JP2006033195A - Crystal oscillator and detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact crystal oscillator having low power consumption and satisfactory frequency temperature characteristics. <P>SOLUTION: First and second oscillator 1A, 1B are used as an oscillator comprising a quartz oscillator and an oscillation circuit, and for example a heterodyne detector is provided for taking out a difference in oscillation frequencies from the oscillators 1A, 1B and outputting the frequency signal of the frequency difference. A resonance frequency at the first oscillator 1A differs from that at the second one 1B, and the frequency temperature characteristics are identical with those at the second oscillator 1B. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a crystal oscillator and a sensing device that senses a sensing object using the crystal oscillator.

As a typical configuration for obtaining the frequency stability with respect to the temperature of the crystal oscillator, OCXO (Oven Controlled Crystal Oscillator) and TCXO (Temperature Compensated Crystal Oscillator) are known. (Non-Patent Document 1). Since OCXO keeps the ambient temperature of the crystal unit constant by a thermostatic bath, high frequency stability of 10 ⁻⁸ to 10 ⁻¹⁰ can be obtained. However, the scope of application is limited such that it is not applicable to mobile devices. Also known is a crystal oscillator called MCXO (Microcomputer Controlled Crystal Oscillator), which outputs to a computer so that its temperature characteristics can be canceled based on the temperature characteristics of the crystal resonators examined in advance. Although high frequency stability of 10 ⁻⁷ to 10 ⁻⁸ is obtained, the frequency stability is inferior to OCXO, so that it is difficult to apply.

  On the other hand, TCXO has a built-in temperature compensation circuit using a temperature sensitive element so as to obtain a good frequency temperature characteristic over a wide range, and has low power consumption, small size and light weight, and wide application range. There are advantages. However, since TCXO cannot obtain frequency stability as high as OCXO, there is a problem that it is difficult to apply when high frequency stability is required.

  For example, recently, the use of a crystal resonator as an apparatus for detecting a trace amount substance in a solution or gas has been studied. This is based on the detection principle that the oscillation frequency (resonance frequency) changes when a trace substance is adsorbed to the quartz resonator. Patent Document 1 describes that the gas concentration is adsorbed to detect the gas concentration. Yes. Patent Document 2 describes an apparatus for detecting a plague marker protein using a crystal resonator. The present inventor is paying attention to such a measuring device, and can detect environmental pollutants whose analysis target is a ppb to ppt level concentration concentration in various fields, such as dioxin, with high sensitivity. I expect.

  However, if an attempt is made to increase the detection sensitivity of a trace substance, a change in frequency due to a temperature change is added to the measured value of the change in frequency, resulting in a detection error. For this reason, in order to increase the detection accuracy, it is required to improve the frequency temperature characteristics of the crystal oscillator. For these reasons, it is desired to produce a crystal oscillator with high frequency stability while taking advantage of TCXO.

Explanation and application of quartz devices: March 2002 Published by Japan Quartz Device Association (pages 18-20) JP-A-6-241972 JP 2001-83154 (paragraphs 0007, 0009 and FIG. 1)

  The present invention has been made under such circumstances, and an object thereof is to provide a crystal oscillator having good frequency temperature characteristics. Still another object is to provide a sensing device capable of detecting a sensing object with high accuracy by using this crystal oscillator.

A crystal oscillator according to the present invention includes a first oscillation unit including a first crystal resonator and a first oscillation circuit for oscillating the first crystal resonator;
A second oscillating unit including a second crystal unit and a second oscillation circuit for causing the second crystal unit to oscillate;
Means for taking out the difference between the oscillation frequency from the first oscillation unit and the oscillation frequency from the second oscillation unit and outputting a frequency signal of the frequency difference;
The oscillation frequency of the first oscillation unit is different from the oscillation frequency of the second oscillation unit, and the frequency temperature characteristic of the first oscillation unit and the frequency temperature characteristic of the second oscillation unit with respect to the temperature change of the crystal resonator It is characterized by having.

