JP2006279798A - Temperature compensated oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the compensation accuracy of oscillation frequency fluctuation due to temperature change without configuring a voltage controlled oscillator.
A temperature-compensated oscillator is provided with SAW oscillators S1 and S2 having different oscillation frequencies f1 + Δf1 and f2 + Δf2, and a mixer B1 for mixing signals of oscillation frequencies f1 + Δf1 and f2 + Δf2 output from the SAW oscillators S1 and S2, respectively. The signals of the oscillation frequencies f1 + Δf1, f2 + Δf2 are input to the mixer B1, and the difference between the signals of the sum of these oscillation frequencies f1 + Δf1, f2 + Δf2 (f1 + Δf1 + f2 + Δf2) and the oscillation frequencies f1 + Δf1, f2 + Δf2 ((f1 + Δf1Δf2)) ) And a signal of the difference ((f1 + Δf1) − (f2 + Δf2)) between the oscillation frequencies f1 + Δf1 and f2 + Δf2 is extracted as an oscillator output by the low-pass filter B2.
[Selection] Figure 1

Description

  The present invention relates to a temperature compensated oscillator, and is particularly suitable for application to a SAW (Surface Acoustic Wave) oscillator.

In a conventional temperature compensated oscillator, in order to suppress fluctuations in the frequency of the oscillator due to temperature changes, the control voltage of the oscillator is controlled while referring to the characteristics of a device having excellent temperature characteristics.
Further, for example, in Patent Document 1, a voltage generation circuit having characteristics opposite to the frequency temperature fluctuation characteristics of a crystal oscillator is provided, and the additional capacitance of the crystal oscillator is controlled based on the voltage output from the voltage generation circuit. Discloses a method for compensating the frequency deviation of a crystal oscillator.
Japanese Utility Model Publication No. 6-85538

  However, it is difficult for the voltage generation circuit to reliably generate the reverse characteristic of the frequency temperature fluctuation characteristic of the crystal oscillator. In other words, the temperature compensation method of the conventional crystal oscillator has a problem that the frequency deviation of the crystal oscillator cannot be completely canceled out by the voltage generation circuit, and the accuracy of compensation of the frequency deviation of the crystal oscillator is poor. In addition, in the conventional crystal oscillator temperature compensation method, the crystal oscillator and voltage generation circuit are made of different materials, so the temperature characteristics of the crystal oscillator and the inverse characteristics of the temperature characteristics of the crystal oscillator are adjusted to match. However, due to the long-term aging operation, the temperature characteristic of the crystal oscillator and the inverse characteristic of the temperature characteristic of the crystal oscillator are separated, and there is a problem that the temperature compensation reliability of the crystal oscillator is poor. Furthermore, in the method disclosed in Patent Document 1, it is necessary to configure a voltage-controlled oscillator in order to compensate for the frequency deviation of the crystal oscillator, and there is a problem that noise characteristics deteriorate compared to a simple oscillator.

  Accordingly, an object of the present invention is to provide a temperature compensated oscillator capable of improving the compensation accuracy of oscillation frequency fluctuation due to temperature change without configuring a voltage controlled oscillator.

In order to solve the above-described problem, according to the temperature compensated oscillator according to one aspect of the present invention, the first and second SAW oscillators having different oscillation frequencies and the oscillations of the first and second SAW oscillators are provided. And a frequency calculation unit that generates a signal corresponding to the difference in frequency.
Thereby, the oscillation frequency of the temperature compensated oscillator can be defined based on the difference between the oscillation frequencies of the first and second SAW oscillators. For this reason, frequency deviations caused by temperature fluctuations can be canceled out without using a voltage generation circuit having a reverse characteristic of the temperature characteristics of the SAW oscillator, and compensation accuracy of oscillation frequency fluctuations due to temperature changes can be improved. In addition, it is not necessary to configure a voltage-controlled oscillator to compensate for the frequency deviation of the SAW oscillator, and noise characteristics can be improved. In addition, the oscillation frequency of the SAW oscillator can be made different from each other without changing the material of the SAW oscillator, and the temperature characteristics of the first and second SAW oscillators can be equally changed even by a long-term aging operation. Therefore, the reliability of temperature compensation of the SAW oscillator can be improved.

