JP2021078039A - Oscillation device - Google Patents

Abstract

To provide an oscillation device having good phase noise characteristics.SOLUTION: An oscillation device includes a substrate 8 mounted with an oscillator 2 and a monolithic crystal filter 3 to which output of the oscillator 2 is input. The oscillator 2, the monolithic crystal filter 3, and an electronic component 9 are housed in a housing space formed by the substrate 8 and a cover 10.SELECTED DRAWING: Figure 2

Description

The present invention relates to an oscillator device including an oscillator and a monolithic crystal filter.

In recent years, the development of MEMS devices using MEMS (Micro Electro-Mechanical Systems) technology has been widely carried out. The MEMS technology is a technology that realizes miniaturization of various machine elements by applying a technology in a semiconductor manufacturing process such as silicon, and is sometimes called a micromachine.

As a MEMS device manufactured by using such a MEMS technique, there is a MEMS oscillator provided with a MEMS oscillator.

In the oscillator using this MEMS oscillator, a PLL circuit in which the output of the MEMS oscillator is input as a reference signal is provided after the MEMS oscillator in order to adjust the output frequency (see, for example, Patent Document 1). ).

Japanese Unexamined Patent Publication No. 2013-110511

Since the oscillator using the MEMS oscillator includes the PLL circuit as described above, phase noise due to circuit components and loop characteristics is generated.

Oscillators widely used in electronic devices such as mobile communication devices are also required to have strict phase noise characteristics, and in particular, good phase noise characteristics are required at offset frequencies of 1 kHz or higher.

The present invention has been made in view of the above points, and an object of the present invention is to provide an oscillator having good phase noise characteristics.

In the present invention, in order to achieve the above object, it is configured as follows.

That is, the oscillator of the present invention includes an oscillator and a substrate on which a monolithic crystal filter to which the output of the oscillator is input is mounted.

According to the oscillator of the present invention, the noise component can be removed and the phase noise characteristic can be enhanced by the monolithic crystal filter to which the output of the oscillator is input.

It is preferable that the oscillator is a MEMS oscillator including a MEMS oscillator, an oscillator circuit, and a PLL circuit to which the output of the oscillator circuit is input.

According to the above configuration, the phase noise of the output of the MEMS oscillator whose phase noise characteristic deteriorates due to the inclusion of the PLL circuit can be reduced by the monolithic crystal filter.

The oscillator may be configured to include an integrated circuit element including the oscillator circuit and the PLL circuit.

According to the above configuration, the oscillator circuit and the PLL circuit can be incorporated in the integrated circuit element to reduce the size of the oscillator.

The oscillation circuit may be a temperature compensation type oscillation circuit.

According to the above configuration, high frequency accuracy can be obtained by compensating for the oscillation frequency deviation due to temperature.

At least, the configuration may include a housing forming an accommodation space for accommodating the oscillator and the monolithic crystal filter.

According to the above configuration, the housing can protect the oscillator and the monolithic crystal filter housed in the housing.

The oscillator mounted on the substrate and the monolithic crystal filter may be resin-sealed.

According to the above configuration, the sealing resin can protect the oscillator and the monolithic quartz filter.

The substrate has the oscillator and the monolithic crystal filter mounted on one of the two main surfaces, and has mounting terminals for mounting the oscillator on the other main surface of the two main surfaces. It may be configured to include a cover that is mounted on the substrate and constitutes the housing together with the substrate.

According to the above configuration, since the oscillator and the monolithic crystal filter are mounted on one main surface of the substrate, it is lower than the configuration in which the oscillator or the monolithic crystal filter is mounted on one main surface of the substrate and the other main surface. It is possible to reduce the height (thinness).

In the substrate, the oscillator is mounted on one main surface of both main surfaces, the monolithic crystal filter is mounted on the other main surface of both main surfaces, and the housing includes the oscillator and the monolithic. It may be configured to form the accommodation space for accommodating the substrate together with the crystal filter.

According to the above configuration, since the oscillator or the monolithic crystal filter is mounted on each main surface of the substrate, the horizontal direction of the substrate is compared with the configuration in which the oscillator and the monolithic crystal filter are mounted on one main surface of the substrate. The area can be reduced to reduce the size.

The substrate may be configured to include electronic components constituting a matching circuit that matches the termination impedance of the monolithic crystal filter.

According to the above configuration, the termination impedance of the monolithic crystal filter is matched by the matching circuit composed of the electronic components mounted on the substrate, so that the filter characteristics of the monolithic crystal filter can be fully utilized.

The monolithic crystal filter may be a 4-pole monolithic crystal filter.

According to the above configuration, the 4-pole monolithic crystal filter can have a steeper attenuation characteristic than the 3-pole or 2-pole monolithic crystal filter, so that the phase noise can be effectively reduced.

