JPH04312004A - Microwave voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To stabilize an oscillation wave by connecting a varactor diode to an element to capacitive impedance through a line of the electrical length of about 90 degree of the oscillation frequency, and using a parallel resonance circuit constituted in this way as the tuning circuit for a microwave voltage tuned oscillator. CONSTITUTION:A microwave voltage controlled oscillator circuit 2 is constituted of a parallel resonance circuit of the varactor diode 9, the line 15, and a capacitor Cr 14, and is made to oscillate at the vicinity of resonance frequency. In the equivalent circuit of the circuit 2, inductance Lv and conductance Gv are made equivalent to the diode 9 when observed through the line 15 so that the characteristic impedance Zi of the line 15 can be represented by Lv=Zi<2>.Cv.Gv=Rv/Zi<2>. Accordingly, the resonance frequency of the tuning circuit can be represented by an expression f=1/(2pi)Cr.Zi<2>.Cv)<0.5>), and adimittance at the time of parallel resonance of the tuning circuit becomes Yr'=Gv=Rv/Zi<2>, and Yr at the time of parallel resonance does not depend on Cv 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave voltage controlled oscillator having a wide range of oscillation frequencies.

0002

[Prior Art] FIG. 9 shows, for example, M published in May 1987.
This is an example of the configuration of a conventional microwave voltage controlled oscillator shown on pages 347 to 353 of ICROWAVE JOURNAL. In the figure, 1 is an amplifier circuit, 2 is a tuning circuit, 3 is a field effect transistor (hereinafter referred to as FET), 4 is a drain terminal of FET 3, 5 is a gate terminal of FET 3, and 6 is a source terminal of FET 3. , 7 is an inductor Ls, 8 is an output matching circuit, 9 is a varactor diode,
10 is the junction capacitance Cv of the varactor diode 9, 11 is the series resistance Rv of the varactor diode, and 12 is the inductor L.
r, 13 is an output terminal.

Next, the operation will be explained. Source terminal 6
is the reference plane, and the reflection coefficient when looking at the amplifier circuit 1 with a load connected to the output terminal 13 is Γa, and the reflection coefficient when looking at the tuning circuit 2 is Γt.The oscillation conditions are the magnitude and phase of the reflection coefficient. is given by Equations 1 and 2. |Γa|-1<|Γt|

(1) ∠Γa=−∠Γt

(2) The circuit is configured so that these above conditions are satisfied. In the amplifier circuit 1, an inductor Ls7, which is a series feedback element, is connected between the gate terminal 5 and the ground plane. Positive feedback occurs around the frequency at which the capacitance Cgs between the gate terminal 5 and source terminal 6 of the FET 3 and this inductor Ls7 resonate in series, and |Γa|>1. Furthermore, the output terminal 13
An output matching circuit 8 is connected in order to reduce the loss due to the load connected to and increase |Γa|. On the other hand, in the tuned circuit 2, the junction capacitance Cv1 of the varactor diode 9
0 and the inductor Lr12 resonate in parallel. Since the phase Γt of the reflection coefficient changes sharply near this parallel resonance frequency, it is easy to satisfy Equation 2. Here, |Γt| is Equation 1
If it is satisfied, oscillation starts. Then, due to the tuning voltage applied to the varactor diode 9, the junction capacitance Cv10
can be varied, so the oscillation frequency can be varied along with the parallel resonance frequency.

0004

Since the conventional microwave voltage controlled oscillator is constructed as described above, the oscillation frequency can be varied by the tuning voltage applied to the varactor diode 9. The varactor diode 9 equivalently has a junction capacitance C
It can be expressed as a series circuit of v10 and series resistance Rv11, and the admittance Yr of the tuned circuit 2 at the time of parallel resonance is given by the following equation. Yr=(2πfCv)2 Rv/{1+(2πfC
vRv)2 } (3) where f is the oscillation frequency. As shown in FIG. 11, the junction capacitance Cv of the varactor diode 9 increases as the tuning voltage decreases. Therefore, the lower the tuning voltage, the larger the admittance Yr that depends on the junction capacitance Cv, as shown in equation 3, and the characteristic admittance Y
approach o. Therefore, the lower the tuning voltage, the smaller the reflection coefficient |Γt| of the tuning circuit 2 given by the following equation, and the equation 1
This makes it difficult to satisfy the oscillation conditions, and as a result, there is a problem that oscillation waves cannot be stably obtained over a wide tuning voltage range. |Γt|=|(Yo−Yr)/(Yo+Yr)|
(4) Furthermore, there is a problem that the oscillation power fluctuates greatly due to the large change in |Γt| due to the tuning voltage.

The present invention has been made to solve the above-mentioned problems, and its object is to provide a microwave voltage-controlled oscillator that can stably generate oscillation waves over a wide frequency range.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the microwave voltage controlled oscillator of the present invention includes a tuned circuit having a varactor diode, and a diode or a diode having negative resistance as an oscillation element. A microwave voltage controlled oscillator equipped with a transistor, in which a varactor diode is connected to an element exhibiting capacitive impedance as a tuned circuit via a line having an electrical length of approximately 90 degrees at the oscillation frequency. This is configured to form a parallel resonant circuit.

[0007]

[Operation] In the microwave voltage controlled oscillator of the present invention constructed as described above, the varactor diode 9 is connected to the capacitive element 14 via the line 15 having an electrical length of approximately 90 degrees at the oscillation frequency. The configured parallel resonant circuit equivalently includes a capacitive element Cr, an inductor Lv that is variable by the tuning voltage of the varactor diode, and an equivalent conductance G.
It is converted into a parallel circuit of v, and the admittance at resonance Yr'
is equal to the equivalent conductance Gv, and the above Gv does not depend on the junction capacitance Cv of the varactor diode. As a result, over a wide range of tuning voltages the reflection coefficient of the tuned circuit |Γ
Fluctuations in t| can be reduced and stable oscillation waves can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 14 is an element exhibiting capacitive impedance, in this example a capacitor Cr, and 15 is a line with a characteristic impedance of Zi having an electrical length of approximately 90 degrees at the oscillation frequency. The same reference numerals are given to the same or corresponding parts as in the conventional example shown.

