JPS6156888B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION For example, a known microwave oscillator uses a three-terminal active element, such as a gallium arsenide field effect transistor (hereinafter referred to as GaAs-FET), as an oscillation element.

Figure 1 shows an example of the configuration of this microwave oscillator. Although not shown, each component is provided on a dielectric substrate made of alumina, for example, with a ground conductor provided in a predetermined pattern on the back side. be.

In FIG. 1, 1 is a GaAs-FET, 1G is its gate electrode, 1S is its source electrode, and 1D is its drain electrode.

2, 3, 4 and 5 are on the surface of the dielectric substrate,
Each microstrip line is formed of a linear conductive layer with a uniform width. One end of the line 2 is connected to the gate electrode 1G of the GaAs-FET 1, and the other end is connected to the ground side via the resistor 6. conductors, respectively, and one end of line 3 is
The other end is connected to the source electrode 1S of the GaAs-FET 1 and the ground side conductor, and further,
One end of the line 4 is connected to the drain electrode 1D of the GaAs-FET 1, and the other end is connected to the microstrip line 5 via a gap capacitance 7 for DC blocking, and this line 5 is used as a high frequency output terminal. Ru.

Basically, the oscillator is configured with the above configuration,
Its equivalent circuit can be shown in FIG.

That is, the microstripline 2 constitutes an impedance element 8, the microstripline 3 constitutes an impedance element 9, and the microstripline 4 constitutes a load 10. These impedance elements 8 and 9 and load 10 constitute a series feedback circuit 11.

The microstrip lines 2, 3, and 4 can become capacitive elements or inductive elements depending on the relationship with the microwave wavelength by appropriately selecting their lengths, and this determines the oscillation frequency. .

By the way, oscillators using GaAs-FETs have advantages such as low noise, high efficiency, and low bias voltage, but the disadvantage is that it is difficult to keep the oscillation frequency constant despite changes in temperature or the passage of time. be.

Therefore, an attempt has been made to stabilize the oscillation frequency by performing frequency discrimination on the output of the oscillator and controlling the oscillation frequency using the discriminated output.

FIG. 3 shows an example of the configuration. In this example, the gate electrode 1G of the GaAs-FET 1 is connected to the microstripline 12, and the resonant frequency is set to the target oscillation frequency f ₀ A cylindrical dielectric resonator 13 having a diameter equal to 1 is provided in an electromagnetically coupled manner. A sub-microstripline 14 is loosely coupled to the dielectric resonator 13 and parallel to the microstripline 12. One end of this sub-microstrip line 14 is an open end.

And microstrip lines 12 and 1
4, the end opposite to the FET 1 with respect to the coupling portion between each line 12, 14 and the dielectric resonator 13 is
These lines are bridged by two lines 15a and 15b, and the widths of the extensions of lines 12 and 14, respectively, between these two lines are widened,
As a result, a 90 degree hybrid coupler 15 is formed. The ends of the coupler 15 in the extending direction of the lines 12 and 14 are connected to a ground conductor via diodes 16 and 17 that are oriented in opposite directions. The connection point between the end of this coupler 15 and these diodes 16 and 17 is connected to each other and to a ground conductor via a resistor 18 and to a terminal 19, from which an output is taken out. It will be done like this.

Here, as shown in Fig. 4, a dielectric resonator M is coupled between two microstrip lines _L1 and _L2 , and a high frequency signal a is supplied from one end of the microstripline _L1 . In this case, the coupling of line _L1 and resonator M acts as a band-stop filter for the signal passing through line _L1 . On the other hand, the line
The coupling between L ₂ and resonator M acts as a bandpass filter. If the signal passing through the coupling part between line _L1 and resonator M is b, and the signal passing through the coupling part between line _L2 and resonator M is c, then [Q ⁻¹ _L = Q ⁻¹ ₀ +4k ₂ ² _t , where Q ₀ is the unloaded Q of the resonator M, k _1t is the coupling coefficient between the resonator M and the line L ₁ , and k _2t is the coupling coefficient between the resonator M and the line L ₂ The coupling coefficient φ ₁ (ω) is the phase amount of the line L ₁ φ ₂ (ω) is the phase amount of the line L ₂ ω ₀ =2πf ₀ , and f ₀ is the resonant frequency of the resonator M].

