United States Patent 9
`Materoetal.
`
`00000
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,768,691
`Jun. 16, 1998
`
`ANTENNA SWITCHING CIRCUITS FOR
`5,325,075—G/1994 Raped 0... .ensccssseeesecsseeesereee 332/103
`
`[54]
`5,386,203
`1/1995 Ishihara ssssssosssnsssseecsesnessnsses 455/82
`RADIO TELEPHONES
`$,390,168
`2/1995 Virpari
`cesssssssssesuecesnsseneceecen 370/30
`5,471,652 VA/1995 Hulk scesssscrseesesessseeesessnssses 455/76
`
`[75}
`
`Inventors: Jorma Matero. Oulu; Matti L Kangas,
`Oulunsalo, both of Finland
`
`[73]
`
`Assignee: Nokia Mobile Phones Limited. Salo,
`Finland
`
`21)
`
`[22]
`
`[51]
`[52]
`
`[58]
`
`[56]
`
`Appl. No.: 692,496
`
`Filed:
`
`Aug. 7, 1996
`
`Ein, CS oeescsesssssssssssesscsessensssnsesnsseesseeeses HO4B 1/44
`
`WS. CD. eeesnnscteresssnscesnnsess 455/78, 455/84; 333/101;
`370/280
`Field of Search. 0.0.0.0... 333/101, 103-104,
`455/73, 78, 82, 83. 84. 575, 132, 272, 99,
`129, 345; 370/276, 277, 278, 280, 282.
`294
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,955,039
`5,079,520
`5,291,474
`5,301,367
`
`....
`9/1990 Rother et al.
`ae
`ses STSITS
`
`
`1/1992 Rapeli
`......
`~~ 33100 A
`3/1994 komen et al.
`.......csscssccsrneeeees 370/30
`
`4/1994 Heimonen ..........cccosececsssenersees 455/76
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`0305603 Al
`0541305 Al
`0581573 Al
`WO 94/14247
`
`.
`3/1989 European Pat. Off.
`5/1993 European Pat. Off...
`2/1994 European Pat. Off.
`.
`6/1994 WIPO.
`
`Primary Examiner—Nguyen Vo
`Attorney, Agent, or Firm—Perman & Green, LLP
`
`[57]
`
`ABSTRACT
`
`Disclosed are various embodimentsofcircuitry for coupling
`first and second transceivers of a dual band radio telephone
`to integral and external antennas. The circuitry uses imped-
`ance matching lengths of transmission lines and switches
`arranged to provide a minimum insertion loss. Also dis-
`closed is an embodiment for use with a single band radio
`telephone, such as a digital TDMA radio telephone that
`either transmits or receives at any given time. Also disclosed
`is an antenna switching arrangementfor a dual band phone
`that eliminates a requirement for duplexers.
`
`17 Claims, 6 Drawing Sheets
`
`x\7
`P
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`li
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`
`ANT SWITCH 1
`
`ANT SWITCH 2
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`4
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`L2
`VL
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`L3
`
`4
`b-~6
`Lt
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`to
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`EXT. ANTENNA
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`L4
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`BAND |
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`IF
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`Db
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`x 4
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`
`6”
`
`7
`
`4
`
`8
`
`BAND 2
`
`<I
`
`ANT SWITCH
`CONTROL
`LINES
`
`1
`
`SAMSUNG 1025
`
`1
`
`SAMSUNG 1025
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 1 of 6
`
`5,768,691
`
`1
`FIG.
`PRIOR ART
`
`ANTENNA SYSTEM 4
`
`
`RECEIVER FRONT END.
`
`TRANSMTTER POWER AMPLIFIER
`
`BAND ! RECEIVER IF PARTS.
`
`SYNTHESIZER.
`
`MODULATOR
`
`
`RECEIVER FRONT END.
