JPH0722841A - Voltage controlled oscillator - Google Patents

Abstract

(57) [Summary] [Object] To provide a voltage controlled oscillator circuit in which the control frequency applied from the control terminal Vt is proportional to the oscillation frequency in a wide voltage range. The present invention relates to a resonance circuit section X having a variable capacitance diode Cv and a negative resistance circuit section Y having an active element Q _1.
By changing the applied voltage supplied from the control terminal Vt to the variable capacitance diode Cv,
This is a voltage-controlled oscillator in which the resonance frequency of the resonance circuit section is changed, and a voltage dividing resistor R ₁ is arranged between the control terminal Vt and the anode terminal of the variable capacitance diode Cv.

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 capable of changing the applied voltage of a variable capacitance diode to change the resonance frequency of a resonance circuit and further the oscillation frequency.

[0002]

2. Description of the Related Art A conventional voltage controlled oscillator (VCO) has a circuit configuration as shown in FIG. In the figure, X
Is a resonance circuit section including microstrip lines SL ₁ and SL ₂ , variable capacitance diode Cv, capacitors C ₁ , C ₃ and C ₄ , and Y is a transistor Q ₁ and resistors R _{5 to} R _5.
6 , a negative resistance circuit portion composed of capacitors C _{5 to} C ₇ , and Z is a transistor Q ₂ and a microstrip line S.
It is an amplifier circuit section including L ₃ , resistors R _{3 to} R ₄ , and capacitors C _{8 to} C ₁₂ .

In the conventional VCO, the control terminal Vt for controlling the frequency and the cathode terminal of the variable capacitance diode Cv are directly connected via the microstrip line SL _2, and the anode terminal of the variable capacitance diode Cv is grounded.

In such a VCO, when a predetermined voltage (hereinafter, referred to as a control voltage) is applied from the control terminal Vt, the voltage across the variable capacitance diode Cv (hereinafter, referred to as a voltage between terminals) is changed to a predetermined value. Capacitance is generated, the microstrip line SL ₁ , the capacitor C ₁ ,
The combined capacitance component of the resonance circuit unit X composed of C ₃ and C ₄ changes, and the resonance frequency changes. As a result, a feedback signal corresponding to the resonance frequency between the transistor Q ₁ and the capacitor C ₆ of the negative resistance circuit section Y is generated, the signal is amplified by the amplification circuit section Z, and is output as an oscillation signal from the output terminal RFout. Derived. That is, the inter-terminal voltage-capacitance change characteristic of the variable capacitance diode Cv is directly reflected in the change in the oscillation frequency of the voltage controlled oscillator.

[0005]

However, as shown in FIG. 5, the oscillation frequency and the control voltage characteristic due to the voltage-capacitance change between the terminals of the variable capacitance diode Cv show that the frequency change when the control voltage exceeds a predetermined value. Linearity is impaired.

This is because the capacitance decreases as the inter-terminal voltage of the variable capacitance diode Cv increases, and the capacitance is saturated at a specific capacitance value.

That is, in the above-mentioned VCO, if the control voltage becomes higher, the rate of change of the capacitance of the variable capacitance diode Cv becomes smaller, and the change width of the oscillation frequency becomes smaller.

When the change rate of the oscillation frequency is not uniform with respect to the control voltage (the linearity is poor), for example, when the oscillation frequency is locked by using a phase locked loop (PLL). The lock time (lock-up time) varies depending on whether the control voltage is high or low. In addition, like a mobile communication device, a signal can be directly input from the control terminal Vt to perform FM.
When modulation is applied (direct modulation method), the degree of modulation (frequency shift) differs depending on whether the control voltage is high or low. Therefore, in reality, a large-scale circuit was added to correct this degree of modulation, but of course the equipment became larger, and the circuit constants in the design also changed significantly, resulting in cost increase. Will end up.

The present invention has been devised in view of the above problems, and an object thereof is to add a simple voltage dividing circuit between a variable capacitance diode and a control terminal to change the variable capacitance diode. It is an object of the present invention to provide a voltage controlled oscillator in which a change in oscillation frequency proportional to a control voltage supplied from a control terminal is obtained by using only a portion having good linearity in terms of capacitance characteristics.

[0010]

A voltage controlled oscillator circuit according to the present invention includes a resonant circuit section having a variable capacitance diode and a negative resistance circuit section having an active element, and a control terminal is connected to the variable capacitance diode. In a voltage controlled oscillator in which the resonance frequency of the resonance circuit section is changed by changing the supplied voltage, the control voltage is a voltage obtained by arranging a voltage dividing resistor between the control terminal and the anode terminal of the variable capacitance diode. It is a controlled oscillator.

