Abstract:
Disclosed is a small-size receiver that exhibits high sensitivity when used with a plurality of frequencies or a plurality of radio communication systems. To provide a small-size, high-sensitivity, direct conversion receiver for use with a plurality of frequencies or a plurality of radio communication systems, the present invention has a high-frequency-input signal path for a low-noise amplifier optimized for use with various frequencies or radio communication systems. The high-frequency-input signal path includes at least one band-pass filter and its input and output matching circuits. A low-loss switching means is used to connect an optimum high-frequency-input signal path to the low-noise amplifier in accordance with a selected operation mode.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a receiver for use at a mobile terminal, and more particularly to a receiver that is capable of receiving a plurality of communications complying with different radio communication specifications.  
           [0003]    2. Description of Related Art  
           [0004]    One example of a conventional receiver is disclosed by EP1098449 and will now be described with reference to FIG. 11, which illustrates a typical example of a conventional receiver. The receiver shown in the figure is a direct conversion receiver that is capable of receiving communications complying with different radio communication specifications. The reference numerals  100  and  101  indicate band-pass filters (hereinafter referred to as the BPFs), which allow signals within a desired frequency band to pass and attenuate spurious signals. The reference numerals  102  and  103  indicate low-noise amplifiers (hereinafter referred to as the LNAs) Components  100  and  102  are used to receive signals within frequency band  1 . Components  101  and  103  are used to receive signals within frequency band  2 . The reference numeral  104  indicates a selector switch for connecting the output of component  102  or  103  to the inputs of frequency conversion mixers  105 ,  106  (hereinafter referred to as the MIXes) at the next stage in accordance with the operating frequency band. This selector switch is electronically implemented by a transistor or diode. The input signals to components  105  and  106  are mixed respectively with local signals Lo and LoB, which have the same frequency as the input signals, in order to output a baseband signal. Local signals Lo and LoB have the same frequency but are 90 degrees out of phase with each other. These local signals are generated by a 90-degree phase shifter  109  and a local signal generator  110 . Output signals  105  and  106  pass through low-pass filters (hereinafter referred to as the LPFs)  107 ,  108  respectively for spurious signal attenuation purposes. As a result, baseband I/Q signals are generated. The LPFs  107 ,  108  are capable of varying their characteristics so as to comply with the radio communication specification for the currently received communication.  
           [0005]    In an embodiment disclosed by EP1098449, the number of LNAs must be equal to the number of operating frequency bands because the selector switch is positioned between the LNAs and MIXes. Therefore, the area of the receiver is increased. Further, the receiver&#39;s sensitivity is degraded due to an increase in the number of operating frequency bands. These problems will now be described with reference to FIGS. 12 and 13.  
           [0006]    [0006]FIG. 12 is prepared by the inventor of EP1098449 with reference to FIG. 11 to describe the configuration in which the number of operating frequency bands is increased. It is presumed that the circuitry enclosed by broken line  114  is integrated into a single IC. The LNAs are generally positioned close to the IC&#39;s LNA pin in order to avoid performance degradation due to parasitic components. It is therefore difficult to arrange a plurality of LNAs so as to encircle a MIX. Consequently, an increase in the number of operating frequency bands causes an increase in the LNA-to-MIX interconnection distance. When the direct conversion method is employed, no image signal exists in principle. It is therefore common that the LNAs and MIXes are directly interconnected without inserting an image attenuation filter in between. As a result, the signal level lowers due to the interconnection&#39;s parasitic capacitance  113 , thereby degrading the receiver&#39;s sensitivity.  
           [0007]    [0007]FIG. 13 is prepared by the inventor of EP1098449 to describe the configuration for solving the problem of sensitivity degradation encountered in the configuration shown in FIG. 12. Since sensitivity degradation is caused by the parasitic capacitance of the LNA-to-MIX interconnection, it can be avoided by using MIXes  115  and  116  for frequency band  3 , optimizing the layout of LNA  112 , MIX  115 , and MIX  116 , and minimizing the length of interconnection among LNA  112 , MIX  115 , and MIX  116 . However, this solution uses a larger number of MIXes than in the configuration shown in FIG. 10, thereby causing an additional increase in the area of the receiver.  
