Patent Publication Number: US-2004047306-A1

Title: Communication terminal adaptable for different communication methods, and antenna duplexer and power amplifier usable in the communication terminal

Description:
BACKGROUND OF THE INVENTION  
       [0001] The invention relates to a communication terminal which is adaptable to at least one communication method in a frequency band of 1 GHz or lower and is adaptable to at least two communication methods in a frequency band over 1 GHz.  
       [0002] The invention further relates to a communication terminal which can perform a handover (communication methods are switched without interruption) between a frequency band of 1 GHz or lower and a frequency band over 1 GHz.  
       [0003] There is a TDMA (Time-Division Multiple Access) as one of accessing methods of cellular phones which are the mainstream at present. The PDC standard (RCRSTD-27 specified by Association of Radio Industries and Businesses (ARIB)) of Japan and the GSM standard (TS100-910 specified by the ETSI, or the like) of various foreign countries such as European countries in the main use the TDMA as an accessing method. In those standards, transmission and reception are time-divisionally executed and the transmission and the reception are executed at different time.  
       [0004] There is a CDMA (Code-Division Multiple Access) as an accessing method which has been spread in U.S.A., Korea, and Japan in recent years. As typical standards, there are TIA IS-95 of U.S.A. and ARIB STDT-53 of Japan and, according to those standards, the transmission and the reception are simultaneously executed.  
       [0005] As literatures showing constructional examples of the foregoing communication terminal which uses both of the TDMA in which transmission timing and reception timing are different and the CDMA in which the transmission and the reception are simultaneously executed, JP-A-2000-156651, JP-A-10-107678, and JP-A10-84299 can be mentioned. According to them, since different communication methods are switched by using a radio frequency switch, interruption of communication occurs when the communication methods are switched.  
       [0006] Services of cellular phones in a frequency range from a 800 MHz band to a 900 MHz band and cellular phones (PHS in Japan) of a 1.8 GHz band or a 1.9 GHz band are provided in respective countries. The expression 800 MHz band, 900 MHz band, 1.8 GHz band, or 1.9 GHz band is used in order to easily express a band including a certain frequency by representing it by the frequency included in such a band or a just frequency near such a band. Usually, such a band lies within a range of ±10% of the representative frequency. For example, the 900 MHz band generally denotes a frequency range of 810 MHz to 990 MHz. In Europe and the like, a dual band terminal which can be connected to the communication services of two of the foregoing different frequency bands, for example, a terminal which is adaptable to the 900 MHz band and the 1.8 GHz band in the GSM is the mainstream.  
       [0007] According to the conventional techniques, a technique for realizing the handover between the TDMA dual band terminal and the CDMA which is used in a communication method of cellular phones of the third generation is not disclosed.  
       SUMMARY OF THE INVENTION  
       [0008] It is an object of the invention to provide a communication terminal which is adaptable to at least one communication method in a frequency band of 1 GHz or lower and is adaptable to at least two communication methods in a frequency band over 1 GHz.  
       [0009] Another object of the invention is provide a construction which can realize a communication terminal which is adaptable to a communication method like a CDMA in which the transmission and the reception are simultaneously executed and a communication method like a TDMA in which the transmission and the reception are executed at different time, thereby enabling a handover between both of those methods. In the invention, in the case where the communication method differs depending on an area, a function for switching the communication methods without interrupting the communication when the user is moved to the area of the different method is defined as “handover” between both methods.  
       [0010] To accomplish the above objects, according to the invention, there is provided a communication terminal which is adaptable to at least two communication methods, wherein communication by a first method can be made in a first frequency band and communication by a second method or a third method can be selected at a frequency band higher than the first frequency band.  
       [0011] According to the invention, there is provided a communication terminal which is adaptable to at least two communication methods, wherein communication by a first method can be made in a frequency band of 1 GHz or lower and communication by a second method or a third method can be selected at a frequency band over 1 GHz.  
       [0012] According to a preferred embodiment, the second method and the third method are different methods and the first method is the same as either the second method or the third method.  
       [0013] According to another preferred embodiment, the second method and the third method are different methods and the first method is different from both of the second method and the third method.  
