JPH07154140A - Voltage controlled oscillation circuit - Google Patents

Abstract

PURPOSE:To extend the variable range of an oscillating frequency by connecting a sub resonance circuit using a frequency around a maximum variable frequency for a turning frequency in parallel to a varactor diode connecting in series to a dielectric resonator as an oscillation element. CONSTITUTION:A sub resonance circuit 2 being a series resonance circuit comprising a coil L1 and a capacitor C6 is connected in parallel to a varactor diode(VC) connecting in series to a dielectric resonator 1 as an oscillating element. The resonance frequency of the circuit 2 is set around a frequency of a maximum variable frequency and a control voltage is applied to the VC via a resistor R6 and the circuit 2 to change the oscillating frequency. That is, when the control voltage gets higher to decrease the capacitance of the VC, the oscillating frequency is increased and when the frequency approaches the maximum variable frequency, the capacitance of the VC is not sufficiently decreased and the impedance is increased. However, the circuit 2 is operated in this case in place of the VC, the impedance is reduced and the oscillating frequency is smoothly increased. Thus, the variable range of the oscillating frequency is extended without deteriorating the C/N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a PLL [Phase Locked
Loop] circuit and other voltage controlled oscillator circuits (VCO [Volta
ge Controlled Oscilator]).

[0002]

2. Description of the Related Art A voltage controlled oscillation circuit is an oscillation circuit that changes an oscillation frequency by applying a control voltage to a variable capacitance diode (varicap) to change the capacitance, and is used for a PLL circuit of a frequency synthesizer, for example. Is used as a local oscillator circuit for transceivers.

By the way, in VSAT (satellite communication), each transmission frequency of 51 channels is 14.0 GHz to 1
It covers the 4.5 GHz band. However, if it is left as it is, 500M is generated between the 0th and 50th channels
Since there is a frequency difference of Hz, in the ODU (outdoor unit) transmission side converter, the 180 MHz band transmission signal is mixed with the local oscillation frequency of 2764 MHz to 2864 MHz for each channel, and this local oscillation frequency is multiplied by four. 14.0G by mixing
A transmission frequency of Hz to 14.5 GHz is obtained. However, even in this case, the local oscillator circuit has a frequency difference of 100 MHz between the 0th channel and the 50th channel.
It is necessary to oscillate in the range of 764 MHz to 2864 MHz. For this purpose, the voltage-controlled oscillator circuit of the PLL circuit used for the frequency synthesizer of the local oscillator circuit needs to control the oscillation frequency of the frequency difference of 200 MHz by adding a margin of 50 MHz to the high and low. A very wide range is required.

[0004]

However, in the conventional voltage controlled oscillator circuit, the variable range of the oscillation frequency depends on the change characteristic of the capacitance of the variable capacitance diode with respect to the control voltage. When the control voltage becomes higher than a certain level, the capacitance of the variable capacitance diode does not become sufficiently small and the characteristic becomes unstable. Therefore, as shown by the solid line in FIG. 5, the characteristic of the oscillation frequency with respect to the control voltage of the voltage controlled oscillation circuit is that the oscillation frequency is proportional to this when the control voltage is low, but becomes higher when the control voltage is higher than a certain level. However, the linearity of the characteristics deteriorated in proportion to this.

Therefore, the conventional voltage controlled oscillator circuit is
When used in an L circuit, the lockable frequency band is limited, and the variable range of the frequency is narrowed. If an attempt is made to lock at a high frequency, the loop becomes unstable and the oscillation frequency itself fluctuates. There was also a fear of starting oscillation. When used as a local oscillation circuit in the VSAT ODU, a sufficient margin cannot be taken in the variable range of the frequency, and the reliability of the circuit deteriorates.

When it is desired to increase the oscillation frequency of the voltage controlled oscillation circuit, conventionally, the capacitance of the capacitor connected in series with the variable capacitance diode is increased to reduce the combined capacitance. However, this merely shifts the variable range of the frequency to the high frequency side and does not expand the variable range. Further, if the capacitance of this capacitor is increased, the C / N ratio of the oscillation circuit may deteriorate due to the resistance component of the variable capacitance diode, and this may also become a load and cause inconvenience such as oscillation stop. .