Further, according to the temperature compensated oscillator according to one aspect of the present invention, the frequency calculation unit includes a mixer that mixes the signals of the oscillation frequencies of the first and second SAW oscillators, and the mixer And a low-pass filter for extracting a difference between the oscillation frequencies of the first and second SAW oscillators from the obtained signal.
As a result, it is possible to extract the difference between the oscillation frequencies of the first and second SAW oscillators with a simple circuit configuration, while suppressing an increase in the circuit configuration of the temperature-compensated oscillator and oscillating due to temperature changes. It becomes possible to improve the compensation accuracy of frequency fluctuation.

Further, according to the temperature compensated oscillator according to an aspect of the present invention, the first and second SAW oscillators are configured such that the amount of change in frequency with respect to temperature coincides with each other.
As a result, by taking the difference between the oscillation frequencies of the first and second SAW oscillators, it is possible to cancel out frequency deviations caused by temperature fluctuations, and to improve the compensation accuracy of oscillation frequency fluctuations due to temperature changes. It becomes.

  Further, according to the temperature compensated oscillator according to one aspect of the present invention, the first and second SAW oscillators include first and second IDT electrodes respectively formed on a thin film piezoelectric body, By changing the film thickness of at least one of the thin film piezoelectric body and the IDT electrode from each other, the amount of change in frequency with respect to the temperature of the first and second SAW oscillators is made to coincide with each other.

  This eliminates the need to use different materials for the first and second SAW oscillators in order to adjust the frequency deviation with respect to the temperatures of the first and second SAW oscillators. The amount of change in frequency with respect to can be matched with high accuracy. For this reason, it is possible to cancel out the frequency deviation due to the temperature variation with high accuracy, to improve the compensation accuracy of the oscillation frequency variation due to the temperature change, and to perform the first and second even by a long-term aging operation. Since the temperature characteristics of the SAW oscillator can be changed equally, the reliability of the temperature compensation of the SAW oscillator can be improved.

  In the temperature compensated oscillator according to one aspect of the present invention, the first and second SAW oscillators further include a temperature characteristic change film formed on the IDT electrode, and the thin film piezoelectric body, By changing the thickness of at least one of the IDT electrode and the temperature characteristic change film from each other, the amount of change in frequency with respect to the temperature of the first and second SAW oscillators is made to coincide with each other.

  Thereby, in order to adjust the frequency deviation with respect to the temperature of the first and second SAW oscillators, it is not necessary to make the materials of the first and second SAW oscillators different from each other, and the degree of freedom of combination can be expanded. Thus, the amount of change in frequency with respect to the temperature of the first and second SAW oscillators can be matched accurately. For this reason, it is possible to cancel out the frequency deviation due to the temperature variation with high accuracy, to improve the compensation accuracy of the oscillation frequency variation due to the temperature change, and to perform the first and second even by a long-term aging operation. Since the temperature characteristics of the SAW oscillator can be changed equally, the reliability of the temperature compensation of the SAW oscillator can be improved.

  In addition, according to the temperature compensated oscillator according to one aspect of the present invention, the first and second surface acoustic wave devices that are stacked on the semiconductor chip and generate surface acoustic waves having different wavelengths, and the semiconductor chip The first and second surface acoustic wave devices are formed and incorporated in the first and second SAW oscillators having different oscillation frequencies, respectively, and formed in the semiconductor chip. And a mixer for mixing the signals of the oscillation frequencies of the second SAW oscillator and a difference between the oscillation frequencies of the first and second SAW oscillators formed from the signals formed in the semiconductor chip and mixed by the mixer. And a low-pass filter for extraction.

  As a result, frequency deviations caused by temperature fluctuations can be canceled out without using a voltage generation circuit having a reverse characteristic of the temperature characteristic of the SAW oscillator, and the surface acoustic wave device is integrated on the semiconductor chip. be able to. For this reason, even when a plurality of surface acoustic wave devices are provided, the temperature difference between these surface acoustic wave devices can be eliminated, and an increase in the mounting area of the surface acoustic wave device can be suppressed, Compensation accuracy of oscillation frequency variation due to temperature change can be improved, and cost increase of the temperature compensated oscillator can be suppressed.