       [0014] According to further another preferred embodiment, the second method is the TDMA and the third method is the CDMA.  
       [0015] According to the invention, a communication terminal which is adaptable to three communication methods can be obtained, and a communication terminal in which even if the user is moved to an area where a frequency and a communication method are different, a connecting destination can be switched without interrupting communication, and excellent use convenience is obtained can be obtained.  
       [0016] Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0017]FIG. 1 is a constructional diagram showing the first embodiment of the invention;  
     [0018]FIG. 2 is a constructional diagram showing the second embodiment of the invention;  
     [0019]FIG. 3 is a constructional diagram showing the third embodiment of the invention;  
     [0020]FIG. 4 is a constructional diagram showing the fourth embodiment of the invention;  
     [0021]FIG. 5 is a flowchart showing an example of a setting flow of an antenna duplexer which is executed by a controller in the first embodiment;  
     [0022]FIG. 6 is a flowchart showing an example of a setting flow of a power amplifier which is executed by the controller in the first embodiment;  
     [0023]FIG. 7 is a flowchart showing an example of a setting flow of the antenna duplexer which is executed by the controller in the first embodiment;  
     [0024]FIG. 8 is a flowchart showing an example of a setting flow of an antenna duplexer which is executed by a controller in the second embodiment; and  
     [0025]FIG. 9 is a flowchart showing an example of a setting flow of the antenna duplexer which is executed by the controller in the second embodiment. 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
     [0026] Embodiments of the invention will be described in detail hereinbelow with reference to FIGS.  1  to  9 . An explanation will now be made with respect to examples on the assumption that the TDMA method of the 900 MHz band is used as a first communication method, the TDMA method of the 1800 MHz band is used as a second communication method, and the CDMA method of the 2 GHz band is used as a third communication method, respectively.  
     [0027] The first embodiment of the invention will be described with reference to FIGS. 1, 5,  6 , and  7 .  
     [0028]FIG. 1 is a system constructional diagram of a TDMA/CDMA duplex communication terminal showing the first embodiment of the invention. The terminal is mainly constructed by: an antenna duplexer  2 ; a modulator/demodulator  4  having a modulator and a demodulator of the TDMA and a modulator and a demodulator of the CDMA; a power amplifier  3  for amplifying an output of the modulator in the modulator/demodulator  4  and supplying it to the antenna duplexer  2 ; a signal processor  5  connected to the modulator/demodulator  4 ; and a controller  6  for controlling the antenna duplexer  2 , modulator/demodulator  4 , power amplifier  3 , and signal processor  5 . An operation unit  92  for executing various inputting operations and a display unit  91  for displaying information inputted from the operation unit, received information, information necessary for the operation, or the like are further connected to the controller  6 . A speaker  93  serving as a receiver and a microphone (hereinafter, abbreviated to “mic”)  94  serving as a transmitter are connected to the signal processor  5 . A signal received by an antenna  1  is supplied to each of the TDMA demodulator and the CDMA demodulator in the modulator/demodulator  4  via the antenna duplexer  2 . Outputs of the TDMA modulator and the CDMA modulator in the modulator/demodulator  4  are supplied to the antenna duplexer  2  via the power amplifier  3 , respectively. An internal construction of each unit will be described hereinbelow.  
     [0029] As shown in FIG. 1, the antenna duplexer  2  has a low-pass filter  29  and a high-pass filter  23  which are connected to the antenna  1 . The low-pass filter  29  is selectively connected to a band-pass filter  21  and a low-pass filter  24  via a change-over switch  22 . The high-pass filter  23  is selectively connected to band-pass filters  27  and  28  and a low-pass filter  25  via a change-over switch  26 . The band-pass filter  27  operates as a duplexer for CDMA. The low-pass filter  29  sets a band (900 MHz band) including a first frequency (low frequency) to a pass band. The high-pass filter  23  sets a band (from a 1800 MHz band to a 2 GHz band) including a second frequency (high frequency) to a pass band. One of signal terminals of the low-pass filter  29  and one of signal terminals of the high-pass filter  23  are constructed as a common terminal and connected to the antenna  1 . The other signal terminal of the low-pass filter  29  is connected to the first radio frequency switch  22  as a change-over switch. The other signal terminal of the high-pass filter  23  is connected to the second radio frequency switch  26  as a change-over switch. One of switching destinations of the first radio frequency switch  22  is connected to a first TDMA demodulator  41  provided in the modulator/demodulator  4  via the band-pass filter  21 , and the other is connected to an output terminal of a first frequency band provided for the power amplifier  3  via the low-pass filter  24 . The first radio frequency switch  22  can switch a signal of the first frequency band in accordance with transmission and reception timings of the TDMA. By the above construction, transmission and reception signal paths of the TDMA in the first frequency band can be properly switched and the signal can be transmitted and received to/from the modulator/demodulator  4 .  