         SUMMARY OF THE INVENTION  
         [0008]    It is therefore an object of the present invention to solve the above-mentioned problems and provide a small-size, high-sensitivity receiver for use with a plurality of frequencies or a plurality of radio communication systems.  
           [0009]    To provide a small-size, high-sensitivity, direct conversion receiver for use with a plurality of frequencies or a plurality of radio communication systems, the present invention has a high-frequency-input signal path for a low-noise amplifier or other amplifier optimized for use with various frequencies or radio communication systems.  
           [0010]    The high-frequency-input signal path includes at least one band-pass filter and its input and output matching circuits. A low-loss switching means is used to connect an optimum high-frequency-input signal path to the low-noise amplifier in accordance with a selected operation mode.  
           [0011]    More specifically, the receiver of the present invention uses a micromechanical switch (MEMS) as the switching means. The micromechanical switch is a mechanical switch that is produced by a method similar to that for semiconductor integrated circuit production. In other words, this micromechanical switch is produced by repeating an insulation film/conductive film accumulation process, associated photolithographic process, and chemical/physical etching process on the entire substrate. The dimensions of the micromechanical switch are several micrometers to hundreds of micrometers in the in-plane direction of the prepared substrate and less than one micrometer to tens of micrometers in the perpendicular direction of the substrate. Various drive methods are applicable to the micromechanical switch, including the use of an electrostatic drive, a magnetic drive, a piezoelectric drive by a piezo element, or a drive provided by a bimetal consisting of a heating element and a plurality of metals having different rates of thermal expansion. As described above, the micromechanical switch differs from common relays and mechanical switches mainly in preparation method, dimensions, and energy required for drive.  
           [0012]    Further, the receiver of the present invention is designed so that the characteristic of at least one of low-noise amplifiers, mixers, and low-frequency filters, which are contained in the receiver, is variable in accordance with the radio communication system from which communications are received. Therefore, the optimum reception characteristics result without regard to the radio communication system from which communications are received.  
           [0013]    More specifically, a high-frequency input path and a switching means are mounted in a single module, and a low-noise amplifier and a circuit forming a receiver connected to the output of the low-noise amplifier are implemented by a single IC.  
           [0014]    Alternatively, the high-frequency input path, the switching means, and the above IC may be mounted in a single module.  
           [0015]    To handle a plurality of frequencies or a plurality of radio communication systems, the radio communication terminal of the present invention uses one of the receivers described above, and uses; for transmissions purposes, a transmitter supporting a plurality of frequencies or a plurality of radio communication systems, and a power amplifier connected to the output of the transmitter. The connection among an antenna, receiver, and power amplifier is made via a front-end block. The front-end block operates so as to establish an appropriate connection according to a selected operation mode. The operation of the radio communication terminal is controlled by a baseband signal processing block. The baseband signal processing block outputs a baseband signal to the transmitter and inputs the receiver&#39;s output signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a block diagram illustrating a first embodiment;  
         [0017]    [0017]FIG. 2 is a Smith chart illustrating the input impedance of a LNA;  
         [0018]    [0018]FIG. 3 illustrates the LNA input impedance that prevails when the input of a LNA is adjusted to match the E-GSM band;  
         [0019]    [0019]FIG. 4 is a block diagram that illustrates how the receiver is configured when wide-band matching is applied for LNA input matching purposes;  
         [0020]    [0020]FIG. 5 is a cross-sectional view of a second embodiment;  
         [0021]    [0021]FIG. 6 is a cross-sectional view of a third embodiment;  
         [0022]    [0022]FIG. 7 is a block diagram illustrating a fourth embodiment;  
         [0023]    [0023]FIG. 8 is a block diagram illustrating a fifth embodiment;  
         [0024]    [0024]FIG. 9 is a block diagram illustrating a sixth embodiment;  
         [0025]    [0025]FIG. 10 is a block diagram illustrating a seventh embodiment;  
         [0026]    [0026]FIG. 11 is a block diagram illustrating a conventional receiver;  
         [0027]    [0027]FIG. 12 is a block diagram illustrating a conventional receiver that is extended to cover three bands; and  
         [0028]    [0028]FIG. 13 is a block diagram illustrating a conventional receiver that is extended to cover three bands. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The receiver for handling a plurality of frequencies or a plurality of systems according to preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0030]    Embodiment 1  
         [0031]    First of all, the configuration of the receiver according to the present invention will be described with reference to FIGS.  1  to  4 .  
