JPS645487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a frequency conversion device, in particular in the microwave frequency range, with a mixer and a frequency stabilized local oscillator.

Recently, terrestrial broadcasting and satellite broadcasting using microwaves near 12 GHz in the SHF band have been planned, and are about to be put into practical use. Very high frequency stability is required.

Local oscillation sources for SHF receivers can be roughly divided into two types: one is to frequency-multiply an oscillator with excellent frequency stability, such as a crystal oscillator or a surface acoustic wave oscillator, and the other is to directly oscillate a semiconductor oscillation element such as a Gunn diode or GaAs FET. There is a method.

Although the former method has excellent temperature stability of the oscillation frequency, it has drawbacks such as a complicated circuit configuration and requiring delicate adjustment, which increases the cost and increases the overall size of the local oscillator.

The latter method involves stabilizing the oscillation frequency of a microwave oscillator using a high-Q dielectric resonator that has a high no-load Q value and excellent temperature stability of the resonance frequency, and a method that stabilizes the oscillation frequency of a microwave oscillator using a high-Q dielectric resonator that has a high no-load Q value and excellent temperature stability of the resonance frequency. Methods have been realized in which the oscillation frequency is stabilized by directly inserting a dielectric material whose relative permittivity changes with temperature into the body resonator, and these methods have a simple circuit configuration and are easy to adjust, resulting in low cost. It has the advantage that it is inexpensive, and the entire local oscillator can be made small and lightweight.

In a local oscillator whose frequency is stabilized by the latter method, the oscillation output and frequency stability are greatly influenced by the load circuit, and the greater the coupling between the local oscillator and the load circuit, the more influenced by the load circuit. In order to reduce the influence of the load circuit, the coupling between the local oscillator and the load circuit should be made as small as possible, but as the coupling between the local oscillator and the load circuit becomes smaller, the oscillation output also becomes smaller.

Therefore, in order to efficiently obtain the local oscillator power required for the mixer (usually around 10 mW) using a local oscillator with low power consumption, it is necessary to reduce the coupling between the local oscillator and the load circuit below a certain limit. I can't do that. In other words, in order to obtain a local oscillator with high efficiency and excellent frequency stability, it is impossible to avoid the influence of the load circuit on the local oscillator.

Conventionally, when applying the oscillation output of a local oscillator whose frequency has been stabilized using a semiconductor oscillation element to a mixer, it is necessary to prevent the local oscillator from mode jumping or stopping oscillation due to the mixer acting as a load circuit for the local oscillator. In addition, in order to prevent the temperature characteristics of the oscillation frequency of the local oscillator from being affected, an isolator is inserted between the local oscillator and the mixer, and the impedance seen from the local oscillator to the mixer side is always matched regardless of the mixer. I was trying to be there. FIG. 1 is a circuit diagram of a conventional frequency conversion device for an SHF receiver. That is, the output of the local oscillator 1 is injected into the local band pass filter 3 through the isolator 2. Then, after passing through a local bandpass filter 3, the signal is guided to a mixer 4. and from the local oscillator 1 to the mixer 4
If you look at the sides, you can see that they are aligned.

Now, for a certain mixer, the frequency characteristic of the voltage standing wave ratio (abbreviated as VSWR) of the impedance when looking from the input terminal T ₁ of the local oscillator bandpass filter 3 to the mixer 4 side without passing through an isolator is determined when VSWR is the minimum. If we consider the frequency as the center frequency and illustrate it, the result will be as shown in Fig. 2. As you will see,
The impedance of mixer 4's diode is
At 12GHz in the SHF band, the VSWR is 1 even at the center frequency (when looking at the mixer 4 side from input terminal _T1 ) due to reasons such as the impedance being lower than 50Ω and the input impedance of the local bandpass filter being mismatched. When the impedances are matched, the VSWR is 1). The center frequency here is the frequency at which the VSWR is minimum.

In a frequency conversion device in which the isolator 2 is removed and the local oscillator 1 and the mixer 4 are simply directly connected via the local bandpass filter 3, the impedance on the mixer 4 side seen from the local oscillator 1 is the second As shown in the figure, due to the lack of matching, not only abnormal characteristics such as mode jump and oscillation stop are exhibited, but also the frequency-temperature characteristics differ from the frequency-temperature characteristics when the load of local oscillator 1 is a matched load. Therefore, the isolator 2 is usually inserted between the local oscillator 1 and the local band pass filter 3 as described above. Therefore, in conventional frequency conversion equipment, the insertion of the isolator 2 increases the size of the equipment and increases the cost.In particular, the increased cost has the drawback of being a serious hindrance to SHF broadcasting, which requires a low-cost SHF receiver. Ta.

