JPH0321053Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement of a temperature-compensated highly stable crystal oscillation circuit.

(Prior art and its problems) FIGS. 1 and 2 show conventional embodiments. FIG. 1 shows an example of a direct compensation type high stability crystal oscillation circuit, and FIG. 2 shows an example of an indirect compensation type high stability crystal oscillation circuit. 1st
In the figure, 1 is a crystal resonator, 2 is a capacitor, and 3
is a variable capacitor for frequency fine adjustment, 4 and 5 are bias resistors of transistor 9, 6 and 7 are capacitors forming an oscillation circuit, 8 is an emitter resistor, 10 is a bypass capacitor, 11 is a power supply terminal, 12 is an output terminal, and 13 is a Bypass capacitor for temperature compensation, 1
4 is a thermistor for low temperature compensation. In the range from room temperature to high temperature, the resistance value of the thermistor 14 is low, and the resistance value of the thermistor 14 is dominant in the parallel impedance constituted by the temperature compensation bypass capacitor 13 and thermistor 14. On the other hand, in the low temperature region, the resistance value of the thermistor 14 is high;
The parallel impedance is determined by the capacitance value of the bypass capacitor 13 and the resistance value of the thermistor 14.

By temperature-compensating the parallel impedances 13 and 14, which are the loads of the crystal resonator 1, as described above, the oscillation frequency characteristics shown by a in FIG. 4 are obtained.
In the figure, the horizontal axis shows temperature and the vertical axis shows frequency stability. In the temperature compensation method shown in Fig. 1, stable frequency temperature characteristics cannot be obtained due to variations in the elements of the bypass capacitor 13 and thermistor 14, and the frequency stability is ±(2
~3)×10 ^-6 is the limit. Also, the crystal oscillator 1 is
Frequency stability had to be guaranteed over the entire ambient temperature range and was very expensive.

In Figure 2, 15 and 16 are high resistance DC voltage supply resistors, and 17 and 18 are variable capacitance diodes 2.
0 is a bias voltage supply resistor, and 19 is a thermistor. The variable capacitance diode 20 serves as a load capacitor for the crystal resonator 1, and the capacitance value of the variable capacitance diode 20 is varied depending on the temperature to compensate for the temperature characteristics of the frequency. The bias voltage of the variable capacitance diode 20 is determined by temperature compensation of the thermistor 19, and has a so-called positive slope, being low in a low temperature region and slightly high in a high temperature region. This temperature compensated bias voltage causes the variable capacitance diode 2 to
The capacitance value of 0 is large in the low temperature range and slightly small in the high temperature range, so the oscillation frequency of the crystal resonator 1 is low in the low temperature range and slightly increases in the high temperature range. The frequency characteristics due to this temperature compensation are shown in Fig. 4b.
Indicated by In the temperature compensation method shown in FIG.
20 is large, making it difficult to obtain stable frequency-temperature characteristics. Therefore, elements 19 and 20
The sensitivity and temperature characteristics of the element and the temperature characteristics of the crystal resonator 1 are classified very precisely and are combined to realize a circuit. Ambient temperature is -30° to +60°
Although the frequency stability is about ±2×10 ^-6 at ℃, the production yield is poor and it is very expensive.

(Purpose) In order to eliminate these drawbacks, the present invention warms the crystal resonator with a simple oven that utilizes the heat generation effect of the POSISTOR, allows the crystal resonator to operate in a high temperature range, and improves the oscillation transistor of the crystal oscillation circuit. A part of the bias resistor is composed of a posistor, and the bias resistor also acts as a resistive load for the crystal oscillator to compensate for the temperature in the room temperature to high temperature range, and the capacitive load of the crystal oscillator is replaced by a capacitor to compensate for the temperature in the low temperature range. By combining this compensation with the temperature characteristics of the oscillation frequency in the high temperature range of the crystal resonator, it is possible to obtain extremely good characteristics of oscillation frequency stability over a wide temperature range at a very low cost.