Therefore, the phase of the signal b changes rapidly around the resonant frequency f ₀ of the resonator M, as shown by the broken line in FIG. On the other hand, as shown by the solid line in the figure, the phase of signal c changes rapidly around the resonant frequency f ₀ of resonator M, but the way the phase changes is the opposite of that of signal b. Become.

Therefore, the gate electrode 1G of GaAs-FET1
The signal obtained on the side passes through the coupling part between the line 12 and the resonator 13, and the phase changes rapidly around the resonant frequency _f0 , as shown by the broken line in FIG. supplied to

On the other hand, the signal passing through the coupling portion between the line 14 and the resonator 13, which has the characteristics shown by the solid line in FIG. 5, is also supplied to the hybrid coupler 15.

In the coupler 15, the signals from the lines 12 and 14 are respectively supplied to the inputs of the lines 14 and 12 through the line 15a with a phase delay of 90 degrees. Therefore, with respect to frequency changes, the signal obtained on the extended side A of the line 12 of the coupler 15 and the signal obtained on the extended side B of the line 14 with respect to the signal obtained on the gate electrode 1G side of the GaAs-FET 1 is The state of the phase difference is shown in FIG. 6.

From this Fig. 6, the output vs. phase characteristic of the signal obtained on the A side is as shown by the broken line in Fig. 7, and the frequency characteristic of the output of the signal obtained on the B side is as shown by the solid line in the same figure. Become something. That is, at the resonant frequency f ₀ , the signal outputs obtained on the A side and the B side have the same level, and at frequencies lower than f ₀ , the components on the B side, and at frequencies higher than f ₀ , the components on the A side,
Each becomes larger.

Since the two detection diodes 16 and 17 are connected in opposite directions, considering their polarity, their common connection point, that is, the output terminal 19, has the output of the A side subtracted from the output of the B side. Therefore, if the characteristics of both diodes 16 and 17 are equal, the terminal 19 will have 0 at the resonant frequency f ₀ , a positive DC output at frequencies lower than f ₀ , and a negative DC output at frequencies higher than f ₀ . You can get each. In other words,
As shown in FIG. 8, a frequency discrimination output V _D having an inverted S-shaped characteristic is obtained which becomes exactly 0 at the frequency f ₀ .

In other words, the 90° hybrid coupler 15 and the diodes 16 and 17 constitute the phase detector 20, and the signal passed through the coupling circuit of the resonator 13 and line 12 passes through the coupling circuit of the resonator 13 and line 14. The phase of the signal is detected, and the phase difference between the two signals is extracted as a DC output _VD .

Then, with this output V _D, for example, GaAs-
The gate electrode of FET1 is controlled, so that
The oscillation frequency is controlled to be _f0 .

As described above, the frequency discrimination circuit generally calculates the difference between the outputs of two diodes configured such that the DC output changes depending on the frequency, as shown in FIG. As shown in the figure, it is configured to obtain an output that changes in one direction with respect to frequency.

Here, the outputs of the two diodes V ₁ and V ₂
Assuming that both diodes are connected in the same direction, V ₁ = K ₁ · p {a ₁ (f - f ₀ ) + V ₀₁ } ...... (1) V ₂ = K ₂ · p {- a ₂ (f − f ₀ ) + V ₀₂ }……(2) [K ₁ and K ₂ are the sensitivities of each diode, a ₁ and a ₂ are the discrimination sensitivities, and V ₀₁ and V ₀₂ are the sensitivities of each diode output. The voltage p at frequency f ₀ is the high frequency input. Taking the difference between both outputs as the frequency discrimination output V _D , V _D = V ₁ − V ₂ = p{a ₁ K ₁ (f − f ₀ ) + a ₂ K ₂ (f − f ₀ ) + K ₁ V ₀₁ − K ₂ V ₀₂ } ...(3). Here, at the target center frequency f=f ₀ , V _D =p(K ₁ V ₀₁ −K ₂ V ₀₂ ) (4). Therefore, as shown in Figure 7, if the target center frequency f = f ₀ and the configuration is such that V ₀₁ = V ₀₂ , then if the sensitivities of the diodes are the same, the frequency discrimination output V will be at f = f ₀ . _D = 0, and even if the high frequency input p fluctuates, it will not be affected by this.
That is, although the output level of the oscillator generally fluctuates as the oscillation frequency changes, this voltage fluctuation does not appear in the frequency discrimination output.