`
`TRANSMTTER POWER AMPLIFIER
`
`BAND 2
`
`
`FIG. 2
`PRIOR ART
`
`TO ANTENNA
`
`RECEIVER FRONT END
`
`
`
`
`TRANSMITTER POWER AMPLIFIER
`
`
`
`FIG. 3
`PRIOR ART
`
`
`
`2
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 2 of6
`
`5,768,691
`
`FIG. 4
`PRIOR ART
`
`-
`n-~
`L
`ANT SWITCH 2
`
`
`
`
`
`la
`
`EXT, ANTENNA
`
`ANT SWITCH
`CONTROL
`LINES
`
`FIG. 5
`
`DUAL BAND
`ANTENNA
`
`SYSTEM
`
`3
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 3 of6
`
`5,768,691
`
`FIG. 6
`
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`p
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`lt
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`oa
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`Xs
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`boon
`L2
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`LLL
`
`ANT SWITCH 1
`
`ANT SWITCH 2
`
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`6
`5 BAND 1
`
`xX
`
`’
`
`9
`
`<I
`
`LSjg zee
`LLL L4
`
`BAND 2
`
`9
`
`Pi
`
`ANT SWITCH
`CONTROL
`LINES
`
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`y
`L4
`VLE
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`—¢4,
`la
`EXT. ANTENNA
`
`FIG. 7
`
`Ly
`WLLL
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`L
`
`L2
`WLLL
`
`L3
`
`WEEE
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`EXT. ANTENNA
`
`.
`
`;
`
`<qf=ANT SWITCH
`INESCe
`
`4
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet4 of6
`
`5,768,691
`
`Ce
`FIG. 8
`PRIOR ART |
`
`7
`
`x1
`EXT. ANTENNA ANT/EXT ANT
`
`FIG. 9
`PRIOR ART
`
`DeRx
`
`CONTROL
`
`FIG. 10\y;----- _
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`3
`
`6
`
`/
`
`8
`
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`
`Tx/Rx
`
`5
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 5 of 6
`
`5,768,691
`
`FIG.
`
`tla
`
`FIG. Ra
`
`
`HTx
`
`FIG.
`
`lib
`
`wN
`
`
`
`
`Tx SLOT
`
`Sw3
`
`HRx
`
`HTx
`
`Sw4
`
`FIG. 12b
`
`
`
`
`Tx SLOT
`
`L2
`
`Sw
`
`HRx
`
`Sw4
`
`HTx
`
`la~O)
`
`Sw3
`
`HRx
`
`Sw4
`
`6
`
`

`

`U.S. Patent
`
`Jun. 16, 1998
`
`Sheet 6 of 6
`
`5,768,691
`
`FIG. 13a
`
`law)
`
`Tx SLOT
`
`FIG. 130
`FIG. 14D
`
`lady
`
`Tx SLOT
`
`lad)
`
`Rx SLOT
`
`FIG. 14a
`
`
`
`
`7
`
`

`

`5,768,691
`
`1
`ANTENNA SWITCHING CIRCUITS FOR
`RADIO TELEPHONES
`
`FIELD OF THE INVENTION
`
`This invention relates generally to methods and apparatus
`for connecting radio frequency (RF) circuits to one or more
`antennasand, in particular, to circuits used in single and dual
`band radio telephones, such as cellular telephones.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`In a dual band mobile phonethe operational bandwidth of
`the antenna presents a difficult problem. By example. such
`a mobile phone may need to be operable in the 800 MHz
`band(e.g., analog AMPS) at one time, and then in the 1.9
`GHz band(e.g., digital PCN) at another time. Preferably, a
`single antenna is used for both bands. However, due to the
`large difference in operational frequencies conventional dual
`band mobile phones typically provide a separate receiver
`front end and a separate transmitter power amplifier section
`for each band.
`FIG.1 illustrates one such conventional construction for
`a dual band mobile phone. A single antenna system 1 is
`connected to a Band 1 receiver front end and transmitter
`power amplifier block 2, and is also connected to a Band 2
`receiver front end and transmitter power amplifier block 3.
`Blocks 2 and 3 are both connected to a common, further
`block 4 that contains the receiver IF circuits, frequency
`synthesizer(s), modulators, demodulators. etc. Not shown in
`FIG. 1 are the remaining portions of the mobile phone, such
`as the keypad, display, user interface controller, etc.
`In some dual band phones, such as a dual band phonethat
`includes a digital TDMA portion, the TDMA transmitter and
`receiver sections are connected to the antenna 1 through a
`duplex filter 5, as is illustrated in FIG. 2. In this case the
`duplex filter 5 is connected to an input of a receiver amplifier
`6, which has an output connected to a bandpass filter 7 and
`a first IF mixer 8. while also being connected to the output
`of a transmitter power amplifier 9.