(Example) An example of this invention will be described below with reference to FIG. The same numbers as in FIGS. 1 and 2 indicate the same functions. In FIG. 3, reference numeral 21 indicates a posistar, and a round dotted line section 22 indicates an oven. 23, 24 are resistances, 25
is a posistor, and the combined resistance value of 23, 24, and 25 is equivalent to the bias resistor 5 in Figure 1, and the crystal oscillator 1
It is also a load. When the oven 22 is added, the temperature of the crystal resonator 1 is compressed to a range of +30°C to +70°C when the ambient temperature is -30°C to +60°C due to the heat generation effect of the POSISTOR 21. When an AT-cut resonator is used as the crystal resonator 1, the temperature characteristic of the frequency becomes the well-known cubic curve when the oven 22 is not used.
By adding , the temperature range is compressed and it is used within the range of the quadratic curve. If the resistance composed of 23, 24, and 25 is not temperature compensated, that is, the second
When the resistor 5 shown in the figure is used, the frequency-temperature characteristic of the oven 22 becomes a quadratic curve c shown by the dotted line in FIG. As can be seen from figure c, within the specified temperature range,
It is extremely difficult to design to a specified frequency stability. Therefore, first, the capacitor 2 and the variable capacitor 3 are used to compensate for the temperature in the low temperature range.

That is, when elements having negative temperature coefficients are used as the capacitors 2 and 3, the capacitance value increases in a low temperature range and the oscillation frequency decreases. On the other hand, in a high temperature range, the capacitance value decreases and the oscillation frequency increases. This situation is shown in d of FIG. Next, the resistor 5 in FIG. 2 is replaced with resistors 23, 24, and 25 shown in FIG. By using the POSISTOR 25, 23, 24, 2
The combined resistance value of 5 is (2
In the high temperature range, it becomes equal to (the resistance value of 23) + (the combined resistance value of the resistance value of the POSISTOR 24 and the resistance 25). That is, the combined resistance value is a substantially constant value in the low temperature to normal temperature range, and increases in the high temperature range. 4 resistance and 5 resistance (or 23,
The combined resistance of 24 and 25) is also the bias resistance of the transistor 9 and is the load of the crystal resonator 1. This method takes advantage of the fact that the oscillation frequency of one crystal resonator changes depending on this load. In a high temperature range, the load seen from the crystal resonator 1 to the transistor 9 side increases as described above, and the oscillation frequency decreases. Further, in the low temperature to normal temperature range, the load hardly changes and the oscillation frequency hardly changes. Now, the capacitors 2 and 3 (variable capacitors) are oven mounted without performing the temperature compensation described above, and the temperature compensation of the resistors 5 and 23, 2
The frequency-temperature characteristic when temperature compensation is performed using resistors 4 and 25 is shown by e in FIG.

Next, as shown in Fig. 3, if we add 22 oven mountings of the present invention, 2 and 3 capacitor temperature compensation circuits, and 23, 24, and 25 temperature compensation circuits, d and e in Fig. 5. A frequency-temperature characteristic is obtained by combining the characteristics shown in FIG. FIG. 6 f shows an example of the oscillation frequency temperature characteristic according to the embodiment of the present invention shown in FIG. The specified oscillation frequency temperature characteristics can be satisfied within the specified temperature range. For example, ambient temperature -
Frequency stability of ±2×10 ^-6 at 30° to +70°C can be easily achieved at a very low cost.

(Effects) The direct temperature-compensated high-stability oscillation circuit devised by this invention can achieve an extremely stable oscillation frequency over a wide temperature range at a very low cost and with a simple circuit configuration, and is more compact and capable of oscillation than conventional ones. For example, a frequency stability of about ±2×10 ⁻⁶ over −30° to +70° C. can be easily achieved.

[Brief explanation of the drawing]

Fig. 1 is a conventional embodiment, Fig. 2 is a conventional embodiment, Fig. 3 is an embodiment of the present invention, Fig. 4 is an example of frequency stability characteristics according to the conventional embodiment, and Fig. 5 is a conventional embodiment. Example of frequency stability according to the embodiment, FIG. 6 is an example of frequency stability according to the present invention. 1: Crystal resonator, 2, 6, 7, 10, 13 are capacitors, 3: Variable capacitor, 4, 5, 8, 1
5, 16, 17, 18, 23, 24: resistance, 9:
Transistor, 11: Power supply terminal, 12: Output terminal, 14, 19: Thermistor, 20: Variable capacitance diode, 21, 25: Posistor, 22: Oven.

Claims (1)

[Scope of utility model registration request] In a temperature compensated crystal oscillator circuit, POSISTOR 2
1 is attached to the case of a crystal resonator, a part of the bias resistance of the oscillation transistor 9 of the crystal oscillation circuit is constituted by a separately provided POSISTOR 25, and the load capacitance of the crystal resonator is A temperature-compensated crystal oscillator circuit characterized by being configured with a capacitor having a negative temperature coefficient.