JP5362344B2 - Multi-stage constant temperature crystal oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermostatic crystal oscillator which prevents characteristics from decreasing due to rise in temperature by making thermal capacity small and facilitating temperature control. <P>SOLUTION: The multistage thermostatic crystal oscillator includes a crystal vibrator 1 and circuit elements 4 of an oscillation stage and a buffer stage, a circuit element 4 of a temperature control circuit having at least a heat generating body and a temperature sensing element and making the operating temperature of the crystal vibrator 1 constant, a first circuit board 5a where the crystal vibrator 1 and the circuit elements 4 of the temperature sensing element and oscillation stage are arranged and a thermal cylinder 10 housing the first circuit board 5a, and a second circuit board 5b where the circuit element 4 of the temperature control circuit excluding at least the circuit element 4 of the buffer stage and the temperature sensing element is arranged and which supports the circuit element 4 apart from the thermal cylinder 10, the heat generating body being the thermal cylinder 10. The thermal cylinder 10 is made of a material having a resistance value for generating Joule heat, and a lead wire 11 for supplying electric power from outside is connected to the thermal cylinder 10. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a multi-stage constant temperature crystal oscillator (hereinafter referred to as a constant temperature oscillator) in the technical field, and more particularly to a constant temperature oscillator having a high frequency stability using a thermal cylinder.

(Background of the Invention)
The constant temperature oscillator has a high frequency stability since the operating temperature of the crystal unit is kept constant, and is applied to a communication device for a base station that requires a frequency deviation in units of ppb (1/1 billion), for example. In recent years, downsizing has been permeated in these base stations and the like. For example, instead of the conventional constant temperature heating cylinder in which a hot wire is wound, there is one in which a chip resistor or the like is used as a heating element.

(Example of prior art, Patent Document 1)
FIG. 4 (abc) is a diagram for explaining a conventional example. FIG. 4 (a) is a sectional view of a constant temperature oscillator, FIG. 4 (b) is an oscillation output circuit, and FIG. 4 (c) is a temperature control circuit. is there.

  The constant temperature oscillator includes a crystal resonator 1, a circuit element 4 constituting an oscillation output circuit 2 and a temperature control circuit 3, first and second circuit boards 5 (ab), and an oscillator container 6. The crystal unit 1 has a crystal piece 1a made of, for example, AT cut or SC cut, and is hermetically sealed in a surface mounting container 1b having external terminals, for example.

  In any of the cuts, it has a frequency-temperature characteristic in which the vicinity of 80 ° C., which is the high temperature side of room temperature 25 ° C. or more, is an extreme value, and the vibration frequency changes with temperature. For example, in the AT cut, a cubic curve (curve a in FIG. 5) is obtained, and in an SC cut, a quadratic curve (curved in FIG. 5) is obtained. The vertical axis in the figure is the frequency deviation Δf / f, where f is the frequency at room temperature and Δf is the frequency difference with respect to the frequency f at room temperature.

  The oscillation output circuit 2 includes an oscillation stage 2a as an oscillation circuit and a buffer stage 2b having a buffer amplifier and the like. The oscillation stage 2a is a Colpitts type having a voltage dividing capacitor (not shown) and an oscillation transistor that form a resonance circuit together with the crystal resonator 1. Here, for example, a voltage control type having the voltage variable capacitance element 4a in the oscillation loop is used. In the figure, Vcc is a power source, Vout is an output, and Vc is a control voltage.

  The temperature control circuit 3 applies a temperature sensitive element 4c (for example, a thermistor) and a temperature sensitive voltage Vt by a resistor 4d to one input terminal of an operational amplifier 4b, and a reference voltage Vr by resistors 4e and 4f to the other input terminal. Then, a voltage difference between the reference voltage Vr and the temperature sensitive voltage Vt is applied to the base of the power transistor 4g, and power from the power source Vcc is supplied to a chip resistor (heating resistor) 4h as a heating element. Thereby, the power to the heating resistor 4h is controlled by the resistance value depending on the temperature of the temperature sensitive element 4c, and the operating temperature of the crystal unit 1 is made constant.

