JPH0119462Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a ladder-shaped ceramic filter used in intermediate frequency filters for in-vehicle/portable radios, pagers, car telephones, etc.

A conventional ladder-shaped ceramic filter is shown in FIGS. 1 and 2. In this method, a plurality of piezoelectric ceramic resonators are prepared, and series resonators (hereinafter referred to as S elements) 1 and parallel resonators (hereinafter referred to as P elements) 2 are arranged alternately. 1,
2 are held between electrode plates 3 having protrusions, insulating plates 4 are placed at appropriate locations, and these are housed in a case 5.

Here, the skirt ratio of the ladder-shaped ceramic filter is determined by the capacitance ratio of the S element 1 and the P element 2, and the mechanical Q of each resonator. That is, the closer the capacitance of the S element 1 is to the capacitance of the P element 2, and the higher the mechanical Q, the higher the skirt ratio can be obtained. However, when the capacitance ratio is reduced, the guaranteed attenuation decreases,
In order to satisfy this requirement, it is only possible to increase the number of circuit stages in the basic L section, which is inappropriate because it increases the number of elements used and increases the size of the product. Furthermore, since the mechanical Q is a characteristic of the material used, it is impossible to adjust it, and the development of new materials with a high Q requires a great deal of time and cost.

The present invention increases the skirt ratio (measured at frequencies higher than the resonance frequency F ₀ ) of the ladder-shaped ceramic filter.
The purpose is to improve filtering characteristics.

Hereinafter, one embodiment of the ladder-shaped ceramic filter of the present invention will be described with reference to FIGS. 3 to 5, with the same numbers assigned to the same parts as above. As shown in Fig. 3, the resonant frequency of the S elements 7 (hereinafter referred to as S ₂ elements) other than the first S element 6 (hereinafter referred to as S ₁ element) on the input and output sides is approximately 1 KHz higher than the above-mentioned S ₁ element. This is a ladder-shaped ceramic filter in which the P elements 2 are connected in series and the P elements 2 are connected in parallel with them.

As shown in FIG. 4, when the resonance frequencies of the frequency characteristics A and B of the S ₁ element 6 and the S ₂ element 7 are the same, the attenuation point D of the filtering characteristic C on the higher frequency side than F ₀ is approximately the same as that of the S ₁ element 6. Since it is determined by ΔfE of _S2 element 7, ΔfG of S2 element 7 is irrelevant. Therefore, even if Δf of the S ₂ element 7 increases, it does not affect the stop band of the filtering characteristic C. In other words, even if the resonant frequency of the S ₂ element 7 increases, the stop band does not change. Passband (generally -
6 dB band) increases when either the resonant frequency of the S ₂ element 7 or the resonant frequency of the S ₁ element 6 deviates higher than F ₀ . Therefore, as in the above embodiment, the S ₂ element 7
By making the resonant frequency of the _S1 element higher than that of the S1 element 6, the skirt ratio can be increased as shown by the filtering characteristic C' in FIG.

With the ladder-shaped ceramic filter of the present invention, the skirt ratio can be increased by 10% without increasing the number of elements used.

[Brief explanation of the drawing]

1 and 2 are a wiring diagram and a sectional view showing a conventional ladder-shaped ceramic filter, FIG. 3 is a wiring diagram showing an embodiment of the ladder-shaped ceramic filter according to the present invention, and FIG. 4 is a wiring diagram showing an embodiment of the ladder-shaped ceramic filter according to the present invention. For purposes of explanation, Figure 5 is a filtering characteristic diagram of a ceramic filter when the resonant frequencies of the _S1 element and the _S2 element are the same.
FIG _{. 3 is a filtering characteristic diagram of a ceramic filter in which the resonant frequency of the S 2} element is higher than that of the S ₁ element. 1, 6, 7... piezoelectric ceramic resonator (series resonator),
2... Piezoelectric ceramic resonator (parallel resonator), 3... Electrode plate, 4... Insulating plate, 5... Case.

Claims (1)

[Scope of utility model registration request] piezoelectric ceramic resonators arranged in series that are connected in series;
Piezoelectric ceramic resonators arranged in parallel and connected in parallel are arranged and housed in a case with electrode plates having protrusions that alternately sandwich them and insulating plates arranged at appropriate locations, and of the piezoelectric ceramic resonators arranged in series, the resonant frequency of the other series resonators other than both ends is set higher than the resonant frequency of the two series resonators arranged at both ends of the input and output sides. Ceramic filter.