JP2004363919A - Bias circuit for high frequency and high-frequency oscillator using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To configure a bias circuit that reflects the signal of desired frequency from a connected transistor with high efficiency and attenuates signals of frequency other than the desired frequency to suppress reflection. <P>SOLUTION: A 1st microstrip line L21 whose electrical length is nearly 1/4 time as long as the wavelength at the resonance frequency of a resonance circuit 1 is connected to the collector of a transistors Tr of an amplifying circuit 2 of an oscillator, a 2nd microstrip line L22 having a specified electrical length is connected to the side of the 1st microstrip line L21 that faces the collector, and a 1st tip-open stub St2 is connected to the connection point (point A). Further, a microstrip line L23 which is electrically connected to a control voltage terminal (Vcc) 51 is connected to the end of the 2nd microstrip line L22 which faces the point A and a 2nd tip-open stub St3 having a specified electrical length is connected through a resistance element R4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-frequency bias circuit, and more particularly to a high-frequency bias circuit used for a circuit for supplying a DC voltage to an active element, and a high-frequency oscillator including the same.
[0002]
[Prior art]
A PLL circuit used for a high frequency circuit such as a microwave generally includes a voltage controlled oscillator. As shown in FIG. 4, the voltage controlled oscillator includes a resonance circuit 1 including a resonator RL1 and a variable capacitance diode VD, and an amplification circuit 2 including a transistor Tr. Here, in order to operate the transistor Tr of the amplifier circuit 2, a DC voltage must be applied to the transistor Tr, and a bias circuit 20 for that purpose is connected to the collector of the transistor Tr.
[0003]
FIG. 4 is a block diagram showing the configuration of a high-frequency oscillator provided with a conventional bias circuit. The same parts as those of a high-frequency oscillator according to an embodiment of the present invention described later are denoted by the same reference numerals and description thereof will be omitted.
[0004]
This bias circuit 20 is generally formed of a macrostrip line, and as shown in FIG. 4, oscillates from a voltage-controlled oscillator disposed between a collector of a transistor Tr and a voltage supply terminal (Vcc) 51. A microstrip line L21 having an electrical length of 1/4 wavelength of the frequency, and one end connected to the voltage supply terminal (Vcc) 51 side of the microstrip line L21, one end of which is open, and the electrical length of the 1/4 wavelength. Stub St2 having an open end.
[0005]
FIG. 5 is a perspective view showing a structural example of a portion of the bias circuit 20 including the microstrip line L21 and the open stub St2.
For the high frequency signal of the desired frequency, the connection point (point A in FIG. 5) of the open end stub St2 of the bias circuit 20 is equivalently short-circuited, and the collector-side end (point B in FIG. 5) of the microstrip line L21 is It is equivalently open. Therefore, the impedance as viewed from the point B to the voltage supply terminal side is infinite, that is, the amplitude of the reflection coefficient is 1 and the phase is 0, so that the high-frequency signal flowing through the transistor Tr is not attenuated. In this manner, a DC driving voltage can be supplied to the transistor Tr without affecting the high-frequency signal transmitted through the transistor Tr, so that a desired oscillation characteristic can be obtained (for example, see Non-Patent Document 1).
[0006]
[Non-patent document 1]
Yoshihiro Konishi, "Basics and Applications of Microwave Circuits", Sogo Denshi Publishing, August 20, 1990, p318-p319
[0007]
[Problems to be solved by the invention]
However, in the above-described conventional bias circuit, the amplitude of the reflection coefficient is 1 with respect to the transistor Tr (active element) at point B in FIGS. 4 and 5 for a high-frequency signal of an unnecessary frequency other than the desired frequency. Even if it does, the impedance will be non-zero.
[0008]
On the other hand, as the transistor Tr used for the high-frequency oscillator, a transistor that exhibits a negative resistance in a predetermined frequency band including a desired frequency is generally used. In this case, when a high-frequency signal of an unnecessary frequency within a frequency band indicating a negative resistance such as noise is input to the transistor Tr, the reflection coefficient of the bias circuit on the voltage supply terminal side from the transistor Tr increases, and Since the transistor Tr has a negative resistance, the transistor Tr oscillates at an unnecessary frequency, and abnormal oscillation occurs as a high-frequency oscillator.
[0009]
It is an object of the present invention to provide a bias circuit for attenuating a high frequency signal of an unnecessary frequency incident from a transistor to suppress reflection, and a high frequency oscillator using the bias circuit to prevent oscillation at an unnecessary frequency.