Also, according to the temperature compensated oscillator according to one aspect of the present invention, the first and second surface acoustic wave devices are formed on the thin film piezoelectric body stacked on the semiconductor chip and on the thin film piezoelectric body. The IDT electrode is provided.
As a result, the surface acoustic wave device can be stacked on the semiconductor chip by depositing the thin film piezoelectric body on the semiconductor chip, and the oscillation frequency fluctuation due to temperature change is reduced while suppressing an increase in mounting area. Can be made.

Further, according to the temperature compensated oscillator according to the aspect of the present invention, the first and second SAW oscillators can be provided by changing the film thickness of at least one of the thin film piezoelectric body and the IDT electrode. The amount of change in frequency with respect to temperature is made to coincide with each other.
Thus, the amount of change in frequency with respect to the temperature of the first and second SAW oscillators can be made to coincide with each other without making the materials of the first and second SAW oscillators different from each other, and the frequency caused by temperature fluctuations The deviation can be canceled with high accuracy.

A temperature compensated oscillator according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit diagram showing a schematic configuration of the temperature compensated oscillator according to the first embodiment of the present invention.
In FIG. 1, the temperature compensated oscillator is provided with SAW oscillators S1 and S2 having different oscillation frequencies f1 + Δf1 and f2 + Δf2, and the SAW oscillators S1 and S2 are provided with surface acoustic wave devices W1 and W2. Δf1 and Δf2 are changes in the frequencies f1 and f2 due to temperature. Here, the surface acoustic wave devices W1 and W2 are provided with IDT (interdigital transducer) electrodes for exciting the surface acoustic waves and reflector electrodes for reflecting the surface acoustic waves. The IDT electrode can be composed of a pair of comb electrodes arranged so as to engage with each other. Further, the arrangement pitches of the IDT electrodes provided in the surface acoustic wave devices W1 and W2 are made different from each other so that the wavelengths of the surface acoustic waves generated by the surface acoustic wave devices W1 and W2 are different from each other. can do. Further, the SAW oscillators S1 and S2 are configured such that the frequency changes Δf1 and Δf2 with respect to the temperature coincide with each other.

An inverter N1 constituting a feedback loop is connected between the comb electrodes of the surface acoustic wave device W1, and the SAW oscillator S1 can be constituted by the surface acoustic wave device W1 and the inverter N1. A resistor R1 is connected between the comb electrodes of the surface acoustic wave device W1, and capacitors C1 and C1 ′ are connected to each comb electrode.
Further, an inverter N2 constituting a feedback loop is connected between the comb-shaped electrodes of the surface acoustic wave device W2, and the SAW oscillator S2 can be constituted by the surface acoustic wave device W2 and the inverter N2. A resistor R2 is connected between the comb electrodes of the surface acoustic wave device W2, and capacitors C2 and C2 'are connected to the comb electrodes.

  Further, the temperature compensated oscillator includes a mixer B1 that mixes signals of oscillation frequencies f1 + Δf1 and f2 + Δf2 output from the SAW oscillators S1 and S2, respectively, and oscillations of the SAW oscillators S1 and S2 from signals mixed in the mixer B1. A low-pass filter B2 that extracts a signal having a frequency difference ((f1 + Δf1) − (f2 + Δf2)) between the frequencies f1 + Δf1 and f2 + Δf2 is provided.

The output from the surface acoustic wave device W1 is fed back via the inverter N1, and a signal having an oscillation frequency f1 + Δf1 is input to the mixer B1. The output from the surface acoustic wave device W2 is fed back via the inverter N2, and a signal having an oscillation frequency f2 + Δf2 is input to the mixer B1.
Then, when signals of the oscillation frequencies f1 + Δf1, f2 + Δf2 are input to the mixer B1, the signal of the sum (f1 + Δf1 + f2 + Δf2) of these oscillation frequencies f1 + Δf1, f2 + Δf2 and the difference between these oscillation frequencies f1 + Δf1, f2 + Δf2 ((f1 + Δf1) − ( f2 + Δf2)) are generated, and these signals are input to the low-pass filter B2. When the signal of the sum (f1 + Δf1 + f2 + Δf2) of the oscillation frequencies f1 + Δf1 and f2 + Δf2 and the difference between these oscillation frequencies f1 + Δf1, f2 + Δf2 ((f1 + Δf1) − (f2 + Δf2)) is input to the low-pass filter B2, the oscillation frequency f1 + Δf1 The signal of the sum of f2 + Δf2 (f1 + Δf1 + f2 + Δf2) is cut off, and the signal of the difference ((f1 + Δf1) − (f2 + Δf2)) between the oscillation frequencies f1 + Δf1 and f2 + Δf2 can be extracted as the oscillator output.