         [0032]    [0032]FIG. 1 illustrates the configuration of a first embodiment of the present invention.  
         [0033]    [0033]FIG. 2 is a Smith chart illustrating the input impedance of a common LNA.  
         [0034]    [0034]FIG. 3 shows an example in which a matching circuit is connected to the input of the above LNA so as to match the E-GSM (Extended Global System for Mobile communications 900) whose receive frequency band ranges from 925 to 960 MHz.  
         [0035]    The two-band receiver of the present invention covers two cellular phone bands that are used in Europe: E-GSM (band: 925 to 960 MHz) and DCS 1800 (Digital Cellular System 1800; band: 1710 to 1785 MHz).  
         [0036]    In FIG. 1, the reference numerals  200  and  201  indicate respective input matching circuits for components  100  and  101 . The reference numerals  202  and  203  indicate respective output matching circuits for components  100  and  101 . The reference numeral  104  indicates a micromechanical switch (hereinafter referred to as the MEMS) for connecting either matching circuit  202  or matching circuit  203  to the LNA  204 . The MEMS is a switch that is produced by a method similar to that for semiconductor integrated circuit production. More specifically, the MEMS is produced by repeating an insulation film/conductive film accumulation process, associated photolithographic process, and chemical/physical etching process on the entire substrate. The dimensions of the MEMS are several micrometers to hundreds of micrometers in the in-plane direction of the prepared substrate and less than one micrometer to tens of micrometers in the perpendicular direction of the substrate. Various drive methods are applicable to the MEMS, including the use of an electrostatic drive, a magnetic drive, a piezoelectric drive by a piezo element, or a drive provided by a bimetal consisting of a heating element and a plurality of metals having different rates of thermal expansion. As described above, the MEMS differs from common relays and mechanical switches mainly in preparation method, dimensions, and energy required for drive. Further, the MEMS is characterized by the fact that its insertion loss is approximately 0.1 dB, which is lower than that of an electronic switch based on a PIN diode or FET. The MEMS is also at an advantage in that it can provide a switch having one input and a plurality of outputs or a plurality of inputs and one output while minimizing the loss.  
         [0037]    MNs  202  and  203  are optimized respectively for the E-GSM and DCS 1800 bands. FIG. 3 indicates that when an optimized matching circuit is used for the E-GSM band, the matching constant is not optimized for the DCS 1800 band. The reason is that the matching circuit is narrow-banded in order to optimize the performance of component  204  (in terms of gain and noise).  
         [0038]    [0038]FIG. 4 illustrates an exemplary modification of the present invention, which was found in an invention process. If one matching circuit, that is, a wide-band matching circuit  207 , is used, as shown in FIG. 4, to provide matching for both the E-GSM and DCS 1800 bands, the performance of the low-noise amplifier  204  degrades, thereby lowering the receiver&#39;s sensitivity for the aforementioned reason.  
         [0039]    The circuitry contained in the IC  206  is implemented by a semiconductor integrated circuit so that a single IC is produced. The circuitry contained in module  205  is implemented as a module that is separate from the IC  206 , because band-pass filters  100  and  101  and MEMS  104  need to be hermetically sealed.  
         [0040]    The operation of the receiver will now be described with reference to FIG. 1.  
         [0041]    While the receiver is in a mode for E-GSM signal reception, a received signal is entered into matching circuit  200 . Matching circuit  200  provides matching between the input of band-pass filter  100  and the antenna connected to the front of matching circuit  200 . Band-pass filter  100  allows 925 MHz to 960 MHz signals to pass and suppresses the signals within the other frequency bands as desired. A SAW filter or dielectric filter is used as band-pass filter  100 . The MEMS  104  is controlled so as to connect matching circuit  202  and low-noise amplifier  204  only. The output signal generated by matching circuit  202  is delivered to the low-noise amplifier  204  via the MEMS  104 . The circuitry contained in the IC  206  is a direct conversion receiver, which performs the same operation as the aforementioned conventional example to output baseband I/Q signals as the input signals for the low-noise amplifier  204 .  