The present invention eliminates the above-mentioned drawbacks of the prior art.The purpose of the present invention is to eliminate abnormal phenomena such as mode jump and oscillation stop even if the isolator is removed, and to maintain the frequency-temperature characteristics exactly the same as in the case of a matched load. A local oscillator and a local bandpass filter as shown,
The object of the present invention is to provide a compact and inexpensive frequency conversion device by showing a combination configuration with a mixer.

The present invention provides a frequency converter in which the impedance viewed from one end of a transmission line coupling a mixer and a local oscillator to the mixer side is mismatched at the frequency of the local oscillator, and the load of the local oscillator is equal to the characteristic impedance of the transmission line. Pushing figure when the load is a matched load (Here, it is the amount defined by the ratio Δf/ΔV of the minute change Δf in the oscillation frequency to the minute change ΔV in the bias voltage applied to the semiconductor oscillation element of the local oscillator. ) and the pushing figure or oscillation output of the local oscillator coupled to the local bandpass filter and mixer via the transmission line are of the same magnitude. By adjusting the electrical length of the pipe line, coaxial line, microstrip line, etc., the oscillation operation when the local oscillator is coupled to the local oscillator bandpass filter or mixer can match the load of the local oscillator. The oscillation operation can be performed in the same way as when it is loaded. Therefore, it is possible to prevent the load impedance of the local oscillator from greatly deviating from the matched load, which would cause the load to become too heavy and exhibit abnormal operation such as mode jump or oscillation stop, and furthermore, the frequency temperature characteristics can be prevented. The feature is that the temperature characteristics are the same as those under matched loads.

An embodiment of the present invention will be described below in terms of a method of coupling a Gunn oscillator and a local bandpass filter when a frequency-stabilized Gunn oscillator is used as a local oscillator of a frequency conversion device. In FIG. 3, the output of the Gunn oscillator 5 is injected into a local bandpass filter 7 through a transmission line 6 having an electrical length θ. Then, after passing through the local band pass filter 7, the signal is guided to a mixer 8. Here, the electrical length θ of the transmission line 6 is set so that the pushing figure when the load of the Gunn oscillator 5 is a matched load is the same as the pushing figure of the Gunn oscillator 5 with the configuration shown in FIG. However, the setting method will be explained using FIGS. 4 and 5.

In Figure 4, a matched load is connected to the Gunn oscillator 5, a capacitive stub, for example, is inserted between the Gunn oscillator and the matched load, and the VSWR of the load impedance of the Gunn oscillator 5 is adjusted by changing the size of the capacitive stub. By changing the distance between the Gunn oscillator 5 and the capacitive stub, the phase of the load impedance of the Gunn oscillator 5 is changed, and thus by changing the load impedance of the Gunn oscillator 5, the oscillation output supplied to the matched load is changed. , this oscillation output Pout is shown on the horizontal axis and the pushing figure is shown on the vertical axis,
Point A is the oscillation output P ₀ and pushing when using a matched load.
This is the position that shows the relationship between the figures. As shown in FIG. 4, the load impedance of Gunn oscillator 5 is
Even if the VSWR and phase change, the oscillation output Pout of Gunn oscillator 5 and the size of the pushing figure are on a one-to-one curve, and the load impedance is
As the oscillation output Pout is increased by changing the phase with the VSWR, the value of the pushing figure increases.

In Fig. 5, the reference plane of the Gunn oscillator 5 is set at the position T2 as shown in Fig. ₃ , and the phase is changed from the VSWR of the load impedance of the Gunn oscillator 5 seen from the reference plane _T2 , so that the Gunn oscillator 5 has an equal output. FIG. 2 is a Rieke diagram showing lines (solid lines) and isofrequency lines (dashed lines) plotted on a Smith chart.

For example, if the impedance seen from one end _T3 of the transmission line 6 to the local bandpass filter 7 side is at point Z in Fig. 5, then the load impedance at point Z is
VSWR will be 2.0. Therefore, by selecting the electrical length θ of the transmission line 6 that corresponds to rotating point Z to point B or point Z to point C around point O,
Point B or point C where the impedance seen from the reference plane T2 of the Gunn oscillator ₅ to the local bandpass filter 7 is the same as the VSWR of the load impedance at point Z.
You can also go there. Since points B and C are both on the equal output line, which is equal to the oscillation output P ₀ under matched load, the pushing figures at points B and C are both on the same output line, which is equal to the oscillation output P 0 under matched load. It's equivalent to figurine.

It has been confirmed that abnormal operations such as mode jump and oscillation stop of Gunn oscillator 5 are more likely to occur as the oscillation output becomes larger, and the operation at points B and C which shows the same oscillation output as the oscillation output under matched load. In this state, the Gunn oscillator 5 does not cause abnormal operations such as mode jump or oscillation stop, as in the case of a matched load.

