JP2006029870A - Crystal oscillator and sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an error corresponding to a change in oscillation frequency of a crystal resonator based on a change in viscosity of a solution when an environmental pollutant such as a plague marker substance or dioxin is detected by using a change in the frequency of the crystal resonator thing.
A drive current flowing through a crystal resonator is detected by a current detector, and the detected current value is input to a differential amplifier via an amplifier and a rectifier circuit. The differential amplifier compares the voltage corresponding to the detected current value with the set voltage V1, and supplies the deviation to the regulator. A voltage corresponding to the deviation is supplied from the regulator to the inverter of the oscillation circuit as a power supply voltage, whereby the drive current of the crystal resonator is maintained at a set value.
[Selection] Figure 1

Description

  The present invention relates to a crystal oscillator and a sensing device that senses a sensing object by detecting a change in the natural frequency of a crystal resonator using this circuit.

  In the field of biotechnology or environmental conservation, it is often necessary to detect the presence or concentration of trace amounts of substances, and therefore, establishment of measurement techniques for trace amounts of pollutants or organic substances is desired. Examples of the sensing object include an epidemic marker protein, an infectious disease bacterium, dioxin, PCB, and a stress marker.

  By the way, for the analysis of epidemic marker proteins such as hepatitis B virus and hepatitis C virus, a technique for optically detecting the agglutination reaction of immune latex is known. Need. Moreover, as a method for measuring dioxins with high accuracy, a method using a high-resolution gas chromatograph mass spectrometer is known as an official analysis method (JIS), but the price of the apparatus is extremely high, and the analysis cost is therefore quite high. Furthermore, there is a drawback that a long period is required for analysis.

  Therefore, the present inventor can easily and quickly measure the above-mentioned trace amount of substance because the natural frequency changes according to the amount of attachment when the object to be detected adheres to the quartz crystal resonator, and as an inexpensive measuring device. We are focusing on crystal units. On the other hand, there is a technique described in Patent Document 1 as an apparatus for detecting a plague marker protein using a crystal resonator. In Patent Document 1, a 9 MHz crystal resonator with one side sealed is placed in a stirring solution of phosphate buffer and CRP antibody-fixed latex, and when the oscillation frequency is stabilized, CRP standard serum is added. It is described that, after about 60 minutes after the oscillation frequency decreases, it converges to a constant value depending on the CRP concentration to be added and can be measured with a sensitivity of 0.01 mg / dl.

  However, there is the following problem when trying to detect the sensing object in the solution with high accuracy using the change in the oscillation frequency of the crystal resonator. That is, when a liquid containing the sensing object is put in the solution, the viscosity of the solution changes although it is extremely small. If the measurement solution is not sealed at the upper part, the viscosity of the solution changes because water evaporates from the solution during measurement. When the viscosity of the solution changes, the resonance resistance component in the equivalent circuit of the crystal unit changes, and the stability of the oscillation frequency decreases. When the resonance frequency of the crystal resonator is f, the drive current of the crystal resonator is I, the resonance resistance of the crystal resonator is R1, and k is a constant, equation (1) holds.

f = k · R1 · I ² (1)
For this reason, when the viscosity of the solution changes, it eventually affects the resonance frequency of the crystal resonator. On the other hand, one of the advantages of using a quartz resonator is that even if a sensing substance is contained in a very small amount, the oscillation frequency changes, so that measurement can be performed with extremely high sensitivity. For this reason, the inventor has devised the measurement circuit so as to detect a very small frequency change with high accuracy for the detection of deposits with masses on the order of ng to pg. When aiming at high-sensitivity measurement, the frequency change of the crystal resonator based on the change in the viscosity of the solution becomes effective for the change in the frequency measurement, and the measurement accuracy decreases.

JP 2001-83154 (paragraphs 0007, 0009, 0019 and FIG. 1)

  The present invention has been made under such circumstances, and an object of the present invention is to provide a crystal oscillator in which the oscillation frequency is stable even if there is a factor that changes the drive current of the crystal resonator. Another object is to provide a sensing device capable of detecting a sensing measurement object such as an epidemic marker protein or an environmental pollutant with high sensitivity and high accuracy by using this crystal oscillation circuit.

The present invention relates to a crystal oscillator in which an oscillation circuit is connected to a crystal resonator.
A current detection unit for detecting a drive current flowing in the crystal unit;
A deviation calculation unit for obtaining a deviation between the current detection value of the current detection unit and a predetermined set value;
And an adjusting unit that adjusts the driving current based on the output of the deviation calculating unit. In this case, the oscillation circuit may include an inverter connected in series to a crystal resonator, and the adjustment unit may be configured as means for adjusting a power supply voltage of the inverter.