         [0042]    While the receiver is in a mode for DCS 1800 signal reception, a received signal is entered into matching circuit  201 . The baseband I/Q signals are then output by performing the same operation as in the E-GSM signal mode. However, the MEMS  104  is controlled so as to connect matching circuit  203  and low-noise amplifier  204  only.  
         [0043]    Therefore, the present embodiment reduces the number of LNAs required for a plurality of frequency bands to one although a plurality of LNAs are required in situations where a switch is provided between a LNA and MIX. Further, since only one LNA is used, receiver sensitivity degradation will not possibly take place although it could occur if the length of the LNA-to-MIX interconnection increases.  
         [0044]    Embodiment 2  
         [0045]    [0045]FIG. 5 is a cross-sectional view of a module  205  according to a second embodiment. A glass ceramic multilayer substrate  600  comprises four dielectric layers  605 - 1 ,  605 - 2 ,  605 - 3 ,  605 - 4 , intervening layers, and front and rear conductive layers  607 . In the embodiment shown in FIG. 5, a SAW filter  601  is used as the BPF. The SAW filter  601  is equivalent to filter  100 / 101  and capable of handling two bands. The SAW filer  601  and MEMS  104  are positioned within grooves in part of dielectric layers  605 - 3  and  605 - 4  and hermetically sealed by installing a metal cover  603  over the underside. Each component is secured to conductor  607 - 2  on the glass ceramic multilayer substrate  600  with conductive adhesives  608 - 1 ,  608 - 2 . The electrical terminals on the SAW filter  601  and MEMS  104  are electrically connected to the multilayer substrate by bonding wires  610 . Particularly, the ground terminals for the bonding wires  610  and MEMS  104  are electrically connected to conductor  607 - 2  on the back surfaces of the components.  
         [0046]    The input/output sections of the bonding wires  610  are connected to a matching circuit. The matching circuit comprises chip components  606 , which are soldered to the uppermost layer of the glass ceramic multilayer substrate  600 , and an inductor, capacitor, and path, which are positioned within the glass ceramic multilayer substrate  600  as internal layers.  
         [0047]    In the embodiment shown in FIG. 5, the chip components  606  are mounted on the front surface of the glass ceramic multilayer substrate  600 , and a metal cap  604  is installed as an electromagnetic shield.  
         [0048]    Embodiment 3  
         [0049]    [0049]FIG. 6 is a cross-sectional view of a metal-bump-based module  205  according to a third embodiment.  
         [0050]    The input and output terminals on the SAW filter  601  are connected to conductors  701 - 1  and  701 - 3  on the ceramic substrate via metal bumps  700 - 1  and  700 - 3 . The SAW filter&#39;s ground terminal is connected to conductor  701 - 2  on the ceramic substrate via metal bump  700 - 2 . Conductor  701 - 2  is connected to backside conductor  607 - 3  on the ceramic substrate via the ceramic substrate&#39;s internal layer interconnection.  
         [0051]    The input and output terminals on the MEMS  104  are connected to conductors  701 - 4  and  701 - 6  on the ceramic substrate via metal bumps  700 - 4  and  700 - 6 . The ground terminal on the MEMS  104  is connected to conductor  701 - 5  on the ceramic substrate via metal bump  700 - 5 . Conductor  701 - 5  is connected to backside conductor  607 - 3  on the ceramic substrate via the ceramic substrate&#39;s internal layer interconnection.  
         [0052]    Embodiment 4  
         [0053]    A fourth embodiment of the present invention will now be described with reference to FIG. 7. The present embodiment furnishes the receiver according to the first embodiment shown in FIG. 1 with an additional capability of handling the 1.9 GHz band of PCS 1900 (Personal Communication System 1900; band: 1930 to 1990 MHz) by adding matching circuits  210 ,  212  and a BPF  211 . In the present embodiment, the MEMS  104  is also replaced with a 3-input, 1-output MEMS  213 .  
