JPS6244569Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric oscillator including a piezoelectric oscillator, an amplifying section, and a reference voltage generating section.

In the piezoelectric oscillator as described above, it is well known that the oscillation frequency of the piezoelectric oscillator changes over time due to the influence of the aging of the piezoelectric oscillator and the aging of the capacitor and resistor that are the oscillator components. Therefore, it is common practice to regularly check the oscillation frequency of piezoelectric oscillators used in communication equipment and to adjust the voltage applied to the variable capacitance diode that forms part of the piezoelectric oscillator's load capacitance. be.

Generally, when a change in frequency over time is adjusted by a voltage applied to a variable capacitance diode or the like, the frequency temperature characteristics are affected.

Figure 1 shows the frequency-temperature characteristics of the above conventional circuit.
3 is a diagram showing three load capacities A, B, and C. FIG. This is because the capacitance value of the variable capacitance diode, which forms part of the piezoelectric resonator's load capacitance, changes.
This is due to changes in the temperature characteristics of the oscillator circuit. The oscillation frequency change rate (Δ/) of the piezoelectric oscillator when the temperature is constant, for example, room temperature, is the relationship shown in Figure 1.
The relationship between Δ/=1/2γ (1+C _L /C ₀ ) (1) is expressed mathematically when the relationship between C L and load capacitance C _L is calculated. Here, C ₀ is the parallel capacitance of the piezoelectric oscillator, and γ is the ratio of this parallel capacitance to the same series capacitance.

In the above equation (1), the load capacity C _L is usually 20
~100pF (of which the capacitance of the variable capacitance diode is
(about 10pF, its temperature coefficient varies but can be several hundred ppm or more), parallel capacitance
C ₀ is usually around 3 to 5 pF and the temperature coefficient is 4 to 5 pF.
As small as 5ppm. Also, the parallel-series capacitance ratio γ is usually 200.
~2000 (series capacitance is 10 ^-2 pF or less),
Its temperature coefficient is almost as small as that of the parallel capacitance C ₀ . Therefore, the value of the frequency temperature change rate Δ/ is mainly determined by the characteristics of the load capacity.

FIG. 2 is a graph showing the relationship of equation (1) above. As is clear from FIG. 2, the oscillation frequency change rate Δ/ with respect to a change in load capacitance varies depending on the value of load capacitance C _L . Therefore,
If the load capacitance changes as the ambient temperature fluctuates, the oscillation frequency will change, resulting in characteristics different from the initial frequency-temperature characteristics. That is, in Figure 2,
If we assume that the frequency-temperature characteristic when the load capacity is at point B is characteristic B in Figure 1 and the temperature coefficient of the load capacity is positive, then when the load capacity is at point A in Figure 2 (in other words, the oscillation frequency is (when the control voltage of the variable capacitance diode is controlled to correct the oscillation wave number to a higher value), the frequency temperature characteristic becomes
The result will be as shown in characteristic C in the figure. On the other hand, in Figure 2,
When the load capacitance is at point C (in other words, when the oscillation frequency increases over time and the oscillation frequency is corrected lower by controlling the control voltage of the variable capacitance diode)
In this case, the frequency-temperature characteristic is as shown in characteristic A in FIG.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a circuit for correcting such changes.

According to the present invention, a piezoelectric oscillator including a piezoelectric oscillator and an amplifier, a load capacitance formed of a series circuit of a variable capacitance diode and a capacitor and forming a load of the piezoelectric oscillator, and a load capacitor that is controlled by the variable capacitor diode. In a piezoelectric oscillator including a reference voltage generating section that provides a voltage, as the capacitor,
There is obtained a piezoelectric oscillator characterized in that a capacitor whose temperature coefficient of capacitance has a sign opposite to that of the variable capacitance diode and whose size is approximately proportional to the capacitance is obtained.

FIG. 3 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 3, 1 is a piezoelectric oscillator, which includes a piezoelectric oscillator XL and an amplifier -R,
2 is a ceramic capacitor that is part of the load capacitance, and its capacitance C ₂ has a negative temperature coefficient α, and 3 is a variable capacitance diode whose capacitance is
_C3 has a positive temperature coefficient β, 4 is a reference voltage generator, 5 is a variable resistor that divides the reference voltage,
6 is a high resistor for AC isolation, 7
is an AC grounded capacitor, 8 is an output terminal, and V _c
is the control voltage. Note that actual values for C ₂ , C ₃ , α, β, etc. will be shown later, but they will be shown here in their general form.

