JP2008219609A - Oscillator circuit for controlling high-frequency voltage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillator circuit for controlling a high-frequency voltage capable of suppressing abnormal oscillation, improving phase noise, and minimizing a circuit. <P>SOLUTION: The oscillator circuit for controlling the high-frequency voltage is comprised of : three or more odd-numbered Π-type low-pass filters; and capacitive variable reactive elements D1, D2 serially connected to their inputs/outputs as a phase shift circuit in a feedback loop of a transistor Q of an amplifying circuit for oscillation. The low-pass filter is comprised of: an inductive reactive element L3 serially connected to the feedback loop; capacitive variable reactive elements D4, D5 connected in parallel to the input/output of the inductive reactive element L3. The inductive reactive element L3 is made to be a micro-strip line formed of a horseshoe-shape, a doughnut-shape, and a U-shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high-frequency voltage-controlled oscillation circuit, and more particularly to a high-frequency voltage-controlled oscillation circuit that suppresses abnormal oscillation and improves phase noise.

  A conventional high-frequency voltage-controlled oscillator circuit includes an oscillation amplifier circuit, an inductive reactance element, and a phase shift circuit formed by a capacitive variable reactance element. A capacitive variable reactance is added to a third-order π-type variable high-pass filter. Elements were connected in series to form a phase shift circuit.

A conventional high-frequency voltage-controlled oscillation circuit will be described with reference to FIG. FIG. 9 is a diagram showing a simple circuit of a conventional high-frequency voltage-controlled oscillation circuit.
As shown in FIG. 9, in the conventional high-frequency voltage controlled oscillation circuit, the collector and base of the transistor Q of the oscillation amplifier circuit are connected by a feedback loop, and variable capacitance diodes D2, D3, D1 are connected in series to the feedback loop. The point between the diode D1 and the diode D3 is connected to one terminal of the coil L1, which is an inductive reactance element, the other terminal is grounded, and the point between the diode D2 and the diode D3 is an induction. One terminal of the coil L2, which is a reactive reactance element, is connected to a terminal, and the other terminal is grounded.
Here, the diode D3 and the coils L1 and L2 form a third-order π-type variable high pass filter (HPF).

FIG. 10 shows the frequency characteristics of the oscillation loop gain of the conventional circuit. FIG. 10 is a diagram showing the frequency characteristics of the oscillation loop gain in the conventional high-frequency voltage-controlled oscillation circuit. In FIG. 10, the horizontal axis represents frequency and the vertical axis represents gain.
The oscillation frequency is 700 MHz in FIG. 10. Therefore, when the phase shift circuit is a high-pass filter, the oscillation loop gain is 0 dB or more at a frequency of 700 MHz or higher, and an unintended oscillation at a frequency of the oscillation frequency or higher. There is a concern that this will occur.

Further, the oscillation spectrum in the oscillation loop in the case of using the prior art will be described with reference to FIG. 11, and the level of the harmonic component will be described with reference to FIG. FIG. 11 is a diagram illustrating an oscillation spectrum in a conventional oscillation loop, and FIG. 12 is a diagram illustrating a level of a harmonic component.
In FIG. 11, “1” on the horizontal axis indicates a desired oscillation frequency, and “2” and thereafter indicate the order of higher harmonics. From FIGS. 11 and 12, the level of the higher harmonics indicates the desired oscillation frequency. It can be confirmed that there is something close to.

  The level of the harmonic component is obtained by calculating the difference from the fundamental wave (first order), and further calculating the distortion rate of each order (= 100 * 10 ^ (difference / 20)) from the second order. The strain rate meter (%) is the sum of the strain rates up to the 9th order.

  As related prior art, US Patent Application Publication US2005 / 0242896A1 (Patent Document 1), JP-A-11-154824 (Patent Document 2), JP-A-2006-279158 (Patent Document 3), Japanese Unexamined Patent Publication No. 2000-228602 (Patent Document 4) and Japanese Unexamined Patent Application Publication No. 2005-086366 (Patent Document 5).

  FIG. 2 shows a specific circuit configuration in Patent Document 1, but if the circuit diagram is simplified, the configuration is the same as that shown in FIG. The diodes D1, D2, D3, and the coils L1, L2 in FIG. 9 correspond to the diodes D3, D2, D4-D7, the coils TL1, TL3, and the coils TL2, TL4 in FIG.

