JPH088643A - Voltage-controlled oscillation device - Google Patents

Abstract

PURPOSE:To improve the stability of oscillation frequency of a voltage-controlled oscillation device(VCO) against changes in ambient temperature. CONSTITUTION:In a circuit where the equivalent electrostatic capacity is varied by the oscillation frequency-controlled voltage Ec and the electrostatic capacity is generated for setting the oscillation frequency, a variable capacity element X1 to which the voltage Ec is applied in the backward bias direction with respect to the voltage Ec is connected in series to a PN junction element X2 which has the same characteristic of the terminal voltage change as the element X1 against the temperature change. So that the forward bias is secured to the voltage Ec. Then the necessary DC positive voltage is applied to the connection point between both elements X1 and X2 from a power supply Vcc via a resistance R1. Meanwhile the voltage Ec is applied to both ends of a series circuit of the elements X1 and X2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a voltage controlled oscillator (V
CO), and more particularly to stabilization of the oscillation frequency against changes in ambient temperature.

[0002]

2. Description of the Related Art FIG. 3 is a principle configuration diagram of a voltage controlled oscillator (VCO). 11 is a basic oscillator, X11 is a variable capacitance element, TH is a thermistor for temperature compensation, and Ec is an oscillation frequency control voltage. . This circuit changes the capacitance of the variable capacitance element X11 by changing the oscillation frequency control voltage Ec, and the basic oscillator 11 generates a signal of a predetermined frequency based on the capacitance. A transistor or a diode is generally used as the variable capacitance element X11. The PN junction interface of these elements is considered as a flat plate capacitor, and the junction capacitance (electrostatic capacitance) is changed by changing the reverse bias as shown in the figure. In this case, the potential difference at the bonding interface has a high dependency on temperature, so temperature compensation must be performed. Conventionally, as a method of this temperature compensation, a method using a temperature sensitive element represented by a thermistor has been generally used.

[0003]

However, in the case of the method using the temperature sensitive element, it is difficult to approximate the temperature change characteristic of the temperature sensitive element to the temperature change characteristic of the variable capacitance element.
Therefore, there is a limit to the stabilization of the output frequency with respect to the temperature change. It is an object of the present invention to provide a device voltage controlled oscillator that further stabilizes the oscillation frequency against changes in ambient temperature.

[0004]

According to the present invention, in a voltage controlled oscillating device, an equivalent capacitance is changed by an oscillation frequency control voltage to form an equivalent capacitance for setting an oscillation frequency. A variable capacitance element to which the same control voltage is applied in the reverse bias direction with respect to the frequency control voltage,
The same variable capacitance element and a PN junction element having the same characteristic of terminal voltage change with temperature change are connected in series with the same variable capacitance element so as to be forward biased with respect to the same oscillation frequency control voltage. A voltage controlled oscillator configured to apply a required DC positive voltage to the connection point between the same PN junction element and the PN junction element, and to apply an oscillation frequency control voltage to both ends of a series circuit of the same variable capacitance element and the same PN junction element. Is provided.

[0005]

As described above, by providing the PN junction element in series with the variable capacitance element, the terminal voltage of the PN junction element changes even if the capacitance of the variable capacitance element changes due to temperature fluctuations. Compensate for capacitance changes. In this case, since the temperature characteristics of the variable capacitance element and the PN junction element are the same, highly accurate compensation is performed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A voltage controlled oscillator according to the present invention will be described below with reference to the drawings. 1 is a circuit diagram of an essential part showing an embodiment of a voltage controlled oscillator according to the present invention, FIG. 2 is a characteristic diagram for explaining the present invention, (A) is an ambient temperature vs. terminal voltage characteristic diagram, and (B) is a characteristic diagram. FIG. 4 is a characteristic diagram of ambient temperature vs. oscillation frequency. FIG.
In the above, 1 is a basic oscillator, X1 is a variable capacitance element of a transistor or a diode, X2 is a PN junction element for temperature compensation, and Ec is an oscillation frequency control voltage for varying the oscillation frequency.

