JP2010085286A - Frequency-measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce pattern noises in a frequency-measuring apparatus that uses a short-gate time count method. <P>SOLUTION: The frequency-measuring apparatus includes a signal source (10) for generating signals to be measured; a short-gate time counter section (20) for continuously counting the signals to be measured at a sampling frequency of a short gate time and outputting a series of count values corresponding to a frequency of the signals to be measured; and a low-pass filter (30) for removing high-frequency components from the series of count values. the combination of the frequency of the signals to be measured and the sampling frequency is defined by an operating point parameter, having a value ranging 0-1 among a ratio a/b between the frequency (a) of the signals to be measured and the sampling frequency (b), and the frequency of the signals to be measured and the sampling frequency are selected by an adjustor (50), in such a way that the value of the operating point parameter should not assume a value (noise peak value) close to a prescribed rational number. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  Some embodiments according to the present invention relate to frequency measurement, and more particularly to a measurement method and apparatus capable of detecting a slight frequency change.

As a frequency measurement method, a direct counting method (Patent Document 1) that counts pulses passing within a predetermined gate time and a reciprocal method that accurately measures the pulse period and obtains the frequency from the reciprocal of the time are known. ing. The direct counting method can be realized with a relatively small circuit, but it is necessary to take a long gate time in order to increase the frequency resolution (for example, the gate time necessary to obtain a resolution of 0.1 Hz is 10 seconds). The reciprocal method can overcome this drawback, but the circuit for accurately measuring the pulse interval is large compared to the direct count format.
JP-T 6-501554

  By the way, when it is desired to detect a small amount of mass change such as the presence or absence of adhesion of an odorous substance to the sensor, a method using the sensor frequency change due to the adhesion of the substance can be considered. For example, by using a QCM (Quartz Crystal Microbalance) method using a crystal resonator, a minute mass change on the surface of the resonator substrate can be converted into a frequency change. For example, various odor sensors can be formed by providing a material to which the odor component adheres on the surface of the vibrator substrate. The odor component is composed of a single substance or a plurality of substances. When the sample gas is applied to the odor sensor to attach an odor component and the mass of the vibrator surface is changed, the frequency changes. By preparing one or more types of sensors and observing this change, it is estimated that a specific odor component exists.

  In order to detect the frequency change of each odor sensor, a counter and a signal processing circuit for detecting the frequency change must be provided at the output of each sensor. Furthermore, even if the frequency of the crystal resonator (for example, 30 MHz) changes depending on the adhered substance, it is only about several Hz to several hundred Hz, and may be a change of 1 Hz or less. As described above, in the direct count method, the frequency resolution is low, and in order to increase the frequency resolution, it is necessary to take a considerably long gate time. As an error in measurement, in addition to a plus / minus one count error and an error due to fluctuation of the trigger level, when the gate time is increased, an error due to the oscillation stability of the crystal resonator is superimposed. Such a drawback can be compensated for by using a reciprocal counter, but the circuit of one counter is large, so that it is not suitable for a sensor array having a large number of sensors.

  Therefore, the present applicant has proposed, for example, a new frequency change measurement method and measurement apparatus with improved frequency measurement resolution in Japanese Patent Application No. 2008-099721.

  As described later, the present invention continuously counts a supplied pulse train signal with a short gate time to obtain a series of count values that behave in a pulse train corresponding to the frequency of the pulse train signal, and this series of count values The frequency change is extracted by obtaining a series of level signals corresponding to the frequency of the pulse train signal supplied by removing high frequency components from the signal.

  Some aspects of the present invention aim to further reduce pattern noise.

  In order to achieve the above object, a frequency measuring apparatus according to the present invention comprises a signal source that generates a signal under measurement in a pulse train and the signal under measurement by continuously counting the signal under measurement at a sampling frequency of a short gate time. A gate time counter unit for outputting a series of count values corresponding to the frequency of the signal, and a low-pass filter for removing a first frequency component from the series of count values and outputting a level signal corresponding to the frequency of the signal under measurement And the frequency of the signal under measurement and the sampling frequency are selected based on a distribution characteristic of a frequency ratio versus noise level between the frequency of the signal under measurement and the sampling frequency, which is obtained in advance. To reduce the noise level in the output of the low pass filter. The frequency component of the low-pass filter and the suppression characteristic (first frequency component) of the frequency band are appropriately set according to the S / N (signal / noise) ratio of the output signal, the response characteristic of the output signal, and the like.

