JPH11264846A - Frequency change measuring device - Google Patents

Abstract

(57) [Problem] To provide a measuring device that measures only the frequency change Δf at high speed and with high resolution without measuring the oscillation frequency as in the related art. SOLUTION: A first oscillator for generating a first pseudo random signal from an output of a first oscillator 1a oscillating at a first frequency f1.
A signal generator 4, a second oscillator 2a oscillating at a second frequency f2 slightly different from the first frequency f1, and a second oscillator 2a having the same pattern as the first pseudo random signal from the output of the second oscillator 2a. Second to generate a pseudorandom signal of 2
The signal generator 5 and the oscillation frequency of the second vibrator 2a are set to the third
Frequency changing means 3 for changing the frequency to f3, a multiplier 6 for multiplying the first pseudo-random signal by the second pseudo-random signal, a low-pass filter 7 for removing high-frequency components of the multiplied signal, and a low-pass filter And calculating means 8 for calculating the time at which the maximum correlation value occurs from the output of 7 and calculating the frequency changed by the frequency changing means 3 from this time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency change measuring device for changing the frequency of a vibrator by a small amount and measuring the change frequency.

[0002]

2. Description of the Related Art In sensing in which a physical phenomenon is detected by using a change in frequency, one of methods for measuring a change in an oscillation frequency depending on an object to be measured is a sensor using a surface acoustic wave. Elastic wave sensors are being researched and developed for wide applications such as odor sensors, dielectric sensors, and viscosity sensors. In general, a sensor using an elastic wave uses a SAW (Surf) by absorbing a substance to be analyzed, for example, an odor molecule onto a film (sensitive film) coated on the sensor.
ace Acoustic Wave The amount of change in velocity is measured as the frequency change of the oscillator.

Usually, a high-frequency amplifier is inserted between both ends of an elastic wave sensor electrode to constitute a feedback circuit. When the feedback gain becomes 1 or more, it operates as an oscillation circuit, and the above-mentioned change in SAW speed appears as a change in frequency Δf. Since this frequency change Δf is proportional to the square of the oscillation frequency, a sensor using an elastic wave that can be manufactured up to the order of GHz is larger than a sensor using a quartz oscillator that oscillates only at a fundamental frequency of several tens of MHz at the maximum. A frequency change can be obtained, and a highly sensitive mass and viscosity sensor can be realized.

Japanese Patent Application Laid-Open No. 7-209164 discloses a sensing method using a quartz oscillator for measuring the concentration of volatile substances such as odors. This method also measures the state of a substance to be analyzed from a change in the frequency of a quartz oscillator, as in the case of the surface acoustic wave sensor.

[0005] These sensors originally have a frequency change Δf.
If only the measurement is performed, the chemical characteristics of the substance to be analyzed can be evaluated. However, there is no optimal means for measuring only Δf, and the oscillation frequency itself is generally measured using a frequency counter.

For measuring the oscillation frequency, there are, for example, the following two measurement methods as disclosed in the February 1994 issue of Transistor Technology. Direct measurement method A method of counting the number of repetitions of a signal arriving in one second and displaying the reciprocal thereof as a frequency. By shortening the interval between gates (1 second), it is possible to reduce the measurement time. However, the frequency resolution deteriorates. For example, when the gate is set to 100 msec, the minimum frequency unit that can be measured is 10 Hz. Reciprocal method This method measures the period (time) using an internal reference clock and displays the reciprocal of the frequency as a frequency.
A high resolution (mHz unit) can be measured up to about Hz, but when an oscillation frequency such as SAW is high, the measurable frequency resolution becomes poor, from several tens to several hundreds Hz.