  As a result, the oscillation frequency of the temperature compensated oscillator can be defined based on the difference ((f1 + Δf1) − (f2 + Δf2)) between the oscillation frequencies f1 + Δf1 and f2 + Δf2 of the SAW oscillators S1 and S2. Here, since Δf1 and Δf2 are configured to coincide with each other, the oscillation frequency of the temperature-compensated oscillator is (f1−f2) regardless of the temperature. For this reason, frequency deviations caused by temperature fluctuations can be canceled out without using voltage generation circuits having inverse characteristics of the temperature characteristics of SAW oscillators S1 and S2, and the compensation accuracy of oscillation frequency fluctuations due to temperature changes can be improved. In addition, it is not necessary to configure a voltage-controlled oscillator to compensate for the frequency deviation of the SAW oscillators S1 and S2, and noise characteristics can be improved.

  Further, it is possible to make the oscillation frequencies of the SAW oscillators S1 and S2 different from each other without changing the materials of the SAW oscillators S1 and S2, and the temperature characteristics of the SAW oscillators S1 and S2 are equal even by a long-term aging operation. It becomes possible to change to. For this reason, it is possible to prevent the temperature characteristics of the SAW oscillators S1 and S2 from deviating depending on the use environment of the SAW oscillators S1 and S2, and to improve the temperature compensation reliability of the SAW oscillators S1 and S2.

2A is a plan view showing a schematic configuration of a temperature compensated oscillator according to the second embodiment of the present invention, and FIG. 2B is a cross-sectional view showing a schematic configuration of the SAW vibrator of FIG. 2A. FIG.
2A, the temperature compensated oscillator is provided with SAW transducers W11 and W12 as the surface acoustic wave devices W1 and W2 of FIG. The temperature compensated oscillator is provided with the semiconductor chip 11 on which the circuit block B11 is formed, and the SAW vibrators W11 and W12 are stacked on the semiconductor chip 11. The circuit block B11 is provided with the inverters N1, N2, resistors R1, R2 and capacitors C1, C1 ′, C2, C2 ′ of FIG. 1, and the oscillation frequency is reduced by incorporating the SAW vibrators W11, W12, respectively. Different SAW oscillators S1 and S2 can be configured. Further, the circuit block B11 includes an oscillation frequency of the SAW oscillators S1 and S2 from a signal mixed by the mixer B1 and the signal mixed by the mixer B1 that mix the signals of the oscillation frequencies f1 + Δf1 and f2 + Δf2 output from the SAW oscillators S1 and S2, respectively. A low-pass filter B2 for extracting a signal having a frequency difference between (f1 + Δf1 and f2 + Δf2) ((f1 + Δf1) − (f2 + Δf2)) can be provided.

In addition, as a semiconductor material which comprises the semiconductor chip 11, Si, Ge, SiGe, SiC, SiSn, PbS, GaAs, InP, GaP, GaN, ZnSe etc. can be used, for example.
As shown in FIG. 2B, a thin film piezoelectric layer 12 is laminated on the semiconductor chip 11. An IDT electrode 13 for generating surface acoustic waves in the thin film piezoelectric layer 12 is formed on the thin film piezoelectric layer 12, and the SAW vibrators W11 and W12 shown in FIG. A temperature characteristic changing layer 14 is laminated on the layer 13. Note that ZnO can be used as the material of the thin film piezoelectric layer 12, and SiO ₂ can be used as the material of the temperature characteristic changing layer 14. Here, the SAW vibrators W11 and W12 are configured such that the arrangement pitches of the IDT electrodes 13 of the SAW vibrators W11 and W12 are different from each other so that the wavelengths λ of the surface acoustic waves generated by the SAW vibrators W11 and W12 are different from each other. Can do.

