JP3235294B2 - Voltage controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator using a surface acoustic wave resonator.

[0002]

2. Description of the Related Art As a conventional voltage controlled oscillator using a surface acoustic wave resonator, as shown in FIGS. 5 and 6, a Colpitts type using a one-port type surface acoustic wave resonator 11 is mainly used. The inductive reactance between the base and the collector of the transistor 12 is constituted by the surface acoustic wave resonator 11 and the variable capacitance diode 13. 5 shows a voltage-controlled oscillator 14 in which a variable capacitance diode 13 is connected in series to the surface acoustic wave resonator 11, and FIG. Voltage controlled oscillator 1 with diode 13 connected in parallel
5

In this case, the combined impedance and phase characteristics of the surface acoustic wave resonator 11 and the variable capacitance diode 13 are represented as shown in FIG.
It occurs at one point fosc at a frequency that becomes inductive between r and the antiresonant frequency fa. (In FIG. 7, the minimum points fm and fn of the impedance do not exactly coincide with the point at the phase of 0 °. However, in the oscillator with a high Q, fm and fn
Because r, fn and fa are so close together,
A description will be given using fr and fa assuming that they approximately match. When the voltage controlled oscillator 14 changes the control voltage Vt applied to the variable capacitance diode 13, the resonance frequency fr changes as shown in FIG.
osc changes. When the voltage-controlled oscillator 15 changes the control voltage Vt applied to the variable capacitance diode 13, the anti-resonance frequency fa changes and the oscillation frequency fosc changes as shown in FIG. Note that the control voltage Vt, the resonance frequency fr, and the anti-resonance frequency fa have a positive correlation.

As described above, the voltage controlled oscillators 14 and 15
The oscillation frequency fosc is controlled by the control voltage Vt applied to the variable capacitance diode 13.

[0005]

However, in the conventional voltage controlled oscillators 14 and 15 described above, the resonance frequency f
Since only r or the anti-resonance frequency fa changes, the variable range of the oscillation frequency fosc is narrow, and a voltage-controlled oscillator capable of controlling the oscillation frequency over a wide range cannot be obtained.

The reactance characteristic formed by the surface acoustic wave resonator 11 and the variable capacitance diode 13 changes depending on the control voltage Vt. FIG. 10 shows the case of the voltage controlled oscillator 14 and the case of the voltage controlled oscillator 15. It is shown in FIG. 11 (however, only the positive side). 10 and 11, when the oscillation condition fluctuates due to noise from the power supply or the like, the frequency change is small under the condition of the steep slope of the reactance characteristic, and the frequency change is large under the condition of the steep slope of the reactance characteristic. Become. That is, the voltage controlled oscillator 14
In the case of (1), the C / N value becomes worse as the control voltage becomes smaller. On the other hand, in the case of the voltage controlled oscillator 15, the C / N value becomes worse as the control voltage becomes larger. There is a problem that a constant C / N value cannot be obtained.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a voltage-controlled oscillator capable of controlling an oscillation frequency over a wide range and having a stable C / N value. is there.

[0008]

To achieve the above object, the present invention provides a voltage controlled oscillator using a surface acoustic wave resonator, wherein the surface acoustic wave resonator includes a first variable capacitance diode. Are connected in series , the second variable capacitance diodes are connected in parallel, and the first and second variable capacitance diodes are connected in parallel .
Are connected to a common tuning terminal .

In a voltage controlled oscillator using a surface acoustic wave resonator, a first variable capacitance diode is connected in series to the surface acoustic wave resonator and a second variable capacitance diode is connected in parallel. A coil or a capacitor is connected in series or in parallel to the first variable capacitance diode or the second variable capacitance diode.

In a voltage controlled oscillator using a surface acoustic wave resonator, a first variable capacitance diode is connected to the surface acoustic wave resonator in series and a second variable capacitance diode is connected in parallel. A parallel circuit of a capacitor and a resistor is connected in series to the first variable capacitance diode or the second variable capacitance diode.

In a voltage controlled oscillator using a surface acoustic wave resonator, a first variable capacitance diode is connected in series to the surface acoustic wave resonator and a second variable capacitance diode is connected in parallel. A series circuit of a capacitor and a coil is connected in parallel to the first variable capacitance diode or the second variable capacitance diode.

[0012]

According to the above construction, the first and second variable capacitance capacitors are provided.
By connecting the electrode to the common tuning terminal
Ri, connected in series to the surface acoustic wave resonator, the resonant frequency of the surface acoustic wave resonator by the first variable capacitance diode, also connected in parallel with the surface acoustic wave resonator, a second variable capacitance Since the anti-resonance frequency of the surface acoustic wave resonator can be changed at the same time by the diode, the variable range of the oscillation frequency is widened.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a voltage controlled oscillator according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, according to the present invention, in a Colpitts oscillation circuit, an inductive reactance between a base and a collector of a transistor is connected in series to one surface acoustic wave resonator and the surface acoustic wave resonator. And a second variable capacitance diode connected in parallel.

That is, the cathode of the variable capacitance diode 1 is connected to the tuning terminal 2 via the resistor R1,
The anode is grounded. One terminal of the surface acoustic wave resonator 3 is connected to the connection point between the cathode of the variable capacitance diode 1 and the resistor R1 via the capacitor C1, and the other terminal of the surface acoustic wave resonator 3 is connected to the capacitor C2, It is connected to the base of the transistor 4 via a series circuit of C3.