Another invention relates to a crystal oscillator including a crystal resonator having an adsorption layer for adsorbing a sensing object formed on the surface thereof, and an oscillation circuit that oscillates the crystal resonator, and a change in the oscillation frequency of the crystal oscillator A sensing device comprising: means for measuring a minute; and means for sensing a sensing object based on a change in oscillation frequency measured by the means.
The crystal oscillator according to the invention is used as the 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. Equivalent to.

  Since the crystal oscillator of the present invention detects the drive current of the crystal resonator and maintains the drive current at a predetermined value, the oscillation frequency is stable even in an environment where the drive current changes. . In addition, if a sensing device is configured using this crystal oscillator, even if it is in contact with the liquid that is the measurement atmosphere, for example, the viscosity of the liquid that is the measurement atmosphere changes during the measurement, or because the sensing target substance is added to the solution. Even if the viscosity changes, since the drive current is constant, the oscillation frequency is stable, the change in frequency can be extracted with high accuracy, and can be sensed with high accuracy.

  FIG. 1 is a diagram showing an embodiment of a crystal oscillator according to the present invention. Reference numeral 1 denotes a crystal resonator having a fundamental frequency of, for example, AT cut of 9 MHz (about 9 MHz). For example, a Colpitts oscillation circuit 2 is connected in series to the crystal resonator 1. The oscillation circuit 2 is configured by connecting a first inverter (inverting amplifier) 21 and a second inverter (inverting amplifier) 22 in series via a capacitor 23. A parallel circuit of a resistor 24 and a capacitor 25 for applying a bias is connected between the input terminal and the output terminal of the inverter 21 in the first stage. A feedback resistor 26 is connected between the input terminal and output terminal of the second stage inverter 22. Reference numeral 31 denotes a power source, and reference numeral 32 denotes an output terminal of the crystal oscillator.

  A current detector 41 that is a current detection unit is provided in an energization path through which the drive current of the crystal unit 1 flows, for example, an energization path between the inverter 22 and the crystal unit 1. On the output side of the current detector 41, an amplifier 42 for amplifying the current detection value detected by the current detector 41 is provided. The current obtained by the current detector 41 is converted into a voltage signal by a circuit (not shown) and input to the amplifier 42. The output side of the amplifier 42 is connected to the negative input terminal of the differential amplifier 44 via the rectifier circuit 43. A set voltage generator 45 that generates a set voltage V1 is connected to the positive input terminal of the differential amplifier 44. The set voltage V1 corresponds to the set value of the drive current of the crystal unit 1, and the differential amplifier 44 calculates the deviation between the detected current value obtained by the current detector 41 and the set value of the drive current. This corresponds to the deviation calculation unit to be obtained.

  A regulator (voltage adjustment unit) 46 is connected to the output side of the differential amplifier 44, and the output (VC) of the regulator 46 is supplied as each power supply voltage of the inverters 21 and 22. In this example, as shown in FIG. 2, the inverter 21 (22) is formed by connecting MOS transistors 20a and 20b in series, and the output (VC) is used as the power supply voltage of the series circuit. The regulator 46 is configured to generate the supply voltage VC to the inverter 21 (22) based on the output from the differential amplifier 44 so that the drive current becomes a set value.

  Next, the operation of the above embodiment will be described. The pulse output from the crystal unit 1 is inverted by the preceding inverter 21, further inverted by the capacitor 23, and input to the succeeding inverter 22. Since the output of the inverter 22 at the subsequent stage is fed back via the feedback resistor 26, the pulse that has finally passed through the capacitor 23 is output from the inverter 22 in its phase. Accordingly, since the phase of the pulse output from the crystal unit 1 returns to the original state via the oscillation circuit 2, oscillation occurs in the crystal unit 1, and a frequency signal having a resonance frequency of, for example, 9 MHz appears at the output terminal 32.

  On the other hand, the drive current flowing through the crystal unit 1 is detected by the current detector 41, the current detection value is amplified by the amplifier 42, further rectified by the rectifier circuit 43, and input to the differential amplifier 44. The differential amplifier 44 compares the voltage corresponding to the detected current value with the set voltage V1, and supplies the deviation to the regulator 46. Assuming that the drive current of the crystal unit 1 is stable at the set value I0, the output of the differential amplifier 44 according to the difference between the voltage corresponding to the detected value of the drive current and the set voltage V1. Based on this, the voltage VC is supplied from the regulator 46 to the inverters 21 and 22.

  Here, it is assumed that the atmosphere in which the crystal unit 1 is placed changes and the resistance of the crystal unit 1 changes and increases, for example, and the drive current decreases slightly from I0 to I1. In this case, since the voltage (current detection value) input to the negative input terminal of the differential amplifier 44 becomes small, the output from the differential amplifier 44 becomes large, and is supplied from the regulator 46 to the inverters 21 and 22. The output voltage VC increases as the drive current decreases from I0 to I1. As a result, the drive current increases from I1 and returns to I0.

