Abstract:
A module for receiving a function circuit and a method of manufacturing such module. In one embodiment, the module includes: (1) an input surface acoustic wave (SAW) circuit, located within the module and couplable to an input of the function circuit, that conditions an input signal provided to the function circuit and (2) an output SAW circuit, located within the module and couplable to an output of the function circuit, that conditions an output signal produced by the function circuit.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention is directed, in general, to surface acoustic wave circuits and, more specifically, to a module having integral surface acoustic wave circuits and method of manufacturing the same.  
         BACKGROUND OF THE INVENTION  
         [0002]    Surface acoustic wave (SAW) devices for use in electronic signal processing have been advantageously adopted by the electronics industry. Such SAW devices have several advantages over more conventional technologies. They can be designed to provide complex signal processing in a single unit, and they also offer an additional benefit from their ability to be mass produced using semiconductor microfabrication techniques. These techniques lead to low cost devices having only small operating characteristic variations from unit to unit. Since SAW devices may be implemented in small, rugged, light-weight and power-efficient modules, they find many important applications especially in mobile, wireless and spaceborne communication systems. Such communication systems typically operate over a wide range of frequencies from about 10 megahertz to about two gigahertz. The specific signal processing capabilities and frequency range of SAW devices may be determined to allow SAW devices to perform several roles in electronic systems.  
           [0003]    An important feature of the SAW device is its geometry, which incorporates two metal patterns having interdigitated conductive lines or traces. Such interdigitated metal structures are formed on a piezoelectric substrate and act as input and output signal paths when an AC signal voltage is applied to one of the metal structures. This AC voltage induces a surface acoustic wave in the underlying substrate wherein the acoustic wave propagates to the output structure. The interdigitated metal lines of the signal receiving portion detects the acoustic wave and converts it into a filtered electrical output signal. SAW devices, operating in the Rayleigh wave mode, can generally be designed to provide bandpass filters that achieve responses that would otherwise require several hundred inductors and capacitors in conventional LC filter designs.  
           [0004]    This characteristic of SAW devices and their ability to be used in other circuit component applications, such as impedance matching devices, make them attractive to circuit designers. Unfortunately, the design and construction of a SAW device is not a commonly understood process, but rather requires extensive specialized knowledge, experience and manufacturing capability to be successful. Even the successful incorporation of an existing SAW device, such as a filter, into a design situation involving other circuit components makes the use of a SAW device a challenging situation. Proper mounting and placement of the SAW device is critical to its successful operation.  
           [0005]    Accordingly, what is needed in the art is a way to enhance and facilitate the use of SAW devices when combined with additional non-SAW related circuit components.  
         SUMMARY OF THE INVENTION  
         [0006]    To address the above-discussed deficiencies of the prior art, the present invention provides a module for receiving a function circuit and a method of manufacturing such module. In one embodiment, the module includes: (1) an input surface acoustic wave (SAW) circuit, located within the module and couplable to an input of the function circuit, that conditions an input signal provided to the function circuit and (2) an output SAW circuit, located within the module and couplable to an output of the function circuit, that conditions an output signal produced by the function circuit.  
           [0007]    The present invention therefore introduces the broad concept of bounding a function circuit (as that term is broadly defined) by SAW circuits and containing the SAW and function circuits within a single module. The SAW circuits improve the characteristics of the function circuit by conditioning the signals going into and coming out of the function circuit. Modularity allows the SAW and function circuits to be employed in various applications as though they are a single component.  
           [0008]    In one embodiment of the present invention, the function circuit is selected from the group consisting of: (1) a power amplifier, (2) a low-noise amplifier, (3) an intermediate frequency amplifier and (4) a voltage-controlled oscillator. Those skilled in the pertinent art will understand, however, that any circuit that accepts and produces signals may find advantageous use within the module of the present invention.  
           [0009]    In one embodiment of the present invention, the output SAW circuit impedance-matches the output signal produced by the function circuit. Of course, the output SAW circuit may perform any filtering or conditioning role.  
           [0010]    In one embodiment of the present invention, the module further includes a common base that supports the input and output SAW circuits and the function circuit. In one embodiment to be illustrated and described, the common base includes ceramic. However, the common base may include silicon, a piezoelectric material, or any other suitable material for providing mechanical support, a substrate for formation of integrated circuitry, or both.  
           [0011]    In one embodiment of the present invention, the module further includes a hermetic enclosure that surrounds the input and output SAW circuits and the function circuit. The hermetic enclosure advantageously isolates the SAW circuits from environmental contaminants and damage that would harm their operation.  
           [0012]    In one embodiment of the present invention, the input and output SAW circuits are located on a common piezoelectric substrate. In a more specific embodiment of the present invention, a crosstalk shield is located between the input and output SAW circuits. Of course, the input and output SAW circuits may be located on separate piezoelectric substrates.  
           [0013]    The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 illustrates a block diagram of a module constructed according to the principles of the present invention;  
         [0016]    [0016]FIG. 2 illustrates a diagram of an embodiment of a module constructed according to the principles of the present invention; and  
         [0017]    [0017]FIG. 3 illustrates a sectioned view of a circuit module showing an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0018]    Referring initially to FIG. 1, illustrated is a block diagram of a module  100  constructed according to the principles of the present invention. The module  100  includes an enclosure  105 , a function circuit  110 , an input SAW circuit  115  and an output SAW circuit  120 . The enclosure  105  is hermetic and surrounds the input and output SAW circuits  115 ,  120  and the function circuit  110 .  
