JP2000013142A - Voltage control piezoelectric oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always secure a large frequency variable range without the aid of a set side substrate pattern and to stabilize ground pattern and to reduce power noise by means of providing a wide ground pattern by constituting a hollow layer which is made into a cavity by removing a substrate peripheral part in an inner layer held by a ground pattern layer and a wiring layer on a multilayer substrate. SOLUTION: In a multilayer substrate where a circuit constituting an oscillator is wired/mounted, a hollow layer 104 which is made into a cavity by removing a peripheral part is provided in an inner layer held by a back ground pattern layer 106 and a surface wiring layer 102 where element parts 103 are mounted and wired. The dielectric constant of air is small to a degree which is almost similar to vacuum. Parasitic capacity generated among the wiring pattern of an oscillation circuit part, a part electrode terminal and a ground pattern can be suppressed to be small and a wide frequency variable range can be secured in the oscillator provided with the hollow layer 104 between the wiring layer 102 and the ground pattern layer 106.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a voltage controlled piezoelectric oscillator whose frequency can be controlled by a control voltage applied from the outside.

[0002]

2. Description of the Related Art A piezoelectric oscillator is one of important electronic components that constitute an electronic device by integrating a piezoelectric vibrator and an oscillation, waveform shaping, frequency dividing circuit and the like in a single package. In recent years, with the trend of downsizing and thinning of electronic devices, the mainstream of piezoelectric oscillators is shifting from the conventional DIP type to the surface mount type. The most common type of surface mount type piezoelectric oscillator is one in which component parts are wired and mounted on a multilayer substrate and packaged with a mold resin, a metal cap, or the like. Is provided with a ground pattern layer that is almost entirely covered with a ground pattern, stabilizing the ground, removing power supply noise, and preventing electrical interference with the electronic equipment set-side board on which the oscillator is mounted as a component. It is planned.

[0003] Among the piezoelectric oscillators, those whose oscillation frequency can be controlled by a control voltage applied from the outside are called voltage-controlled piezoelectric oscillators, and are widely used mainly for synchronization in mobile communication and image display fields. The basic configuration of the voltage controlled piezoelectric oscillator is as shown in FIG. 2. By applying a control voltage from the outside to the variable capacitance element 203 connected in series to the piezoelectric vibrator 201 to change the capacitance value, This is a mechanism for changing the frequency of the output clock signal.

[0004]

When a voltage controlled oscillator is formed on a multilayer substrate having an earth pattern layer, the frequency can be varied by the parasitic capacitance generated between the circuit wiring pattern and the component electrode terminal and the earth pattern. There is a problem that the range is reduced. As a countermeasure against this problem, Japanese Patent Application Laid-Open No. Hei 10-22734 discloses an invention which aims to secure a variable frequency range by removing a ground pattern under a component and a wiring pattern in a window shape.

However, considering the actual use situation, since the piezoelectric oscillator is often used in a state of being mounted in close contact with the electronic device set board, the oscillator of the present invention in which the ground pattern is removed from the window is provided. Is greatly affected by the wiring pattern on the set substrate side.
For example, if the ground pattern on the set board side is placed directly below the window-shaped part from which the ground pattern has been removed, the effect of the ground pattern removal is negated, and the stray capacitance generated between the oscillation circuit wiring and the set board ground pattern causes the frequency to drop. The variable range is narrowed. If the set board pattern under the window is not a ground pattern, a desired frequency variable range can be obtained.However, such an oscillator whose frequency variable range is influenced by the set board wiring pattern can be viewed from the user side. It becomes a very difficult product to use.

In the above-mentioned invention in which all the circuit components and the earth pattern under the wiring pattern are removed, the area of the earth pattern is greatly reduced. Therefore, the original ground pattern for stabilizing the ground and removing the power supply noise is provided. There is also a problem that the meaning is lost.

[0007]

In order to solve the above-mentioned problems, a voltage controlled piezoelectric oscillator according to the present invention has a hollow inside a cavity except for a peripheral portion of a substrate, on an inner surface layer sandwiched between an earth pattern layer and a wiring layer. It is characterized by being constituted on a multilayer substrate having layers.

According to another aspect of the present invention, there is provided a voltage controlled piezoelectric oscillator according to the present invention, wherein an inner surface layer sandwiched between an earth pattern layer and a wiring layer has a hollow structure in which a wiring pattern of an oscillation circuit portion and a part directly below a component electrode terminal are hollowed out. It is characterized by being constituted on a multilayer substrate having layers.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) It is well known that the oscillation frequency when a capacitor is added in series to a piezoelectric vibrator and an oscillation circuit is formed can be approximated by the following equation. f = fs (1 + C1 / 2 (C0 + CL)) where fs is the series resonance frequency of the piezoelectric vibrator, C0 and C1
Are the parallel equivalent capacitance and the series equivalent capacitance of the vibrator, respectively.
CL indicates the load capacity. In the voltage controlled piezoelectric oscillator, a variable capacitance element is used as a part of the load capacitance CL, and the oscillation frequency is made variable by changing the capacitance value by an external control voltage.