The oscillation frequency of FIG. 1 is substantially determined by the electrostatic capacitance value (C1) of the variable capacitance element X1, and the oscillation frequency is changed by changing the capacitance value with the oscillation frequency control voltage Ec. Is the same as the conventional one (FIG. 3).
However, as shown in the figure, the variable capacitance element X1 having a reverse bias relationship with the oscillation frequency control voltage Ec has the same control voltage Ec.
PN junction element X2 is provided in series in the forward direction with respect to
In addition, if the required positive DC voltage is applied to the connection point between X1 and X2 via the resistor R1, the variable capacitance elements X1 and PN are connected.
The series circuit with the junction element X2 operates as follows with respect to changes in ambient temperature. Now, considering the case where the oscillation frequency control voltage Ec is constant and the ambient temperature T rises, the terminal voltage (junction voltage) V1 of the reverse-biased variable capacitance element X1 decreases as shown in FIG. 2 (A). . Due to this voltage decrease, the capacitance value C1 of the variable capacitance element X1 increases as shown by the dotted line in the figure.

On the other hand, the terminal voltage (junction voltage) V2 of the forward-biased PN junction element X2 also has the same temperature characteristic as that of the variable capacitance element X1 and therefore drops similarly (FIG. 2 (A) V2). However, since the voltage across the series circuit of X1 and X2 is constant at the oscillation frequency control voltage Ec, V1 decreases due to the decrease in V1.
Is relatively increased, and the capacitance value C1 of the variable capacitance element X1 decreases as shown by the solid line in the figure. That is,
The increase in C1 is compensated in the decreasing direction by the PN junction element X2, and the change in the capacitance value C1 is totally suppressed. The terminal voltage of the variable capacitance element X11 (V1 as in FIG. 1) and the terminal voltage Vth of the thermistor TH in the conventional configuration (FIG. 3) are shown together. As shown in the figure, in the present invention, the change in the terminal voltage with respect to the temperature has the same characteristics in the variable capacitance element X1 and the PN junction element X2, but they differ in the conventional thermistor method. In this way, the capacitance value C1 of the variable capacitance element X1 is made constant with respect to temperature,
The oscillation output of the basic oscillator 1 is also stabilized. FIG. 2 (B) is a characteristic diagram showing the relationship of the output frequency with respect to the temperature change, and (a) shows the case according to the present invention, and (b) the conventional case (FIG. 3). As shown in the figure, by applying the present invention, frequency fluctuation is prevented and stabilized.

[0009]

As described above, according to the present invention, a PN junction element having the same temperature characteristic is provided in a direction opposite to that of the variable capacitance element which determines the oscillation frequency in the voltage controlled oscillator. Since they are provided in series, the change in the capacitance of the variable capacitance element with respect to temperature is suppressed and stabilized by the same PN junction element, and as a result, the oscillation frequency with respect to temperature change is stabilized compared to the temperature compensation by the conventional thermistor. Therefore, a highly accurate signal output can be obtained.
Further, since the present invention is the addition of the PN junction element, it can be configured with a simple circuit. From the above, the present invention is effective in improving the performance of a voltage controlled oscillator used in many fields by a simple method.

[Brief description of drawings]

FIG. 1 is a main part circuit diagram showing an embodiment of a voltage controlled oscillator according to the present invention.

FIG. 2 is a characteristic diagram for explaining the present invention, (A) is a characteristic diagram of ambient temperature vs. terminal voltage, and (B) is an ambient temperature versus oscillation frequency characteristic diagram.

FIG. 3 is a main part circuit diagram showing an embodiment of a conventional voltage controlled oscillator.

[Explanation of symbols]

 1 Basic oscillator EC Oscillation frequency control voltage X1 Variable capacitance element X2 PN junction element R1 Resistor C1 Variable capacitance element X1 capacitance

Claims (2)

[Claims] 1. In a voltage controlled oscillator, a circuit in which an equivalent capacitance changes with an oscillation frequency control voltage to form an equivalent capacitance that sets an oscillation frequency, and a reverse bias is applied to the oscillation frequency control voltage. In the direction of the variable capacitance element, a variable capacitance element and a PN junction element having the same characteristic of the terminal voltage change with respect to the temperature change are connected in series with the variable capacitance element and with respect to the same oscillation frequency control voltage. Forward bias, and apply a required positive DC voltage to the connection point between the same variable capacitance element and the same PN junction element, and apply it to both ends of the series circuit of the same variable capacitance element and the same PN junction element. A voltage controlled oscillator, characterized in that it is configured to apply an oscillation frequency control voltage. 2. The voltage controlled oscillator according to claim 1, wherein the PN junction element is formed by connecting a plurality of PN junction elements in series.