         [0019]    In the illustrated embodiment, the input SAW circuit  115  is coupled between a module input  106  having a module input signal INPUT of the module  100  and an input  107  of the function circuit  110 . The input SAW circuit  115  conditions the module input signal INPUT to provide a filtered form of the module input signal INPUT as an input signal Fin to the function circuit  110 . The output SAW circuit  120  is similarly coupled between an output  108  of the function circuit  110  and a module output  109  having a module output signal OUPUT. The output SAW  120  conditions by impedance-matching an output signal Fout of the function circuit  110  to the requirements of the module output signal OUTPUT. Alternatively, the input and output SAW circuits  115 ,  120  may reverse their conditioning roles, may both provide a filtering form of conditioning or may both provide an impedance-matching form of conditioning.  
         [0020]    The function circuit  110  is a power amplifier, in the illustrated embodiment. However, in alternative embodiments, the function circuit  110  may also be a low-noise amplifier, an intermediate frequency amplifier, a voltage-controlled oscillator or any other such circuit that would appropriately benefit from placement between the input and output SAW circuits  115 ,  120 .  
         [0021]    Turning now to FIG. 2, illustrated is a diagram of an embodiment of a module  200  constructed according to the principles of the present invention. The module  200  includes a hermetic enclosure  205  having a module input  206  and a module output  207 , a SAW assembly  210 , a common base  220  and a function circuit  225 . The SAW assembly  210  includes a common piezoelectric substrate  215 , an input SAW circuit  216 , an output SAW circuit  217  and a crosstalk shield  218 .  
         [0022]    In the illustrated embodiment of the present invention, the module  200  provides for receiving the function circuit  225 . The input SAW circuit  216  is coupled to the function circuit  225  and conditions an input signal Fin provided to the function circuit  225 . The output SAW circuit  217  is also coupled to the function circuit  225  and conditions an output signal Fout produced by the function circuit  225 . The input SAW circuit  216  is a bandpass filter in this embodiment, and the output SAW circuit  217  is an impedance-matching network that converts the output impedance of the function circuit  225  to a module output impedance required by the module  200 .  
         [0023]    The SAW assembly  210  and the function circuit  225 , which is a low-noise amplifier in the illustrated embodiment, may be positioned on the common base  220  as shown in FIG. 2. The common base  220  contains electrical contacts, generally designated  230 A-D, that provide interconnection paths from a module input signal INPUT that traverses through the various identified circuits of the module  200  to emerge as a module output signal OUTPUT.  
         [0024]    As illustrated in FIG. 2, the input SAW circuit  216  and the output SAW circuit  217  share the common piezoelectric substrate  215 . In this embodiment, the crosstalk shield  218  provides a signal isolation barrier between the input and output SAW circuits  216 ,  217 . The crosstalk shield  218  prevents signals within each of the input and output SAW circuits  216 ,  217  from interfering with the other since they are in close proximity and share the common piezoelectric substrate  215 .  
         [0025]    As discussed in the embodiment of FIG. 1, the input SAW  216  filters the module input signal INPUT to provide the input signal Fin to the function circuit  225 . The output SAW circuit  217  is similarly coupled between the function circuit  225  and the module output  207  to provide the module output signal OUTPUT. The output SAW circuit  217  conditions by impedance-matching the output signal Fout of the function circuit  225  to the requirements of the module output signal OUTPUT. A collection of modules constructed according to the principles of the present invention may be cascaded, as needed. Alternatively, more than one set of SAW  5  circuits and their associated function circuit may be cascaded within a single hermetic enclosure.  
         [0026]    Turning now to FIG. 3, illustrated is a sectioned view of a circuit module  300  showing an embodiment of the present invention. The module  300  includes a ceramic common base  305  having a module input  326  and a module output  327 , an input SAW circuit  310 , an output SAW circuit  315 , a function circuit  320  and a ceramic top enclosure  335  that provides a hermetic seal  330 . The module  300  illustrates a method of manufacturing an embodiment of a circuit module constructed according to the principles of the present invention.  
         [0027]    First, the ceramic common base  305  is provided. Then, the input SAW circuit and the output SAW circuit  315  are placed on the ceramic common base  305 . In the illustrated embodiment of FIG. 3, input and output SAW circuits  310 ,  315  are formed on separate piezoelectric substrates. In an alternative embodiment, the input and output SAW circuits  310 ,  315  may be formed on a common piezoelectric substrate. Next, the function circuit  320  is placed on the ceramic common base  305  between the input and output SAW circuits  310 ,  315 .  
         [0028]    A first bond wire  325 A is connected between the module input  326  and an input to the input SAW circuit  310 . A second bond wire  325 B is connected between an output of the input SAW circuit  310  and an input of the function circuit  320 . A third bond wire  325 C is connected between an output of the function circuit  320  and an input of the output circuit  315 . A fourth bond wire  325 D is connected between an output of the output SAW circuit  315  and the module output  327 . Finally, the ceramic top enclosure  335  is placed in position on the ceramic common base  305  during appropriate ambient conditions, and the module  300  is hermetically sealed.  
         [0029]    In summary, the present invention introduces the prevailing concept of bounding a function circuit, as that term is broadly defined, by SAW circuits and containing the SAW and function circuits within a single module. The SAW circuits improve the characteristics of the function circuit by conditioning the signals going into and coming out of the function circuit. Modularity allows the SAW and function circuits to be employed in various applications as though they are a single component.  
         [0030]    Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.