  On the other hand, if the resistance of the crystal unit 1 is reduced and the drive current is changed from I0 to I2 that is slightly larger, in this case, the voltage (current detection value) input to the negative input terminal of the differential amplifier 44 increases. As a result, the output from the differential amplifier 44 is reduced, so that the output voltage VC supplied from the regulator 46 to the inverters 21 and 22 is reduced by the increase in the drive current from I0 to I2. As a result, the drive current decreases from I2 and returns to I0.

  In this way, the driving current is controlled to be constant even if the atmosphere in which the crystal unit 1 is placed changes and the resistance thereof changes. For this reason, the oscillation frequency of the crystal resonator is stabilized. For example, when the crystal oscillator according to this embodiment is applied to a sensing device as described later, it is possible to perform highly reliable sensing, and as a clock generator. When used, there is an effect that a stable clock signal can be supplied to the application device.

  In the present invention, instead of using the current detector 41 as means for detecting the drive current of the crystal unit 1, an impedance component such as a resistor, a capacitor, or an inductance component is provided in the current path through which the drive current flows, and the voltage at both ends thereof is measured. You may make it detect. FIG. 3 shows an example in which a resistor 47 is used as an impedance component. The voltage across the resistor 47 is input to the amplifier 48, and a voltage corresponding to the potential difference of the resistor 47, that is, a voltage corresponding to the drive current is extracted from the amplifier 48. And input to the rectifier circuit 43. Even if it is such a structure, the same effect is obtained.

  Next, a sensing device to which the crystal oscillator of the present invention is applied will be described with reference to FIG. Reference numeral 5 denotes a Langevin type crystal resonator which has one surface of the quartz piece 50 sealed with quartz or the like and the other surface exposed, and is immersed in the solution 52 in the container 51. If the terminology is the same as that of the previous embodiment, the crystal piece corresponds to a crystal unit. However, in order to make the explanation easy to understand, a unit in which the crystal piece and quartz are integrated (Lanjban type crystal vibration) The child) will be referred to as the crystal resonator 5 for explanation. The resonance frequency of the crystal unit 5 is 9 MHz, for example.

  An adsorbing layer for adsorbing (capturing) a substance to be sensed, for example, an adsorbing layer containing an antibody for selectively capturing and adsorbing a plague marker substance is formed on the surface of the crystal unit 5 that contacts the solution. ing. Reference numeral 53 denotes an oscillation circuit that oscillates the crystal unit 5, and the crystal oscillator including the crystal unit 5 and the oscillation circuit 53 includes a circuit that makes the drive current constant as described above.

  Reference numeral 6 denotes a reference frequency generator, which outputs a 10 MHz reference frequency signal with extremely high frequency stability. 61 is a heterodyne detector corresponding to a means for extracting the frequency difference between the frequency signal from the oscillation circuit 53 and the reference frequency signal from the reference frequency generator 6 and outputting a frequency signal corresponding to the frequency difference. An amplifier 63 is connected to the subsequent stage of the heterodyne detector 6 via a low-pass filter 62. A counter 64 that is a counting unit that counts pulses from the amplifier 63 is connected to the subsequent stage of the amplifier 63, and a data processing unit 65 that performs data processing based on the count value is provided to the subsequent stage of the counter 64. ing.

  Next, the operation of this sensing device will be described. When the crystal unit 5 is immersed in a predetermined solution, the crystal oscillates in a state where the oscillation frequency is slightly lower than that in the atmospheric air due to the solution adhering to the crystal surface. Note that the above-described differential amplifier 44 provided for making the drive current constant has an operating point set in accordance with the drive current that flows in the state where the crystal unit 5 is immersed in the solution. If the oscillation frequency of the crystal unit 5 is 9 MHz, the heterodyne detector 61 extracts a 1 MHz frequency signal that is a frequency difference between a 10 MHz frequency signal that is a reference frequency and a 9 MHz frequency signal from the oscillation circuit 53. The noise is removed from the frequency signal by the low-pass filter 62, and the level of the 1 MHz frequency signal is amplified by the amplifier 63. Next, the frequency signal of 1 MHz is counted by the counter 64 and the count value is stored in the data processing unit 65.

  Subsequently, when a solution containing a sensing object such as a plague marker protein is supplied into the solution 52 in the container 51 and stirred, the plague marker protein is applied to the adsorption layer made of antibodies on the surface of the crystal resonator 5. The resonance frequency (natural frequency) of the crystal unit 5 changes by Δf in accordance with the amount of adsorption. Therefore, the oscillation frequency from the oscillation circuit 53 is 9 MHz−Δf, and therefore the frequency of the frequency signal from the heterodyne detector 61 is 1 MHz + Δf, which is counted by the counter 64. The count value is compared with the previous count value in the data processing unit 65, Δf is obtained as a change in frequency, and the concentration of the epidemic marker protein is determined based on the relational expression (calibration curve) obtained in advance. It can be measured.