FIG. 6 is for explaining another effect of the present invention, and shows the relationship between the pushing figure of the gun oscillator 5 and the amount of temperature change in the oscillation frequency. Point D
is the case where the load of Gunn oscillator 5 is a matched load.
This figure 6 shows that even if the load impedance of the Gunn oscillator 5 is different, as long as the pushing figure has the same size, the amount of temperature change in the oscillation frequency of the Gunn oscillator 5 is the same. It shows. This means that there is a one-to-one relationship between the temperature characteristics of the pushing figure and the oscillation frequency.

Furthermore, by examining the pushing figure of the Gunn oscillator 5 from Figures 4 and 6, the temperature characteristics of the oscillation output and oscillation frequency supplied to the load can be predicted, and the temperature characteristics of the oscillation output and oscillation frequency can be predicted as a pair. It can be said that they are in the same relationship.

Therefore, both when the load of Gunn oscillator 5 is a matched load and when the loads corresponding to points B and C are on the equal output line shown in FIG. 5, pushing All the figures have the same size, and from the relationship shown in FIG. 6, the amount of temperature change in the oscillation frequency also has the same size. In this way, even if the impedance viewed from the reference plane _T2 of the Gunn oscillator 5 to the local bandpass filter 7 is at point Z, which is out of the matching state, the difference between the Gunn oscillator 5 and the local bandpass filter By providing a transmission line between them and selecting the electrical length of the transmission line so that the load impedance of the Gunn oscillator 5 changes from point Z to point B or point C, the pushing figure, oscillation output, and oscillation of the Gunn oscillator 5 can be controlled. Characteristics such as frequency temperature characteristics can be set in the same way as the characteristics when using a matched load.

FIG. 7 shows another embodiment of the present invention, and the same parts as in FIG. 3 are given the same numbers and will be described. The output of the Gunn oscillator 5 is injected into the local band pass filter 7 through a transmission line 9 of variable electrical length such as a phase shifter. Then, after passing through the local band pass filter 7, the signal is guided to a mixer 8.

In the above embodiment, the Gunn oscillator is used as the local oscillator, but any local oscillator whose oscillation conditions such as oscillation output, oscillation frequency, frequency temperature characteristics, etc. are affected by the load circuit can be used as the Gunn oscillator. Not limited to oscillators,
A GaAs FET oscillator, impact oscillator, etc. may also be used.

As explained above, according to the present invention, in a frequency conversion device in which the impedance seen from one end of a transmission line coupling a mixer and a local oscillator to the mixer side is mismatched at the frequency of the local oscillator, When coupling the local oscillator bandpass filter and mixer via a transmission line, the pushing figure when the load of the local oscillator section is a matched load and the local oscillator bandpass filter and mixer coupled via the transmission line. By setting the electrical length of the transmission line so that the pushing figure of the local oscillator is the same size as the pushing figure of the local oscillator, it is possible to prevent the local oscillator from exhibiting abnormal operation such as mode jump or oscillation stop. Furthermore, it also has the effect of making the frequency temperature characteristics the same as the temperature characteristics under matched load. In addition, an isolator for preventing abnormal operation of the local oscillator, which is required in conventional frequency converters, is no longer necessary, and the entire device can be made smaller, lighter, and lower in cost. Further, by increasing the coupling between the local oscillator and the load circuit, the oscillation efficiency can be increased, so that the power consumption of the local oscillator can be reduced.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional frequency converter, and Figure 2 is the input terminal of a local bandpass filter.
₃ is a block diagram showing an embodiment of the present invention. FIG. 4 is a characteristic diagram showing the relationship between the oscillation output of the local oscillator and the pushing figure. Figure 5 is a Rieke diagram showing the load characteristics of a local oscillator, Figure 6 is a characteristic diagram showing the relationship between the pushing figure of a frequency stabilized local oscillator and the amount of temperature change in oscillation frequency, and Figure 7 is a diagram showing the relationship between the pushing figure of a frequency stabilized local oscillator and the amount of temperature change in the oscillation frequency. FIG. 3 is a block diagram showing another embodiment. 1... Local oscillator, 6, 9... Transmission line, 7...
...Local bandpass filter, 8...Mixer.

Claims (1)

[Claims] 1. A frequency conversion device in which the impedance viewed from one end of a transmission line coupling a mixer and a local oscillator to the mixer side is mismatched at the frequency of the local oscillator, and the electrical length of the transmission line is set to The magnitude of the frequency change of the local oscillator with respect to the bias voltage change or bias current change of the local oscillator when the load is a matched load that is equal to the characteristic impedance of the transmission line, and 1. A frequency conversion device, characterized in that the magnitude of a change in frequency of the local oscillator is set to be the same with respect to a change in bias voltage or a change in bias current of the local oscillator when the local oscillator is coupled with the mixer.