United States Patent (19)
`Schlang et al.
`
`54) DUAL BAND MOBILE STATION
`75 Inventors: Jeffrey A. Schlang, Raleigh; Ronald D.
`Boesch, Morrisville, both of N.C.
`
`73 Assignee: Ericsson Inc., Research Triangle Park,
`N.C.
`
`21 Appl. No.: 08/823,068
`
`6
`
`USOO5963852A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,963,852
`Oct. 5, 1999
`
`5,796,772 8/1998 Smith et al. ............................ 375/200
`FOREIGN PATENT DOCUMENTS
`0800 283 A2 10/1997 European Pat. Off..
`WO 89/07865 8/1989 WIPO.
`WO 98/00927 1/1998 WIPO.
`Primary Examiner Nguyen Vo
`Assistant Examiner-Charles N. Appiah
`Attorney, Agent, or Firm-Robert A. Samra
`
`f
`52) -rr. /76;
`58 Field of Search .................................. 455/76, 83, 84,
`455/86, 188.1, 180.1, 552, 553, 550, 85
`Ref
`Cited
`eferences Cite
`U.S. PATENT DOCUMENTS
`
`56
`56)
`
`- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 455 It's A dual band mobile Station including a main channel Syn
`
`thesizer and an offset Synthesizer for generating the transmit
`frequency and the receive intermediate frequency (IF)
`required for operation in each of two different bands char
`acterized by different transmit-receive channel offsets.
`According to the present invention, the main channel Syn
`thesizer does not have to change its frequency when the
`mobile Station Switches between transmission and reception
`
`4,223,406 9/1980 Someno - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 455/180.1
`
`in either of the two bands So long as a common IF is Selected
`
`- - - - i.. for both bands, which is equal to one or the other of the
`E. 6.E. NR s al. ..
`5.410747 4/1995 ON erSpaugn ......................
`channel offsets. This IF selection also allows for a reduction
`2 : --- Y-2
`magari et al. ...................... 455/118
`5,465,409 11/1995 Borras et al. ...
`... 455/260
`in the tuning range of the main channel Synthesizer.
`5,519,885 5/1996 Vaisanen ................................... 455/76
`5,732,330 3/1998 Anderson et al. ........................ 455/76
`
`10 Claims, 5 Drawing Sheets
`
`
`
`172
`
`174
`
`176
`
`178
`
`170
`
`
`
`
`
`BPF
`
`FURTHER F
`PROCESSING
`
`
`
`130
`
`132
`
`
`
`OFFSET
`SYNTHESIZER
`
`Ex.1020
`APPLE INC. / Page 1 of 12
`
`

`

`U.S. Patent
`
`Oct. 5, 1999
`
`Sheet 1 of 5
`
`5,963,852
`
`
`
`FIC. 1
`(PRIOR ART)
`
`Ex.1020
`APPLE INC. / Page 2 of 12
`
`

`

`U.S. Patent
`
`Oct. 5, 1999
`
`Sheet 2 of 5
`
`5,963,852
`
`Yoo -
`
`A
`
`FIG. 2 (PRIOR ART)
`B
`c | A
`B
`
`c
`
`FIG. 3 (PRIOR ART)
`
`BAND
`
`BAND
`
`| || 1
`
`TX PCS
`BAND
`
`RX PCS
`BAND
`
`||
`
`|.
`
`||
`
`FIC. 4
`(PRIOR ART)
`,
`
`FREQUENCY (MHz)
`
`
`
`
`
`CELL
`BAND
`
`
`
`BANDWIDTH NUMBER OF
`CHANNELS
`
`
`
`BOUNDARY
`CHANNELS
`
`(NOT USED)
`A'
`
`A'
`
`5
`
`2 5
`
`
`
`
`
`
`
`53
`
`33
`5
`
`35
`5
`
`50
`
`83
`
`(990)
`991
`991
`
`333
`333
`334
`534
`666
`667
`667
`716
`716
`717
`717
`799
`799
`
`
`
`TRANSMITTER CENTER
`FREQUENCY (MHz)
`MOBILE
`BASE
`(824010) (869.010)
`824.040
`869,040
`825.000
`870.000
`825.030
`834,990
`85020
`844.980
`890.010
`845.010
`891.480
`46.480
`46.510 | 891.510
`848.970
`893.970
`
`FIC. 6
`(PRIOR ART)
`
`Ex.1020
`APPLE INC. / Page 3 of 12
`
`

