Patent Publication Number: US-2010113089-A1

Title: Multimode wireless communication apparatus and high frequency integrated circuit therefore

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2002-307792, filed Oct. 23, 2002 and is a Continuation Application of U.S. application Ser. No. 10/372,269, filed Feb. 25, 2003, the contents of which are incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a multimode wireless communication apparatus conformed with a plurality of communication standards and a high frequency integrated circuit therefor. 
     (2) Description of the Related Art 
     Communication modes (communication protocols) in wireless terminals are broadly divided into a wireless communication protocol for mobile telephone network such as GSM, EDGE, GPRS, PDC, cdmaOne, cdma2000, and W-CDMA each using a public network of a wide area (hereinafter, called public network wireless communication protocol), and a communication protocol for wireless LAN such as IEEE802.11a, 11b, 11g, and 11h and HiperLAN/2 using a local network. The wireless communication protocol using a local network also includes, for example, a short-range wireless communication protocol such as by Bluetooth or UWB. 
     In the specification, the local network wireless communication protocol includes the above short-range wireless communication protocol. A wireless terminal (wireless communication apparatus) having two communication modes, one for the public network wireless communication protocol and the other for local network wireless communication protocol will be called a multimode wireless terminal. 
     In the field of wireless communication, recently, a mobile telephone network having a wide service area is rapidly spreading. Meanwhile, in the metropolitan area, information service using a local high-speed network such as a wireless LAN has also started. Thus, various wireless communication systems coexist today. A mobile telephone terminal has advantages such that a communication area is wide and communication can be continued even when the user is moving among cells at high speed. However, the bit rate is as low as 9.6 to 384 kbits/second and the communication cost is expensive. On the other hand, at present, information service areas of a wireless LANs are limited to, for example, service areas called hot spots in the metropolitan area. Unlike mobile telephone systems, the wireless LAN cannot provide communication service to the user who is moving at high speed. However, as compared to a mobile telephone, the wireless LAN can provide a higher bit rate service (for example, 22 to 54 Mbps), its communication cost is overwhelmingly cheaper, and there exist a number of service areas which are free of communication charges. 
     Consequently, the demand for a multimode terminal adapted to a plurality of communication standards, so that both of the services can be received by a single wireless terminal is increasing. A multimode wireless terminal conventionally proposed has plural kinds of transceivers adapted to different communication protocols (communication modes), so that the user can selectively use one of communication modes or use two modes in parallel independently of each other. 
     SUMMARY OF THE INVENTION 
     As described above, the mobile telephone network and the wireless LAN have contradictory advantages and disadvantages. Consequently, it is considered to be more advantageous from the viewpoints of power consumption and communication costs of a wireless terminal to use the communication functions of a mobile telephone network and a wireless LAN while dynamically switching communication modes in accordance with the service area and user&#39;s purpose, than to use the communication functions independently of each other. 
     However, a conventional multimode terminal does not switch the communication modes at all or switching of the communication modes is up to the user. Therefore, the terminal functions are not efficiently used. A conventional multimode wireless terminal having a plurality of transceivers for respective communication modes has a problem of a large circuit scale. A terminal which shares a transceiver circuit for a plurality of communication modes has a problem that it takes time to switch the communication modes. 
     An object of the invention is to provide a multimode wireless communication apparatus capable of switching the communication mode at high speed. 
     Another object of the invention is to provide a multimode wireless communication apparatus having a radio frequency unit commonly used in a plurality of communication modes and capable of switching the communication mode at high speed. 
     Another object of the invention is to provide a multimode wireless communication apparatus capable of executing two communication modes in a time sharing manner. 
     Further another object of the invention is to provide a high frequency integrated circuit for a multimode wireless communication apparatus capable of switching the communication mode at high speed. 
     To achieve the above objects, a multimode wireless communication apparatus of the invention comprises: a radio frequency unit having controllable communication modes; and a control unit for making the radio frequency unit operate periodically in a first communication mode and, after predetermined time interval, switching the communication mode to a second communication mode, and the control unit includes determining means for suppressing the switching of the radio frequency unit to the second communication mode when occurrence of a predetermined event is detected from a signal received during a period in which the radio frequency unit is operating in the first communication mode and determining whether communication in the first communication mode should be continued or not. 
