JPH0319505A - Surface acoustic wave oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain an oscillation output having a phase difference of 90 deg. stably and accurately by forming two sets of output transducers at a position receiving a surface acoustic wave excited by an oscillation transducer and differentiating the distance from the oscillation transducer. CONSTITUTION:A surface acoustic wave element consists of a surface acoustic wave delay line having oscillation transducers 45, 46, an amplifier 2, and a phase shifter 43. Then 1st and 2nd output transducers 47, 48 are formed to the outside in the surface acoustic wave propagation direction of the oscillation transducer 46. The output transducers 47, 48 are made up of interdigital electrodes and the surface acoustic wave propagation direction distances l1, l2 from the 2nd oscillation transducer 46 of both the output transducers 47, 48 are differentiated. Since output signals having a phase difference of 90 deg. are obtained by the electrode structure of the surface acoustic wave device, the variance in the output level is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an improvement in a surface acoustic wave oscillation circuit using a surface acoustic wave delay line or a surface acoustic wave resonator, and in particular, relates to an improvement in a surface acoustic wave oscillation circuit using a surface acoustic wave delay line or a surface acoustic wave resonator. 6. Related to a surface acoustic wave oscillator circuit used in a modulation/demodulation circuit using two carrier signals [Prior Art] In recent years, wireless communication devices such as pagers and cordless telephones have become widespread. These wireless communication devices generally use angle modulation such as FM or PM as a modulation method. Conventionally, superheterodyne type receiver circuits have been widely used as angle modulation type receiving circuits. Although the superheteron system achieves good reception characteristics, it uses an intermediate frequency stage, so (a) it requires an expensive frequency selection element such as a crystal filter, and (b) it requires an intermediate frequency stage. Since it is not possible to implement LSI up to the frequency stage, it has been difficult to reduce the size, power consumption, and cost of the device.

In response to this, a modulation/demodulation method called a direct conversion method has been proposed in recent years.

The configuration of a receiver using an example of this circuit will be explained with reference to FIG. The high frequency signal received by antenna l is transmitted to high frequency amplifier 2.
and is filtered by a high frequency band filter 3.
The filtered high frequency signals are applied to mixers 4 and 5, respectively. On the other hand, a carrier signal generated by a carrier wave oscillator 6 and filtered by a bandpass filter 7 is applied to one mixer 5 via a bathophore amplifier 8. The output of buffer amplifier 8 is also given to 90° phase shifter 9. The second carrier signal whose phase is shifted by 90° by the 90° phase shifter 9 is applied to the other mixer 4 via the bumper amplifier IO. The received signals immediately dropped to the Haasband by mixers 4 and 5 are applied to low-pass filters 11 and 12, respectively.
, 14, the differentiating circuit 1516 and the mixing R17.18 are ti
The outputs of mixers 17 and 18 are connected to differential amplifier l.
9 to obtain a demodulated output.

In the above structure, since the intermediate frequency filter used in the superheterodyne method is not required, the circuit section after the part shown by the broken line A, that is, the circuit section after the baseband section, should be configured with a single LSI chip. I can do it.

In the case of the above direct conversion method, the carrier wave oscillation circuit is required to generate an accurate and highly stable frequency carrier wave signal. Therefore, specifically, a carrier wave oscillation circuit shown in FIG. 3 or FIG. 4 is used.

However, in the outgoing wave oscillation circuit shown in Figure 3, the crystal oscillator 2
The oscillation signal of the oscillation circuit 21 having 0 is multiplied by the multiplier circuit 22, and a specific harmonic is extracted by the tank circuit 23. In addition, 24.25 is the buffer amplifier,
26 is 90'! 27 and 28 indicate variable resistors for level adjustment.

On the other hand, in the configuration shown in FIG. 4, a voltage controlled oscillator 31 made of an LC circuit is used.
, low-pass filter 32, phase comparator 33, and divider 34. A loop is configured. 3
5 indicates TCXO, 36 indicates 90° phase shifter, 37.38
is level AI! Adjustable variable resistors, 39 and 40 are buffers.
Shows the amplifier.

[Technical problem to be solved by the invention] In the carrier wave oscillation circuit shown in FIG.
Another problem is that it requires a complicated circuit configuration such as a multiplier circuit 22 and a tank circuit 23, making the carrier wave oscillation circuit large-scale. In addition, in the carrier wave oscillator using the voltage controlled oscillator 31 shown in FIG. 4, the frequency accuracy is improved by PLL, but the SSB phase noise characteristics are not so good, so in FM etc., the S/N ratio of the demodulated signal is The problem is that it gets worse. Furthermore, in the direct comparison run method, it is important to balance the level between signals with a 90° phase difference, and it is necessary to compensate for loss using a 90° phase shifter and adjust the level. A large number of circuit components such as variable resistors 27, 28, 37, and 38 for level adjustment are required.