  By adopting such a configuration, it is possible to obtain a short gate time count type frequency measurement device in which the pattern noise level is suppressed (the level is low).

When the operating point parameter (ratio of the frequency to be measured and the sampling frequency) is close to a simple rational value (not a simple rational value itself), the pattern noise is large. For example, in ΔΣ modulation, there is an input value whose output generates a periodic sequence, and pattern noise that occurs when an input close to this is added is known. However, the idea is different between the pattern noise avoidance method in the ΔΣ modulation and the pattern noise avoidance method in the short gate time count method.

In the case of ΔΣ modulation, a high-order configuration or a multistage configuration is devised to suppress pattern noise itself. This is due to handling an input signal change comparable to the dynamic range. In the case of the short gate time count method, it is possible to design the input signal change width to be within a certain range with respect to the dynamic range, so by appropriately selecting the operating point parameter without changing the configuration Pattern noise can be avoided.

  The combination of the frequency of the signal under measurement and the sampling frequency is defined by an operating point parameter that is a value between 0 and 1 in the ratio a / b between the frequency a of the signal under measurement and the sampling frequency b. The frequency of the signal under measurement and the sampling frequency are set so that the value of the operating point parameter does not become a value near a predetermined rational number (noise peak value, etc.) that increases the noise level. desirable. By using the operating point parameter, it is possible to represent (understand) the distribution of pattern noise with a smaller amount of data.

  The operating point parameter is described as follows. Operating point parameter = measured frequency ÷ sampling frequency−Int (measured frequency ÷ sampling frequency) where Int (c) is a function that returns the integer part of c. It can be seen from the definition formula that the operating point parameter takes a value between 0 and 1. The intensity of the pattern noise is a complex function of the operating point and has symmetry with an operating point parameter of 0.5. That is, the pattern noise intensity at the operating point parameter 0.5-d has the property of being equal to the pattern noise intensity at the operating point parameter 0.5 + d (0 <d ≦ 0.5). As will be described later, the relationship between the noise intensity and the operating point is shown in the range of operating points 0 to 0.5 (see FIG. 9).

  The predetermined rational numbers include simple rational numbers such as 1/1, 1/2, 1/3, 1/4, 1/5, 2/3,. When g is an integer and h is a natural number, the predetermined rational number can be generally expressed as g / h. In particular, there is a tendency that the maximum value (peak) of pattern noise appears near an operating point parameter that is a simple rational number that satisfies 0 ≦ g ≦ h ≦ i (i = 10) (the sampling frequency used and the required SN). Depending on the ratio requirements). The larger i is, the more rational numbers satisfying 0 ≦ g ≦ h ≦ i. Therefore, this corresponds to an increase in the number of points considered as the corresponding operating point. Depending on the required specifications, it may be necessary to consider up to i = 20. As a special example, in measurement with an operating point parameter that is a rational number, there is no pattern noise because the signal under measurement and the sampling signal are not misaligned.

  The neighborhood value of the predetermined rational number is the value of the operating point parameter when the pattern noise level that appears in the output of the low-pass filter exceeds the reference value when the operating point parameter is variously set. By avoiding the neighborhood value, it is possible to avoid generation of pattern noise exceeding the reference value from the low-pass filter.

  And a frequency adjustment unit that adjusts the frequency of the signal under measurement and / or the sampling frequency, and the frequency adjustment unit determines the frequency of the signal under measurement and the sampling frequency as a value of the operating point parameter. It is desirable to set so as to be away from the neighborhood value of the predetermined rational number. This makes it possible to automatically select the frequency of the signal under measurement and the sampling frequency to a frequency with less pattern noise.

  Furthermore, an operating point calculation unit that calculates an operating point parameter from the output of the short gate time counter unit, a storage unit that stores a range of operating point parameters excluding the vicinity of the predetermined rational number, and a control unit that controls each unit The operating point calculation unit calculates an operating point parameter by obtaining an average value from an output sequence of the short gate time counter unit within a certain section, and the control unit operates from the operating point calculation unit. It is desirable to have a function of receiving a point parameter and changing the frequency of the signal under measurement or the sampling frequency through the frequency adjustment unit. As a result, it is possible to measure and adjust the operating point parameters based on individual measurement environments, and to cope with product variations and changes over time.