  In this case, during the measurement, the viscosity of the solution 52 changes due to evaporation, and the resistance of the crystal unit 5 changes, for example, becomes smaller. Even if the drive current of the crystal unit 5 changes, the drive current becomes the set value. Therefore, the drive current is stable. In addition, the viscosity of the solution is changed by putting the plague marker protein in the solution, so that the drive current tends to change. In this case, the drive current is stable.

  If the measurement sensitivity is not so high, the change in frequency based on the change in drive current does not appear as a measurement value. However, if the measurement sensitivity is increased, a measurement error occurs. Therefore, if the drive current is controlled to be maintained at the set value as in this embodiment, the change in frequency based on the change in drive current does not appear in the measured value. Can be measured with high accuracy. In other words, this means that measurement sensitivity can be increased, for example, measurement can be performed with extremely high sensitivity.

  The sensing device of the present invention is suitable for measuring a component in blood. This is because the viscosity of blood varies from person to person, and since the viscosity increases during measurement due to exposure of the blood to air, if the drive current is not controlled, the drive current will change significantly, resulting in a frequency measurement error. Because it grows.

  In the above embodiment, the counter 64 and the means for obtaining the change in frequency based on the counter value in the data processing means 65 correspond to the means for measuring the change in the oscillation frequency. The means for obtaining the concentration of the sensing object based on the change and the calibration curve corresponds to the means for sensing the sensing object based on the change in the oscillation frequency.

  In the sensing device of the present invention, it is not limited to immersing the crystal resonator in the solution, the solution may be hung on the surface of the crystal resonator 5, and is not limited to detecting the epidemic marker protein, It may be one that senses a virus or an environmental pollutant such as dioxin or PCB (polychlorinated biphenyl). The sensing device may be used as a concentration sensor or a presence / absence sensor of a sensing object. Furthermore, the frequency difference corresponding to the difference between the frequency of the frequency signal from the oscillation circuit 53 and the frequency of the frequency signal from the reference frequency generator 6 is not limited to counting as it is. included. Further, the oscillation frequency of the oscillation circuit 53 may be directly counted without using the reference frequency generator 6.

  The environment in which the crystal unit is placed is not limited to the solution, but may be a slurry, a supercritical fluid, or a gas atmosphere such as a gas atmosphere higher than atmospheric pressure. The crystal unit is not limited to being applied to the sensing device, and even when applied to a device other than the sensing unit, the crystal unit can oscillate because the driving current can be made constant even in an environment where the driving current changes. This is an effective technique because the frequency is stable.

  As an example showing that the frequency changes when the viscosity of the environment in which the crystal unit is placed changes, it can be mentioned that the frequency of the crystal unit is different between the air and the water as described above. The resonance resistance in the equivalent circuit of the crystal unit is about 270Ω in water and about 12Ω in air. For this reason, the drive current of the crystal resonator is 1 mA in water and 5 mA in air, and the change in frequency is about 0.2 ppm. Therefore, by making the drive current constant as in the present invention, the change that would have changed in frequency if the drive current changed does not appear in the frequency measurement result.

1 is a circuit diagram showing an embodiment of a crystal oscillation circuit according to the present invention. It is a circuit diagram which shows a part of said crystal oscillation circuit. 1 is a circuit diagram showing an embodiment of a crystal oscillation circuit according to the present invention. It is a lineblock diagram showing an embodiment of a sensing device concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal oscillator 2 Oscillator circuits 21 and 22 Inverter 41 Current detector 42 Amplifier 43 Rectifier circuit 44 Differential amplifier 46 Regulator 5 Crystal oscillator 52 Solution 53 Oscillator circuit 6 Reference frequency generation part 61 Heterodyne detector 64 Counter

Claims (3)

In a crystal oscillator in which an oscillation circuit is connected to a crystal unit,
A current detection unit for detecting a drive current flowing in the crystal unit;
A deviation calculation unit for obtaining a deviation between the current detection value of the current detection unit and a predetermined set value;
A crystal oscillator comprising: an adjustment unit that adjusts the drive current based on an output of the deviation calculation unit. The oscillation circuit includes an inverter connected in series to a crystal resonator,
The crystal oscillator according to claim 1, wherein the adjustment unit is means for adjusting a power supply voltage of the inverter. A crystal oscillator including a crystal resonator on which an adsorption layer for adsorbing a sensing object is formed and an oscillation circuit for oscillating the crystal resonator, and means for measuring a change in the oscillation frequency of the crystal oscillator And a means for sensing a sensing object based on a change in oscillation frequency measured by the means,
3. A sensing device using the crystal oscillator according to claim 1 or 2 as the crystal oscillator.

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