`

`U.S. Patent
`
`Oct. 5, 1999
`
`Sheet 3 of 5
`
`5,963,852
`
`
`
`
`
`
`
`PCS
`BAND
`
`BANDWIDTH NUMBER OF BOUNDARY
`CHANNELS
`CHANNELS
`
`
`
`TRANSMITTER CENTER
`FREQUENCY (MHz)
`MOBILE
`BASE
`
`
`
`NOT USED
`
`5
`
`497
`
`164
`
`H
`
`5
`
`5
`
`498
`
`1
`1
`165
`
`2
`498
`499
`500
`501
`502
`665
`
`667
`6
`68
`1165
`1166
`1167
`1168
`1332
`1333
`1334
`1335
`1498
`1499
`1500
`1501
`1502
`1998
`
`1930.050
`1930.080
`1944.960
`1944.990
`1945.020
`1945.050
`1945.080
`1949.970
`1950.000
`1950.030
`1950.060
`1964.970
`1965.000
`1965.050
`1965.060
`1969.980
`1970.010
`1970.040
`1970.070
`1974.960
`1974.990
`1975.020
`1975.050
`1975.080
`1989.960
`1989.990
`
`
`
`1864.920
`
`1869.930
`
`1884.930
`
`1885.020
`1889.940
`
`1894.920
`
`1895.010
`1895.040
`1909.920
`1909.950
`
`E, F
`E,
`
`
`
`
`
`
`
`NOT USED
`
`5
`
`164
`
`15
`
`1
`497
`
`FIG. 6
`(PRIOR ART)
`
`Ex.1020
`APPLE INC. / Page 4 of 12
`
`

`

`U.S. Patent
`
`Oct. 5, 1999
`
`Sheet 4 of 5
`
`5,963,852
`
`30
`
`
`
`RX
`
`
`
`
`
`T
`X
`
`FIC. 7
`(PRIOR ART)
`54
`36
`
`FIRST LO
`
`
`
`52
`
`CHANNEL
`SYNTHESIZER
`
`IQ
`MODULATOR
`
`Q
`
`FIRST
`
`40
`
`4.
`2
`
`SECOND
`IF
`
`38
`
`TX OFFSET
`SYNTHESIZER IN 44
`
`FIC. 8
`(PRIOR ART)
`PCs' S
`
`
`
`
`
`TX LO
`PCS BAND
`
`
`
`RX LO
`CELL BAND
`
`TX LO
`CELL BAND
`
`
`
`MAIN
`
`CANNEL / 2
`SYNTHESIZER
`
`OFFSET
`SYNTHESIZER IN 44
`
`Ex.1020
`APPLE INC. / Page 5 of 12
`
`

`

`U.S. Patent
`
`Oct. 5, 1999
`
`Sheet 5 of 5
`
`5,963,852
`
`
`
`Z
`Z
`|
`
`
`
`
`
`
`
`
`
`
`
`(JEZISEHINÅS
`
`
`
`TENNWHO NIWW
`
`ONWE SOd XI
`
`?JOIVT^OOW
`
`Ex.1020
`APPLE INC. / Page 6 of 12
`
`

