JPS6027217A - Composite type piezo-electric band pass filter - Google Patents

Abstract

PURPOSE:To improve the freedom of design at a filter characteristic by displacing a part of plural multimode/monolithic piezo-electric resonators by a Jaumann circuit using single mode/monolithic piezo-electric resonators. CONSTITUTION:In a band pass filter using double mode resonators Q1, Q2, etc. and having 75MHz center frequency and 57KHz and 29KHz band width respectively, the double mode resonator Q2 can be formed, but the Q1 is reduced at its interval between electrodes and it is difficult to realize the Q1 because of the restriction due to the magnitude of an electricity/machine coupling factor. Therefore, the resonator Q1 which is difficult to realize out of the double mode resonators Q1 and Q2 is displaced by the Jaumann circuit using single mode resonators Q3, Q4. Consequenetly, the freedom in the design of the filter is improved, its attenuation can be sufficiently sectured and its production cost and capacity is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric bandpass filter, and more particularly to a composite piezoelectric bandpass filter that is fully complexed with a multimode piezoelectric resonator and a single mode one.

When all piezoelectric resonators such as crystals are used to construct a bandpass filter, there are two main methods: a method using a combination of single-mode resonators, and a method using a multi-mode resonator and configuring it as a monolithic filter.

When comparing these two methods, the monolithic
Although the filter is superior in terms of price and size, it has the disadvantage that there are large design and manufacturing constraints on the electrode spacing of the multimode resonator, and there is less freedom in the bandwidth of the filter.

The present invention was made in order to eliminate the drawbacks of the conventional monolithic filter using a multi-mode resonator as described above and to increase the degree of freedom in designing filter characteristics.
It is an object of the present invention to provide a composite piezoelectric bandpass filter that replaces a Yarman circuit using a partial view of a plurality of multi-mode piezoelectric resonators connected in cascade: a single-mode piezoelectric co-resonator.

Below is a detailed description of the invention based on examples! 1IVc Explain.

Figure 1 shows the conventional filter -? The circuit diagram shown in FIG. 11 has an approximate characteristic of a 4th order non-polar delay maximum flatness characteristic, a center frequency (fo) of -75 MHz, and a bandwidth of 3 dB reduction of 40 kHz.

In this case, the bandwidths of dual mode resonators Ql and Q2 are 57 kI-Iz and 29 kHz, respectively.

As is well known, a dual mode resonator is a bandpass filter that uses two vibrations in symmetric and antisymmetric modes that are generated by acoustic coupling between two electrodes placed close to each other on a single piezoelectric plate. However, if quartz is used as the piezoelectric material, Q2 can be realized in the above design example due to restrictions due to the magnitude of the electro-mechanical coupling coefficient, but Q2 will result in a narrower electrode spacing. It is not possible to realize a filter that is difficult to realize.

If it is difficult to actually realize a dual mode resonator in this way, it is common to connect all the Yarman circuits in cascade using only single mode resonators to form a full configuration, as shown in Part *. there were.

However, when constructing a fill using the method described above, although there is a degree of freedom in design, the circuit is complex and has many parts, and it is clear that it is disadvantageous in terms of cost and size compared to the circuit shown in Figure 1. .

In order to solve these problems, in the present invention, Qlf, which is difficult to realize among the dual mode piezoelectric resonators Q1 and Q2 in the circuit shown in FIG. This is replaced with a Yarman circuit, and an example of this is shown in Part *.

It will be understood that the circuit shown in FIG. 4 requires one less piezoelectric resonator than the one in the *th circuit, resulting in a cheaper and smaller filter.

On the other hand, as a result of employing the circuit configuration according to the present invention, the filter characteristics are also improved. Fig. 7 is a diagram showing the attenuation characteristics of each filter.As is clear from comparing the two, when looking at the spurious near the center frequency f o (-75MH2), an improvement of 8d13 can already be seen, and for example, the attenuation amount is 40 Comparing the number of spurious components across the line metal of 'dB, it can be seen that while there are six spurious components in the conventional circuit configuration, this number has been reduced to only two in the present invention. . . reason. Part 3. In the case of the F7゜2 configuration, the frequency of the sub-resonance generated in the single mode resonators Q3 to Q6 overlaps with 11t to the same extent, resulting in a large decrease in attenuation, whereas in the case of the This is because the probability that the sub-resonant frequencies of Q2 and the single mode resonators Q3 and Q4 overlap at the same position is reduced, and the amount of spurious attenuation is improved.

Although the embodiments and effects of the present invention have been described above only for circuits of order 4, it goes without saying that the present invention can be applied to fill circuits of even higher orders.

Further, in the embodiments of the present invention, a double mode piezoelectric resonator and a single mode piezoelectric resonator are all used, but a triple mode or more multimode resonator may be used instead of the double mode resonator. It is possible.

Since the present invention is configured and functions as explained above, it not only allows greater freedom in designing the filter and also secures the attenuation amount for the prostitute, but also has a remarkable effect on cost and volume reduction. It is something that plays.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a configuration example of a piezoelectric band fill using two double-mode piezoelectric resonators vertically, and Figure 2 is a total of two Yarman circuits using single-mode piezoelectric resonators that have been commonly used in the past. A circuit diagram showing an example of the configuration of a piezoelectric band filter connected in cascade of sections, FIG. 3 is a circuit diagram showing one embodiment of a composite piezoelectric band filter according to the present invention, (2) shows the fill characteristics of the conventional circuit configuration and the characteristics of the filter according to the present invention, respectively. Ql and Q2 double mode piezoelectric resonator Q3 to Q6 single mode pressure 11C resonator patent applicant
Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] In a bandpass filter in which a plurality of multimode monolithic piezoelectric resonators are connected in series, a Yarman circuit uses all single mode piezoelectric resonators as part of the plurality of multimode monolithic piezoelectric resonators. A composite piezoelectric bandpass filter characterized by replacing the .