Patent Document 2 describes that in a temperature-compensated oscillator, a temperature compensation capacitor is used for the output capacitive reactance circuit of the amplifying element to compensate for temperature fluctuations in the input / output feedback section inductive reactance circuit.
Patent Document 3 describes a low-pass filter that includes inductors L1, L2, L3, a capacitor C2, and a variable capacitance diode VD in an amplitude modulator.

Patent Document 4 describes a resonant line in which the reactance between one end of a plurality of microstrip lines and the ground is set to a length that is equivalently inductive and the ends are connected to each other. Yes.
Patent Document 5 describes that in a broadband high-frequency power amplifier circuit, a microstrip line is used as a series impedance functional inductance, and the series impedance functional inductance is formed in a U-shaped pattern.

US2005 / 0242896A1 Publication JP-A-11-154824 JP 2006-279158 A JP 2000-228602 A Japanese Patent Laying-Open No. 2005-086366

  However, in the conventional high-frequency voltage controlled oscillation circuit, when the phase shift circuit is a high-pass filter, the gain of the oscillation loop is maintained at 1 or higher even at a frequency higher than the oscillation frequency. When the parasitic component is higher than the oscillation frequency, the reactance component cannot be ignored, and the phase condition of the oscillation may be satisfied at an unintended high frequency, thereby causing abnormal oscillation at an unintended frequency higher than the oscillation frequency. There was a problem of fear.

  Furthermore, by using a high-pass filter for the phase shift circuit, the level of higher-order harmonics in the oscillation loop becomes relatively high, and noise components generated by mixing the higher-order harmonics are added to the oscillation frequency signal. There was a problem that the phase noise was deteriorated.

  In addition, in the third-order π-type high-pass filter, two inductive reactance elements (coils L1 and L2 in FIG. 9) are required, and in order to increase the Q of the elements, an actual product is formed on a substrate. Since two transmission lines were applied, there was a problem that miniaturization of the product was restricted.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-frequency voltage-controlled oscillation circuit capable of suppressing abnormal oscillation, improving phase noise, and miniaturizing the circuit.

  The present invention for solving the problems of the conventional example described above, in a high-frequency voltage-controlled oscillation circuit including an oscillation amplifier circuit, an odd-numbered π-type low-pass filter of the third order or higher and a feedback loop of the oscillation amplifier circuit, An inductive reactance in which a low-pass filter is connected in series to the feedback loop is provided with a phase-shift circuit that realizes a band-pass filter characteristic having capacitive variable reactance elements connected in series on the input side and output side of the low-pass filter And a capacitive variable reactance element connected in parallel to the input side and the output side of the inductive reactance element.

  The present invention is characterized in that, in the above-described high-frequency voltage-controlled oscillation circuit, the capacitive variable reactance element in the phase shift circuit is a varicap.

  The present invention is characterized in that, in the above-described high-frequency voltage-controlled oscillation circuit, the capacitive variable reactance element in the low-pass filter is a varicap.

  The present invention is characterized in that, in the high-frequency voltage-controlled oscillation circuit, the inductive reactance element in the low-pass filter is formed by a microstrip line.

  The present invention is characterized in that, in the above-described high-frequency voltage-controlled oscillation circuit, the shape of the microstrip line is a horseshoe shape, a donut shape, and a U-shape that has been bent at 45 degrees.

  According to the present invention, the feedback loop of the oscillation amplifier circuit includes an odd-numbered or higher-order π-type low-pass filter and a capacitive variable reactance element connected in series to the input side and the output side of the low-pass filter. Provided with a phase shift circuit, the low-pass filter includes an inductive reactance element connected in series to the feedback loop, and a capacitive variable reactance element connected in parallel to the input side and the output side of the inductive reactance element. Since it is a voltage-controlled oscillation circuit, characteristics like a band-pass filter can be achieved by controlling the capacitance with a capacitive variable reactance element, abnormal oscillation can be suppressed, phase noise can be improved, and adjustment with a simple configuration is easy An effect of realizing a simple circuit.

  According to the present invention, since the inductive reactance element in the low-pass filter is the above-described high-frequency voltage-controlled oscillation circuit formed by a microstrip line, the product can be reduced in size without deteriorating phase noise. is there.