Therefore, an object of the present invention is to achieve 90% by using a relatively simple circuit structure.
The object of the present invention is to provide an oscillation circuit that can stably and accurately obtain an oscillation output having a phase difference of . C) Means for Solving Technical Problems) The present invention is an improved surface acoustic wave oscillation circuit in which a surface acoustic wave oscillation element is inserted in the feedback system of an amplifying means. That is, a surface acoustic wave oscillation element in which an oscillation transducer made of comb-like electrodes interposed with each other is formed on a piezoelectric substrate is inserted into a feedback system of an amplification means having a gain exceeding the insertion loss of the surface acoustic wave oscillation element. In the surface acoustic wave oscillation circuit formed by
At least 2! The output transducer of J1 is formed at a position that receives the surface wave excited by the oscillation transducer, and the distances from the oscillation transducer of the at least two sets of output transducers are made different, so that the 90 It is characterized by being configured to obtain an output signal with a phase difference of °. The above-mentioned surface acoustic wave oscillator includes a surface acoustic wave delay line,
Alternatively, one using a surface acoustic wave resonator can be used. C effect] Since the oscillation circuit is constructed using a surface acoustic wave oscillation element with a high equivalent Q, the fundamental wave can be directly oscillated, and the SSB phase noise of the oscillation signal can be reduced. In addition, the output signal taken out from the output transducer is taken out via a surface acoustic wave filter composed of an oscillation transducer and an output transducer. Therefore, it is possible to reduce spurious waves such as harmonics. Furthermore, since an output signal having a 90" phase difference is obtained by the electrode structure of the surface acoustic wave device, variations in the output level are also reduced. (Explanation of Embodiment) FIG. 1 shows an embodiment of the present invention. A schematic horizontal diagram is shown. 1st
Referring to the figure, a surface acoustic wave delay line 4l is inserted into the feedback system of the amplifier 42. 43 indicates a phase shifter. The surface acoustic wave delay line 4l has a structure in which first and second oscillation transducers 45 and 46 are arranged on a piezoelectric substrate 44 at a predetermined distance apart. Each of the oscillating transducers 45 and 46 is composed of comb-shaped electrodes that are interposed with each other. They are also being exploited to have high profits. Therefore, the surface acoustic wave delay line having the oscillation transducers 45 and 46, the amplifier 42, and the phase shifter 43 constitute a surface acoustic wave oscillation element. Up to this point, there is no difference from known surface acoustic wave oscillators. The feature of this embodiment is that the second oscillation transducer 46
The first and second output transducers 47 and 48 are formed outside in the surface wave propagation direction. Each of the output transducers 47 and 48 is also composed of interdigitated interdigitated electrodes, provided that the distance Me,,it in the surface wave propagation direction from the second oscillation transducer 46 to both output transducers 47 and 48 is It has been different.

That is, the difference between 7!1 and At is (1/4) when the wavelength of the excited surface acoustic wave is λ! the output transducer 47.4
A phase difference of 90° is provided between the output signals taken from 8.

A phase difference of 90° is a distance Hi! +. Since it is given by the difference between p-t, the output transducer 47.
If the structures of the output transducers 47 and 48 are kept the same, there will be almost no difference in level between the output signals taken out from the output transducers 47 and 48.

Note that the distance Ml+. The difference in lt does not necessarily have to be ■/4)λ; if it is (n±l/4)λ, it is also 9
A phase difference of 0° can be obtained. Furthermore, if there is a difference in the load applied to the output transducer 47 on the 4th day, and the phase difference deviates slightly from 90 degrees, the l. ,12. may be corrected by {m.

Similarly, if there is a difference in the output signal levels of both output transducers 47 and 48 due to differences in load conditions, etc.
Correction may be made by varying the electrode crossing width and logarithm of each output transducer 47, 48. In short, in practical conditions, as long as the output signal levels of the output transducers 47 and 48 are approximately the same and the phase difference between the two output signals is 90°, the electrode structure and distance of each output transducer 47 and 48 and the distance 1+, f2x
etc. can be changed as appropriate. In the embodiment shown in FIG. 1, a surface acoustic wave delay device is constituted by the first and second oscillation transducers 45 and 46.
It operates as an oscillation circuit, and the output of the oscillation circuit is outputted via a surface acoustic wave filter composed of a second oscillation transducer 46 and output transducers 47 and 48. Therefore, output signals in which spurious waves such as harmonics are suppressed can be extracted from the output transducers 47 and 48. Therefore, it can be seen that one surface acoustic wave element has three i-functions: an oscillation element, a bandpass filter, and a phase shifter. Of the oscillation transducers, in order to effectively utilize the energy of the surface waves excited by the excitation side transducer 46, the output transducers 47 and 48 are connected to the transducer 4 with the excitation transducer 46 in between.
It is desirable to place it on the opposite side from 5. In the embodiment shown in FIG.
An output transducer 49 is formed. Although this third output transducer 49 is not necessarily an essential component of the present invention, the third output transducer 49
By forming 9, a monitor output signal can be taken out, and it is possible to use the monitor output signal as il for, for example, an I) L L operation.

