JPH0221172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature compensated crystal oscillator circuit that is connected in series to a crystal resonator and that performs temperature compensation in a high temperature range.

[Description of prior art]

Crystal resonators have been widely used as stable signal sources. Many crystal resonators are AT-cuts that have cubic temperature characteristics, and are used as crystal oscillators. In order to temperature-compensate the characteristics of this cubic curve, either an indirect compensation circuit that has a bias circuit that includes a temperature-sensitive element and a variable capacitance element such as a varicap, or a capacitor connected in series with a crystal resonator, and Alternatively, a direct compensation circuit or the like in which temperature-sensitive elements are connected in parallel is used.

However, although the direct compensation circuit can compensate in the low temperature range, it is difficult to compensate in the high temperature range, especially in the high temperature range above 70°C, because the characteristics of the crystal resonator body change greatly as the temperature rises.

[Object and structure of the present invention]

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a crystal oscillator that is stable even in a high temperature range. In a temperature compensated crystal oscillator circuit in which a capacitor for high temperature range compensation and a capacitor for low temperature range compensation are connected in series with a resonator, a diode controlled by a control circuit including a temperature sensing element is connected in parallel with the capacitor for high temperature range compensation. A temperature compensated crystal oscillator circuit connected to the

[Explanation of Examples]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 1 is a crystal oscillator, transistor TR,
Resistors R1, R2 and R3, R4 and capacitor C
1, C2 and C3, C4. Note that terminal A is connected to ground, terminal B is connected to output, and terminal C is connected to power supply. A low temperature range compensation circuit 3 is connected in series to the crystal resonator 1 to compensate for the low temperature range. The low temperature range compensation circuit 3 includes a temperature sensing element TH1 and a resistor R in parallel with the capacitor C7.
6. Capacitor C6 is connected. In addition,
VC and C7 are capacitors for finely adjusting the frequency. Further, a capacitor C5 is connected in series to the crystal resonator 1 to compensate for high temperature range. A diode D is connected in parallel to a capacitor C5 that compensates for the high temperature range, forming a high temperature range compensation circuit 5. Diode D is thermistor TH2
A bias circuit 4 consisting of a resistor 4 and a bias circuit of the oscillation circuit are connected to resistors R3 and R4, and the current I flowing through the diode D changes depending on the resistance value of each resistor and thermistor. That is, the current I flowing through the diode D changes due to the potential difference between the intersection point X and the intersection point Y. As a result, the impedance of diode D changes, and the apparent capacitance of capacitor C5 connected in parallel changes. For example, as the temperature increases, the thermistor TH
The resistance of diode D becomes smaller, and the current flowing through diode D becomes larger. Then, the impedance of the diode D becomes smaller and the capacitance of the capacitor C5 becomes larger in appearance, lowering the oscillation frequency.

Here, the relationship between the impedance of the diode and the current uses the region where Z=1/k·I ² . Here, Z is the impedance of the diode D, k is a constant, and I is the current flowing through the diode D.

In this way, the impedance of the diode connected in parallel to the compensation capacitor in the high temperature range changes at the rate of the square of the flowing current I. In conventional circuits, compensation begins to take effect at temperatures around 40 to 50 degrees Celsius, where it does not require much compensation, and at temperatures above 65 degrees Celsius, it becomes dependent on the characteristics of the crystal oscillator itself. This is because the slope of the rate of change in resistance of the thermistor connected in parallel with the capacitor is small. However, in the present invention, the compensation effect does not appear unless the temperature is 50°C or higher, but the circuit of the present invention facilitates temperature compensation at 65°C or higher, which could not be achieved conventionally. This is because the slope of the impedance change of the diode connected in parallel to the capacitor is steeper than that of the thermistor, so it can cope with the frequency increase in the high temperature range of the crystal resonator.
Even at 80°C, it has become possible to reduce the amount to ±2 ppm or less.

In this example, the thermistor TH2 was inserted between the power supply and the diode D as a compensation control circuit, but
The same effect can be obtained even if the polarity of the diode D is reversed and the thermistor TH3 is connected between the diode D and the ground between the diode D and the ground as shown in FIG.

FIG. 3 shows frequency-temperature characteristics in which the characteristics of the crystal resonator itself are represented by dotted lines, and the characteristics of a conventional temperature-compensated crystal oscillator are represented by solid lines. The vertical axis is frequency change, and the horizontal axis is temperature. Here, in the conventional temperature compensated crystal oscillator, temperature compensation is not effective in a high temperature range due to the influence of the characteristics of the crystal resonator itself.

FIG. 4 shows the frequency-temperature characteristics of the temperature compensated crystal oscillator according to the present invention. The dotted line is the characteristic of the crystal resonator itself, and the solid line is the characteristic of the temperature compensated crystal oscillator according to the present invention. The present invention has made it possible to perform temperature compensation over a wide range, which was not possible in the past.

[Effects of the present invention]

Conventionally, it was possible to compensate for the temperature only up to the high temperature range (65 to 70 degrees Celsius) where the frequency variation width of the crystal resonator becomes large, but the impedance of the diode connected in parallel to the high temperature compensation capacitor of the present invention can be compensated for by including the temperature sensing element. Since it is controlled by a bias circuit, it is possible to compensate up to around 80℃. In this way, it is possible to perform temperature compensation over a wide range of high temperatures, and it also has the advantage that the number of parts is small compared to conventional compensation methods, and adjustment can be made easily.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a temperature compensated crystal oscillator of the present invention, and FIG. 2 is a circuit diagram showing another embodiment of the present invention. FIG. 3 shows the frequency-temperature characteristics of the crystal resonator itself and a conventional temperature-compensated crystal oscillator circuit, and FIG. 4 shows the frequency-temperature characteristics of the temperature-compensated crystal oscillator according to the present invention. 1... Crystal resonator, 2... Oscillation circuit, 3... Diode, 4... Bias circuit, C5... High temperature compensation capacitor.

Claims (1)

[Claims] 1. In a temperature-compensated crystal oscillator circuit that uses a crystal resonator with a cubic frequency-temperature characteristic and has a high-temperature range compensation capacitor and a low-temperature range compensation capacitor connected in series with the crystal resonator, a temperature-sensitive element is used. A temperature-compensated crystal oscillation circuit, characterized in that a diode controlled by a control circuit including the temperature-compensated crystal oscillation circuit is connected in parallel with the high-temperature range compensating capacitor.