Next, the operation will be explained. The tuned circuit 2 of the microwave voltage controlled oscillator according to the present invention constitutes a parallel resonant circuit with a varactor diode 9, a line 15, and a capacitor Cr14, and oscillates around its resonant frequency. Figure 2
2 shows an equivalent circuit of this tuned circuit 2. In the figure, inductor Lv and conductance Gv are equivalent circuits of varactor diode 9 seen through line 15, and can be expressed by equations 5 and 6, respectively, where Zi is the characteristic impedance of line 15. Lv=Zi2 ・Cv

(5) Gv=Rv/Zi2

(6) From this, the resonant frequency f of the tuned circuit can be expressed by the following equation. f=1/{2π(Cr・Zi2・Cv)1/
2 } (7) As is clear from FIG. 2, the admittance Yr' of the above-mentioned tuned circuit at the time of parallel resonance can be expressed by the following equation. Yr′=Gv=Rv/Zi2

(8) Therefore, the admittance Yr' is given by the characteristic impedance Zi of the line 15 and the series resistance 11 of the varactor diode 9, and the admittance Yr' at the time of parallel resonance of the tuned circuit with the conventional configuration shown in FIG. There is no dependence on Cv10 as shown in Equation 2. As a result, in the tuning circuit 2 of the microwave voltage controlled oscillator, the change in the reflection coefficient |Γt| due to the tuning voltage is reduced, as shown in FIG. 3, so that oscillation waves can be stably obtained even with a low tuning voltage. Can be done.

In the above explanation, the capacitor Cr14 is used as an element exhibiting capacitive impedance in the tuning circuit 2.
Although the explanation has been given using an example, the open-end stub 16 shown in FIG.
Alternatively, a short-circuiting stub 17 at the tip as shown in FIG. 6 may be used. In addition, the open-end stub 16 and the short-circuited stub 17 may be configured with a coaxial line made of a material exhibiting a high dielectric constant such as barium titanate. This has the advantage of providing a voltage controlled oscillator.

In the above explanation, the capacitor Cr14 is used as an element exhibiting capacitive impedance in the tuning circuit 2.
Although this has been explained using an example, similar effects can be obtained by using a resonator exhibiting parallel resonance characteristics such as a ferrimagnetic thin film resonator, a ferrimagnetic spherical resonator, or a surface acoustic wave resonator.

In the above explanation, the line 15 of the tuning circuit 2 having an electrical length of approximately 90 degrees has been taken as an example.
The coupling line 18 shown in FIG. 8 or the interdigital coupling line 19 as shown in FIG. 8 may be used. When such lines are used, there is an advantage that there is no need to provide a DC blocking circuit between the FET 3 and the varactor diode 9.

In the above explanation, the FE is used as an oscillation element.
Although the description has been made using a T (field effect transistor) as an example, other transistors or diodes having negative resistance such as a Gunn diode or an Imput diode may be used to achieve the same effect.

[0014]

As described above, according to the present invention, a varactor diode is connected to an element exhibiting capacitive impedance through a line having an electrical length of approximately 90 degrees at an oscillation frequency. By using a parallel resonant circuit as a tuning circuit of a microwave voltage-tuned oscillator, it is possible to obtain a microwave voltage-controlled oscillator that can stably obtain oscillation waves over a wide frequency range.

[0015]

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the tuning circuit of FIG. 1;

FIG. 3 is a diagram showing the reflection coefficient of the tuned circuit viewed from point s in FIG. 1;

FIG. 4 is a diagram showing the junction capacitance of a varactor diode in the tuning circuit of FIG. 1;

FIG. 5 is another embodiment of the capacitor used in the tuning circuit of the microwave voltage controlled oscillator of the present invention.

FIG. 6 is another embodiment of the capacitor used in the tuning circuit of the microwave voltage controlled oscillator of the present invention.

FIG. 7 is another embodiment of a line having an electrical length of 90 degrees used in the tuning circuit of the microwave voltage controlled oscillator of the present invention.

FIG. 8 is another embodiment of a line having an electrical length of 90 degrees used in the tuning circuit of the microwave voltage controlled oscillator of the present invention.

FIG. 9 is a circuit diagram showing a conventional microwave voltage controlled oscillator.

10 is a diagram showing the reflection coefficient of the tuned circuit viewed from point s in FIG. 9; FIG.

11 is a diagram showing the junction capacitance of a varactor diode in the tuning circuit of FIG. 9; FIG.

[Explanation of symbols]

1 Amplifying circuit 2 Tuning circuit 3 FET 4 Drain terminal of FET 5 Gate terminal of FET 6 Source terminal of FET 7 Inductor Ls 8 Output matching circuit 9 Varactor diode 10 Junction capacitance of varactor diode Cv11 Varactor diode - series resistance Rv13 output terminal 14 capacitor Cr 15 line

Claims (1)

[Claims] Claim 1: In a microwave voltage controlled oscillator comprising a tuned circuit having a varactor diode and a diode or transistor having negative resistance as an oscillation element, an element exhibiting capacitive impedance as the tuned circuit. A microwave voltage controlled oscillator characterized in that a parallel resonant circuit is constructed by connecting a varactor diode through a line having an electrical length of approximately 90 degrees at the oscillation frequency.