Regarding the difference between the oscillation frequencies of the first oscillating unit and the second oscillating unit, the maximum output of the first oscillating unit in the resonance curve when the oscillating output voltage and frequency are taken on the vertical axis and the horizontal axis, respectively. it is preferred that the 1/2 ^1/2 or more frequency bands values are obtained and 1/2 ^1/2 or more values are obtained frequency band of the maximum output voltage of the second oscillation of the voltage do not overlap each other However, it is not a requirement that they do not overlap. The first crystal unit and the second crystal unit may be formed on a common crystal piece. That is, by providing an elastic boundary layer on the crystal piece, the crystal piece is divided into a first vibration region and a second vibration region that vibrate independently of each other, and the first vibration region and the second vibration region are divided. An electrode is provided in each vibration region to constitute a first crystal resonator and a second crystal resonator. In this case, the elastic boundary layer is a groove or a conductive layer formed in the surface portion of the crystal piece.
In another aspect of the invention, there is provided a crystal oscillator including a crystal resonator on which an adsorption layer for adsorbing a sensing object is formed, a means for measuring a change in the oscillation frequency of the crystal oscillator, and a measurement by this means Means for sensing an object to be sensed based on the amount of change in oscillation frequency,
The crystal oscillator of the present invention is used as the crystal oscillator, and the adsorption layer is formed on one of the first crystal oscillator and the second crystal oscillator.

  In this sensing device, the means for measuring the change in the oscillation frequency of the crystal oscillator is either when counting the frequency and measuring the change in the frequency, or when measuring the frequency period to obtain the change in the frequency. Also applies. Means for sensing the sensing object based on the change in the oscillation frequency include means for obtaining the concentration of the sensing object using a relational expression (calibration curve) between the change in the oscillation frequency and the concentration of the sensing object. Corresponds.

  According to the present invention, when the ambient temperature of the crystal resonator changes, the oscillation frequencies of both the first oscillation unit and the second oscillation unit change in the same way. By doing so, the change in the frequency with respect to the temperature change is reduced, and a favorable frequency-temperature characteristic is obtained.

  FIG. 1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention. If a component composed of a crystal resonator and an oscillation circuit is referred to as an oscillation unit, this crystal oscillator includes an oscillation frequency from the first oscillation unit 1A, the second oscillation unit 1B, and the oscillation units 1A and 1B. And a heterodyne detector 2 which is a mixer constituting frequency difference output means for extracting the difference between the two and outputting a frequency signal of the frequency difference.

  The configuration of the first oscillating unit 1A will be described. 3A is an AT-cut crystal resonator, for example. For example, a Colpitts type oscillation circuit 4A is connected in series to the crystal unit 3A. This oscillation circuit 4A is configured by connecting a first inverter (inverting amplifier) 41 and a second inverter (inverting amplifier) 42 in series via a capacitor 43. A parallel circuit of a resistor 44 and a capacitor 45 for bias is connected between the input terminal and the output terminal of the first stage inverter 41. A feedback resistor 46 is connected between the input terminal and the output terminal of the second stage inverter 42. Reference numeral 47 denotes a power supply unit, and 11A denotes an output terminal of the first oscillation unit 1A.

  The second oscillation circuit 4B of the second oscillation unit 1B has the same configuration as that of the first oscillation circuit 4A except for the oscillation frequency. Used. Note that 3B is a second crystal resonator, and 11B is an output terminal of the second oscillation unit 1B.

