Oscillators – With outer casing or housing – With temperature modifier
Reexamination Certificate
2000-01-07
2001-03-27
Mis, David (Department: 2817)
Oscillators
With outer casing or housing
With temperature modifier
C331S158000
Reexamination Certificate
active
06208213
ABSTRACT:
TECHNICAL FIELD
This invention relates to radio electronics and more particular to frequency oscillators with piezoelectric crystal resonators.
BACKGROUND ART
Various versions of stable thermostatically controlled quartz crystal oscillators are known to the prior art (see, for example U.S. Pat. No. 4,985,687 and French Patent No. 2,660,499, 2). To achieve temperature stability up to ±1×10
−8
prior art frequency oscillators usually employed a one-stepped thermostatic circuit. This allows a most simple, economical and compact design of oscillator to be achieved. To achieve stability above ±1×10
−9
a two-stepped thermostatic circuit is used. A higher precision is achieved in this case at the cost of more complex and cumbersome design (see. Ingberman M. I., Fromberg E. M, Graboi L. P., Thermostatic Methods in Communication Technology., M., Sviaz, 1979, page 17, and also Godkov V. D., Gromov S. S., Nikitin N. V., Thermostatic Methods and Wireless Appliances, Moscow, Goskomizdat, 1979, page 46).
RU 2081506 describes a crystal oscillator with a one-stepped thermostatic circuit, which circuit contains a circuit board with elements of the oscillator system mounted thereon. The circuit board is installed in a hermetically sealed outer housing. All temperature controlled elements of the system, including a thermostat with built-in crystal resonator, heating elements, a temperature detector and a thermostatic regulator with a thermosensitive bridge circuit are located in the central part of the circuit board. The central part of the circuit.board is separated from its peripheral part by means of through cuts, both parts being connected at the ends of the cuts by narrow bridging strips.
This oscillator has obvious advantages, such as a simple design, small size and low cost, but it does not allow temperature stability of ±1×10
−9
to be achieved. This limitation is explained by insufficient uniformity of temperature distribution and insufficient precision in maintaining a constant temperature.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a thermostatically controlled crystal oscillator attaining a high temperature stability of the frequency without use of a double thermostatic circuit.
A more specific object of the present invention is to resolve a technical contradiction between a necessity for uniform temperature distribution at the crystal resonator, which requires placing the resonator out of a thermal flow field, for example by increasing the distance between a crystal resonator and a heater and a necessity for very accurate control of temperature, which requires a temperature detector and the heater being placed as close to the resonator as possible.
It is also a further object of the invention to improve accuracy of temperature control.
The foregoing objects are achieved by using the combination of essential features as specified in independent claims.
Thus, according to one embodiment of the present invention, the required uniformity of the temperature field at the crystal resonator is achieved in a thermostatically controlled crystal oscillator with a circuit board divided into central and a peripheral part by means of through cuts (similar to those employed in the oscillator disclosed in RU 2081506). These parts are joined together at the end of each cut with narrow bridging strips. All thermostatically controlled elements of the oscillator are located in the central part of the circuit board. They include a crystal resonator in a separate casing, and a thermostatic regulator with heating elements. The circuit board is installed in a hermetically sealed outer housing. In addition, according to the present invention, the crystal resonator in the separate casing is tightly adjoined to the bottom of an inner case. This inner case is shaped as an inverted open box made of material that is an excellent heat conductor (or, in other words, possesses a high thermal conductivity). The inner case is fixed to the circuit board using heat-conductive rods, that go through the central part of the circuit board in close proximity to the narrow bridging strips. The bottom of the inner case is tightly adjoined to the circuit board, preferably by a layer of highly heat-conductive glue. The heating elements and a temperature detector are mounted on the outer side walls of the inner case.
Preferably, the open side of the box is covered by a thin cover that is made of material that is an excellent heat conductor, and there is a heat-insulating space between the cover and the body of the crystal resonator. Further, according to the preferred embodiment, a cover is attached to the those ends of the heat-conducting rods which extend from the opposite side of the circuit board. A heat-insulating space is provided between said cover and the thermostatically controlled elements located in the central part of the circuit board, while the cover is made from material of a high thermal conductivity.
Owing to the presence of the above-described features, for any point chosen at random on the surface of thermostatically-controlled elements, a certain matching point can be found along the path of the heat flow being dispersed into the surrounding medium in any possible direction. Said matching point, while having virtually the same temperature as the selected one, is separated from it by a heat-insulating space possessing a large heat resistance. In this way, the crystal oscillator as well as other thermostatically controlled elements of the circuit (also located in the central part of the circuit board) are in a zone of uniform temperature distribution, outside of the heat flow path. This constitutes one of the major preconditions of achieving a high temperature stability.
The described embodiment of the present invention ensures minimum heat loss directly from the surface of the thermostatically controlled elements, and consequently minimises temperature variations through the volume of these elements, especially of the resonator.
According to another embodiment of the present invention, aimed at providing high accuracy of thermostatic regulation, the circuit board of a thermostatically controlled crystal oscillator is divided into a central part and a peripheral part by means of through cuts (similar to those described in RU 2081506). Both parts are joined together at the end of each cut with narrow bridging strips. All thermostatically controlled elements of the oscillator are located in the central part of the circuit board. These elements include a crystal resonator in its own casing, a thermostatic regulator with heating elements and a thermosensitive bridge circuit having a reference arm and a main thermosensitive arm with a main temperature detector. The circuit board is installed in a hermetically sealed outer housing. According to the present invention, the thermosensitive bridge circuit is provided with an additional thermosensitive arm with an additional temperature detector. This additional arm is coupled to the main thermosensitive arm by means of a coupling resistor. The aforementioned additional temperature detector can be installed at any location in the oscillator, as long as the temperature at this location (taken under normal outside conditions) is lower than the temperature of the crystal resonator, at least by 0.5° C.
Introduction of the additional temperature detector makes it possible to minimise the inherent design static error of the thermostatic regulator which is caused by that the heaters are physically remote from the thermostatically controlled elements of the circuit. Moreover, the above-specified temperature difference between the crystal resonator and the additional temperature detector provides the opportunity for the effective tuning of the thermostatic regulator.
The most complete attainment of the above-specified objects of the present invention is ensured by employment of the preferred embodiment of the temperature controlled crystal oscillator according to the present invention a
Anastasyev Sergej Vladimirovich
Dubinchik Anatoly Ivanovich
Kitanin Eduard Leontyevich
Volkov Alexander Anatolyevich
Vorokhovsky Yakov Leonidovich
Mis David
Otkrytoe Aktsionernoe Obschestvo “Morion”
Tolpin Thomas W.
Welsh & Katz Ltd.
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