First, to qualitatively explain the operating characteristics of the circuit shown in FIG. 3, in such a circuit, the temperature coefficient of the load capacitance differs depending on the capacitance value of the variable capacitance diode. That is, when the control voltage V _c is high and the capacitance C ₃ of the variable capacitance diode is small, the temperature coefficient of the load capacitance C _L mainly depends on the temperature coefficient β of the variable capacitance diode, and on the other hand, the control voltage V _c
When the capacitance value of the variable capacitance diode is low and the capacitance value of the variable capacitance diode is large, the temperature coefficient of the load capacitance C _L is mainly controlled by the temperature coefficient α of the added ceramic capacitor 2. Therefore, it can be seen that the capacitance value and temperature coefficient of the added ceramic capacitor 2 should be appropriately selected.

Next, to explain quantitatively, as can be seen from equation (1), in order for the frequency temperature change rate Δ/ to be constant regardless of temperature, the load capacity C _L must be constant regardless of temperature. This is the most important thing. By the way, the load capacitance C _L is the capacitance C ₂ of the added ceramic capacitor and the capacitance of the variable capacitance diode connected in series, and if T represents the temperature, dC ₂ /dT=αC ₂ , dC ₃ /dT =βC ₃ From the expression, C _L =C ₂ +C ₃ /C ₂ +C ₃ δC _L /δC ₂ dC ₂ /dT+δC _L /δC ₃ d
C ₃ /dT=0 C ₃ ² /(C ₂ +C ₃ ) ²・αC ₂ +C ₂ ² /(C ₂ +
C ₃ ) ²・βC ₃ = 0 C ₃ α + C ₂ β = 0 or temperature coefficient of 2/temperature coefficient of 3 =
α/β=−C ₂ /C ₃ (2). Equation (2) shows that if the temperature coefficients of the capacitance C ₂ of the ceramic capacitor 2 and the capacitance C ₃ of the variable capacitance diode are opposite in sign and the size is proportional to the capacitance value, then the load capacitance C _L is approximately independent of the temperature. means constant. For example, the capacitance C ₃ of variable capacitance diode 3 is 10 pF, and the temperature coefficient is 1/150.
0, a ceramic capacitor 2 with a capacitance of 20 pF and a negative temperature coefficient of 1/750 may be used.

Figure 4 shows the frequency temperature change rate when the relationship of equation (2) is established, and it is possible to obtain characteristics that have almost no effect on the frequency temperature characteristics even by frequency shift. .

Although an example of the characteristics of two capacitors was shown in the above embodiment, it goes without saying that the present invention is not limited to this. For example, the temperature coefficient of the variable capacitance diode 2 may range from 1/2000 to 1/2000 or a wider range, and the capacitor to be added may be other than a ceramic capacitor.
In short, any capacitance may be used as long as the relationship between the temperature coefficient and the size of the two capacitances C ₂ and C ₃ substantially satisfies equation (2). Furthermore, the above means that if there is a variable capacitance diode with a negative temperature coefficient, it is sufficient to use a capacitor with a positive temperature coefficient as the additional capacitor.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the frequency temperature characteristics of a conventional circuit, Fig. 2 is a diagram showing the relationship between load capacitance and oscillation frequency, Fig. 3 is a diagram showing the configuration of an embodiment of the present invention, and Fig. 4 1 is a diagram showing an example of frequency-temperature characteristics obtained by the present invention. Explanation of symbols: 1 is a piezoelectric oscillator, 2 is a ceramic capacitor, 3 is a variable capacitance diode, 4 is a reference voltage generator, 5 is a variable resistor, 6 is a resistor, 7 is a capacitor, 8 is an output terminal, -R represents an amplifier section, _Vc represents a control voltage, and XL represents a piezoelectric oscillator.

Claims (1)

[Scope of utility model registration request] a piezoelectric oscillator including a piezoelectric oscillator and an amplifier;
In a piezoelectric oscillator including a load capacitor formed of a series circuit of a variable capacitance diode and a capacitor and forming a load of the piezoelectric oscillator, and a reference voltage generator that provides a control voltage to the variable capacitor diode, as the capacitor, A piezoelectric oscillator characterized in that a capacitor is used whose temperature coefficient of capacitance is opposite in sign to the temperature coefficient of capacitance of the variable capacitance diode and whose size is approximately proportional to the capacitance.