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a voltage-controlled oscillation circuit in which the oscillation frequency is changed by changing the capacitance by applying a control voltage to a variable capacitance diode. It is characterized in that a sub-resonant circuit whose tuning frequency is near the frequency is connected in parallel with the variable capacitance diode.

Further, the present invention is characterized in that a dielectric resonator is used as the oscillation element.

Furthermore, the present invention is characterized in that the sub-resonant circuit connected to the variable capacitance diode is a series resonant circuit including a series circuit of a coil and a capacitor.

[0010]

The voltage controlled oscillator circuit changes the circuit constant of the tuning circuit by applying a control voltage to the variable capacitance diode to change the capacitance, thereby changing the oscillation frequency. In the conventional voltage controlled oscillator circuit, when the control voltage becomes higher than a certain level, the capacitance of the variable capacitance diode does not decrease in proportion thereto, and the linearity of the oscillation frequency deteriorates.

However, according to the configuration of the present invention, as the control voltage increases and the oscillation frequency approaches the maximum variable frequency, the tuning frequency of the sub-resonant circuit connected in parallel with the variable capacitance diode approaches. The sub-resonant circuit functions in place of the variable capacitance diode to smoothly raise the oscillation frequency.

Therefore, according to the present invention, since the sub-resonance circuit can be tuned near the maximum variable frequency to supplement the variable capacitance diode, deterioration of the linearity of the oscillation frequency near the maximum variable frequency can be prevented and the oscillation frequency can be changed. The range can be expanded. Moreover, since the sub-resonant circuit is connected in parallel with the variable capacitance diode, there is no possibility that the C / N ratio of the oscillation circuit will deteriorate.

Further, the present invention is characterized in that a dielectric resonator is used as an oscillation element of the voltage controlled oscillation circuit. As described above, the high-frequency voltage-controlled oscillation circuit using the dielectric resonator as the oscillation element normally uses the dielectric resonator as the inductive element in the Colpitts type oscillation circuit. The variable capacitance diode is connected in series or in parallel with the dielectric resonator.

Furthermore, the present invention is characterized in that the sub-resonant circuit is constituted by a series resonant circuit including a coil and a capacitor. In this case, the coil has the characteristic of blocking the high frequency component and allowing the direct current component to pass as it is, so that the control voltage of the variable capacitance diode can be applied via the coil of the series resonance circuit.

[0015]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention and is a circuit diagram of a voltage controlled oscillator circuit using a λ / 2 type dielectric resonator.

This embodiment shows a case where a λ / 2 type dielectric resonator is used as the oscillation element of the voltage controlled oscillation circuit.

This voltage controlled oscillator circuit uses a Colpitts type oscillator circuit in which two feedback capacitors C1 and C2 connected in series between the collector and the base of a transistor Q whose collector is grounded are connected to the emitter for feedback. ing. Here, RE is an emitter resistance, R1 to R4 are bias resistances, and C3 is a ground capacitor. A bias voltage is applied to the terminal B.

The dielectric resonator 1 is connected in parallel to the two feedback capacitors C1 and C2 and is used as an inductive element. The dielectric resonator 1 is an oscillating element in which a through hole is provided in a ceramic dielectric, and an outer conductor and an inner conductor are provided on the outer peripheral surface of the ceramic dielectric and the inner peripheral surface of the through hole, respectively. Since the λ / 2 type is used as described above, the outer conductor and the inner conductor are open at both ends of the through hole.

The variable capacitance diode VC is connected in series to the dielectric resonator 1. That is, the transistor Q
Dielectric resonator 1 via coupling capacitor C4 to the base of
Is connected to one end of the inner conductor, and the other end of the inner conductor of the dielectric resonator 1 is connected to the cathode of the variable capacitance diode VC via a coupling capacitor C4. And
The anode side of the variable capacitance diode VC is grounded. The outer conductor of the dielectric resonator 1 is also grounded.

