Patent Abstract:
A system and method for processing signals in a mobile terminal routes received signals to signal processing units based on the bands in which the signals are located. Routing is preferably performed by a m-pole/n-throw electric switch where m≧1 and n≧1. The signal processing units may process signals in, for example, the DCN, PCS and GPS bands although other bands are possible. By using an electric switch instead of, for example, a diplexer circuit, the system and method significantly reduces insertion loss while simultaneously increasing the degree of isolation among the different bands of the received signals. Optimal receiver sensitivity is also achieved in each respective band.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a receiving apparatus for a mobile terminal, and more particularly to an apparatus and a method for branching signals received by a mobile terminal in different communication bands. 
   2. Background of the Related Art 
     FIG. 1  is a block diagram showing a general CDMA mobile terminal, which includes an antenna  10 , a radio frequency (RF) unit  20 , an intermediate frequency (IF) unit  30 , a baseband analog (BBA) unit  40 , a baseband modem  50 , and an input/output unit  60 . The RF unit  20  converts a high frequency signal to an intermediate frequency signal of a modulated carrier, and the IF unit  30  converts the intermediate frequency signal to a baseband frequency signal. The BBA unit  40  converts an analog signal output from the IF unit to a baseband digital signal. The baseband modem  50  controls an input/output signal of a display panel included in input/output unit  60  and of a keypad. The baseband modem further controls voice input/output on a microphone and an earphone. 
     FIG. 2  is a block diagram showing the structure of RF unit  20  of the CDMA mobile terminal. As shown, when an RF signal is received from an outer part, a received frequency signal is separated from the RF signal input from antenna  10  by a duplexer  21 . The received frequency signal is then amplified by a low noise amplifier (LNA)  26  and converted into an intermediate frequency signal by a down-conversion mixer (DMIX)  28  after passing through a band pass filter  27 . The converted intermediate signal is amplified in an IF amplifier  29  and sent to the IF unit  30 . 
   In a transmission process, an intermediate frequency signal output from the IF unit  30  is converted into an RF signal by an up-conversion mixer (UMIX)  25 . This signal is then amplified by a driver amplifier  23  after passing through a band pass filter  24 , and the power of the signal output from the driver amplifier is amplified by a power amplifier  22 . The resulting signal is sent to a base station through the antenna. 
   CDMA mobile terminals of the aforementioned type have been adapted to perform a function of satellite-based global positioning system (GPS). Terminals of this type support one or more bands including an 800 MHz DCN band, a Korea-type 1.8 GHz PCS band, a U.S. type 1.9 GHz PCS band, and 1.5 GHz GPS band. That is, the CDMA mobile terminal which performs the GPS function is divided into a dual-band terminal which operates in DCN and GPS bands or PCS and GPS bands and a tri-band terminal which operates in DCN, PCS and GPS bands. 
     FIG. 3  shows a conventional receiving apparatus of a mobile terminal using a single antenna supporting the tri-band, and  FIG. 4  shows a conventional receiving apparatus of a mobile terminal using a dual-band antenna and a single band antenna. As shown therein, since the mobile terminal is operated in one or more bands, a circuit for branching an RF signal by respective bands is required in the antenna supporting the multi-bands. For example, in case of a U.S. type tri-band terminal having the most complex configuration, one antenna  70  supporting the tri-band of DCN, PCS and GPS may be used, or a dual band antenna supporting the DCN and PCS and single band antenna  90  supporting only the GPS may be used respectively. 
   The single antenna supporting the tri-band of DCN, PCS and GPS as shown in  FIG. 3  will now be described in greater detail. An RF signal received by the tri-band antenna  70  is branched to a duplexer of DCN band  75  and to another diplexer of GPS and PCS band  72  by a diplexer  71 . After that, the diplexer  72  transmits the input signal to an RF band pass filter  73  of GPS band when the input signal is in 1.5 GHz band, and transmits the input signal to a PCS duplexer  74  of PCS band when the input signal is in 1.9 GHz band. That is, diplexers  71  and  72  are a kind of manual filter made by integrating two band pass filters. Functionally, diplexer  71  outputs an input signal from antenna  70  to an input stage of a DCN transceiver if the input signal is in the 800 MHz band, and outputs through diplexer  72  the input signal to an input stage of a GPS or PCS transceiver if the input signal is in the 1.5 to 1.8 GHz band. 
   The dual-band antenna supporting the DCN and PCS bands and the single-band antenna  90  supporting the GPS band shown in  FIG. 4  will now be described in greater detail. The RF signal received by the dual band antenna  80  is branched to a PCS diplexer  83  when it is in the PCS band, and to a DCN duplexer  82  when it is in the DCN band after passing diplexer  81 . In addition, the GPS signal is received by additional antenna  90  of the GPS band and input into an RF band pass filter  91 . 
