JP6403438B2 - Surface acoustic wave oscillator - Google Patents

Description

  The present invention relates to an oscillator using a surface acoustic wave element, and more particularly to a configuration of a surface acoustic wave oscillator capable of temperature compensation.

Conventionally, surface acoustic wave (SAW) oscillators have been widely used in wireless communication devices such as mobile phones and wired communication devices, and the SAW oscillator has a configuration shown in FIG. 5, for example. ing.
5A, the SAW oscillator includes a SAW element 1, a phase shifter 2 that adjusts the phase from the SAW element 1, and an amplifier circuit (AMP) 3. The output of the amplifier circuit 3 is supplied to the SAW element 1. A feedback circuit for feedback is formed.

  As shown in FIG. 5B, the SAW element 1 has a comb-shaped electrode (IDT: Inter Digital Transducer) formed on a piezoelectric substrate such as quartz, and passes a signal in a frequency band of the center frequency f1. It also has characteristics.

According to such a configuration, the phase shifter 2 advances (or delays) the output signal of the SAW element 1 by a fixed phase φp [rad], and outputs the signal to the amplifier circuit 3. The output of 3 is fed back to the SAW element 1, whereby the oscillation operation is performed.
Here, the gain of the amplifier circuit 3 is Ge [dB], the gain of the SAW element 1 is Gsaw [dB], the gain of the phase shifter 2 is Gp [dB], and the phase of the amplifier circuit 3 is advanced by φe [rad] ( If the phase is advanced (or delayed) by φSaw [rad] by the SAW element 1, the oscillation condition can be expressed as follows.
Gsaw + Ge + Gp ≧ 0 and φsaw + φe + φp = 2nπ (n is a positive number)

JP-A-1-284002

  By the way, it is known that the phase characteristic of the SAW element 1 varies depending on the temperature. The variation width of the phase variation due to the temperature also varies depending on the type of the piezoelectric material (substrate) constituting the SAW element 1. There is a problem of end. Therefore, in order to eliminate the temperature fluctuation in the SAW oscillator, the oscillation SAW element 1 with a small temperature fluctuation is required, and it is required to use a piezoelectric material having excellent temperature stability such as crystal.

However, when quartz is used as the piezoelectric material of the oscillating SAW element 1, there is a problem that only a narrow-band oscillator can be realized due to a small electromechanical coupling coefficient.
In addition, the oscillation frequency varies due to variations in the manufacturing of the oscillation SAW element 1, and thus the yield is very poor.

On the other hand, conventionally, as shown in the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 1-284002), an external temperature sensor for detecting the ambient temperature is provided, and according to the temperature change detected by this temperature sensor, It is also disclosed that a temperature adjuster is used to adjust the deviation of the oscillation frequency to perform reliable temperature compensation.
However, the SAW oscillator provided with the external temperature sensor as described above has a structure that is not suitable for miniaturization, and is difficult to adopt in recent small portable communication devices.

  The present invention has been made in view of the above problems, and the object thereof is to achieve good temperature compensation even when using an oscillation surface acoustic wave element made of a piezoelectric material having low temperature stability, and to provide an external temperature. An object of the present invention is to provide a surface acoustic wave oscillator that can be downsized without using a sensor.

  In order to achieve the above object, a surface acoustic wave oscillator according to claim 1 has an oscillation function and also has a function of converting frequency fluctuations based on temperature changes into signal level (amplitude) fluctuations. And a detection circuit that outputs the signal level fluctuation obtained from the surface acoustic wave element as a DC (direct current) voltage, and a temperature compensation phase shifter that adjusts the phase of the oscillation signal based on the detection output from the detection circuit The temperature compensation of the oscillation frequency is performed by phase control of the temperature compensation phase shifter.

  According to the above configuration, for example, the surface acoustic wave element for oscillation and the surface acoustic wave element for level conversion are provided, and in the output signal from the surface acoustic wave element for oscillation, The frequency variation is converted into a level (amplitude) variation and obtained from the surface acoustic wave element for level conversion. This level fluctuation is converted into a DC voltage by a detection circuit, and the phase is adjusted by the DC voltage in the temperature compensation phase shifter. As a result, the oscillation frequency is temperature compensated.

According to the surface acoustic wave oscillator of the present invention, even when an oscillating surface acoustic wave element made of a piezoelectric material having low temperature stability is used, it is possible to perform good temperature compensation for temperature change, and a communication device having high temperature stability. can get. Further, there is no need to adopt a conventional narrow band oscillator using a surface acoustic wave element for crystal oscillation, and there is an effect that it is possible to cope with variations in oscillation frequency due to manufacturing variations.
Furthermore, since an external temperature sensor is not used, there is an advantage that the apparatus can be miniaturized and can be easily applied to a small portable communication device.

It is a circuit diagram which shows the structure of the surface acoustic wave oscillator of the Example which concerns on this invention. It is a figure which shows the structure of the SAW element of the surface acoustic wave oscillator of an Example. It is a circuit diagram which shows the structure of the phase shifter for temperature compensation of an Example. It is a wave form diagram which shows operation | movement of an Example. The structure of a conventional surface acoustic wave oscillator is shown, in which FIG. (A) is a circuit diagram and FIG. (B) is a diagram of a SAW element.