FIG. 5 is a diagram showing a schematic configuration of a second embodiment of the present invention. Here, two second oscillation transducers 46a46b are formed on the piezoelectric substrate 44 at symmetrical positions with the first oscillation transducer 45 in between. 2
The second oscillation transducers 46a and 46b are
They may be arranged obliquely symmetrically with the first oscillation transducer 45 in between. Further, the second oscillation transducer 46a. The distance of 46b from the first oscillation transducer 45 is 1/2
It may be shifted by an integral multiple of the wavelength.

In this embodiment, in a delay device constituting a surface acoustic wave oscillator, second oscillation transducers 46a. 46b, bidirectional loss is reduced. Therefore, since the loss of insertion of the surface acoustic wave delay device is reduced, it is said that oscillation is easier. Other structures are similar to the embodiment shown in FIG.
Corresponding parts will be given corresponding reference numbers and their explanation will be omitted.

In the embodiment shown in Fig. 1, when the loss of the surface acoustic wave delay device is reduced, multiple reflections between the electrodes in the oscillation transducer 45 and 46 become large, the phase characteristics of the delay line are distorted, and the oscillation frequency becomes unstable. There is a risk that On the other hand, in the embodiment shown in FIG. 5, multiple reflections between electrodes are reduced by impedance matching with the first oscillation transducer 45, so that a low cost reduction can be achieved. In the embodiment shown in FIG. 5, three oscillation transducers are formed, but five or seven or more oscillation transducers may be provided.

FIG. 6 is a schematic diagram of a third embodiment of the present invention.
Here, on the piezoelectric substrate 44, similar to the embodiment in FIG.
A first oscillation transducer 45 and two second oscillation transducers 46a and 46b are formed to constitute a surface acoustic wave delay line. The difference from the embodiment in FIG. 5 is that the output transducers 47 and 48 are replaced by the second oscillation transducer 46a.
, 46b are formed at a predetermined distance from each other. That is, the output transducer 4
7.48 is the first and second oscillation transducer 45.
They are placed on opposite sides with 46a and 46b in between. Therefore, loss due to bidirectionality is reduced. In addition,
The 90" phase difference provided between the output signals taken from the output transducers 47 and 48 is equal to the distance 1+ shown.
．． It is formed by making lt different by (n±1/4)λ. In addition, in the first to third embodiments, by providing a reflector on the outside of the output transducer in the surface wave propagation direction, leakage of surface acoustic waves is reduced, thereby further reducing loss. is also possible. It should also be pointed out that in the first to third embodiments, sound absorbing materials, vano cages, etc. are omitted for illustration purposes. Furthermore, characteristics improvement techniques used in ordinary surface acoustic wave devices may be used as appropriate, such as forming a shield electrode, weighting the comb-like electrodes of the transducer, and adopting split electrodes. FIG. 7 is a schematic diagram of the fourth embodiment of the present invention. At the center of the pressure 11g plate 44, a transducer 51 is formed which is made up of interdigitated electrodes pressed together. In this embodiment, this transducer 5
An oscillation circuit is constructed using the impedance characteristics of No. 1, that is, using a surface acoustic wave resonator. A Kolbitz type oscillation circuit 52 is connected between one comb-shaped electrode and the other comb-shaped electrode of the transducer 5l, and the oscillation circuit 41 is connected thereto. It goes without saying that such an oscillation circuit can also be regarded as an oscillation circuit in which a surface acoustic wave element is inserted in the feedback system of an amplifier circuit.

On the other hand, output transducers 47 and 48 are located on both sides of the transducer 51 in the surface wave propagation direction at a distance l. ,12
They are formed separately from each other. On the outside of the output transducers 47 and 48 in the surface wave propagation direction, there are
Grating reflections H53 and 54 are formed.

In this embodiment, the output transducers 47 and 48 are:
It is configured to be inserted into a surface acoustic wave resonator, and is therefore used to detect standing waves of the resonator.

By shifting the positional relationship between the output transducers 47 and 48 and the standing wave, that is, the distance l? , l2, the output transducer 41.48
A 90° phase difference is provided between the output signals taken from the .

