JP2559594B2 - Crystal oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention has a field of application of a crystal oscillator, and particularly relates to a crystal oscillator using a thermostatic chamber in which microphonic noise is prevented.

(Background of the Invention) A crystal oscillator has good frequency stability and is used as, for example, a reference frequency source for communication equipment. Particularly, in the high stability type, the crystal oscillator is housed in a constant temperature bath to prevent the frequency change due to the frequency-temperature characteristic of the crystal oscillator and obtain an oscillation frequency within a predetermined deviation. In recent years, a crystal oscillator that has less microphonic noise due to, for example, impact of communication device noise has been desired.

(Prior Art) FIGS. 3 and 4 are views for explaining a conventional example of this type of crystal oscillator. 3 is a block diagram of the crystal oscillator, FIG. 4 (a) is an exploded view of the crystal unit, and FIG. 4 (b).
Is a diagram of a constant temperature oven, and FIG. 6C is a cross-sectional view of the constant temperature oven containing the crystal oscillator.

The crystal oscillator is composed of a crystal resonator 1, a constant temperature bath 2, and an oscillation circuit 3.
And a temperature control circuit 4.

In the crystal unit 1, a holding member 7 is erected on a pair of lead wires 6 projecting from a surface of a metal base 5, and outer peripheral portions of both ends of a crystal piece 8 are electrically and mechanically connected to each other to cover a metal cover 9. Become. The crystal piece 8 is formed by AT cutting, for example, and the excitation electrodes 11 are formed by extending the extraction electrodes 10 on the outer peripheral portions on both main surfaces.
Is formed. The pair of holding members 7 has a slit 12 in a flat plate material.
Then, the outer peripheral portions of both ends of the crystal piece 8 are inserted and held.

The constant temperature bath 2 has a heating wire on the surface of a metal cylinder 13 which is open at one end.
14 is wound and houses the crystal unit 1. Normally, the metal base 5 of the crystal unit 1 is set to the opening side and the metal cover 9 is used.
The head of the is contacted with the metal cylinder 13, and the resin 15 is applied to the opening surface, for example, to prevent heat dissipation from the inside of the tank. Then, the temperature control circuit 4 controls the current to the heating wire 14 to keep the temperature inside the constant temperature bath constant, prevent the frequency change due to the frequency temperature characteristic of the crystal unit, and obtain a stable frequency.

(Disadvantage of Prior Art) However, in the crystal oscillator having such a configuration, as shown in FIG. 5, capacitances C ₁ and C ₂ are generated between the metal cover of the crystal resonator and the excitation electrode of the crystal piece. That is, as shown in FIG. 3B, the capacitors C ₁ and C ₂ are connected to both sides of the crystal unit and are at the ground potential, for example. Therefore, for example, when there is an external shock or the like, the quartz piece swings in the metal cover to change the values of the capacitances C ₁ and C ₂ , and for example, phase modulation of the oscillation frequency causes so-called microphonic noise. . Particularly, in recent years, the housings of electronic devices have been reduced in size and weight, and external shocks are directly transmitted to the crystal oscillator, which is more problematic than conventional cases.

(Object of the Invention) An object of the present invention is to provide a crystal oscillator in which noise generation due to impact is prevented.

(Solution) The present invention is characterized in that an air gap is provided between a constant temperature bath and a crystal oscillator to provide an elastically coupled structure, and a stray capacitance is generated between the constant temperature bath and the crystal oscillator.

(Operation) Since the thermostatic chamber and the crystal unit are elastically coupled, it is possible to absorb external shock and reduce the swing of the plate surface of the crystal piece. The stray capacitance generated between the constant temperature bath and the crystal unit is little changed by external shock and is connected in series to the capacitances C ₁ and C ₂ between the crystal piece and the metal cover. Therefore, even if the capacitances C ₁ and C ₂ change, the influence of C ₁ , C ₂ , and C _{3 on} the combined reactance X _C is reduced. Hereinafter, examples will be described.

(Embodiment) FIG. 1 is a diagram for explaining an embodiment of the present invention, in which FIG. 1 (a) is an exploded view of a thermostat containing a crystal unit, and FIG. 1 (b) is the same as FIG. It is an AA 'sectional view.

The same parts as those in the above-mentioned conventional drawing are given the same numbers and their explanations are omitted together with the oscillation circuit and the temperature control circuit.

