JP2563136B2 - Voltage controlled oscillator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a voltage-controlled oscillator whose oscillation frequency can be varied by controlling a control voltage input from the outside.

[Prior Art] For example, a voltage controlled oscillator (VCO) shown in FIG. 4 is known as an oscillator whose oscillation frequency can be varied by controlling a voltage input from the outside.

This voltage controlled oscillator is a Colpitts type oscillator, is connected to the input terminal 10 via a choke coil L11, and has variable capacitance diodes D11, D between both ends of the coil L12 and the ground.
12 is connected to the resonance circuit 11 and is connected to the resonance circuit 11 via a coupling capacitor C11.
Active circuit 1 that oscillates at a frequency according to the resonance frequency of 1
2, a buffer circuit 13 for extracting the output of the active circuit 12 at the time of oscillating operation, and capacitors C12, C13 connected between the input and output of the active circuit 12 and determining the feedback amount of the active circuit 12 based on the capacitance ratio. And a feedback circuit (14). The oscillation frequency of the active circuit (12) is controlled by applying a control voltage from the input terminal (10) to the variable capacitance diodes (D11, D12) in the resonance circuit (11). The oscillated signal is output from the output of the active circuit 12 through the buffer circuit 13.

By the way, in the above-described oscillator, the capacitance ratio of the capacitors C13 and C12 in the feedback circuit 14 is fixed, and the amount of feedback is also constant regardless of the frequency.

[Problems to be Solved by the Invention] In the conventional technology as described above, since the feedback amount between the input and output of the active circuit 12 is fixed, the frequency range in which oscillation is possible is determined by the feedback amount of the feedback circuit 14.

By the way, when low frequency oscillation is performed, if the control voltage is increased as shown in Fig. 5, it will be 1170MHz.
It is possible to obtain a linear oscillation output up to the front and back, but after that, the oscillation frequency saturates, and the desired oscillation output was not obtained, and it was not possible to cope with high frequency oscillation. Also, the sixth
As shown in the figure, there is a problem that the level decreases as the oscillation frequency increases.

When high frequency oscillation is performed, abnormal oscillation occurs when the amount of applied control voltage is small and the oscillation frequency is low as shown in FIG.
There is a drawback that the level fluctuation in the lower frequency region of 00 MHz becomes large.

Therefore, when performing low-frequency oscillation, use a capacitor
An experiment was performed by setting the capacitance of C13 larger than usual and, when performing high frequency oscillation, setting the capacitance of capacitor C13 smaller than usual. As a result, they have found that in each case the above drawbacks are resolved.

On the other hand, there is no particular problem when used in a state where the frequency is limited to either the low frequency oscillation or the high frequency oscillation described above, but in a communication device that requires a frequency of octave or higher, it is possible to increase the frequency from low frequency to high frequency. It is necessary to perform wideband oscillation up to the frequency. For this purpose, a plurality of oscillators with fixed capacitor capacitances are configured in advance according to the desired oscillation frequency, these oscillators are connected to a switch circuit, and the oscillators are selectively connected based on the switching of the switch circuit. Then, a desired oscillation frequency can be obtained.

However, such a configuration requires a plurality of oscillators,
Since the switch circuit is used to select one of these oscillators, there is a problem that the circuit becomes complicated and the cost is increased.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to control voltage vs. oscillation frequency over a high range from a low frequency to a high frequency without complicating the circuit configuration. It is to provide a voltage controlled oscillator having a linear relationship and a small level fluctuation.

[Means for Solving the Problems] In order to achieve the above object, the voltage controlled oscillator according to the present invention includes at least first variable capacitance diodes D1 and D2 whose capacitance is varied by a control voltage, and a coil L1. A resonance circuit 1 having one end connected to the ground, an active circuit 3 having the other end of the resonance circuit coupled to the input side and outputting a signal having an oscillation frequency according to the resonance frequency of the resonance circuit, A capacitor C7 connected between the input and output of the circuit for feeding back the output signal of the active circuit, and connected so as to form a capacitance between the output of the active circuit and the ground, the capacitance being variable by the control voltage. A second variable-capacitance diode D4 for maintaining a constant feedback amount between the input and output of the active circuit through the capacitor, the control voltage being set to the first variable diode D4. It is characterized in that the oscillation frequency is varied by applying it to the variable capacitance diode, and the control voltage is applied to the second variable capacitance diode so that the feedback amount becomes constant regardless of the oscillation frequency.

[Operation] When a control voltage is applied to the first variable capacitance diodes D1 and D2 connected to the ground side of the resonance circuit 1, the resonance frequency changes with the application of the control voltage, and The active circuit 3 oscillates according to the resonance frequency and outputs an oscillation signal. The control voltage is also applied to the second variable capacitance diode D4 which is connected so as to form a capacitance between the active circuit 3 and the ground to change the capacitance. As a result, the capacitance ratio between the output signal feedback capacitor C7 connected between the input and output of the active circuit 3 and the second variable capacitance diode D4 is controlled. as a result,
The oscillation intensity is controlled so that the feedback amount of the active circuit 3 determined by the impedances of the variable capacitance diode D4 and the capacitor C7 is constant regardless of the oscillation frequency.