However, in reality, it is difficult to make the characteristics of the two diodes the same, and it is almost impossible to make the characteristics of the two diodes satisfy the above-mentioned equation (4). For this reason, the influence of the high frequency input p appears on the output V _D , and it is not possible on the output side to distinguish between fluctuations in the output V _D due to this high frequency input p and changes in the output V _D due to frequency changes, so accurate frequency discrimination signals can be obtained. There is a drawback that it cannot be obtained.

Therefore, a device has been devised that can eliminate the influence of level fluctuations in the oscillation output.

Figure 9 is an example of this, in which a directional coupler with length λ/4 (λ
A microstrip line 21 made of a conductive layer having a uniform width (wavelength at an oscillation frequency f ₀ ) is provided close to the line 5 . And that
The end on the GaAs-FET 1 side is bent in the direction perpendicular to the line 5, and the terminal 22 is led out from the tip, and the cathode of the diode 23 is bent.
It is connected to the ground side conductor through a parallel circuit between the anodes and a resistor 24. Further, the other end of the line 21 is connected to a ground conductor via a resistor 25.

In this way, a voltage V _M corresponding to the oscillation output level of the oscillator can be obtained at the terminal 22, although the characteristic is almost flat against frequency changes.

Then, the voltage V _M obtained at this terminal 22,
The voltage V _D obtained at the terminal 19 is supplied to the divider 26 and divided by V _D /V _M , and the divided output is obtained from the terminal 27 as a frequency discrimination output. The oscillation frequency is controlled by applying the oscillation frequency to the gate electrode of the oscillator.

Here, if the output level of the oscillator fluctuates and the signal V _D obtained at the terminal 19 becomes kV _D , the signal V _M obtained at the terminal 22 also becomes kV _M in accordance with the variation in the output level. Therefore, the output of the divider 26 is independent of the fluctuation in the output of the oscillator.

Therefore, the frequency discrimination output is a voltage that follows only the frequency fluctuations and is not affected by the output fluctuations of the oscillator, and if the oscillator is controlled by this, the oscillation frequency is stabilized at f ₀ .

However, even with this method, there are the following disadvantages.

That is, for example, as shown in FIG. 9, a frequency discrimination circuit is provided on the gate electrode 1G side of the GaAs-FET 1 constituting the oscillator, and a directional coupler is provided on the drain side to obtain an output according to fluctuations in the oscillation output level. If provided, gate electrode 1G of FET1
The level change of the high frequency signal on the side of the FET and the level change of the high frequency signal on the drain electrode 1D side are
Due to the non-linear operation of , the correspondence may not necessarily be linear.

Therefore, it is conceivable to provide a coupler on the gate electrode side of the FET, but this is not preferable because the oscillation conditions for the oscillator become severe.

In addition, the directional coupler used to obtain output according to fluctuations in the oscillation output level must have uniform characteristics within the frequency band used by the frequency discriminator, regardless of frequency changes; Band couplers have the disadvantage that desired operation cannot be expected.

The present invention aims to provide a frequency discrimination circuit that can eliminate the above-mentioned drawbacks.

Hereinafter, an example of the circuit of the present invention will be described with reference to FIG. 10, taking as an example the case where the frequency of the output of the microwave oscillator as described above is discriminated.

That is, in this example, the two detection diodes 31 and 32 are connected to the hybrid coupler 1.
5 and the ground conductor in the same direction. The output V ₁ of the diode 31 is supplied to the inverting input terminal of the operational amplifier 33, and the output V ₂ of the diode 32 is supplied to the non-inverting input terminal of the operational amplifier 33.
The difference between V ₁ and V ₂ is taken to obtain a DC voltage equal to the output V _D shown in equation (3) above.