     More specifically, the radio frequency unit is comprised of a high frequency integrated circuit including at least one analog component having operation characteristic controllable with a reference parameter value, and the control unit switches the communication mode of the radio frequency unit by changing the reference parameter value for determining the operation characteristic of the high frequency integrated circuit. 
     According to an embodiment of the invention, the high frequency integrated circuit includes a reference register in which the reference parameter value for determining the operation characteristic of the analog component is set, a first register for storing a parameter value for the first communication mode, a second register for storing a parameter value for a second communication mode, and a switch for selectively supplying the parameter value stored in one of the first and second registers to the reference register, and the control unit switches the communication mode of the radio frequency unit by controlling the switch to change the reference parameter value set in the reference register. 
     A key feature of the invention resides in that the determining means determines whether the first communication mode should be continued or switched to the second communication mode in accordance with a predetermined mode selection rule. 
     In an embodiment of the invention, the above determining means has means to inquire a user which operation mode to select next in accordance with the mode selection rule, and selects either the first communication mode or the second communication mode in accordance with the instruction from the user. The radio frequency unit includes a transmission power amplifier connected to an on/off controllable power source, and the control unit turns off the power source for the transmission power amplifier before switching the operation mode of the radio frequency unit and, after the operation mode is switched, turns on the power source for the transmission power amplifier. 
     According to the invention, a high frequency integrated circuit for a multimode wireless communication apparatus including at least one analog component having operation characteristic controllable with a reference parameter value, comprises: a reference register in which the reference parameter value for determining the operation characteristic of the analog component is set; a first register for storing a first parameter value for a first communication mode; a second register for storing a second parameter value for a second communication mode; a switch for selectively connecting one of the first and second registers to the reference register so as to set the first parameter value or the second parameter value as the reference parameter value; a switch control circuit for controlling the switch in accordance with a mode selection signal supplied from an external signal line; and a write control circuit for writing a parameter for the first mode and a parameter for the second mode supplied from the external signal line to the first and second registers, respectively. The mode selection signal is supplied to the switch control circuit via the write control circuit. 
     The other objects and characteristic configurations of the invention will become apparent from description of embodiments with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of a wireless communication apparatus (multimode wireless terminal) to which the invention is applied. 
         FIG. 2  is a diagram showing an example of a sequence of switching a communication mode in the multimode wireless terminal of the invention. 
         FIG. 3A  is a configuration diagram showing an example of a conventional RF-IC control circuit for a multimode wireless terminal. 
         FIG. 3B  is a diagram for explaining a parameter setting sequence for switching the communication mode in a conventional RF-IC. 
         FIG. 4A  is a block diagram showing a first embodiment of an RF-IC control circuit for a multimode wireless terminal according to the invention. 
         FIG. 4B  is a diagram for explaining a parameter setting sequence for switching the communication mode in the multimode wireless terminal of the first embodiment of the invention. 
         FIG. 5  is a block diagram showing a second embodiment of the RF-IC control circuit for the multimode wireless terminal according to the invention. 
         FIG. 6  is a block diagram showing a third embodiment of the RF-IC control circuit for the multimode wireless terminal according to the invention. 
         FIG. 7A  is a block diagram showing a fourth embodiment of the RF-IC control circuit for the multimode wireless terminal according to the invention. 
         FIG. 7B  is a diagram for explaining a parameter setting sequence for switching the communication mode in a multimode wireless terminal of the fourth embodiment of the invention. 
         FIG. 8A  is a flowchart showing a mode switching control routine executed by a control processor  16  in  FIG. 1  in the multimode wireless terminal of the first embodiment of the invention. 
         FIG. 8B  is a flowchart showing the details of incoming call processing  520  in  FIG. 8A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a wireless communication system designed on the premise that a terminal performs communication while moving from cell to cell, such as a mobile telephone, in order to enable a wireless terminal (mobile terminal) to be located whenever a call is made for the terminal, each of the mobile terminals executes a communication protocol for registering its position to a base station which is reachable from it&#39;s present position. Even when the user does not perform communication, each mobile terminal periodically receives a specific signal transmitted from a base station nearby, thereby monitoring the necessity to register it&#39;s position to a new base station and the presence or absence of a call to the terminal itself. Such a signal receiving process is generally called standby reception. In order to increase available communication time of a mobile terminal by suppressing the consumption of it&#39;s battery, the repeating cycle of the standby reception is set to be relatively long (about 1 second) and a protocol is determined so as to complete each standby receiving process in short time. 
