JPH0645826A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To make linear the characteristic of an input voltage versus output frequency affecting the characteristic of a peripheral circuit in the voltage controlled oscillator using a variable capacity diode. CONSTITUTION:Different voltages are impressed to a variable capacity diode 6 and a variable capacity diode 7 at a certain rate, and the anode terminal of the variable capacity diode 6 is grounded through a capacitor 5 so that the impedances of resistors 3 and 4 to decide the voltages to be impressed can not affect the oscillation characteristics. Thus, the relation of the input voltage versus output frequency at the voltage controlled oscillator using the variable capacity diodes 6 and 7 is made linear over a wide range, and the characteristic of the peripheral circuit is not degraded.

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,
In particular, it relates to a voltage controlled oscillator using a variable capacitance diode.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a first conventional voltage controlled oscillator. The variable capacitance diode 7 is connected to the anode terminal and the cathode terminal to the control voltage input terminal 1 via the resistor 2. In the variable capacitance diode 7, when the potential of the cathode is made higher than that of the anode, the inter-terminal capacitance changes according to the voltage value applied between the terminals. By utilizing the fact that the inter-terminal capacitance of the variable capacitance diode 7 is changed by the positive potential applied to the control voltage application terminal 1, the resonance point of the oscillation circuit is changed and the output frequency is determined.

The capacitor 12 is connected between the base and the emitter of the transistor 17, and the capacitor 13 is connected via the capacitor 18 between the collector and the emitter of the transistor 17. Capacitor 18 generally has a sufficiently large capacitance value and is considered to be a short circuit when an AC operation is considered. The variable capacitance diode 7 connected in series with the capacitor 9, the coil 10 and the capacitor 8 is connected in parallel, and the transistor 1 is connected via the capacitor 11 and the capacitor 18.
7 is connected between the base and the collector. The oscillation frequency determined by each circuit constant is taken out to the output terminal 20 through the capacitor 19. The relationship between the input voltage and the output frequency of the voltage controlled oscillator is determined by the output frequency and the characteristics of the variable capacitance diode 7.

FIG. 7 is a correlation diagram of input voltage vs. output frequency of the first conventional voltage controlled oscillator. The slope of the graph shown in FIG. 7, that is, the relationship between the input voltage and the output frequency can be changed by the capacitance of the capacitor 8. However, if the capacitance of the capacitor 8 is made sufficiently larger than the capacitance of the variable capacitance diode, The slope of the graph of 7 is the maximum, and a larger slope cannot be given. As a means for obtaining a larger inclination, in the second conventional example shown in FIG. 4, a method of connecting the variable capacitance diode 24 in parallel with the variable capacitance diode 7 has been adopted. By adding the variable capacitance diode 24, the relationship between the input voltage and the output frequency has the characteristic shown in FIG.

[0005]

In this conventional voltage controlled oscillator, the variable capacitance diode 7 is used to control the output frequency in the first conventional example. Therefore, the relationship between the input voltage and the output frequency is as shown in FIG. It was non-linear.
In addition, the second conventional example also has a problem that it becomes non-linear as shown in FIG. 8 and deteriorates the characteristics of the peripheral circuit connected to the voltage controlled oscillator.

[0006]

SUMMARY OF THE INVENTION A voltage controlled oscillator according to the present invention comprises a variable capacitance diode whose capacitance value changes according to an applied voltage of an input signal, and an oscillation circuit which outputs an oscillation frequency corresponding to the change of the capacitance value. And a voltage division circuit to which the applied voltage different for each of the plurality of variable capacitance diodes is supplied.

[0007]

In the voltage-controlled oscillator of the present invention, the variable-capacitance diodes have different anode potentials by the voltage dividing circuit so that the respective variable-capacitance diodes are different from the voltage applied to the control voltage application terminal. Behaves as if it were a characteristic. The characteristic of the output frequency with respect to the input voltage is determined by the circuit constant of the voltage dividing circuit.

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

The variable capacitance diode 7 has its anode terminal grounded and its cathode terminal connected to the control voltage input terminal 1 via the resistor 2. The variable capacitance diode 6 has its anode terminal biased to a voltage determined by the resistors 2, 3, and 4, and its cathode terminal connected to the control voltage input terminal 1 via the resistor 2.

With this configuration, the voltage applied to the variable capacitance diode 7 and the variable capacitance diode 6 has a constant ratio due to the resistors 3 and 4. By setting the resistors 3 and 4 to appropriate values, the characteristic of the input voltage versus the output frequency becomes linear in the operation of the voltage controlled oscillator as shown in FIG. 5 in a wide input voltage range.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. The variable capacitance diode 7 has an anode terminal grounded and a cathode terminal connected to the control voltage input terminal 1 via the resistor 2. The variable capacitance diode 6 has an anode terminal connected between the resistor 3 and the resistor 21. Further, the variable capacitance diode 22 has an anode terminal connected between the resistor 21 and the resistor 4, and is biased to a voltage determined by the resistor 2, the resistor 3, the resistor 21, and the resistor 4,
Each cathode terminal is connected to the control voltage input terminal 1 via the resistor 2.

With this configuration, the voltage applied to the variable capacitance diode 7, the variable capacitance diode 6 and the variable capacitance diode 22 has a constant ratio due to the resistors 3, 21 and 4. By setting the resistors 3, 21, and 4 to appropriate values, the input voltage vs. output frequency characteristic is wider than that of the first embodiment shown in FIG. 5, as shown in FIG. Becomes linear.

In the first and second embodiments, the capacitors 5 and 23 are sufficiently smaller than the oscillation frequency because the resistors 3, 21 and 4 do not affect the oscillation characteristics in the AC characteristics. The constant is chosen to be the impedance.

[0014]

As described above, the present invention has the voltage dividing circuit for supplying different applied voltage to each variable capacitance diode whose capacitance value changes according to the applied voltage of the input signal. The characteristics of the output frequency and the output frequency can be made linear over a wide range, and the characteristics of the peripheral circuits can be prevented from being deteriorated.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a voltage controlled oscillator of a first conventional example.

FIG. 4 is a circuit diagram showing a voltage controlled oscillator of a second conventional example.

FIG. 5 is a correlation diagram showing the characteristics of the input voltage and the output frequency of the first embodiment.

FIG. 6 is a correlation diagram showing characteristics of an input voltage and an output frequency of the second embodiment.

FIG. 7 is a correlation diagram showing characteristics of an input voltage and an output frequency of the first conventional example.

FIG. 8 is a correlation diagram showing the characteristics of the input voltage and the output frequency of the second conventional example.

[Explanation of symbols]

1 control voltage input terminal 2,3,4,14,16,21 resistance 5,8,9,11,12,13,18,19,23
Capacitors 6,7,22,24 Variable capacitance diode 10 Coil 15 Power supply 17 Transistor 20 Output terminal

Claims (2)

[Claims] 1. A voltage controlled oscillator having a variable capacitance diode whose capacitance value changes according to an applied voltage of an input signal, and an oscillation circuit which outputs an oscillation frequency corresponding to the change of the capacitance value. A voltage-controlled oscillator having a voltage division circuit to which the applied voltage different for each capacitance diode is supplied. 2. The voltage controlled oscillator according to claim 1, wherein the voltage dividing circuit has a capacitor that reduces an impedance given to a characteristic of the oscillation circuit.