  Both the first and second circuit boards 5 (ab) are formed with wiring patterns. For example, the first circuit board 5a is made of ceramic, and the second circuit board 5b is made of glass 9 epoxy. The crystal resonator 1 is disposed on one main surface of the first circuit board 5a, and the heating resistor 4h and the temperature sensitive element 4c of the temperature control circuit 3, for example, are disposed on the other main surface. Then, the liquid heat conductive resin 7 is applied and cured from above the heating resistor 4h and the temperature sensitive element 4c.

  On the second circuit board 5b, the circuit elements 4 of the oscillation output circuit 2 and the temperature control circuit 3 other than these are disposed on both main surfaces, and in particular, the circuit element 4 of the oscillation stage 2a is disposed in the central region. The first and second circuit boards 5 (ab) are electrically and mechanically connected by metal pins 8a and have a two-stage structure in which the plate surfaces face each other. In this case, the heat conductive resin 7 applied on the heating resistor 4h and the temperature sensitive element 4c is in close contact with the central region of the second circuit board 5b, and is thermally coupled to the second circuit board 5b, in particular, the oscillation stage 2a. The operating temperature of the circuit element 4 becomes constant.

  The oscillator container 6 is composed of a metal wire 6b sealed by resistance welding or the like, and a lead wire hermetically sealed by glass 9 at least at four corners, that is, a gas-tight terminal 8b. The second circuit board 5b is electrically and mechanically connected to the hermetic terminal 8b of the metal base 6a and hermetically sealed together with the first circuit board 5a.

In such a case, the operating temperature of the crystal resonator 1 that governs the frequency temperature characteristic of the oscillation output Vout is made constant, and the circuit elements 4 forming the oscillation circuit (oscillation stage) 2a are also made constant. Therefore, since the operating temperature is constant not only in the crystal resonator 1 but also in the oscillation stage 2a, the frequency deviation Δf / fo can be set, for example, in units of ppb without being affected by these frequency temperature characteristics. However, fo is a nominal value of the oscillation frequency, and Δf is a deviation from the nominal value fo.
JP 2005-341191 A JP 2005-223395 A

(Problems of conventional technology)
However, in the constant temperature oscillator having the above-described configuration, not only the crystal element 1 and the circuit element 4 of the oscillation stage 2a that affect the oscillation frequency but also the other circuit elements 4 such as the buffer stage 2b are provided on the oscillator container 6. Accommodate. Therefore, the heat capacity (space product) in the oscillator container 6 also increases, and the temperature distribution becomes non-uniform, which makes it difficult to control the temperature.

  For this reason, for example, as shown in FIG. 6, only the first circuit board 5a in which the crystal resonator 1, the circuit element 4 of the oscillation stage 2b and at least the temperature sensitive element 4c of the temperature compensation circuit 3 are disposed is recessed. The heat cylinder 10 is housed. The crystal unit 1 is formed, for example, by holding a crystal piece 1a by a supporter (not shown) in a metal base 1c from which a pair of lead wires 1d is led, and joining a metal cover 1b by resistance welding or the like.

  Then, the thermal cylinder 10 is held (supported) on the upper surface side of the second circuit board 5b in which the circuit elements 4 excluding at least the temperature sensitive element 4c of the temperature compensation circuit 3 and the circuit elements 4 of the buffer stage 2b are disposed on the lower surface. Then, it has been considered that the heat cylinder 10 is heated by the heating resistor 4h disposed on the upper surface side of the second circuit board 5b, and the temperature in the heat cylinder 10 is controlled to be constant. Reference numeral 7 denotes a heat conductive sheet.

  Thereby, since the space product in the thermal cylinder 10 which accommodates the 1st circuit board 5a can be made small, temperature distribution is made uniform and temperature control is made easy. However, even in this case, since the heating resistor 4h is thermally coupled to the bottom surface of the thermal cylinder 10, the heat distribution is concentrated on the bottom surface side, so that a uniform temperature distribution cannot be obtained, which makes temperature control difficult. In particular, when frequency stability in ppb units is required, the problem becomes significant.