     On the other hand, in a wireless communication system designed on the premise of using a local high-speed network such as a wireless LAN, there is no rule in the communication standard regarding an intermittent standby reception processing as performed in a mobile telephone terminal. Therefore, in order to make the user obtain information service from a wireless LAN while moving around, each wireless terminal has to periodically measure the signal intensity of a common channel in the wireless LAN and determine whether the terminal can communicate with the wireless LAN in the present position or not. A terminal once connected to the wireless LAN basically enters a receivable state, monitors data on the network, and receives the desired data. 
     The multimode wireless terminal of the invention is characterized in that, in order to enable communication in both communication modes of a mobile telephone terminal and a wireless LAN terminal, the operation mode of the terminal is automatically switched to a local network wireless communication mode (wireless LAN mode) at intervals of standby receptions periodically repeated in the mobile telephone mode. 
       FIG. 2  shows an example of a sequence of switching the communication mode in a multimode wireless terminal according to the invention. 
     According to the invention, as shown in  FIG. 2 , during intervals T 12  ( 211 ,  212 , . . . ) between intermittent standby receptions T 11  ( 201 ,  202 , . . . ) of a mobile telephone mode (public network wireless communication mode) repeated in predetermined cycles T 1 , the communication mode of the terminal is changed to the wireless LAN mode (local network wireless communication mode). The mobile telephone mode is one of, for example, GSM, PDC, EDGE, GPRS, cdmaOne, cdma2000, and W-CDMA, and the wireless LAN mode is one of, for example, IEEE802.11a, IEEE802.11b, IEEE802.11g, IEEE802.11h, HiperLAN/2, Bluetooth, and UWB. 
     If the terminal is located in an area where the wireless LAN can be used, by using the periods T 12 , a packet transmission and receiving processing via the wireless LAN is executed. At the time of switching the communication mode, there is the possibility that a transmission signal spectrum goes out of a restricted range (spectrum mask) defined by a wireless communication standard due to a transient response of a power amplifier or the like in a transmitter circuit. Consequently, as shown by Δt in  FIG. 2 , switching of the communication mode is executed after the power source for a transmission power amplifier is turned off once. 
     In the case where there is an incoming call during the standby reception period T 11  of the mobile telephone mode, the incoming call is treated in accordance with a mode selection rule designated by the user in advance. For example, when a mobile telephone preference mode is designated as the mode selection rule, the mobile telephone mode is continued, as shown by a period T 13  in  FIG. 2 , even after a standby reception period  203  in which an incoming call is detected, and communication via the wireless LAN is interrupted until speech communication is finished. 
     If a wireless LAN preference mode is designated as the mode selection rule, an incoming call is ignored and, after the standby reception period  203 , communication in the wireless LAN mode in the period T 12  is repeated. The communication mode after the incoming call may be selected according to the choice of the user each time an incoming call is detected. Specifically, when a user selection mode is designated as the mode selection rule, automatic switching to the wireless LAN mode is stopped, the user is requested to select a communication mode on which priority is to be placed, and the operation mode is switched to a communication mode designated by the user. 
       FIG. 1  is a configuration diagram showing an example of a multimode wireless terminal to which the mode switching shown in  FIG. 2  is applied. 
     The multimode wireless terminal is comprised of: a front end unit  11  connected to an antenna  10 ; a radio frequency unit  12  connected to the front end unit  11 ; a radio frequency unit interface  13  including an analog to digital (A/D) converter  131  and a digital to analog (D/A) converter  132 ; a baseband unit  14  including a modulation and demodulation unit (modem)  141  and a digital signal processor (DSP)  142 ; a control processor (CPU)  16  connected to the DSP  142  via an internal bus  18 ; a user interface  15 ; and a random access memory (RAM)  17 A and a read only memory (ROM) or flash memory  17 B connected to the internal bus  18 . The switching of the communication mode of the terminal is conducted by the control processor  16  in cooperation with the DSP  142 . 