The resonant frequency of the first oscillating unit 1A is lower than the resonant frequency of the second oscillating unit 1B, and the frequency-temperature characteristics thereof are aligned with the frequency-temperature characteristics of the second oscillating unit 1B. FIG. 2 is a graph in which the vertical axis and the horizontal axis represent the gain and frequency, respectively, and represent the resonance curves of the oscillation units 1A and 1B (for convenience, the resonance curves are labeled with the corresponding oscillation units). is there. The gain here is an oscillation output voltage. The difference between the oscillation frequencies of the oscillation units 1A and 1B, that is, the difference between the resonance frequencies of the crystal resonators 3A and 3B is determined according to the device to which the crystal oscillator of the present invention is applied. It is preferable not to make it approach too much. For example, in FIG. 2, the resonance curves of the two are completely separated and there is no risk of mutual interference, but the oscillation output voltage is 1/2 ^1/2 or more of the maximum value (peak value) (the power is half). When the frequency bands BW1 and BW2 overlap each other and the overlap increases, the oscillation operation is obtained when the difference between the oscillation frequencies of the oscillation units 1A and 1B is taken as the output of the crystal oscillator of this embodiment. May become unstable.

  Although the present inventor has grasped this point by experiment, it cannot be said that it is always unstable, and the oscillation operation is not necessarily unstable unless the degree of overlap of the frequency bands BW1 and BW2 is large. is not. Therefore, it can be said that it is preferable to determine the oscillation frequencies of the oscillating units 1A and 1B so that the frequency bands BW1 and BW2 do not overlap each other. However, the overlap does not prevent the present invention from being implemented.

  FIG. 3 is a diagram illustrating an example of the frequency temperature characteristics of the oscillating units 1A and 1B, and the frequency temperature characteristics of both are aligned with each other. The term “consistent” here does not limit the frequency temperature characteristic curves of the two to match completely. When the difference between the frequency temperature characteristics of the two is taken, It means the case where it is better than the temperature characteristics. The frequency-temperature characteristic is the frequency with respect to the temperature of the environment where the oscillation unit 1A (1B) is placed when the crystal resonator 3A (3B) and the oscillation circuit 4A (4B) are placed in the same environment. Although this corresponds to a change, for example, when the crystal unit 3A (3B) and the oscillation circuit 4A (4B) are placed in different environments as in a sensing device described later, the environment in which the crystal unit 3A (3B) is placed. This corresponds to a change in the frequency of the oscillating units 1A and (1B) with respect to the temperature.

  A configuration example of the crystal resonator 3A (3B) is shown in FIG. In the example of FIG. 4A, for example, by providing a groove 32 as an elastic boundary layer from one edge to the other edge at the center of one surface and the other surface of the AT-cut square crystal piece 31, A first vibration region 33 and a second vibration region 34 that are divided into left and right are formed, and electrodes 35 and 36 (on the other surface side) are formed on both surfaces of each of the first vibration region 33 and the second vibration region 34. These electrodes are not visible in FIG. 4), and constitute the first crystal resonator 3 </ b> A and the second crystal resonator 3 </ b> B. If an elastic boundary layer is provided on the crystal piece 31 to form the first vibration region 33 and the second vibration region 34, the regions 33 and 34 vibrate independently of each other. If the crystal pieces of the first crystal unit 3A and the second crystal unit 3B are made common in this way, the temperature characteristics of both are substantially the same, which is an effective configuration.

  The grooves 32 are not limited to being provided on both sides of the crystal piece 31 but may be provided only on one side of the crystal piece 31 as shown in FIG. As an elastic boundary layer, for example, a conductive layer 37 may be formed over the entire circumference at the center of the crystal piece 31 as shown in FIG. The conductive layer 37 is not necessarily formed over the entire circumference, but may be formed, for example, on one surface of the crystal piece 31.

  In order to make the oscillation frequencies of the first oscillating unit 1A and the second oscillating unit 1B different, those having different structures of the crystal resonator 3A and the crystal resonator 3B, for example, the first crystal piece 31 in FIG. The thicknesses of the vibration region 33 and the second vibration region 34 may be different, but the crystal resonator 3A and the crystal resonator 3B have the same structure, and the crystal resonator 3A and the crystal resonator 3B are the same. For example, capacitors may be connected in series to 3B, and the capacitance values of these capacitors may be varied to vary the resonance frequency values.