The relationship between the load capacitance CL and the frequency variation Δf = f−fs with respect to the specific fs, C0 and C1 is generally shown in FIG.
In the graph, there is a tendency that the slope of the frequency change amount becomes larger as the value of the load capacitance CL becomes smaller.
Therefore, in the voltage controlled oscillator, an oscillation circuit is formed in a region where the load capacitance CL is as small as possible, and the voltage controlled oscillator is designed so as to secure a maximum frequency variable width within a limited variable capacitance range of the variable capacitance element.

When a circuit is formed on a multilayer substrate having an earth pattern layer in which almost all of the layers are covered with an earth pattern, a parasitic capacitance proportional to the facing area between the circuit wiring pattern and the component electrode terminals and the earth pattern layer is generated. Although it occurs, even if the parasitic capacitance is large, it is only a few picofarats, so that it is rarely a problem in the case of a normal circuit.

However, as described above, in the voltage controlled piezoelectric oscillator in which the oscillation circuit is formed in a region where the load capacitance is extremely small and the frequency variable range is determined by the change in the load capacitance, the oscillation circuit wiring pattern, the component electrode terminals, and the ground pattern Parasitic capacitance generated between layers greatly affects the frequency variable range. Specifically, the addition of the parasitic capacitance raises the combined load capacitance and reduces the frequency variable range. Referring to the graph of FIG. 3, when the variable capacitance range is shifted from ΔCL1 to ΔCL2 by the parasitic capacitance Cp, the frequency variable range is greatly reduced from Δf1 to Δf2, even though the variable capacitance width is the same. .

FIG. 1 shows a basic configuration of the present invention for solving the above problems. In a multi-layer board on which the circuits that make up the oscillator are wired and mounted, the inner surface layer sandwiched between the backside ground pattern layer and the front wiring layer where components are mounted and wired is hollowed out, excluding the periphery It is characterized by having a hollow layer formed.

The capacitance generated between the two electrodes is proportional to the dielectric constant of the material filled between the two electrodes. In the case of glass epoxy resin, which is often used as a printed circuit board material, the relative dielectric constant with respect to vacuum has a large value of about 4 to 5, and in the case of an inorganic ceramic substrate, which is often used for high-precision oscillators, , The relative permittivity is even larger, about 10. For this reason, the parasitic capacitance generated between the wiring pattern of the oscillation circuit portion and the component electrode terminal and the ground pattern also becomes large.

On the other hand, the permittivity of air is as small as about the same as vacuum, and in the oscillator of the present invention having a hollow layer between the wiring layer and the ground pattern layer, the wiring pattern of the oscillation circuit portion and the component electrode terminals The parasitic capacitance generated between the ground pattern and the ground pattern can be suppressed to a very small value, and a wide frequency variable range can be secured.

FIG. 1 shows a case where the present invention is applied to a two-layer substrate having a wiring layer 102 on the front surface and an earth pattern layer 106 on the rear surface. However, the present invention is applied to a multi-layer substrate having more layers. In this case, the same effect can be obtained. In this case, as shown in FIG. 4, wiring is performed in the surface layer 402 and several layers close to the surface layer, an earth pattern layer 406 is provided with the hollow layer 404 interposed therebetween, and electrodes are arranged on the back layer 407. In many cases, in addition to the ground pattern layer, a power supply pattern layer in which almost the entire layer is covered with a power supply pattern is provided on the multilayer substrate, but the power supply pattern layer in this case is equivalent to the ground pattern layer in terms of AC. In order to reduce the parasitic capacitance, the same treatment as the ground pattern layer is required.

As a method of manufacturing the above-mentioned hollow structure substrate, a method of laminating two substrates each having an inner surface corresponding to a hollow portion removed, or a method of laminating substrate materials from which a hollow portion has been removed in advance. It can be manufactured by the above method.

(Embodiment 2) In the oscillator described in FIGS. 1 and 4, a hollow layer in which the entire layer is hollowed out except for the peripheral portion of the substrate is provided inside the substrate. And wiring to the external electrode must be performed using a narrow part around the substrate that is not hollowed out,
When the number of external electrodes is large, it becomes difficult to pass wiring.

Although it has been described above that the frequency variable range is reduced by the parasitic capacitance generated between the circuit wiring pattern and component electrode terminals and the ground pattern layer, the target wiring pattern and component electrode terminals are limited to the oscillation circuit portion. Even if a parasitic capacitance is added to other circuit wiring patterns, component electrode terminals, component packages, and the like, it hardly affects the frequency variable range.