The method of varying the distance 1 ml lg is the same as in the first embodiment, but more preferably, the output transducers 47 and 48 are set at an angle of ±45° (1/8
wavelength) is preferred. This is because if it deviates by 0° or 90'' with respect to the standing wave, the output level will fluctuate greatly. Note that if the reflectors 53 and 54 have little effect, the standing wave will Since this does not occur, the difference in the distances @l,,!!■ only needs to be a relative shift of 90 degrees.Also, the output transducers 47 and 48 are connected to the grating reflectors 53 and 54.
It may also be configured in such a way that it can be embedded inside. Further, the output transducers 47 and 48 may be arranged in parallel in a direction orthogonal to the surface wave propagation direction, as in the first embodiment, in a manner that bisects the surface wave propagation path.

〔Effect of the invention〕

As described above, in the present invention, the oscillation circuit is equivalently configured using a high-Q surface acoustic wave delay line or surface acoustic wave resonator. Therefore, the fundamental wave can be directly oscillated,
Moreover, the SSB phase noise of the oscillation signal can be effectively reduced.

Additionally, since the output signal is extracted from the surface acoustic wave resonator or surface acoustic wave delay line through the surface acoustic wave filter and the output transducer, it is also possible to reduce spurious waves such as harmonics. Furthermore, since output signals having a phase difference of 90° are obtained based on the difference in distance between the output transducer and the oscillation transducer, the phase difference between the output signals and the output reherence are determined by the electrode structure. Therefore, there is little variation in phase difference and output level, making it possible to eliminate adjustment. Therefore, according to the present invention, the three functions of the oscillation element, the bandpass filter, and the multiphase filter can be integrated into one chip, so that it is possible to achieve miniaturization, weight reduction, and cost reduction.

The surface acoustic wave oscillation circuit of the present invention is applicable not only to direct conversion type modulation/demodulation circuits, but also to various types of oscillation circuits that generate a 90° phase difference output, such as 4-layer PSK modulation/demodulation circuits and SSB modulation circuits. It should be pointed out that the present invention can be applied to modulation/demodulation circuits.

[Brief explanation of drawings]

No.! The figure is a schematic diagram of a surface acoustic wave oscillator circuit according to the first embodiment of the present invention, FIG. 2 is a circuit diagram for explaining a demodulation circuit of a direct conversion receiver, and FIGS. The figures are circuit diagrams for explaining a conventional carrier wave oscillation circuit, FIG. 5 is a schematic configuration diagram of a surface acoustic wave oscillation circuit according to a second embodiment of the present invention, and FIG. 6 is a schematic diagram of a surface acoustic wave oscillation circuit according to a second embodiment of the present invention. FIG. 7 is a schematic diagram of a surface acoustic wave oscillation circuit according to a fourth embodiment of the present invention. In the figure, 41 is a surface acoustic wave delay line, 42 is an amplifier,
44 is a piezoelectric substrate, 45 is a first oscillation transducer, 46 is a second oscillation transducer, and 47.48 is an output transducer. 26=

Claims (6)

[Claims] (1) A surface acoustic wave oscillation element having a piezoelectric substrate and an oscillation transducer formed on the piezoelectric substrate and consisting of comb-like electrodes interposed with each other, and an insertion loss of the surface acoustic wave oscillation element. In the surface acoustic wave oscillation circuit, the surface acoustic wave oscillation circuit is provided with an amplification means having a gain exceeding At least two comb-shaped electrodes inserted into each other
The sets of output transducers are formed at positions where they can receive the surface waves excited by the oscillation transducers, and the at least two sets of output transducers have different distances in the surface wave propagation direction from the oscillation transducers. A surface acoustic wave oscillator circuit configured to obtain a phase difference of 90° between output signals taken out from at least two sets of output transducers. (2) The surface acoustic wave oscillator is arranged on a piezoelectric substrate with a first
2. The surface acoustic wave oscillation circuit according to claim 1, comprising a surface acoustic wave delay line formed by forming the second oscillation transducer at a predetermined distance. (3) The elasticity according to claim 2, wherein at least two sets of the first oscillation transducers are arranged symmetrically or diagonally symmetrically with at least one set of the second oscillation transducers sandwiched therebetween. Surface wave oscillation circuit. (4) At least two sets of the output transducers are arranged symmetrically with the first or second oscillation transducer in between, and the distance from the first or second oscillation transducer in the surface wave propagation direction. 3. The surface acoustic wave oscillator circuit according to claim 2, wherein a phase difference of 90° is provided between the output signals by the difference in . (5) The two sets of output transducers are arranged in parallel in a direction perpendicular to the surface wave propagation direction, and the surface wave propagation direction from the first or second oscillation transducer of the two sets of output transducers is 3. The surface acoustic wave oscillator circuit according to claim 2, wherein the phase difference between the output signals is 90 degrees due to the distance difference. (6) The surface acoustic wave oscillation circuit according to claim 1, wherein the oscillation transducer of the surface acoustic wave oscillation element is constituted by a surface acoustic wave resonator consisting of a pair of interdigitated electrodes.