The control voltage of the variable capacitance diode VC is applied to the cathode side of the variable capacitance diode VC via the current limiting resistor R5 and the sub resonance circuit 2. The bypass capacitor (pass capacitor) C7 connected to the control voltage application side of the current limiting resistor R5 is for preventing the oscillation frequency from leaking to the control voltage source side.

The sub-resonant circuit 2 has a coil L1 inserted between a variable capacitance diode VC and a current limiting resistor R5.
And a capacitor C6 inserted between the connection point of the coil L1 and the current limiting resistor R5 and the ground. The coil L1 and the capacitor C6 form a series resonance circuit connected in parallel to the variable capacitance diode VC, and are set so as to tune near the maximum variable frequency of the voltage controlled oscillator circuit.

In the voltage controlled oscillator circuit having the above-mentioned configuration, two capacitive elements in the Colpitts type oscillator are constituted by the feedback capacitors C1 and C2, and the inductive element is constituted by the dielectric resonator 1 to oscillate. I do. Then, the oscillation frequency can be changed by changing the capacitance of the variable capacitance diode VC connected in series to the dielectric resonator 1 by the control voltage. That is, when the control voltage is increased and the capacitance of the variable capacitance diode VC is decreased, as shown in FIG. 5, the oscillation frequency is increased and these are in a proportional relationship while the control voltage is low.

However, when the control voltage further increases and approaches the maximum frequency in the variable range, the capacitance of the variable capacitance diode VC does not become sufficiently small and the impedance also increases. However, in the case of the voltage controlled oscillator circuit of the present embodiment, the sub-resonant circuit 2 connected in parallel to the variable capacitance diode VC tunes around the maximum variable frequency, so that the series resonant circuit formed by the coil L1 and the capacitor C6 is connected. Impedance drops. Therefore, in the vicinity of this maximum variable frequency, the sub-resonant circuit 2 functions in place of the variable capacitance diode VC, so that the oscillation frequency rises smoothly within a certain range as shown by the alternate long and short dash line in FIG. become.

As a result, according to the voltage controlled oscillator circuit of the present embodiment, the range having the linearity in the characteristics of the control voltage and the oscillation frequency is further extended to the high frequency side by the sub-resonance circuit 2, and the variable range of the oscillation frequency is widened. Will be able to. Therefore, this voltage controlled oscillator circuit is used in the PLL circuit of the frequency synthesizer to make the ODU of VSAT.
Even when it is used as a local oscillation circuit in, the oscillation frequency can be controlled with a sufficient margin in the high and low frequency ranges.

FIG. 2 shows a second embodiment of the present invention and is a circuit diagram of a voltage controlled oscillator circuit using a λ / 4 type dielectric resonator. The constituent members having the same functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

This embodiment shows a case where a λ / 4 type dielectric resonator is used as the oscillation element of the voltage controlled oscillation circuit.

In the λ / 4 type dielectric resonator 3, as shown in the figure, the inner conductor and the outer conductor are open at one end and short-circuited at the other end. Therefore, as in the first embodiment, one end of the inner conductor of the dielectric resonator 3 is connected to the base of the transistor Q via the coupling capacitor C4, but the variable capacitance diode VC also has a coupling capacitor C5 on the cathode side. Is connected to one end side of the inner conductor of the dielectric resonator 3.

The sub-resonant circuit 2 has the same structure as that of the first embodiment, and the current limiting resistor R5 and the bypass capacitor C7 are also connected in the same manner so that the control voltage is applied to the variable capacitance diode VC via these. Has become.

Also in the case of this embodiment, when the control voltage becomes high and approaches the maximum variable frequency, the variable capacitance diode V
The sub-resonant circuit 2 functions in place of C to smoothly raise the oscillation frequency. Therefore, as in the case of the first embodiment, the variable range of the oscillation frequency can be expanded to the high frequency side.

FIG. 3 shows a third embodiment of the present invention and is a circuit diagram of a voltage controlled oscillator circuit using a λ / 2 type dielectric resonator as a sub-resonant circuit. The constituent members having the same functions as those of the embodiment shown in FIGS. 1 and 2 are designated by the same reference numerals and the description thereof will be omitted.