`

`1
`DUAL BAND MOBILE STATION
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to wireleSS communication
`Systems and, more particularly, to mobile Stations which
`operate in two separate radio frequency (RF) bands Such as
`those used for providing cellular telephone Services and
`personal communication Services (PCS), respectively.
`2. Related Prior Art Systems
`The architecture for a typical cellular radio System is
`shown in FIG. 1. A geographical area (e.g., a metropolitan
`area) is divided into Several Smaller, contiguous radio cov
`erage areas, called “cells,” such as cells C1-C10. The cells
`C1-C10 are served by a corresponding group of fixed radio
`stations, called “base stations.” B1-B10, each of which
`includes a plurality of RF channel units (transceivers) that
`operate on a Subset of the RF channels assigned to the
`system, as well known in the art. The RF channels allocated
`to any given cell (or Sector) may be reallocated to a distant
`cell in accordance with a frequency reuse plan as is also well
`known in the art. In each cell, at least one RF channel is used
`to carry control or Supervisory messages, and is called the
`“control” or “paging/access' channel. The other RF chan
`nels are used to carry Voice conversations, and are called the
`“voice” or “speech” channels. The cellular telephone users
`(mobile subscribers) in the cells C1-C10 are provided with
`portable (hand-held), transportable (hand-carried) or mobile
`(car-mounted) telephone units, collectively referred to as
`“mobile stations.” Such as mobile stations M1-M5, each of
`which communicates with a nearby base Station. Each of the
`mobile stations M1-M5 includes a controller
`(microprocessor) and a transceiver, as well known in the art.
`The transceiver in each mobile Station may tune to any of the
`RF channels specified in the system (whereas each of the
`transceivers in the base stations B1-B10 usually operates on
`only one of the different RF channels used in the corre
`sponding cell).
`When turned on (powered up), each of the mobile stations
`M1-M5 enters the idle state (standby mode) and tunes to and
`continuously monitors the Strongest control channel
`(generally, the control channel of the cell in which the
`mobile station is located at that moment). When moving
`between cells while in the idle State, the mobile station will
`eventually “lose” radio connection on the control channel of
`the “old” cell and tune to the control channel of the “new”
`cell. The initial tuning to, and the change of, control channel
`are both accomplished automatically by Scanning all the
`control channels in operation in the cellular System to find
`the “best” control channel. When a control channel with
`good reception quality is found, the mobile Station remains
`tuned to this channel until the quality deteriorates again. In
`this manner, the mobile station remains “in touch' with the
`System and may receive or initiate a telephone call through
`one of the base stations B1-B10 which is connected to the
`MTSO 20.
`With continuing reference to FIG. 1, the base stations
`B1-B10 are connected to and controlled by a mobile tele
`phone switching office (MTSO) 20. The MTSO 20, in turn,
`is connected to a central office (not specifically shown in
`FIG. 1) in the landline (wireline) public Switched telephone
`network (PSTN) 22, or to a similar facility such as an
`integrated system digital network (ISDN). The MTSO 20
`Switches calls between wireline and mobile Subscribers,
`controls signalling to the mobile stations M1-M5, compiles
`billing Statistics, Stores Subscriber Service profiles, and pro
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,963,852
`
`2
`vides for the operation, maintenance and testing of the
`system. An important function of the MTSO 20 is to perform
`a “handoff of a call from one base station to another base
`station B1-B10 as one of the mobile stations M1-M5 moves
`between cells. The MTSO 20 monitors the quality of the
`voice channel in the old cell and the availability of voice
`channels in the new cell. When the channel quality falls
`below a predetermined level (e.g., as the user travels away
`from the old base station towards the perimeter of the old
`cell), the MTSO 20 selects an available voice channel in the
`new cell and then orders the old base station to send to the
`mobile Station on the current voice channel in the old cell a
`handoff message which informs the mobile Station to tune to
`the Selected Voice channel in the new cell.
`The original cellular radio Systems, as described generally
`above, used analog transmission methods, Specifically fre
`quency modulation (FM), and duplex (two-way) RF chan
`nels in accordance with the well known Advanced Mobile
`Phone Service (AMPS) standard. According to the AMPS
`Standard, each control or voice channel between the base
`Station and the mobile Station uses a pair of Separate fre
`quencies consisting of a forward (down link) frequency for
`transmission by the base Station (reception by the mobile
`Station) and a reverse (uplink) frequency for transmission by
`the mobile station (reception by the base station). The AMPS
`System, therefore, is a single-channel-per-carrier (SCPC)
`System allowing for only one voice circuit (telephone
`conversation) per RF channel. Different users are provided
`access to the same Set of RF channels with each user being
`assigned a different RF channel (pair of frequencies) in a
`technique known as frequency division multiple access
`(FDMA).
`More recently, there has been a shift from analog to digital
`technology in order to increase the capacity of cellular
`Systems and meet the needs of an ever growing Subscriber
`base. The newer digital AMPS (D-AMPS) systems use
`digital voice encoding (analog-to-digital conversion and
`voice compression) and time division multiple access
`(TDMA) to multiply the number of voice circuits
`(conversations) which can be accommodated on an AMPS
`RF channel (i.e., to increase capacity). As shown in FIG. 2,
`in D-AMPS each of the forward and reverse RF channels is
`divided into repeating time slots which may be occupied by
`three different mobile stations (A, B and C). It will be noted
`that the corresponding transmit and receive slots for any
`mobile station are offset in time from each other by at least
`one time slot so that the mobile station will not have to
`transmit and receive at the same time (thus, in TDMA mode,
`unlike FDMA mode, it is not necessary to use a duplexer for
`Separating the transmit and receive signals). From the per
`spective of any of the mobile stations (A, B or C), its time
`Slots on the forward and reverse channels are organized as
`a repeating Sequence of a transmit slot followed by a receive
`slot that is followed by a mobile assisted handoff (MAHO)
`slot, as shown in FIG. 3 (during the MAHO slot the mobile
`Station performs signal quality measurements on RF chan
`nels designated by the System So as to assist the System in
`performing handoff).
`Along with the recent Shift to digital technology in
`cellular Systems, there has been an increasing shift towards
`the use of lightweight pocket telephones by Subscribers who
`desire to receive wireleSS Service not only while driving but
`also while walking around in their homes or offices or in the
`public Streets or meeting places. This desire is reflected in
`the emerging concept of “personal communication Services'
`(PCS). The goal of PCS systems is to provide a user moving
`around, for example, inside an office building, a factory, a
`
`Ex.1020
`APPLE INC. / Page 7 of 12
`
`

