JPH0416490Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a temperature compensation circuit for a crystal oscillator that has a simplified structure and improved characteristics, in which the compensation circuit is directly connected to a crystal resonator.

[Prior Art] Conventionally, there have been indirect compensation crystal oscillators in which a variable capacitance element is connected in series with a crystal resonator, and a compensation voltage generated from a temperature compensation circuit consisting of a thermistor and a resistor network is applied to the variable capacitance element. Furthermore, there is a directly compensated crystal oscillator in which a thermistor and a capacitor are connected in series with a crystal resonator.

The frequency-temperature characteristic of the crystal resonator has a third-order coefficient in the AT-cut crystal resonator used here, and in order to use this crystal resonator in an oscillator and compensate for a wide temperature range, it is necessary to use a low temperature Temperature compensation is performed separately for the high-temperature side and the high-temperature side. The conventional circuit is the circuit diagram in Figure 3, which includes a crystal oscillator X and a low temperature compensation circuit A.
and high temperature compensation circuit B are connected in series. In the low temperature compensation circuit A, a thermistor TH1 and a resistor R1 are connected in parallel to a capacitor C2. A capacitor C3 is connected in series with the thermistor TH1 and the resistor R1. In addition, high temperature compensation circuit B has a thermistor TH connected in parallel with capacitor C4.
2 and resistor R2 are connected in series. In addition,
Resistors R1 and R2 are adjustment resistors and capacitor VC
is a frequency adjustment capacitor. The oscillator is a widely used clap circuit.

However, even if you compensate for this kind of circuit, even if you try to widen the temperature range on the high and low temperature sides, if you try to keep it within the specification at -10℃ or below and above 80℃, it will deviate from the specification in the medium temperature range. There were drawbacks such as a state of overcompensation.

In the graph in Figure 2, the vertical axis is the frequency deviation and the horizontal axis is the temperature. The dashed-dotted curve 1 is the frequency-temperature characteristic of the crystal unit alone, and the dotted-line curve is the frequency-temperature characteristic of the conventional temperature compensation circuit. It represents -
The frequency deviation becomes large below 10℃ and above 80℃.

As another prior art, Utility Model Application No. 81208/1983 (Utility Application No. 165049/1983) has a configuration in which a high temperature compensation thermistor and a low temperature compensation thermistor are connected in parallel, and a compensation capacitor is connected to each of them.
The present invention is a temperature compensation circuit with further improved characteristics.

[Problems to be solved by the invention] In order to widen the temperature range of a temperature compensation circuit for a crystal oscillator, compensation sensitivity is increased by using a configuration in which a compensation capacitor is used for both high and low temperatures.

[Configuration of the present invention] The configuration of the present invention is such that in a temperature compensation circuit connected in series to a crystal resonator, a first capacitor is connected in parallel with a first thermistor, and the first thermistor and the second thermistor are connected in series. This is a temperature compensation circuit for a crystal oscillator, in which a second capacitor is connected in parallel with the first thermistor and the second thermistor connected in series.

[Operation and Examples] FIG. 1 is a circuit diagram showing an example of the present invention. A low temperature compensation circuit A surrounded by a dashed line and a high temperature compensation circuit B surrounded by a dotted line are connected in series with a crystal resonator. In the circuit configuration of the present invention, a crystal oscillator X, a first capacitor C4, and a first thermistor TH3 are connected in series as a low temperature compensation circuit A, and a second capacitor C5 is connected in a series circuit of the first capacitor C4 and the first thermistor TH3. connected in parallel. Further, as the high temperature compensation circuit B, a second thermistor TH4 is connected in series with the crystal resonator X, and a first capacitor C4 is connected in parallel with the second thermistor TH4. Note that resistors R3 and R4 are adjustment resistors, and VC is a frequency adjustment capacitor.

The difference from the conventional circuit is that in the present invention, capacitor C4 is used for compensation on both the high temperature side and the low temperature side. In other words, capacitor C2 in the conventional circuit diagram 3
High temperature compensation circuit B is added to the function of capacitor C2.
The circuit also serves as capacitor C3. As a result, capacitor C4 is used as a high-temperature side compensation, and capacitor C4 is used as a low-temperature side compensation.
4 and capacitor C5 are used. When making adjustments, by changing the capacitance of capacitor C4, you can independently change the compensation on the high temperature side, and by changing the capacitance of capacitor C5, you can change the slope (rotation) of the temperature characteristics from the high temperature side to the low temperature side. be able to. This is because the conventional circuit has a high temperature compensation circuit and a low temperature compensation circuit connected in series, but in this invention, the low temperature compensation circuit and the high temperature compensation circuit are connected in parallel using the first capacitor. As a result, the resistance loss of the compensation circuit decreases, and the resistance change due to temperature change of the thermistor becomes larger in appearance.
Compensation sensitivity is increased.

In this way, in this invention, the capacitor C of the conventional circuit is
By using both C2 and C3, the temperature characteristics on the low-temperature side and the high-temperature side can be widened. This is because the compensation sensitivity is increased by using such a circuit, so that compensation can be performed over a wide range. Furthermore, since the capacitor C4 serves both as high-temperature compensation and low-temperature compensation, it is useful for reducing the number of parts and has the advantage of reducing the number of adjustment parts.

Figure 2 is a graph comparing the frequency characteristics of the compensation circuit of the present invention and the conventional temperature compensation circuit, where the dashed line 1 is the frequency temperature characteristic of a single crystal resonator, and the dotted line 2 is the frequency temperature characteristic of the conventional temperature compensation circuit. The solid line 3 represents the frequency-temperature characteristic of the temperature compensation circuit of the present invention.

[Effect of the invention] This invention increases the sensitivity of the compensation circuit, so
The compensation range on the high temperature side and low temperature side is expanded, and the frequency temperature characteristics below -10℃ and above 80℃ can be improved. Moreover, the circuit configuration is simpler than before, and the number of adjustment steps can be reduced, making it an easy-to-manufacture oscillator. Ta.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
The figure is a graph showing frequency-temperature characteristics using the temperature compensation circuit of the present invention and the conventional temperature compensation circuit, and FIG. 3 is a diagram of the conventional temperature compensation circuit. X...Crystal resonator, TH3...First thermistor, TH4...Second thermistor, C4...First capacitor, C5...Second capacitor.

Claims (1)

[Scope of utility model registration request] In a temperature compensation circuit connected in series to a crystal resonator, a first capacitor C4 is connected in parallel with a first thermistor TH3 for low temperature compensation, and the first thermistor TH3 and a second thermistor TH4 for high temperature compensation are connected in series. , the first thermistor connected in series.
A temperature compensation circuit for a crystal resonator oscillator, characterized in that a second capacitor C5 is connected in parallel with TH3 and a second thermistor TH4.