In the voltage controlled oscillator circuit of this embodiment, the dielectric resonator 1 used as an oscillating element has a λ / similar to that of the first embodiment.
I use two types. However, it is also possible to use the λ / 4 type dielectric resonator 3 as in the second embodiment.

The sub-resonant circuit 2 is composed of a λ / 2 type dielectric resonator 4. That is, the inner conductor of the dielectric resonator 4 is inserted between the cathode side of the variable capacitance diode VC and the current limiting resistor R5, and the outer conductor of the dielectric resonator 4 is grounded. The dielectric resonator 4 is set so that the series resonance frequency is near the maximum variable frequency of the voltage controlled oscillator circuit. Note that the λ / 4 type dielectric resonator 4 cannot be used for this sub-resonant circuit 2.

Also in the case of this embodiment, when the control voltage becomes high and approaches the maximum variable frequency, the dielectric resonator 4 of the sub-resonant circuit 2 is tuned and the oscillation frequency can be smoothly increased. Therefore, as in the case of the first and second embodiments, the variable range of the oscillation frequency can be expanded to the high frequency side.

FIG. 4 shows a fourth embodiment of the present invention and is a circuit diagram of a voltage controlled oscillator circuit using an air core coil. The constituent members having the same functions as those of the embodiments shown in FIGS. 1 to 3 are designated by the same reference numerals and the description thereof will be omitted.

This embodiment shows a case where an air-core coil is used as an oscillating element of a voltage controlled oscillating circuit.
The other configurations are exactly the same, except that the dielectric resonator 1 in the first embodiment shown in FIG. 4 is replaced by the air-core coil L2 shown in FIG.

The voltage controlled oscillator circuit of the present embodiment is based on the first
~ Used in a frequency band lower than that of the voltage controlled oscillator circuit of the third embodiment. However, also in this case, when the control voltage becomes high and approaches the maximum variable frequency, the sub-resonant circuit 2 functions in place of the variable capacitance diode VC to smoothly raise the oscillation frequency. ~ Third
This is the same as the embodiment, and this makes it possible to expand the variable range of the oscillation frequency to the high frequency side.

[0038]

As is apparent from the above description, according to the voltage controlled oscillator circuit of the present invention, the sub-resonant circuit prevents the deterioration of the linearity of the oscillation frequency in the vicinity of the maximum variable frequency, thereby changing the oscillation frequency. The effect is that the range can be expanded.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, in which λ /
FIG. 6 is a circuit diagram of a voltage controlled oscillator circuit using two types of dielectric resonators.

FIG. 2 shows a second embodiment of the present invention, in which λ /
FIG. 7 is a circuit diagram of a voltage controlled oscillator circuit using four types of dielectric resonators.

FIG. 3 shows a third embodiment of the present invention and is a circuit diagram of a voltage controlled oscillator circuit using a λ / 2 type dielectric resonator as a sub-resonant circuit.

FIG. 4 is a circuit diagram of a voltage controlled oscillator circuit using an air core coil according to a fourth embodiment of the present invention.

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

[Explanation of symbols]

 1 Dielectric Resonator 2 Sub Resonant Circuit 3 Dielectric Resonator 4 Dielectric Resonator VC Variable Capacitance Diode L1 Coil C6 Capacitor

Claims (3)

[Claims] 1. In a voltage controlled oscillator circuit for varying an oscillation frequency by applying a control voltage to a variable capacitance diode to change a capacitance, a sub-resonance circuit having a tuning frequency near a maximum variable frequency is connected in parallel with the variable capacitance diode. A voltage controlled oscillator circuit characterized by being connected to. 2. The voltage controlled oscillator circuit according to claim 1, wherein a dielectric resonator is used as the oscillator element. 3. The voltage controlled oscillator circuit according to claim 1, wherein the sub-resonant circuit connected to the variable capacitance diode is a series resonant circuit including a series circuit of a coil and a capacitor.