Acoustic surface wave filter module and method of manufacturing the same

Abstract

In order to reduce the parts required for matching of an SAW filter module, the SAW filter module 10 obtains matching for coupling SAW filters 10 A to 10 D with RF-IC 20 using impedance matching circuits 11 A to 11 D. The real part of output impedance Z saw of the SAW filter is closely matched with the real part of input impedance Zic of an RF-IC. The impedance matching circuit modifies the imaginary part of the output impedance Zm of the SAW filter module according to the imaginary part of the input impedance Zic of the RF-IC 20. The impedance matching circuit composed of one piece of inductance or capacitor, or a plurality of inductors or capacitors in parallel connection, ans formed as a print pattern on a module substrate, in which the real part R saw and the real part Ric are in a relation nearly of 0.8 Ric<R saw<1.2 Ric.

1 . A surface acoustic wave filter module, comprising: 
 a surface acoustic wave filter distinguishing received high frequency signals in a radio terminal, and    an impedance matching circuit to obtain impedance matching for coupling the surface acoustic wave filter with the high frequency signal-processing device, wherein    said surface acoustic wave filter is structured so that the real part of the output impedance is matched with the real part of the input impedance of said high frequency signal-processing device; and    said impedance matching circuit connects a matching element to an output port of the surface acoustic wave filter module only in parallel so that the output impedance of said surface acoustic wave filter module and the input impedance of the high frequency signal-processing device are in a complex conjugation relation.    
   
   
       2 . A surface acoustic wave filter module provided with a plurality of systems, said system comprising: 
 a surface acoustic wave filter distinguishing received high frequency signals in a radio terminal, and    an impedance matching circuit to obtain impedance matching for coupling the surface acoustic wave filter with the high frequency signal-processing device, wherein    the surface acoustic wave filter of respective systems has a configuration such that the real part of the output impedance is matched with the real part of the input impedance of said high frequency signal-processing device, and    the impedance matching circuit of respective systems connects a matching element with an output port of the surface acoustic wave filter module only in parallel so that the output impedance of said surface acoustic wave filter module and the input impedance of said high frequency signal-processing device are in a complex conjugation relation.    
   
   
       3 . The surface acoustic wave filter module according to claims  1  or  2 , wherein the real part R saw of the output impedance of said surface acoustic wave filter is made to be 0.8 Ric<R saw<1.2 Ric to the real part Ric of the input impedance of said high frequency signal-processing device.  
   
   
       4 . The surface acoustic wave filter module according to claims  1  or  2 , wherein adjustment of the real part of the output impedance of said surface acoustic wave filter is performed by adjusting at least one of the number of the electrodes, the overlap width, the film thickness of the electrode, and the pitch and shape of the electrode, of IDT and/or reflector.  
   
   
       5 . The surface acoustic wave filter module according to claims  1  or  2 , wherein the matching element of said impedance matching circuit is at least one of the inductor element and the capacitor element.  
   
   
       6 . A method of manufacturing a surface acoustic wave filter module including a surface acoustic wave filter to distinguish received high frequency signals in a radio terminal, and an impedance matching circuit to obtain impedance matching for coupling the surface acoustic wave filter with the high frequency signal-processing device, said method comprising the steps of: 
 obtaining data for the real part and the imaginary part of the input impedance of said high frequency signal-processing device;    forming the surface acoustic wave filter by matching the real part of the output impedance of said surface acoustic wave filter with the real part of the data; and    connecting matching elements to the output ports of the surface acoustic wave filter module only in parallel so that the output impedance of said surface acoustic wave filter module and the input impedance of said high frequency signal-processing device are in a complex conjugation relation.