         [0054]    Embodiment 5  
         [0055]    A fifth embodiment of the present invention will now be described with reference to FIG. 8. In the receiver according to the present embodiment, a variable-characteristic LNA  300  and variable-characteristic MIXes  301 ,  302  are used in replacement of the counterparts  204 ,  105 ,  106  of the first embodiment shown in FIG. 1. Components  300 ,  301 , and  302  are designed so that their characteristics vary as needed to match the radio communication system from which the receiver receives communications. The term “characteristics” as used herein means gain, dynamic range, noise characteristic, and current consumption.  
         [0056]    Embodiment 6  
         [0057]    A sixth embodiment of the present invention will now be described with reference to FIG. 9. In the receiver according to the present embodiment, modules  205  and  206  of the first embodiment shown in FIG. 1 are replaced by a single module  400 . When the embodiment shown in FIG. 1 is adopted, a cellular terminal manufacturer generally purchases modules  205  and  206  and develops a cellular terminal with them. In such a situation, the matching constants of matching circuits  202  and  203  vary with the characteristics of a transmission line between modules  205  and  206 . Therefore, the terminal manufacturer must formulate a design so as to provide optimum transmission line characteristics for the matching constants of matching circuits  202  and  203 . In the present embodiment, however, the module manufacturer producing module  400  designs matching circuits  202  and  203  and transmission line. Therefore, the design can easily be accomplished. Further, the terminal manufacturer purchases an optimally designed module  400 . As a result, terminal development will easily be achieved.  
         [0058]    Embodiment 7  
         [0059]    A seventh embodiment of the present invention will now be described with reference to FIG. 10. FIG. 10 illustrates the configuration of a cellular terminal that handles the E-GSM and DCS 1800 bands. The cellular terminal comprises an antenna  504 , modules  400 ,  501 , and a baseband signal processing block  502 . Module  400  is obtained by adding a front-end block  503  and a transmitter  507  to the module shown in FIG. 9. A receiver  206  and the transmitter  507  are both built in the same IC. The front-end block  503  establishes an appropriate connection among components  504 ,  200 ,  201 , and  501  depending on whether the cellular terminal is transmitting or receiving and the radio communication system is of an E-GSM type or DCS 1800 type. The baseband signal processing block  502  performs a demodulation, error correction, or other appropriate signal process on the signal output from the receiver  206  to obtain a desired voice signal or data signal, modulates the signal to a voice signal or data signal for a transmission from the antenna, performs an error correction or other appropriate signal process on the modulated signal, and enters the processed signal to the transmitter  507 . The signal used between the baseband signal processing block  502  and module  400  is in an analog I/Q signal form. However, this is merely an exemplary form. For example, the digital I/Q signal form is also applicable. The operation of the cellular terminal is controlled by control signals  505 ,  506 , which are output from the baseband signal processing block  502 . The transmitter  507  performs a frequency conversion, gain addition, spurious signal elimination, or other desired process on the signal entered from the baseband signal processing block  502 , and outputs the processed signal to a PA module  501 . The PA module adds desired gain to the output signal from the transmitter  507  and outputs the resulting signal to the front-end block  503 .  
         [0060]    The scopes of circuit integration and modularization for the configuration shown in FIG. 10 are merely cited as examples. Various other scopes of circuit integration and modularization are also applicable.  
         [0061]    In the foregoing embodiments, a two-band receiver covering both the E-GSM and DCS 1800 bands is mainly described. However, it goes without saying that some other two-band receivers, such as a receiver covering a combination of the E-GSM and W-CDMA (1995 MHz to 2180 MHz) bands, three-band receivers covering the E-GSM, DCS 1800, and W-CDMA bands, and receivers covering four or more bands can also be implemented by applying the same extension method as described above.  
         [0062]    The receiver according to the present invention is at an advantage in that it can be downsized because the LNAs and mixers used for a receiver handling a plurality of radio communication systems can be integrated into a single whole.