JP2001085940A - Voltage controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the C/N of an oscillated signal by avoiding deterioration in Q by a choke inductor element to connect an anode of a varactor diode to ground in terms of DC. SOLUTION: The voltage controlled oscillator is provided with a 2-terminal network reactance circuit 8 that is connected between a base and a collector of an oscillation transistor(TR) 1 in terms of high frequencies and providing an inductive impedance at an oscillated frequency. The 2-terminal network reactance circuit 8 has an inductive element 8a, a 1st varactor diode 8c whose anode is connected to one end of the inductive element 8a and whose cathode is connected to the other end of the inductive element 8a via a DC cut-off capacitor, and a 2nd varactor diode 8d whose anode is connected to the other end of the inductive element 8a. Then the level of the one end of the inductive element 8a and the anode of the 1st varactor diode 8c are fixed to a DC level and the same control voltage is applied to the cathode of the 1st varactor diode 8c and the 2nd varactor diode 8d respectively.

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 two varactor diodes to widen a variable range of an oscillation frequency.

[0002]

2. Description of the Related Art A circuit configuration of a conventional voltage controlled oscillator is shown in FIG.
Shown in In FIG. 2, the collector of the oscillation transistor 21 to which the power supply voltage Vb is applied is a DC cut capacitor 2
2, a high-frequency ground is provided, and a feedback capacitor 23 is connected between the base and the emitter. Further, another feedback capacitor 24 is connected between the emitter of the oscillation transistor 21 and the ground, so that the feedback capacitor 24 is connected between the emitter and the collector in terms of high frequency.

An anode of a first varactor diode 26 is connected to a base of the oscillation transistor 21 via a DC cut capacitor 25, and a second varactor diode 2 is connected to a cathode of the first varactor diode 26.
7 is connected to the second varactor diode 2
One end of an inductance element 28 is connected to the anode of 7, and the other end is connected to the ground. Therefore, the DC cut capacitor 25, the first varactor diode 2
6, the second varactor diode 27 and the inductance element 28 are connected between the base and collector of the oscillation transistor 21 in a high-frequency state in a state where they are connected in series with each other.

The anode of the first varactor diode 26 is connected to ground by a choke inductance element 29, and the cathodes of the first varactor diode 26 and the second varactor diode 27 are connected via a resistance element 30 having a large resistance value. Thus, the control voltage Vc is applied. The oscillation frequency can be changed by changing the value of the control voltage Vc.

At this time, since the first varactor diode 26 and the second varactor diode 27 are connected in series with each other and in series with the inductance element 28, the range of change of the oscillation frequency is widened.

[0006]

In the above configuration, the first varactor diode 2 connected in series with each other
6. The whole of the second varactor diode 27 and the inductance element 28 exhibit inductive characteristics at the oscillation frequency to form a parallel resonance circuit with the feedback capacitors 23 and 24, and the choke inductance element 29 is connected in parallel to these. Therefore, there is a problem that the Q of the parallel resonance circuit is reduced and the C / N of the oscillation signal is deteriorated.

Therefore, the voltage controlled oscillator of the present invention aims at improving the C / N of the oscillation signal by eliminating the Q reduction due to the choke inductance element for connecting the anode of the varactor diode to the ground in a DC manner. I have.

[0008]

In order to solve the above problems, a voltage controlled oscillator according to the present invention comprises: an oscillation transistor;
A feedback capacitor connected between the base and the emitter and between the emitter and the collector of the oscillating transistor at a high frequency; and a two-terminal connected between the base and the collector of the oscillating transistor at a high frequency and exhibiting inductive characteristics at the oscillating frequency A two-terminal network reactance circuit having an inductance element, an anode connected to one end of the inductance element, and a cathode connected to the other end of the inductance element via a DC cut capacitor. Varactor diode, and a second varactor diode having an anode connected to the other end of the inductance element, wherein the one end of the inductance element and the anode of the first varactor diode are fixed at a DC potential. And the first varactor die Applying a control voltage value of each of the cathode to the same value of over de and the second varactor diode and to vary the oscillation frequency by changing the control voltage.

Further, in the voltage controlled oscillator according to the present invention, the collector of the oscillation transistor is grounded at a high frequency, and the one end of the inductance element and the anode of the first varactor diode are directly connected to ground. The cathode of the second varactor diode was connected to the base of the oscillation transistor at a high frequency.

[0010]

FIG. 1 shows a circuit configuration of a voltage controlled oscillator according to the present invention. A power supply voltage Vb is applied to the collector of an oscillation transistor 1 and grounded by a DC cut capacitor 2 at a high frequency. One feedback capacitor 3 is connected between the base and the emitter. Further, another feedback capacitor 4 is connected between the emitter of the oscillation transistor 1 and the ground. As a result, the feedback capacitor 4 is connected between the emitter and the collector and connected in series with the feedback capacitor 3 in terms of high frequency.

A bias voltage is applied to the base of the oscillation transistor 1 by bias resistance elements 5 and 6, and a bias voltage is applied to the emitter by a bias resistance element 7.

A two-terminal network reactance circuit 8, which is inductive at the oscillation frequency, is connected between the base of the oscillation transistor 1 and the ground. As a result, a common-collector oscillator is formed.

