JPS5827405A - Delay feedback type oscillator - Google Patents

Abstract

PURPOSE:To use a filter easy for its manufacture and to improve the noise characteristics, by passing through a signal to a narrow-band filtering means to suppress unnecessary oscillatin mode after converting the signal into a low frequency. CONSTITUTION:Denoting a main oscillation frequency passig through a series circuit consisting of a surface acoustic wave filter delay element 1 and an amplifier 4 as fA and an oscillation frequency of a local oscillator 7 as fB, when a difference frequency (fA-fB) is generated at the 1st frequency mixer 8, a band- pass filter 6 can use a comparatively low frequency, then a filter with stable characteristics such as quartz filter can be used. The 2nd frequency mixer 9 is mixed with (fA-fB) and fB to generate the fA again.

Description

[Detailed Description of the Invention] This relates to an oscillator, and the purpose is to improve noise characteristics.
As shown in the figure. In FIG. 1, reference numeral 1 denotes a surface acoustic wave delay element, which is constructed by placing piezoelectric transducers 2 and 3 on a piezoelectric substrate. 4 is an amplifier, and 6 is an output terminal.

Here, if the phase shift amount of the surface acoustic wave delay element 1 is φ1, and the phase shift amount of other circuit parts is φB, the oscillation phase condition of the oscillator in FIG. )・・・・・・・・・
...(1).

If the distance between the centers of piezoelectric transducers 2 and 3 is l, the sound speed of the surface acoustic wave is V, and the oscillation frequency is f, then・
・・・・・・・・・・・・・・・(21f1), +2
), the oscillation frequency f is fmia(2Nπ-φB)...
It is expressed as (3). The effective Q of the surface acoustic wave delay element is Q=-×πf・
・・・・・・・・・・・・・・・・・・・・・・・・
(4) ■ Since it is effective to increase the effective Q in order to improve the 07N of a delayed feedback oscillator, β is usually chosen to be sufficiently large. Therefore, since the value of N in equation (1) is sufficiently large at a value of about 100 to 1000, φB is sufficiently small compared to 2Nπ and can be ignored. Therefore, formula (3) is: NV f;−・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・(5) β As shown in Figure 2(a), there are many frequencies that can oscillate, and the interval between them is (V#). be.

FIG. 2 (bl shows the bandpass characteristic of the surface acoustic wave delay element 0) The bandpass characteristic of the surface acoustic wave delay element 1 is
It is determined by the logarithm of the elements of the piezoelectric transducer 2.3. In FIG. 2 (bl), adjacent oscillation frequencies are selected as attenuation poles, but the design is normally such that at least 10 dB of attenuation can be obtained at these adjacent oscillation frequencies.

By giving an amplitude difference in this way, Fig. 2tc)
As shown in the figure, there is only one frequency that can be oscillated.

A delayed feedback oscillator is suitable for use as a high C/H oscillator because the effective Q can be easily increased by increasing the delay time.

However, if the delay time is increased in order to increase the effective Q, l shown in Figure 1 becomes longer, and as is clear from equation (6), the frequency interval at which oscillation can be performed becomes narrower, so the band characteristics of the piezoelectric transducer become needs to be sufficiently narrow. 1st
In order to narrow the bandpass width of the comb-shaped piezoelectric transducer shown in the figure, it is necessary to increase the number of pairs of electrodes.
Particularly in the case of an oscillator that operates in an ultra-high frequency band, there is a drawback that the manufacturing yield of the comb-shaped electrodes of the piezoelectric transducer section is poor.

For this reason, there has been a drawback that the effective Q of an ultra-high frequency oscillator using a surface acoustic wave delay element cannot be high, and the C/N ratio is restricted.

The present invention provides a delayed feedback oscillator that eliminates these drawbacks and can also newly function as a wideband oscillator. By applying the present invention, a high C/H oscillator can be easily realized. .