`

`5,963,852
`
`15
`
`25
`
`35
`
`40
`
`3
`warehouse, a shopping mall, a convention center, an airport,
`or an open area with the ability to transmit and/or receive
`telephone calls, facsimile, computer data, and/or paging and
`text messages. PCS systems use digital technology (TDMA)
`as with D-AMPS systems, but generally operate on lower
`power and use Smaller cellular structures (called “micro
`cells” or “picocells”) as compared with AMPS/D-AMPS
`systems. Furthermore, while AMPS/D-AMPS systems oper
`ate in the 800 MHz band reserved for cellular operators
`many years ago, PCS systems operate in the 1900 MHz band
`which was recently released for use by PCS operators in the
`United States.
`The differences between the frequency plans for PCS and
`AMPS/D-AMPS systems are shown in FIGS. 4-6. Referring
`first to FIG. 4, the AMPS/D-AMPS band (hereinafter some
`times referred to as the “cell band') spans frequencies in the
`range 824–894 MHz, and consists of a transmit (mobile
`station to base station) band over the range 824-849 MHz
`and a corresponding receive (base Station to mobile station)
`band over the range 869–894 MHz. The PCS band, on the
`other hand, spans frequencies in the range 1850-1990 MHz,
`and consists of a transmit (mobile Station to base station)
`band over the range 1850-1910 MHz and a corresponding
`receive (base station to mobile station) band over the range
`1930–1990 MHz. As shown in FIGS. 5-6, each of the RF
`channels in the cell and PCS bands is associated with a
`particular channel number and group (assigned to a particu
`lar operator), and consists of a carrier (center) frequency in
`the associated transmit band and a corresponding carrier
`frequency in the associated receive band. It will be seen that
`for both AMPS/DAMPS and PCS, the adjacent channel
`separation is 30 KHZ. However, the transmit-receive (TX
`RX) offset is 45 MHz for AMPS/D-AMPS and 80.04 MHz
`for PCS.
`Thus, at present, different types of wireleSS Systems are in
`use, including AMPS (analog/FDMA) and D-AMPS
`(digital/TDMA) systems operating in the 800 MHz band,
`and PCS systems operating in the 1900 MHz band. As a
`result, there is a need or a market for mobile Stations which
`operate only in AMPS mode, “dual-mode” mobile stations
`which can operate in both AMPS and D-AMPS modes, and
`“dual-band' mobile stations which can operate in both the
`cell and PCS bands. The design of cost-effective transceivers
`for dual-band mobile Stations, in particular, has proved to be
`difficult due to the relatively large frequency Separation
`between the cell and PCS bands and the use of different
`TX-RX offsets in the two bands. Those difficulties may be
`better understood by reference to FIG. 7 which shows a
`typical design for a single band (e.g., AMPS/D-AMPS)
`transceiver.
`Referring to FIG. 7, an incoming (received) Signal in the
`869-894 MHZ range is passed through a band pass filter
`(BPF) 30 which attenuates out-of-band signals and noise.
`The output of the BPF 30 then is mixed with the output of
`a main channel Synthesizer (first local oscillator) 32 in a
`mixer 34 to produce a pair of Sum and difference
`frequencies, as well known in the art. These signal products
`are passed through a BPF 36 which filters out the (higher)
`Sum frequency leaving only the difference (lower) fre
`quency. The effect of this first mixing and filtering Stage is
`to downconvert the received signal into a first intermediate
`frequency (IF) signal, which is presented at the output of the
`BPF 36. This first IF signal is further downconverted into a
`Second IF Signal by mixing it with the output of an auxiliary
`synthesizer (second local oscillator) 38 in a mixer 40, and
`then filtering the output of the mixer 40 in a BPF 42 so as