  In any case, the second circuit board 5b is also provided with the buffer stage 2b other than the oscillation stage 2a and the circuit element 4 of the temperature control circuit 3, and is exposed to a high temperature similarly to the oscillation stage 2a. That is, the quartz resonator 1 that determines the oscillation frequency, the buffer stage 2b other than the oscillation stage 2a, and the numerous circuit elements 4 of the temperature control circuit 3 are exposed to high temperatures. Therefore, these circuit elements 4 have a characteristic deterioration due to a temperature rise, and there is a problem that an oscillation output characteristic including an oscillation frequency at room temperature becomes unstable.

  Note that the capacity after the buffer stage 2b on the load capacity (series equivalent capacity) viewed from the crystal unit 1 that determines the oscillation frequency is extremely small and can be almost ignored. Therefore, the influence on the oscillation frequency due to the frequency temperature characteristics of the circuit elements 4 in the buffer stage 2b can be ignored, and there is basically no need to keep the operating temperature of these circuit elements 4 constant. Further, since the temperature control circuit 3 is independent of the oscillation output circuit 2 without being electrically connected, there is no influence on the oscillation frequency. As a result, there is a problem that the characteristics of the buffer stage 2b of the oscillation output circuit 2 and the circuit element 4 of the temperature control circuit 3 are lowered due to temperature rise.

(Object of invention)
The present invention reduces the heat capacity, makes the temperature distribution constant, and facilitates temperature control. It is another object of the present invention to provide a constant temperature oscillator that prevents deterioration of characteristics due to temperature rise of circuit elements other than the crystal resonator and the oscillation stage.

According to the present invention, as shown in the claims (Claim 1), a crystal unit having a crystal piece sealed and sealed and having an external terminal, an oscillation stage that forms an oscillation output circuit together with the crystal unit, and the A buffer stage circuit element for buffering and amplifying the output of the oscillation stage; a heating element for heating the crystal oscillator; and a temperature sensitive element for detecting an operating temperature of the crystal oscillator. A circuit element of a temperature control circuit that keeps constant, a first circuit board on which at least the crystal resonator, the temperature sensitive element, and the circuit element of the oscillation stage are disposed, and a first airtight that supports the first circuit board A thermal cylinder that accommodates the first circuit board through which a terminal penetrates the bottom surface, a circuit element of the temperature control circuit excluding at least the circuit element of the buffer stage and the temperature sensitive element, and the hermetic terminal is connected And said A second circuit board and a crystal oscillator of a thermostatic type in which a multi-stage type having an oscillator for container accommodating the heat pipe and the second circuit board spaced apart from said heat pipe to support the cylinder, the The heating element for heating the crystal unit is the thermal cylinder, the thermal cylinder is formed in a concave shape with a material having a resistance value for generating Joule heat, and the opening end face of the concave shape is closed by an insulating substrate. And a lead wire that is electrically connected to the upper end sides of the opposite side surfaces of the thermal cylinder and supplies electric power from the outside.

  With such a configuration, the heat cylinder is directly used as a heating element by Joule heat based on the resistance value of the heat cylinder itself. Then, the crystal resonator and the circuit element of the oscillation stage that most affect the oscillation output (frequency) are arranged on the first circuit board and accommodated in a heat cylinder as a heating element, and the circuit elements such as the buffer stage are heated. Arranged on the second circuit board outside the cylinder. Therefore, temperature control can be facilitated by reducing the heat capacity of the heat cylinder and making the temperature distribution uniform.

  In this case, the capacity of the buffer stage and the circuit elements of the temperature control circuit viewed from the crystal resonator (oscillation stage) is extremely small. Therefore, even if the circuit elements of the buffer stage and the temperature control circuit have frequency temperature characteristics, the change of the load capacity (series equivalent capacity) seen from the crystal unit can be ignored, and the influence on the oscillation frequency at the oscillation stage is Can be ignored.

  The circuit elements of the buffer stage and the temperature control circuit are disposed on the second circuit board, and are thermally shut off with a gap from the thermal cylinder. Therefore, the circuit elements of the buffer stage and the temperature control circuit are not exposed to high heat, and do not reach an extremely high temperature but become a temperature higher than room temperature. Accordingly, the circuit elements of the buffer stage and the temperature control circuit prevent deterioration of characteristics due to high-temperature operation, and maintain, for example, good oscillation output characteristics including the oscillation frequency at normal temperature. From these facts, the frequency stability can be increased with the frequency deviation as a unit of ppb.