  According to the present invention, since the microstrip line has the above-described high-frequency voltage-controlled oscillation circuit having a horseshoe shape, a donut shape, and a 45-degree bent U-shape, the phase noise is not deteriorated. There is an effect that the product can be further downsized.

[Outline of the embodiment]
Embodiments of the present invention will be described with reference to the drawings.
The present invention relates to a high-frequency voltage-controlled oscillation circuit in which a third-order or higher-order π-type low-pass filter is connected as a phase shift circuit to a feedback loop of an oscillation amplifier circuit, and a capacitive variable reactance connected in series with its input / output The low-pass filter is composed of an inductive reactance element connected in series to the feedback loop and a capacitive variable reactance element connected in parallel to the input and output of the inductive reactance element. The frequency to be used can be selected by controlling the capacitance of the capacitive variable reactance element of the filter, and further, the gain of the low frequency is attenuated by controlling the capacitance of the capacitive variable reactance element connected in series to the feedback loop. It can have characteristics like a bandpass filter, suppress abnormal oscillation, improve phase noise, and adjust with a simple configuration. In which can be realized is easy circuit.

  Further, the present invention is the above-described high-frequency voltage-controlled oscillation circuit, wherein the inductive reactance element is configured by a microstrip line, and the shape thereof is a horseshoe shape, a donut shape, and a 45-degree bent U shape, The module shape can be reduced in size without deteriorating noise.

[Points of embodiment]
The main points of the embodiment of the present invention are that, first, the oscillation condition is not satisfied at a frequency other than the target oscillation frequency, and second, the oscillation loop gain at a frequency higher than the oscillation frequency is reduced, thereby generating oscillation. This is because high-order harmonics generated on the loop are reduced, and the amount of noise added to the desired oscillation frequency is reduced.

In order to realize the second essential point, the phase shift circuit may be a low-pass filter. However, in order to realize the first essential point at the same time, the phase shift circuit needs to be a band-pass filter.
However, since an ordinary bandpass filter has more elements than a lowpass filter and tuning is difficult, in the embodiment of the present invention, the bandpass filter is divided into a third-order π-type variable lowpass filter and the lowpass filter. The phase shift circuit is composed of a capacitive variable reactance element connected in series with the input and output. As a result, the number of elements is reduced as compared with a normal bandpass filter, and cost reduction and size reduction are realized.

  Further, in the phase shift circuit according to the embodiment of the present invention, a π-type variable low-pass filter is used, and the inductive reactance element in the filter is, for example, mounted as a transmission path in terms of element Q, cost, and variation. It is desirable to apply a microstrip line formed on the substrate. Thereby, the transmission line which was two conventionally can be deleted in one, and size reduction of a product is realizable.

  Furthermore, the microstrip line is not greatly changed in phase noise, whether it is a linear layout, a donut shape, or a U-shape that has been bent by 45 degrees. By applying a U-shaped shape that has been bent, the size and cost of the product can be reduced.

[Simplified configuration of this circuit: Fig. 1]
Next, a high-frequency voltage-controlled oscillation circuit according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram showing a simplified circuit of a high-frequency voltage-controlled oscillation circuit according to an embodiment of the present invention.
As shown in FIG. 1, a high-frequency voltage-controlled oscillation circuit (this circuit) according to an embodiment of the present invention includes a transistor Q of an oscillation amplifier circuit, a third-order π-type variable low-pass filter, and a low-pass filter. It is basically composed of a capacitive variable reactance element connected in series with the input and output.
A variable band-pass filter characteristic is realized by a third-order π-type low-pass filter and a capacitive variable reactance element connected in series to the input and output of the low-pass filter.

The transistor Q of the oscillation amplifier circuit has its collector and base connected by a feedback loop.
The third-order π-type variable low-pass filter is provided in the feedback loop, and the inductive reactance element coil L3 connected in series, and the capacitive variable reactance element diodes D4 and D5 connected in parallel to both ends of the coil L3. Has been.
The cathodes of the diodes D4 and D5 are connected to both ends of the coil L3, and the anodes of the diodes D4 and D5 are grounded.
Although the low-pass filter is a third-order π-type variable low-pass filter in FIG. 1, it may be a third-order or higher-order odd-order π-type variable low-pass filter.