     The radio frequency unit  12  includes at least a radio frequency integrated circuit (RF-IC)  30  subjected to mode switching control which will be described later and a transmission power amplifier (PA)  40 . The user interface  15  is comprised of an analog interface  15 A connected to the DSP  142  and a digital (data) interface  15 B connected to the internal bus  18  and the modem  141 . The analog interface  15 A is coupled with a speaker  20  and a microphone  21 . A display unit  22  and a keyboard  23  are coupled with the digital interface  15 B. 
     A received signal from the antenna  10  is input to the front end unit  11 , separated from a transmission signal by an antenna switch (or duplexer) and filtered. After that, the resultant signal is input to the radio frequency unit  12 . The RF-IC  30  of the radio frequency unit  12  has circuit functions of a filter, an amplifier, a mixer, and the like and the received signal is converted to a baseband signal by the RF-IC  30 . The baseband signal output from the RF-IC  30  is converted to a digital signal by the A/D converter  131  in the interface  13  and the digital signal is demodulated by the modem  141  in the baseband unit  14 . When a demodulated signal is a voice signal, it is processed by the DSP  142  and the processed signal is output to the analog interface  15 A. In the case where the demodulated signal is data, the data is output to the digital interface  15 B or internal bus  18 . 
     The transmission voice signal input from the microphone  21  and the transmission data output from the control processor  16  are subjected to a process such as error correction coding or the like by the DSP  142 . The resultant signal is modulated by the modem  141 . The modulated transmission signal is converted to an analog signal by the D/A converter  132  and, after that, the analog signal is converted to a radio frequency transmission signal in a desired frequency band by the RF-IC  30  in the radio frequency unit  12 . The radio frequency transmission signal is amplified by the power amplifier  40  and filtered by the front end unit  11 . After that, the resultant signal is transmitted from the antenna  10 . 
     The control processor (CPU)  16  executes various programs for data processing or communication control in response to the user operation from the keyboard  23 . The control processor  16  also executes a communication mode switching control routine which will be described later and performs setting of various parameters to the RF-IC  30  and a mode switching via the DSP  142 . The setting of parameters and the mode switching are instructed to the RF-IC  30  via a signal line L 1 . Turn-on/off of the power source for the transmission power amplifier  40  is instructed via a signal line L 2 . 
       FIG. 3A  shows main components of a control circuit of a conventional RF-IC for a multimode wireless terminal. For simpler explanation, the diagram shows, as components of the RF-IC, a filter  32 , a variable gain amplifier  33 , and a mixer  34  which construct a receiving circuit and, in correspondence with the above components, a plurality of reference registers (a filter coefficient register  302 , a gain adjustment register  303 , and a local frequency register  304 ) which are formed in a reference register block  300 . In an actual RF-IC, the receiving circuit includes other analog components in addition to the above components. On the substrate of the RF-IC, not only the above receiving circuit but also a transmission circuit having an operation characteristic controllable with reference parameter values is formed. 
     In the multimode wireless terminal, as shown in  FIG. 3A , by employing a circuit configuration in which the operation characteristics of some of the analog components formed on the RF-IC are changed depending on the value of reference parameters set in the reference register block  300 , a plurality of different communication modes are realized by a single RF-IC. Reference parameters to be set in the reference register block  300  vary according to the kind of analog components. For example, the parameter for a mixer which is set in the reference register  304  indicates the frequency of a local signal to be supplied to the mixer. The parameter for the variable gain amplifier set in the reference register  303  indicates a gain coefficient of an amplifier. The parameter for a filter set in the reference register  302  indicates a filter coefficient. 
     Each of reference parameter may be comprised of a multi-bit parameter in which each bit designates the potential of one of terminals of an analog component. For example, “0” bit corresponds to GND potential and “1” bit corresponds to Vdd. In the case of correcting the characteristic of a nonlinear component such as the power amplifier by predistortion or the like, the parameter to be set in the reference register may also include a calibration correction value. 
     In the conventional RF-IC, these reference parameters are supplied from an external signal input pin  31  to a configuration value write control circuit  305 . By switching a switch  306  by the configuration value write control circuit  305 , the parameters are selectively set into the specific registers  302  to  304  in the reference register block  300 . Each of the analog components such as the filter  32 , variable gain amplifier  33 , and mixer  34  operates with an operation characteristic depending on the reference parameter value indicated by the corresponding reference register. 
     The external signal line used for setting the above parameters into the reference registers is generally of a serial bus type for sequentially transferring data bit by bit, in order to realize smaller size of an IC package by reducing the number of external signal pins of the RF-IC as much as possible. 
