JPH0540569Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a temperature compensation circuit for a crystal oscillation circuit that improves the temperature characteristics of the crystal oscillation circuit used in local oscillators of various communication devices.

[Conventional technology]

In order to improve the fluctuation of the oscillation frequency of a crystal oscillator circuit with respect to temperature, that is, the temperature characteristics, conventional methods have been to use a high-precision crystal with a small temperature coefficient of vibration over a wide temperature range, or to use a temperature-sensitive resistor such as a thermistor. The temperature compensation circuit used to compensate for changes in the oscillation frequency is used.

[Problem that the invention attempts to solve]

High-precision crystals are expensive and have the problem of increasing the cost of the oscillator. Furthermore, when using a temperature compensation circuit such as a thermistor, desirable temperature characteristics can be obtained in a low temperature range, but there is a problem in that the temperature characteristics are worsened in the room temperature range due to the temperature coefficient of the thermistor, etc. in the compensation circuit. be.

[Means for solving problems]

In order to solve the above problems, the present invention provides a crystal oscillation circuit having a temperature compensation circuit that includes a first temperature sensing element and performs temperature compensation in a low temperature range.
A second temperature sensing element is connected in parallel with the temperature compensation circuit, and its impedance changes depending on the output voltage of the second temperature sensing element, so that the temperature detected by the second temperature sensing element is lower than the temperature above the temperature compensation circuit. When the temperature range deviates from the normal temperature range, the temperature compensation circuit is gradually disabled according to changes in the difference between the detected temperature and the predetermined temperature in the low temperature range, so that the crystal oscillation circuit is not temperature compensated. A crystal oscillation circuit characterized by having a transistor to be operated is provided.

[Effect]

The temperature compensation circuit is turned on in a desired compensation temperature range by a switch element that is turned on and off by the second temperature sensing element, and is turned off in other temperature ranges. As a result, the temperature compensation circuit is connected to the oscillation circuit to perform temperature compensation only in the target compensation temperature range, and is completely disconnected from the crystal oscillation circuit in other temperature ranges, resulting in worsening of temperature characteristics in that temperature range. is prevented.

〔Example〕

A temperature compensation circuit for a crystal oscillation circuit as an embodiment of the present invention is shown in FIG. The circuit shown in FIG. 1 is used in a local oscillator of a wireless communication device, and is configured to perform temperature compensation in a low temperature range.

In Figure 1, the oscillation circuit part is a crystal resonator.
Qx, capacitors C1 to C3, variable capacitor VC1 for adjusting oscillation frequency, low temperature range compensation circuit consisting of thermistor TH2 and capacitor C4, transistor Q1 for turning on and off the low temperature range compensation circuit, inverters Q2, Q3, etc. The oscillation output is output from terminal T1. Transistor Q1
The base of is connected to the power supply VB through a parallel circuit of thermistor TH1 and resistor R1, and
grounded through resistor R2, which provides the base bias voltage and connects the thermistor
Resistor R1 and resistor R depending on the output voltage of TH1
2 changes.

The operation of the circuit of FIG. 1 will be explained below with reference to FIGS. 2 and 3.

The base potential of transistor Q1 is connected to resistor R1,
R2 is determined by the resistance value of the thermistor TH1, but since the resistance value of the thermistor TH1 changes depending on the temperature, the base potential also changes depending on the temperature, and the conduction state of the transistor Q1 also changes depending on the temperature. In the case of the circuit shown in FIG. 1, the higher the temperature, the higher the base voltage becomes, and therefore the transistor Q1 becomes conductive. In this way, the transistor Q1 is connected in parallel with the low temperature range compensation circuit, and its impedance changes depending on the output voltage of the thermistor TH1, so that the temperature detected by the thermistor TH1 is within a predetermined temperature range (for example -30 to -10℃), the degree of contribution of the temperature compensation circuit in the crystal oscillation circuit is gradually lowered as it moves away from the compensable temperature range according to changes in the difference between the detected temperature and the predetermined temperature range. .

Figure 2 shows the transistor Q1 due to temperature changes.
Indicates the current state. In Figure 2, the horizontal axis shows the temperature T [°C], and the vertical axis shows the degree of shriveling of transistor Q1 [%], and 100% on the vertical axis indicates that transistor Q1 is completely shriveled. 0% corresponds to a completely conductive state. In Figure 2, the characteristics represented by the solid line A are the characteristics when the resistors R1 are 15kΩ and R2 are 2.2kΩ, and the characteristics represented by the dashed line B are the characteristics R
The characteristics when 1 is 18kΩ and R2 is 2.7kΩ, and the characteristics represented by the two-dot chain line C are when R1 is 22kΩ and R2 is 22kΩ.
This is the characteristic for 3.3kΩ.