     [0030] The second radio frequency switch  26  has three switching destinations. The first one is connected via the band-pass filter  28  to a second TDMA demodulator  46  provided in the modulator/demodulator  4 . The second one is connected via the low-pass filter  25  to an output terminal of the second frequency band provided for the power amplifier  3 . The third one is connected to a duplexer  27  for CDMA. The duplexer  27  for CDMA is connected to a CDMA demodulator  45  provided in the modulator/demodulator  4  and connected via the power amplifier  3  to a CDMA modulator  44  provided in the modulator/demodulator  4 . The second radio frequency switch  26  can switch the signal of the second frequency band in accordance with the timings for transmission and reception of the TDMA and can switch a connecting destination to the connection to the duplexer  27  for CDMA. By the above construction, transmission and reception signal paths of the TDMA and CDMA in the second frequency band can be properly switched and the signal can be transmitted and received to/from the modulator/demodulator  4 .  
     [0031] The power amplifier  3  has a signal path for amplifying the first frequency band and a signal path for amplifying the second frequency band. The signal path for amplifying the first frequency band is a path between a first TDMA modulator  42  in the modulator/demodulator  4  and the low-pass filter  24  in the antenna duplexer  2 . An output of the first TDMA modulator  42  is supplied to the antenna  1  by a radio frequency amplifier  31  via the first radio frequency switch  22  and the low-pass filter  29 .  
     [0032] The signal path for amplifying the second frequency band is a signal path between a second TDMA modulator  43  or the CDMA modulator  44  provided in the modulator/demodulator  4  and the low-pass filter  25  or the duplexer  27  for CDMA in the antenna duplexer  2 . Radio frequency switches  32  and  34  for switching the paths of the input and output signals are provided at the front stage (on the side of the modulator/demodulator  4 ) and the post stage (on the side of the antenna duplexer  2 ) of a radio frequency amplifier  33  provided in the above signal path, respectively. The radio frequency switch  32  at the front stage of the radio frequency amplifier  33  is selectively connected to the second TDMA modulator  43  at the time of the TDMA signal process and connected to the CDMA modulator  44  at the time of the CDMA signal process. The radio frequency switch  34  at the post stage of the radio frequency amplifier  33  is selectively connected to the low-pass filter  25  at the time of the TDMA signal process and connected to a transmission input of the duplexer  27  for CDMA at the time of the CDMA signal process. By the above construction, the amplification of the transmission signal of the second frequency band, that is, in the frequency range from the 1800 MHz band to the 2 GHz band can be executed by one radio frequency amplifier  33 , and the circuit can be simplified.  
     [0033] The modulator/demodulator  4  has: the CDMA modulator  44 ; CDMA demodulator  45 ; first TDMA demodulator  41 ; first TDMA modulator  42 ; second TDMA modulator  43 ; and second TDMA demodulator  46 . Each of the CDMA modulator  44 , the first TDMA modulator  42 , and the second TDMA modulator  43  modulates the output of the signal processor  5  in accordance with each method and outputs a transmission signal to the antenna duplexer  2  via the power amplifier  3  for amplifying it so that the signal is transmitted as a radio wave. Since the power amplifier amplifies an input of about 1 mW to an output of about 200 mW and handles a large electric power, a heat generation amount is large. Further, since the power amplifier includes the change-over switches  32  and  34 , it is provided as an independent block. Each of the CDMA demodulator  45 , the first TDMA demodulator  41 , and the second TDMA demodulator  46  demodulates the output of the antenna duplexer  2  in accordance with each method and outputs the demodulated signal to the signal processor  5 . Since it is unnecessary to amplify the output of the antenna duplexer  2  into a large electric power, in the embodiment, this output is supplied to the CDMA demodulator  45 , first TDMA demodulator  41 , and second TDMA demodulator  46  without passing through the power amplifier. If it is necessary to amplify the signal, an amplifying circuit is provided in the CDMA demodulator  45 , first TDMA demodulator  41 , and second TDMA demodulator  46 .  
