JPS5921529Y2 - voltage controlled oscillator - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voltage controlled oscillator, and particularly to a voltage controlled oscillator that maintains frequency linearity without changing the reference value of the oscillation frequency and can adjust the frequency control sensitivity. be.

Voltage-controlled oscillators, such as voltage-controlled crystal oscillators, utilize the fact that the oscillation frequency changes due to changes in the equivalent reactance of the oscillation circuit as seen from the crystal resonator, and a variable capacitance diode is usually used to cause the reactance change. A control voltage is applied to the variable capacitance diode.

FIG. 1 shows a conventional example of this type of voltage controlled crystal oscillator.

In the figure, TR1 is an oscillation transistor, Dl is a variable capacitance diode, Xl is a crystal oscillator, C1 and C2 are phase inverting capacitors, C3 and C5 are DC blocking capacitors, C4 is an emitter bypass capacitor, R1 and R2 are each A DC applying resistor, R3 a feedback resistor, R4 and R5 each a base bias resistor, R6 a collector resistor, and R7 an emitter resistor.

The circuit shown in FIG. 1 basically forms a Colpitts type oscillation circuit, and the oscillation frequency in this case is determined by the series resonance frequency in the crystal resonator X1 and the oscillation circuit resistance as seen from the crystal resonator X1.

Here, a control voltage ■ is applied to the variable capacitance diode D1. is applied and this control voltage VF is changed, the diode D
Due to the change in capacitance of 1, the actance of the oscillator circuit changes,
The oscillation frequency changes accordingly.

If the capacitance on the circuit side seen from crystal oscillator X1 is CL, then
The rate of change of the series resonance frequency and oscillation frequency of the crystal resonator X1 is given by the following equation.

That is, (where co is the equivalent parallel capacitance of crystal resonator X1, C
1 is the equal series capacitance of the crystal resonator X1.

) The characteristics of the voltage controlled crystal oscillator are that the oscillation frequency matches the nominal frequency when the control voltage VF applied to the variable capacitance diode D1 has a standard value, and that the oscillation frequency matches the nominal frequency with respect to changes in the control voltage VF. It is important to obtain a frequency change of .

However, in the conventional oscillator shown in Fig. 1, the voltage-frequency characteristics are uniquely determined by the constant of the crystal resonator For this purpose, the constant of the crystal oscillator X1, the characteristics of the variable capacitance diode D1,
The design was extremely difficult as it required a comprehensive selection of circuit constants and other factors.

The purpose of the present invention is to solve the above-mentioned problems by making it easier to design and manufacture a circuit in order to obtain a predetermined voltage-frequency characteristic, and to freely select control sensitivity. It is intended to.

Therefore, the voltage controlled oscillator of the present invention includes a variable reactance element to which a control signal is applied and whose reactance changes in response to the control signal, and a crystal oscillator is provided in series with the circuit including the variable reactance element. A voltage controlled oscillator comprising: a first reactance element connected in series to the variable reactance element; and a second reactance element connected in parallel to the series circuit of the variable reactance element and the first reactance element. A synthesized reactance circuit is provided, and the synthesized reactance circuit is connected in series with the crystal resonator,
The reactance of the composite reactance circuit is determined so that when the control signal for the variable reactance element takes the standard value, the reactance of the composite reactance circuit matches the reactance of the variable reactance element alone when the control signal takes the standard value; The reactance element is characterized in that the values of each of the reactance element and the second reactance element are selected.

The present invention will be explained below with reference to FIG. 2 and FIGS. 3A and 3B.

FIG. 2 shows the configuration of an embodiment of the voltage controlled oscillator according to the present invention, FIG. 3A shows an example of its characteristics, and FIG. 3B shows the combination of the first and second capacitors given in the characteristics. ing.

In FIG. 2, TRI, Di, XLCl to C5,
R1 to R7 represent the numbers corresponding to those in FIG. 1, C6 represents the first capacitor, and C7 represents the second capacitor.

In the case of the present invention, the combined capacitance of the variable capacitance diode D1, the first capacitor C6, and the second capacitor C7 is selected to be equal to the capacitance of the diode D1 when the control voltage (2) is at a standard value.

That is, the noactance CL on the circuit side when C6-(1) and C7-0 is the same as in the case of FIG.

Here, let us consider the case where the first and second capacitors C6 and C7 are combined in various squares under the above conditions.

G can take a value from o (PF) (when C6 = ω) to a value equal to the capacitance of diode D1 when control voltage VF for diode D1 is a standard value, and C6
, C7, the amount of change is largest when C7=0.
D (CD is the diode D when the control voltage VF is the standard value
When the capacity is 1), it becomes 0.

Therefore, it becomes possible to arbitrarily select the frequency change based on the control voltage vF applied to the t-diode D1.

FIG. 3A shows the voltage-frequency characteristics when capacitors C6 and C7 are combined as shown in FIG. 3B.

As is clear from FIG. 3A, the voltage-frequency characteristics differ depending on the various combinations A to G of C6 and C7, but in each case, the control voltage VF is the standard value (4 volts in this example).
, the frequency f is the reference frequency (6 in this example)
315.7 KH2).

Further, the voltage-frequency characteristics in each of the above combinations A to G are given by a substantially straight line.

As described above, according to the present invention, frequency linearity can be maintained with a simple configuration and frequency control sensitivity can be easily adjusted, making it possible to extremely easily design and manufacture an oscillator.

In the above-described embodiment, a variable capacitance diode was used as the variable reactance element, and a capacitor was used as the first and second reactance elements, but it is possible to obtain the same effect by using other reactance elements. Needless to say.

Further, although a Colpitts type crystal oscillator is shown as the oscillation circuit, it goes without saying that other circuit types may be used.

[Brief explanation of the drawing]

FIG. 1 shows an example of a conventional voltage controlled oscillator, FIG. 2 shows the configuration of an embodiment of the present invention, FIG. 3A shows an example of its voltage-frequency characteristics, and FIG. Each combination of glue actance elements is shown. In the figure, Xl represents a crystal resonator, Dl represents a variable reactance element such as a variable capacitance diode, C6 represents a first reactance element such as a capacitor, and C7 represents a second reactance element such as a capacitor.

Claims (3)

[Scope of utility model registration request] (1) A variable reactance element to which a control signal is applied and whose reactance changes in response to the control signal,
A voltage controlled oscillator including a crystal resonator connected in series to a circuit including the variable reactance element, a first reactance element connected in series to the variable reactance element, the variable reactance element and the first
A composite reactance circuit including a second reactance element connected in parallel to a series circuit with the variable reactor and the reactance element is provided, and the reactance circuit is connected in series with the crystal resonator and the variable reactor and the reactive element are connected in parallel. When the control signal takes the standard value, the composite reactance circuit's resistance is determined to match the resistance of the variable reactance element alone when the control signal takes the standard value, and A voltage controlled oscillator characterized in that the voltage controlled oscillator is configured such that each value of the second reactance element is selected. (2) A variable capacitance diode is used as the variable reactance element, and a capacitor is used as each of the first and second reactance elements, as described in claim (1) of the above utility model registration claim. voltage controlled oscillator. (3) Claim (1) of the above utility model registration, characterized in that the voltage controlled oscillator is constituted by a Colpitts type crystal oscillator, and the variable reactance element is connected in series with the crystal resonator. Or the voltage controlled oscillator according to item (2).