   Diplexers  71 ,  72  and  81  for branching the signal in the mobile terminal are undesirable because they have an insertion loss (e.g., a loss when the signal is passed) of 0.5˜0.8 dB, and have an isolation corresponding to the isolated degree between bands of 15˜20 dB. The insertion loss is generated as a result of signals passing through two or more diplexers in order to branch the multi-band signal, and therefore receiver sensitivity is lowered. For example, insertion loss can be increased to 1˜1.5 dB in case that the two diplexers  71  and  72  in  FIG. 3  are used. Also, in case of the GPS having isolation between bands as an important factor, isolation of about 15˜20 dB can be too weak to block the interrupt between the different bands. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
   Another object of the present invention is to provide an apparatus and a method for branching a signal in a mobile terminal by blocking interrupts between different bands using an electric switch between input stages of an antenna and a transceiver. 
   To achieve these and other objects and advantages, the present invention provides an apparatus for branching a signal in a mobile terminal comprising an electric switch for branching an RF signal input from an antenna by respective bands using electric switching method and outputting the divided signal into an input stage of a transceiver, and a CPU applying a band selecting signal for controlling the electric switch. 
   The present invention also provides a method for branching a signal in a mobile terminal by electrically switching an RF signal input by a band-selecting signal of a CPU, branching the signal to a port corresponding a respective band, and outputting the signal to an input stage of a transceiver. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a CDMA mobile terminal; 
       FIG. 2  is a block diagram showing an RF part of the CDMA mobile terminal of  FIG. 1 ; 
       FIG. 3  is an exemplary view showing a receiving apparatus of a general mobile terminal using a single antenna supporting tri-band; 
       FIG. 4  is an exemplary view showing a receiving apparatus of a general mobile terminal using a dual band antenna and a single band antenna; 
       FIG. 5  is a brief view showing a configuration of a signal branching apparatus for a mobile terminal according to the present invention; 
       FIG. 6  is a view showing a configuration of a single-pole triple throw (SP3T) switch of a mobile terminal according to the present invention; and 
       FIG. 7  is a brief view showing another embodiment of a signal branching apparatus for the mobile terminal according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 5  is a diagram showing a signal-branching apparatus for a mobile terminal according to one embodiment of the present invention. This apparatus includes multi-band antenna  70  receiving radio frequency (RF) signals of DCN, PCS and GPS bands, and a single-pole triple throw (SP3T) switch  101  for branching the signal received through the multi-band antenna by bands using an electric switching method after receiving the RF signal. A DCN duplexer  102  receives a DCN band signal input through the SP3T switch  101  and separates a received frequency signal, a PCS duplexer  103  receives a PCS band signal input through the SP3T switch  101  and separates a received frequency signal, and an RF band pass filter  104  receives an RF signal of GPS band through the SP3T switch  101  and separates the received frequency signal. Also included is a CPU  100  which applies a band-selecting signal for branching the signal received through antenna  70  by bands to the SP3T switch  101 . The aforementioned electric switching method may be a software procedure set by the CPU. 
   Operation of the signal-branching apparatus of the present invention will now be described. First, the SP3T switch  101  receives RF signals of DCN, PCS and GPS bands through the multi-band antenna  70 , and divides the signal by bands by electrically switching the signal according to a band-selecting signal of the CPU  100 . At that time, the CPU applies the band-selecting signal to the SP3T switch through a general purpose input/output (GPIO) port in order to process DCN, PCS and GPS modes which are presently under processing. 
   If the present mode is DCN mode, the DCN duplexer  102  receives a DCN signal through the SP3T switch, separates a received frequency signal, and applies the signal to an inner signal processing unit. If the present mode is PCS mode, PCS duplexer  103  receives the PCS signal through the SP3T switch, separates the received frequency signal, and applies the signal to an inner signal processing unit. If the present mode is GPS mode, RF band pass filter  104  receives the RF signal of GPS band through the SP3T switch, separates the received frequency signal, and applies the signal to an inner signal processing unit. That is, the SP3T switch receives one input signal, and branches it to one of three output ports according to the band-selecting signal of the CPU. If desired, the same inner signal processing unit may be used to process signals output from two or more of the duplexers  102  and  103  and band pass filter  104 . Those skilled in the art can appreciate that the present invention may be adapted to include more or less than three output ports (i.e., receive and route signals in more or less than three communication bands) if desired. 
     FIG. 6  shows an exemplary structure of the SP3T switch according to the present invention. As shown, the SP3T switch branches the signal to one of the three output terminals when an input signal is received through the antenna. At that time, the switch is controlled in such way that one of the three output paths is decided after receiving a digital low/high control signal from the CPU. 
   The electric switch such as the SP3T switch has a low insertion loss (e.g., about 0.3 dB), and has higher isolation between bands compared with the conventional arrangements previously described. As a result, the transmit/receive function of the transceiver/receiver of the present invention in each respective band is substantially improved. The isolation of the electric switch is superior because although the resistance value is very low between the input/output terminals which are electrically connected, other output terminals are placed in a short-circuited status. That is, there is insertion loss when the input signal passes through the switch, and the switch has a higher isolation for the other output terminals, and therefore, the switch can be used for branching the RF signal instead of using the diplexer used in conventional circuits. 