  The frequency adjustment unit recalculates the frequency of the signal under measurement and the sampling frequency based on the operating point parameter when the operating point parameter calculated by the operating point calculating unit is in a range near the predetermined rational number. It is desirable to adjust. The frequency adjusting unit includes at least one of a circuit constant including a circuit voltage of an oscillation circuit of the signal source, a frequency divider that divides the output of the signal source, a multiplier that multiplies the output of the signal source, and the sampling frequency. It is desirable to adjust any one or a combination of two or more of these.

  Furthermore, in order to suppress the pattern noise level, for example, the filter characteristics such as the time constant can be adjusted by adjusting the number of stages of the low-pass filter (analog filter), the number of taps (digital filter), or other design parameters. good.

  The frequency measuring device of the present invention is convenient for use in devices such as a mass detection device and an odor detection device using the QCM (Quartz Crystal Microbalance) method.

  Embodiments of the present invention will be described below with reference to the drawings. First, an outline of a frequency measuring apparatus using the “short gate time counting method” proposed in Japanese Patent Application No. 2008-099721 will be described with reference to FIGS. In each figure, the same reference numerals are given to corresponding parts.

In FIG. 1, a signal source 10 generates a pulse train signal. The signal source (pulse generator) 10 is, for example, a crystal oscillator having an oscillation frequency f ₀ of 30 MHz, and corresponds to a detection unit such as an odor sensor, a gas sensor, or a biosensor described later. When an odor substance or the like adheres to the crystal resonator, the oscillation frequency decreases according to the amount of adhesion. This pulse train signal is supplied to a short gate time counter section (hereinafter also simply referred to as “short gate counter section”) 20. The short gate time counter unit 20 performs pulse counting of the supplied pulse train signal without interruption in a short gate time. The count value has a corresponding relationship with the frequency (time interval) of the pulse train signal, and is sequentially supplied to the low-pass filter (LPF) 30.

  FIG. 2 shows a first configuration example of the short gate time counter unit 20. It is desirable that the short gate time counter unit 20 counts the pulse train signal supplied from the signal source without interruption (no dead period is provided for the input signal).

  Therefore, in the first embodiment, the first counter 21 and the second counter 22 are provided with two counters. The pulse train signal is supplied to both the first counter 21 and the second counter 22. The control unit 23 sends a gate signal and a reset signal to both counters, and supplies the outputs of both counters to the low-pass filter 30 via a switch. Count values are alternately output from both counters, and when one is counting, the other resets or transfers data, thereby avoiding a dead period that occurs during counter reset or data transfer. The control unit 23 may be configured as hardware, or may be configured as software using a personal computer or the like.

  FIG. 3 shows a second configuration example of the short gate counter unit 20. In this embodiment, one counter 24 is used. The counter 24 is a direct counting type counter, and always counts the sampled pulse signal and outputs an accumulated value (not reset). The output of the counter 24 is sent to a subtracter 25 and a register 26 that holds the previous accumulated value. The subtracter 25 subtracts the previous cumulative value from the current cumulative value output from the counter 24 to obtain the current count value, and supplies it to the low-pass filter 30. The overall operation of the apparatus is the same as that of the measuring apparatus of FIG.

  FIG. 4 shows an example in which the low-pass filter 30 is configured by an analog circuit. In this example, a low-pass filter including resistors R1 to R3, capacitors C1 and C2, and an operational amplifier OP1 is connected in two stages. By appropriately selecting these circuit constants, a first frequency component (or a high frequency equal to or higher than the first frequency) is obtained from the output signal of the counter 24 converted into an analog signal (by a D / A converter (not shown)). (Component) is removed (suppressed). The cut-off frequency and signal response characteristic of the low-pass filter are appropriately set according to the S / N (signal / noise) ratio of the output signal, the waveform response characteristic of the output signal, and the like. When output from the short gate time counter 20 in 1-bit serial, it can be input to the low-pass filter 30 as it is. When the short gate counter 20 outputs n bits, it can be input via a DA converter corresponding to n bits output.

  FIG. 5 shows an example in which the low-pass filter 30 is configured by a moving average filter (digital filter). In the figure, 31 is an adder, 32 is a shift register, 33 is a subtractor, 34 is an inverter, 35 is a control unit for supplying an operation timing clock to each unit, and 36 is a divider.

