JP3105623B2 - Constant temperature controlled crystal oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant temperature controlled crystal oscillator in which a crystal oscillator is placed in a thermostat to stabilize an oscillation frequency, and more particularly to a configuration of the thermostat.

[0002]

2. Description of the Related Art Conventionally, a digital oscillator has been used as a highly stable crystal oscillator.
Frequency temperature compensated crystal oscillator (DTCXO) is proposed
ing. This DTCXO has, for example, the oscillation of a crystal oscillator.
The temperature characteristics of the frequency are
Some are compensated by a combination circuit with a sensor. But
The components of the oscillation circuit and the crystal unit may
If the oscillation frequency changes, readjust the oscillation circuit
If the oscillation frequency is modified, the required temperature compensation
There is a problem that the nature also changes and it will not be reproduced,
Long-term stability could not be guaranteed.

[0003] For this reason, a crystal oscillator or the like is stored in a thermostat.
To a high temperature point where the crystal unit operates stably.
By setting the operating temperature of the
So-called constant temperature that eliminates the need for frequency temperature compensation control
Controlled crystal oscillators are exclusively used. This constant temperature control
FIG. 2 shows an example of the shaker. A quartz oscillator (not shown ) having a high quality factor (Q) is housed in the case 3 and supported on the printed board 4 by the lead wires 34. A heater winding 31 as a heating element is wound around the case 3, and the case 3 supports a control transistor 32 that supplies power to the heater winding 31. Further, a temperature sensor 33 such as a platinum wire is attached to the case 3.

The printed circuit board 4 is provided with an oscillation circuit 41 having an LCR structure, and is supported on the printed circuit board 5 by four heat insulating studs 42. Voltage stabilizing circuit and the power supplied from outside the printed circuit board 5, such as the heater power control circuit 51 for controlling the control transistor 32 in the output voltage of the temperature sensor 33 is provided, the base by four studs 52 2 supported. The base 2 is provided with a through terminal 21 supported via an insulator such as glass. Through this through terminal 21, power is supplied and the output of the oscillator is taken out. The base 2 is covered with a lid 1 made of metal, plastic, or the like, and attached to the base 2 with screws 12. In this case, lid 1
And the base 2 may be fitted together or partially soldered.

Further, a heat insulator 11 such as asbestos or urethane is adhered to the inside of the lid 1 to obtain a heat shielding effect with the outside. Therefore, this constant temperature control water
In the crystal oscillator, the crystal resonator is maintained at a required temperature by the heater winding 31 in the case 3 and the influence of the outside air temperature is suppressed by the casing of the base 2 and the lid 1, and the frequency is stabilized while maintaining the constant temperature state. Will be achieved.

[0006]

SUMMARY OF THE INVENTION Such a conventional constant temperature
When a controlled crystal oscillator is used in an outdoor wireless device or the like, it must be configured as an oscillator that minimizes frequency fluctuations in response to a sudden change in external temperature (thermal shock). Things are considered desirable. However, when the heat capacity is large, there is a problem that the so-called rise time from power-on to the frequency stabilization becomes long. In addition, when the heat capacity is large, there is a problem that power consumption for maintaining the inside at a constant temperature becomes large and the external shape becomes large. SUMMARY OF THE INVENTION An object of the present invention is to provide a constant-control crystal oscillator that can reduce the size and reduce power consumption while alleviating thermal shock.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a casing for a thermostat.
Crystal oscillator, oscillation circuit, temperature control circuit and heat generation
Constant temperature controlled crystal oscillator equipped with body and temperature sensor
The casing consists of a metal base and a metal lid.
A dense structure, and a foil-like heat insulating material is partially and
By dispersing and attaching, the inside of the casing and
Adjustable heat transfer resistance to the amount of heat transferred between the outside
And

[0008]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the present invention, and the same reference numerals are given to the same portions as those of the conventional configuration shown in FIG. Here, the base 2 and the lid 1 that constitute the casing are each made of metal, and the contact portion between the lid 1 and the base 2 is joined with solder or the like to make the inside of the casing airtight. In addition, a conventional thermal insulator is not provided on the inner surface of the lid 3, so that convection of gas inside the casing can be smoothly performed. Instead, a heat insulating sheet 13 made of a thin heat insulating material is attached to the outer surface of the lid 1. This heat insulating sheet 13
Is attached in an arbitrary size and at an arbitrary place, partially and dispersedly.

