JPH0654845B2 - Microwave oscillator - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a microwave oscillator, and more particularly, to a microwave oscillator having a wide frequency tuning characteristic which is configured by a microwave integrated circuit.

[Technical Background of the Invention and Problems Thereof] In recent years, a microwave oscillator composed of a microwave integrated circuit (hereinafter referred to as MIC) and a monolithic microwave integrated circuit (hereinafter referred to as MMIC) has been developed, and has various configurations. Things are made.

In particular, a microwave oscillator whose frequency is variable by controlling the bias voltage of a varactor diode (hereinafter referred to as VCO) is compact and has good performance characteristics.

A conventional example of this VCO using a field effect transistor (hereinafter referred to as FET) will be described with reference to FIG.

That is, on the dielectric substrate (2) such as a ceramic in which the ground plane (1) is formed by the metal film on the back surface, the MIC is also formed by the metal film pattern, and the FE connected to this MIC is formed.
By connecting a high impedance circuit (5) and a resistor (6) between the source terminal (4) of the T (3) and the ground plane (1) at the oscillation frequency, the FET (3) becomes a drain terminal (7). It operates as a two-terminal negative resistance element between the gate terminal and the gate terminal (8). A capacitor (9) is connected to the drain terminal (7) and is grounded to the ground plane (1) via a ground pattern (10). The structure described above is called a grounded-drain oscillator because the drain terminal (7) is equivalently installed.

The gate terminal (8) is connected to one end of the resonance circuit (12) by the transmission line via the capacitor (11), and the other end of the resonance circuit (12) is connected to the varactor diode (13) and is connected to the ground. It is grounded to the ground plane (1) through the pattern (14).

The DC bias to the FET (3) is
The varactor bias voltage applied to the varactor diode (13) is applied from the varactor bias terminal (16) to the high resistance (17).
And (18). The oscillation output is output from the gate terminal (8) to the output terminal (20) via the capacitor (19).

The equivalent circuit of this VCO is as shown in FIG. In the figure, the same symbols as in FIG. 1 indicate the same parts. The output circuit is omitted, and the FET (3) is represented by the negative resistance (21) between the drain terminal (7) and the gate terminal (8).

That is, one end of the resonance circuit (12) by the transmission line is connected to the gate terminal (8) through the capacitor (11), and the resonance circuit (1
The varactor diode (13) is connected to the other end of 2) and the ground plane is connected via the reactance (22) by the ground pattern (14).
Grounded at (1).

The drain terminal (7) is connected to the capacitor (9) and the ground pattern (1
It is grounded to the ground plane (1) via the reactance (23) by (0).

If the operating frequency is not too high, the reactance
The reactance components of (22) and (23) can be ignored because they are sufficiently low, and in the conventional example, the negative resistance (21) and one end of the varactor diode (13) are directly grounded to the ground plane (1). It is treated as a thing.

Thus, the conventional VCO keeps the drain terminal (7) at the same potential as the ground plane (1) at the oscillation frequency,
One end of the varactor diode (13) connected to (12) is also grounded.
By setting the same potential as in (1), an oscillator having frequency tuning characteristics was constructed.

The conventional example shown here is called a drain grounding method, but other conventional examples include a source grounding method and a gate grounding method, both of which keep one of the three terminals of the FET at the ground potential. There is something in common.

However, the conventional VCO configured by the MIC described above has the following problems as the oscillation frequency increases.

First, the size of the capacitor (9) shown in FIG. 1 cannot be ignored in the oscillation frequency band and acts as an inductance, so the reactance (23) shown in FIG. 2 cannot be ignored. Therefore, one end of the negative resistance (21) does not become the ground potential, and the tuning sensitivity of the oscillator decreases.

Secondly, the length in the thickness direction of the dielectric substrate (2) of the ground patterns (10) and (14) shown in FIG. 1 and the metal portion connecting them to the ground plane (1) is also ignored in the oscillation frequency. I can't do it, second
Since the reactances (22) and (23) in the figure become large, the tuning sensitivity of the oscillator decreases as in the problem in Figure 1.

Thirdly, if there are many connection points and the connection is not perfect, the loss of the circuit increases and the reliability deteriorates.

Fourth, the tuning sensitivity is lowered because a sufficient microwave voltage is not applied to the varactor diode (13).