`to select the lower frequency from the mixer 40.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`As also shown in FIG. 7, the main channel synthesizer 32
`can be used in conjunction with a transmit offset Synthesizer
`44 (third local oscillator) to upconvert a baseband signal into
`a transmit signal in the desired 824-849 MHz range. The
`baseband Signal may be comprised of in-phase (I) and
`quadrature (Q) components representative of a user speech
`Signal (as well known in the art). During transmission, the
`output of the main channel synthesizer 32 is mixed with the
`output of the transmit offset synthesizer 44 in a mixer 46 to
`produce a pair of Sum and difference frequencies that are
`modulated with the baseband signal in an IQ modulator 48.
`The output of the IQ modulator 48 then is passed through a
`BPF 50 so as to select the desired transmit frequency.
`The transceiver of FIG. 7 can be configured to receive or
`transmit in any RF channel within the cell band by appro
`priate Setting of the main channel Synthesizer 32, the aux
`iliary synthesizer 38 and/or the transmit offset synthesizer
`44. For example, if the desired transmit and receive fre
`quencies are 824.04 MHZ and 869.04 MHz, respectively, the
`main channel synthesizer 32 can be set to operate at 979.56
`MHz. The mixer 34 will generate a sum frequency signal at
`1848.6 and a difference frequency signal at 110.52 MHz.
`The higher frequency is filtered out in the BPF 36 and the
`lower frequency (first IF) is mixed with the output of the
`auxiliary Synthesizer 38, which may be set to operate at
`110.97 MHz. The mixer 40 will generate a sum frequency
`Signal at 221.49 MHZ and a difference frequency Signal at
`0.45 MHz (450 KHz). The higher frequency is filtered out in
`the BPF 42 and the lower frequency (second IF) is delivered
`for further IF processing (not shown).
`In the transmit direction, the transmit offset synthesizer 44
`may be set to operate at 155.52 MHz. This 155.52 MHz
`signal is mixed with the 979.56 MHz signal from the main
`channel Synthesizer 32 in the mixer 46 which generates a
`sum frequency signal at 1135.08 MHz and a difference
`frequency signal at 824.04 MHz. After modulation in the IQ
`modulator 48, the higher frequency (and other harmonics)
`can be filtered out in the BPF 50 leaving the desired transmit
`frequency at 824.04 MHz for delivery to an antenna (not
`shown in FIG. 7).
`It will be readily appreciated that by Setting the main
`channel synthesizer 32 within the range 979.56-1004.49
`MHz all of the desired transmit and IF frequencies for cell
`band operation can be generated in the manner described
`above (with the transmit offset synthesizer 44 set to 155.52
`MHZ and the first IF fixed at 110.52 MHZ for all transmit and
`receive frequencies).
`The basic transceiver design as shown in FIG. 7 and
`illustrated above for AMPS/D-AMPS operation can also be
`used for operation in the PCS band. However, for dual band
`operation, Such a design requires the use of two Separate
`AMPS/D-AMPS and PCS transceivers having different syn
`thesizers 32, 38 and 44 due to the substantially different
`frequency ranges and the substantially different TX-RX
`offsets for the cell and PCS bands, respectively. For a dual
`band mobile Station, Such a design may not be cost effective
`or practical Since it requires the use of a total of six different
`Synthesizers, which would increase the cost, Size and current
`drain of the mobile station.
`One approach to minimizing the transceiver hardware
`required for dual band operation is shown in FIG. 8. This
`approach contemplates the sharing of hardware between the
`cell band and PCS band operations. According to this
`approach, the main channel Synthesizer 32 is used to gen
`erate a local oscillator (LO) signal for downconverting a
`received Signal in the cell band into an intermediate fre
`
`Ex.1020
`APPLE INC. / Page 8 of 12
`
`