     In a conventional multimode wireless terminal, switching of the operation mode of the RF-IC is realized by changing the reference parameters in response to a user operation. In this case, each time the mode is switched, for example, as shown in  FIG. 3B , all of parameters P 302 , P 303 , P 304 , . . . to be set in the reference register block  300  have to be supplied serially from the external signal input pin  31 . Consequently, hundreds of clocks is required to switch the mode. 
     The conventional RF-IC is adopted on a premise that the mode switching is of low frequency such that one communication mode selected by the user continues for several minutes or longer. In this case, if the user sets the terminal in the wireless LAN mode, the terminal loses the function of a mobile telephone. Therefore, as long as the user does not switch the operation mode of the terminal to the mobile telephone mode by re-setting the reference parameters, standby reception of the mobile telephone is not executed. 
       FIG. 4A  shows a first embodiment of the control circuit of the RF-IC  30  for a multimode wireless terminal according to the invention. 
     As described by referring to  FIG. 2 , in order to frequently switch the communication mode of the multimode wireless terminal in relatively short cycles, the values of various reference parameters set in the reference register block  300  of the RF-IC  30  have to be changed at high speed. 
     When all of the reference parameters are input from the external signal input pin  31  each time the mode is switched as in the conventional technique, overhead for setting the parameters increases and, as a result, the operation period in the wireless LAN mode has to be shortened. 
     For example, when it is assumed that the reference register block  300  of the RF-IC  30  has 24 registers each having a 16-bit width, in order to set parameters from the serial bus (signal line L 1 ), 384(=16×24) clocks are necessary. If the operation clock of the RF-IC  30  is 15 MHz, it takes about 25 msec for the parameter setting. Therefore, if the standby reception processing is repeated at the intervals of one second, there is a problem such that half of the period T 1  shown in  FIG. 2  would be consumed for the parameter setting for the mode switching. 
     To reduce the overhead of the parameter setting to the reference register block  300  which occurs at the time of switching the communication mode, in the first embodiment of the invention, the RF-IC  30  is provided with a parameter storing register block  400 . When the power source of the terminal is turned on, configuration parameter values to be used as reference parameters for respective communication modes are supplied from the signal line L 1  and stored in the register block  400 . Each time the switching of the communication mode is required, the configuration parameter values of a desired mode are transferred from the register block  400  to the reference register block  300  in parallel. 
     For example, when a mobile telephone is defined as a mode  1  and the wireless LAN is defined as a mode  2 , parameter storing registers  402  to  404  for the mode  1  and parameter storing registers  412  to  414  for the mode  2  are prepared in the parameter storing register block  400 , in correspondence with the registers  302  to  304  in the reference register block  300 . The configuration parameter bits stored in one of the registers  402  and  412  are selectively transferred in parallel to the register  302  via a mode switch  312  in accordance with the communication mode. Similarly, configuration parameter bits stored in one of the registers  403  and  413  are selectively transferred in parallel to the register  303  via a mode switch  313 , and configuration parameter bits stored in one of the registers  404  and  414  are selectively transferred in parallel to the register  304  via a mode switch  314 . 
     The mode switches  312  to  314  connect either the group of parameter storing registers  402  to  404  for the mode  1  or the group of the parameter storing registers  412  to  414  for the mode  2  to the group of the registers  302  to  304 . 
     With the configuration, for example, when the terminal power is turned on, various configuration parameters are supplied to the RF-IC in the form described by referring to  FIG. 3B  and the parameters for the modes  1  and  2  are set in the parameter storing registers  402  to  404  and parameter storing registers  412  to  414 , respectively. After that, only by changing the set value (mode selection bit) in the mode register  311 , the reference parameter values in the parameter reference registers  302  to  304  can be instantaneously changed. 
     The location of the register area to which the configuration parameter is to be written can be designated by, for example, a control code output to the signal line L 1  from the DSP  142  prior to the parameter itself. Therefore, a configuration value write controller  401  can control a switch  411  in accordance with the control code received from the signal line L 1 , so that the parameter values received from the signal line L 1  are selectively set in the registers in the parameter storing register block  400 . By setting a mode selection bit received thereafter from the signal line L 1  to the mode register  311 , it is able to operate the switches  312  to  314  so as to change the reference parameter values, thereby switching the communication mode of the RF-IC  30  at high speed. 
