JPH0296405A - Surface acoustic wave oscillator - Google Patents

Abstract

PURPOSE:To improve the temperature compensation characteristic by forming a film resistance in which the resistance value is changed by temperature, on a piezoelectric substrate and using it as the temperature taking element to constitute a temperature compensating circuit. CONSTITUTION:A frequency control circuit 14 is connected to an oscillating circuit 11 including a surface acoustic wave resonator 13, further, a temperature compensating circuit 16 including temperature taking elements 17 and 18 is connected to the circuit 14 and the temperature compensation of the circuit 11 is executed. The resonator 13 respectively forms film resistances 27 and 28 in which the resistance value is changed by the temperature on a piezoelectric substrate 131. Such film resistances 27 and 28 are respectively used as the elements 17 and 18 to constitute the circuit 16. By the constitution, since the resonator 13 and the elements 17 and 18 are unified on the same substrate 131, the temperature difference between both is hardly eliminated and the temperature compensation characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface acoustic wave oscillator using a surface acoustic wave device and having a temperature compensation circuit for the oscillation frequency.

[Conventional technology]

A conventional example of this type of surface acoustic wave oscillator is shown in FIG.

That is, a frequency control circuit 4 including a variable capacitance diode 5 is connected to an oscillation circuit 1 including an oscillation transistor 2 and a surface acoustic wave resonator 3 which is one of the surface acoustic wave devices, and further, to this frequency control circuit 4, In this example, a temperature compensation circuit 6 including a thermistor 7.8 with negative characteristics is connected as a temperature measuring element.

Since the thermistor 7.8 detects the ambient temperature and indicates a resistance value according to the temperature, the temperature compensation circuit 6 outputs a tuning voltage Vt as a function of temperature, and the capacitance of the variable capacitance diode 15 changes accordingly. As a result, the oscillation frequency of the oscillation circuit 1 is controlled according to the temperature.

The frequency-temperature characteristic of this oscillation circuit 1 alone is, for example, as shown by the solid line in FIG. The oscillation frequency can be temperature compensated. Such a characteristic of the tuning voltage Vt can be realized using at least two thermistors 7.8 as in this example.

[Problem to be solved by the invention]

However, in the conventional surface acoustic wave oscillator as mentioned above,
Since the surface acoustic wave resonator 3 and the thermistor 7.8 are independent components, a temperature difference inevitably occurs between them, which causes a problem in that the temperature compensation characteristics deteriorate.

Furthermore, for the same reason as above, there is a problem that the number of parts is large and each takes up space, which hinders the reduction in size and weight of the surface acoustic wave oscillator.

Such problems similarly exist in other types of surface acoustic wave oscillators using other types of surface acoustic wave devices.

Therefore, the main object of the present invention is to provide a surface acoustic wave oscillator that solves the above-mentioned problems.

(Means for Solving the Problems) In the surface acoustic wave oscillator of the present invention, a film resistor whose resistance value changes depending on temperature is formed on a piezoelectric substrate constituting a surface acoustic wave device, and this is used to construct a temperature compensation circuit. It is characterized by being used as a temperature measuring element.

[Effect]

According to the above configuration, since the surface acoustic wave device and the temperature sensing element of the temperature compensation circuit are integrated on the same substrate, the temperature difference between them is almost eliminated, and therefore the temperature compensation characteristics are improved. Moreover, for the same reasons as above, the number of parts and space can be reduced, so the surface acoustic wave oscillator can be made smaller, lighter, and less expensive.

〔Example〕

FIG. 1 is a circuit diagram showing a surface acoustic wave oscillator according to an embodiment of the present invention.

The surface acoustic wave oscillator of this embodiment is basically of the surface acoustic wave resonator type similar to the one shown in FIG. Oscillation circuit 11 including surface acoustic wave resonator 13
, a frequency control circuit 14 including a variable capacitance diode 15
, further connect the frequency control circuit 14 with the temperature compensation circuit 16 including the two temperature detection elements 17 and the temperature compensation circuit 16, and then, for example, adjust the tuning voltage V [
The oscillator circuit 11 is configured to output a temperature of 100 Ω, thereby compensating the temperature of the oscillation circuit 11.

However, as shown in FIG. 2, for example, the surface acoustic wave resonator 13 in this embodiment has an interdigital transducer (hereinafter abbreviated as IDT) 132 in the center on a piezoelectric substrate 131, and a grid-shaped reflection transducer on the left and right sides. vessels 133 and 1
34, and further the same piezoelectric substrate 1
31, and in this example, the surface acoustic wave resonator 13
In order to prevent the Q from decreasing, two film resistors 27 and 28 whose resistance value changes depending on the temperature are formed at right angles outside the surface acoustic wave waveguide.

As this film resistance 27.2 days, for example, platinum (pt)
Alternatively, a thin or thick film of nickel (Ni 2 ) may be used, whereby a negative temperature coefficient can be obtained like a thermistor.

Such film resistors 27 and 2 are used as temperature measuring elements 17 and 18, respectively, constituting the temperature compensation circuit 16 in FIG.