Further, the SAW oscillators S1 and S2 in which the SAW vibrators W11 and W12 are incorporated can be configured such that the amount of change in frequency with respect to temperature coincides. Here, by adjusting at least one of the film thickness d ₁ of the thin film piezoelectric layer 12, the film thickness d ₂ of the IDT electrode 13, or the film thickness d ₃ of the temperature characteristic change film layer 14, the SAW oscillator S 1, The slope of the frequency deviation with respect to the temperature of S2 can be adjusted.

FIG. 3 is a diagram showing a method of adjusting the frequency deviation of the temperature compensated oscillator of FIG.
In FIG. 3, for example, when the thin film piezoelectric layer 12 is made of ZnO and the temperature characteristic changing layer 14 is made of SiO ₂ , the film thickness d ₁ of the thin film piezoelectric layer 12 or the film thickness d ₂ of the IDT electrode 13 is set as follows. by increasing the thickness d ₃ of either reducing or temperature characteristic changing layer 14, it is possible to moderate the gradient of the frequency deviation with respect to temperature T. On the other hand, by increasing the film thickness d ₁ of the thin film piezoelectric layer 12 or the film thickness d ₂ of the IDT electrode 13 or decreasing the film thickness d ₃ of the temperature characteristic changing layer 14, the slope of the frequency deviation with respect to the temperature T is increased. Can be steep.

  Thereby, in order to adjust the frequency deviation of the SAW oscillators S1 and S2 with respect to the temperature T, it is not necessary to use different materials for the SAW oscillators S1 and S2, and the amount of change in frequency with respect to the temperature T of the SAW oscillators S1 and S2 can be accurately determined. Can be matched well. For this reason, it is possible to cancel out the frequency deviation due to the temperature variation with high accuracy, to improve the compensation accuracy of the oscillation frequency variation due to the temperature variation, and to perform the SAW oscillators S1, S2 even by a long-term aging operation. Therefore, the temperature compensation reliability of the SAW oscillators S1 and S2 can be improved.

FIG. 4 is a cross-sectional view showing a schematic configuration of a temperature compensated oscillator according to the third embodiment of the present invention.
In FIG. 4, an element formation region 22 is provided in the semiconductor chip 21, and elements such as transistors, resistors, and capacitors are formed in the element formation region 22. Further, an interlayer insulating film 23 is formed on the semiconductor chip 21 provided with the element forming region 22, and a wiring layer 24 connected to the element forming region 22 is formed on the interlayer insulating film 23. A pad electrode 25 connected to the wiring layer 24 is formed on the interlayer insulating film 23. Then, in the elements and wiring layers 24 formed in the element formation region 22, the inverters N1, N2, the mixer B1, the low-pass filter B2, the resistors R1, R2, and the capacitors C1, C1 ′, C2, C2 ′, etc. Can be configured.

A thin film piezoelectric layer 26 is formed on the interlayer insulating film 23 so as to avoid the pad electrode 25. On the thin film piezoelectric layer 26, IDT electrodes 27a and 27b for generating surface acoustic waves in the thin film piezoelectric layer 26 are formed, and surface acoustic wave devices W21 and W22 are formed, and IDT electrodes 27a and 27b are formed. A temperature characteristic changing layer 28 is laminated. Note that ZnO can be used as the material of the thin film piezoelectric layer 26, and SiO ₂ can be used as the material of the temperature characteristic changing layer 28. The IDT electrodes 27a and 27b are connected to the element formation region 22 via the pad electrode 25, and the SAW oscillators S1 and S2 of FIG. 1 are configured. Here, by making the arrangement pitch of the IDT electrodes 27a and 27b different from each other, the wavelengths λ ₁ and λ _{2 of the} surface acoustic waves generated by the surface acoustic wave devices W21 and W22 may be different from each other. it can. Further, the temperature of the SAW oscillators S1 and S2 is adjusted by adjusting the thickness of at least one of the thin film piezoelectric layer 26, the IDT electrodes 27a and 27b, and the temperature characteristic changing film layer 28 for each of the surface acoustic wave devices W21 and W22. The amount of change in frequency with respect to can be configured to match each other.