`

`5,963,852
`
`15
`
`S
`quency (IF) signal. The output of the main channel Synthe
`sizer 32 is also mixed with the output of the offset synthe
`sizer 44 in a mixer 52 to generate an LO Signal at the output
`of a band pass filter (BPF) 54 for upconverting a source
`signal for transmission in the cell band. In PCS mode, the
`output of the BPF 54 is mixed with the output of the main
`channel synthesizer 32 in a mixer 56 to produce an LO
`signal at the output of a BPF 58 for upconverting a source
`signal for transmission in the PCS band. To downconvert a
`received PCS signal into an IF signal, the frequency of the
`main channel Synthesizer 32 can be doubled in a frequency
`doubler 60 and used as the receive LO signal. It will be
`appreciated that the transceiver design shown in FIG. 8
`reduces the required hardware for dual band operation by
`using the output of the main channel Synthesizer 32 as the
`main LO signal for cell band operation and by remixing or
`doubling of this LO signal for PCS band operation, thus
`taking advantage of the fact that the PCS band is roughly
`twice the frequencies of the receive cell band.
`The desired frequencies in the cell and PCS bands can be
`generated in the circuit of FIG. 8 by setting the offset
`channel synthesizer 44 to a frequency of 155.52 MHZ and by
`tuning the main channel Synthesizer 44 to frequencies in the
`range 979.56–100449 MHz and 1002.78–1050.255 MHz
`for operation in the cell band and PCS band, respectively.
`25
`Thus, for example, the transmit and receive (first) IF fre
`quencies at the upper and lower edges of the cell and PCS
`bands can be generated as follows (all numbers in MHz):
`TX Cell Band:
`979.56-155.52824.04
`100449-155.52=848.97
`RX IF Cell Band:
`979.56-869.04=110.52
`1004.49-893.97=110.52
`TX PCS Band:
`10O2.78-155.52+10O2.78=1850.04
`1032.735-155.52-1032.735-1909.95
`RX IF PCS Band:
`(1020.3x2)-1930.08=110.52
`(1050.255x2)-1989.99=110.52
`It will be seen that while the approach of FIG. 8 reduces
`hardware requirements for dual band operation (as well as
`providing for a common IF (at 110.52 MHz), which sim
`plifies IF processing), it imposes certain design requirements
`on the voltage controlled oscillator (VCO) and the loop filter
`in the main channel Synthesizer 32 (as well known in the art,
`a frequency Synthesizer Such as the main channel Synthe
`sizer 32 is comprised of a VCO which is tuned in a phase
`locked loop including a loop filter for passing an error
`voltage input signal to the VCO). Specifically, the VCO in
`the main channel synthesizer 32 of FIG.8 must be tunable
`within a greater-than-70-MHz range (979.56-1050.255
`MHz). As will be readily recognized by persons of ordinary
`skill in the art, Such a wide tuning range may be difficult to
`implement in practice and may also increase the phase noise
`and the oscillator gain (ratio of output frequency change to
`input tuning voltage) of the VCO in the main channel
`synthesizer 32. These effects, in turn, could lead to the
`generation of exceSS noise Signals outside the designated 30
`KHZ channel bandwidth. These “out-of-channel” signals
`may have Sufficient energy to cause radio interference with
`adjacent channels.
`In addition, it will be observed that in the PCS mode the
`main channel synthesizer 32 in FIG.8 must “hop” between
`two different frequencies (e.g., 1002.78 MHz and 1020.3
`
`35
`
`6
`MHz) when switching between transmit and receive modes.
`In a typical TDMA system (as illustrated in FIG.3), a mobile
`Station may have to transition from the transmit slot to the
`receive slot in as little as 1.8 ms or less. Therefore, the main
`channel synthesizer 32 in FIG.8 must be “fast locking” (i.e.,