  The heating target by the heating element is basically the minimum element of the crystal resonator and the oscillation stage circuit element, and the other circuit elements are outside the heat cylinder. Therefore, the heating target is the minimum necessary circuit element and the minimum heat capacity, and the heat cylinder is directly used as a heating element, so that energy efficiency can be improved.

In the second aspect , in the first aspect, the thermal cylinder is made of stainless steel or tungsten. Thereby, the material of the heat cylinder is clarified and specified. Incidentally, the resistance value of stainless steel is 3Ω and tungsten is 2Ω, so that Joule heat can be sufficiently generated to make the heat cylinder a heating element.

(First embodiment)
FIG. 1 is a cross-sectional view of a constant temperature oscillator for explaining an embodiment of the present embodiment. In addition, the same number is attached | subjected to the same part as a prior art example, and the description is simplified or abbreviate | omitted.

  As described above, the constant temperature oscillator is a multistage type in which the first and second circuit boards 5 (ab) are stacked in the vertical direction, and the first circuit board 5 a is accommodated in the thermal cylinder 10. And these are enclosed in the container 6 for oscillators by the solder sealing of the metal base 6a and the cover 6b. In this example, the crystal resonator 1 in which the crystal piece 1a is hermetically sealed on the lower surface of the first circuit board 5a, and the upper surface includes the circuit element 4 of the oscillation stage 2a, the temperature sensitive element 4c, a trimmer capacitor, and the like. An element is disposed. Circuit elements 4 excluding the temperature sensitive element 4c of the buffer stage and the temperature control circuit are disposed on the lower surface of the second circuit board 5b. However, the power transistor of the temperature compensation circuit 3 is disposed on the first circuit board 5a as necessary.

  The heat cylinder 10 has a hermetic terminal 8a having a concave shape and penetrating the bottom surface, and is made of, for example, a stainless steel plate having a resistance value of 3Ω or a tungsten metal plate having a resistance value of 2Ω. And the outer periphery of the 1st circuit board 5a is supported by the front-end | tip of the airtight terminal 8a used as the inside of the concave shape penetrated the bottom face of the thermal cylinder 10, and an opening end surface is obstruct | occluded by the insulating board 10a. Further, the tip of the airtight terminal 8a that is recessed outside and penetrates the bottom surface of the thermal cylinder 10 is connected to and supported by the outer periphery of the second circuit board 5b. In this case, the bottom surface of the thermal cylinder 10 is supported separately from the second circuit board 5b.

  The outer periphery of the second circuit board 5b is supported by the first hermetic terminal 8b of the metal base 6a. The first hermetic terminal 8b is electrically connected to the buffer stage and the temperature compensation circuit 3 including ground. And the metal base 6a has the 2nd airtight terminal 8c outside the 1st airtight terminal 8b, and is electrically connected with the upper end side of the side surface which the thermal cylinder 10 opposes by the metal wire 11 as a lead wire. It should be noted that the lead wire as the second hermetic terminal 8c can be directly connected by solder or the like without depending on the metal wire 11.

  In such a case, electric power from the outside through the second hermetic terminal 8 c and the metal wire 11 is applied to the upper end side of the opposite side surface of the thermal cylinder 10. Since the heat cylinder 10 having a high resistance value generates heat due to Joule heat, the heat cylinder 10 itself becomes a heating element. Therefore, as in the conventional example, the heating efficiency is higher than in the case of using the heating resistor and the heat conductive sheet, so that the energy efficiency can be increased.

In this case, since electric power (voltage) is applied particularly to the upper end side of the opposite side surface of the thermal cylinder 10, the current circulates through the side surface and the bottom surface of the thermal cylinder 10. Accordingly, Joule heat that circulates in the heat cylinder 10 and the heat cylinder 10 is heated as a whole, so that the temperature distribution inside the heat cylinder 10 is made uniform. This facilitates temperature control.

  Further, in this example, the second circuit board 5b is disposed away from the thermal cylinder 10, so that it is thermally insulated from the thermal cylinder 10. Accordingly, the circuit element 4 of the buffer stage 2b and the temperature control circuit 3 is not forced to operate at high temperature by the heating resistor 4h, although the outside air temperature is normal temperature. As a result, for example, the oscillation output characteristics including the oscillation frequency at normal temperature are favorably maintained.