`In conventional practice the required band switching has
`been accomplished with a mechanical relay or switch 10, as
`is shown in FIG.3. In FIG. 3 the circuitry shown in FIG. 2
`is duplicated for each band, with the Band 2 circuits being
`designated with prime symbols ('). At any given time the
`switch 10 connects either the Band 1 or the Band 2 trans-
`ceiver circuitry to the antenna 1.
`However, this approach has at least two significant dis-
`advantages. First. the use of a mechanical switch has the
`disadvantage of requiring a large and bulky component with
`a slow switching time. To overcome this problem the
`mechanical switch can be replaced with an electronic switch,
`The foregoing and other problems are overcome and the
`such as a FET or a pin diode. However, the use of an
`objects of the invention are realized by antenna switching
`electronic switch is disadvantageous in that it introduces a
`circuitry in accordance with embodiments of this invention.
`significant insertion loss into the RF path. A typical insertion
`loss for an electronic switch is on the order of 0.5 dB. This
`In a first embodiment of this invention there is provided
`insertion loss must be compensated for by using a higher
`antenna switching circuitry for use in a radio telephone of a
`transmitter power which, in turn, increases the power con-
`type that includes a first transceiver operable in a first
`sumption and reduces the battery life of the mobile phone.
`frequency band and a second transceiver operable in a
`Furthermore, if operation in one of the bands is required to
`second frequency band. Theradio telephone further includes
`be a duplex analog mode, the antenna switching circuitry
`a first antenna port and a second antenna port. The antenna
`must exhibit a high degree of linearity to avoid spurious
`switching circuitry includes a first pair of transmission lines
`responses generated by the transmitter signal within the
`(L1 and LA) each having a first node coupled to an input/
`antenna switch 10. Also, the receiver sensitivity is impaired
`output port of the first transceiver. A second node of L1 is
`since the switch insertion loss also degrades the receiver
`switchably coupled to the first antenna port and a second
`noise figure.
`node of L4 is switchably coupled to the second antennaport.
`Theradio telephone further includes a second pair of trans-
`One benefit of the approach shown in FIG. 3 is that it
`mission lines (L2 and L3) each havingafirst node coupled
`provides good isolation between bandfilters (in this case the
`8
`
`2
`duplex filters, or duplexers, 5 and 5"), which thereby enables
`an optimum performance on both bands. However, the high
`insertion loss and required linearity can overshadow the
`benefit of this arrangement, and makeits use undesirable for
`many applications.
`Reference can also be made to FIG. 4 for illustrating a
`conventional approach for implementing antenna switching
`in a dual band mobile phone. when an external antenna
`connector 1a is required. That is, the antenna 1 may be an
`integral or master antenna that is provided as part of the
`mobile phone. while antenna connector 1a is also provided
`to enable the mobile phone to be connected to a second,
`external antenna. In addition to the Band 1 and Band 2
`transceiver circuitry shown in FIG. 3, a second antenna
`switch 11 is connected in series with the band switch 10. and
`suitable antenna switch control lines are provided from a
`controller (not shown) of the mobile phone to control the
`state of the antenna switches 10 and 11. Assuming that the
`second switch 11 is also an electronic switch. it can be
`appreciated that the total insertion loss can be doubled over
`the FIG.3 configuration. This in turn compoundsatleastthe
`power consumption and receiver sensitivity problems that
`were described above with respect to FIG.3.
`FIG.9 illustrates a conventional antenna/external antenna
`switching arrangement for a single band digital (e.g..
`TDMA)mobile phone. Thefirst antenna switch 10 functions
`as a transmit/receive switch for the receiver and transmitter,
`and is coupled to a receive bandpass filter 5a and a transmit
`bandpass filter 5b. The second antenna switch 11 is
`employed for switching between the antenna 1 and the
`external antenna connector la. As in the embodiment of
`FIG. 4, a significant disadvantage of this technique is the
`doubling of the insertion loss due to the twoserially coupled
`antenna switches 10 and 11.
