Elliptical surface acoustic wave filter

A surface acoustic wave and filter technology, applied in the field of filters, can solve the problems of limitation, deterioration of out-of-band suppression, and reduction of filter bandwidth, etc., to achieve the effect of increasing out-of-band suppression

Active Publication Date: 2020-04-17
天通瑞宏科技有限公司
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

image 3 The frequency response of the filter structure shown is Figure 4 As shown, it can be seen from the figure that this method reduces the width of the filter bandwidth is limited, and as the bandwidth is reduced, the out-of-band rejection is severely deteriorated

Method used

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Embodiment Construction

[0030] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention will be described below in conjunction with specific examples, but this should not be construed as a limitation of this patent.

[0031] The elliptic filter, also known as the Cauer filter, is a filter with ripples in the passband and stopband. Compared with other types of filters, elliptic filters have the smallest passband and stopband fluctuations under the condition of the same order. It has the same fluctuation in the passband and stopband, which is different from the Butterworth filter which is flat in the passband and stopband, and the passband is flat, the stopband is rippled or the stopband is flat, the passband is rippled Chebyshev filter.

[0032] The low-pass prototype transfer function of the elliptic filter is,

[0033]

[0034] where R n is the nth-order Jacobian elliptic function, ω o...

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Abstract

The invention discloses an elliptical surface acoustic wave filter. The elliptic surface acoustic wave filter comprises at least four resonance units, a first resonance unit and a second resonance unit are connected in series, and a third resonance unit and a fourth resonance unit are connected in parallel between a reference potential point and a series point of the first resonance unit and the second resonance unit; the resonant frequencies of the third resonant unit and the fourth resonant unit are different; the circuit structures of the four (first to fourth) resonance units are the same;a circuit structure formed by all the resonance units satisfies a transfer function Gn(omega) of the elliptic filter. According to the elliptic surface acoustic wave filter, any relative filter bandwidth can be realized on a piezoelectric substrate with a high electromechanical coupling coefficient.

Description

technical field [0001] The invention relates to the technical field of filters, in particular to an elliptical surface acoustic wave filter. Background technique [0002] Traditional low-loss surface acoustic wave filters mostly use trapezoidal structures, such as figure 1 As shown, the filter of this ladder structure only includes two kinds of resonators, that is, the series arm resonant unit and the parallel arm resonant unit. Including two kinds of resonators Zs and Zp, first define the resonance frequency and anti-resonance frequency of the series resonator as frs and fap respectively, and the resonance frequency and anti-resonance frequency of the parallel resonator as frp and fap respectively. When fap≈frs, a band-pass filter whose center frequency is fap≈frs can be formed. In addition, the filter has two transmission zero points of f=fas and f=frp, which determine the passband edge of the filter. Its frequency response is as figure 2 As shown, the structure can a...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H03H9/64H03H9/145H03H9/02
CPCH03H9/64H03H9/145H03H9/02535
Inventor 王华磊周一峰廖庆嵩吴长春沈旭铭
Owner 天通瑞宏科技有限公司
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