     FIG. 7  is a diagram showing a signal-branching apparatus according to another embodiment of the present invention. This apparatus includes a dual-band antenna  80  which receives signals in PCS and DNS bands and a GPS antenna  90  which receives signals in a GPS band. Also included is a DP3T switch  111  for branching signals received through the dual band antenna and the GPS antenna, by modes using an electric switching method, after receiving the RF signals. A DCN duplexer  112  receives the DCN-band signal input through the DP3T switch and divides received frequency signal, a PCS duplexer  113  receives the PCS-band signal input through the DP3T switch and separates the received frequency signal, and an RF band pass filter  114  receives the RF signal through the DP3T switch and separates the received frequency signal. A CPU  200  applies a band-selecting signal to the DP3T switch for branching the signals received through the dual-band antenna  80  and the GPS antenna  90  by respective modes. While antenna  80  has been described as a dual-band antenna, those skilled in the art can appreciate that is antenna may receive more than two bands if desired. 
   Operation of the signal-branching apparatus according to the foregoing embodiment of the present invention will now be described. First, the DP3T switch receives RF signals through the dual-band antenna  80  and the GPS antenna  90  and branches the signals by modes by electrically switching the signals. The terminal CPU applies the band-selecting signal (branch control signal) to the DP3T switch  17  through a general purpose input/output (GPIO) port in order to process the DCN, PCS and GPS modes which are presently under processing. 
   If the present mode is DCN mode, the DCN duplexer  112  receives the DCN band signal input through the DP3T switch, separates the received frequency signal, and applies the signal to an inner signal processing unit. If the present mode is PCS mode, the PCS duplexer  113  receives the PCS signal through the DP3T switch, separates the received frequency signal, and applies the signal to the inner signal processing unit. If the present mode is GPS mode, the RF band pass filter  114  receives the RF signal of the GPS band through the DP3T switch, separates the received frequency signal, and applies the signal to the inner signal processing unit. Therefore, the DP3T switch receives two input signals and may branch one of the two to one of the three output terminals according to the band-selecting signal of the CPU. 
   In addition to the SP3T and the DP3T switches described above, the electric switch of the present invention may be configured to receive a plurality of input signals and to branch the signals to one of a plurality of output ports according to the band-selecting signal of the CPU. That is, the electric switch can be configured as a single-pole double throw (SPDT), a single-pole quadruple throw (SP4T), a double-pole double throw (DPDT), a double-pole quadruple throw (DP4T) or a switch circuit using a PIN diode. Also, the electric switch may be fabricated using, for example, a GaAs FET or a diode according to semiconductor fabrication process or using silicon device such as BiCMOS, CMOS, SiGe HBT and Bipolar. 
   The mobile terminal of the present invention uses the electric switch in order to branch the RF signal received through the antenna to the duplexers of respective bands, instead of using the diplexer. Accordingly, the mobile terminal according to the present invention has an effect that an optimal receiver sensitivity can be maintained at respective bands since signals of other bands do not interrupt, by reducing the insertion loss and increasing the isolation between bands using the electric switch. 
   The CPU of the present invention may generate a band-selecting signal in at least the following ways. A multi-mode terminal supporting various modes (DCN, PCS, etc.) may include PRL (Preferred Roaming List) software. The PRL includes the modes supported by the terminal and channel information of the various modes used by the provider, and these may be scanned sequentially. It may be the case that a large geographical region such as the U.S.A. may not be covered by one mode. Consequently, one region may be supported by DCN and another region by PCS. 
   When the multi-modal terminal supporting DCN and PCS is turned on in a certain region, the CPU of the terminal may perform a sequential scan based on information included in the PRL. For example, a phase-locked loop (PLL) frequency synthesizer may set a frequency corresponding to the PCS-band channel and demodulate signals accordingly. If a normal CDMA signal is not demodulated, it may be concluded that there is no PCS signal. Then, the frequency synthesizer may set and demodulate signals based on the DCN-band channel. During these operations, the CPU may output a control signal corresponding to the present mode, and the path of SP3T of a similar switch may be set as corresponding to the output (a kind of feedback control). 
   In the case of GPS, a slightly different approach may be taken. Up to this point, the terminal may not find a GPS signal at any time. It may, however, receive the signal through the GPS path only in the following two cases. In the first case, GPS information is required from the base station to the terminal during the telephone call. In the second case, the user requires the GPS information (for example, when the user dials 911 in the U.S.A.). In this case, the telephone call is connected with the base station first, and the base station requires the GPS information to the terminal. 
   Consequently, the CPU changes the mode according to its own information, or according to the request of the base station. And, since the CPU recognizes the present mode and the mode which will be changed, the CPU outputs the band-selecting signal corresponding to the modes and the switches such as the SP3T receive the signal to set the path. 
   As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.

Technology Classification (CPC): 7