JPS5941624Y2 - surface wave filter - Google Patents

Description

[Detailed Description of the Invention] The present invention aims to provide a surface wave filter whose input and output impedances can be adjusted.

It is empirically known that the input/output impedance of a surface acoustic wave filter varies by 10% or more due to variations in the comb spacing of the comb-shaped electrodes, the width of the combs, and the characteristics of the material that excites and propagates the surface wave.

Therefore, when implementing a surface wave filter in a circuit, an adjustable trimmer capacitor or variable coil must be installed to absorb variations in input/output impedance, which increases the cost of the entire device and increases the number of installation steps. There are drawbacks to doing so.

Therefore, the present invention takes the above points into consideration and attempts to provide a surface wave filter whose input and output impedances can be adjusted.Examples of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, a metal film such as aluminum or gold is provided on a substrate 1 made of glass or the like capable of propagating surface waves by means such as vacuum evaporation, and this metal film is then photoetched. The comb-shaped electrodes 2, 3, the full-surface electrodes 4, 5, and the connecting portions 14, 15 for connecting the two are provided by molding.

On the substrate 1 on which these 2, 3, 4, 5, 14, and 15 are provided, zinc oxide is sputtered to a predetermined thickness by sputter deposition to form a zinc oxide layer 6.

On this zinc oxide layer 6, there are full-surface electrodes 7, 8 which are opposite to the comb-shaped electrodes 2, 3 and determine the characteristics of the filter, and at least one electrode 9 is arranged opposite to the whole-surface electrodes 4, 5, respectively.
e y 9 f t 9 g p 9 h t 91
tloj, 10k, 101.10m are provided.

Connect each electrode with a terminal a t b e Cp d p
l*rn is provided in e p f jg p11*1tJ .

A circuit diagram of this surface wave filter is shown in FIG.

Terminals a and c are signal input terminals, d and b are signal output terminals, C1p C2p C3p C4, C5, C15yC
7, C8, C9, ci, and co are capacitances formed between the electrodes.

Input impedance can be adjusted by selectively connecting terminal C and terminal e=i, and output impedance can be adjusted by selectively connecting terminal d and terminal j=m.

1 and 12 are resin absorbers provided to absorb unnecessary surface waves.

The comb-shaped electrodes 2 and 3, the full-surface electrodes 4 and 5, the full-surface electrode 1°8, and the electrodes 9e to 9i and 10j to 10m can be made in the same process as in the prior art, and the manufacturing process is not particularly complicated.

As described above, according to the present invention, it is possible to obtain a surface wave filter whose input and output impedances can be adjusted.

[Brief explanation of the drawing]

Fig. 1 is a Shinjo side view of a surface wave filter according to an embodiment of the present invention, Fig. 2 is a partially cutaway perspective view of the same surface wave filter,
FIG. 3 is a circuit diagram of the same surface wave filter. 1...Substrate, 2, 3...Comb-shaped electrode, 4
, 5...Full surface electrode, 6...Zinc oxide layer, 7,8...Full surface electrode, 9e~9i, 10j~
10m... Electrode.

Claims (1)

[Scope of utility model registration request] At least a pair of comb-shaped electrodes and a full-surface electrode connected thereto are formed on a substrate capable of propagating surface waves, and a zinc oxide layer is formed on the substrate provided with these electrodes. A surface wave filter, comprising: an electrode for determining frequency characteristics provided on the zinc oxide layer and facing the comb-shaped electrode; and one or more electrodes formed on the zinc oxide layer facing the entire surface electrode.