  The count value output from the counter is supplied to both the adder 31 and the shift register 32 having a storage area corresponding to the number of taps. In the shift register 32, N data for which the average value is to be calculated sequentially move in synchronization with the other data. The other value of the adder 31 is supplied with the total value of the previous calculation, and the adder adds the new count value and the previous total value. The count value of the first (old) data is removed from the cumulative addition value by the shift register 32 by the subtracter 33, and this is used as the new total value. The new total value is returned to the adder as the previous total value, and the new total value is divided by the number of target data N by the divider 36. A moving average value is obtained by performing such calculation for all data. Here, the divider has a function of scaling the output value to the frequency (Hz), but it can be omitted if the scaling need not be taken care of. When the moving average filter has a multi-stage configuration, a divider may be disposed only in the final stage.

  FIG. 6 shows an example of count value output in the short gate time counter 20. In this example, the pulse train signal is counted at a sampling frequency of 100 Hz (gate time 0.01 seconds). When the sampling frequency is 100 Hz, the frequency resolution is also reduced to 100 Hz, so that information of 100 Hz or less of the supplied pulse train signal cannot be detected from only one count value, but 100 count values can be obtained per second. Become. The frequency which is 100 times the count value is distributed in a pulse shape on the time axis between 30,072,300 Hz and 30,072,400 Hz.

  Here, a quantization error (± 1 count error) in sampling will be described. For example, consider the case of measuring a pulse train signal that is stable at 123.34 Hz with a direct count counter.

  When the gate time is 10 seconds: 1233 counts or 1234 counts every 10 seconds

Display of 123.3 Hz or 123.4 Hz multiplied by 1/10 (every 10 seconds)
It becomes. (Measurement error is 0.1Hz)

  When the gate time is 1 second: 123 or 124 counts per second

  The display is 123 Hz or 124 Hz (every second). (Measurement error is 1 Hz)

  When the gate time is 0.1 seconds: 12 or 13 counts every 0.1 seconds

  This is multiplied by 10 to display 120 Hz or 130 Hz (every 0.1 second). (Measurement error is 10Hz)

  When the gate time is 0.01 seconds: 1 count or 0 count every 0.01 seconds

  This is multiplied by 100 to display 100 Hz or 200 Hz (every 0.01 seconds). (Measurement error is 100Hz)

  Thus, when a pulse train signal that is stable at a certain frequency is counted, the count values are distributed in a pulse train having an amplitude between two values determined by the gate time. On the other hand, even if the frequency of the pulse train signal to be counted fluctuates, the count values are still distributed in a pulse train having an amplitude between two values as long as the fluctuation is within the measurement error. For example, when the gate time is 0.01 seconds, as long as the variation in the frequency of the pulse train signal to be counted is within 100 to 200 Hz, a display of 100 Hz or 200 Hz can be obtained.

  As shown in FIG. 6, in the short gate time count method in which sampling is performed with a short gate time of less than 1 second, the count value behaves as a pulse train, and the frequency (roughness) of the pulse train changes according to changes in the frequency to be measured. The magnitude of the vibration frequency corresponds to the density of the pulse train. Information on the frequency of the pulse train signal to be counted exists in the low frequency component of the frequency spectrum of the count value that behaves as a pulse train. Therefore, the frequency information of the pulse train signal to be counted can be demodulated by extracting the low frequency component from the count value by the low pass filter (removing the harmonic component due to the quantization error).

  FIG. 7 shows an example in which the above-described sequence of count values (see FIG. 6) is applied to a (digital) low-pass filter 30 with 512 taps to remove high frequency components. As shown in the figure, the change in the frequency of the supplied pulse train signal is output as a continuous (analog) curve. It is possible to detect a region that cannot be measured by counting at a sampling period of 100 Hz, in particular, a frequency change of 1 Hz or less.

  As described above, in the short gate time counting method, when the gate time is shortened (the sampling frequency is increased), each measurement error increases, but a series of measurement values is obtained, and a high-frequency component ( Alternatively, a certain frequency component) can be removed, and the frequency measurement resolution is improved. As described above, the characteristics of the low-pass filter are appropriately designed according to the required S / N of the output signal, signal responsiveness, and the like. In the short gate time count method, the circuit scale can be kept small, so that multi-channeling is easy. By using an analog low-pass filter, there is an advantage that an analog output can be handled.

  Although the short gate time count method has the above-described advantages, as a result of various experiments, the short gate time count method depends on the combination of the frequency of the signal under measurement (pulse train signal) output from the signal source 10 and the sampling frequency of the short gate time counter 20. It was found that noise (noise) may occur (level increase). Noise generated in the short gate time counting method will be described with reference to FIGS.