According to the present invention, a monolithic crystal filter to which the output of an oscillator is input can remove unnecessary noise components to obtain good phase noise characteristics.

FIG. 1 is a schematic configuration diagram of an oscillator according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the oscillator of FIG. FIG. 3 is a diagram showing the configuration of the first and second matching circuits of FIG. FIG. 4 is a characteristic diagram of the monolithic crystal filter of FIG. FIG. 5 is a diagram showing the phase noise characteristics of the oscillator of FIG. 1 and the comparative example. FIG. 6 is a schematic cross-sectional view of the oscillator of another embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of the oscillator of still another embodiment of the present invention. FIG. 8 is a diagram showing the phase noise characteristics of the oscillator of another embodiment of the present invention and the comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an oscillator according to an embodiment of the present invention.

The oscillator 1 of this embodiment includes a temperature-compensated MEMS oscillator 2 and a monolithic crystal filter (MCF) 3 that removes noise from the output of the MEMS oscillator. The first and second matching circuits 20 and 21 for matching the terminal impedance are provided on the input / output side of the monolithic crystal filter 3.

The temperature-compensated MEMS oscillator 2 includes a MEMS oscillator 4 and an IC chip 5 as an integrated circuit element. The IC chip 5 constitutes an oscillation circuit together with the MEMS oscillator 4, and includes a temperature compensation type oscillation circuit 6 including a temperature compensation circuit and the like, and a PLL circuit 7 in which the output of the oscillation circuit 6 is input as a reference signal. Is built-in.

In the MEMS oscillator 2, a PLL circuit 7 is provided after the oscillation circuit 6 in order to adjust its output frequency, and phase noise due to the circuit components and loop characteristics of the PLL circuit 7 is generated.

In this embodiment, in order to reduce the phase noise of the MEMS oscillator 2, the monolithic crystal filter 3 is provided after the MEMS oscillator 2 as described above.

FIG. 2 is a schematic cross-sectional view of the oscillator 1 of this embodiment.

In the oscillator 1 of this embodiment, a temperature-compensated MEMS oscillator 2, a monolithic crystal filter 3, and an electronic component 9 such as a coil or a capacitor are mounted on an upper surface of a component mounting board 8 made of a printed wiring board. It is mounted by being joined by solder 32. A cover 10 is mounted on the board 8 for mounting components, and the board 8 and the cover 10 form a housing 26 that constitutes a storage space for accommodating the MEMS oscillator 2, the monolithic crystal filter 3, and the electronic component 9. To.

Since the temperature-compensated MEMS oscillator 2, the monolithic crystal filter 3, and the electronic component 9 are mounted on the upper surface which is one of the two main surfaces of the substrate 8 in this way, each main surface of the substrate 8, for example, the upper surface. Compared with a configuration in which a temperature-compensated MEMS oscillator 2 is mounted on the bottom surface and a monolithic crystal filter 3 is mounted on the lower surface, the height of the oscillator 1 can be reduced (thinner).

The temperature-compensated MEMS oscillator 2 houses and airtightly seals the MEMS element 11 including the MEMS oscillator 4, the IC chip 5 incorporating the temperature-compensated oscillator circuit 6 and the PLL circuit 7. It includes a package 12 to stop.

The package 12 has an accommodating recess 16 having an open upper portion, a base 13 accommodating and holding the MEMS element 11 and the IC chip 5, and a lid that closes the upper opening of the base 13 to airtightly seal the accommodating recess 16. It is equipped with 14. The lid 14 is joined to the peripheral edge of the opening of the base 13 by seam welding or the like by a rectangular annular seal ring 15 made of Kovar or the like. This joining is performed in an inert gas atmosphere such as nitrogen gas or in a vacuum atmosphere, and the space inside the package 12 is filled with an inert gas such as nitrogen gas or is evacuated.

The base 13 has a substantially rectangular shape in a plan view, is made of a ceramic material such as alumina, and is formed by laminating ceramic green sheets and integrally firing them in a concave shape with an open upper portion.

The accommodating recess 16 of the base 13 has a substantially rectangular shape in a plan view, and stepped portions 13a higher than the bottom surface of the accommodating recess 16 are provided on the inner peripheral walls at both ends of the base 13 in the long side direction (left-right direction in FIG. 2). Has been done. A plurality of connection electrodes (not shown) having a conductor wiring pattern for connecting the IC chip 5 are formed on the upper surface of each step portion 13a.

The inactive surface (lower surface) of the IC chip 5 opposite to the active surface (upper surface) is bonded to the lower surface of the accommodating recess 16 of the base 13 with an adhesive.

A plurality of electrode pads (not shown) connected to the connection electrodes of the base 13 are formed on the peripheral portion of the active surface of the IC chip 5. Further, an electrode pad (not shown) for mounting the MEMS element 11 is formed on the center side of the active surface of the IC chip 5.