     [0034] The signal processor  5  has a function for forming modulation data and outputting it to the demodulator provided in the modulator/demodulator  4  and executes a process for converting an output signal from the modulator provided in the modulator/demodulator  4  into data, or the like.  
     [0035] The controller  6  has a central processing unit (CPU) and discriminates a communication frequency band, the communication method of either the TDMA or the CDMA, and whether the communication is the reception or the transmission of the TDMA in accordance with a preinstalled program. In an interlocking relational manner with those conditions, the controller  6  controls the switching operations of the radio frequency switches provided in the antenna duplexer  2  and power amplifier  3 . The switching control will be described with reference to FIGS. 5 and 6.  
     [0036] Upon switching of the switches in the antenna duplexer  2 , as shown in FIG. 5, the CPU discriminates whether the communication method is the TDMA or not (step T 1 ). If it is not the TDMA, the radio frequency switch  26  is connected to the duplexer  27  side (step T 2 ), thereby allowing the signal to be transferred to the CDMA demodulator  45 . In case of the TDMA, whether the frequency lies in the 900 MHz band or not is discriminated (step T 3 ). If it is not the 900 MHz band, whether the communication mode is a transmission mode or not is discriminated (step T 4 ). If it is not the transmission mode, the radio frequency switch  26  is connected to the TDMA demodulator  46  side (step T 5 ). If it is the transmission mode in step T 4 , the radio frequency switch  26  is connected to the TDMA modulator  43  side (step T 6 ). If it is determined in step T 3  that the frequency lies in the 900 MHz band, whether the communication mode is a transmission mode or not is discriminated in step T 7 . If it is not the transmission mode, the radio frequency switch  22  is connected to the TDMA demodulator  41  side (step T 8 ). On the other hand, if it is the transmission mode in step T 7 , the radio frequency switch  22  is connected to the TDMA modulator  42  side (step T 9 ).  
     [0037] Upon switching of the radio frequency switches provided in the power amplifier  3 , the CPU discriminates whether the communication method is the TDMA or not as shown in FIG. 6 (step T 1 ). If it is not the TDMA, the radio frequency switch  32  is connected to the CDMA modulator  44  side and the radio frequency switch  34  is connected to the duplexer  27  side in step T 30 . Thus, the signal from the CDMA modulator  44  is amplified by the amplifier  33  and supplied to the duplexer  27 . In case of the TDMA, the radio frequency switch  32  is connected to the TDMA modulator  43  side and the radio frequency switch  34  is connected to the radio frequency switch  26  side in step T 31 . Thus, the signal from the TDMA modulator  43  is amplified by the amplifier  33  and supplied to the radio frequency switch  26 .  
     [0038] Subsequently, the switching operation shown in FIG. 7 will be descried. That is, the CPU discriminates whether the method is the TDMA or not (step T 1 ). If it is not the TDMA, the radio frequency switch  26  is connected to the duplexer  27  side (step T 2 ), thereby allowing the signal to be transferred to the CDMA demodulator  45 . On the other hand, in case of the TDMA, whether the communication mode is the transmission mode or not is discriminated (step T 10 ). If it is not the transmission mode, the radio frequency switch  26  is connected to the TDMA demodulator  46  side and the radio frequency switch  22  is connected to the TDMA demodulator  41  side (step T 11 ). In case of the transmission mode in step T 10 , the radio frequency switch  26  is connected to the TDMA modulator  43  side via the low-pass filter  25  and the radio frequency switch  22  is connected to the TDMA modulator  42  side (step T 12 ). Thus, the switching between the TDMA of the low frequency (first frequency band) and the TDMA of the high frequency (second frequency band) can be performed.  