The connection point between the capacitors C2 and C3 is
Connected to the tuning terminal 2 via the resistor R2 and to the cathode of the variable capacitance diode 5.
The anode of the variable capacitance diode 5 is connected to a connection point between the surface acoustic wave resonator 3 and the capacitor C1, and is grounded via a resistor R3, so that a voltage controlled oscillator 6 is formed.

The resistors R1, R2 and R3 are for applying an appropriate DC voltage to the variable capacitance diodes 1 and 5, and the capacitors C1, C2 and C3 are for cutting off the DC component.

The voltage controlled oscillator 6 configured as described above
When the control voltage Vt is applied from the tuning terminal 2 to the variable capacitance diodes 1 and 5 serving as variable reactance units, the reactance of the variable capacitance diodes 1 and 5 changes, and as shown in FIG. Changes the resonance frequency fr of the combined impedance of the surface acoustic wave resonator 3 and the variable capacitance diode 1. The variable capacitance diode 5 changes the anti-resonance frequency fa of the combined impedance of the surface acoustic wave resonator 3 and the variable capacitance diode 5. Change.
Therefore, the oscillation frequency fosc between the resonance frequency fr and the anti-resonance frequency fa can be significantly changed.

Further, as shown in FIG. 3, the slope of the reactance characteristic is constant even when the control voltage Vt changes, so that even if the oscillation condition fluctuates due to noise from a power supply or the like, the frequency change does not occur. The amount does not change, and a stable C / N value is obtained over the variable range of the oscillation frequency.

In order to expand the variable range of the reactance by the variable capacitance diodes 1 and 5, as shown in FIGS. 4 (a) to 4 (d), a variable reactance section is added to the variable capacitance diodes 1 and 5. A configuration in which a coil L1 is connected in series, variable capacitors 1 and 5, a capacitor C4
And a parallel circuit of a resistor R4, a configuration in which a series circuit of a capacitor C5 and a coil L2 is connected in parallel to the variable capacitance diodes 1 and 5, and a capacitor C6 in parallel with the variable capacitance diodes 1 and 5. Configuration.

The resistor R4 in FIG. 4 (b) is for passing a DC current to the variable capacitance diodes 1 and 5,
The capacitor C5 in FIG. 4C is for blocking a direct current flowing through the coil L2. FIG.
The coil L1, the capacitor C4, and the resistor R4 in (a) and (b) are connected to the anode side of the variable capacitance diodes 1 and 5, but may be connected to the cathode side.

With these configurations, the variable range of the reactance by the variable capacitance diodes 1 and 5 is expanded, and the oscillation frequency fosc can be controlled over a wider range.

[0022]

As described above, according to the voltage controlled oscillator of the present invention, two variable capacitance diodes connected in series and in parallel to the surface acoustic wave resonator enable the surface acoustic wave resonator and the two Since the resonance frequency and the antiresonance frequency of the combined impedance of the variable capacitance diode can be changed simultaneously, the variable range of the oscillation frequency is widened, and a voltage controlled oscillator capable of controlling the oscillation frequency over a wide range can be obtained. Also, even if the oscillation conditions fluctuate due to noise from the power supply or the like, the amount of change in the frequency does not change, so that a stable C
/ N value is obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing the combined impedance and phase characteristics of the surface acoustic wave resonator of FIG. 1 and two variable capacitance diodes.

FIG. 3 is a diagram showing a combined reactance characteristic of the surface acoustic wave resonator of FIG. 1 and two variable capacitance diodes.

FIGS. 4A to 4D are circuit diagrams of a variable reactance unit according to the second to fifth embodiments.

FIG. 5 is a circuit diagram of a conventional series-type voltage controlled oscillator.

FIG. 6 is a circuit diagram of a conventional parallel type voltage controlled oscillator.

FIG. 7 is a diagram illustrating the combined impedance and phase characteristics of the surface acoustic wave resonator and the variable capacitance diode.

FIG. 8 is a diagram showing the combined impedance and phase characteristics of a surface acoustic wave resonator and a variable capacitance diode in a conventional series-type voltage-controlled oscillator.

FIG. 9 is a diagram showing the combined impedance and phase characteristics of a surface acoustic wave resonator and a variable capacitance diode in a conventional parallel type voltage controlled oscillator.

FIG. 10 is a diagram showing a combined reactance characteristic of a surface acoustic wave resonator and a variable capacitance diode in a conventional series-type voltage-controlled oscillator.

FIG. 11 is a diagram showing a combined reactance characteristic of a surface acoustic wave resonator and a variable capacitance diode in a conventional parallel type voltage controlled oscillator.

[Explanation of symbols]

 1,5 Variable capacitance diode 3 Surface acoustic wave resonator 4 Transistor 6 Voltage controlled oscillator

Claims (4)

(57) [Claims] In a voltage controlled oscillator using a surface acoustic wave resonator, a first variable capacitance diode is connected to the surface acoustic wave resonator in series and a second variable capacitance diode is connected in parallel. , The first and second variable capacitance capacitors
A voltage controlled oscillator characterized by connecting an electrode to a common tuning terminal . 2. The voltage controlled oscillator according to claim 1, wherein a coil or a capacitor is connected in series or in parallel to said first variable capacitance diode or said second variable capacitance diode. 3. The voltage controlled oscillator according to claim 1, wherein a parallel circuit of a capacitor and a resistor is connected in series to said first variable capacitance diode or said second variable capacitance diode. 4. The voltage controlled oscillator according to claim 1, wherein a series circuit of a capacitor and a coil is connected in parallel to said first variable capacitance diode or said second variable capacitance diode.