[0007]

As described above, although a sensor using a SAW device can be expected to perform high-sensitivity sensing, there is a problem that sufficient performance cannot be obtained due to low frequency measurement accuracy. Was. Further, there is a similar problem in a sensor using a quartz oscillator.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides a measuring apparatus for measuring only the frequency change Δf at high speed and with high resolution without measuring the oscillation frequency as in the prior art. With the goal.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, a first oscillator oscillating at a first frequency f1 is provided.
First signal generating means for generating a first pseudo-random signal from the output of the vibrator; a second vibrator oscillating at a second frequency f2 slightly different from the first frequency f1; Second signal generating means for generating a second pseudo random signal having the same pattern as the first pseudo random signal from the output, frequency changing means for changing the oscillation frequency of the second vibrator to a third frequency f3, A multiplier for multiplying the first pseudo-random signal and the second pseudo-random signal; a low-pass filter for removing a high-frequency component of the multiplied signal; and a time when a maximum correlation value is generated from an output of the low-pass filter. Calculating means for calculating the frequency changed by the frequency changing means from the calculated time.

The third frequency f3 is a frequency obtained by changing the second frequency f2, and is a frequency close to the second frequency f2. Since the second frequency f2 is slightly different from the first frequency f1, the third frequency f3 is also slightly different from the first frequency f1. The multiplied value of the first pseudo-random signal of the first frequency f1 and the second pseudo-random signal of the third frequency f3 becomes the maximum value when the phases of the respective cycles of both random signals coincide with each other, and this maximum value is generated in the period τ. I do. τ =
P / Δf, where P is a constant, a first pseudo-random signal M1 of frequency f1 and a third pseudo-random signal M2 of frequency f3.
Represents the number of bits (the number of clocks) constituting one cycle of
f = f1−f3. When this period τ is obtained from the output of the low-pass filter, f3 is known because f1 is known. Since f3 = f2 + x, and f2 is known, the frequency x changed by the frequency changing means can be obtained.

[0011] In the invention according to claim 2, the frequency changing means causes a gas generating an odor to adhere to the second vibrator.

When a thin film is applied to the vibrator and a gas generating odor is attached thereto, the generated frequency changes, and the concentration of the gas can be detected from the amount of change.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention. 1a is a first crystal oscillator, 1b is a first oscillation circuit for generating a clock signal of frequency f1 by the oscillator 1a, 2a is a second crystal oscillator, and 2b is slightly higher than the frequency f1 by the oscillator 2a. The second oscillation circuit generates a clock signal having a different frequency f2. Numeral 3 is a frequency changing means for changing the oscillation frequency of the second quartz oscillator 2a. The container 32 stores a volatile solution serving as a specimen 31, a dry air cylinder 33 filled with dry air, and a dry air cylinder 33. A pressure reducing valve 34 for reducing the pressure and a flow control valve 35 for controlling the flow rate of the dry air are provided, and the dry air is sent into the container 32 by a syringe needle 36 inserted into a lid of the container 32, and is sent from another syringe needle 36. Dry air and vaporized gas are sent to the second crystal resonator 2a.
A film is applied on the electrode of the second quartz-crystal vibrator 2a, and the frequency changes due to gas adhesion. This changed frequency is assumed to be f3.

The first signal generator 4 generates a first pseudo random signal M1 having a predetermined pattern at a frequency f1. The second signal generator 5 generates a second pseudo-random signal M2 having the same pattern as the signal M1 at the frequency f2 or f3. The multiplier 6 multiplies the signal M1 and the signal M2. The low-pass filter 7 removes the high-frequency component of the multiplied signal, and the calculation unit 8 obtains the frequency difference Δf = f1−f3 from the time interval τ between the maximum correlation values of the multiplied signal, and the frequency change Δf1 due to the attached gas. = F3−f2 = f1−Δf−f2.

FIG. 2 is a block diagram showing the functions of FIG. The first oscillating unit 1 generates a clock signal of the frequency f1, and the first signal generator 4 generates a pseudo random signal M1 of the frequency f1. The second oscillator 2 generates a clock signal having a frequency f2 slightly different from f1. Frequency changing means 3
Changes the frequency f2 to a slightly different frequency f3.
The second signal generator 5 generates a pseudo random signal M2 having the same pattern as M1 at the frequency f2 or f3. The functions of the multiplier 6, the low-pass filter 7, and the operation unit 8 are the same as those described with reference to FIG.