  As a result, it is possible to cancel out frequency deviations caused by temperature fluctuations without using a voltage generation circuit having a reverse characteristic of the temperature characteristics of the SAW oscillators S1 and S2, and the surface acoustic wave device on the semiconductor chip 21. W21 and W22 can be integrated. Therefore, even when a plurality of surface acoustic wave devices W21 and W22 are provided, it is possible to eliminate the temperature difference between these surface acoustic wave devices W21 and W22, and the mounting area of the surface acoustic wave devices W21 and W22. Increase of the oscillation frequency can be suppressed, and the compensation accuracy of the oscillation frequency fluctuation due to the temperature change can be improved, and the cost increase of the temperature compensated oscillator can be suppressed.

1 is a circuit diagram showing a schematic configuration of a temperature compensated oscillator according to a first embodiment of the present invention. The figure which shows schematic structure of the temperature compensation type | mold oscillator which concerns on 2nd Embodiment of this invention. The figure which shows the adjustment method of the frequency deviation of the temperature compensation type | mold oscillator of FIG. Sectional drawing which shows schematic structure of the temperature compensation type | mold oscillator which concerns on 3rd Embodiment of this invention.

Explanation of symbols

  S1, S2 SAW oscillator, W1, W2, W21, W22 surface acoustic wave device, R1, R2 resistance, C1, C1 ′, C2, C2 ′ capacitor, B1 mixer, B2 low-pass filter, N1, N2 inverter, W11, W12 SAW vibrator, B11 circuit block, 11, 21 semiconductor chip, 12, 26 thin film piezoelectric layer, 13, 27a, 27b IDT electrode, 14, 28 temperature characteristic changing layer, 22 element forming region, 23 interlayer insulating film, 24, 29 wiring layers, 25 pad electrodes

Claims (8)

First and second SAW oscillators having different oscillation frequencies;
A temperature-compensated oscillator comprising: a frequency calculation unit that generates a signal corresponding to a difference between oscillation frequencies of the first and second SAW oscillators. The frequency calculator is
A mixer for mixing signals of oscillation frequencies of the first and second SAW oscillators;
The temperature-compensated oscillator according to claim 1, further comprising a low-pass filter that extracts a difference between oscillation frequencies of the first and second SAW oscillators from a signal mixed by the mixer.   The temperature-compensated oscillator according to claim 1 or 2, wherein the first and second SAW oscillators are configured such that the amount of change in frequency with respect to temperature coincides with each other. The first and second SAW oscillators include first and second IDT electrodes respectively formed on a thin film piezoelectric body,
The frequency change amount with respect to the temperature of the first and second SAW oscillators is made to coincide with each other by making the film thicknesses of at least one of the thin film piezoelectric body and the IDT electrode different from each other. 3. The temperature compensated oscillator according to 3. The first and second SAW oscillators further include a temperature characteristic changing layer formed on the IDT electrode,
By changing the film thickness of at least one of the thin film piezoelectric body, the IDT electrode, and the temperature characteristic changing layer, the amount of change in frequency with respect to the temperature of the first and second SAW oscillators is made to coincide with each other. The temperature compensated oscillator according to claim 4. First and second surface acoustic wave devices that are stacked on a semiconductor chip and generate surface acoustic waves having different wavelengths;
A feedback circuit that forms first and second SAW oscillators formed on the semiconductor chip and having different oscillation frequencies by incorporating the first and second surface acoustic wave devices, respectively;
A mixer formed on the semiconductor chip for mixing signals of oscillation frequencies of the first and second SAW oscillators;
A temperature-compensated oscillator comprising: a low-pass filter that is formed on the semiconductor chip and extracts a difference between oscillation frequencies of the first and second SAW oscillators from a signal mixed by the mixer. The first and second surface acoustic wave devices include:
A thin film piezoelectric body laminated on the semiconductor chip;
The temperature compensated oscillator according to claim 6, further comprising an IDT electrode formed on the thin film piezoelectric body.   The frequency change amount with respect to the temperature of the first and second SAW oscillators is made to coincide with each other by making the film thicknesses of at least one of the thin film piezoelectric body and the IDT electrode different from each other. 7. The temperature compensated oscillator according to 7.

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