The constant temperature effect of the constant temperature controlled crystal oscillator having such a configuration by the constant temperature bath will be described. First, the inventor performed analysis through analogy of heat transfer engineering and a heat / electric circuit in a thermostat, and experiments. (Table 1) is an example of physical properties used for calculating the heat capacity of various materials.

[Table 1]

[0010] When the case of the thermostat is made of plastic, it is unevenly affected by the heat generated by the surrounding electronic circuits. A temperature difference was observed between the base and the base. Therefore,
The temperature difference could be made extremely small by forming the base and the lid from metal and making the lid and the base airtight. Further, it was found that the heat capacity (= specific heat × mass) of the metal was smaller than that of the plastic when considering the strength.

On the other hand, the heat capacity of a gas such as air is two orders of magnitude smaller than that of a solid material and can be ignored, and the heat diffusion rate is high, making it an ideal heat resistor. As a result, natural convection occurs in the thermostatic layer. Heat transfer coefficient between gas and metal wall is 10-20W
m ⁻² k ⁻¹ could be estimated. In addition, the thermostat that does not perform airtightness is
In high altitude mountains, the heat transfer coefficient decreases as the atmospheric pressure decreases,
Since the rising characteristic at the time of turning on the power is slow, it is preferable to make the airtight, and this also contributes to the improvement of the moisture resistance .

Another component of heat transfer is heat radiation from the heater windings. Consider the heater winding as a black body and set the maximum temperature
The equivalent thermal resistance at 75 ° C is about 1250cm ² kW
It becomes ^-1 . FIG. 3 shows an equivalent circuit obtained by inferring the above consideration by analogizing heat generation power to constant current, temperature to voltage, heat transfer resistance to resistance, and heat capacity to capacity. Where V
“a” represents the ambient temperature in volts, and “Vs” represents the maximum set temperature of the crystal resonator housing case 3 in volts. Further, the thermal energy watts generated in the printed circuit board 5, the printed circuit board 4, and the case 3 in each of the parts I _S , I ₄ , and I _HH are read as ampere. C ₃ , C ₄ , C
₂ and C ₁ are the heat capacity of the crystal oscillator housing case 3 portion, the heat capacity of the printed board 4 and the oscillation circuit 41, the heat capacity of the crystal oscillator itself, the lid 1, base 2 and printed board 5 of the casing and the control circuit, respectively. The equivalent heat capacity of all 51 is represented by farads. Since these heat capacities are proportional to the volume , if the dimensions are reduced by half, the heat capacities are reduced to 1/4 to 1/8
Can be made smaller.

Further, r _1a is the equivalent heat transfer resistance from the outer wall of the lid 1 and the base 2, and r ₁₀ , r ₃₀ and r ₄₀ are the gas inside the casing, the inner wall of the lid 1 and the base 2 and the printed board 5, respectively. Equivalent heat transfer resistance between the metal part on the surface of the printed circuit board, the equivalent heat transfer resistance between the gas inside the casing and the crystal resonator housing case 3, and the metal part on the surface of the printed circuit board 4 The equivalent heat transfer resistance between them is expressed in ohms. r _2X and r _3X represent equivalent heat transfer resistances generated between the gas inside the crystal resonator housing case 3 and the crystal oscillator and the inner wall of the housing case 3. Since these equivalent heat transfer resistances are inversely proportional to the surface area of the metal in contact with the gas, halving the dimensions approximately quadruples the equivalent thermal resistance.

