JP2011029753A - High-frequency oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency oscillator capable of raising output power without deteriorating phase noise characteristics. <P>SOLUTION: A high-frequency oscillator of a serial feedback type includes a bipolar transistor 1 used as an active element for oscillation, an inductor 2 which includes one end connected to a base terminal or a gate terminal of the bipolar transistor 1 and the other end grounded and has induction performance at a predetermined oscillation frequency, an inductor 3 which includes one end connected to a collector terminal or a drain terminal of the bipolar transistor 1 and the other end grounded and has induction performance at the oscillation frequency, and a capacitor 4 which includes one end connected to an emitter terminal or a source terminal of the bipolar transistor 1 and the other end grounded and has capacitance at the oscillation frequency. The oscillator further includes a phase shift circuit 5 which is connected in series between the base terminal or the gate terminal and the collector terminal or the drain terminal to change the phase of the input signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-frequency oscillator that operates mainly in a microwave band or a millimeter wave band.

  A conventional high-frequency oscillator includes a parallel resonant circuit in which first and second series resonant circuits are connected in parallel, and an active element inserted between the parallel resonant circuit and the oscillation output terminal and having a negative resistance. ing. The first series resonant circuit includes an inductor and a capacitor connected in series, and the second series resonant circuit includes an inductor, a capacitor, and a varactor diode connected in series. In the second series resonance circuit, the resonance frequency is variably set according to the magnitude of the DC voltage applied to the varactor diode (see, for example, Non-Patent Document 1).

In the above high-frequency oscillator, the series resonance frequency of the second series resonance circuit is set such that the series resonance frequency of the first series resonance circuit is set higher than the oscillation frequency and the parallel resonance frequency of the parallel resonance circuit becomes the oscillation frequency. Is set lower than the oscillation frequency. At this time, by making the series resonance frequency and the series resonance frequency close to each other, the phase gradient of the parallel resonance circuit in the vicinity of the oscillation frequency can be increased.
Therefore, the external Q of the parallel resonant circuit in the vicinity of the oscillation frequency can be remarkably increased, and a high-frequency oscillator having low phase noise characteristics can be obtained.

Kenji Kawakami and four others, “Q-value analysis of a two-frequency resonant circuit used in a low-phase noise oscillator”, October 2006, IEICE, IEICE Technical Report MW 2006-117, p. 57-60

However, the prior art has the following problems.
In the conventional high frequency oscillator, the phase noise is reduced by increasing the external Q of the parallel resonance circuit. Here, if the external Q of the parallel resonant circuit is increased, the loss of the resonant circuit increases, so that the loop gain decreases and the gain suppression amount of the active element decreases.
Therefore, the loss of the resonance circuit and the gain of the active element are balanced in a state where the output power of the active element is low, so that there is a problem that the oscillation power is lowered.

  The present invention has been made to solve the above-described problems, and can increase the output power without degrading the phase noise, while maintaining the phase noise characteristics even in a low phase noise oscillator. The object is to obtain a high-frequency high-frequency oscillator.

  A high-frequency oscillator according to the present invention includes a transistor used as an active element for oscillation, a first terminal connected to the base terminal or the gate terminal of the transistor, the other terminal grounded, and an inductive property at a predetermined oscillation frequency. One end of the reactance unit is connected to the collector terminal or drain terminal of the transistor, the other end is grounded, and the second reactance unit is inductive at the oscillation frequency, and one end is connected to the emitter terminal or source terminal of the transistor. Is connected to the other end, and is grounded at the other end, and has a third reactance unit having a capacitance at the oscillation frequency, and a series feedback type high-frequency oscillator comprising a base terminal or a gate terminal, a collector terminal or a drain Connected in series with the terminal to change the phase of the input signal In which further comprises a phase section.

According to the high frequency oscillator according to the present invention, the phase shift means connected in series between the base terminal or gate terminal and the collector terminal or drain terminal changes the phase of the input signal. Accordingly, the voltage at the base terminal or the gate terminal can be increased by shifting and feeding back a part of the signal output from the collector terminal or the drain terminal.
Therefore, the output power can be increased without degrading the phase noise, and a high-output high-frequency oscillator can be obtained while maintaining the phase noise characteristics even in a low-phase noise oscillator.