[Embodiment] FIG. 1 is a diagram showing an embodiment of the voltage controlled oscillator according to the present invention.

The voltage controlled oscillator according to this embodiment is a Colpitts type oscillator and is applied to a communication device that requires a frequency of octave or higher.The oscillation frequency is variably controlled by a control voltage input from the outside, and the resonance The circuit is roughly composed of an oscillation circuit 5 including a circuit, a coupling control circuit 2, an active circuit 3, and a capacitance ratio variable circuit 4, and a buffer circuit 6 for taking out the output of the oscillation circuit 5.

The resonance circuit 1 is composed of a coil L1 and variable capacitance diodes D1 and D2 connected between both ends of the coil L1 and the ground. One end of the resonance circuit 1 is connected to an input terminal 7 via a choke coil L2. Connected to the other end of the coupling control circuit 2,
It is connected to each of the active circuit 3 and the capacitance ratio variable circuit 4. The barrier capacitances of the variable capacitance diodes D1 and D2 in the resonance circuit 1 are controlled by the control voltage supplied from the input terminal 7 via the choke coil L2, and thereby the oscillation frequency is controlled.

The coupling control circuit 2 is connected between the resonance circuit 1 and the active circuit 3, and the choke coil L3 is connected between the connection point P1 of the series circuit including the variable capacitance diode D3 and the capacitor C1 and the ground.
Is connected. The coupling control circuit 2 controls the barrier capacitance of the variable capacitance diode D3 via the choke coil L3 so that the coupling strength between the resonance circuit 1 and the active circuit 3 becomes constant regardless of the oscillation frequency. Have control over. That is, in capacitive coupling, the impedance of the capacitance changes depending on the frequency, and the strength of the coupling also changes. Therefore, if the oscillation frequency is high, the capacitance is decreased, and if the oscillation frequency is low, the capacitance is increased so that the coupling becomes constant. Are controlled.

The active circuit 3 oscillates at the resonance frequency of the resonance circuit 1 supplied via the coupling capacitor C2,
In this example, an npn type transistor T1 is provided, and a series circuit including a resistor R1 and a capacitor C3 is connected between the base of the transistor T1 and the ground. The collector of the transistor T1 is grounded, and the emitter of the transistor T1 is connected to the power supply via the resistor R2.
A capacitor C4 is connected between R2 and ground.
Further, the buffer circuit 6 is connected to the emitter of the transistor T1 via the coupling capacitor C5,
A capacitor C6 and a resistor R3 are connected between both ends of the coupling capacitor C5 and the ground. Further, a resistor R4 is connected between a connection point P2 between the coupling capacitor C5 and the buffer circuit 6 and the power supply,
This resistor R4 and the resistor connected to the base of transistor T1
L-type connected resistors R5 and R6 are connected between R1 and R1, and resistors R4 and R5 form a voltage dividing circuit. In this active circuit 3, the transistor T1 oscillates at a frequency that is variable with the application of the control voltage, and outputs its output to the buffer circuit 6.

In the capacitance ratio variable circuit 4, the choke coil L4 is connected to one end of the coupling capacitor C2, the capacitor C7 is connected to the other end, and the capacitor C8 is connected between the choke coil L4 and the capacitor C7. , And C8 are connected to the emitter of the transistor T1. In addition, a variable capacitance diode is connected between the choke coil L4 and ground.
D4 is connected, and its barrier capacitance value is controlled by the control voltage supplied from the input terminal 7. By varying the capacitance ratio between the capacitance of the variable capacitance diode D4 and the capacitors C7 and C8, these capacitances can be changed. The amount of feedback supplied from the emitter of the transistor T1 to the base, which is determined by the impedance of, is controlled to be constant. That is, when the oscillation frequency is high, the capacitance of the variable capacitance diode D4 is reduced, and when the oscillation frequency is low, the variable capacitance diode D4 is reduced.
By increasing the capacitance in D4 and controlling the capacitance ratio (capacitor C7 to capacitor C8 and the capacitance of the variable capacitance diode D4), the feedback amount determined by the impedance of these capacitors is made constant with respect to the oscillation frequency. There is.

The buffer circuit 6 includes an npn-type transistor T2, and the transistor T2 of the active circuit 3 is the transistor T1.
The oscillation signal output by is amplified and output. A capacitor C9 is provided at the collector of the transistor T2, and a resistor R7 is connected between the capacitor C9 and the ground.
Further, a capacitor C10 is connected between the emitter of the transistor T2 and the ground, and a resistor R8 is connected between the emitter and the power supply.