A capacitive variable reactance element diode D1 is connected in series between the base of the transistor Q and the low-pass filter.
The diode D1 has an anode side connected to the base of the transistor Q and a cathode side connected to a low-pass filter.
A diode D2 of a capacitive variable reactance element is connected in series between the collector of the transistor Q and the low-pass filter.
The diode D2 has an anode connected to the collector of the transistor Q and a cathode connected to a low-pass filter.

  Thus, since the phase shift circuit is a band-pass filter, the oscillation loop gain is 0 dB or more only in the vicinity of the oscillation frequency, and unintended oscillation cannot occur at a frequency equal to or lower than the oscillation frequency.

[Oscillation spectrum: Fig. 2, Spectrum level: Fig. 3]
Next, the oscillation spectrum in this circuit is shown in FIG. 2, and the level of the oscillation spectrum is shown in FIG. 3 in comparison with the prior art (FIG. 12). FIG. 2 is a diagram showing an oscillation spectrum in the oscillation loop of this circuit, and FIG. 3 is a diagram showing the level of harmonic components of this circuit.
In FIG. 2, “1” on the horizontal axis indicates a desired oscillation frequency, and “2” and subsequent numbers indicate the orders of higher harmonics. From FIG. 2 and FIG. Obviously, the level of higher harmonics is lower, and the distortion rate is improved from 140% (conventional) to 21%.
This makes it difficult for noise components generated by mixing higher-order harmonics to be added to the signal of the oscillation frequency, thereby realizing better phase noise characteristics than before.

[Specific circuit: Fig. 4]
Next, a specific circuit of this circuit will be described with reference to FIG. FIG. 4 is a configuration diagram of a specific circuit of this circuit.
As shown in FIG. 4, the specific circuit of this circuit includes an oscillation amplifier circuit (Amplifier) 1, a buffer amplifier circuit (Amplifier) 2, an output matching unit (LPF) 3, and an output of the oscillation amplifier circuit 1. Is provided between the output side of the oscillation amplifier circuit 1 and the input side of the inductive reactance element 4 in the feedback loop. The capacitive variable reactance element 5, the capacitive variable reactance element 6 provided between the output side of the inductive reactance element 4 and the input side of the oscillation amplifier circuit 1 in the feedback loop, and the inductive reactance element 4 Capacitive variable reactance elements 7 and 8 provided at both ends of the input side and the output side are provided.

The output matching unit 3 includes a low pass filter.
The capacitive variable reactance elements 5 to 8 are constituted by varicap diodes.
The anode of the diode of the capacitive variable reactance element 5 is connected to the output side of the oscillation amplifier circuit 1, and the cathode is connected to the input side of the inductive reactance element 4.
The anode of the diode of the capacitive variable reactance element 6 is connected to the input side of the oscillation amplifier circuit 1, and the cathode is connected to the output side of the inductive reactance element 4.
The anodes of the diodes of the capacitive variable reactance elements 7 and 8 are grounded, and the cathode is connected to the input / output side of the inductive reactance element 4.

  The inductive reactance element 4 and the capacitive variable reactance elements 7 and 8 constitute a third-order π-type variable low-pass filter, and the low-pass filter and the capacitive variable reactance elements 5 and 6 constitute a phase shift circuit.

  In the varicap diodes of the capacitive variable reactance elements 7 and 8, the frequency to be used can be arbitrarily selected by controlling the capacitance (the peak can be freely selected [set]), and the capacitive variable reactance elements 5 and 6 can be selected. In the varicap diode, the gain at a low frequency can be attenuated by controlling the capacitance so that the phase noise characteristic can be improved.

  Further, the inductive reactance element 4 is configured by a microstrip line, and in particular, by making its shape a horseshoe shape, a donut shape, and a 45-degree bent U shape, without deteriorating the phase noise, The module shape can be reduced in size.

[Specific Configuration of Inductive Reactance Element 4: FIGS. 5 and 6]
Next, specific first and second configuration examples (first and second configuration examples) of the inductive reactance element 4 will be described with reference to FIGS. 5 and 6. FIG. 5 is a diagram illustrating a first configuration example of the inductive reactance element, and FIG. 6 is a diagram illustrating a second configuration example of the inductive reactance element.
A first configuration example of the inductive reactance element 4 is a donut shape as a microstrip line as shown in FIG. 5, and a second configuration example of the inductive reactance element 4 is a microstrip line as shown in FIG. The strip line has a U-shape that is 45 degrees vented.