Therefore, when the size of the entire thermostat is reduced, the heat capacity is reduced and the required power consumption can be reduced. Further, since the rise time characteristic at the time of turning on the power is proportional to heat capacity × equivalent heat transfer resistance, the rise time characteristic can be shortened. In deriving the equivalent circuit shown in FIG. 3, the printed board 5 is assumed to have the same temperature as the base 2, so that the stud 52 is made of metal. or,
The through terminal 21 and the base 2 insulated with glass are regarded as having the same temperature. FIG. 4 is an equivalent circuit obtained by simplifying FIG. 3, in which the experimental results are included.

FIG. 5 shows the rise characteristics of power consumption with the ambient temperature as a parameter. The horizontal axis represents the elapsed time after power-on, and the vertical axis represents power consumption. The rise characteristic of the power consumption can be almost explained by the equivalent circuit of FIG. still,
Although the printed circuit board 4 provided with the oscillation circuit 41 is slightly affected by changes in the external ambient temperature, the influence on the oscillation frequency can be relatively easily reduced by a temperature correction circuit using a varactor diode.

In the conventional structure shown in FIG. 2, the power consumption of the heater is controlled by the shape and size of the heat insulating material 11 provided in the casing and the mounting position. And the unevenness of the temperature distribution of the printed circuit board 4 becomes large. As a result, the temperature correction becomes inappropriate or the oscillation frequency fluctuates. For this reason, it is desired that the temperature of the inner wall of the casing be uniform and that no object be placed in such a manner as to obstruct convection or cause turbulence. Therefore, in the present invention, the heat insulating sheet 13 is dispersed and attached to the outer wall of the lid 1 of the casing as a means for increasing the equivalent heat transfer resistance without increasing the heat capacity. Thereby, the equivalent heat transfer resistance r of FIG.
_1a can be set to a relatively large value from 24Ω to 48Ω in FIG. 4, and the power consumption can be controlled by the heater winding 31 and the like.

[0017]

As described above, according to the present invention present invention, casings
A metal base and a metal lid in an airtight structure;
Paste the foil-like heat insulating material partially and dispersed on the surface,
Transmission between the inside and outside of the casing due to the thin insulation material
The heat transfer resistance to the amount of heat that can be adjusted is adjustable, so even in an outdoor environment where temperature changes are severe, a short rise time after operation, good frequency stability, low power consumption and a small size constant temperature controlled crystal oscillator can be obtained. be able to.

[Brief description of the drawings]

FIG. 1 is a sectional view of a constant temperature controlled crystal oscillator of the present invention.

FIG. 2 is a cross-sectional view of a conventional constant temperature controlled crystal oscillator .

3 is an equivalent circuit diagram of an equivalent heat transfer of the thermostatic chamber according to the present invention.

FIG. 4 is an equivalent circuit diagram of a specific example obtained by simplifying FIG. 3;

FIG. 5 is a rise characteristic diagram of power consumption.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lid 2 Base 3 Crystal oscillator storage case 4, 5 Printed board 13 Heat insulation sheet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-221642 (JP, A) JP-A 57-155810 (JP, U) JP-A 63-4014 (JP, U) JP-A 63-155 191714 (JP, U) Japanese Utility Model 1-195706 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03B 5/30-5/42 H03H 9/00 H05K 5/00- 13/00

Claims (1)

(57) [Claims] A quartz oscillator is provided in a casing of a thermostat.
Equipped with a vibration circuit, a temperature control circuit, a heating element, and a temperature sensor.
In the constant temperature controlled crystal oscillator,
An airtight structure comprising a metal base and a metal lid, and the lid
Paste the foil-like heat insulation material partially and dispersed on the surface
The heat transmitted between the inside and the outside of the casing
Characterized in that the heat transfer resistance to the quantity can be adjusted
Temperature controlled crystal oscillator .