FIG. 3 shows an M-sequence signal generator in which the first signal generator 4 and the second signal generator 5 generate a pseudo-random signal. The M-sequence signal generator is usually used as a pseudo-random signal generator. A shift register 11 having a seven-stage configuration of flip-flops synchronized with the clock signals f1, f2, or f3 is provided, and the output signals of the fifth-stage and seventh-stage flip-flops are output via the exclusive OR circuit 12 to the first-stage flip-flop. The clock signal is supplied to the flip-flop of each stage, and an output signal is obtained from the flip-flop of the seventh stage.
A sequence code can be generated.

FIG. 4 shows the output of an M-sequence signal generator constituted by three stages of shift registers. The M-sequence code generated in this way is a cyclic cyclic code formed by a combination of codes "1" and "0" or "+" and "-". In FIG. 4, signals of "1" and "0" are used. Has occurred. The cycle when the M-sequence signal is circulated and generated is shown in FIG.
, Since 7 bits are generated, one cycle is completed when 2 ⁷ −1 = 127 signals are generated. Then, the same signal as that of the previous cycle is generated from the next 128th signal, and this cycle is repeatedly circulated. Generally, the M-sequence signal is a partially random signal, but is used as a signal utilizing an autocorrelation function.

Hereinafter, a method of measuring the frequency variation Δf1 = f3-f2 added by the frequency varying means 3 will be described. The frequencies f1 and f2 are slightly different frequencies and are known because they are oscillated by a crystal oscillator. The first signal generator 4 generates a pseudo-random signal M1 having a frequency f1, and the second signal generator 5 generates a pseudo-random signal M2 having a frequency f2 or f3. Pseudo-random signal M1
And M2 have slightly different frequencies, but are signals of the same pattern. If the respective periods are T1 and T2, they are expressed by the following equations. T1 = P / f1 (1) T2 = P / (f2 or f3) (2) where P is the number of bits for one period of the pseudo random signal.
In the case of the M-sequence signal generator of FIG. 3, P = 127. In the following, unless otherwise specified, f2 or f3
Is represented by f3.

As shown in FIG. 5, the difference Δt between the periods T1 and T2 is represented by the following equation. Δt = T1−T2 = P / f1−P / f3 = P · (f3−f1) / (f1 · f3) (3)

Next, the maximum correlation value that the pseudo random signals M1 and M2 can have will be described. One of the features of the M-sequence pseudo-random signal is periodic autocorrelation. FIG. 6 shows a time τ between the maximum correlation values when the phases of two pseudo-random signals match. Referring to FIGS. 5 and 6, τ is represented by the following equation. τ = (T1 / Δt) × T2 (4) The number in the parenthesis on the right side indicates the number of Δt included in T1, and when T2 is arranged by this number, T1 and T2 are obtained as shown in FIG.
Are aligned. Therefore, multiplying this number by T2 yields τ. Δf = f3-f1, (1),
Substituting equations (2) and (3) into equation (4) yields the following. τ = P / Δf (5)

When the M-sequence pseudo-random signals M1 and M2 are multiplied by a multiplier 6 and high-frequency components are removed by a low-pass filter 7, signals M1 and M2 shown in the lower part of FIG. 6 are obtained, from which τ is measured. it can. In equation (5), P
Is a constant, and if this τ can be measured, Δf can be calculated. Δf = f3−f1, and f1 is a fixed number of periods, so that f3 can be obtained. In FIG. 1, the amount of decrease in frequency at which gas molecules adhere to the second crystal resonator and decrease is Δf1 = f3−f2, and f2 is a constant.
This reduction amount Δf1 can be calculated.

