JPH06252640A - Voltage controlled oscillator - Google Patents

Abstract

(57) [Abstract] [Purpose] Regarding the voltage controlled oscillator circuit that controls the oscillation frequency by the control voltage, while expanding the frequency variable range,
Improves linearity and stabilizes output level. [Structure] L composed of an inductance 1 and an electrostatic capacitance 2
In the Clap-type oscillator circuit in which the output signal of the transistor amplifier 3 having the C resonance circuit connected to the input side is divided by the first and second electrostatic capacitances 4 and 5 and positively fed back to the input side,
The capacitance 2 of the C resonance circuit is configured by the first variable capacitance diode, and at least one of the positive feedback first and second capacitances 4 and 5 is configured by the second variable capacitance diode. , A control voltage is applied to the first variable capacitance diode via the resistor 8 to control the oscillation frequency, and a control voltage is applied to the second variable capacitance diode via the resistor 9 to feedback the capacitance. To control.

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 circuit which controls an oscillation frequency by a control voltage. The voltage controlled oscillator circuit includes an FM modulator, an FM demodulator, a phase locked loop (P
LL), frequency synthesizers, etc., are widely used. The required performance of this voltage controlled oscillator differs depending on the purpose of use, but in general, the variable range of the oscillation frequency, the control voltage is linear with the oscillation frequency, the stability of the output level, and the low noise. There are characteristics, etc. For example, in a frequency synthesizer, its output frequency will be limited by the frequency range that can be generated by the voltage controlled oscillator circuit. Therefore, in order to realize a synthesizer with a wide frequency range, a voltage controlled oscillator circuit with a wide variable range of the oscillation frequency is indispensable.

An FM modulator for FM-modulating a video signal and transmitting it at a radio frequency is required to have linearity so that the change of the output frequency with respect to the change of the control voltage becomes constant over a wide frequency range. . In particular, a technique for transmitting an analog signal through an optical transmission line is being developed, but an FM modulator having good linearity is also required for this purpose. Further, in any application field, it is desired that the output level does not change even if the oscillation frequency is changed.
As described above, there is a demand for the voltage controlled oscillator circuit to expand the variable range of the oscillation frequency, improve the linearity, stabilize the output level, and the like.

[0003]

2. Description of the Related Art FIG. 7 is an explanatory view of a conventional example, in which Q is a transistor, R _{1 to} R ₄ are resistors, L is an inductance, and C.
_{1 to} C ₄ are capacitors, VD is a variable capacitance diode, +
V is a power supply voltage. Power supply voltage + V is applied to the collector of transistor Q, and power supply voltage + V is applied by resistors R ₂ and R _3.
Is divided, a bias voltage is applied to the base, a resistor R ₄ is connected to the emitter, an output signal is derived, this output signal is divided by capacitors C ₃ and C ₄ and fed back to the base, and a capacitor is connected to the base. A configuration in which an LC resonance circuit composed of an inductance L and a capacitor C ₁ is connected via C ₂ is called a Clap type oscillation circuit. In this case, the capacitors C ₂ , C ₃ , and C ₄ have a larger electrostatic capacitance than the capacitor C ₁ of the LC resonance circuit and are selected so as not to affect the oscillation frequency.

The capacitor C ₁ of the LC resonance circuit of this Clapp oscillator is a variable capacitance diode VD, and a control voltage is applied to this variable capacitance diode VD via a resistor R ₁ , so that the capacitance of the variable capacitance diode VD becomes electrostatic. It is possible to configure a voltage controlled oscillator circuit in which the capacitance is changed, thereby changing the resonance frequency of the LC resonance circuit, and the oscillation frequency is controlled by the control voltage.

As described above, the voltage controlled oscillation circuit applies a control voltage to the variable capacitance diode VD to change its electrostatic capacitance, and the frequency variable range and linearity are changed according to the characteristics of the variable capacitance diode VD. Etc. will be decided. Therefore, conventionally, the variable capacitance diode V
Efforts were made to improve the characteristics of D.

The variable capacitance diode VD utilizes a depletion layer generated by applying a reverse bias voltage to the pn junction surface, and this depletion layer can be regarded as a kind of capacitor. Then, the capacitance changes due to the change in the thickness of the depletion layer due to the change in the reverse bias voltage applied. As a result, the resonance frequency of the LC resonance circuit using the variable capacitance diode VD changes. As a method for improving the variable characteristic of the variable capacitance diode VD, a so-called super staircase junction configuration is known in which the distribution of the impurity concentration of the pn junction is rapidly changed near the junction surface and is gradually decreased as the distance from the junction surface increases. ing.