     [0039] In the above embodiment, the antenna duplexer  2  and power amplifier  3  can be constructed as a module comprising a radio frequency board, chip parts, and the like. The power amplifier  3  is not limited to the module but can be also constructed by a semiconductor monolithic. The modulator/demodulator  4  can be also constructed by a semiconductor monolithic. In the embodiment, the signal processor  5  is constructed by a DSP (Digital Signal Processor), thereby raising a processing speed, and the controller  6  is constructed by a CPU.  
     [0040] According to the embodiment, the low-pass filter  29  which sets the first frequency band (900 MHz band) to a pass band and the high-pass filter  23  which sets the second frequency band (from the 1800 MHz band to the 2 GHz band) to a pass band are provided in the antenna connecting portion of the antenna duplexer  2  and the frequency is separated. Therefore, the communication of the first frequency band and the communication of the second frequency band can be simultaneously made, and the handover between both communication methods of the CDMA of the second frequency band and the TDMA of the first frequency band can be realized.  
     [0041] In the embodiment, since the first frequency band (900 MHz band) and the second frequency band (from the 1800 MHz band to the 2 GHz band) are frequency-separated by the duplexer, the simultaneous communication can be performed.  
     [0042] The second embodiment of the invention will now be described with reference to FIGS. 2, 8, and  9 . FIG. 2 is a diagram showing a system construction of a TDMA/CDMA duplex communication terminal in the second embodiment. In the embodiment, although a construction of the antenna duplexer  2  differs from that in the first embodiment, other hardware constructions are similar to those in the first embodiment. A difference between the constructions of the antenna duplexers  2  will be described hereinbelow.  
     [0043] According to the antenna duplexer  2  in the second embodiment, a third radio frequency switch  72  for switching paths of the TDMA signal and the CDMA signal is provided in the antenna connecting portion. The low-pass filter  29  which sets the first frequency band to the pass band and the high-pass filter  23  which sets the second frequency band to the pass band are connected to a TDMA signal path which is switched by the third radio frequency switch  72 . The duplexer  27  for CDMA is connected to a CDMA signal path which is switched by the third radio frequency switch  72 .  
     [0044] The other signal terminal of the low-pass filter  29  is connected to the first radio frequency switch  22  which can switch the signal of the first frequency band in accordance with the transmission and reception timings of the TDMA. One of switching destinations of the first radio frequency switch  22  is connected to the first TDMA demodulator  41  provided in the modulator/demodulator  4  via the band-pass filter  21 , and the other is connected to the output terminal of the first frequency band provided for the power amplifier  3  via the low-pass filter  24 . By the above construction, the transmission and reception signal paths of the TDMA in the first frequency band can be properly switched and the signal can be transmitted and received to/from the modulator/demodulator  4 .  
     [0045] The other signal terminal of the high-pass filter  23  is connected to a fourth radio frequency switch  71  which can switch the signal of the second frequency band in accordance with the transmission and reception timings of the TDMA. One of switching destinations of the fourth radio frequency switch  71  is connected to the second TDMA demodulator  46  provided in the modulator/demodulator  4  via the band-pass filter  28 , and the other is connected to the output terminal of the second frequency band provided for the power amplifier  3  via the low-pass filter  25 . By the above construction, the transmission and reception signal paths of the TDMA in the second frequency band can be properly switched and the signal can be transmitted and received to/from the modulator/demodulator  4 .  
     [0046] The controller  6  controls the switching operations of the radio frequency switches provided in the antenna duplexer  2  and power amplifier  3  in an interlocking relational manner with the conditions such as communication frequency band, communication method of TDMA or CDMA, reception or transmission of the TDMA, and the like. The switching operations of the radio frequency switches  32  and  34  provided in the power amplifier  3  are shown in FIG. 6 in a manner similar to those in the first embodiment.  
