JPH0332242B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency transistor oscillator, and particularly to a voltage controlled oscillator using a varactor diode as an oscillation frequency variable element.

Conventionally, this type of voltage controlled oscillator is often used as a signal source for a transmitter/receiver. Therefore, the oscillation signal is required to have a good signal-to-noise ratio (S/N). Moreover, a wide oscillation frequency band is required in order to increase the multi-channel nature of the transmitter/receiver and increase the versatility of the oscillator. Furthermore, it is desired that the ratio of change in oscillation frequency (modulation sensitivity) to the oscillation frequency control voltage applied to the varactor diode be large.

FIG. 1 shows a conventional example of a voltage controlled oscillator using a microstripline as a resonator. In the figure, TR is a transistor, C1, C
2, C3, C4 and C5 are capacitors, L1 is a chiyoke coil, X1 is a varactor diode, S
1 indicates a microstrip line, and 1 indicates an oscillation frequency control voltage terminal. In the figure, the voltage V _X1 across the varactor diode X1 during oscillation can be expressed by the following equation.

_{V X1} =V _{APC + V}

Therefore, the maximum value V _X1 (max) and the minimum value V _{X1 of V} X1
(min) can be expressed by the following formula.

_{V X1} (max) ₌ V _APC + |V _{V | (} 2) _V

Furthermore, V _V can be expressed by the following formula.

V _V = C5/C5 + C _X1・V (4) However, V is the high frequency voltage generated at the right end of the stripline S1, and _C
is the capacitance value.

Therefore, according to equation (3), the higher the oscillation level and the lower the oscillation frequency control voltage applied to the varactor diode, the more likely the varactor diode X1 will be shifted in the forward direction. Furthermore, modulation sensitivity can be increased by increasing the capacitance value of C5, but as a result, the high frequency voltage applied to varactor diode X1 increases according to equation (4), so varactor diode X1 is transferred in the forward direction. It becomes easier.

As mentioned above, when the varactor diode is forward-directed by the high frequency voltage of the oscillation signal, the capacitance value changes and the resistance value equivalently decreases, resulting in a rapid deterioration of the S/N of the oscillation signal, which causes further oscillation. Abnormal phenomena such as stoppages and parasitic oscillations often occur. As described above, in the conventional example shown in FIG. 1, the oscillation frequency control voltage cannot be lowered very much and the oscillation frequency band cannot be widened, so there are limits to the multi-channel transceiver and the versatility of the oscillator.

In order to solve the drawbacks of the conventional example shown in FIG. 1, it is sufficient to prevent the varactor diode X1 from being switched in the forward direction. One method is to reduce the high frequency voltage _VV applied to the varactor diode.

Figure 2 shows capacitor C to apply the above method.
The first
This is another conventional voltage controlled oscillator in which the high frequency voltage applied to each varactor diode is reduced compared to the conventional example shown in the figure. In the figure, C6 is a capacitor, and L2 and L3 are chiyoke coils. The one shown in Fig. 2 is a very effective voltage controlled oscillator, but compared to the voltage controlled oscillator shown in Fig. 1, in addition to the varactor diode Since L2 and L3 and capacitor C6 are increased, there is a drawback that the number of parts increases. Furthermore, since the chiyoke coil L3 is constructed of individual parts, there is a drawback that the oscillation frequency varies.

It is an object of the present invention to provide a voltage controlled oscillator that prevents the varactor diode from being transferred in the forward direction, has a stable operation with good S/N ratio, has a small number of parts, and has a wide oscillation frequency band. .

According to the present invention, at least one cascade connection circuit consisting of two varactor diodes connected so that their polarities are opposite to each other, a microstrip line connected in parallel to this circuit, and a cascade connection circuit of the varactor diodes. and means for applying an oscillation frequency control voltage between the connection point between the varactor diodes and the microstrip line so that all of the varactor diodes constituting the cascade circuit are biased in the reverse direction. is obtained.

Hereinafter, the present invention will be explained by way of examples with reference to the drawings.