Each electrode pad of the IC chip 5 is electrically connected to a corresponding connection electrode formed on the step portion 13a of the base 13 by a bonding wire 17.

The MEMS element 11 is an element manufactured by using the above-mentioned MEMS technique, includes a MEMS oscillator (Si resonator), and has a movable portion airtightly sealed. The MEMS device 11 of this embodiment is manufactured by using an SOI (Silicon on Insulator) wafer, which is a silicon wafer having a structure in which a silicon single crystal layer is formed on an oxide film.

The MEMS element 11 is smaller than the outer shape of the IC chip 5, and is joined to the IC chip 5 so that its active surface faces the active surface of the IC chip 5. That is, in the MEMS element 11, the electrode pad on the active surface and the connection pad of the IC chip 5 are flip-chip connected by a metal bump such as an Au bump.

The connection electrode of the base 13 is connected to the external connection terminal 18 formed on the lower surface of the base 13 by a conductor wiring pattern (not shown) formed inside the base 13.

A conductor wiring pattern for connecting the MEMS oscillator 2, the monolithic crystal filter 3, and the electronic component 9 is formed on the component mounting substrate 8, and the mounting terminal 19 for mounting the oscillator 1 is formed on the lower surface thereof. Is provided.

The monolithic crystal filter 3 of this embodiment is a 4-pole monolithic crystal filter.

Generally, matching circuits 20 and 21 for terminating impedance matching are provided on the input / output end side of the crystal filter as described above.

FIG. 3 is a diagram showing the first and second matching circuits 20 and 21 of this embodiment.

The oscillation signal from the temperature-compensated MEMS oscillator 2 is input to the input terminal 35, and the oscillation signal of the oscillator 1 is output from the output terminal 36.

The first matching circuit 20 on the input end side of the monolithic crystal filter 3 includes a coil 22 connected in series between the input terminal 35 and the input side of the monolithic crystal filter 3, and the input side of the coil 22 and the monolithic crystal filter 3. A capacitor 23 having one end connected to and the other end grounded is provided between the two.

One end of the second matching circuit 21 is connected between the coil 24 connected in series between the output terminal 36 and the output side of the monolithic crystal filter 3, and between the coil 24 and the output side of the monolithic crystal filter 3. It also has a capacitor 25 whose other end is grounded.

The coils 22 and 24 and the capacitors 23 and 25 of the matching circuits 20 and 21 are mounted as electronic components 9 on the upper surface of the board 8 for mounting the components of FIG. 2 above.

FIG. 4 is a diagram showing the filter characteristics of the monolithic crystal filter 3 of this embodiment, and the filter characteristics are the filter characteristics of the monolithic crystal filter 3 in which the termination impedances are matched. In FIG. 4, the vertical axis represents the signal attenuation (dB), and the horizontal axis represents the signal frequency (kHz).

The monolithic crystal filter 3 of this embodiment has a center frequency of 40.000 MHz and a pass bandwidth of 6 kHz.

As described above, since the monolithic crystal filter 3 has a narrow pass band and 4 poles, the attenuation characteristics can be steeper than those of 3 poles and 2 poles, and unnecessary noise components can be effectively attenuated. Can be done.

FIG. 5 is a diagram showing the phase noise characteristics of the oscillator 1 of this embodiment and the oscillator of the comparative example.

The oscillator of the comparative example is an oscillator that does not include the monolithic crystal filter 3 and the first and second matching circuits 20 and 21, that is, an oscillator composed of only the temperature-compensated MEMS oscillator 2 of FIG.

In FIG. 5, the vertical axis is the phase noise (dBc / Hz), the horizontal axis is the offset frequency (Hz), the solid line L1 shows the phase noise characteristics of the oscillator 1 of the present embodiment, and the broken line L2 is the phase of the comparative example. It shows the noise characteristics.

It can be seen that in the oscillator 1 of the present embodiment shown by the solid line L1, the phase noise is remarkably reduced when the offset frequency is 1 kHz or more, as compared with the oscillator 1 of the comparative example shown by the broken line L2.

As described above, according to the present embodiment, the noise component contained in the output of the temperature-compensated MEMS oscillator 2 is removed by the monolithic crystal filter 3 to significantly reduce the phase noise, particularly the phase noise when the offset frequency is 1 kHz or more. can do.