`able to move from one frequency and Settle at another
`frequency very quickly). AS will be readily recognized by
`perSons of ordinary skill in the art, a faster locking time
`requires the use of wider loop filter in the main channel
`Synthesizer 32 which, in turn, may result in increased phase
`noise at the output of the VCO and, consequently, in the
`modulated transmit Signal.
`In light of the Shortcomings of the prior art, there is a need
`for a dual band transceiver architecture which allows the
`VCO in the main channel synthesizer 32 to operate in a
`narrower tuning range and to remain at the same frequency
`when Switching between transmit and receive modes. AS
`will be seen below, Such an advantageous architecture is
`provided by the present invention.
`SUMMARY OF THE INVENTION
`In one aspect, the present invention provides a mobile
`Station which operates in first and Second radio frequency
`(RF) bands, each band comprising pairs of transmit and
`receive RF channels, the frequencies of the transmit and
`receive channels in any pair in the first band being Separated
`by a first channel offset and the frequencies of the transmit
`and receive channels in any pair in the Second band being
`Separated by a Second channel offset. The mobile Station
`comprises a main frequency Synthesizer for generating a
`main Signal; an offset frequency Synthesizer for generating
`an offset Signal; means for combining the main Signal with
`the offset signal to produce a signal corresponding to a
`Selected transmit RF channel in the first band; means for
`combining the main Signal with a signal corresponding to a
`receive RF channel, that is paired with the selected transmit
`RF channel in the first band, to produce an intermediate
`frequency (IF) signal having a frequency f.; means for
`Scaling the frequency of the main Signal to produce a Scaled
`Signal corresponding to a Selected transmit RF channel in the
`Second band; means for combining the Scaled signal with a
`Signal corresponding to a receive RF channel, that is paired
`with the selected transmit RF channel in the second band, to
`produce an IF signal having a frequency f.; and means for
`programming the main and offset SynthesizerS Such that the
`f, and f frequencies are both equal to either the first or the
`Second channel offset thereby allowing the main Synthesizer
`to remain at the same frequency when operating on any pair
`of transmit and receive channels in the first or Second band.
`This mobile station can be used, for example, where the first
`and second bands are the cell and PCS bands, respectively.
`In another aspect, the present invention provides a method
`of operating a mobile Station in first and Second radio
`frequency (RF) bands, each band comprising pairs of trans
`mit and receive RF channels, the frequencies of the transmit
`and receive channels in any pair in the first band being
`Separated by a first channel offset and the frequencies of the
`transmit and receive channels in any pair in the Second band
`being Separated by a Second channel offset. The method
`comprises the Steps of generating a main frequency Signal in
`the mobile Station; generating an offset frequency Signal in
`the mobile station; if the mobile station is to be operated in
`the first band, combining the main Signal with the offset
`Signal to produce a signal corresponding to a Selected
`transmit RF channel in the first band; if the mobile station is
`to be operated in the first band, combining the main Signal
`with a signal corresponding to a receive RF channel, that is
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Ex.1020
`APPLE INC. / Page 9 of 12
`
`