`
`OBJECTS OF THE INVENTION
`
`It is a first object of this invention to provide an improved
`mobile phone that overcomesthe foregoing and other prob-
`lems.
`
`It is a further object of this invention to provide embodi-
`ments of circuitry for coupling both single band and dual
`band mobile phones to two antennas, and that avoids the
`doubling of the insertion loss due to the use of two series-
`connected electronic switches.
`
`It is another object of this invention to provide embodi-
`ments of switching circuitry for coupling a dual band mobile
`phone to two antennas, without requiring a duplexer.
`
`SUMMARYOF THE INVENTION
`
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`to an input/output port of the second transceiver. A second
`port. The first switch further has a second switching state for
`node of L2 is switchably coupled to the first antenna port and
`coupling the outputport of the transmitter to the first antenna
`a second node of L3 is switchably coupled to the second
`port through the second node of L1. In thefirst switching
`antenna port. The switching is accomplished such that when
`state of the first switch the second node of L1 is open-
`the second node of L1 is coupledto thefirst antenna port, the
`circuited, Also included is a second switch that is operated
`second node of both L2 and LA is open circuited and the
`in phase with the first switch, and that has a first switching
`second node of L3 is coupled to the second antenna port.
`state for coupling the output port of the transmitter to the
`When the second node of L2 is coupled to the first antenna
`second antenna port. The second switch further has a second
`port. the second node of both L1 and L3 is open circuited
`switching state for coupling the input port of the receiver to
`and the second node of L4 is coupled to the second antenna
`the second antenna port through the second node of L2. In
`port.
`thefirst switching state of the second switch the second node
`of L2 is open-circuited. In this embodimentthere is only one
`The lengths of the transmission lines are as follows
`switch in series between one of the antenna ports and the
`L1=L4=)/2for the first frequency band; and L2=L3=A/2 for
`input of the receiver or the output of the transmitter. The
`the second frequency band.
`lengths of the transmission lines are as follows: L1=A/2 for
`The first frequency band can include a frequency of about
`the second frequency band (transmit band) and L2=A/2 for
`800 MHz, for example the first transceiver may be used for
`the first frequency band (receive band).
`duplex FM analog signals, and the second frequency band
`Also disclosed is an antenna switching arrangementfor a
`can include a frequency of about 1900 MHz, and may be
`dual band phonethat eliminates a requirementfor duplexers,
`used for TDMA, phase modulated signals.
`while enabling individual ones of four switches to be
`In a further embodiment of this invention a first pair of
`separately optimized for their intended function (transit or
`transmission lines (L1 and L2) each hasafirst node coupled
`receive) and also frequency band.
`to the first antenna port, a second node of L1 is switchably
`coupled to the input/output port ofthe first transceiver, and
`a second node of L2 is switchably coupled to the input/
`output node of the second transceiver. A second pair of
`transmission lines (L3 and L4) each has a first node coupled
`to the second antenna port, a second node of L3 is switch-
`ably coupled to the input/output port of the first transceiver.
`and a second node of L4 is switchably coupled to the
`input/output node of the second transceiver.
`In this
`embodiment, when the second node of L1 is coupled to the
`input/output port of the first transceiver, the second node of
`both L2 and L3 is open circuited and the second node of L4
`is coupled to the input/output port of the second transceiver.
`Whenthe second node of L2 is coupled to the input/output
`port of the second transceiver, the second node of both L1
`and L4 is open circuited and the second node of L3 is
`coupled to the input/output port of the first transceiver.
`For this embodimentthe lengths of the transmission lines
`are as follows: L2=L4=)/2forthe first frequency band, and
`L1=L3=A/2 for the second frequency band. such that the
`transmissionline that is left open-ended has a length of A/2
`for the frequency band in use.
`Further in accordance with this embodiment the second
`node of L1 and the second node of L3 are coupled through
`a first switch to the input/output port ofthefirst transceiver,
`and the second node of L2 and the second node of L4 are
`coupled through a second switch to the input/output port of
`the second transceiver. In this case the first switch is selected
`to minimize an insertion loss for frequencies within the first
`frequency band, and the second switch is selected to mini-
`mize an insertion loss for frequencies within the second
`frequency band.