Fifth, if complete grounding is not possible, each part of the circuit will have a complicated circuit configuration represented by series parallel of L, C, and R, causing unnecessary resonance and unstable operation. , The oscillation output decreases.

Sixth, when the frequency is changed by changing the bias of the varactor diode (13), the oscillation frequency is not determined only by the resonance frequency of the resonator, and as a result, a wide tuning characteristic cannot be obtained. These are more remarkable as the oscillation frequency becomes higher.

[Object of the Invention]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a microwave oscillator that operates stably up to a high frequency band and has a wide frequency tuning characteristic.

[Outline of Invention]

That is, the present invention has a first terminal, a second terminal, and a third terminal, the third terminal is grounded through a high impedance circuit, and the first terminal and the second terminal are connected to each other. A transistor configured to obtain negative resistance operation, having a total length of about ½ wavelength, the first terminal and the second terminal
And a varactor diode connected in series across the central division of the two-division transmission line.

Example of Invention

Next, one embodiment of the VCO of the present invention will be described with reference to FIG.

The present embodiment is an example of a VCO having a MIC structure using FETs.

That is, MI is formed by a metal film pattern on a dielectric substrate (32) such as a ceramic having a ground plane (31) formed on the back surface by a metal film.
C is formed. The gate terminal (35) of the FET (34) is connected to one end of the first transmission line (33) composed of this MIC.

The drain terminal (38) of the FET (34) is connected to one end of the second transmission line (36) via the capacitor (37).

A varactor diode (39) is connected to the other ends of the first and second transmission lines (33) and (36) to form a resonance circuit.

A high impedance circuit (41) and a resistor are provided between the source terminal (40) of the FET (34) and the ground plane (31) at the oscillation frequency.
By connecting (42), FET (34) becomes the drain terminal.
It is the same as the conventional example that it can operate as a negative resistance element having approximately two terminals between (38) and the gate terminal (35).

Furthermore, the DC bias to the FET (34) is the bias terminal (43)
The varactor bias voltage to the varactor diode (39) is applied from the varactor bias terminal (44) through the high resistances (45) and (46), and the oscillation output is the drain terminal (38).
From the output via the capacitor (47) to the output terminal (48).

The microwave equivalent circuit of this embodiment is as shown in FIG. Also, in FIG. 4, the same reference numerals as those in FIG. 3 indicate the same parts, and the output circuit is omitted. The FET (34) is a negative resistance element (49) between the gate terminal (35) and the drain terminal (38). )
Is expressed as.

That is, the gate terminal (35) of the FET (34) is connected to the first transmission line (3
3) is connected, the second transmission line (36) is connected to the drain terminal (38) through the capacitor (37), and the other ends of the first and second transmission lines (33) and (36) are connected. A varactor diode (39) is connected to. In addition, (31) in FIG. 4 is the ground plane (3
It corresponds to 1).

Next, the operation principle of this embodiment will be described.

First, the vicinity of the FET (34) will be described. Since the source terminal (40) shown in FIG. 3 is connected to high impedance, almost no microwave current flows in the operating state and the source terminal (40) is in an open state.

Therefore, the microwave currents flowing from the gate terminal (35) to the drain terminal (38) are almost equal, and the FET (34)
As shown in the figure, it can be represented by a two-terminal negative resistance (49) consisting of a gate terminal (35) and a drain terminal (38). At this time, when the microwave current of the negative resistance (49) is (I _ab ), and the terminal voltage is (V _ab ), the negative resistance value (-Z _ab ) is Z _ab = V _ab / I _ab .
The terminal voltage between terminals (b) and (b,) is (V _b ) microwave current (I _b ) The terminal voltage between terminals (a) and (a ') is (V _a ) Microwave current is (I _a ).

Next, the resonance circuit will be described.

That is, FIG. 5 shows the resonance circuit by an F matrix, and each terminal pair is represented by (a) (a '), (b) (b'), and each terminal pair (a) (a ' ), (B) (b '), and (V _a ) (V _b ) the terminal current is (I _a ) (I _b ), V _a = AV _b + BI _b ...... (1) I _a = represented by _{CV b + DI b ...... (2} ).