1 is a circuit diagram showing a high-frequency oscillator according to Embodiment 1 of the present invention. It is explanatory drawing which shows operation | movement of the high frequency oscillator which concerns on Embodiment 1 of this invention. It is an equivalent circuit diagram of a general series feedback oscillator. It is a circuit diagram which shows another phase shift circuit of the high frequency oscillator which concerns on Embodiment 1 of this invention. It is a circuit diagram which shows another phase-shift circuit of the high frequency oscillator which concerns on Embodiment 1 of this invention. It is a circuit diagram which shows the high frequency oscillator which concerns on Embodiment 2 of this invention.

Hereinafter, preferred embodiments of the high-frequency oscillator according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals.
In the following embodiments, description will be made using bipolar transistors as transistors, but the same can be said for field effect transistors. In this case, the base terminal, collector terminal, and emitter terminal of the bipolar transistor and the gate terminal, drain terminal, and source terminal of the field effect transistor can be replaced and interpreted.

Embodiment 1 FIG.
1 is a circuit diagram showing a high-frequency oscillator according to Embodiment 1 of the present invention.
In FIG. 1, this high-frequency oscillator is a series feedback type high-frequency oscillator, and includes a bipolar transistor 1, an inductor 2 (first reactance unit), an inductor 3 (second reactance unit), and a capacitor 4 (third reactance unit). ) And a phase shift circuit 5 (phase shift means). The phase shift circuit 5 includes a capacitor (not shown) that cuts off the DC current.

The bipolar transistor 1 is used as an active element for oscillation. The base terminal of the bipolar transistor 1 is grounded via the inductor 2. The collector terminal of the bipolar transistor 1 is grounded via the inductor 3. The emitter terminal of the bipolar transistor 1 is grounded via the capacitor 4.
At this time, the inductors 2 and 3 are inductive at a predetermined oscillation frequency, and the capacitor 4 is capacitive at a predetermined oscillation frequency.

  The phase shift circuit 5 is connected in series between the base terminal and the collector terminal, and changes the phase of the input signal. Specifically, the phase shift circuit 5 is configured by a microstrip line 51 (transmission line) having a length of approximately ½ wavelength (λ / 2) with respect to the oscillation frequency, for example, as shown in FIG. ing.

Here, a general series feedback oscillator is considered. FIG. 3 is a schematic equivalent circuit diagram of a general series feedback oscillator.
In FIG. 3, the relationship between the RF voltage Vb at the base terminal of the bipolar transistor and the RF voltage Vc at the collector terminal in the oscillation state is expressed by the following equation (1).

  In the equation (1), the base-collector capacitance Cbc and the emitter capacitance Ce are sufficiently small, so the above equation (1) can be approximated as the following equation (2).

From the equation (2), it can be seen that in the oscillation state, the RF voltage Vb at the base terminal of the bipolar transistor and the RF voltage Vc at the collector terminal are in an almost opposite phase relationship.
Therefore, the RF voltage at the base terminal is increased by shifting the phase of the RF voltage at the collector terminal by approximately 180 °, and synthesizing the RF voltage at the base terminal in phase with the base terminal, thereby increasing the output power extracted from the collector terminal. Can be increased.

Returning to FIG. 2, as described above, the microstrip line 51 has a length of approximately λ / 2 with respect to the oscillation frequency. Shift the phase and output this signal to the base terminal.
As a result, the signal voltage at the base terminal and the signal voltage at the collector terminal are synthesized in phase, the high frequency input voltage to the bipolar transistor 1 is increased, and the output power of the high frequency oscillator is increased. At this time, the phase shift circuit 5 (microstrip line 51) has a frequency characteristic in the amount of phase shift, and tends to increase the slope of the loop phase with respect to the frequency. The phase noise characteristic is not deteriorated.

As described above, according to the first embodiment, the phase shift means connected in series between the base terminal and the collector terminal changes the phase of the input signal. Thereby, the voltage of the base terminal can be increased by shifting and feeding back a part of the signal output from the collector terminal. The phase shift means is composed of a transmission line having a length of approximately λ / 2 with respect to a predetermined oscillation frequency.
Therefore, the output power can be increased without degrading the phase noise, and a high-output high-frequency oscillator can be obtained while maintaining the phase noise characteristics even in a low-phase noise oscillator.

  In the first embodiment, the microstrip line 51 having a length of approximately λ / 2 with respect to a predetermined oscillation frequency is described as an example as the phase shift means. However, the present invention is not limited to this. Instead of the microstrip line 51, a phase shift circuit 60 (phase shift means) as shown in FIG. 4 may be used to change the phase of the input signal.