`In a still further embodiment of this invention there is
`disclosed antenna switching circuitry for use in a radio
`telephone of a type that includes a transmitter operable in a
`first frequency band when transmitting and a receiver oper-
`able in a second frequency band when receiving. The radio
`telephone further includes a first antenna port and a second
`antenna port. In this embodiment the antenna switching
`circuitry includes a pair of transmission lines (1 and L2)
`each having a first node and a second node.A first node of
`L2 is coupled to an input port of the receiver anda first node
`of L1 is coupled to an output port of the transmitter. Also
`included is a first switch having a first switching state for
`coupling the input port of the receiver to the first antenna
`
`The above set forth and other features of the invention are
`made more apparent in the ensuing Detailed Description of
`the Invention when read in conjunction with the attached
`Drawings. wherein:
`FIG. 1 is block diagram that illustrates a portion of a
`conventional dual band mobile phone;
`FIG.2 is a simplified schematic diagram of a conventional
`receiver front end and transmitter power amplifier that are
`coupled to an antenna through a duplexer;
`FIG. 3 is a simplified schematic diagram of a portion of
`a conventional dual band mobile phone that includes two
`receiver front ends,
`transmitter power amplifiers, and
`duplexers that are coupled to an antenna through an antenna
`switch;
`FIG.4 illustrates a conventional arrangementfor coupling
`the circuitry of FIG. 3 to one of two antennas;
`FIG.5 illustrates a first embodimentof this invention that
`eliminates the antenna switch of FIG. 4 through the use of
`a single, dual band antenna with two feed lines;
`FIG.6 illustrates one of the preferred embodiments ofthis
`invention that employs impedance matching lengths of
`transmission line to couple the duplexers to two antenna
`switches;
`FIG.7 illustrates a presently preferred embodimentofthis
`invention that also employs impedance matching lengths of
`transmission line;
`that can be
`FIG. 8 illustrates a conventional circuit
`employed in the embodiment of FIGS. 6 and 7 in place of
`the Band 2 (TDMA) duplexer;
`FIG.9 illustrates a conventional arrangement for coupling
`to one of two antennas in a single band mobile phone;
`FIG. 10 illustrates a preferred embodimentof this inven-
`tion for coupling to one of two antennas in a single band
`mobile phone, and that also employs the impedance match-
`ing lengths of transmission line;
`FIGS.11a and 114 illustrate a switching arrangementfor
`a lower frequency band using the integral antenna for a
`receive slot and a transmit slot. respectively;
`FIGS.12a and 12d illustrate a switching arrangementfor
`the lower frequency band using the external antenna for the
`receive slot and the transmitslot, respectively;
`9
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`45
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`DETAILED DESCRIPTION OF THE
`INVENTION
`
`5
`FIGS. 13a and 13» illustrate a switching arrangement for
`an upper frequency band using the integral antenna for the
`receive slot and the transmit slot, respectively; and
`FIGS. 14a and 14b illustrate a switching arrangementfor
`the upper frequency band using the external antenna for the
`receive slot and the transmit slot, respectively.
`
`6
`L2=L3=A/2 for the frequency of Band 2.
`By example, and assuming that the frequency of Band 1
`is 800 MHzandthat the frequency of Band 2 is 1900 MHz.
`then the length of L1 and LA can be about 95 mm, and the
`length of L2 and L3 can be about 45 mm. In the presently
`preferred embodiment of the invention L1-LA are electri-
`cally conductive traces that are disposed on a printed circuit
`board dielectric substrate. The electrically conductive traces
`can be fabricated as meander lines, and their total lengths
`can be reduced through the use of lumped impedance
`FIG.5 illustrates a first embodimentof this invention that
`elements to achieve the equivalent phase shift. With these
`eliminates the antenna switch of FIG. 3 through the use of
`dimensionsthe open end of the transmission lines reflects a
`a single, dual band antenna 12. In the embodimentof FIG.
`high impedanceat the duplex filter antenna ports P® and P1.