The two-terminal network reactance circuit 8 includes an inductance element 8a, a first element having an anode connected to one end of the inductance element 8a, and a cathode connected to the other end of the inductance element 8a via a DC cut capacitor 8b. It is composed of a varactor diode 8c and a second varactor diode 8d having an anode connected to the other end of the inductance element 8a.

Then, one end of the inductance element 8a and the anode of the first varactor diode 8c are directly connected to the ground to be fixed at a DC potential, and the cathode of the second varactor diode 8d is connected to the DC cut capacitor 9d. As a result, it is connected to the base of the oscillation transistor 1 at a high frequency. Thereby, the two-terminal network reactance circuit 8 is connected at a high frequency between the base and the collector of the oscillation transistor, and forms a parallel resonance circuit together with the feedback capacitors 3 and 4 connected in series to each other.

A control voltage Vc is commonly applied to the respective cathodes of the first varactor diode 8c and the second varactor diode 8c via feed resistance elements 10 and 11 having large resistance values. The oscillation frequency can be changed by changing the value of the control voltage Vc.

Since the two-terminal network reactance circuit 8 is a series-parallel resonance circuit, the inductance of the inductance element 8a is compared with the conventional one in order to make the oscillation frequency the same as that of the conventional voltage controlled oscillator (FIG. 2). Needs to be reduced to about 1/3. Also, in this case, the change rate of the oscillation frequency with respect to the change of the control voltage is almost the same as that of the related art.

According to the above configuration, the anode of the first varactor diode 8c and one end of the inductance element 8a in the two-terminal network reactance circuit 8 are directly connected to the ground, and the anode of the second varactor diode 8d is connected to the inductance element. Therefore, the parallel resonance circuit does not require an extra circuit element for applying the control voltage Vc to the first varactor diode 8c and the second varactor diode 8d, and the Q does not decrease. Therefore, the C / N of the oscillation signal is improved. Also,
Since the anodes of the first varactor diode 8c and the second varactor diode 8d are DC-connected to the ground, slight fluctuations such as ripples in the power supply voltage are not applied to these varactor diodes.
/ N is improved.

When a grounded base or emitter grounded oscillator is used, the DC cut capacitor 2 is connected between the base and the ground or between the emitter and the ground, and the feedback capacitor 4 is connected between the emitter and the collector. . Then, instead of connecting one end of the inductance element 8a and the anode of the first varactor diode 8c to the ground, they may be connected to the collector of the oscillation transistor 1 and fixed at a DC potential. At this time,
The power supply voltage Vb is applied to the collector of the oscillation transistor 1 via another choke inductance element (not shown).

[0019]

As described above, the voltage controlled oscillator according to the present invention comprises a two-terminal network reactance circuit which is connected between the base and collector of the oscillation transistor at a high frequency and exhibits inductive characteristics at the oscillation frequency. The net reactance circuit includes an inductance element, a first varactor diode having an anode connected to one end of the inductance element and a cathode connected to the other end of the inductance element via a DC cut capacitor, and an anode connected to the other end of the inductance element. And a second varactor diode connected thereto, one end of the inductance element and the anode of the first varactor diode are fixed at a DC potential, and the respective cathodes of the first varactor diode and the second varactor diode Apply the same control voltage value to Since the oscillation frequency is changed, the parallel resonance circuit including the two-terminal network reactance circuit and the feedback capacitor needs an extra circuit element for applying a control voltage to the first varactor diode and the second varactor diode. And there is no decrease in Q. Therefore,
The C / N of the oscillation signal is improved.

In the voltage controlled oscillator of the present invention, the collector of the oscillation transistor is grounded at high frequency, one end of the inductance element and the anode of the first varactor diode are directly connected to ground, Since the cathode is connected to the base of the oscillating transistor at a high frequency, minute fluctuations such as ripples in the power supply voltage are not applied to these varactor diodes.
/ N is improved.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a voltage controlled oscillator of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional voltage controlled oscillator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillation transistor 2 DC cut capacitor 3, 4 Feedback capacitor 5, 6, 7 Bias resistance element 8 Two-terminal network reactance circuit 8a Inductance element 8b DC cut capacitor 8c First varactor diode 8d Second varactor diode 9 DC cut capacitor 10 , 11 Feeding resistance element

Claims (2)

[Claims] 1. An oscillation transistor, a feedback capacitor connected between the base and the emitter of the oscillation transistor and between the emitter and the collector at a high frequency, and connected between the base and the collector of the oscillation transistor at a high frequency. A two-terminal network reactance circuit that exhibits inductive characteristics at an oscillation frequency, wherein the two-terminal network reactance circuit has an inductance element, an anode connected to one end of the inductance element, and a cathode connected to the inductance element via a DC cut capacitor. A first varactor diode connected to the other end of the first varactor diode, and a second varactor diode having an anode connected to the other end of the inductance element. The one end of the inductance element and the first varactor diode DC potential with the anode of And the same control voltage value is applied to the respective cathodes of the first varactor diode and the second varactor diode, and the oscillation frequency is changed by changing the control voltage. Voltage controlled oscillator. 2. The collector of the oscillation transistor is grounded at a high frequency, the one end of the inductance element and the anode of the first varactor diode are directly connected to ground, and the cathode of the second varactor diode is connected to the ground. 2. The voltage controlled oscillator according to claim 1, wherein the voltage controlled oscillator is connected to the base of the oscillation transistor at a high frequency.