     [0047] A switching control will be described with reference to FIGS. 8 and 9. The CPU discriminates whether the communication method is the TDMA or not (step T 1 ). If it is not the TDMA, the radio frequency switch  72  is connected to the duplexer  27  side (step T 13 ), thereby allowing the signal to be transferred to the CDMA demodulator  45 . If it is the TDMA, the radio frequency switch  72  is connected to the sides of the filters  23  and  29  (step T 14 ). Subsequently, whether the frequency lies within the 900 MHz band or not is discriminated (step T 15 ). If it is not the 900 MHz band, whether the communication mode is the transmission mode or not is discriminated (step T 16 ). If it is not the transmission mode, the radio frequency switch  71  is connected to the TDMA demodulator  46  side (step T 17 ). If the communication mode is the transmission mode in step T 16 , the radio frequency switch  71  is connected to the TDMA modulator  43  side (step T 18 ). If it is determined in step T 15  that the frequency lies within the 900 MHz band, whether the communication mode is the transmission mode or not is discriminated in step T 19 . If it is not the transmission mode, the radio frequency switch  22  is connected to the TDMA demodulator  41  side (step T 20 ). If the communication mode is the transmission mode in step T 19 , the radio frequency switch  22  is connected to the TDMA modulator  42  side (step T 21 ).  
     [0048] Subsequently, the switching operation shown in FIG. 9 will be described. That is, the CPU discriminates whether the communication method is the TDMA or not (step T 1 ). If it is not the TDMA, the radio frequency switch  72  is connected to the duplexer  27  side (step T 13 ), thereby allowing the signal to be transferred to the CDMA demodulator  45 . If it is the TDMA, the radio frequency switch  72  is connected to the sides of the filters  23  and  29  (step T 14 ). Subsequently, whether the communication mode is the transmission mode or not is discriminated (step T 22 ). If it is not the transmission mode, the radio frequency switch  71  is connected to the TDMA demodulator  46  side and the radio frequency switch  22  is connected to the TDMA demodulator  41  side (step T 23 ). If the communication mode is the transmission mode in step T 22 , the radio frequency switch  71  is connected to the TDMA modulator  43  side and the radio frequency switch  22  is connected to the TDMA modulator  42  side (step T 24 ). Thus, the switching operation can be performed between the TDMA of the low frequency and the TDMA of the high frequency.  
     [0049] According to the embodiment, the third radio frequency switch  72  for switching the paths of the TDMA signal and the CDMA signal is provided in the antenna connecting portion of the antenna duplexer  2  and the terminal which can automatically or manually switch the CDMA and the TDMA and use them can be realized. The manual switching is performed by inputting the desired method from the operation unit  92 . For example, a dedicated switch can be also provided as an operation unit for the operation unit  92  (such a switch can be also allocated to the existing key on software). It is also possible to display a selection picture plane onto the display unit  91  and select and decide the desired method by a key input.  
     [0050] The third embodiment of the invention will be described with reference to FIG. 3. FIG. 3 is a diagram showing a system construction of a TDMA/CDMA duplex communication terminal in the embodiment. According to the third embodiment, although a construction of the antenna duplexer  2 , power amplifier  3 , and modulator/demodulator  4  differs from that of the first embodiment, other hardware constructions are similar to those of the first embodiment. A difference of the constructions of the antenna duplexer  2 , power amplifier  3 , and modulator/demodulator  4  between the first and third embodiments will be described hereinbelow.  
     [0051] According to the third embodiment, the radio frequency switch  34  for switching the transmission signal of the second frequency band which has been provided in the power amplifier  3  in the first embodiment is provided in the antenna duplexer and the radio frequency switch  32  for switching the transmission signal of the second frequency band is provided in the modulator/demodulator  4 . According to this construction, there is a feature such that the construction of the power amplifier  3  can be simplified.  
     [0052] According to the third embodiment, the low-pass filter  29  which sets the first frequency band (900 MHz band) to the pass band and the high-pass filter  23  which sets the second frequency band (from the 1800 MHz band to the 2 GHz band) to the pass band are provided in the antenna connecting portion of the antenna duplexer  2  and the frequency is separated. Therefore, the communication of the first frequency band and the communication of the second frequency band can be simultaneously made and a handover between both communication methods of the CDMA and TDMA can be realized.  
     [0053] The fourth embodiment of the invention will be described with reference to FIG. 4. FIG. 4 is a diagram showing a system construction of a TDMA/CDMA duplex communication terminal in the embodiment. According to the fourth embodiment, although a construction of the antenna duplexer  2  and power amplifier  3  differs from that of the second embodiment, other hardware constructions are similar to those of the second embodiment. A difference of the constructions of the antenna duplexer  2  and power amplifier  3  between the second and fourth embodiments will be described hereinbelow.  