`5 there are two feedlines, preferably each having an imped-
`Asillustrated in FIG. 6, if it is desired to use the Band 1
`ance of 50 ohms. A first feedline 12a connects the Band 1
`circuitry with the antenna 1, or the Band 2 circuitry with the
`(e.g.. 800 MHz analog) duplexer 5 to a first element 12b of
`external antenna connector 1a. the lines L2 and LA are open
`the dual band antenna 12. A second feedline 12c connects
`ended, and the signal path through switches 14 and 16is to
`the Band 2 (e.g.. 1.9 GHz TDMA)duplexer 5' to a second
`the antenna 1 for the Band1 circuitry (through L1) andto the
`element 12d of the dual band antenna 12. The elements 12b
`external antenna connector la for the Band 2 circuitry
`and 12d are each electrically optimized for operation in their
`(through L3). If it is desired instead to use the Band 1
`respective bands, and may be disposed on a common
`circuitry with the external antenna connector 1a, or the Band
`antenna substrate or core and separated by a suitable dielec-
`2 circuitry with the antenna 1, then the antenna switch
`tric material. The antenna elements 12b and 12d are so
`control line is energized to place the moveable contact of
`implemented that the electrical isolation between them is
`both switches 14 and 16 to the lower position. In this case
`sufficiently high to prevent loading between the antenna
`the lines L1 and L3 are open ended, and the signal path
`ports of the dual band RF sections.
`through switches 14 and 16is to the antenna 1 for the Band
`This embodiment eliminates the insertion loss due to the
`2 circuitry (through L2) and to the external antenna con-
`use of bandor antenna switches, and thus also eliminates the
`nector la for the Band 1 circuitry (through L4).
`need to compensate for the insertion loss with a higher
`FIG.7 illustrates a presently preferred embodimentofthis
`transmitter power. Furthermore, since antenna band switch-
`invention that also employs the impedance matching lengths
`ing is accomplished without mechanical or electrical delays.
`of transmission line (L1-LA). However,
`in FIG. 7 the
`it is well suited for use in applications where fast hand-offs
`switches 14 and 16 are moved so as to be located between
`between bands are required. Also, no antenna switching
`the lengths of transmission line and the duplexers 5 and 5’.
`control signals need to be generated or routed. no additional
`In addition, and as is shown, the switches 14 and 16 are
`printed circuit board area is required to implement the
`operated out of phase.
`The lengths of the transmission lines L1-L4 between the
`antenna band switching function, and no spurious responses
`antenna ports and the switches in the embodimentof FIG. 7
`are generated. since there are no nonlinear components
`are as follows:
`involved. Also, the high degree of isolation between elec-
`trical antennas that can be achieved makes possible the use
`L2=L4=)/2 for the frequency of Band 1; and
`of conventional duplex or band filters in the antennacircuits
`L1=L3=)/2 for the frequency of Band 2.
`on both bands. Also, the receiver sensitivity is improved
`Asillustrated in FIG.7,if it is desired to use the Band 1
`since the absence of the switch insertion loss does not
`circuitry with the antenna 1, or the Band2 circuitry with the
`degrade the receiver noise figure.
`external antenna connector 1a, the lines L2 and L3 are open
`FIG.6illustrates one of the presently preferred embodi-
`ended, andthe signal path through switches 14 and 16is to
`45
`ments ofthis invention that employs lengths of transmission
`the antenna 1 for the Band1 circuitry (through L1) andto the
`line (L1-L4)to couple the duplexers 5 and 5' to two antenna
`external antenna connector la for the Band 2 circuitry
`switches 14 and 16. The embodiment of FIG. 6 thus over-
`(through L4). If it is desired instead to use the Band 1
`comes the problems associated with the conventional
`circuitry with the external antenna connector 1a. or the Band
`approach shown in FIG. 4 for connecting to two different
`2 circuitry with the antenna 1, then the antenna switch
`antennas. such as the integral antenna 1 and the external
`control line is energized to place the moveable contact of
`antenna connector 1a. Although the embodiment of FIG. 6
`switch 14 to the lower position and the moveable contact of
`employsthe twoelectronic switches 14 and 16 (or mechani-
`switch 16 to the upper position. In this case the lines L1 and
`cal switchesif so desired), there is only one switch in the RF
`L4 are open ended, and the signal path through switches 14
`signal path. As such, the insertion loss is not doubled as in
`and 16is to the antenna 1 for the Band 2 circuitry (through
`the case of FIG. 4. The antenna 1 and the external antenna
`L2) andto the external antenna connector 1a for the Band 1
`that is connected to the antenna connector 1a are assumed to
`circuitry (through L3).