When the voltage controlled oscillator circuit is applied to an FM modulator, in order to improve its linearity, for example, Japanese Patent No. 1 is used.
The specification of 0137758, JP-A-57-10762 and JP-A-57-10763 are known.
The improvement of the linearity in these cases is intended to improve the linearity by providing a means for compensating the frequency characteristic, but the output level cannot be stabilized.

[0008]

In the voltage controlled oscillator circuit based on the above-mentioned Clap type oscillator circuit, the output signal is fed back to the input side due to the capacitance division by the capacitors C ₃ and C _4. Oscillation continues,
Since the capacitor C ₄ is connected in parallel with the resistor R ₄ connected to the emitter of the transistor Q, the impedance of the capacitor C ₄ becomes smaller and the amount of feedback tends to decrease as the oscillation frequency becomes higher.

Therefore, the conventional voltage controlled oscillator circuit has the characteristics shown in FIG. That is, the horizontal axis represents the control voltage [V], the vertical axis represents the frequency [MHz], and the output level [dB].
m], the capacitor C ₂ is 470 pF, the capacitor C ₃ is 12 pF, the capacitor C ₄ is 24 pF, the resistor R ₁ is 10 kΩ, and the resistor R ₄ is 470 Ω, and the control voltage is linearly increased from 0V. Curve a
As shown in, the oscillation frequency gradually increased from 305 MHz. However, the oscillation stopped when the control voltage was set to 3.5V. The oscillation frequency at that time was about 380 MHz. Therefore, the variable range of the oscillation frequency was about 75 MHz.

The output level is -5 dBm to -12 dB so as to be inversely proportional to the oscillation frequency, as shown by the curve b.
It changed to m. Even when the values of the capacitors C ₃ and C ₄ are variously changed, the range of the oscillation frequency is slightly different, but the range of change is about 100 MHz.
Even if the circuit constant is set so as to further widen this change range, the linearity becomes very poor, and the output level is greatly reduced so as to be inversely proportional to the oscillation frequency similar to the curve b. there were. An object of the present invention is to expand the frequency variable range, improve linearity, and stabilize the output level.

[0011]

A voltage controlled oscillator circuit according to the present invention will be described with reference to FIG. 1. A voltage controlled oscillator circuit of a transistor amplifier 3 having an LC resonance circuit composed of an inductance 1 and a capacitance 2 connected to an input side thereof is described. In the Clap type oscillation circuit which divides the output signal by the first and second electrostatic capacitances 4 and 5 and positively feeds back to the input side, the electrostatic capacitance 2 of the LC resonance circuit is first
Of the variable capacitance diode of
At least one of the second capacitances 4 and 5 is composed of a second variable capacitance diode, the oscillation frequency is controlled by a control voltage applied to the first variable capacitance diode, and the second variable capacitance diode is used. A control voltage is applied to the circuit to control the feedback amount. Further, 6 and 7 are capacitances for blocking direct current, 8 and 9 are resistors for applying a control voltage, 10 is a resistor for output, and 11 and 12 are resistors for bias voltage.

Further, the control voltage applied to the first variable capacitance diode is applied to the second variable capacitance diode via the level shifter.

[0013]

The capacitance 2 of the LC resonance circuit connected to the input side base of the transistor amplifier 3 via the capacitance 7 is used as the first variable capacitance diode, and the control voltage is changed to the first variable capacitance via the resistor 8. A voltage-controlled oscillation circuit that changes the resonance frequency of the LC resonance circuit by applying the capacitance diode is configured. When the capacitance 5 of the positive feedback capacitances 4 and 5 is the second variable capacitance diode as shown in the figure, the control voltage is applied to the second variable capacitance diode via the resistor 9. The capacitance of the variable capacitance diode can be reduced as the oscillation frequency is increased. Therefore, it is possible to prevent the feedback amount from decreasing as the oscillation frequency becomes higher, and to maintain the desired feedback amount, so that the oscillation can be continued up to the high frequency range, and the linearity is improved and the output level is improved. Can be stabilized. Further, the capacitance 4 for positive feedback may be a variable capacitance diode. Also, both capacitances for positive feedback 4,
5 may be a variable capacitance diode.

Further, the level shifter changes the electrostatic capacitance due to the control voltage applied to the first variable capacitance diode which constitutes the electrostatic capacitance 2 of the LC resonance circuit, and applies it to the second variable capacitance diode for positive feedback. It is for making the change of the electrostatic capacitance due to the control voltage proportional and a different value,
Various configurations such as a Zener diode, an operational amplifier, and a resistor can be used.