     According to the embodiment, initial setting of configuration parameters in the parameter storing register block  400  takes relatively long time. However, in order to switch the communication mode of the RF-IC  30 , for example, as shown by CNT 1  and CNT 2  in  FIG. 4B , it is sufficient to supply short control data including a mode selection bit to the RF-CI  30 . Consequently, the switching of the operation mode can be completed in short time At equivalent to only a few clocks. 
       FIGS. 8A and 8B  show flowcharts of a mode switching control routine  500  corresponding to the first embodiment. The control routine  500  is executed by the control processor (CPU)  16  when the power of the terminal is turned on. 
     The control processor  16  executing the mode switching control routine  500  sets, first, the configuration parameters for the mode  1  into the parameter storing registers  402  to  404  on the RF-IC  30  via the DSP  142  (step  501 ). Various parameter values required for the configuration parameters for the mode  1  and mode  2  are stored in advance in a parameter table in the ROM  17 B. Therefore, when the control processor  16  transmits the configuration parameters for the mode  1  read out from the ROM together with the write control command to the DSP  142 , the DSP  142  transfers the received parameters together with a control code for the write control circuit  401  to the signal line L 1 , and the write control circuit  401  in the RF-IC  30  selectively writes the parameters received from the signal line L 1  to the registers  402  to  404  specified by the control code. Like in step  501 , the control processor  16  sets the configuration parameters for the mode  2  to the parameter storing registers  412  to  414  in the RF-IC  30  in cooperation with the DSP  142  (step  502 ). 
     After the parameter initial setting, the control processor  16  instructs the DSP  142  to execute the initial processing in the mode  1  (mobile telephone mode) (step  503 ). In response to the instruction, the DSP outputs to the signal line L 1  an instruction of switching the communication mode to the mode  1  and executes a predetermined communication procedure for registering the terminal position to a base station of the mobile telephone network. The instruction of switching the communication mode to the mode  1  output to the signal line L 1  includes a mode selection bit indicative of switching to the mode  1  and a control code indicating that the destination of the mode selection code is the mode register  311 . 
     On completion of registration of the terminal position, the control processor  16  starts a timer T 1  (step  504 ) and instructs the DSP  142  to switch the radio frequency unit to the mode  1  (step  505 ). Upon receiving the mode switching instruction from the control processor  16 , the DSP  142  once turns off the power source of the transmission power amplifier  40  via the signal line L 2 , outputs an instruction of switching to the mode  1  to the signal line L 1 , and returns the power source of the transmission power amplifier  40  to the on state. By the operation, standby reception of predetermined time T 11  is started. By monitoring a signal output from the modem  141  to the internal bus  18  during the standby reception period T 11 , the control processor  16  determines whether an incoming call event occurs or not (step  506 ). 
     If there is an incoming call in the mode  1 , the control processor  16  executes an incoming call processing  520  shown in  FIG. 8B . If there is no incoming call during the standby reception period T 11 , the control processor  16  instructs the DSP  142  to switch the radio frequency unit to the mode  2  (wireless LAN mode) (step  507 ). 
     When the switching instruction to the mode  2  is received from the control processor  16 , the DSP  142  turns off the power source of the transmission power amplifier  40  via the signal line L 2 , outputs a switching instruction to switch the operation mode of the radio frequency unit to the mode  2  to the signal line L 1 , and returns the power source of the transmission power amplifier  40  to the on state. The switching instruction to the mode  2  includes the mode selection bit indicative of switching to the mode  2  and a control code indicating that destination of the mode selection bit is the mode register  311 . 
     After switching the RF-IC  30  to the mode  2 , the control processor  16  executes the data transmission and receiving processing for the wireless LAN until interruption of the timer T 1  occurs (step  509 ). When interruption of the timer T 1  occurs (step  508 ), the control processor  16  returns to step  505  and instructs the DSP  142  to switch the RI-IC  30  to the mode  1 . 
     By the control procedure, as long as there is no incoming call to the terminal, the data transmission and receiving processing for the wireless LAN can be executed at the intervals of the standby reception periods. That is, the incoming call standby reception processing in the mode  1  and the data transmission and receiving processing for the wireless LAN in the mode  2  are executed in a time sharing manner. 