[0011]

According to the present invention, the voltage dividing resistor for the control voltage supplied from the control terminal is arranged between the control terminal and the anode terminal of the variable capacitance diode.

Therefore, for example, in the case where the variable capacitance diode changes the oscillation frequency of the VCO up to a terminal voltage of 3.5 V, which has good linearity, and the control voltage supplied from the control terminal changes from 1 to 4.5 V, what if,
When the applied voltage is 4.5V, the voltage applied to the actual variable capacitance diode is converted to 3.5V by the voltage dividing resistance of the control voltage.

With this configuration, since the VCO characteristic of the voltage-capacitance change between the terminals of the variable capacitance diode can be selected and used only in the portion having good linearity, it is proportional to the control voltage supplied from the control terminal. It is possible to derive the oscillation frequency.

For this reason, there is no difference in the time for locking (lock-up) using the phase locked loop (PLL), and the degree of modulation (frequency shift) is different when the control voltage is high and when it is low. Device, the device can be kept small, and the design is not complicated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A voltage controlled oscillator according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a voltage controlled oscillator (VC) of the present invention.
It is a figure which shows the voltage control oscillation circuit used for O). In the figure, X is the microstrip lines SL ₁ and S
L ₂ , variable capacitance diode Cv, capacitor C ₁ ~
A resonant circuit section composed of C ₄ , voltage dividing resistors R ₁ and R ₂ ,
Y is a transistor Q ₁ , resistors R _{5 to} R ₆ , and a capacitor C
_A negative resistance circuit section composed of _{5 to} C ₇ , where Z is a transistor Q ₂ , a microstrip line SL ₃ , and a resistor R ₃ to.
This is an amplifier circuit section composed of R ₄ and capacitors C _{8 to} C ₁₂ .

In the resonance circuit section X of the VCO described above, the control terminal Vt is connected to the cathode terminal of the variable capacitance diode Cv via the microstrip line SL ₂ , and at the same time, is connected to one end of the resistor R ₁ which is a voltage dividing circuit. It is connected. Further, the other end of the resistor ₁ is connected to the resistor R ₂ which is a voltage dividing circuit and is also connected to the anode terminal of the variable capacitance diode Cv. Further, a bypass capacitor C ₂ is connected between the anode terminal of the variable capacitance diode Cv and the ground, and the other end of the voltage dividing resistor R ₂ is also connected to the ground.

Therefore, the control voltage supplied from the control terminal Vt for controlling the frequency is the voltage dividing resistors R ₁ and R _2.
The voltage divided into two and applied to the resistor R ₁ becomes the inter-terminal voltage applied to the variable capacitance diode Cv.

The voltage between the predetermined terminals divided by the voltage dividing resistors R ₁ and R ₂ is applied to the variable capacitance diode Cv, the capacitance component of the resonance circuit changes, and the resonance frequency changes. As a result, a feedback signal is generated between the transistor Q _{1 of} the negative resistance circuit section Y and the capacitor C ₆ in correspondence with the resonance frequency, the signal is amplified by the amplification circuit section Z, and a predetermined signal is output from the output terminal RFout. It is derived as a signal of the oscillation frequency.

In the present invention, as described above, the resistance R
The control voltage of the control terminal Vt is divided by a predetermined voltage division ratio determined by ₁ and R ₂ , and the divided voltage is applied across the variable capacitance diode Cv as an inter-terminal voltage.

This voltage division ratio is based on the variable capacitance diode Cv.
The resistance values of the resistors R ₁ and R ₂ are determined so that the voltage-capacitance characteristic of ( ₁₎ is in the range in which the VCO has a good characteristic.

For example, when the applied voltage of the control terminal Vt changes from 1 to 4.5V and the oscillation frequency of the variable capacitance diode Cv changes uniformly up to 3.5V, the applied voltage of the control terminal Vt is 4. When it takes 5V,
The voltage dividing ratio is set to 3.5 / 4.5 so that the variable capacitance diode Cv is set to 3.5V by the voltage dividing resistors R ₁ and R ₂ .

As a result, the supply range of the control voltage of the control terminal Vt is set to the voltage between the terminals of the variable capacitance diode −.
The capacitance characteristic can be converted and used so as to correspond to a range in which the linearity of the VCO is excellent, and the resonance frequency of the resonance circuit or the oscillation frequency of the entire oscillation circuit is proportional to the control voltage of the control terminal Vt. Can be generated at.