FIG. 4 is a circuit diagram showing another phase shift circuit 60 of the high frequency oscillator according to Embodiment 1 of the present invention.
In FIG. 4, the phase shift circuit 60 includes a 90 ° hybrid 61 formed of a microstrip line, varactor diodes 62 and 63, and high-frequency blocking choke coils 64 and 65. A control voltage Vθ is externally applied to the high frequency blocking choke coils 64 and 65 opposite to the varactor diodes 62 and 63. The 90 ° hybrid 61 is provided with a first terminal 71, a second terminal 72, a third terminal 73, and a fourth terminal 74.

The signal (microwave) input to the first terminal 71 of the 90 ° hybrid 61 is distributed to the second terminal 72 and the third terminal 73 with a phase difference of 90 °, and these signals are supplied to the varactor diode 62. , 63 and reflected from the fourth terminal 74 in the same phase. Here, the phase shift amount of the phase shift circuit 60 is a function of the capacity of the varactor diodes 62 and 63, and the phase shift amount can be continuously changed by changing the control voltage Vθ from the outside.
In this case, in-phase synthesis of the signal voltage at the base terminal and the signal voltage at the collector terminal can be achieved over the entire oscillation band by changing the amount of phase shift in accordance with the change in the oscillation frequency.

Further, instead of the microstrip line 51 shown in FIG. 2, a field effect transistor 80 as shown in FIG. 5 may be used as a phase shift circuit to change the phase of the input signal.
FIG. 5 is a circuit diagram showing still another phase shift circuit (field effect transistor 80) of the high frequency oscillator according to Embodiment 1 of the present invention.

In FIG. 5, the field effect transistor 80 has a delay (phase shift) characteristic between the drain (D) and the source (S), and by changing the gate bias voltage Vg applied to the gate (G), The channel length between the drain (D) and the source (S) changes, and the amount of phase shift can be continuously changed.
Also in this case, by changing the amount of phase shift according to the change of the oscillation frequency, the in-phase synthesis of the signal voltage of the base terminal and the signal voltage of the collector terminal can be performed over the entire oscillation band.

Embodiment 2. FIG.
FIG. 6 is a circuit diagram showing a high frequency oscillator according to Embodiment 2 of the present invention.
In FIG. 6, a resonance circuit 6 (first reactance unit) is connected to the base terminal of the bipolar transistor 1 instead of the inductor 2 shown in FIG. Here, the resonance circuit 6 is configured by, for example, a microstrip line. Other configurations are the same as those in FIG.

As described above, according to the second embodiment, the same effect as in the first embodiment can be obtained.
Moreover, phase noise can be reduced by using at least one of the first reactance unit, the second reactance unit, and the third reactance unit as a resonance circuit.

Note that this high-frequency oscillator may be used as a voltage-controlled oscillator by configuring the resonance circuit 6 to include a varactor diode (variable reactance element).
Also in this case, the same effect as in the second embodiment can be obtained.

  1 Bipolar Transistor, 2, 3 Inductor, 4 Capacitor, 5 Phase Shift Circuit (Phase Shift Means), 6 Resonant Circuit, 51 Microstrip Line (Transmission Line), 60 Phase Shift Circuit (Phase Shift Means), 61 90 ° Hybrid ( Transmission line), 80 field effect transistor (phase shift means).

Claims (6)

A transistor used as an active element for oscillation;
A first reactance unit having one end connected to the base terminal or the gate terminal of the transistor and the other end grounded, and having inductivity at a predetermined oscillation frequency;
A second reactance unit having one end connected to the collector terminal or drain terminal of the transistor and the other end grounded, and having inductivity at the oscillation frequency;
A series feedback type high-frequency oscillator comprising: a third reactance unit having one end connected to the emitter terminal or the source terminal of the transistor and the other end grounded, and having capacitance at the oscillation frequency;
A high-frequency oscillator characterized by further comprising phase shifting means connected in series between the base terminal or gate terminal and the collector terminal or drain terminal to change the phase of the input signal. The high-frequency oscillator according to claim 1, wherein the phase-shifting means is a transmission line. The high-frequency oscillator according to claim 2, wherein the transmission line has a length of approximately ½ wavelength with respect to the oscillation frequency. 3. The high-frequency oscillator according to claim 1, wherein the phase shift means variably sets a phase shift amount according to a control voltage applied from the outside. 5. The device according to claim 1, wherein at least one of the first reactance unit, the second reactance unit, and the third reactance unit is a resonance circuit. High frequency oscillator. 6. The device according to claim 1, wherein at least one of the first reactance unit, the second reactance unit, and the third reactance unit includes a variable reactance element. The high frequency oscillator described in 1.

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