[0010]
[Means for Solving the Problems]
The present invention provides a high-frequency bias circuit for supplying a predetermined DC voltage to an active element of a high-frequency circuit, wherein a desired frequency of a desired frequency flowing through the active element is supplied between the active element and a voltage supply terminal for supplying a DC voltage to the active element. A first microstrip line having an electrical length of about 1/4 wavelength in a high-frequency signal and a second microstrip line different from the first microstrip line are connected in series from the active element side in order, and A first open-end stub having a high-frequency signal of a desired frequency and having an electrical length of about 1/4 wavelength is connected to a connection point between the first microstrip line and the second microstrip line, and further, a voltage supply terminal A series circuit comprising a resistance element and a second open-end stub is connected to a connection point between the first and second microstrip lines.
[0011]
Further, a high frequency oscillator according to the present invention includes the high frequency bias circuit, an active element for supplying a DC voltage from the high frequency bias circuit, and a resonance circuit connected to the active element.
[0012]
With this configuration, in the case of a high-frequency signal of a desired frequency, the high-frequency signal is equivalently short-circuited at the connection point between the first microstrip line and the first open-end stub, and the second microstrip connected to this is connected. The high-frequency signal does not propagate to the line or the series circuit of the second open-end stub and the resistor. Then, the reflection coefficient of the high-frequency bias circuit when the voltage supply terminal side is viewed from the active element, that is, the amplitude of the reflection coefficient at the end of the first microstrip line on the active element side is 1 and the phase becomes 0. As a result, in the high-frequency signal of the desired frequency, the high-frequency bias circuit side has an infinite impedance and is open. Therefore, the high-frequency signal flowing through the active element is not affected by the high-frequency bias circuit and the power supply circuit connected to the voltage supply terminal, and the high-frequency oscillator oscillates according to predetermined characteristics.
[0013]
On the other hand, in the case of a high-frequency signal of an unnecessary frequency other than the desired frequency, the end of the first microstrip line of the high-frequency bias circuit on the active element side is not equivalently opened, and from this end, the high-frequency bias circuit side The input impedance does not become infinity. Further, since the connection point of the first open stub of the high frequency bias circuit is not short-circuited, the high frequency signal flowing through the active element propagates to the voltage supply terminal side. Here, the propagated high-frequency signal is attenuated by the resistance connected between the second microstrip line and the second open-end stub. The amplitude becomes less than 1. For this reason, the high-frequency signal of the unnecessary frequency flowing to the active element enters the high-frequency bias circuit and is attenuated by the resistance of the high-frequency bias circuit, so that reflection from the high-frequency bias circuit to the active element is suppressed. Thus, even if the active element has negative resistance, the high-frequency oscillator does not oscillate at an unnecessary frequency.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
A high-frequency oscillator including a high-frequency bias circuit (hereinafter, simply referred to as a “bias circuit”) according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of a high-frequency oscillator including a bias circuit according to the present embodiment.
[0015]
As shown in FIG. 1, the high-frequency oscillator according to the present embodiment is entirely configured by a microstrip line, and includes a resonance circuit 1 and an amplification circuit 2.
In the resonance circuit 1, a series circuit of a microstrip line L11, a variable capacitance diode VD, and a microstrip line L12 is provided between the control voltage terminal (Vct) 50 and the ground. One end of a coupling line RL1 composed of two microstrip lines formed in parallel is connected to a connection point between the variable capacitance diode VD and the microstrip line L11. Further, a high-frequency bypass capacitive element C1 is provided between the control voltage terminal 50 and the ground.
[0016]
The amplifier circuit 2 includes a series circuit including a bias circuit 2, a transistor Tr, a resistor R3, and an inductance element L0, between the drive voltage supply terminal (Vcc) 51 and the ground. The other end of the coupling line RL1 of the resonance circuit 1 is connected to the base of the transistor Tr. Between the connection point between the emitter of the transistor Tr and the resistance element R3 and the output terminal 52, a coupling line RL2 composed of two microstrip lines formed in parallel is provided.
[0017]
A series circuit of resistance elements R1 and R2 is provided between a predetermined point of a bias circuit 21 described later and the ground, and a connection point of the resistance elements R1 and R2 is connected to a base of the transistor Tr.
[0018]
An open-end stub St1 having an electrical length of 1/4 wavelength of the resonance frequency of the desired frequency signal is provided at a connection point (point B in the drawing) between the collector of the transistor Tr and the bias circuit 21. Further, an open-end stub St4 functioning as a capacitive element is also provided at a connection point between the emitter of the transistor Tr and the resonator RL2.
[0019]
In the bias circuit 21, a first microstrip line L21 having an electrical length of 1/4 wavelength of a desired frequency signal is provided between the collector (point B) of the transistor Tr and the drive voltage supply terminal (Vcc) 51. A second microstrip line L22 different from the first microstrip line L21 and a further microstrip line L23 are connected in series. Further, a first open-end stub St2 having an electrical length of approximately 1/4 wavelength of a high-frequency signal of a desired frequency is connected to a connection point (point A) between the first microstrip line L21 and the second microstrip line L22. Connected to Further, a series circuit including a resistance element R4 and a second open-end stub St3 is connected to the drive voltage supply side (connection point with the microstrip line L23) of the second microstrip line L22.