  First, FIG. 8 is a block diagram showing a configuration of an experimental apparatus for experimenting generation of pattern noise. The pulse generator 10 is used as a signal source, and the frequency of the signal under measurement is variously changed. The sampling frequency of the short gate counter unit 20 is 100 Hz, and the low-pass filter unit 30 is a three-stage moving average filter (30 taps).

  FIG. 9 is a graph showing the pattern noise level with respect to the ratio between the frequency to be measured and the sampling frequency (operating point parameters 0 to 0.5). The pattern noise level is shown as a relative value (arbitrary unit) with a maximum value of 1.

The operating point parameter is used for the purpose of grasping the characteristics, and is defined as follows.
Operating point parameter = measured frequency / sampling frequency-Int (measured frequency / sampling frequency)

  Here, Int (c) is a function that returns the integer part of c. It can be seen from the definition formula that the operating point parameter takes a value between 0 and 1. The level (intensity) of the pattern noise is a complex function of the operating point parameter and has symmetry at the operating point 0.5. That is, the pattern noise level intensity at the operating point 0.5-d has the property of being equal to the pattern noise intensity at the operating point 0.5 + d (0 <d ≦ 0.5). Therefore, in FIG. 9, the relationship between the noise intensity and the operating point is shown in the range of operating points 0 to 0.5.

  FIG. 10 shows a graph when the measured frequency is 501.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.01. In the figure, the horizontal axis represents time, the vertical axis represents frequency, the solid line represents the short gate time count value, the short dotted line represents the frequency to be measured, and the long dotted line represents the output of the low-pass filter unit 30 (the same applies to FIG. 18 below). is there.). Although the measured frequency is a constant value, it can be seen that the output of the low-pass filter unit 30 has a frequency change periodically (a constant interval in time) and pattern noise is generated.

  Similarly, FIG. 11 shows a graph when the measured frequency is 503.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.03. The output of the low-pass filter unit 30 has a continuous frequency fluctuation, and pattern noise is continuously generated.

  FIG. 12 shows a graph when the measured frequency is 505.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.05. Pattern noise is continuously generated in the output of the low-pass filter unit 30, but the fluctuation range is smaller than that in the case of the operating point parameter 0.03.

  FIG. 13 shows a graph when the measured frequency is 510.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.10. The output of the low-pass filter unit 30 is the same as the measured frequency, and no pattern noise is generated.

  FIG. 14 shows a graph when the measured frequency is 550.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.50. The output of the low-pass filter unit 30 is the same as the measured frequency, and no pattern noise is generated.

  FIG. 15 shows a graph when the measured frequency is 549.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.49. It can be seen that a frequency change periodically appears in the output of the low-pass filter unit 30 to generate pattern noise.

  FIG. 16 shows a graph when the measured frequency is 547.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.47. A small frequency variation is seen in the output of the low-pass filter unit 30, and it can be seen that pattern noise exists.

  FIG. 17 shows a graph when the measured frequency is 534.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.34. Periodic frequency fluctuations are seen in the output of the low-pass filter unit 30, and it can be seen that pattern noise exists.

  FIG. 18 shows a graph in the case where the measured frequency is 566.00 Hz, the sampling frequency is 100 Hz, and the operating point parameter is 0.66 (corresponding to 0.34). Periodic frequency fluctuations are seen in the output of the low-pass filter unit 30, and it can be seen that pattern noise exists. Compared with the case of FIG. 17 (operating point parameter 0.34), the frequency fluctuation width is the same, but the tendency of increase / decrease in frequency fluctuation is reversed.

  FIG. 19 is obtained by adding pattern noise levels corresponding to the operating point parameters shown in FIGS. 10 to 18 to the graph of FIG.

  In the group of operating point parameters 0.01, 0.03, and 0.05, which is a neighborhood value of the operating point parameter 0.0 (= corresponding to 1.0), the pattern noise level becomes closer to the operating point parameter 0.0. It has become big.

  In FIG. 19, although not clear on the graph display, a position 1.0 (= 1/1 /) on the horizontal axis where the operating point parameter is represented by a simple rational number (for example, 1/1 to 1/10). 1), 0.5 (= 1/2), 0.33 (= 1/3), 0.25 (= 1/4), 0.2 (= 1/5), 0.66 (...) 2/3), 0.1 (= 1/10),..., The pattern noise level is zero. In the example shown in FIG. 13 and FIG. 14, the operating point parameter matches a simple rational value (1/10, 1/2), so that pattern noise does not occur.