[Characteristics of microstrip line: FIGS. 7 and 8]
Next, the characteristics of the microstrip line will be described with reference to FIGS. FIG. 7 is a diagram showing a representative impedance magnitude of the microstrip line shown in the first and second configuration examples, and FIG. 8 is a microstrip shown in the first and second configuration examples. It is the figure which showed the phase of the typical impedance of a line. In FIG. 7, the horizontal axis represents frequency, the vertical axis represents the magnitude of impedance, and in FIG. 8, the horizontal axis represents frequency and the vertical axis represents phase.
7 and 8 indicate the impedance characteristics in this circuit, and the dotted line indicates the ideal impedance characteristics of the inductor.
The feature of this circuit is that the microstrip line functions equivalently as an inductor at the oscillation frequency.

[Effect of the embodiment]
According to this circuit, a phase shift circuit is formed as a phase shift circuit in the feedback loop of the oscillation amplifier circuit, and an odd-numbered π-type low-pass filter of the third order or higher and a capacitive variable reactance element connected in series to the input and output thereof, The low-pass filter is composed of an inductive reactance element connected in series to the feedback loop and a capacitive variable reactance element connected in parallel to the input and output of the inductive reactance element. The frequency to be used can be selected by controlling the capacitance of the reactance element, and the gain of the low frequency is attenuated by controlling the capacitance of the capacitive variable reactance element connected in series to the feedback loop. Characteristics, suppress abnormal oscillation, improve phase noise, and realize a circuit that is easy to adjust with a simple configuration There is a kill effect.

  In addition, according to the present circuit, the inductive reactance element is configured by a microstrip line, and the shape thereof is a horseshoe shape, a donut shape, and a U shape that has been bent at 45 degrees, so that phase noise is not deteriorated. The module shape can be reduced in size.

  The present invention is suitable for a high-frequency voltage-controlled oscillation circuit that can suppress abnormal oscillation, improve phase noise, and reduce the size of the circuit.

It is a block diagram which shows the simple circuit of the voltage controlled oscillation circuit for high frequencies which concerns on embodiment of this invention. It is a figure which shows the oscillation spectrum in the oscillation loop of this circuit. It is a figure which shows the level of the harmonic component of this circuit. It is a block diagram of the concrete circuit of this circuit. It is a figure which shows the 1st structural example of an inductive reactance element. It is a figure which shows the 2nd structural example of an inductive reactance element. It is the figure which showed the magnitude | size of the typical impedance of the microstrip line shown to the 1st, 2nd structural example. It is the figure which showed the phase of the typical impedance of the microstrip line shown to the 1st, 2nd structural example. It is a figure which shows the simple circuit of the conventional voltage control oscillation circuit for high frequency. It is a figure which shows the frequency characteristic of the oscillation loop gain in the conventional voltage control oscillation circuit for high frequency. It is a figure which shows the oscillation spectrum in the conventional oscillation loop. It is a figure which shows the level of a harmonic component.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Oscillation amplifier circuit, 2 ... Buffer amplifier circuit, 3 ... Output matching part, 4 ... Inductive reactance element, 5 ... Capacitive variable reactance element, 6 ... Capacitive variable reactance element, 7 ... Capacitive variable reactance element, 8 ... Capacitive variable reactance element

Claims (5)

In a high-frequency voltage-controlled oscillation circuit including an oscillation amplifier circuit,
Provided in the feedback loop of the oscillation amplifier circuit is a phase shift circuit having an odd number or higher-order π-type low-pass filter and a capacitive variable reactance element connected in series to the input side and output side of the low-pass filter ,
The low-pass filter includes an inductive reactance element connected in series to the feedback loop, and a capacitive variable reactance element connected in parallel to an input side and an output side of the inductive reactance element. Voltage controlled oscillator circuit.   2. The high frequency voltage controlled oscillation circuit according to claim 1, wherein the capacitive variable reactance element in the phase shift circuit is a varicap.   2. The voltage controlled oscillation circuit for high frequency according to claim 1, wherein the capacitive variable reactance element in the low-pass filter is a varicap.   4. The high frequency voltage controlled oscillation circuit according to claim 1, wherein the inductive reactance element in the low pass filter is formed by a microstrip line.   5. The high frequency voltage-controlled oscillation circuit according to claim 4, wherein the microstrip line has a horseshoe shape, a donut shape, and a U-shape that has been bent at 45 degrees.

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