When I _a = I _b Is obtained. However, AD-BC = 1 Here, if A = D, V _a = -V _b , and this condition means that the two-terminal pair circuit represented by the F matrix is a symmetrical circuit.

FIG. 6 shows an F matrix when V _a = −V _b = V, I _a = I _b = I, A = D and the terminals (a ′) and (b ′) in FIG. 5 are commonly grounded. Impedance Z between terminals (a) and (b) is It is represented by.

FIG. 7 shows a symmetrical resonance circuit realized by connecting the F matrix shown in FIG. 6 to one end (c) (d) of two transmission lines with a length of l ₀ and a characteristic impedance of Z _0. is there. At this time, points (c) and (d) are at ground potential, so the impedance between terminals (a) and (b) is
(Z) is Becomes However, β is a phase constant and is ignored because the transmission line loss is small.

That is, in the circuit of FIG. 7, reactance resonance occurs at a frequency corresponding to the vicinity of βl ₀ π / 2, and if the negative resistance element (49) described in FIG. 4 is connected to the terminals (a) and (b). It becomes possible to oscillate under the condition that the total reactance of the series circuit = 0.

That is, when a capacitor (C _V ) varactor diode (39) is connected as shown in FIG. 8 (a), this equivalent circuit has a capacitance of C ₀ = 2C _V as shown in FIG. 8 (b). Are connected in series, and the intermediate point is grounded.

The voltage and current distribution when this circuit resonates is 8th.
It will be as shown in Figure (c). That is, the position at which the capacitor (C ₀ ) is at ground potential is (l _c ) from terminals (c) and (d), respectively.
The condition that the circuit resonates in this state is Is. In this case, β = 2π / λ, so (l ₀ -l _c ) =
It resonates at a frequency of λ / 4, and the resonance frequency changes due to the change of (C ₀ ).

Thus, if a variable reactance element such as a varactor diode (39) is connected in series between the terminals (c) and (d), the varactor diode (39) is equivalently grounded without another reactance component. It was done. Therefore, the resonance frequency change sensitivity between the terminals (a) and (b) can be increased, and a wide frequency tuning characteristic can be obtained.

FIG. 9 shows a VCO in which a negative resistance element (49) is connected between the terminals (a) and (b) of FIG. 8, and the ground plane is omitted.

That is, by directly connecting the varactor diode (39) between the terminals (c) and (d) closest to the ground potential of the symmetrical circuit, a VCO having a wide frequency tuning sensitivity can be realized. These terminals (c) and (d) are structurally located at positions where the varactor diode (39) is easily connected, and are easy to configure even when the frequency is high.

That is, the circuit of FIG. 9 shows the equivalence to the VCO of FIG. 4, and it can be seen that the VCO of the present invention operates stably up to a high frequency band and can have a wide frequency tuning characteristic.

FIG. 10 is a graph showing the changes in the oscillating frequency with respect to the varactor bias voltage of the VCO according to the conventional example and the example of the present invention.
T, the varactor diode, the capacitor, and the characteristic impedance of the transmission line forming the resonance circuit are made the same,
This is a case where VCOs having the same output are constructed and compared, and the frequency tuning range of the VCO of this embodiment is about twice that of the VCO of the conventional example.

In the above-mentioned embodiment, the case where it is used as the FETWC oscillator is explained.
A similar configuration is possible by using R).

Next, another embodiment of the VCO of the present invention using TR will be described with reference to FIG. However, the description of the same parts as in FIG. 3 will be omitted.

That is, the TR (50) is close to a two-terminal negative resistance element between the collector terminal (53) and the base terminal (54) by connecting a high impedance, for example, a resistor (52) to the emitter terminal (51). Make it work. In this case, the emitter terminal (51)
When a microwave current flows through the device, it does not operate as a complete two-terminal element, and the microwave currents flowing through the collector terminal (53) and the base terminal (54) differ. Therefore, strictly speaking, V _a and V _b and I _a and I _b explained in the operating principle of the previous embodiment are not equal to each other, and the maximum point of the microwave current in the resonance circuit also moves, so that the larger current You will be approaching the terminal.

Therefore, the position where the frequency tuning sensitivity becomes maximum is also different.
The mounting position of the varactor diode (55) may be determined according to the operating condition of R (50), but in practice, it may be at the center.