  Next, operations and effects of the above-described embodiment will be described. The pulse output from the crystal unit 3A (3B) is inverted by the preceding inverter 41, further inverted by the capacitor 43, and input to the succeeding inverter 42. Since the output of the inverter 42 at the subsequent stage is fed back via the feedback resistor 46, the pulse that has passed through the capacitor 43 is output from the inverter 42 as it is. Accordingly, since the phase of the pulse output from the crystal unit 3A (3B) returns to the original state via the oscillation circuit 4A (4B), oscillation occurs in the crystal unit 3A (3B), and the first oscillation unit 1A and the first oscillation unit 1A The oscillating outputs of the two oscillating units 1B, for example, sine waves, appear at the output terminals 11A and 11B, respectively.

  The oscillation outputs of these output terminals 11A and 11B are input to the heterodyne detector 2, from which a frequency signal of the frequency difference between the two is output.

  Now, in the graph of frequency temperature characteristics of FIG. 3, for example, if the ambient temperature in which the crystal resonator 3A (3B) is placed is changed from 15 ° C. to 40 ° C., the oscillation frequency (resonance frequency) of the first oscillation unit 1A. ) Becomes lower. However, since the oscillation frequency (resonance frequency) of the second oscillating unit 1B is also lowered, the frequency difference is not much different from that at 15 ° C. That is, when the ambient temperature changes, the oscillation frequencies of both the first oscillation unit 1A and the second oscillation unit 1B change in the same way, so if one of the oscillation frequencies decreases, the other oscillation frequency also decreases. If one oscillation frequency increases, the other oscillation frequency also increases.

  Therefore, by taking the frequency difference between the two, roughly speaking, the change in one frequency with respect to the temperature change is subtracted from the change in the other, which is almost the same as the change. Become invisible. That is, the crystal oscillator of this embodiment has good frequency-temperature characteristics. If the frequency-temperature characteristics of the first oscillating unit 1A and the second oscillating unit 1B match, the change in frequency with respect to temperature change is Even if they do not coincide with each other, even if they do not coincide with each other, they are better than the single frequency temperature characteristics. Since the frequency temperature characteristic is improved by taking out the frequency difference between the two oscillating units 1A and 1B in this way, the apparatus is not large, unlike OCXO, and is small in size and power consumption. Small and wide application range including portable devices.

  Next, a sensing device using the crystal oscillator of the present invention will be described with reference to FIGS. The first crystal resonator 3A and the second crystal resonator 3B of the crystal oscillator of this example employ the structure shown in FIG. 4A and are formed on a common crystal piece. The groove 32 is formed in a V shape as shown in FIG. A signal line 5A is connected to the electrodes on both surfaces of the first crystal unit 3A, and the signal line 5A is connected to the first oscillation circuit 4A. The signal lines 5B are connected to the electrodes on both surfaces of the second crystal unit 3B, and the signal line 5B is connected to the second oscillation circuit 4B. In FIG. 6, the signal lines 5A and 5B are not shown for convenience of illustration.

  Further, one side (the other side) of the first crystal unit 3A and the second crystal unit 3B is sealed with an adhesive by a container 61 having an upper surface opening made of, for example, resin. One surface of the second crystal unit 3B is exposed. As shown in FIGS. 6 and 7, an adsorption layer 62 that adsorbs, for example, dioxin, which is a substance to be sensed, is formed on one surface of the first crystal unit 3A. This adsorption layer 62 contains an antibody that reacts with and captures dioxins. On the other hand, a dummy layer 63 having the same thickness and the same density as the adsorption layer 62 is also formed on one surface of the second crystal unit 3B. The dummy layer 63 is not capable of adsorbing dioxins, and is provided so that the characteristics of the crystal resonators 3A and 3B are the same when no dioxins are captured by the adsorption layer 62. That is, in this example, the crystal resonators 3A and 3B are configured to vibrate at the same frequency as long as the environment is the same, and the resonance frequency is varied by changing the capacitance of the capacitor connected to them. ing.