[0020]
A high frequency bypass capacitive element C2 is provided between the drive voltage supply terminal 51 and the ground.
[0021]
The resonance circuit 1 of such a high-frequency oscillator controls the resonance frequency of the resonance circuit 1 by utilizing the fact that the capacitance value of the variable capacitance diode VD changes according to the voltage value applied to the variable capacitance diode VD. That is, the load capacity is determined by setting the voltage value supplied to the control voltage terminal (Vct) 50 to a predetermined value, and the resonance frequency of the resonance circuit 1 including the coupling line RL1 is determined. The signal of the resonance frequency obtained by the resonance circuit 1 is input from the coupling line RL1 to the base of the transistor Tr of the amplification circuit 2.
[0022]
On the other hand, a DC voltage is supplied to the transistor Tr of the amplifier circuit 2 from the drive voltage supply terminal 51, and a predetermined bias voltage is supplied to the base and the collector of the transistor Tr. Thereby, the transistor Tr inputs and outputs a signal to and from the resonance circuit 1 due to its negative resistance, and oscillates with the resonance circuit 1 at the resonance frequency of the resonance circuit 1. This oscillation signal is extracted from the emitter of the transistor Tr, and the oscillation signal is output from the output terminal 52 via the coupling line RL2. At this time, the resonator RL2 suppresses spurious components.
[0023]
Here, since the bias circuit 21 is provided with the first open-end stub St2 at the end of the first microstrip line L21 opposite to the end on the transistor Tr side, the first microstrip line L21 has a first open stub St2. The connection point (point A) between the first microstrip line L21 and the first open stub St2 is equivalently short-circuited, and the connection point (point B) between the first microstrip line L21 and the transistor Tr is equivalent. It is open to the public. When the point A is short-circuited in this way, the point A is grounded for a signal of a desired frequency, and the circuit between the second microstrip line L22 and the drive voltage terminal 51 does not function. Further, when the point B is opened, the reflection coefficient viewed from the bias circuit side from this point has an amplitude of 1 and a phase of 0, so that the impedance viewed from the transistor Tr to the bias circuit 21 becomes infinite, A signal of a desired frequency is not input to the bias circuit 21 side. Thereby, it is possible to prevent a signal of a desired frequency from being input to the bias circuit 21 and losing a signal amplified by the transistor Tr. Further, since the open-ended stub St1 is formed on the collector of the transistor Tr, the open-ended stub St1 functions as a grounding circuit that grounds the collector of the transistor Tr in a predetermined frequency band including a desired frequency. Signal can be further suppressed. Thus, the transistor Tr can amplify the signal of the desired frequency and oscillate the signal with higher efficiency.
[0024]
On the other hand, in the case of a signal having a frequency other than the desired frequency such as noise, the signal is propagated from the first microstrip line L21 to the second microstrip line L22 because the point A of the bias circuit 21 is not short-circuited. . As a result, the phase of the reflection coefficient when the bias circuit 21 is viewed from the transistor Tr is not zero. Here, as described above, since the second open-end stub St3 is connected to the side of the second microstrip line L22 facing the point A via the resistor R4, the resistance element R4 is set to about 10Ω. With a relatively low resistance value, the signal passing through the microstrip line L22 propagates through the resistance element R4. The signal input to the resistance element R4 is consumed and attenuated regardless of the frequency. That is, the amplitude of the reflection coefficient as viewed from the transistor Tr toward the bias circuit 21 becomes smaller than 1, and the signal having a frequency other than the desired frequency incident on the bias circuit 21 from the transistor Tr is consumed or attenuated and reflected on the transistor Tr. The signal is suppressed. This can prevent the transistor Tr from oscillating at a frequency other than the desired frequency.
[0025]
Next, FIGS. 2 and 3 show simulation results of the above-described configuration and the conventional configuration.
2 (a) is a Smith chart showing impedance viewed bias circuit 21 of the configuration of the present embodiment from the transistor Tr side, a diagram showing a (b) its reflection characteristic S _11.
Further, FIG. 3 (a) is a Smith chart showing impedance viewed bias circuit 20 of conventional construction from the transistor Tr side, a diagram showing a (b) its reflection characteristic S _11.
In the simulation, the desired frequency was set to 20 GHz, and the characteristic impedance of the circuit (the transistor Tr side circuit) was set to 50Ω. In the configuration of the present embodiment, the electrical length between the second microstrip line L22 and the second open-end stub St3 shown in FIG. 1 (this embodiment) is set to be approximately １ ／ wavelength of the desired frequency, The microstrip line L23, the capacitor C2, and the drive voltage supply terminal (Vcc) 51 are omitted.