In the case of a VCO using TR (50), the resonance circuit connects the first transmission line (57) to the base terminal (54) via the capacitor (56), and the collector (53) to the capacitor (58). ) Is connected to the second transmission line (59), and the varactor diode (55) is connected to the other ends of the first and second transmission lines (57) and (59).
Connect.

The capacitors (56) and (58) are necessary for separating the bias voltage to the TR (50) and the varactor diode voltage to the varactor diode (55), but they are not essential to the operating principle of the present invention.

Further, since the VCO of the present invention has a certain microwave voltage with respect to the ground plane at both terminals of FET and TR, the effect of the present invention can be obtained even if the output is taken out from any of the three terminals. Source terminal with impedance connected
It is better not to use (40) and the emitter terminal (51) as output terminals.

〔The invention's effect〕

As described above, the VOO according to the present invention has the following effects.

First, since a wide tuning characteristic can be obtained by connecting a varactor diode in series at approximately the center of the transmission line forming the resonance circuit, oscillation operation at a high frequency can be easily realized.

Secondly, since it is not necessary to keep the three terminals of the transistor at the ground potential, it is possible to realize a VCO having stable negative resistance characteristics in a wide frequency range and high tuning sensitivity.

Thirdly, the capacitor to be used does not necessarily have to operate as a capacitor having a low reactance value only because it is used as a DC block, and stable oscillation can be obtained even if it operates as an inductance, so a wide range of capacitors can be used. .

Fourthly, since the circuit is simple, unnecessary resonance does not occur and the circuit operates stably up to a high frequency.

Fifth, since the microwave circuit is not directly connected to the ground plane, it can be formed on a plane and can be formed not only by MIC but also by MMIC.

As described above, according to the present invention, it is possible to provide a microwave oscillator having a circuit that is simpler than the conventional VCO, has a wide tuning characteristic, and operates stably up to a high frequency. Is extremely large.

[Brief description of drawings]

FIG. 1 shows a FET as an example of a conventional microwave oscillator.
FIG. 2 is a plan view for explaining a microwave oscillator having a frequency tuning mechanism by an MIC using the MIC, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG. 3 is a FET as an embodiment of the microwave oscillator of the present invention. FIG. 4 is an explanatory plan view of a microwave oscillator having a frequency tuning mechanism by the MIC, FIG. 4 is an equivalent circuit diagram of FIG. 3, and FIGS. 5 to 9 are diagrams showing the operation principle of FIG. FIG. 5 is an explanatory diagram showing a resonance circuit in an F matrix, and FIG. 6 is FIG. 5 showing V _a = −V _b = V, I _a = I _b = I, A =
D, an explanatory view showing the F matrix when the terminals (a ') and (b') are grounded in common, and FIG. 7 shows the F matrix of FIG. 6 having a length l ₀ and a characteristic impedance Z ₀ of 2 8 is an explanatory view of a resonance circuit in which one end of a transmission line is connected, and FIG. 8 (a) is an explanatory view of a resonance circuit in which a varactor diode is connected between the ends of two transmission lines in FIG. 7 and FIG. b) is the equivalent circuit diagram of FIG. 8 (a), FIG. 8 (c)
Is the voltage and current distribution diagram when Fig. 8 (a) resonates,
FIG. 10 is an equivalent circuit diagram of a main part of the microwave oscillator using FIG. 8, and FIG. 10 is a graph showing the change in oscillation frequency with respect to the varactor bias voltage of the conventional example and this example,
FIG. 11 is a plan view showing another embodiment of the present invention. 1, 31 ...... Ground plane, 2, 32 ...... Dielectric substrate 3, 34 …… FET 12, 33, 36, 57, 59 …… Transmission line 13, 39, 55 …… Varactor diode 50 …… Bipolar transistor

Claims (1)

[Claims] 1. A first terminal, a second terminal, and a third terminal, wherein the third terminal is grounded through a high-impedance circuit, and a negative terminal is provided between the first terminal and the second terminal. A transistor that is configured to obtain a resistance resistance operation,
A two-divided transmission line having a total length of about ½ wavelength and connected between the first terminal and the second terminal, and a varactor diode connected in series across the central divided portion of the two-divided transmission line. And a microwave oscillator.