JPS60194601A - Temperature compensation type crystal oscillator - Google Patents

Abstract

PURPOSE:To shorten the rise time of the crystal oscilltor and to reduce its cost by connecting a heating element to a preheating power source through a switch which can be switched to the power source of the crystal oscillator, and providing a current limiting means which limits a preheating current to the heating element between the switch and the preheating power source. CONSTITUTION:Electric power is applied to a preheating power source terminal 102 and the preheating current is held below a specific value through a current limiting resistance 24. Consequently, when the switch 201 is switched from a side (a) to a side (b), the heating element heats up enough, so the crystal oscillator 51 starts oscillating speedily. Actually, the time when the temperature is stabilized after power-on operation is about 10sec and shortened by preheating.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application in Aviation The present invention relates to a temperature compensated crystal oscillator (hereinafter abbreviated as TCXO) using a heating element that generates heat at low temperatures.

<Prior art> TCXOs can be roughly divided into analog types that combine reactance elements with temperature characteristics and compensate for temperature by changing the load capacity of the crystal resonator, and TCXOs that digitize the information detected by the temperature sensing element There are three types: a digital type in which signal processing is performed to correct the temperature characteristics of the sensor, and a heating type using a heating element used in the present invention. Among these, the analog type and digital type have complicated circuit configurations and are expensive, but 14! It is characterized by a short rise time when the power is turned on. On the other hand, the heat-generating type has a simple circuit configuration and is inexpensive compared to the other two methods, so it is desirable to be used in many fields, but the temperature of the heat-generating element is limited to a certain value. The disadvantage is that it takes time to complete.

In particular, in in-vehicle wireless equipment using TCXO,
Its power is supplied by a battery.

A longer preheating time for a TCXO means that more current needs to be applied, and therefore,
When supplying power to the radio when the engine is stopped, if too much current is applied, the battery will discharge too much and the engine will not be able to start.

This will be explained below with reference to the drawings.

FIG. 1 is a circuit diagram showing a conventional heat generating TCXO.

In FIG. 1, 51 is a crystal resonator, 11 is a transistor, 41 is a coil for adjusting the oscillation frequency, 21 to 26 are bias resistors, 61 is a bypass capacitor, 62
is a feedback capacitor.

61 indicates a heating element. When the temperature of the heating element 61 decreases, its resistance decreases, power consumption increases, and the amount of heat generated increases. As a result, the crystal-motor 51 is prevented from falling below a certain temperature. In FIG. 1, the crystal resonator 51 and the heating element 61 are mounted in close contact with each other so that the heat of the heating element 61 is well transmitted to the crystal resonator 51.

FIG. 2 is a diagram showing temperature changes of the crystal resonator 51.

Figure 2 shows the elapsed time t (see) after power-on and the temperature Tx of the crystal resonator 51 when the power supply voltage Vcc is applied to the power supply terminal 101 at a low ambient temperature (-20°C).
(°C) is shown. As shown in the figure, the elapsed time until the temperature reaches room temperature (25° C.) is about 30 (ase). In other words, the conventional crystal oscillator cannot be used immediately after the power is turned on, and it is necessary to wait about 30 seconds.

Object of the invention The object of the invention is to eliminate the above-mentioned drawbacks. To this end, by preheating the heating element and further providing a current limiting means to minimize the current during preheating, it is possible to provide a heat-generating TCXO that has a short rise time and is inexpensive. It is.

<Structure of the Invention> The present invention provides a crystal oscillator whose temperature is compensated by a heating element that generates heat when the temperature becomes low, in which the heating element is connected to a preheating power source via a switch that can be switched to the power source of the crystal oscillator. The present invention is further characterized in that a current limiting means for limiting the preheating current to the heating element is provided between the switch and the preheating power source.

<Examples> Examples of the present invention will be described below with reference to the drawings.

FIG. 6 is a circuit diagram showing one embodiment of the present invention. 6th
In the drawings, the same reference numerals as in FIG. 1 are the same structural members and have the same functions. The preheating circuit for the heating element 61, which is one of the features of the present invention, is as follows:
Preheating power supply (Va) terminal 102, current limiting resistor 24. Power supply (V
cc) Consists of a preheating switch f201 that performs switching between the preheating power source (VH) and the preheating power supply (VH). The switch 201 is
It is connected to the contact a side during preheating, and to the contact a side during operation (oscillation).

Next, the operation will be explained.

First, power is normally applied to the preheating power supply terminal 102, and the current limiting resistor 24 is used to keep the preheating current below a certain value. Like this 4: By doing switch 201
At the time when switching from the a side to the b side, the heating element 61
Since the crystal resonator 51 is sufficiently heated, oscillation of the crystal resonator 51 starts immediately.

This is clear from the graph shown in FIG. Similar to FIG. 2, FIG. 4 shows the temperature Tx (tl:) of the crystal resonator 51 when the power supply voltage Vcc is applied at t=0 at the ambient temperature (-20° C.) and the progress after the power is turned on. time i
(16O). The difference from Fig. 82 is that the crystal resonator 51 is preheated until 1=0.
In this embodiment, the temperature is maintained close to 0 (° C.). As shown in FIG. 4, in this embodiment, the time required for the temperature to become constant after power is turned on is as short as about 10 seconds due to preheating. If the preheating current is increased, it is possible to shorten the rise time, but since the preheating current shortens the lifespan of batteries such as automobiles, the preheating current should be kept at a few milliamperes or less. desirable.

Further, by isolating the heating element 61 and the crystal resonator 51 from the surroundings using a heat insulating material, it is possible to sufficiently shorten the rise time of the crystal oscillator even if the preheating current is small.

<Effects of the Invention> As explained above, the present invention is configured to preheat the heating element by a preheating circuit having a current limiting means, and therefore has the effect of being inexpensive and making it possible to shorten the rise time. There is.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional heat-generating temperature-compensated crystal oscillator, Figure 2 is a diagram showing temperature changes in the crystal resonator in the oscillator of Figure 1, and Figure 186 is an embodiment of the present invention. The circuit diagram of FIG. 4 corresponds to FIG. 2, and is a diagram showing the temperature change of the crystal resonator in the case of the present invention. 11 ......transistor. 21-26...Resistance for bias. 24 ・・・・・・・・・Current limiting resistor. 61 ...... Capacitor for bypass. 62 ...... Capacitor for feedback. 41 ・・・・・・・・・Coil for adjusting the oscillation frequency. 51 ......Crystal oscillator. 61...Heating element. 101 ・・・・・・・・・Power terminal. 102 ...... Preheating power supply terminal. 201......Preheating switch tt...
・・・・・・Elapsed time after power on (sea) rT
x...Temperature (°C) of the crystal oscillator 51. Vcc......Power supply voltage. V) l・・・・・・Preheating power supply voltage. Patent applicant: NEC Corporation Figure 1 Figure 2 Figure 3 Figure t (sec) Figure 4

Claims (2)

[Claims] (1) In a crystal oscillator that is temperature-compensated by a heating element that generates heat when the temperature becomes low, the heating element is
A temperature compensated crystal oscillator characterized in that it is connected to the power supply of the crystal oscillator via a switch that can be switched. (2) The temperature according to claim 1, characterized in that a current-limiting flat membrane is provided between the switch and the preheating power source for limiting the preheating current to the heat-generating child. Compensated crystal oscillator.