Simulating effects of temperature on acoustic microwave filters

Abstract

A method of designing an acoustic microwave filter comprises generating a proposed filter circuit design having an acoustic resonant element with a defined admittance value, introducing a lumped capacitive element in parallel and a lumped inductive element in series with the resonant element, selecting a first capacitance value for the capacitive element and a first inductance value for the inductive element, thereby creating a first temperature modeled filter circuit design, simulating the first temperature modeled filter circuit design at a first operating temperature, thereby generating a first frequency response, selecting a second capacitance value for the capacitive element and a second inductance value for the inductive element, thereby creating a second temperature modeled filter circuit design, simulating the second temperature modeled filter circuit design at a second operating temperature, thereby generating a second frequency response, and comparing the first and second frequency responses to the frequency response requirements.

What is claimed is: 
     
         1 . A computerized filter design system for designing a filter circuit design, comprising:
 a user interface configured for receiving circuit parameter values and frequency response requirements from a user and outputting a final filter circuit design to the user;   memory storing a filter design software program; and   a processor configured for executing the filter design software program to (a) generate a proposed filter circuit design having a plurality of circuit elements comprising an acoustic resonant element having an admittance value derived from the circuit parameter values, (b) introduce a lumped capacitive element in parallel and a lumped inductive element in series with the acoustic resonant element, (c) selecting a capacitance value for the lumped capacitive element and an inductance value for the lumped inductive element, thereby creating a temperature modeled filter circuit design that shifts the defined admittance value of the acoustic resonant element to an admittance value, (d) simulating the temperature modeled filter circuit design at an operating temperature, thereby generating a frequency response, (e) comparing the frequency response to the frequency response requirements, and (f) generating the final filter circuit design based on the comparison.   
     
     
         2 . The computerized filter design system of  claim 1 , wherein the frequency response requirements comprise one or more of a frequency dependent return loss, insertion loss, rejection, and linearity. 
     
     
         3 . The computerized filter design system of  claim 1 , wherein the acoustic resonant element is one of a surface acoustic wave (SAW) resonator, a bulk acoustic wave (BAW) resonator, a film bulk acoustic resonator (FBAR), and a microelectromechanical system (MEMS) resonator. 
     
     
         4 . The computerized filter design system of  claim 1 , wherein the frequency response requirement comprises a pass band. 
     
     
         5 . The computerized filter design system of  claim 4 , wherein the passband is in the 500-3500 MHz range. 
     
     
         6 . The computerized filter design system of  claim 4 , wherein the passband is in the 300 MHz to 10.0 GHz range. 
     
     
         7 . The computerized filter design system of  claim 4 , wherein the passband is in the 300 MHz to 300 GHz range. 
     
     
         8 . The computerized filter design system of  claim 1 , wherein the frequency response requirements comprise a passband and a stopband. 
     
     
         9 . The computerized filter design system of  claim 1 , wherein the processor is configured for executing the filter design software program to further model the acoustic resonant element as a Butterworth-Van Dyke (BVD) model. 
     
     
         10 . The computerized filter design system of  claim 1 , wherein the processor is configured for executing the filter design software program to further model the acoustic resonant element with a Coupling of Modes (COM) model. 
     
     
         11 . The computerized filter design system of  claim 1 , wherein the processor is configured for executing the filter design software program to further model the acoustic resonant element with a Finite Element Model (FEM). 
     
     
         12 . The computerized filter design system of  claim 1 , wherein the proposed filter circuit design has an Nth order ladder topology. 
     
     
         13 . The computerized filter design system of  claim 1 , wherein the capacitance value and the inductance value are selected as functions of the operating temperature. 
     
     
         14 . The computerized filter design system of  claim 13 , wherein the capacitance value is selected to be equal to the product of a first scaling factor, the area of the acoustic resonant element of the proposed filter circuit design, and the difference between the operating temperature and a baseline temperature, and the inductance value is selected to be equal to the product of a second scaling factor and the difference between the operating temperature and the baseline temperature. 
     
     
         15 . The computerized filter design system of  claim 1 , wherein the capacitance value is in the range of range of −40 pF-40 pF. 
     
     
         16 . The computerized filter design system of  claim 1 , wherein the capacitance value is in the range of range of −4 pF-4 pF. 
     
     
         17 . The computerized filter design system of  claim 1 , wherein the inductance value is in the range of −10 nH-10 nH. 
     
     
         18 . The computerized filter design system of  claim 1 , wherein the inductance value is in the range of −1 nH-1 nH. 
     
     
         19 . The computerized filter design system of  claim 1 , wherein the processor is configured for executing the filter design software program to generate an initial filter circuit design having the circuit parameter values, and optimizing the initial filter circuit design to create the proposed filter circuit design, wherein the lumped capacitive element and lumped inductive element are introduced into the proposed optimized filter circuit design. 
     
     
         20 . The computerized filter design system of  claim 19 , wherein the filter design software program is divided into a filter design synthesizer, a filter optimizer, and a filter design engine, wherein the processor is configured for executing the filter design synthesizer to generate the initial filter circuit design, for executing the filter optimizer to optimize the initial filter circuit to create the proposed filter circuit design, and simulating the temperature modeled filter circuit design at the operating temperature, thereby generating the frequency response, and for executing the filter design engine to introduce the lumped capacitive element in parallel and the lumped inductive element in series with the acoustic resonant element, selecting the capacitance value for the lumped capacitive element and the inductance value for the lumped inductive element, thereby creating the temperature modeled filter circuit design, comparing the frequency response to the frequency response requirements, and generating the final filter circuit design based on the comparison.