice signals are demodulated
`and reproduced by speaker 45 as audible speech. Of
`45
`course, keypad 3 may be operated to dial a desired
`telephone number so that the user may communicate
`with a desired recipient.
`It will be appreciated that the signal processing, mod
`ulating and demodulating circuitry included in portable
`unit 1 is conventional and functions in an analog mode.
`Hence, voice signals are communicated in analog form
`between the portable unit and the cellular base station
`when the portable unit is used as a separate, indepen
`dent, stand alone device.
`When the portable unit is received by mobile unit 5,
`matching contacts 2 and 6 provide electrical connection
`between these units and, in the preferred embodiment,
`the power supply of the mobile unit, and particularly
`the energy source of the vehicle in which the mobile
`unit is disposed, serves to energize the circuitry in
`60
`cluded in the portable unit. For example, adapter 7 may
`be particularly shaped to receive the portable unit; and
`the proper positioning of the portable unit within the
`adapter facilitates the connection of contacts 2 and 6. In
`addition, connector 42 is coupled between the portable
`and mobile units, for example, by inserting plugs 43 and
`44 in suitable sockets provided in the portable and mo
`bile units, respectively. Alternatively, contacts 2 and 6
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`may include a multiple pin/socket connector to estab
`lish multiple signal paths between the portable and mo
`bile units when portable unit 1 is received by mobile
`unit 5. Preferably, however, the portable and mobile
`units are interconnected by means of connector 42 to
`enable the user to remove the portable unit from
`adapter 7 and use the handset thereof in much the same
`way as a telephone is used to communicate with a cellu
`lar base station. Once the portable and mobile units are
`connected, voice signals derived from the portable unit
`are transmitted via mobile unit 5 to main antenna 25
`and, similarly, voice signals which are received from
`the cellular base station are received at main antenna 25
`and supplied to portable unit 1 via the mobile unit.
`In the preferred embodiment, it is not necessary to
`provide mobile unit 5 with analog modulating
`/demodulating circuitry. Rather, it is sufficient merely
`for digital communications unit 8 to operate in a digital
`mode for the transmission and reception of voice sig
`nals. As will be described below, in the event that mo
`bile station 10 (which now is comprised of intercon
`nected portable unit 1 and mobile unit 5) communicates
`with a ‘cellular base station exhibiting only analog trans
`mission/reception capabilities, as may be the case if the
`cellular base station is located in suburban and exurban
`environments, voice signals derived from microphone
`40 are modulated by the analog modulator included in
`portable unit 1; and these analog voice signals are cou
`pled via connector 42 to mobile unit 5 whereat they are
`RF modulated and transmitted by main antenna 25. The
`usual RF circuitry and low gain antenna 11 included in
`portable unit 1 are bypassed when the portable and
`mobile units are connected. Similarly, when voice sig
`nals are transmitted from a cellular base station by ana
`log modulation, those analog modulated voice signals
`are received by main antenna 25, RF demodulated by an
`RF receiver circuit included in mobile unit 5 and cou
`pled to portable unit 1 whereat the demodulated analog
`voice signals are subjected to analog demodulation. The
`resultant demodulated voice signals are converted to
`audible sounds by speaker 45.
`However, if mobile station 10 communicates with a
`cellular base station having digital capabilities; and if
`such communication is by way of digital modulation,
`such as in accordance with the dual mode cellular stan
`dard TIA IS-54, the analog modulating/demodulating
`circuitry included in portable unit 1 is bypassed and the
`digital modulating circuitry included in, for example,
`digital communications unit 8 is utilized. Now, voice
`signals derived from microphone 40 in portable unit 1
`' are coupled to mobile unit 5 whereat they are converted
`to digital signals, encoded, processed and modulated
`(such as by ‘HM shifted, differentially encoded quadra
`ture phase shift keying); and the resultant digital voice
`signals are RF modulated by an RF transmit circuit and
`supplied to main antenna 25 for transmission to the
`cellular base station. Similarly, digital voice signals that
`are received from the cellular base station are supplied
`by main antenna 25 to the RF receiver circuit included
`in mobile unit 5 to provide RF demodulation of the
`digital voice signals. The resultant digital signals then
`are processed, error corrected, decoded and converted
`to analog signals by digital communication unit 8. These
`analog voice signals then are coupled to portable unit 1
`and converted to audible sounds by speaker 45.