[0015]

FIG. 2 is an explanatory view of the first embodiment of the present invention, in which Q is a transistor, R _{1 to} R ₅ are resistors, and C _{1 to} C _{5 are shown.}
Is a capacitor (capacitance), L is an inductance, + V
Is the power supply voltage. A case where the capacitor C ₁ forming the LC resonance circuit is the first variable capacitance diode VD ₁ and the positive feedback capacitor C ₄ is the second variable capacitance diode VD ₂ is shown.

The control voltage is applied to the _first variable capacitance diode VD ₁ via the resistor R ₁ to change the resonance frequency of the LC resonance circuit, and the second variable capacitance diode VD ₂ is changed via the resistor R _5. Applied to the capacitor C ₃ ,
C _4, changes the voltage dividing ratio of the output signal due to C _5. A resistor R ₄ is connected to the emitter of the transistor Q, and the capacitor C ₃ is connected between the emitter and the base,
The output signal divided by the capacitors C ₄ and C ₅ is fed back to the base as the input side of the transistor amplifier.
Also, as in the conventional example, the power supply voltage + V is set by the resistors R ₂ , R _3.
Is divided and a bias voltage is applied to the base.

When the control voltage is increased to reduce the capacitance of the _first variable capacitance diode VD ₁ and the resonance frequency of the LC resonance circuit is increased, the second variable capacitance diode VD _{2 is} increased.
Is controlled so that the electrostatic capacitance of is also small. Therefore, the amount of feedback from the emitter of the transistor Q to the base does not decrease. As a result, the oscillation does not stop even if the oscillation frequency is increased, so that the variable range of the oscillation frequency can be expanded. Also, by selecting the feedback amount in relation to the gain of the transistor Q, the output level can be stabilized and the linearity can be improved.

FIG. 3 is a characteristic measurement curve diagram of the embodiment of the present invention. Like the characteristic measurement curve diagram of the conventional example shown in FIG. 8, the horizontal axis represents the control voltage [V] and the vertical axis represents the frequency [MHz]. And the output level [dBm]. The circuit constant is also the same as in the case of the conventional example shown in FIG. 8, the resistance R _{5 is set} to 15 kΩ, the control voltage is applied to the first variable capacitance diode VD ₁ via the resistance R _1, and the second Variable capacitance diode VD
_A control voltage was applied to ₂ through the resistor R ₅ , and the control voltage was increased from 0V.

As a result, the oscillation continues even when the control voltage is 8 V, and the oscillation frequency is about 300 M as shown by the curve A.
The change range was about 250 MHz from Hz to 550 MHz. This indicates that the change range is twice or more that of the conventional example. Further, as can be seen from the curve A, the linearity is also improved. Further, the output level is in the range of -2 dBm to -5 dBm as shown by the curve B, which is remarkably stabilized as compared with the conventional example. The output level is
Further stabilization is possible by selecting the circuit constant.

FIG. 4 is an explanatory view of the second embodiment of the present invention. The same reference numerals as those in FIG. 2 indicate the same parts, and VD ₃ is a variable capacitance diode. In this embodiment, the positive feedback capacitor C ₃ is the second variable capacitance diode VD ₃ . A difference between the bias voltage applied to the base of the transistor Q and the control voltage applied via the resistor R ₅ is applied to the second variable capacitance diode VD ₃ . Therefore, the first variable capacitance diode VD
_{When the} control voltage applied to ₁ is increased to raise the oscillation frequency, the voltage applied to the second variable capacitance diode VD ₃ is decreased and its capacitance is increased. Thereby,
Even if the oscillation frequency becomes high, the amount of feedback is prevented from decreasing, and the variation range of the oscillation frequency can be expanded.

FIG. 5 is an explanatory view of the third embodiment of the present invention. The same reference numerals as those in FIG. 2 indicate the same parts, and VD ₂ and VD ₃
Shows a variable capacitance diode in which both positive feedback capacitors C ₃ and C ₄ are variable capacitance diodes. In this case, when the control voltage is increased to reduce the capacitance of the _first variable capacitance diode VD ₁ and the resonance frequency of the LC resonant circuit is increased, the variable capacitance diode VD ₂
The control voltage applied to the variable capacitance diode VD ₃ also decreases and the control voltage applied to the variable capacitance diode VD ₃ decreases, and the capacitance increases. As a result, it is possible to reliably prevent a reduction in the feedback amount when the oscillation frequency is increased, to further expand the range of variation of the oscillation frequency and to improve the linearity.

FIG. 6 is an explanatory view of the fourth embodiment of the present invention. The same reference numerals as those in FIG. 2 indicate the same parts, ZD is a Zener diode, and R ₆ is a resistor. In this embodiment, the Zener diode ZD is used as a level shifter, and the control voltage is applied to the _first variable capacitance diode VD ₁ of the LC resonance circuit via the resistor R ₁ and the second variable capacitance diode. A control voltage shifted by the Zener voltage by the Zener diode ZD is applied to VD ₂ by the resistor R ₅
Is applied via.