[0026]
As shown in FIG. 2B, in the bias circuit of the present embodiment, the reflection loss at the desired frequency (20 GHz) is as small as about 0.6 dB, and the reflection loss at the frequency (10 GHz) 50% lower than the desired frequency is about 1 dB. 0.8 dB, and the return loss can be increased to about 3.0 dB at a frequency (30 GHz) 50% higher than the desired frequency.
[0027]
As described above, in the configuration of the present embodiment, since no signal is incident on the bias circuit at the desired frequency, loss of the signal flowing through the transistor can be suppressed. Further, since a signal is incident on the bias circuit at a frequency other than the desired frequency and is attenuated, oscillation does not occur even in a frequency range in which the transistor Tr has a negative resistance. Thus, it is possible to oscillate and output only a signal of a desired frequency with high efficiency without oscillating a signal of a frequency other than the desired frequency.
[0028]
On the other hand, as shown in FIG. 3B, in the conventional bias circuit, at the desired frequency (20 GHz), the reflection loss is about 0.6 dB as in the configuration of the present embodiment, but the frequency is 50% lower than the desired frequency. The reflection loss hardly changes in a predetermined frequency band including the desired frequency so that the reflection loss is about 0.3 dB at (10 GHz) and about 1.1 dB at a frequency (30 GHz) 50% higher than the desired frequency. .
[0029]
As described above, in the conventional configuration, even at a frequency other than the desired frequency, the signal is almost reflected without entering the bias circuit. The oscillation circuit oscillates because the reflection loss does not change, that is, the frequency band in which the signal is almost reflected coincides with the frequency band in which the transistor Tr has a negative resistance. As a result, abnormal oscillation occurs with a signal having a frequency other than the desired frequency.
[0030]
In the above-described simulation, the electrical length of the second microstrip line connected to the resistance element and the second open-end stub was set to の 長 wavelength of the desired frequency. By adjusting the length of the second open-end stub, it is possible to adjust the reflection characteristics of signals in frequency bands other than the desired frequency. For example, by setting the electrical length of the second open-end stub to be 波長 wavelength of a predetermined frequency to be attenuated, a signal of the predetermined frequency can be greatly attenuated.
[0031]
【The invention's effect】
According to the present invention, the input impedance as viewed from the active element through which the high-frequency signal of the desired frequency flows becomes infinite, almost eliminates the reflection loss, and this signal is input to the high-frequency signal of a frequency other than the desired frequency. A bias circuit that increases the return loss by consuming and attenuating can be configured.
[0032]
Further, according to the present invention, by using the bias circuit for a voltage supply circuit of an active element of a high-frequency oscillator, a high-frequency signal of a desired frequency oscillates efficiently and a high-frequency signal of an unnecessary frequency other than the desired frequency does not oscillate. An oscillator can be configured.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a high-frequency oscillator including a bias circuit according to an embodiment of the present invention. FIG. 2 is a Smith chart illustrating impedance of a bias circuit 21 having a configuration according to the present embodiment as viewed from a transistor Tr side. and Smith chart showing impedance viewed Fig 3 shows the conventional bias circuit 20 shown the reflection characteristic S ₁₁ from the transistor Tr side, and FIG. 4 shows shows the reflection characteristic S ₁₁ conventional bias circuit FIG. 5 is a block diagram showing a configuration of a high-frequency oscillator provided with the circuit. FIG. 5 is a perspective view showing a partial structure of the bias circuit shown in FIG.
1-Resonance circuit 2-Amplification circuit 21-Bias circuit 50 of amplification circuit 2-Control voltage input terminal 51-Drive voltage input terminal 52-Output terminal R4-Resistance element St2-First end open stub St3-Second end Open stub L21-first microstrip circuit L22-second microstrip circuit

Claims (2)

In a high frequency bias circuit for supplying a predetermined DC voltage to an active element of a high frequency circuit,
A first microstrip line having an electrical length of approximately 1/4 wavelength with a high-frequency signal of a desired frequency flowing through the active element, between the active element and a voltage supply terminal for supplying the DC voltage to the active element; A second microstrip line different from the first microstrip line is connected in series from the active element side,
Connecting a first open-end stub having an electrical length of approximately 1/4 wavelength with the high-frequency signal of the desired frequency to a connection point between a first microstrip line and a second microstrip line;
A high-frequency bias circuit, wherein a series circuit including a resistance element and a second open-end stub is connected to a connection point between the voltage supply terminal and a second microstrip line. A high-frequency oscillator comprising: the high-frequency bias circuit according to claim 1; the active element that supplies the DC voltage from the high-frequency bias circuit; and a resonance circuit connected to the active element.

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