  Such crystal resonators 3A and 3B are called Langevin type crystal resonators, and a measurement atmosphere such as a solution comes into contact with the exposed surface. In the example of FIG. 5, it is used by being immersed in the solution in the container 64, but the solution may be hung on one surface of the crystal resonators 3A and 3B.

  Returning to FIG. 5, the low-pass filter 71, the amplifier 72, and the counter 73 that counts the frequency signal (pulse) are connected to the subsequent stage of the heterodyne detector 2, and the data processing unit 74 is connected to the subsequent stage of the counter 73. Is provided.

  Next, the operation of this sensing device will be described. The oscillating frequency of the first oscillating unit 1A (the part made up of the first crystal resonator 3A and the first oscillating circuit 4A) is, for example, 31.07 MHz, and the second oscillating unit 1B (second crystal resonator) The oscillation frequency of the part composed of 3B and the second oscillation circuit 4B is 30 MHz. When the quartz vibrators 3A and 3B are immersed in a predetermined solution, for example, in ultrapure water, the crystal oscillates in a state where the oscillation frequency is slightly lower than that of the atmospheric air by, for example, about 5000 Hz because the solution adheres to the quartz surface. At this time, a frequency signal having a frequency corresponding to the difference between the oscillation frequency of the first oscillation circuit 4A and the oscillation frequency of the second oscillation circuit 4B is extracted from the heterodyne detector 2, and the frequency signal is passed through the low-pass filter 71. The signal is input to the amplifier 72, amplified here, and input to the counter 73. The frequency signal is counted by the counter 73 and the frequency is obtained by the data processing unit 74. When this frequency is stabilized, the value is stored in the memory of the data processing unit 74 as a blank value.

  Subsequently, when a sensing object, for example, a solution containing dioxin is supplied into the solution in the container 64 and stirred, the dioxin is selectively trapped by the anti-dioxin antibody, and the adsorption layer on the surface of the crystal unit 3A. The resonance frequency (natural frequency) of the crystal resonator 3A changes by Δf in accordance with the amount of adsorption. Therefore, since the count value of the frequency in the counter 73 changes by Δf, the data processing unit 74 compares the stable frequency in this state with the frequency corresponding to the blank value in the previous memory, so that Δf is the frequency. The concentration of dioxin can be measured based on a relational expression (calibration curve) obtained in advance and obtained as a change. This density is displayed on a display unit (not shown), for example. The detected density may be compared with a preset density and output as “present” if the density is higher than the set density and as “absent” if the density is lower than the set density.

  In the above embodiment, the means for obtaining the change in the frequency based on the counter value in the counter 73 and the data processing means 74 corresponds to a means for measuring the change in the oscillation frequency. The means for obtaining the concentration of the sensing object based on the minute and the calibration curve corresponds to the means for sensing the sensing object based on the change in the oscillation frequency.

  Even if the temperature in the container 64 changes during measurement, the difference in resonance frequency between the crystal resonators 3A and 3B is taken out, so that the frequency stability is high as already described in detail. The change of is small. Therefore, even if the measurement sensitivity is increased, it is possible to detect the detection target substance with high accuracy. The sensing object may be, for example, a plague marker protein, an infectious disease bacterium, a PCB, or the like. Further, the present invention is not limited to sensing substances in liquids, and can be applied to sensing substances in gases, for example, toxic gases or smells.

  By using an AT-cut crystal resonator having a fundamental wave of 14.4 MHz as the first crystal resonator 3A and the second crystal resonator 3B, and connecting a 20 pF capacitor and a 30 pF capacitor as load capacitors, respectively, the oscillation frequency is reduced. The first oscillating unit 1A and the second oscillating unit 1B which are different from each other are configured. The first oscillator 1A and the second oscillator 1B are placed in a temperature vessel in which the temperature can be precisely adjusted, and the frequency after being left for 1 hour at various temperatures between -10 ° C and 60 ° C is counted by a counter. did. Regarding the frequencies, the respective oscillation frequencies from the first oscillating unit 1A and the second oscillating unit 1B, the frequency of the difference between them, and the frequency of their sum were counted. The absolute values of the oscillation frequencies from the first oscillating unit 1A and the second oscillating unit 1B are shown in FIG. 8, and the absolute values of the frequencies of these differences are shown in FIG. FIG. 10 shows relative values based on the frequency of 25 ° C. as the frequency of FIG. 8 and FIG.