The constant temperature bath 16 is formed by attaching a lid 17 to the opening surface of the metal cylinder 13 around which the heating wire 14 as described above is wound. The glass part 18 is on the lid 17.
An airtight terminal 20 is formed by penetrating the terminal 19 therethrough. The crystal oscillator 21 cuts the lead wire 6 led to the outside to cut the short lead 22.
And Then, the metal base 5 is positioned on the lid 17 side of the constant temperature chamber 16, and a crystal oscillator is provided with a gap between the metal base 5 and the inner wall of the constant temperature chamber.
Holds 21. Silicone rubber, for example, is filled as the elastic material 23 in this space. The protruding end of the airtight terminal 20 and the crystal unit
The short lead 22 of 21 is connected by a thin metal wire 24. As the metal thin wire 24, for example, Jun Fromm wire coated with an insulating tube (not shown) is used.

In the crystal oscillator having such a structure, the elastic material 23 is
The external shock applied to 16 is buffered to reduce the oscillation of the crystal oscillator 21. Since the crystal oscillator 21 is housed in the thermostatic chamber as a short lead 22 in a hollow shape, the cushioning action of the elastic material 23 is further enhanced. The thin metal wire 24 reduces the heat conduction between the airtight terminal 20 and the short lead 22 and is effective also in the thermal insulation from the outside.

Then, as shown in the sectional view of FIG.
A capacitance C ₃ is formed between the metal cover 9 of 21 and the thermostat 16. That is, as shown in FIG. 2B, one end of the capacitances C ₁ and C ₂ between the metal cover 9 and the excitation electrode 11 described above is connected to both ends of the crystal unit 16 and the other end is common. As an equivalent circuit with one end of the capacitor C ₃ added. The other end of the capacity C ₃ becomes an AC ground potential through the heating wire 14 wound around the metal cylinder 13. These combined capacity C is (C ₁ + C ₂ ) ・ C ₃ / (C
₁ + C ₂ + C ₃ ). The capacitance C ₃ is a smaller value than the capacitances C ₁ and C ₂ and has a constant value with respect to the external impact of the capacitance. Therefore, the reactance X _C of the combined capacitance C is dominated by the capacitance C ₃ and reduces the influence of the changes in the capacitances C ₁ and C ₂ . As described above, in the present embodiment, it is possible to reduce the microphonic noise due to the external impact both structurally and electrically.

(Other Matters) In the above-described embodiment, the crystal resonator is used as a short lead and is connected to the airtight terminal by a thin metal wire, but the effect can be obtained even if the lead wire is directly led out from the lid. Further, as the elastic material, silane rubber is exemplified, but urethane rubber or the like may be used. The present invention can be modified in various ways,
The point is that a structure in which a space is provided between the crystal unit and the thermostat to form an elastically coupled structure and a capacitance C ₃ is formed between the two is within the technical scope of the present invention.

(Effect of the Invention) Since the present invention has an elastic coupling structure by providing a gap between the constant temperature chamber and the crystal unit, and causes stray capacitance between the constant temperature chamber and the crystal unit, noise due to impact is prevented. It is possible to provide a prevented crystal oscillator.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, in which FIG.
FIG. 3 is an exploded view of a thermostatic chamber containing a crystal oscillator, and FIG. 3B is a sectional view taken along the line AA ′ of FIG. 2A and 2B are views for explaining the operation of one embodiment of the present invention. FIG. 2A is a sectional view taken along the line BB ′ of FIG. 1A, and FIG. 2B is of FIG. It is an electrical equivalent circuit diagram. FIG. 3 is a block diagram showing a conventional example of a crystal oscillator. FIG. 4 (a) is an exploded view of a crystal unit for explaining a conventional example, FIG. 4 (b) is a view of a thermostatic chamber, and FIG. 4 (c) is a front sectional view of a thermostatic chamber containing the crystal unit. is there. FIG. 5 (a) is a side sectional view of a thermostatic chamber containing a crystal oscillator, and FIG. 5 (b) is an electrically equivalent circuit diagram of FIG. 5 (a). 13 …… Metal cylinder, 14 …… Heat wire, 15 …… Constant bath, 7 …… Lid body, 20 …… Airtight terminal, 21 …… Crystal resonator, 23 …… Filling material, 24 …… Metal fine wire

Claims (1)

(57) [Claims] 1. A crystal oscillator in which a crystal resonator hermetically sealed by a metal cover is housed in a metal cylinder of a thermostatic chamber, wherein an elastic agent is filled in a space between the thermostatic chamber and the crystal oscillator, When a new stray capacitance C3 is generated between the metal cylinder and the metal cover of the crystal unit, and when the stray capacitance between the excitation electrode of the crystal unit and the metal cover is C1, C2, A crystal oscillator characterized in that the stray capacitance C3 is smaller than C1 and C2.