JPH0567085B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a three-terminal piezoelectric resonator, such as a three-terminal piezoelectric oscillator used in an oscillation circuit, or a three-terminal piezoelectric filter used in connection with an intermediate frequency amplification circuit. It is related to.

<Conventional technology and problems> For example, in an AM radio intermediate frequency amplification circuit, the output side impedance of the previous stage MIX circuit is 300KΩ and 7pF in parallel, whereas the input side impedance of a ceramic filter is this impedance. The impedance is about 2KΩ, which is much lower than that of the

Therefore, if a ceramic filter is directly connected to the MIX circuit, matching loss will occur and the filter waveform will not be the same as it should be.

Therefore, in the radio receiving circuit as shown in Fig. 5, an intermediate frequency transformer 3 is inserted between the MIX circuit 1 and the ceramic filter 2, and the filter 2 is connected to the secondary side. , impedance matching and coupling degree adjustment.

However, there are problems in that the use of an intermediate frequency transformer not only increases the cost, but also increases the overall size and requires a large installation space.

Further, as shown in FIG. 6, when connecting the three-terminal filter element 2, if the three-terminal filter element 2 is connected directly, the degree of coupling is too high, resulting in large ripples.

By the way, if the area of the connection side electrode is made smaller, the degree of coupling will be reduced, but on the contrary, the spurious suppression effect will be worsened, so as shown in the figure, a capacitor is usually inserted in series to reduce the degree of coupling.

However, the insertion of the capacitor 4 has the same problems as the above-described intermediate frequency transformer in that it increases cost and requires a large installation space.

This invention was made to solve the above problems, and can be directly connected to the MIX circuit, eliminating the need for intermediate frequency transformers and coupling capacitors that were necessary for matching the degree of coupling. The purpose of the present invention is to provide a three-terminal piezoelectric resonator that can perform the following steps.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a dot-shaped electrode approximately at the center of one main surface of the piezoelectric substrate and a predetermined dot-shaped electrode around the dot-shaped electrode. A ring-shaped electrode is formed with a gap of
On the other hand, in a three-terminal piezoelectric resonator in which a common electrode is formed on the main surface, the degree of polarization of the piezoelectric substrate between the dot-shaped electrode and the common electrode or between the ring-shaped electrode and the common electrode is set to the other side. It is smaller than the polarization degree of .

<Function> A piezoelectric substrate made of piezoelectric ceramic or the like is polarized and used. An input/output electrode is provided on one main surface and a common electrode is provided on the other main surface to form a three-terminal piezoelectric resonator.

When polarizing piezoelectric ceramics, etc., the degree of polarization between the input electrode and the common electrode or between the output electrode and the common electrode is lowered, and the value of the turns ratio n of the phase inverting transformer in the equivalent circuit shown in Fig. 2 is mainly reduced. Make it smaller.

Although the coupling between the input/output electrodes and the piezoelectric substrate becomes weaker, there is no deterioration of spurious characteristics even if they are connected directly to the circuit.

<Example> Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4 of the accompanying drawings.

FIG. 1 shows the structure of a three-terminal filter 11, in which input and output electrodes 13 and 14 are provided on one main surface of a piezoelectric substrate 12 using piezoelectric ceramic, and a common electrode 15 is provided on the entire other main surface. It is designed to operate in vibration mode.

The polarization of the piezoelectric substrate 12 is reduced mainly between the input electrode 13 and the common electrode 15 and between the output electrode 14 and the common electrode 15.
The value of is decreasing.

As shown in the figure, the input/output electrodes 13 and 14 provided on one main surface of the piezoelectric substrate 12 consist of a dot electrode at the center of the piezoelectric substrate and a ring electrode along the outer periphery. It may be used as an output electrode, and the control side of the polarization degree can be freely selected, and as shown in the equivalent circuit shown in FIG. 2, the coupling becomes coarser in the portion where the polarization degree is lowered.

Figure 3 shows the state in which it is connected to a MIX circuit, and the side with controlled polarization is used as the input electrode side.

In this case, a low pass filter 16 is installed on the output side electrode.
You can also connect and use it.

Figure 4 shows a case in which a plurality of three-terminal filters are connected in series, and the output electrode of the first stage filter 11 and the input electrode of the second stage filter each have dot electrodes with controlled polarization. By using the coupling capacitor 4 shown in FIG.
can be omitted.

Note that a three-terminal piezoelectric resonator may be incorporated into an oscillation circuit and used as an oscillator, and in this case as well, it may be preferable to lower the degree of polarization as in the case of using it as a filter, so the present invention is limited to the filter. I would like to clarify that this is not the case.

<Effects> As described above, according to the present invention, the degree of polarization between the input electrode and the common electrode or between the output electrode and the common electrode in the three-terminal piezoelectric resonator is controlled and lowered, so that frequency conversion is possible. Impedance matching in circuits, etc. can be performed without using intermediate frequency transformers or coupling capacitors, and by omitting the use of these, it is possible to reduce costs and reduce the size of the installation space.

Furthermore, since it is only necessary to control and lower the degree of polarization of the piezoelectric substrate, the area of the electrode does not change and the spurious characteristics do not deteriorate.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a three-terminal piezoelectric resonator of the present invention, FIG. 2 is an equivalent circuit diagram of the same as the above, FIGS. 5 and 6 are circuit diagrams showing examples of the use of a conventional three-terminal filter. 11... Three-terminal filter, 12... Piezoelectric substrate, 13... Input electrode, 14... Output electrode, 15
...Common electrode.

Claims (1)

[Claims] 1. A dot-shaped electrode is formed approximately at the center of one main surface of the piezoelectric substrate, and a ring-shaped electrode is formed around the dot-shaped electrode with a predetermined gap,
On the other hand, in a three-terminal piezoelectric resonator in which a common electrode is formed on the main surface, the degree of polarization of the piezoelectric substrate between the dot-shaped electrode and the common electrode or between the ring-shaped electrode and the common electrode is set to the other side. A three-terminal piezoelectric resonator characterized in that the polarization degree is smaller than that of the three-terminal piezoelectric resonator.