For example, considering the case where the circuit shown in FIG. 5 which is generally used as a voltage controlled piezoelectric oscillator is constituted by a single component, the influence on the frequency variable width is caused by Cp1, Cp2, Cp2, and Cp2 generated in the oscillation circuit loop. Cp3
Of the control voltage input terminal 503.
Parasitic capacitances such as p4 and Cp5 and Cp6 attached to the waveform shaping amplifier 505 have almost no effect. Although not shown in FIG. 5, even when a frequency dividing circuit, an output control circuit, and the like are provided at the subsequent stage of the waveform shaping amplifier 505, the wiring pattern of these circuits and the component electrode terminals and the ground pattern may be provided. The generated parasitic capacitance hardly affects the frequency variable width.

Therefore, even when an oscillator is formed on a multilayer substrate having a hollow layer in which only the wiring pattern and component electrode terminals constituting the oscillation circuit are hollowed immediately below the wiring layer and the ground pattern layer, the entire layer is also hollow. This has the same effect of ensuring a variable frequency range as in the case where the hollow layer is provided. However, since it is difficult in manufacturing to provide a hollowed portion with the pattern shape of the wiring of the oscillation circuit portion and the electrode terminal of the component as it is, as shown in FIG. Is realistic.
The portion of the hollow layer 604 that is not hollowed out can be used not only for wiring between the upper and lower layers, but also for wiring in the layer.

In FIG. 5, the case where the circuit is constituted by a single component is considered, but the case where an oscillator IC is used can be similarly considered. In the case where the portion surrounded by the two-dot chain line in FIG.
Since the parasitic capacitance of Cp2 and Cp3 affects the frequency variable range, at least the wiring between the IC 701 and the variable capacitance element and immediately below each electrode, and the wiring between the IC 701 and both ends of the piezoelectric element 702 and immediately below each electrode must be at least hollow. There is. There are various other variations of the voltage-controlled oscillation circuit, such as a configuration in which a variable capacitance element is provided for both load capacitors, and a configuration in which a variable capacitance element is provided adjacent to the piezoelectric vibrator. Is also applicable.

[0023]

As described above, the voltage-controlled piezoelectric oscillator of the present invention can always secure a large frequency variable range regardless of the set-side substrate pattern, and has a wide ground pattern to stabilize the ground and provide a power supply. Excellent noise reduction.

[Brief description of the drawings]

FIG. 1 shows a basic configuration of a piezoelectric oscillator according to the present invention.

FIG. 2 is a basic configuration diagram of a voltage controlled oscillation circuit.

FIG. 3 is a graph of load capacity versus frequency change.

FIG. 4 is a configuration diagram of the present invention when a multilayer substrate is used.

FIG. 5 is a diagram showing a parasitic capacitance generated in the voltage controlled oscillation circuit.

FIG. 6 shows a basic configuration of a piezoelectric oscillator according to a second embodiment.

FIG. 7 is a diagram illustrating parasitic capacitance when an oscillator IC is used.

[Explanation of symbols]

 101 Package 102, 403, 602 Substrate wiring layer 103 Elemental component 104, 404, 604 Substrate hollow layer 106, 406, 606 Earth pattern layer 107 External electrode 108 Earth pattern 201, 502 Piezoelectric vibrator 202 Oscillator circuit 203, 504 Variable capacitance element 501 Oscillation amplifier

Claims (2)

[Claims] 1. A voltage controlled piezoelectric oscillator in which a constituent circuit including a piezoelectric vibrator, an amplifier, and a load capacitance including a variable capacitance element is wired and mounted on a multilayer substrate.
The back surface layer or the inner surface layer adjacent to the back surface has an earth pattern layer in which almost the entire surface is covered with an earth pattern, and is sandwiched between the earth pattern layer and a wiring layer in which components are mounted and wiring is performed. A voltage controlled piezoelectric oscillator comprising a hollow layer in which an entire layer except a peripheral portion is hollowed out on an inner surface layer. 2. A voltage controlled piezoelectric oscillator in which a constituent circuit including a piezoelectric vibrator, an amplifier, and a load capacitance including a variable capacitance element is wired and mounted on a multilayer substrate.
The back surface layer or the inner surface layer adjacent to the back surface has an earth pattern layer in which almost the entire surface is covered with an earth pattern, and is sandwiched between the earth pattern layer and a wiring layer in which components are mounted and wiring is performed. A voltage-controlled piezoelectric oscillator comprising, on an inner surface layer, a hollow layer in which a wiring pattern of an oscillation circuit portion and a component electrode terminal are directly hollowed.