Next, an embodiment will be described. In FIG. 1, an AT-cut crystal unit having a frequency of 20 MHz (f1 = f2 = 20 MHz) is used as a first crystal unit 1a and a second crystal unit 2a, and chloroform is formed on an electrode of the second crystal unit 2a. Ucon 900000 diluted with was applied. As a result, the mass of the second crystal resonator 2a increases, and the frequency f
2 decreases. Measured value of time τ between maximum correlation values τ = 0.07
673716 sec is obtained, and is substituted into the equation (5).
When a stage shift register is used, since P = 2 ⁿ -1 = 127, Δf = −1655 Hz (the value is assumed to be − because the frequency decreases) is obtained. From Δf = f2-f1, f2 =
19.998345 MHz is obtained.

Next, the sample 31 is placed in the container 32 shown in FIG.
Hexanone was used and the measurement time was 30 seconds. FIG. 7 shows the change in the time τ between the maximum correlation values due to the addition of the sample 31, A shows τ when Ucon 900000 diluted with chloroform was applied on the electrode of the second quartz oscillator 2 a, and B shows this τ. This shows a state in which the sample 31 adheres to the applied film, the frequency of the second crystal resonator 2a decreases, and τ decreases according to the equation (5).

FIG. 8 shows a state in which the frequency of the second quartz-crystal vibrator 2a is reduced due to the adhesion of the sample 31. Frequency decrease is Δf
1 = f3−f2. The horizontal axis indicates the measurement time, and the vertical axis indicates the frequency decrease amount Δf1 (−). Hexanone gas molecules adhere to the second crystal oscillator 2a with high accuracy,
And it can measure at high speed.

The case where a quartz oscillator is used as the oscillating element has been described above. As a result of an experiment using a SAW, a change in frequency can be similarly measured with high accuracy and high speed.

[0026]

As is apparent from the above description, the present invention measures only the amount of change in frequency when measuring the change in frequency due to the attachment of a sample to a vibrator, as in the prior art. In contrast to measuring the changed frequency, it is possible to measure accurately and at high speed. For this reason, for example, SAW
It is also possible to perform high-speed and high-resolution measurement of a change in the frequency of an element that oscillates at a high frequency such as described above. Further, since the circuit configuration is simple, an inexpensive device can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram illustrating functions of the present invention.

FIG. 3 is a diagram showing a configuration of a pseudo random signal generator.

FIG. 4 is a diagram schematically showing pseudo random signals M1 and M2.

FIG. 5 is a diagram illustrating a difference between the periods of the pseudo random signals M1 and M2.

FIG. 6 is a diagram illustrating a time τ between the maximum correlation values of the pseudo random signals M1 and M2.

FIG. 7 is a diagram schematically showing that a sample adheres to a second crystal resonator and τ changes.

FIG. 8 is a diagram showing a state in which the frequency changes due to the attachment of a sample.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st oscillation part 1a 1st crystal oscillator 1b 1st oscillation circuit 2 2nd oscillation part 2a 2nd crystal oscillator 2b 2nd oscillation circuit 3 Frequency change means 4 1st signal generator 5 2nd signal generator 6 Multiplication Instrument 7 Low-pass filter 8 Operation unit 11 Shift register 12 Exclusive OR circuit 31 Sample 32 Container 33 Dry air cylinder 34 Pressure reducing valve 35 Flow control valve 36 Syringe needle

Claims (2)

[Claims] 1. A first signal generating means for generating a first pseudo-random signal from an output of a first vibrator oscillating at a first frequency f1, and a second frequency f2 slightly different from the first frequency f1. A second oscillator that oscillates at the second oscillator, a second signal generator that generates a second pseudo random signal having the same pattern as the first pseudo random signal from an output of the second oscillator, Frequency changing means for changing the oscillation frequency to a third frequency f3, a multiplier for multiplying the first pseudo-random signal by the second pseudo-random signal, and a low-pass filter for removing a high-frequency component of the multiplied signal; Calculating means for calculating the time at which the maximum correlation value occurs from the output of the low-pass filter and calculating the frequency changed by the frequency changing means from the time. Measurement device. 2. The frequency change measuring device according to claim 1, wherein said frequency changing means causes a gas generating an odor to adhere to said second vibrator.