Passband filter having an asymmetrical filter response
First Claim
1. A filter comprising:
- an array of acoustic resonators which cooperate to establish a target passband of frequencies having a high frequency end and a low frequency end, said acoustic resonators being configured such that said target passband has an insertion loss profile in which a minimum insertion loss is located at least near said high frequency end of said target passband and a maximum insertion loss is located at least near said low frequency end of said target passband, said insertion loss profile within said target passband having a progressive decline from said minimum insertion loss to said maximum Insertion loss, said minimum insertion loss being substantially less than insertion toss at said low frequency end of said target passband.
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Abstract
A filter, such as a transmit filter of a duplexer, includes an array of acoustic resonators that cooperate to establish an asymmetrically shaped filter response over a target frequency passband. The acoustic resonators are preferably film bulk acoustic resonators (FBARs). The filter response defines an insertion loss profile in which a minimum insertion loss within the target passband is located at or near a first end of the frequency passband, while the maximum insertion loss is located at or near the opposite end of the frequency passband. In the transmit filter embodiment, the minimum insertion loss is at or near the high frequency end of the filter response, which is tailored by selectively locating poles and zeros of the array of FBARs.
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Citations
14 Claims
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1. A filter comprising:
an array of acoustic resonators which cooperate to establish a target passband of frequencies having a high frequency end and a low frequency end, said acoustic resonators being configured such that said target passband has an insertion loss profile in which a minimum insertion loss is located at least near said high frequency end of said target passband and a maximum insertion loss is located at least near said low frequency end of said target passband, said insertion loss profile within said target passband having a progressive decline from said minimum insertion loss to said maximum Insertion loss, said minimum insertion loss being substantially less than insertion toss at said low frequency end of said target passband. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A filter comprising:
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a plurality of series FBARs coupled in electrical series, said series FBARs being configured and being cooperative to provide first response characteristics at a first side of a filter response over a selected bandwidth, said first response characteristics including a steep roll-off from a first filter response region of minimum attenuation; and
at least one shunt FBAR connected between adjacent series FBARs to provide second response characteristics at a second side of said filter response over said selected bandwidth, said second response characteristics having a minimum attenuation that is substantially greater than said minimum attenuation of said first filter response region, said filter response thereby being asymmetric about a center frequency of said target bandwidth, wherein attenuation of said first and second sides of said filter response is tailored by selectively adjusting at least one of effective coupling coefficients and impedances of said series and shunt FBARs. - View Dependent Claims (8, 9, 10)
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11. A method of forming a filter comprising:
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fabricating a plurality of FBARs, said FBARs having at least two resonant frequencies; and
interconnecting said FBARs such that said FBARs are cooperative to provide a selected filter response over a passband of interest, said steps of fabricating and interconnecting including;
(a) defining a region of tow attenuation at a first frequency end of said passband of interest and a region of substantially higher attenuation at a second frequency end of said passband of interest; and
(b) establishing said selected filter response within said passband of interest to provide a progressive increase in attenuation from said region of low attenuation at said first frequency end to said region of substantially higher attenuation at said second frequency end. - View Dependent Claims (12, 13, 14)
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Specification