`

`5,963,852
`
`7
`paired with the selected transmit RF channel in the first
`band, to produce an intermediate frequency (IF) signal
`having a frequency f; if the mobile Station is to be operated
`in the Second band, Scaling the frequency of the main Signal
`to produce a Scaled Signal corresponding to a Selected
`transmit RF channel in the second band; if the mobile station
`is to be operated in the Second band, combining the Scaled
`Signal with a signal corresponding to a receive RF channel,
`that is paired with the selected transmit RF channel in the
`Second band, to produce an IF Signal having a frequency f;
`and Selecting the frequencies of the main and offset Signals
`So that the f and f frequencies are both equal to either the
`first or the second channel offset. In this method, as before,
`the first and second bands can be the cell and PCS bands,
`respectively.
`These and other aspects, objects and advantages of the
`present invention will become readily apparent from the
`accompanying drawings and the detailed description of the
`invention as set forth below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The present invention will be better understood and its
`numerous objects and advantages will become apparent to
`those skilled in the art by reference to the following draw
`ings in which:
`FIG. 1 shows the architecture of a conventional cellular
`radio System including a plurality of mobile Stations and
`base Stations communicating over a plurality of radio fre
`quency (RF) channels;
`FIG. 2 shows a time division multiple access (TDMA)
`format for the forward (base station to mobile station) and
`reverse (mobile station to base station) RF channels in the
`system of FIG. 1;
`FIG.3 shows the TDMA sequence from the perspective of
`one of the mobile stations in FIG. 1;
`FIG. 4 shows the transmit and receive frequency bands for
`cellular Systems and communication Services (PCS) Systems
`as Specified in known industry Standards,
`FIG. 5 shows the RF channel allocation within the cellular
`frequency band(s) of FIG. 4;
`FIG. 6 shows the RF channel allocation within the PCS
`frequency band(s) of FIG. 4;
`FIG. 7 is a block diagram of a single band transceiver
`which can be used in a mobile Station operating in either the
`cellular band or the PCS band (but not both);
`FIG. 8 is a simplified block diagram of a dual band
`transceiver which can be used in a mobile Station operating
`in both the cellular band and the PCS band;
`FIG. 9 is a block diagram of a mobile station which may
`be used in accordance with the present invention; and
`FIG. 10 is a circuit diagram of an exemplary construction
`of the RF section in FIG. 9, as taught by the present
`invention.
`
`DETAILED DESCRIPTION
`Referring now to FIG. 9, there is shown a simplified block
`diagram of an exemplary mobile station 100 which may be
`used in accordance with the present invention. The mobile
`station 100 comprises a microphone 102, a loudspeaker 104,
`a keyboard or keypad 106, an alphanumeric or graphical
`display 108, a user interface 110, a microprocessor 112, a
`program memory 114, a random access memory (RAM)
`116, an electrically erasable programmable read only
`memory (EEPROM) 118, a radio frequency (RF) section
`120 and an antenna 122.
`
`8
`The user interface 110 includes Speech and data process
`ing circuitry (not specifically shown) Such as a codec for
`performing analog-to-digital (A/D) conversion of a transmit
`Speech Signal from the microphone 102 and digital-to
`analog (D/A) conversion of a received speech Signal des
`tined for the loudspeaker 104. The user interface 110 further
`includes a digital signal processor (DSP) for performing
`gain/attenuation, filtering, compression/decompression,
`channel coding/decoding and any other desired processing
`(e.g., in accordance with the applicable AMPS/D-AMPS or
`PCS standard) of speech and user or control data. In the
`preferred embodiment, the user interface 110 supplies
`in-phase (I) and quadrature (Q) modulation waveforms to
`the RF Section 120.
`The microprocessor 112 controls the overall operation of
`the mobile station 100 through software programs stored in
`the program memory 114. These programs may include, for
`example, executable instructions for each of the transmit and
`receive operations on the digital control channel (DCCH)
`and the digital traffic channel (DTCH) as specified, for
`example, in the industry standard known as IS-136. The
`RAM 116 holds the values of temporary variables used in
`the execution of these instructions. Parameters whose values
`must be preserved after power is turned off in the mobile
`station 100 may be stored in the EEPROM 118 (or in a
`Similar non-volatile or flash memory). Such parameters may
`include, for example, the mobile identification number
`(MIN), the electronic serial number (ESN) of the mobile
`station 100, and the system identification of the home system
`(SIDH) of the mobile station 100.
`Generally speaking, the RF section 120 includes RF
`processing circuitry (not specifically shown in FIG. 9) Such
`as an RF transmitter for modulating the I and Q data onto an
`analog carrier Signal, upconverting the modulated Signal to
`the Selected channel frequency and then amplifying and
`transmitting the Signal through the antenna 122. The RF
`Section 120 further includes an RF receiver for downcon
`Verting a modulated Signal received through the antenna 122
`into at least one intermediate frequency (IF) signal that may
`be then demodulated before being processed in t