     In the incoming call processing  520 , as shown in  FIG. 8B , the mode selection rule designated by the user in advance is judged (step  521 ). When a speech preference mode is designated as the mode selection rule (step  530 ), the control processor  16  executes an output processing for indicating the incoming call (step  531 ). The incoming call is notified to the user, for example, by outputting flashing display indicative of an incoming call on the display unit  22  or outputting a melody indicative of an incoming call to the speaker  20 . The control processor  16  waits for a response from the user to the incoming call (step  532 ). If there is no response, the control processor  16  repeats the incoming call indication  531  until the calling party disconnects the call (step  533 ). 
     When the user performs an input operation to respond to the incoming call, the wireless terminal enters a speech mode in which voice signals are communicated via the DSP. The control processor  16  monitors disconnection of the call in this state (step  534 ). When the call is disconnected, the control processor  16  returns to step  504  in  FIG. 8A , restarts the timer T 1 , and repeats the steps  505  to  509 . 
     When a wireless LAN preference mode is designated as a mode selection rule (step  550 ), the control processor  16  records incoming call data such as incoming call time and telephone number of the caller into the RAM  17 A (step  551 ), disconnects the call (step  522 ), and returns to step  507  in  FIG. 8A . In this case, the incoming call is ignored and, by using the intervals between the call standby reception periods, the data transmission and receiving processing for the wireless LAN is intermittently executed. It is also possible to omit the disconnection of the call (step  522 ) and allow the caller to disconnect the call. 
     When a user&#39;s selection preference mode is designated as a mode selection rule (step  540 ), the control processor  16  outputs a menu screen (or icon) for mode selection on the display unit  22  (step  541 ) and treats the incoming call in accordance with the communication mode selected by the user on the menu screen. If the user selects the speech preference mode, steps  531  to  534  are executed. If the user selects the wireless LAN preference mode, steps  551  and  552  are executed. 
     In the first embodiment described above, the multimode terminal capable of switching between two kinds of communication modes has been described. There is, however, a case that selectable three or more kinds of communication modes are desired to be offered, depending on a service area where the wireless terminal exists. If a frequent mode switching occurs among all of communication modes, a number of registers equal to the number of kinds of communication modes have to be prepared in the parameter storing register block  400  in correspondence with registers in the reference register block  300 . In this case, the number of parameter storing registers and the circuit scale of the RF-IC  30  increases. In order to reduce the circuit scale of the RF-IC  30 , for example, it is sufficient to make specific groups of configuration parameters always reside in the parameter storing register block  400  with respect to communication modes which are frequently switched, and to supply the other configuration parameters with respect to a communication mode having relatively long switching intervals from the ROM  17 B to the parameter storing register block  400  each time the communication mode is selected. 
       FIG. 5  shows a second embodiment of the control circuit of the RF-IC  30  for the multimode wireless terminal according to the invention. 
     For example, in a wireless terminal of a carrier frequency hopping type, which selects a frequency to be used from a group of carrier frequencies according to a predetermined sequence different for each user terminal to perform communications while periodically switching the carrier frequency, the local frequency to be set in a mixer has to be changed for every call. When the carrier frequency hopping is employed as the mobile telephone mode (mode  1 ), reference parameters to be set in the local frequency configuration register  304  in the RF-IC  30  have to be updated for each call. In this case, it is not sufficient to switch the parameter storing registers like the first embodiment. 
     The second embodiment is directed to shorten the time required to change the reference parameters under such conditions. In the second embodiment, for the local frequency configuration register  304 , reference parameters are set from the DSP via the signal line L 1  and the state of the register  304  is monitored by the mode judging and switching circuit  312 . For the other reference registers ( 302  and  303 ) in the reference register block  300 , the mode judging and switching circuit  312  changes the reference parameters by switching the status of the switches  312  and  313  at a predetermined timing. Selection of a communication mode is performed based on the value of at least a part of parameters set in the register  304 . 
     According to the embodiment, parameter data to be supplied from the external signal input pin  31  at the time of operation mode switching is only a parameter value for local frequency, so that the communication mode can be switched at higher speed as compared with the prior art. 
       FIG. 6  shows a third embodiment of the control circuit in the RF-IC  30  for the multimode wireless terminal according to the invention. 