  Incidentally, in the constant temperature oscillator of this embodiment, the frequency deviation Δf / fo with respect to the ambient temperature has a frequency stability within ± 2 ppb in the range of −20 to 80 ° C., for example, as shown in FIG. 2 (straight line A). Become. On the other hand, for example, as shown in FIG. 2, when the buffer stage 2b and the circuit element 4 of the temperature control circuit 3 are arranged on the lower surface of the second circuit board 5b on which the heating resistor 4h is arranged, the frequency The change Δf / f is ± 10 ppb (straight line B in FIG. 2).

  Therefore, the effect in the case where the buffer stage 2b and the circuit element 4 of the temperature control circuit 3 in this embodiment are separated from the heating resistor 4h to avoid a thermal influence becomes clear. Note that the frequency deviation Δf / f decreases with increasing temperature on any straight line AB, but on the contrary, the frequency deviation Δf / f may increase, depending on the temperature characteristics of the circuit side and the crystal unit. To do.

(Other matters)
In the above embodiment, the heat cylinder 10 is a single metal plate. However, as shown in FIG. 3, for example, a metal laminate plate is formed by printing a metal paste 12 such as tungsten on a ceramic laminate surface to form a concave shape, and then firing it. It may be. In this case, tungsten on the tip side is exposed and fired, and the metal wire 11 is connected. Even in this case, the same effect is obtained. In addition, the crystal resonator in which the crystal piece 1a is held by the supporter (not shown) on the metal base 1c from which the pair of lead wires 1d is led and the metal cover 1b is joined is described as an example. The same applies to the case where the crystal resonator is used.

It is sectional drawing of the constant temperature oscillator explaining embodiment of this invention. It is a frequency deviation characteristic explaining the effect | action of embodiment of this invention. It is sectional drawing of the constant temperature oscillator explaining other embodiment of this invention. FIG. 2A is a cross-sectional view of a constant temperature oscillator, FIG. 2B is a schematic diagram of an oscillation circuit, and FIG. 2C is a temperature control circuit diagram. It is a frequency-temperature characteristic view of a crystal resonator having an AT cut and an SC cut for explaining a conventional example. It is sectional drawing of the constant temperature type oscillator explaining the other example of a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Crystal oscillator, 2 Oscillation output circuit, 3 Temperature control circuit, 4 Circuit element, 5 Circuit board, 6 Metal container, 7 Thermally conductive resin, 8 Airtight terminal (metal pin), 9 Glass, 10 Thermal cylinder, 11 Metal Wire, 12 metal paste.

Claims (2)

A crystal unit in which a crystal piece is hermetically sealed and having an external terminal;
An oscillation stage that forms an oscillation output circuit together with the crystal oscillator, and a buffer stage circuit element that buffers and amplifies the output of the oscillation stage;
A circuit element of a temperature control circuit that has at least a heating element that heats the crystal unit and a temperature sensitive element that detects an operating temperature of the crystal unit, and makes the operating temperature of the crystal unit constant;
A first circuit board on which at least the crystal resonator, the temperature sensitive element, and the circuit element of the oscillation stage are disposed;
A first airtight terminal that supports the first circuit board passes through a bottom surface, and a thermal cylinder that houses the first circuit board;
The circuit element of the temperature control circuit excluding at least the circuit element of the buffer stage and the temperature sensitive element is disposed, and the airtight terminal is connected to support the thermal cylinder and to be separated from the thermal cylinder A substrate,
A constant temperature crystal oscillator having a multi-stage shape having the thermal cylinder and an oscillator container containing the second circuit board,
The heating element for heating the crystal unit is the thermal cylinder , the thermal cylinder is formed in a concave shape with a material having a resistance value for generating Joule heat, and the concave opening end surface is closed by an insulating substrate. And
A constant temperature crystal oscillator comprising a lead wire that is electrically connected to the upper end sides of the opposite side surfaces of the thermal cylinder and supplies electric power from the outside. In claim 1,
The thermostat is made of stainless steel or tungsten, and is a constant temperature crystal oscillator.