In other words, as shown in FIG. 2, when the relationship between the control voltage of the control terminal Vt and the oscillation frequency is examined, when the control voltage of the conventional VCO exceeds 3.5 V, the linearity is impaired due to the characteristic of the oscillation frequency. However,
In the present invention, the linearity of the change of the oscillation frequency f can be maintained even if the control voltage is applied up to about 4.5V.

However, in this case, although apparently the linearity of the oscillation frequency f is achieved with respect to the control voltage up to 4.5 V, the terminal voltage actually applied to the variable capacitance diode Cv does not change. Therefore, the change width of the capacitance becomes small, and the change width and the change rate of the oscillation frequency become small. In order to improve this, it is important to increase the capacitance of the capacitor C ₃ connected in series with the variable capacitance diode Cv as compared with the conventional one. By doing so, as shown in FIG. 3, it is possible to prevent the combined capacitance of the capacitance components of the entire resonance circuit unit X from changing, and it is possible to improve the sensitivity of the frequency change to the control voltage.

As described above, according to the present invention, the oscillation circuit has an oscillation frequency proportional to the control voltage from the control terminal Vt, and the optimum circuit can be easily designed in the frequency control by the PLL method, and the lockup can be performed. Time can be improved. Further, in the FM modulation of the direct modulation method, since the modulation sensitivity is uniform, it is possible to transmit a sound with higher sound quality.

According to the present inventors, the voltage between terminals 1 to 3.
A variable capacitance diode Cv, 3 pF that exhibits a uniform change in the oscillation frequency of the VCO at 5 V (capacity 11 pF to 6 pF).
₁ k as the voltage dividing resistors R ₁ and R ₂ for a conventional VCO having a resonance frequency of 860 MHz and having a capacitor C ₂
Omega, added 330 ohms, further, the linearity of the oscillation frequency with respect to VCO the control voltages of the present invention was changed to a capacitor C ₂ of 3.5pF to equal the sensitivity of the change in the oscillation frequency with respect to control voltage of the conventional 3. Expanded to 5V-4.5V, and the sensitivity is 10% from the conventional 11MHz / V.
It was possible to confirm that there was no problem within the range of substantial variation that changed to 6 MHz / V.

In the embodiment described above, the resistance R ₁ ,
The R ₂ , the capacitor C ₂ , and the variable capacitance diode Cv are respectively set in consideration of the resonance frequency and the range of the applied voltage of the control voltage.
It may be determined variously and is not limited to the above circuit constants.

[0029]

As described above, according to the present invention, since the voltage between terminals applied to the variable capacitance diode is determined by the voltage dividing resistance, only the portion where the linearity of the voltage-capacitance characteristic of the variable capacitance diode is good. It can be operated.

Therefore, the voltage controlled oscillator circuit can obtain a frequency change proportional to the control voltage supplied from the control terminal.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing a relationship between a control voltage and an oscillation frequency in the oscillation circuit of the voltage controlled oscillator according to the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the potential difference across the variable capacitance diode and the combined capacitance due to an increase in the capacitance value of the capacitor C ₃ in the oscillation circuit of the voltage controlled oscillator of the present invention.

FIG. 4 is a circuit diagram illustrating a circuit configuration of a conventional voltage controlled oscillator.

FIG. 5 is a characteristic diagram showing a relationship between a control voltage and an oscillation frequency in an oscillation circuit of a conventional voltage controlled oscillator.

[Explanation of supplements]

X ... ・ Resonance circuit section Y ・ ・ ・ ・ ・ ・ Negative resistance circuit section Z ・ ・ ・ ・ Amplification circuit section SL ₁ , SL ₂ , SL ₂・ ・ Microstrip line Cv・ Variable capacitance diodes C _{1 to} C ₁₁ ... Capacitors R ₁ and R ₂ ... Dividing resistors R _{3 to} R ₇ ... Resistors

Claims (1)

[Claims] 1. A resonance circuit section including a resonance circuit section having a variable capacitance diode and a negative resistance circuit section having an active element, wherein resonance voltage of the resonance circuit section is changed by changing a voltage supplied to the variable capacitance diode from a control terminal. A voltage controlled oscillator having a variable frequency, wherein a voltage dividing resistor for controlling an applied voltage is arranged between the control terminal and an anode terminal of a variable capacitance diode.