FIG. 1 shows a configuration of a surface acoustic wave (SAW) oscillator according to the embodiment, and FIG. 2 shows a configuration of the SAW element of FIG.
As shown in FIG. 1, the SAW oscillator includes the SAW element 10, the temperature compensation phase shifter 12, the phase shifter 2 and the amplifier circuit (AMP) 3, which are the same as the conventional one, and is arranged in a loop shape. A detection circuit 14 is provided which constitutes a feedback circuit to the element 10, detects the level of the SAW element 10, and inputs the detection output to the temperature compensation phase shifter 12.

  As shown in FIG. 2, the SAW element 10 of the embodiment includes an oscillation SAW element 10a having the same configuration as the conventional SAW element 1 and a level conversion SAW element 10b. The oscillation SAW element 10a includes: The signal from the amplifier circuit 3 is input, the oscillation signal is output to the temperature compensation phase shifter 12, and the level conversion SAW element 10b receives the signal from the amplifier circuit 3 and has a frequency based on the temperature change. A level output obtained by converting the fluctuation into the amplitude level fluctuation is output to the detection circuit 14.

  That is, the level converting SAW element 10b is designed to have an amplitude characteristic having an inclination with respect to the frequency by adjusting the weighting of the IDT (comb-shaped electrode) (adjusting the electrode shape or the like). Specifically, as shown in FIG. 4C, for example, the characteristic is set such that the higher the frequency, the lower the amplitude level (the higher the frequency, the greater the loss). Since the level converting SAW element 10b is required to have temperature stability, it is preferable to use quartz having excellent temperature stability as the piezoelectric material.

  Further, the phase shifter 2 adjusts the frequency in a steady state as in the prior art, and the detection circuit 14 converts the level fluctuation output from the level converting SAW element 10b into a DC (direct current) voltage. The temperature compensation phase shifter 12 adjusts the phase (phase shift amount) of the oscillation frequency input from the oscillation SAW element 10a based on the DC voltage.

  FIG. 3 shows a specific configuration of the temperature compensating phase shifter 12. The phase shifter 12 according to the embodiment includes a capacitor C between an input (IN) terminal and an output (OUT) terminal. The resistor R, the varicap VD, and the coil L are connected as shown in the figure, and the DC voltage from the detection circuit 14 is input from the terminal 12a.

The embodiment has the above configuration, and the operation thereof will be described next.
First, a signal from the oscillation circuit 3 of the oscillation loop is input to the oscillation SAW element 10a and is also input to the level conversion SAW element 10b in a branched form. When the ambient temperature changes and the oscillation frequency of the oscillation loop varies, the output level from the level converting SAW element 10b varies.

  As shown in FIGS. 4A to 4C, for example, in the case of a fluctuation between a dotted line and a one-dot chain line, the fluctuation fc of the oscillation frequency is converted into a level fluctuation Ac. That is, when the temperature changes from a predetermined temperature to a high temperature and the characteristic shown in FIG. 4 changes from a solid line to a dotted line, the phase advances and the oscillation frequency of the oscillation loop shifts to a low band. On the other hand, the output level of the level converting SAW element 10b rises as shown in FIG. This increased voltage is converted into a DC voltage by the detection circuit 14 and then supplied to the temperature compensation phase shifter 12 so that the phase is controlled, the oscillation frequency is shifted to the high frequency side, and the temperature is compensated. The Conversely, when the temperature changes to a low temperature and changes from a solid line to a one-dot chain line in the figure, the oscillation frequency shifts to a high band and the output level of the level converting SAW element 10b decreases, but the phase is controlled by the DC voltage. As a result, the oscillation frequency is shifted to the low frequency side and temperature compensation is performed.

The configuration of the embodiment has the following advantages.
(1) A low-loss broadband device can be used as the oscillation SAW device 10a, and a broadband oscillator with good temperature stability can be obtained. As a broadband oscillator, there is a dielectric oscillator in addition to the SAW oscillator. Compared with this, the conventional SAW oscillator has a weak point that the temperature stability is low, but this weak point is eliminated.
(2) An external temperature sensor is not required, and the oscillation SAW element 10a and the level conversion SAW element 10b are mounted in the same package, so that the size can be reduced. Since the output of the level converting SAW element 10b may be a small signal, the loss of the level converting SAW element 10b does not affect the oscillator performance.
(3) The influence of yield due to manufacturing variations of the oscillation SAW element 10a can be avoided by simple adjustment. That is, the frequency can be adjusted by adjusting the amount of phase shift of the phase shifters 2 and 12, and adjustment in mounting can be made unnecessary. Further, it is possible to cope with constant adjustment or use of a variable element.
(4) Since the loss of the oscillation loop is small, a high gain amplifier circuit is unnecessary and the saturation level can be set high.

In the embodiment, the phase shifter 2 for adjusting the frequency in the steady state is provided. However, the temperature compensation phase shifter 12 can also serve as the phase shifter 2.
In the embodiment, the loop oscillation configuration is used. However, the present invention can be applied to a non-loop oscillation configuration using a SAW element as a resonator.

1,10 ... SAW (surface acoustic wave) element,
2 ... Phase shifter 3 ... Amplifier circuit (AMP)
10a: SAW element for oscillation,
10b ... Level conversion SAW element 12 ... Temperature compensation phase shifter,
14: Detection circuit.

Claims (1)

A surface acoustic wave element having an oscillation function and a function of converting frequency fluctuations based on temperature changes into signal level fluctuations;
A detection circuit that outputs a signal level variation obtained from the surface acoustic wave element as a DC voltage;
A temperature compensation phase shifter for adjusting the phase of the oscillation signal based on the detection output from the detection circuit;
A surface acoustic wave oscillator that performs temperature compensation of an oscillation frequency by phase control of the temperature compensation phase shifter.

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