FIG. 3 is a diagram showing a first embodiment of the voltage controlled oscillator of the present invention. This embodiment will be explained below.

First, a cascade connection circuit of two varactor diodes X1 and X2, which are connected so that their polarities are opposite to each other, and a microstrip line S2 are connected in parallel, and a connection point 2 between the varactor diodes and a microstrip line S2 are connected in parallel. During this period, an oscillation frequency control voltage is applied so that the varactor diodes X1 and X2 are biased in the opposite direction. The oscillation frequency control voltage is applied from terminal 1 via chiyoke coil L1. In Figure 3, the high frequency voltage applied to each varactor diode is:
Similarly to FIG. 2, the high frequency voltage applied to the varactor diode X1 shown in FIG. 1 is reduced. The circuit shown in FIG. 3 according to the present invention is different from the circuit shown in FIG.
Since the voltage is applied to the varactor diode through the two current coils, the current coil L2 and the capacitor C6 can be omitted. In the circuit of Fig. 3, the impedance of the stripline S2 as seen from point 3 becomes infinite.
If the length of is selected, the circuit becomes electrically equivalent to the circuit shown in FIG. However, the varactor diodes X1 and
By selecting the length of S2 so that the parallel resonance frequency of the parallel circuit composed of the two cascaded circuits and the stripline S2 is close to the oscillation frequency, the modulation sensitivity can be increased and the oscillation frequency band can be expanded. is possible. In other words, the length of stripline S2 is selected so that the impedance of stripline S2 viewed from point 3 is close to the capacitance value of the cascaded circuit of varactor diodes X1 and X2 and the inductance that causes parallel resonance. Although the same effect can be obtained with the strip line S2 by using the inductance of individual components, the oscillation frequency is
In the UHF band, the inductance required to cause parallel resonance is extremely small, only a few nH, and if it is constructed from individual components, the deviation in inductance and the accuracy of the mounting position will greatly affect the variation in oscillation frequency. Therefore, it is better to construct the strip line using printing technology with high dimensional accuracy and manufacture it at the same time as other circuit patterns, since this can reduce the variation in the oscillation frequency.

In the circuit shown in Figure 3, the combined impedance of the circuit network consisting of the capacitors C4 and C5, the stripline, S2, and the varactor diodes X1 and X2 when viewed to the right from the right end of the microstripline S1 is the capacitance. (hereinafter abbreviated as C _S ). The impedance of the capacitance C _S is converted by the microstrip line S1,
The impedance seen from the left end of the stripline S1 and the capacitance C _S acts as an inductance. Therefore, the circuit of FIG. 3 is equivalent to a Colpitts oscillator circuit.

The effects of the varactor diodes X1 and X2 and the stripline S2 described above are as follows. The parallel circuit of diodes X1 and X2 and the stripline S2 responds to changes in the oscillation frequency control voltage applied to terminal 1 by changing the impedance as seen from the lower end of capacitor C5 shown in FIG. This is provided to make the value change larger than the value shown in the figure. In other words, by connecting the inductance formed by the microstrip line S2 in parallel to the series circuit of varactor diodes X1 and X2, the oscillation frequency applied to terminal 1 can be controlled more easily than in the case of only varactor diode X1 in FIG. Impedance changes can be increased with respect to voltage changes.

To explain further, in response to changes in the oscillation frequency control voltage applied to the oscillation frequency control voltage terminal 1, the first
In the circuit shown in Fig. 3 and Fig. 3, the impedance viewed from the lower end of the capacitor C5 to the ground side is determined. In the circuit shown in FIG. 1, if the capacitance value of the diode X1 is C _X1 and the impedance seen from the lower end of the capacitor C5 toward the ground is Z1, then Z1=-j1/ωC _X1 (1).