     In the first and second embodiments, configuration parameters are loaded from the external input pin  31  via the configuration value write controller  401  to all of registers prepared in the parameter storing register block  400  at the time of initial setting. However, depending on the wireless communication method, some parameters to be set in the RF-IC are unconditionally determined and will not be changed later. For example, in W-CDMA as a third generation mobile telephone, the frequency characteristics of the output signal are specified by a standard. 
     Consequently, an FIR filter coefficient on the output signal side decided at the time of circuit design will not be changed later. 
     In such a case, it is unnecessary to write the same parameter values into the parameter storing register each time the initial setting is performed. For example, like in the register  402  in  FIG. 6 , a register as a part of the parameter storing register block  400  may be replaced with a ROM for holding fixed parameters. When the filter coefficient for the mode  2  is also a fixed value, the register  412  can be also replaced with a ROM. By replacing a part of the register area  400  with a ROM as described above, it is able to shorten the time required for parameter initial setting and to reduce power consumption. 
       FIG. 7A  shows a fourth embodiment of the control circuit of the RF-IC  30  for the multimode wireless terminal according to the invention. 
     In the first embodiment, configuration parameter values are transferred as reference parameter values from the parameter storing register block  400  to all of the parameter reference registers ( 302  to  304 ). In an actual application, there is a case such that configuration parameters have to be set from the parameter storing register block  400  with respect to only a part of the reference registers. 
     The fourth embodiment is characterized in that, for example, like an amplifier gain parameter, a specific parameter of which set value is desired to be changed even in the same communication mode depending on special situations such as a radio propagation state in a wireless path is supplied from the external signal input pin  31  to the parameter reference register  303 , and the other parameters are set from the parameter storing register block  400  to the parameter reference register. 
     In the embodiment, for example, special parts such as mixers  34 A and  34 B, which become difficult to share the same circuit depending on a combination of selectable communication modes or analog components to be dedicated to respective modes because it is advantageous from the viewpoint of performance and power consumption, are excluded from targets of parameter switching. For some parts of which parameter set values are the same even when the communication mode changes, it is naturally unnecessary to switch the configuration parameters. 
     In the embodiment, as shown in  FIG. 7B , it is sufficient to supply control data CNT 1  and CNT 2  including, for example, a control code P 401 , a mode selection bit P 311 , and an amplifier gain adjustment parameter P 303  to the RF-IC  30  each time the communication mode is switched. 
     As described above, according to the invention, by properly combining parameter transfers from the holding register to the reference register in balance in accordance with the required performance of an analog component, the time required to switch the communication mode can be shortened while suppressing increase in the scale of the IC and the influence on performance. 
     In the embodiment shown in  FIG. 8B , any one of the speech preference mode, wireless LAN preference mode, and user&#39;s selection preference mode is designated according to the mode selection rule in the incoming call processing. However, further another mode may be designated according to the mode selection rule. For example, a parallel execution mode of executing voice communication by a mobile telephone and data communication by a wireless LAN in parallel in a time sharing manner may be designated. 
     Since voice data is transmitted and received every 125 μsec, data of the wireless LAN can be communicated in a time sharing manner by using the intervals of voice data communication in the parallel execution mode. According to the invention, since the communication mode can be switched at high speed, for example, by increasing the operation speed of the RF-IC  30 , control processor  16 , and DSP  142  or decreasing the data bit rate of the wireless LAN in the parallel execution mode, it is able to offer such a form of communication service that the user is allowed to perform speech communication by a mobile telephone in parallel with display of received data from the wireless LAN to the display unit  22 . 
     As obvious from the foregoing embodiments, according to the invention, the communication mode can be switched at high speed. Consequently, it is able to provide a multimode wireless terminal capable of executing plural kinds of communication modes of different communication protocols, like the mobile telephone and the wireless LAN communication, while periodically switching the communication modes. 
     In the embodiments, the multimode terminal for switching the communication mode between the mobile telephone mode (public network wireless communication) and the wireless LAN mode (local network communication) has been described. The method of switching the communication mode according to the invention is also applicable to a combination of communication modes other than the embodiments. For example, alternate switching may be performed between first and second communication modes of the wireless LAN in order to detect a wireless LAN system from which the terminal can receive data, so that a user can enjoy information distribution service provided by the detected wireless LAN system.