`FIG. 2 is a block diagram of one embodiment of the
`relevant portion of the electronics included in portable
`unit 1 and mobile unit 5, and the electrical interconnec
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`tion of these units. For convenience, those elements
`which are disposed in portable unit 1 are illustrated to
`the left of the vertical broken line in FIG. 2; and those
`elements which are included in mobile unit 5 are illus
`trated to the right of this line. It will, nevertheless, be
`appreciated that various switches which are illustrated
`as being disposed in one unit may, alternatively, be
`disposed in the other.
`As shown, portable unit 1 is comprised of a duplexer
`12, signal receiving circuitry including an RF mixer 15,
`an analog demodulator 18 and audio output circuitry
`21, and signal transmitting circuitry including audio
`input circuitry 23, an analog modulator 19 and an RF
`mixer 17. Duplexer 12 is adapted to operate in a receive
`or transmit mode and is coupled to low gain antenna 11
`to receive analog voice signals from a cellular base
`station and to transmit analog voice signals to that cellu
`lar base station. The duplexer is coupled to both the
`signal receiving circuitry and the signal transmitting
`circuitry. A ?lter amplifier 13 couples duplexer 12 to
`RF mixer 14 to supply RF analog voice signals to the
`mixer.
`Mixer 15 is adapted to RF demodulate the analog
`voice signals and, in this respect, a local oscillator 16,
`preferably formed as a frequency synthesizer, supplies
`to the mixer a local oscillating signal of a frequency
`corresponding to a desired cellular channel. For exam
`ple, voice signals may be transmitted in either analog or
`digital form from a cellular base station with an RF
`frequency in the range of 869 MHz to 894 MHz. Fre
`quency synthesizer 16 supplies an appropriate RF oscil
`lating signal to mixer 15 under the control of a central
`control unit 22 (to be described) so as to recover the
`voice signals from the channel transmitted by the cellu
`lar base station.
`Mixer 15 is coupled to analog demodulator 18 via a
`receiver switch 20. Typically, frequency modulation
`(FM) is used in the analog modulating mode and, there
`fore, analog demodulator 18 is comprised of an FM
`demodulator. The PM demodulator is provided with
`voice and control outputs, the control output being
`coupled to central control unit 22 and the voice output
`being coupled to audio output circuit 21 by way of a
`mode switch 35A. As will be described below, mode
`switch 35A is used to couple to the audio output cir
`45
`cuitry demodulated voice signals that had been trans
`mitted to either the analog mode or the digital mode.
`Hence, for convenience, this switch is referred to as a
`mode switch, indicative of its use to couple voice sig
`nals that have been transmitted in the analog mode or in
`the digital mode.
`The control output of FM modulator 18 recovers
`control data from the signals transmitted by the cellular
`base station, such as a voice channel assignment signal.
`The remaining control signals are not relevant to the
`present invention per se. It will be appreciated that
`central control unit 22 responds to the voice channel
`assignment signal to determine the particular mixing
`frequency to be produced by frequency synthesizer 16.
`Central control unit 22 preferably includes a conven
`tional microprocessor whose functions relevant to the
`instant invention may be summarized as follows:
`The central control unit determines the particular
`mixing frequency produced by frequency synthesizer 16
`in response to the voice channel assignment signal that
`is received from the cellular base station.
`v
`The central control unit detects when portable unit 1
`is connected to mobile unit 5 (as when the mobile unit
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`receives the portable unit, as mentioned above) to pro—
`duce a portable/base selector signal. This selector signal
`is coupled to receiver switches 20A and 20B and to
`transmit switches 24A and 248 whose functions are
`described below. Suffice it to say that these switches
`exhibit a ?rst state when the portable unit is used as a
`stand alone unit and a second state when the portable
`unit is connected to the mobile unit. When in this sec’
`ond state, the RF receiver circuit included in the mobile
`unit is used to couple voice signals received from the
`cellular base station to PM demodulator 18.
`The central control unit 22 senses when voice signals
`are communicated with the cellular base station in ana
`log or digital form. When analog transmission is used,
`the central control unit supplies an “analog” mode sig
`nal to mode switches 35A, 35B and 35C and to mode
`switches 34A, 34B and 34C, to be described. Con
`versely, when digital transmission is selected, the cen
`tral control unit supplies a “digital” mode signal to these
`mode switches.