In this embodiment, when the first and second variable capacitance diodes VD ₁ and VD ₂ have the same structure, the capacitance of the first variable capacitance diode VD ₁ by the control voltage and the second capacitance The variable capacitance diode VD ₂ is made different from the electrostatic capacitance, and the changing direction of the electrostatic capacitance is made the same to expand the variable range of the oscillation frequency.

Instead of the level shifter using the Zener diode ZD, the level of the control voltage is shifted by subtracting the reference voltage from the control voltage by a subtracting circuit using an operational amplifier, etc., and the first variable capacitance diode VD ₁
The voltage of a predetermined level difference with respect to the voltage applied to the second
It is also possible to adopt a configuration in which the variable capacitance diode VD ₂ is applied. It is also possible to give a level difference between the voltage applied to the first variable capacitance diode VD ₁ and the voltage applied to the second variable capacitance diode VD ₂ by combining resistance voltage division and the like. Also in the embodiment shown in FIGS. 4 and 5, a level shifter is provided so that the voltage applied to the variable capacitance diodes VD ₂ and VD ₃ with respect to the voltage applied to the first variable capacitance diode VD _1. Can be given a level difference.

Further, a frequency-modulated signal is output from the voltage-controlled oscillation circuit using the control voltage of the voltage-controlled oscillation circuit of each of the above-mentioned embodiments as an image signal, and this output signal is used as a drive signal for the laser diode to output light from the laser diode. Can be transmitted by an optical transmission line. That is, it is possible to configure an optical brightness modulator that drives a laser diode by an output signal of a voltage controlled oscillation circuit having a wide variable range of oscillation frequency and good linearity.

[0026]

As described above, according to the present invention, the capacitance 2 of the LC resonance circuit including the inductance 1 and the capacitance 2 is constituted by the first variable capacitance diode, and the output signal of the transistor amplifier 3 is obtained. At least one of the first and second electrostatic capacitances 4 and 5 for positive feedback of is constituted by the second variable capacitance diode, and the electrostatic capacitance of the first variable capacitance diode is changed by the control voltage. Change the oscillation frequency, and at the same time, change the electrostatic capacitance of the second variable capacitance diode to prevent the reduction of the feedback amount due to the change of the oscillation frequency, so that the oscillation does not stop even when the oscillation frequency is high. Can be Therefore, the variable range of the oscillation frequency can be expanded. At the same time, there is an advantage that the linearity can be improved and the feedback level can be maintained at a desired value to stabilize the output level.

Further, by providing a level shifter including a Zener diode ZD and an operational amplifier, the voltage applied to the second variable capacitance diode is shifted by the level of the level shifter with respect to the voltage applied to the first variable capacitance diode. , The capacitance of the first variable capacitance diode is made different from the capacitance of the second variable capacitance diode, and the reduction of the feedback amount when the oscillation frequency is changed is prevented, and the variation range of the oscillation frequency is , The linearity is improved, and the output level is stabilized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of the first embodiment of the present invention.

FIG. 3 is a characteristic measurement curve diagram of an example of the present invention.

FIG. 4 is an explanatory diagram of a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a conventional example.

FIG. 8 is a characteristic measurement curve diagram of a conventional example.

[Explanation of symbols]

 1 Inductance configuring an LC resonance circuit 2 Capacitance configuring an LC resonance circuit 3 Transistor amplifier 4,5 Capacitance for positive feedback 6,7 Capacitance for blocking DC 8,9 Resistance for applying control voltage 10 Output resistance 11, 12 Bias voltage resistance

Claims (2)

[Claims] 1. Inductance (1) and capacitance (2)
A clapper that positively feeds back to the input side by dividing the output signal of the transistor amplifier (3) having an LC resonance circuit composed of and connected to the input side by the first and second electrostatic capacitances (4) and (5). In the positive oscillation circuit, the capacitance (2) of the LC resonance circuit is constituted by a first variable capacitance diode, and the first and second positive feedback diodes are provided.
At least one of the electrostatic capacitances (4) and (5) of the second variable capacitance diode is configured, and the oscillation frequency is controlled by the control voltage applied to the first variable capacitance diode. A voltage-controlled oscillation circuit having a configuration in which a control voltage is applied to the variable capacitance diode to control the feedback amount. 2. The voltage controlled oscillator circuit according to claim 1, wherein the control voltage applied to the first variable capacitance diode is applied to the second variable capacitance diode via a level shifter. .