As can be seen from this result, compared to the frequency temperature characteristics at each oscillation frequency from the first oscillating unit 1A and the second oscillating unit 1B, the frequency temperature characteristic of the difference is greatly improved. It can be seen that it is expressed as a function. Although the sum of the oscillation frequencies from the first oscillating unit 1A and the second oscillating unit 1B is not shown, it is a cubic curve and the frequency-temperature characteristics are deteriorated.

1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention. It is a characteristic view which shows the resonant frequency of the two oscillation parts used for said crystal oscillator. It is a characteristic view which shows the frequency temperature characteristic of two oscillation parts used for said crystal oscillator. It is a perspective view which shows the structural example of the two crystal oscillators used for said crystal oscillator. It is a lineblock diagram showing an embodiment of a sensing device concerning the present invention. It is a vertical side view which shows the structural example of the crystal oscillator used for said sensing apparatus. It is a top view which shows the structural example of the crystal oscillator used for said sensing device. It is a characteristic view which shows the frequency temperature characteristic of the two oscillation parts incorporated in the crystal oscillator used for the experiment for verifying the effect of this invention. It is a characteristic view which shows the frequency temperature characteristic of the crystal oscillator used for the said experiment. FIG. 10 is a characteristic diagram in which the frequencies shown in FIGS. 8 and 9 are expressed as relative values with respect to a frequency at a temperature of 25 ° C.

Explanation of symbols

1A, 1B Oscillator 2 Heterodyne detector 3A, 3B Crystal resonator 31 Crystal piece 32 Groove 37 Conductive layer 4A, 4B Oscillator circuits 41, 42 Inverter

Claims (5)

A first oscillating unit including a first crystal resonator and a first oscillation circuit for causing the first crystal resonator to oscillate;
A second oscillating unit including a second crystal unit and a second oscillation circuit for causing the second crystal unit to oscillate;
Means for taking out the difference between the oscillation frequency from the first oscillation unit and the oscillation frequency from the second oscillation unit and outputting a frequency signal of the frequency difference;
The oscillation frequency of the first oscillation unit is different from the oscillation frequency of the second oscillation unit, and the frequency temperature characteristic of the first oscillation unit and the frequency temperature characteristic of the second oscillation unit with respect to the temperature change of the crystal resonator A crystal oscillator characterized by In the resonance curves when the oscillation output voltage and frequency are taken on the vertical axis and the horizontal axis, respectively, the frequency band in which a value of 1/2 ^1/2 or more of the maximum output voltage related to the first oscillation unit is obtained and the second 2. The crystal oscillator according to claim 1, wherein a frequency band in which a value of 1/2 ^1/2 or more of the maximum output voltage of the oscillation unit is obtained does not overlap with each other.   By providing an elastic boundary layer on the crystal piece, the crystal piece is divided into a first vibration region and a second vibration region that vibrate independently of each other, and the first vibration region and the second vibration region. 3. The crystal oscillator according to claim 1, wherein an electrode is provided to each of the first crystal resonator and the second crystal resonator.   4. The crystal oscillator according to claim 3, wherein the elastic boundary layer is a groove or a conductive layer formed in a surface portion of a crystal piece. A crystal oscillator including a crystal resonator on which an adsorption layer for adsorbing a sensing object is formed, means for measuring a change in the oscillation frequency of the crystal oscillator, and a change in the oscillation frequency measured by the means A sensing device comprising: means for sensing a sensing object based on minutes;
The crystal oscillator according to any one of claims 1 to 4 is used as the crystal oscillator, and the adsorption layer is formed on one of the first crystal oscillator and the second crystal oscillator. Sensing device.

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