According to the above configuration, the surface acoustic wave resonator 13 and the temperature measuring elements 17 and 18 of the temperature compensation circuit 16 are based on the same base Fi131.
Since they are integrated, so to speak, unlike the conventional case where a thermistor or the like, which is an independent component, is used as the temperature measuring element, there is almost no temperature difference between the two, and therefore the temperature compensation characteristics are improved.

That is, it is possible to obtain a surface acoustic wave oscillator whose oscillation frequency is stable over a wide temperature range.

Moreover, for the same reasons as above, the number of parts and space can be reduced, so the surface acoustic wave oscillator can be made smaller, lighter, and less expensive.

Furthermore, according to the membrane resistors 27 and 28 mentioned above, the resistance value can be set variously depending on the total length of the path, so unlike the conventional example in which an existing element such as a thermistor is used as a temperature measuring element. , the degree of freedom in circuit design increases, and the series and parallel fixed resistances (
(see R in FIG. 1) can be omitted, thereby further simplifying the circuit configuration.

FIG. 3 is a block diagram showing a surface acoustic wave oscillator according to another embodiment of the invention.

This surface acoustic wave oscillator is an example of a delay line type, and includes a surface acoustic wave filter (which can also be seen as a delay line) 33 and a phase shifter 34 including a variable capacitance diode between the input and output sections of an amplifier 31. The phase shifter 34 is inserted to form an oscillation loop, and the above-mentioned tuning voltage Vt is supplied from the temperature compensation circuit 36 to the phase shifter 34 to perform temperature compensation of the oscillation frequency. 32 is an output directional coupler.

Moreover, this surface acoustic wave filter 33 has two IDTs on the left and right sides of the piezoelectric substrate 331, for example, as shown in FIG.
332 and 333, and a shield electrode 334 is formed therebetween to prevent direct connection between the two, and furthermore, in this example, on the same piezoelectric substrate 331, at right angles to the outside of the surface acoustic wave waveguide, Two film resistors 37 and 38 whose resistance value changes depending on the temperature similar to the film resistors 27 and 28 are formed.

Such membrane resistors 37 and 38 are used as temperature measuring elements constituting the temperature compensation circuit 36 in FIG.

Therefore, in this embodiment as well, the same effects as in the previous embodiment can be obtained.

Moreover, a two-port surface acoustic wave resonator can be used instead of the surface acoustic wave filter 33, and in that case, a membrane resistor may be formed on the piezoelectric substrate in the same manner as in the above example.

Note that the circuit configuration of the temperature compensation circuit 16 or 36 and the number of temperature sensing elements thereof are not necessarily limited to those shown in the example above, and various configurations may be adopted depending on the desired characteristics. obtain.

Further, the circuit configuration of the surface acoustic wave oscillator is not necessarily limited to the above example.

Further, it is not necessarily necessary to form the same number of film resistors as the temperature sensing elements of the temperature compensation circuit on the piezoelectric substrate of the surface acoustic wave device such as the surface acoustic wave resonator 13 or the surface acoustic wave filter 33 as described above. A film resistor as described above may be used as a part of the required temperature measuring element.

Furthermore, depending on the circuit configuration of the temperature compensation circuit, multiple film resistors may be wired to each other in advance on the piezoelectric substrate of the surface acoustic wave device, and in this way, external wiring can be simplified. .

〔Effect of the invention〕

As described above, according to the present invention, since the surface acoustic wave device and the temperature sensing element of the temperature compensation circuit are integrated on the same substrate, the temperature difference between them is almost eliminated, and therefore the temperature compensation characteristics are improved. do.

Moreover, for the same reasons as above, the number of parts and space can be reduced, so the surface acoustic wave oscillator can be made smaller, lighter, and less expensive.

Furthermore, since the resistance value of the membrane resistor can be set variously depending on the total length of the path, the degree of freedom in circuit design increases and it is possible to select the series and parallel fixed resistances necessary to obtain the desired characteristics. It is also possible to omit it.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a surface acoustic wave oscillator according to an embodiment of the present invention. FIG. 2 is a plan view showing an example of the surface acoustic wave resonator shown in FIG. 1. FIG. FIG. 3 is a block diagram showing a surface acoustic wave oscillator according to another embodiment of the invention. FIG. 4 is a plan view showing an example of the surface acoustic wave filter shown in FIG. 3. FIG. 5 is a block diagram showing an example of a conventional surface acoustic wave oscillator. FIG. 6 is a diagram showing an example of frequency-temperature characteristics of a single oscillation circuit. 13...Surface acoustic wave resonator, 16...Temperature compensation circuit, 17.18...Temperature measuring element, 27.28...Membrane resistance, 33...Surface acoustic wave filter, 36...Temperature Compensation circuit, 37.38... membrane resistance.

Claims (1)

[Claims] (1) In a surface acoustic wave oscillator using a surface acoustic wave device and having a temperature compensation circuit for the oscillation frequency, a film resistor whose resistance value changes depending on temperature is provided on the piezoelectric substrate constituting the surface acoustic wave device. 1. A surface acoustic wave oscillator, characterized in that the surface acoustic wave oscillator is formed with a temperature sensor and is used as a temperature measuring element constituting the temperature compensation circuit.