  With the operating point parameters 0.49 (see FIG. 15) and 0.47 (see FIG. 16) in the vicinity of the operating point parameter 0.5 (off from a simple rational number), the noise level increases. Compared to the vicinity of 0, the pattern noise intensity is small.

  Note that the operating point parameter 0.34 (see FIG. 17) and the operating point parameter 0.66 (FIG. 18) have a symmetrical positional relationship with respect to the operating point parameter dependence of the pattern noise level on the basis of 0.50. .

  As described above, by defining the ratio between the frequency to be measured and the sampling frequency as the operating point parameter, the pattern resulting from the combination of the frequency to be measured and the sampling frequency in the noise level characteristic in the range of the operating point parameter 0-0.5. It is possible to grasp the noise level.

  According to the above results, by appropriately selecting or setting the value of the operating point parameter, specifically, by avoiding the combination of the measured frequency and the sampling frequency where the operating point parameter is close to a simple rational number. Pattern noise can be suppressed.

  Next, a frequency measurement apparatus using the short gate time count method with reduced pattern noise will be described.

  To adjust the operating point parameter: (1) Adjust the frequency of the signal under measurement. (2) Change the frequency of the signal under measurement apparently. (3) The sampling frequency can be adjusted.

  For (1) above, the oscillator frequency is adjusted (f). Specifically, adjustment of the circuit constant of the oscillator and adjustment of the applied voltage of the oscillation circuit are applicable. For (2), a frequency divider / multiplier is placed in front of the counter unit. For (3), the frequency of the clock signal of the short gate time count unit is adjusted.

  (Example 1)

  FIG. 20 shows a first embodiment of the frequency measuring apparatus according to the present invention. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

  In this embodiment, the frequency of the signal under measurement output from the signal source 10 is changed from 30,026,502 Hz to 30,026,110 Hz, and the sampling frequency of the short gate time counter unit 20 is set to 1000 Hz. Thereby, the operating point parameter of the gate time counter unit 20 is set from about 0.50 to about 0.11. The low-pass filter 30 includes a three-stage moving average filter (2400 taps).

  FIG. 21 shows a configuration example of the crystal oscillator of the signal source 10, which is a one-stage inverter oscillation circuit. In this circuit, a feedback resistor Rf is connected between the input and output terminals of the first inverter. A series circuit of a crystal resonator and resistors Rx and Rd is connected between the input and output terminals. A capacitor Cg is connected between the input terminal of the first inverter and the ground, and a capacitor Cd is connected between the connection point of the resistors Rx and Rd and the ground. The output terminal of the first inverter is connected to the input terminal of the second inverter as a buffer amplifier, and an oscillator output is obtained from the output terminal of the second inverter.

  Of these circuit components, the oscillation frequency can be adjusted by adjusting the circuit constants of the resistors Rf, Rd, Rx, capacitors Cg, Cd, and circuit voltage. In this embodiment, the oscillation frequency is changed by adjusting a circuit voltage that can be easily controlled from the outside, but is not limited thereto.

  FIG. 22 shows an output change example of the low-pass filter 30 when water vapor is adsorbed and desorbed from the crystal resonator. The circuit voltage of the oscillator is 5 [V] and oscillates at 30,026,502 Hz before the operation parameter adjustment. The sampling frequency of the short gate counter is 1000 Hz, and the operating point parameter is 0.50 (more accurately, it is 0.502 and a value close to 0.50). Since a large pattern noise is generated, the low-pass filter 30 uses a three-stage moving average filter (2400 taps) in order to cancel (suppress) this.

  FIG. 23 shows an experiment of water vapor adsorption / desorption similar to FIG. 22 with the operating point parameter set to around 0.11. The circuit voltage of the oscillator is lowered to 4.55 [V] and is oscillated at 30,026,110 Hz. The sampling frequency of the short gate counter is 1000 Hz, and the operating point parameter is 0.11. The low-pass filter 30 is a three-stage moving average filter (number of taps 2400). Pattern noise is satisfactorily suppressed and the SN ratio is improved.

  FIG. 24 is similar to the case of FIG. 23, the operating point parameter is set near 0.11, only the low-pass filter 30 is changed to a two-stage moving average filter (240 taps), and water vapor adsorption / desorption is performed. This is an experiment. While suppressing the S / N ratio to be equal to or less than the example of FIG. 22 (operating point parameter 0.50), the responsiveness can be increased 10 times (the number of taps is 1/10).