FIG. 3 shows an embodiment of the present invention. In FIG. 3, 1 is a surface acoustic wave delay element, 4 is an amplifier, and 6 is an output terminal, which have the same reference numerals as in the conventional circuit shown in FIG. 1. It has the same function as the original. The configuration in FIG. 3 differs from the configuration in FIG. 1 in that the first and second frequency mixers 8 and 9
．． This is because the intermediate frequency band pass filter 6 and local oscillator 7 are added. Now, surface acoustic wave delay element 1. The main oscillation frequency that passes through the series circuit of amplifier 4 is set to fm1 local oscillator 7.
The oscillation frequency of is fB, and the first frequency mixer 8 (f
By generating the difference frequency of mu fB), a relatively low frequency bandpass filter 6 can be used.
Filters with stable characteristics in a narrow band such as crystal filters and ceramic filters can be used. The second frequency mixer 9 mixes (fm fB) and fm and returns f
cause a problem. At this time, fB changes and (fu+Δf
n) Even if the output frequency of the second frequency mixer 9 is
M・・・・・・・・・・・・・・・・・・・・・
......(6) and the variation of fn ΔfB
is irrelevant. Therefore, the frequency stability of the local oscillator 7 has no relation to the stability of the main oscillation frequency f.

A feature of the present invention is that, especially when using a delay element with a long delay time, the narrowband filter required to suppress unnecessary oscillation modes is converted to a relatively low frequency and then passed through. By doing so, the bandpass characteristic of the surface acoustic wave delay element 1 can be made broadband, the number of pairs of interdigitated electrodes of the piezoelectric transducer can be reduced, and the manufacturing yield can be improved. The required narrowband bandpass characteristics are provided by the second bandpass filter 6. Since this second filter is also inserted after frequency conversion, it can be used for a relatively low frequency band and is easy to manufacture. At this time, it is necessary to select the value of ft+ so that the image frequency in the frequency mixer section and the frequency that can be oscillated do not overlap.

FIG. 4 shows another embodiment in which an oscillator is configured to oscillate by selecting one of a plurality of possible oscillation frequencies, and the same functional parts as in FIG. 3 are indicated by the same symbols. The difference from FIG. 3 is that the local oscillator 1o is a voltage-controlled variable frequency oscillator, and a variable voltage source 11 is attached to change the oscillation frequency. As is clear from equation (6), since they are arranged at equal frequency intervals, they are suitable for application to communication devices with fixed channel intervals. Now, when the variable resistor VR of the variable voltage source 11 is turned, the voltage controlled variable frequency oscillator 10
The oscillation frequency of changes continuously. Therefore, if the center frequency of the narrowband bandpass filter is fC + the oscillation frequency of the voltage controlled variable frequency oscillator is fB, then (fn+fc) is the selected center frequency, and due to the narrowband bandpass characteristic, adjacent frequencies that can oscillate If there is a difference of about 10 dB in the amplitude characteristics between the two, oscillation will definitely occur at a frequency with a large amplitude.

Using the circuit of FIG. 4, a discontinuously variable frequency oscillator can be realized using a continuously variable frequency oscillator.

However, the difference is that a voltage variable phase shifter 12 is inserted before the signal delay element 1. The phase shifter 12 changes the oscillation phase condition to change the possible frequency of one oscillation, and at the same time, the frequency mixer 8.9. Narrowband filter 6, voltage variable oscillator 1
The oscillation frequency can be continuously varied by following the passing center frequency of the variable band filter section constituted by o.

FIG. 6 is a diagram showing the structure of an element in which a surface acoustic wave delay element and a surface acoustic wave resonator are integrated.

FIG. 7 is a diagram showing the configuration of a delayed feedback oscillator using the elements shown in FIG. 6, and the basic configuration is the same as that in FIG. 3.