Further, the output V ₁ of the diode 31 and the output V ₂ of the diode 32 are combined via resistors 35 and 36, respectively, and the combined output is sent to the inverting amplifier 34.
taken out through.

Here, the output V _AD of the amplifier 34 is V _AD =V ₁ +V ₂ =p{(a ₁ K ₁ −a ₂ K ₂ )(f −f ₀ )+K ₁ V ₀₁ +K ₂ V ₀₂ } …… (5).

Then, the output V _D of the amplifier 33 and the amplifier 34
_{The output} V _{AD is} supplied to the _{divider 37} , _and from _this divider ₃₇ , ₁ V ₀₁ −K ₂ V ₀₂ }/〓{(a _{1
The following output V D ' is obtained .} As is clear from equation (6), the output V _D ' is completely unrelated to the level of the high frequency input p.

Here, as can be seen from Fig. 7, the output V _AD changes almost linearly with changes in frequency within the frequency range used by the frequency discriminator, so the characteristics of the output V _D and the output V _D ' is not significantly different. Therefore, in the present invention, this output V _D ' is obtained as a frequency discrimination output.

Therefore, according to the present invention, since the output of the frequency discrimination diode itself is used to detect fluctuations in the output level of the oscillator, fluctuations in the output level of the oscillator can be detected in the same manner as obtaining the frequency discrimination output.
It can be obtained on the gate electrode side of the FET. Moreover, the oscillation conditions do not become severe. Therefore, since the two have a linear correspondence, the output V _D ' becomes an accurate frequency discrimination output.

Further, since it is not necessary to use a directional coupler like the example shown in FIG. 9, the output V _AD corresponding to the output level of the oscillator has almost no frequency dependence as in the case where this coupler is used. In other words, if the two diodes are well balanced, a ₁ K ₁ a ₂ K ₂ is obtained, so the output V _AD becomes almost independent of frequency.

Note that even if the dielectric resonator 13 in the illustrated example is used alone, it contributes to stabilizing the output of the oscillator against temperature changes and the like. That is, the impedance element 8 of the equivalent circuit in FIG.
In the figure, a dielectric resonator 13 coupled to line 2)
shall be included. Then, this dielectric resonator 1
3, the feedback circuit 1 closes to the target oscillation frequency.
Since the reactance of 1 can be changed by a large amount, the oscillation frequency can be made more stable than in the case of the configuration shown in FIG.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a microwave oscillator, Figure 2 is its equivalent circuit diagram, Figure 3 is a diagram showing an example of a microwave oscillator equipped with a frequency discrimination circuit, and Figures 4 to 8 are its equivalent circuit diagram. FIG. 9 is a diagram for explaining a frequency discrimination circuit, FIG. 9 is a diagram showing another example of a frequency discrimination circuit for the output of a microwave oscillator, and FIG. 10 is a diagram for explaining an example of the frequency discrimination circuit according to the present invention It is a figure which shows the example of the case where it is used for frequency discrimination. 1 is GaAs-FET, 3, 4, 5, 12 and 14
1 is a microstrip line, 15 is a 90 degree hybrid coupler, 16, 17 and 31, 32 are detection diodes, 33 is an operational amplifier as a subtracter, 34 is an amplifier, and 37 is a divider.

Claims (1)

[Claims] 1 A microstrip line to which an oscillation signal from an oscillator is supplied at one end and electromagnetically coupled to a dielectric resonator having a resonant frequency equal to the desired oscillation frequency, and a sub-microstrip line electromagnetically coupled to the dielectric resonator. a hybrid coupling configured to branch a signal from the microstrip line to the sub-microstrip line and branch a signal from the sub-microstrip line to the microstrip line. a pair of diodes connected in opposite directions to a pair of output terminals of the coupler, and a difference signal of signals having a phase difference from each other and an inverted signal of the sum signal obtained from the diodes. A frequency discrimination circuit comprising: a division circuit, and a frequency discrimination signal for controlling the oscillation frequency of the oscillator is obtained from the division circuit.