`be two-band antennas each having a single feedline. An
`It should be noted that, in the embodiment of FIG.7, the
`external booster amplifier can also be coupled to the external
`switch 14 is only required to carry the frequency of the Band
`antenna connector la if so desired.
`1 signal, while the switch 16 is only required to carry the
`frequency of the Band 2 signal. For the example where the
`Whenthe antenna1 is in use the unused bandcircuitry is
`Band 1 frequency is about 800 MHz and the Band 2
`always coupled to the external antenna connector la. If
`frequency is about 1900 MHz,it can be appreciated that the
`external antenna connector 1a is in use, then the unused
`switches 14 and 16 can be separately optimized for their
`bandcircuitry is always coupled to antenna 1. Preferably, the
`respective frequency bands. That is. a single switch thatis
`antenna impedance for both bands is 50 ohms. The lengths
`selected for a minimum insertion loss at 800 MHz may
`of the transmission lines L1-L4 from the duplexfilters 5 and
`exhibit a higher loss at 1900 MHz. The embodiment of FIG.
`5' to the antenna switches 14 and 16 are as follows:
`7 avoids this potential problem by enabling both switchesto
`L1=L4=)/2 for the frequency of Band 1; and
`10
`
`55
`
`65
`
`10
`
`

`

`5,768,691
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`7
`be separately specified for their respective frequency bands.
`As such, for many applications the embodiment of FIG. 7
`may be preferred over the embodiment of FIG. 6.
`The presently preferred embodimentofthis is not limited
`for use only with a FM/TDMA phase modulated (AMPS/
`TDMA) dual band mobile phone. but can be used as well
`with, by example, an AMPS/CDMA mobile phone, as well
`as with an AMPS/NAMPS/CDMAmobile phone.
`Furthermore. and referring to FIG. 10, the teachingofthis
`invention applies as well to single band mobile phones, such
`as digital (e.g.. TDMA) mobile phonesthat transmit at one
`time in one band of frequencies and that receive at another
`time in another band of frequencies. In FIG. 10 only one
`control signal is employed as compared to the embodiment
`of FIG.9, and the lengthsof transmission line L1 and L2 are
`connected as shown. When operating with the integral
`antenna 1 the antenna switches 10 and 11 are operated in
`phase to couple the integral antenna 1 to the receiver 6
`through switch 10 when receiving (the illustrated position)
`and to couple the integral antenna 1 to the transmitter 9,
`through switch 10 and L1, when transmitting. The unused
`transmitter is coupled to the external antenna coupler la
`through switch 11 when receiving, and the unused receiver
`is coupled to the external antenna coupler la through switch
`11 and L2 when transmitting. When operating with the
`external antenna the polarity of the control signal
`is
`reversed, the receiver or transmitter in use is coupled to the
`external antenna coupler la, and the unused receiver or
`transmitter is coupledto the integral antenna 1. In either case
`there is only one electronic switch in the receive or transmit
`path to the active antenna, andthusthe insertion loss is about
`one half of the insertion loss of the embodiment of FIG. 9.
`Thelengths of the transmission lines L1 and L2 from the
`filters 5a and Sb in the embodiment of FIG. 10 are as
`follows:
`L1=1/2 for the transmit band of frequencies; and
`L2=)/2 for the receive band of frequencies.
`Asisillustrated in FIG. 8 for the case where, by example,
`the Band 2 is a TDMA band,the duplexer 5' can be replaced
`with a TR switch 18, a receivefilter 20, and a transmitfilter
`22. The TR switch 18 is controlled with a TX/RX signal for
`setting the switch to either couple the receiver front end or
`the transmitter power amplifier output to the node PI. Such
`an arrangementis known in the prior art, and can be used to
`replace a conventional duplex filter in a TDMA mobile
`phone. Since thefiltering requirements for the TX and RX
`bandfilters in TDMA mobile phones are not as stringent as
`in the case analog mode mobile phones, it is possible to
`achieve an adequate level of performance with this arrange-
`ment. This circuit can replace the duplex filter 5° in FIGS.3,
`4.5, 6 and 7. If Band 1 is also a TDMA-only band.then the
`duplex filter 5 in the above mentioned Figures can also be
`replaced with this circuit.