In the voltage controlled oscillator configured as described above, when the control voltage of the choke coil L2 is applied, the barrier capacitance of each variable capacitance diode D1, D2 in the resonance circuit 1 changes, and the oscillation frequency is variably controlled. The oscillation output at the time is from the transistor T1 of the active circuit 3 to the buffer circuit 6
Be taken out through.

Here, the feedback amount in the transistor T1 in the active circuit 3 is kept substantially constant by the capacitance ratio variable circuit 4. That is, when the oscillation frequency increases with the application of the control voltage, the variable capacitance diode D4 of the variable capacitance circuit 4 is controlled to be small by the control voltage, and the capacitance of this diode D4 causes the transistor
The feedback amount of T1 is made constant, and the oscillation frequency changes linearly. When the control voltage is low and the oscillation frequency is low, the variable capacitance diode D4 is largely controlled, and the amount of feedback of the transistor T1 is kept constant by the capacitance of the variable capacitance diode D4, and the oscillation frequency changes linearly.

FIG. 2 shows the frequency characteristic with respect to the control voltage supplied to the resonance circuit via the choke coil, and FIG. 3 shows the output level characteristic with respect to the frequency.

From these characteristic diagrams, according to the oscillator of the embodiment described above, linear characteristics are obtained over a wide range from low frequency to high frequency, and the total Q is kept constant. Moreover, the C / N is kept constant, and a high level oscillation output can be obtained.

Also, the oscillator of this embodiment is different from the configuration in which a plurality of oscillators are switched and selected by a switch circuit by using a variable capacitance diode in the capacitance ratio variable circuit 4, and the cost is reduced without complicating the circuit with one oscillator. Can be configured.

By the way, in the above-described embodiment, the configuration in which the npn type transistors T1 and T2 are used for the active circuit 3 and the buffer circuit 6 has been described, but the same effect can be obtained even in a circuit using FET (field effect transistor).

[Effects of the Invention] As described above, in the voltage controlled oscillator according to the present invention, the output signal feedback capacitor is connected between the input and output of the active circuit that outputs the signal of the oscillation frequency according to the resonance frequency of the resonance circuit. , A second variable-capacitance diode is connected to form a capacitance between the output of the active circuit and the ground in order to maintain a constant feedback amount between the input and output of the active circuit through this capacitor, When the reverse voltage to the first variable capacitance diode is increased, the capacitance of the second variable capacitance diode decreases, so that the first variable capacitance diode that changes the oscillation frequency and the feedback to the active circuit. The second variable capacitance diode, which keeps the amount constant regardless of the oscillation frequency, can be varied with the same control voltage, so it can be used over a wide range from low frequencies to high frequencies. As a result, the output level becomes constant, and it is possible to obtain an oscillation output with a linear change in oscillation frequency. Moreover, in the past, the output level decreased as the frequency became higher, and the C / N deteriorated by that amount, but it became constant at the high output level, so the C / N of the oscillation output also changed with respect to the oscillation frequency. Has a certain effect. Furthermore, since a plurality of oscillators can be configured by one without switching and selecting with a switch circuit as in the prior art, the circuit configuration is simple and inexpensive.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a voltage controlled oscillator according to the present invention, FIG. 2 is a diagram showing frequency characteristics with respect to a control voltage of the oscillator, and FIG. 3 is an output level characteristic with respect to frequency of the oscillator. 4 and FIG. 4 are circuit configuration diagrams showing an example of a conventional voltage controlled oscillator, FIG. 5 is a diagram showing frequency characteristics with respect to control voltage of an oscillator used in a low frequency band, and FIG. 6 is used in a low frequency band. FIG. 7 is a diagram showing the output level characteristic with respect to the frequency of the oscillator used, FIG. 7 is a diagram showing the frequency characteristic with respect to the control voltage of the oscillator used in the high frequency band, and FIG. 8 is the frequency characteristic of the oscillator used in the high frequency band. It is a figure which shows an output level characteristic. 1 ... Resonance circuit, 3 ... Active circuit, 4 ... Capacitance ratio variable circuit, 5 ... Oscillation circuit, D1 to D4 ... Variable capacitance diode.

Claims (1)

(57) [Claims] 1. A first variable capacitance diode (D1, D2) whose capacitance is varied by a control voltage, and a coil (L1).
And a resonance circuit (1) whose one end is connected to the ground, and the other end of the resonance circuit is coupled to the input side, and outputs a signal having an oscillation frequency according to the resonance frequency of the resonance circuit. Forming a capacitance between the output of the active circuit and the ground, and a capacitor (C7) connected between the active circuit (3) and the input / output of the active circuit for feeding back the output signal of the active circuit. , The capacitance is changed by the control voltage,
A second variable capacitance diode (D4) for making the amount of feedback between the input and output of the active circuit constant through the capacitor, and applying the control voltage to the first variable capacitance diode. A voltage controlled oscillator, wherein the oscillation frequency is varied and the control voltage is applied to the second variable capacitance diode so that the feedback amount is constant regardless of the oscillation frequency.