  FIG. 25 is a comparative example with the case of FIG. 24, in which the operating point parameter is set near 0.50, the low-pass filter 30 is a two-stage moving average filter (240 taps), and similarly to the case of FIG. This is an experiment of water vapor adsorption / desorption. It can be seen that the influence of the pattern noise is large, and the two-stage moving average filter (number of taps 240) is not used without adjusting the operating point parameter.

  (Example 2)

  Next, the noise reduction effect due to the increase of the noise level and the correction of the operating point parameter due to the time-dependent change of the crystal oscillator will be described.

  In order to suppress a change with time of the oscillation frequency of the crystal oscillator, an aging process may be applied to the vibrator (dielectric material) in advance.

  FIG. 26 shows a low-pass filter 30 after aging processing is applied to a crystal resonator used in a frequency measuring apparatus (operating point parameter 0.11, two-stage moving average filter (240 taps)) having the characteristics shown in FIG. An output characteristic example is shown. In the aging process, the oscillation circuit voltage is raised to 7 [V] and the operation is performed for a predetermined time in the overvoltage driving state. Thereafter, when the oscillation circuit voltage was returned to 4.55 [V], the oscillation frequency changed from 30,026,110 Hz before aging to 30,026,145 Hz. The operating point parameter is shifted from about 0.11 to about 0.145 by the aging process. For this reason, as shown in FIG. 26, the influence of the pattern noise appears remarkably in the output of the frequency measuring device (the output of the low-pass filter) after the aging process of the crystal resonator.

  FIG. 27 shows an example in which the value of the resistance Rf of the oscillation circuit constant is adjusted in order to cope with the generation of pattern noise after the aging process. When the oscillation frequency was set to 30,026,035 Hz (operating point parameter 0.035), pattern noise was suppressed.

  Similarly, FIG. 28 shows an example in which the oscillation circuit voltage is adjusted (not the value of the resistance Rf of the oscillation circuit constant) in order to cope with the generation of pattern noise after the aging process. When the voltage was set to 4.70 [V] and the oscillation frequency was set to 30,026,298 Hz (operating point parameter 0.298), pattern noise was suppressed.

  By selecting the ratio of the oscillation frequency and sampling frequency of the signal under measurement so that the operating point parameter value (see FIG. 19) has a low pattern noise level, the pattern in the frequency detection output in the short gate time count method is selected. The noise level can be suppressed and the SN ratio of the output signal can be improved.

  (Example 3)

  FIG. 29 is a block diagram illustrating an example of a frequency measurement device having a function of adjusting operating point parameters. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

  In the frequency measuring apparatus of this embodiment, in addition to the signal source 10, the short gate time counter unit 20, and the low-pass filter 30 described above, an operating point calculation unit 70, a (frequency) adjustment unit 50, and a storage unit 60 are further provided. It has. The oscillation frequency fo of the signal source 10 is configured to be controllable from the outside. For example, as described above, the circuit constants (resistance value, capacitance, oscillation circuit voltage) of the crystal oscillation circuit can be set from the outside. Further, adjustment by a so-called voltage controlled oscillator (VCO), a configuration in which a multiplication amount of a phase locked loop type PLL oscillator, or the like may be adopted. The sampling frequency fs of the short gate time counter unit 20 is a fixed frequency.

  The operating point calculation unit 70 calculates the operating point parameter = fo / fs−Int (fo / fs) from the measurement frequency fo of the signal under measurement based on the count value output from the short gate time counter unit 20 and the sampling frequency fs. Perform the following calculation. The calculation result is output to the adjustment unit 50.

  The adjustment unit 50 has a function of adjusting the frequency fo of the signal under measurement of the signal source 10 with reference to the operating point parameter held in the storage unit 60 in accordance with an adjustment command issued from a control computer (not shown) or an operator. Prepare. A function of issuing an adjustment command to itself by interrupting at certain intervals may be provided.

  The storage unit 60 stores one or a plurality of operating point parameter ranges, frequency information, and the like in which the pattern noise level is below the reference. The operating point parameter range in which the pattern noise level is below the reference value is 0.41 to 0.44 or the like. Further, one or a plurality of frequencies of the signal under measurement fo having a pattern noise level equal to or lower than a reference value may be stored in the storage unit.

  The adjustment unit 50 selects the operating point parameter or the oscillator frequency fo corresponding to the operating point parameter in accordance with the adjustment command, and sets the oscillator frequency fo of the signal source 10. As a result, a frequency measuring device with a suppressed pattern noise level can be obtained.