In FIG. 7, the same circuit parts as in FIG. 3 are indicated by the same symbols. In FIG. 7, a surface acoustic wave resonator 27,
In combination with the amplifier 28, a circuit corresponding to the local oscillator 7 in FIG. 3 is constructed.

In FIG. 6, on the surface of the same piezoelectric substrate 290, there are formed a signal delay element consisting of piezoelectric transducers 19 and 20, a first resonator consisting of a piezoelectric transducer 21 and reflective electrodes arranged around it, and a piezoelectric transformer. A second resonator consisting of a deducer 22 and reflective electrodes arranged around it is arranged. The first resonator corresponds to 6 in FIG. 7, and the second resonator 6d corresponds to 27. .

Although the embodiments shown in FIGS. 6 and 7 show examples in which three sets of surface acoustic wave elements are combined, there may be cases where it is possible to construct them at a lower cost by dividing them for manufacturing reasons.

However, the resonant elements or signal delay elements used in the bandpass filter 6 and the local oscillator 1o in FIG. 3 do not necessarily have to be composed of surface acoustic wave elements.

As explained above, according to the present invention, the narrow-band P-wave generator means required when constructing a high-stability oscillator using a conventional delayed feedback oscillator can be replaced with a second frequency different from the main oscillation signal band. Since it is possible to create the second
By appropriately selecting the frequency band of , it is possible to use an inexpensive fill element that is easy to manufacture, and to achieve a high C/H.

In addition, by configuring the signal delay element and the oscillation element of the local oscillator on the same piezoelectric substrate, it has the advantage of being easy to manufacture, making it possible to realize an inexpensive and highly stable oscillator, and its industrial value is great. be.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram showing the configuration of a conventional delayed feedback oscillator.
2(al to (C)) are diagrams showing the principle of a delayed feedback oscillator, FIG. 3 is a block diagram showing the configuration of a delayed feedback oscillator in an embodiment of the present invention, and FIG. 6 is a block diagram showing the third embodiment of the present invention, FIG. 6 is a plan view showing an example of the surface acoustic wave element used in the present invention, and FIG. 7 is a block diagram showing the third embodiment of the present invention. It is a block diagram showing an example of a mounting configuration of the elements shown in Fig. 6. 4... Signal amplifier, 1... Signal delay element, 8... First frequency. Mixer, 9...
・Second frequency mixer, 6...Band pass filter, 7...Local oscillation Name of agent Patent attorney
Toshio Nakao and 1 other person ink 1 figure H-no- 12 figures

Claims (1)

[Scope of Claims] (1) a signal amplifier; and first frequency conversion means for converting the output of the signal amplifier to a frequency lower than the signal frequency;
a second frequency converting means for returning the output from the first frequency converting means to the original signal frequency after passing through the band mud wave means; and a delay means for delaying the output from the second frequency converting means. a feedback oscillation loop is formed by using the output of the delay means as an input of the signal amplifier, and the signal pass band of the band offshore means is configured to be narrower than the signal pass band of the signal delay means. Delayed feedback oscillator with special features. (2) First. 2. The delayed feedback oscillator according to claim 1, wherein the second frequency conversion means includes two sets of frequency mixers and one set of local oscillators. By changing the oscillation frequency of the local oscillator,
3. The delayed feedback oscillator according to claim 2, wherein the oscillation frequency of the delayed feedback oscillator is changed. (4) Using a surface acoustic wave signal delay element as the signal delay means, and using a surface acoustic wave band offshore wave element as the oscillation frequency selection element of the local oscillator, at least the signal delay element and the band mud wave element. 3. The delayed feedback oscillator according to claim 2, wherein the oscillator is formed on the same piezoelectric substrate. (5) A surface acoustic wave signal delay element is used as the signal delay means, and a surface acoustic wave band F-wave element is used as the band offshore circuit means inserted between the two sets of frequency mixers. 2. A delayed feedback oscillator according to claim 1, wherein said band F-wave element and said band F-wave element are formed on the same piezoelectric substrate.