`Reference is now made to FIGS. Ia. 11b, 12a, 12b, 13a.
`13b, 14a and 14b for illustrating, in accordance with a
`further embodiment of this invention. preferred antenna
`switching circuitry for a dual band TDMA-based digital
`cellular phone. It should be noted that the same concepts
`may be used also in a single band mobile phones, although
`the advantages are not as great.
`In FIGS, 11-14 the following nomenclature is used:
`LRx=lower band receiver; LTx=lower band transmitter;
`=upper band receiver; and HT'x=upper band transmitter.
`In accordance with this aspect of the invention there are
`four (in a single-band phone two) solid state RF switches.
`The switches are connected so that there is only one switch
`between the selected antenna and the transmitter or receiver.
`
`35
`
`65
`
`10
`
`15
`
`25
`
`30
`
`35
`
`45
`
`30
`
`8
`This embodimentof the invention eliminates the use of the
`duplex filters, and therefore the insertion loss is very low.
`Reducing the insertion loss can provide an increase in the
`total talk time of the mobile phone before the battery is
`required to be recharged.
`The switches are controlled synchronously so that only
`the receiver is connected to a selected antenna during the RX
`timeslot and only the transmitter is connected to the selected
`antenna during the TX timeslot. All the other circuits are
`disconnected from the antenna when not being used (idle).
`The open switches are matchedso that they are seen as a
`high impedance from the active signal path. This can be
`accomplished using. by example, transmission lines (e.g..
`microstrips) having a length of n*A/2 (A=wavelength in that
`line) between the circuits (see FIGS. lla and 115). The
`transmission line can be eliminated if the distance between
`switches is very short, ¢.g.. if they are integrated into the
`same integrated circuit package. In this case the switches
`could share some IC pins.
`This embodiment of the invention is particularly useful
`for systems where the frequency of the higher band is a
`multiple of the frequency of the lower band, e.g. GSM (900
`Mhz) and PCN (1800 MHz). By example, the PCN fre-
`quency band is approximately two times that of the GSM
`frequency band. so transmission lines having lengths of
`L=2*X/2 for PCN and L=1*A/2 for GSM can be used.
`In that only a transmitted or a received signal goes
`through any one switch, the switches may be optimized for
`best performance. By example, the transmission switches
`can be selected for high power operation, while the reception
`switches can be selected for low noise and small size.
`Furthermore.
`the insertion loss and bandwidth of the
`switches can be minimized since both the high and low
`bands have their own associated non-shared switches.
`FIGS. 11-14illustrate all possible switch positions for
`both bands when either receiving or transmitting with either
`the mobile phone’s own (integral) antenna or the external
`antenna. In FIGS. Ha and 11it has been assumedthatthe
`switches are spaced apart by a distance that requires the use
`of the above-mentioned transmission lines (designated as
`L1-L8)for each switch. In FIGS. 12-14it is been assumed
`that the lower band switches are very near to each other, and
`that the high band switches are also near each other. In this
`case the transmission lines L1 and L2 are located only
`between the low and high band switches. There may be two
`separate antennas or one combined dual band antennain the
`mobile phone.
`The switching arrangements shown in FIGS. 11-14 insure
`that the mobile phone’s integral antenna is switched off to
`reduce loss and unwantedradiation when using the external
`antenna (such as when using the antenna of a vehicle).
`Furthermore, during reception the transmitter is discon-
`nected from the antenna to reduce insertion loss, while
`during transmission the receiver is disconnected from the
`antenna to reduce the insertion loss and to provide for a
`simpler inputfiltering arrangement. In addition, it should be
`noted that the embodiments of FIGS. 11-14 eliminate the
`need for a conventional duplexfilter while also eliminating
`any serially coupled switches and the inherent higher inser-
`tion loss. This embodimentof the invention thus provides a
`low insertion loss and less complex antenna coupling
`arrangementfor a digital dual band phone. As wasindicated
`above. and as in several of the other embodiments of this
`invention,the individual switc