     [0054] According to the fourth embodiment, the radio frequency switch  34  for switching the transmission signal of the second frequency band which has been provided in the power amplifier  3  in the second embodiment is provided in the antenna duplexer. The fourth embodiment is characterized in that in the power amplifier  3 , there is no need to provide a switch for an output unit where a large electric power passes but a switch is provided only for an input unit of a relatively small electric power, so that an internal circuit construction can be simplified.  
     [0055] According to the fourth embodiment, the third radio frequency switch  72  for switching the paths of the TDMA signal and the CDMA signal is provided in the antenna connecting portion of the antenna duplexer  2 , and the terminal which can automatically or manually switch the CDMA and the TDMA and use them can be realized in a manner similar to the second embodiment.  
     [0056] For example, the TDMA in the foregoing embodiments is used in the cellular phones according to each system such as PDC (RCR STD-27) of Japan, GSM (TS100-910, etc.) of Europe, TIA IS-136 and UWC-136 of U.S.A., or the like. The CDMA is used in the cellular phones according to each of the systems such as ANSI JSTD-008 of U.S.A., ARIB STD-T63 and ARIB STD-T64 of Japan which are generally called cellular phones of the third generation, and a similar system of Europe.  
     [0057] In the above embodiments, there are the following frequency bands as a first frequency band. That is, ARIB STD-T53 (CDMA) of Japan (the reception side: 860-870 MHz, the transmission side: 915-925 MHz, the reception side: 843-846 MHz, the transmission side: 898-901 MHz, the reception side: 832-834 MHz, the transmission side: 887-889 MHz), IS-95 (CDMA, AMPS, TDMA) of U.S.A. and Korea (the reception side: 869-894 MHz, the transmission side: 824-849 MHz), GSM900 (TDMA) of Europe (the reception side: 921-960 MHz, the transmission side: 876-915 MHz), and PDC (TDMA) of Japan (the reception side: 810-826 MHz, 870-885 MHz, the transmission side: 925-956 MHz, the reception side: 834-846 MHz, the transmission side: 893-895 MHz). The AMPS is an analog method. If the first frequency band is the CDMA and AMPS, the band-pass filter  21 , radio frequency switch  22 , and low-pass filter  24  become one duplexer.  
     [0058] There are the following frequency bands as a second frequency band. That is, IMT-2000 (CDMA) (the reception side: 2110-2170 MHz, the transmission side: 1920-1980 MHz, the transmission and reception sides: 2000-2025 MHz), PCS (CDMA, TDMA) of North America (the reception side: 1930-1990 MHz, the transmission side: 1850-1910 MHz), PCS (CDMA) of Korea (the reception side: 1805-1870 MHz, the transmission side: 1715-1780 MHz), GSM1800 (TDMA) of Europe (the reception side: 1805-1880 MHz, the transmission side: 1710-1785 MHz), and PDC1.5G (TDMA) of Japan (the reception side: 1477-1501 MHz, the transmission side: 1429-1453 MHz).  
     [0059] When specific numerical values are designated as frequencies in the above embodiments, not only the frequencies specified by the numerical values but frequencies of a range necessary to make communication are included. Although the invention has been described on the assumption that a boundary frequency of the first and second frequency bands is set to 1 GHz, the invention is not limited to it but it is sufficient that a high/low relationship between the frequencies is held.  
     [0060] In the first and third embodiments of the invention shown in FIGS. 1 and 3, the handover between both communication methods of the TDMA in the first frequency band and the CDMA in the second frequency band is possible. The handover between the methods is not limited to the TDMA and the CDMA. For example, a handover between a first communication method whereby the transmission and the reception are executed at different time like a TDMA and a second communication method whereby the transmission and the reception are simultaneously executed like a CDMA is also possible. The second communication method is not limited to the method whereby the reception and the transmission are always simultaneously executed but it is also possible to use, for example, a method whereby the reception is intermittently executed during the transmission or a method whereby the transmission is intermittently executed during the reception.  
     [0061] It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.