As is clear from Figure 2, the transistor Q
1 has a base potential at a high level and becomes conductive in a temperature range above room temperature. In this state, the oscillation frequency is determined by the combined capacitance of capacitors C1 and C2, and the combined capacitance of capacitor C3 and variable adjustment capacitor VC1. In this case, the series circuit of thermistor TH2 and capacitor C4 for compensating the temperature characteristics of the oscillation frequency in the low temperature range is gradually short-circuited by the transistor Q1, and the temperature change of thermistor TH2 affects the oscillation frequency. Moreover, since the short circuit by the transistor Q1 is gradually performed, discontinuity in the change in the oscillation frequency is prevented. Furthermore, in the present invention, the degree of contribution of the temperature compensation circuit to the crystal oscillation circuit is gradually lowered as it moves away from the compensable range, thereby eliminating discontinuities in oscillation frequency changes due to temperature changes and oscillating. Eliminates unstable frequency temperature range.

When the temperature drops from the normal temperature range, the base potential of transistor Q1 decreases, and when the temperature drops below a certain temperature determined by the resistance values of resistors R1 and R2 and the temperature coefficient of thermistor TH1, the base potential of transistor Q1 decreases due to the decrease in temperature. It will now be moved to a dormant state. As a result, the oscillation frequency is mainly controlled by capacitor C.
1. It is now determined by capacitor C3 and variable capacitor VC1, and the thermistor
Since TH2 is connected in series with capacitor C2, temperature characteristics in a low temperature range can be compensated by the thermistor TH2.

FIG. 3 shows how the temperature characteristics have been improved by the circuit shown in FIG. In Figure 3, the horizontal axis is the temperature T
[°C], and the vertical axis represents the frequency change △F [ppm].
In the figure, the solid line A is the temperature characteristic when R1 = 15kΩ, R2 = 2.2kΩ, and the dashed line b is the temperature characteristic when R1 = 18kΩ, R2
Temperature characteristics when = 2.7kΩ, chain double-dashed line C is R1 =
This is the temperature characteristic when 22kΩ, R2 = 3.3kΩ,
The characteristics indicated by the broken line D are bare characteristics when temperature compensation is not performed.

As is clear from FIG. 3, the frequency change ΔF with respect to temperature is significantly improved in the low temperature region. For example, at -30℃, the bare characteristic D is -
7.13ppm, while characteristic A is −4.22ppm,
Characteristic B is improved to -4.31ppm, and characteristic C is improved to -4.42ppm. As shown in Fig. 3, the bare characteristics (dotted line D) in the room temperature range above -10 degrees Celsius and the characteristics (solid line) after the compensation is disabled from the low temperature range to the room temperature range are as follows:
A slight deviation occurs due to the characteristics of

Various modifications can be made to the implementation of the present invention. For example, the circuit shown in Figure 1 is intended to compensate for the temperature characteristics in the low temperature range, but
The present invention is not limited to this, and it is also possible to configure the compensation circuit to be connected to the oscillation circuit to perform temperature compensation only in the normal temperature range or high temperature range, for example.

[Effect of idea]

According to the present invention, since the temperature compensation circuit is activated only in a desired temperature range, the oscillation frequency is not adversely affected by the temperature compensation circuit in other temperature ranges, and a wide temperature range is achieved. The temperature characteristics of the oscillation circuit can be improved over a period of time. Furthermore, since an expensive and highly accurate crystal resonator is not required, the price of the oscillation circuit can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a temperature compensation circuit for a crystal oscillation circuit as an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the thermal cutoff state of transistor Q1 of the circuit shown in Fig. 1, and Fig. 3. FIG. 1 is a characteristic diagram showing the state of improvement in temperature characteristics by the circuit of FIG. R1-R3...Resistor, C1-C6...Capacitor, VC...Variable capacitor, TH1, TH2...
...Thermistor, Q1...Transistor, Q2, Q
3...Inverter, Qx...Crystal resonator.

Claims (1)

[Scope of Claim for Utility Model Registration] A crystal oscillation circuit having a temperature compensation circuit that includes a first temperature sensing element and performs temperature compensation in a low temperature range, wherein a second temperature sensing element is connected in parallel with the temperature compensation circuit; The impedance of the second temperature sensing element changes depending on the output voltage of the second temperature sensing element, and when the temperature detected by the second temperature sensing element deviates from the low temperature range to the normal temperature range, the detected temperature and the low temperature A crystal oscillation circuit comprising a transistor that gradually disables the temperature compensation circuit according to a change in the difference between the temperature range and a predetermined temperature, thereby operating the crystal oscillation circuit without temperature compensation.