Next, let Z3 be the impedance seen from the bottom end of capacitor C5 in Fig. 3 to the ground side, and calculate the combined capacitance value of the cascaded circuit of diodes X1 and X2.
C _T , and if the inductance of the microstripline S2 is L2, then Z3 = 1/1/jωL ₂ +jωC _T =jωC _T /C _T /L ₂ −ω ² C _T ² = j
ωC _T L ₂ /C _T (1−ω ² C _T L ₂ )=jωC _T L ₂ /C _T (1−ω ² C _T L
₂ )...(2) Next, it will be explained what kind of control voltage V _APC should be supplied to the terminal 1 to obtain the uniquely desired oscillation frequency (f _V ).

First, the control voltage V _APC to terminal 1 is fixed at a value convenient for control. Next, the inductance of the stripline S2 is adjusted so that the resonant frequency of the above-mentioned parallel resonant circuit is near the oscillation frequency _fV .
Find L ₂ . After determining the inductance L2, the control voltage V _APC to the terminal 1 is changed, the corresponding value of the oscillation frequency f _V is measured, and a characteristic diagram of the voltage V _APC and the frequency f _V is created. According to the created characteristic diagram of V _APC- f _V , a control voltage V _APC is supplied to terminal 1 to obtain the desired oscillation frequency f _V. In this way,
For a certain control voltage V _APC , a desired oscillation frequency f _V can be uniquely determined and obtained.

FIG. 4 shows a voltage controlled oscillator according to a second embodiment of the present invention. In this voltage controlled oscillator, varactor diodes X3 and X4 are connected to a cascade circuit made up of varactor diodes X1 and
By connecting the cascaded circuits constructed of
The total capacitance value made up of is the same as the capacitance value of X11 varactor diodes in FIG. This second embodiment also requires only a microstrip line in addition to the varactor diode, as in the first embodiment, and the number of components is small. The modulation sensitivity can be increased by optimizing the length of the stripline S2 because
It is similar to FIG. In this way, by connecting in parallel the cascade circuit of two varactor diodes connected so that their polarities are opposite to each other, the number of cascades per varactor diode can be further increased than that of the first embodiment shown in FIG. It was possible to reduce the high frequency voltage applied to the

In addition, by connecting multiple varactor diode cascade circuits in parallel, it is possible to prevent the varactor diodes from forwarding in a high-output oscillator, thereby creating a stable voltage-controlled oscillator with good S/N ratio. It has also become possible to configure

In the above embodiment, a high frequency oscillator using the microstripline S1 as a resonator has been described, but it is obvious that other high frequency oscillators may be used.

Further, in the above embodiment, a positive voltage is applied to the oscillation frequency control voltage terminal 1, but it is possible to connect the varactor diodes so that the positive and negative poles are all reversed and apply a negative voltage to the terminal 1. It is obvious that it is good.

As described above, according to the present invention, it is possible to construct a high-output voltage controlled oscillator with good S/N ratio, stable operation, and wide oscillation frequency band, which is highly effective.

[Brief explanation of drawings]

1 and 2 show conventional voltage controlled oscillators, and FIGS. 3 and 4 show voltage controlled oscillators according to first and second embodiments of the present invention, respectively. Symbol explanation: TR is a transistor, C1, C
2, C3, C4, C5, C6 are capacitors, X
1, X2, X3, X4 are varactor diodes, S
1, S2 is a microstrip line, L1, L
2 and L3 represent a chiyoke coil, and 1 represents an oscillation frequency control voltage terminal, respectively.

Claims (1)

[Claims] 1 At least one cascaded circuit consisting of two varactor diodes connected so that their polarities are opposite to each other, a microstrip line connected in parallel to this circuit, and the varactor diodes mutually connected in the cascaded circuit of varactor diodes. and means for applying an oscillation frequency control voltage between the connection point of the voltage controlled oscillator and the microstrip line so that all of the varactor diodes constituting the cascade circuit are biased in the reverse direction. The capacitance value of the varactor diode is connected to a resonant circuit, and the capacitance value of the varactor diode is set so that the parallel resonant frequency of the parallel circuit composed of the cascade circuit of the varactor diodes and the microstrip line is close to the oscillation frequency of the voltage controlled oscillator. and a voltage controlled oscillator characterized in that the length of the microstrip line is selected.