`In the illustrated embodiment, mode switch 35A ex
`hibits two states: an analog mode state in which the
`output of FM demodulator 18 is coupled to audio out
`put circuitry 21 and a digital mode state in which the
`output of a digital signal processor 30 (to be described)
`is coupled to the audio output circuitry.‘ It is appreci
`ated that mode switch 35A, as well as the other
`switches illustrated in FIG. 2, may be implemented as
`conventional solid-state switching devices.
`Audio output circuitry 21 includes equalizing, ?lter
`ing, noise reduction and amplifying circuitry conven
`tionally used and known to those of ordinary skill in the
`art.
`In the transmitting circuitry, audio input circuitry 23
`is coupled to microphone 40 to receivevoice signals
`therefrom. The audio input circuitry is adapted to ?lter,
`equalize and amplify the voice signals in a manner
`known to those of ordinary skill in the art. The resultant
`voice signals produced by the audio input circuitry are
`coupled by mode switch 34A to analog modulator 19
`when this mode switch is in its analog mode. However,
`when mode switch 34A is in its digital mode, it couples
`the voice signals to digital signal processor 30.
`Analog modulator 19 is compatible with analog de
`modulator 18 and, in the illustrated embodiment, com
`prises an FM modulator. The frequency modulated
`voice signals produced thereby are coupled to mixer 17
`by transmit switch 24A. in the embodiment described
`herein, transmit switch 24A assumes a ?rst state to cou
`ple frequency modulated voice signals from the FM
`modulator to mixer 17 when portable unit 1 is used as a
`stand alone device. However, when the portable unit is
`connected to mobile unit 5, central control unit 22 dis
`poses transmit switch 24A in a second state such that
`55
`r the frequency modulated voice signals are not coupled
`to mixer 17.
`Mixer 17 is coupled to frequency synthesizer 16 and
`receives a mixing signal of suitable frequency there
`from. For example, voice signals may be transmitted to
`a cellular base station with a transmission frequency in
`the range of 824 MHz to 849 MHZ. The frequency
`synthesizer supplies a mixing signal of appropriate fre
`quency to mixer 17 as may be determined by central
`control unit 22 in response to the voice channel assign
`ment signal that is received from the cellular base sta
`tion. The resultant RF analog voice signals produced by
`mixer 17 are coupled to duplexer 12 by a power ampli
`
`35
`
`65
`
`7
`
`

`
`9
`?er 14 and are transmitted to the cellular base station by
`antenna 11.
`FIG. 2 illustrates the relevant portions of mobile unit
`5 which is comprised of an RF receiver circuit 36, a
`digital demodulator 29, an RF transmit circuit 37, a
`digital modulator 31 and a digital signal processor 30.
`The RF receiver and transmit circuits 36 and 37 are
`coupled to main antenna 25 by a duplexer 26 which is
`similar to aforementioned duplexer 12 and, in the inter
`est of brevity, is not described further herein.
`RF receiver circuit 36 is comprised of a ?lter ampli
`?er 27, which may be similar to ?lter ampli?er 13, and
`a mixer 28 which may be similar to aforementioned
`mixer 15. Filter ampli?er 27 is coupled to duplexer 26
`and supplies to mixer 28 the RF voice signals received
`in analog or digital form from the cellular base station.
`Mixer 28 is coupled to frequency synthesizer 16 by
`receiver switch 20B and thus receives a mixing signal of
`a frequency determined by central control unit 22 in
`accordance with the voice channel assignment signal
`received from the cellular base station. It will be appre
`ciated that receiver switches 20A and 20B cooperate
`such that when one is closed the other is opened.
`The output of mixer 28 is coupled to PM demodula
`tor 18 in portable unit 1 by mode switch 35C. As will be
`described, when mobile unit 5 operates in its analog
`mode, voice signals received from the cellular base
`station by way of main antenna 25 are RF demodulated
`and supplied to PM demodulator 18 for analog demodu
`lation. It is seen that, when the portable and mobile units
`are connected and voice signals are communicated in
`the analog mode, FM demodulator 18 receives fre
`quency modulated voice signals from mixer 28 in place
`of frequency modulated voice signals that otherwise
`would be supplied thereto by mixer 15. That is, the
`portable unit receives voice signals from the cellular
`base station by way of mobile unit 5.
`The output of mixer 28 also is coupled to digital de
`modulator 29 by way of mode switch 35B. Although
`FIG. 2 illustrates mixer 28 with two separ