JPS61118001A - Crystal oscillation circuit - Google Patents

Abstract

PURPOSE:To prevent fluctuation of an oscillating frequency against the change in ambient temperature by connecting a capacitive element having a temperature characteristic cancelling temperature change of a capacitance between an emitter and a base of an oscillation transistor (TR) between the emitter and base. CONSTITUTION:The capacitive element C having an opposite temperature characteristic to that of the emitter-base capacitance of the oscillation TR Q against ambient temperature is connected between the base and emitter. The capacitive element C consists of the 1st capacitor C1, the 2nd capacitor C2, a variable capacitor V, a thermister T and a resistor R. When ambient temperature rises, the resistance value of the thermister T is decreased and a voltage impressed to the variable capacitor V is lowered, then the capacitance of the variable capacitor V is decreased, resulting that the capacitance in a series circuit comprising the 1st capacitor C1, the 2nd capacitor C2 and the variable capacitor V is reduced, and the capacitance change in the series circuit is cancelled together with the emitter-base capacitance of the oscillation TR Q.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a crystal oscillation circuit, and more particularly, to a technique for stabilizing the oscillation frequency against changes in ambient temperature in a crystal oscillation circuit.

[Background Art 1-1 In an emitter-follower type crystal oscillator circuit as shown in Fig. 2, the capacitance between the emitter and the base increases proportionally as the ambient temperature rises, as shown in Fig. 3. Therefore, the load capacitance of the oscillation transistor QIll with respect to the crystal resonator X changes, and 1) 14
As shown in the figure, there is a problem in that the oscillation frequency decreases as the ambient temperature increases. Therefore, even if a crystal resonator X with good temperature stability is used, the oscillation frequency will fluctuate as the ambient temperature changes.

[Objective of the Invention 1 The present invention has been made in view of the above points, and its main purpose is to oscillate a capacitive element that cancels the temperature characteristics of the capacitance between the emitter and base of an oscillating transistor. Emitter 4 of the transistor for use.

An object of the present invention is to provide a crystal oscillation circuit in which the oscillation frequency does not change even if the ambient temperature changes by connecting between the bases.

(Disclosure of the Invention 1 (Example) Examples of the present invention will be described below based on the drawings. In this example, an example in which the present invention is applied to a non-adjustable circuit as shown in FIG. 2 will be described. The invention is not limited to this, and can also be applied to crystal oscillation circuits such as via λ circuits.

The one shown in Figure 2 is equipped with a crystal oscillator
This is a crystal oscillation circuit that is a 14-channel rectifier circuit and does not have a tuning circuit. In place of the capacitor C0 between the emitter and the base of the oscillating transistor Q, as shown in Figure 1, a capacitor C0 having a temperature characteristic opposite to the change in the capacitance between the emitter and the base of the oscillating trunk Q with respect to the ambient temperature is used. Capacitive element C is connected. The capacitive element C is composed of a first capacitor C1, a second capacitor C2, a varicap V, a thermistor T, and a resistor R. The first capacitor C1, the varicap ■, and the second capacitor C2 are connected in series a,
This series circuit is inserted between the emitter and base of one oscillating runnostar Q. The output voltage of a voltage dividing circuit constructed by connecting a thermistor T and a resistor R to a high voltage is applied to the varicap (2). However, when the ambient temperature rises, the resistance value of the thermistor T decreases, and the voltage applied to the varicap V decreases, resulting in a decrease in the capacitance of the varicap The capacitance of the series circuit of the capacitor C2 and the varicap V of 2 is reduced, and the change in capacitance of this series circuit is offset by the change in the capacitance between the emitter and the base of the oscillating Y runno input Q. In other words, the load capacitance seen from the crystal oscillator X maintains a substantially constant value even if the ambient temperature changes, and the oscillation frequency is stabilized. Here, the first capacitor C1 and the second capacitor C have relatively large capacitances, and serve to isolate the varicap V by a single direct current.

[Effect of the Invention J] As described above, the present invention provides an emitter between the emitter and the base of the oscillation trunk, and the base Mtif! Since we connected a capacitive element with temperature characteristics that offset the temperature change of ,
This has the advantage that capacitance changes between the emitter and base of the oscillation transistor due to ambient temperature are canceled out, and the oscillation frequency does not vary with changes in ambient temperature.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a main part showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a crystal oscillation circuit according to the present invention, and FIG. 3 is an operation having temperature-capacitance characteristics of an oscillation transistor. The explanatory diagram, tA4, is an operation explanatory diagram showing changes in oscillation frequency with respect to ambient temperature. C is a capacitive element, C1 and C2 are capacitors, T is a thermistor, ■ is a varicap, and X is a crystal resonator.

Claims (1)

[Claims] (1) In an emitter follower type crystal oscillation circuit, a crystal oscillation circuit is characterized in that a capacitive element having temperature characteristics that cancels temperature changes in the capacitance between the emitter and the base is connected between the emitter and the base of the oscillation transistor. circuit.