In the oscillator 1 of the above embodiment, the temperature-compensated MEMS oscillator 2, the monolithic crystal filter 3, and the electronic component 9 are mounted on one of the two main surfaces (upper surface in FIG. 2) of the substrate 8 for mounting the component. However, the mounting terminal 19 is provided on the other main surface (lower surface in FIG. 2) of the board 8 for mounting components, but as another embodiment of the present invention, for example, as in the oscillator 1A shown in FIG. It may be mounted on each main surface of the board 8A for mounting components. That is, for example, the MEMS oscillator 2 is mounted on one main surface of the component mounting substrate 8A, the monolithic crystal filter 3 is mounted on the other main surface, and the component mounting substrate 8A is mounted via the lead terminal 27. It may be supported on the base substrate 28 and electrically connected. In this case, a component in which a MEMS oscillator 2, a monolithic crystal filter 3, and an electronic component 9 are mounted in a housing 26A composed of a base substrate 28 having a mounting terminal 29 for mounting the oscillator 1A and a cover 30. Accommodates the mounting substrate 8A.

According to this configuration, the area of the substrate 8A for mounting components in the horizontal direction can be reduced as compared with the configuration of FIG. 2, and space can be saved.

Further, instead of accommodating the MEMS oscillator 2, the monolithic crystal filter 3, and the electronic component 9 in the accommodation space of the housings 26 and 26A, for example, as in the oscillator 1B shown in FIG. 7, the MEMS oscillator 2, the monolithic The entire crystal filter 3 and the electronic component 9 may be sealed with the resin 31.

The oscillator of the above embodiment is a MEMS oscillator using a MEMS oscillator, but as another embodiment of the present invention, it may be applied to a crystal oscillator using a crystal oscillator instead of the MEMS oscillator. ..

In a temperature-compensated crystal oscillator, phase noise is generated due to circuit components of the temperature-compensated circuit, etc. Therefore, phase noise is reduced by providing a monolithic crystal filter to which the output of the temperature-compensated crystal oscillator is input. be able to.

FIG. 8 is a diagram showing the phase noise characteristics of an oscillator using a temperature-compensated crystal oscillator instead of the temperature-compensated MEMS oscillator 2 of the above embodiment shown in FIG. 1 and an oscillator of a comparative example. is there. The oscillator of the comparative example is an oscillator composed of only a temperature-compensated crystal oscillator that does not include the monolithic crystal filter 3 and the first and second matching circuits.

In FIG. 8, the vertical axis represents the phase noise (dBc / Hz), the horizontal axis represents the offset frequency (Hz), and the solid line L3 shows the phase noise characteristics of the oscillator of the embodiment using the temperature-compensated crystal oscillator. , The broken line L4 shows the phase noise characteristic of the comparative example.

Even in the oscillator using the temperature-compensated crystal oscillator shown by the solid line L3, the phase noise is sufficiently reduced at the offset frequency of 1 kHz or more as compared with the oscillator of the comparative example shown by the broken line L4. I understand.

The number of poles of the monolithic crystal filter of each of the above embodiments is 4, but the number of poles is not limited to 4 poles, and a monolithic crystal filter such as 3 poles or 2 poles may be used.

Although each of the above embodiments has been described by applying to a temperature-compensated oscillator, the present invention may be applied to an oscillator having no temperature-compensated function.

1,1A, 1B oscillator 2 Temperature-compensated MEMS oscillator 3 Monolithic crystal filter 4 MEMS oscillator 5 IC chip 6 Temperature-compensated oscillator circuit 7 PLL circuit 8 Board for mounting parts 9 Electronic parts 10 Covers 20, 21 No. 1, 2nd matching circuit 26 housing

Claims (10)

A substrate on which an oscillator and a monolithic crystal filter into which the output of the oscillator is input is mounted.
An oscillator characterized by this. The oscillator is a MEMS oscillator including a MEMS oscillator, an oscillator circuit, and a PLL circuit to which the output of the oscillator circuit is input.
The oscillator according to claim 1. The oscillator includes an integrated circuit element including the oscillator circuit and the PLL circuit.
The oscillator according to claim 2. The oscillator circuit is a temperature-compensated oscillator circuit.
The oscillator according to claim 2 or 3. It comprises at least a housing forming an accommodation space for accommodating the oscillator and the monolithic crystal filter.
The oscillator according to any one of claims 1 to 4. The oscillator mounted on the substrate and the monolithic crystal filter are resin-sealed.
The oscillator according to any one of claims 1 to 4. The substrate has the oscillator and the monolithic crystal filter mounted on one of the two main surfaces, and has mounting terminals for mounting the oscillator on the other main surface of the two main surfaces. Ori,
A cover mounted on the substrate and constituting the housing together with the substrate is provided.
The oscillator according to claim 5. In the substrate, the oscillator is mounted on one main surface of both main surfaces, and the monolithic crystal filter is mounted on the other main surface of both main surfaces.
The housing forms the accommodation space for accommodating the substrate together with the oscillator and the monolithic crystal filter.
The oscillator according to claim 5. An electronic component constituting a matching circuit for matching the terminal impedance of the monolithic crystal filter is mounted on the substrate.
The oscillator according to any one of claims 1 to 8. The monolithic crystal filter is a 4-pole monolithic crystal filter.
The oscillator according to any one of claims 1 to 9.

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