  Although not shown, a pilot signal fo having a known frequency is input to the short gate time counter 10 for comparison, and by observing the output of the low-pass filter 30, the pattern noise level for the oscillator frequency fo can be obtained. By sweeping the frequency, the operating point parameter versus pattern noise characteristic (corresponding to FIG. 19) can be easily measured.

  According to the configuration of this embodiment, the operating point parameter can be adjusted with a relatively simple configuration.

  Example 4

  FIG. 30 is a block diagram illustrating another example of a frequency measurement device having a function of adjusting operating point parameters. In the figure, parts corresponding to those in FIGS. 1 and 29 are denoted by the same reference numerals, and description thereof will be omitted.

  In addition to the signal source 10, the short gate time counter unit 20, and the low-pass filter 30, the frequency measurement device of this embodiment further includes an operating point calculation unit 70, an adjustment unit 50, and a storage unit 60. Yes. The oscillation frequency fo of the signal source 10 and the sampling frequency of the short gate time counter unit 20 are configured to be externally controllable. For example, as described above, the circuit constants (resistance value, capacitance, oscillation circuit voltage) of the crystal oscillation circuit can be set from the outside. For example, adjustment by a so-called voltage controlled oscillator (VCO) or changing the multiplication amount of a phase locked loop type PLL oscillator may be used. The clock frequency of an internal sampling clock circuit (not shown) of the short gate time counter unit 20 can be set from the outside.

  The operating point calculation unit 70 calculates the operating point parameter = fo / fs−Int (fo / fs) from the measurement frequency fo of the signal under measurement based on the count value output from the short gate time counter unit 20 and the sampling frequency fs. Perform the following calculation. The calculation result is output to the adjustment unit 50.

  The adjusting unit 50 has a function of adjusting the frequency fo of the signal under measurement of the signal source 10 and the sampling frequency fs of the short gate time counter 20 with reference to the operating point parameter from the operating point calculating unit 70 according to the command signal. Prepare. The storage unit 60 stores one or more operating point parameter ranges and frequency information whose pattern noise level is below the reference. The stored data stores, for example, one or a plurality of operating point parameter ranges in which the pattern noise level is a reference value or less. Further, one or a plurality of combinations of the frequency of the signal under measurement whose pattern noise level is below the reference value and the sampling frequency may be stored in the storage unit 60.

  For example, the adjustment unit 50 selects the sampling frequency fs first, and determines the frequency fo of the signal under measurement based on the selected operating point parameter value. When the frequency fo of the signal under measurement is selected first, the sampling frequency fs is determined based on the selected operating point parameter value. More specifically, the adjustment unit 50 adjusts circuit constants to be controlled in accordance with the frequency to be set. Such an operation may be repeated.

  Also in this embodiment, a voltage controlled oscillator (VCO) can be used as an oscillator, or a PLL (phase locked loop) circuit can be used in combination.

  According to the configuration of the present embodiment, since the frequencies fo and fs of both the signal source 10 and the short gate time counter unit 20 can be adjusted, the pattern noise can be suppressed by combining various frequencies fo and fs. it can.

  (Example 5)

  FIG. 31 is a block diagram illustrating another example of a frequency measurement device having a function of adjusting operating point parameters. In the figure, parts corresponding to those in FIG. 30 are denoted by the same reference numerals, and description thereof will be omitted.

  In this example, a frequency division / multiplication unit 40 is further provided between the signal source 10 and the short gate time counter unit 20. The frequency divider / multiplier 40 may be a frequency divider, a frequency multiplier, or a combination of a frequency divider and a frequency multiplier. The frequency divider / multiplier 40 can change the apparent frequency fo from the short gate time counter 20 to mfo (m is a frequency conversion magnification and is a rational number determined by the parameters of the frequency divider and the multiplier). Other configurations are the same as those shown in FIG.

  Also in this embodiment, the storage unit 60 stores one or more operating point parameter ranges and frequency information whose pattern noise level is below the reference. The stored data stores, for example, one or a plurality of operating point parameter ranges in which the pattern noise level is a reference value or less. Moreover, you may memorize | store in the memory | storage part one or several combination of the frequency of the to-be-measured signal in which a pattern noise level becomes below a reference value, and a sampling frequency.

  The operating point calculation unit 70 calculates the operating point parameter = mfo / fs−Int (mfo / fs) from the measurement frequency fo of the signal under measurement based on the count value output from the short gate time counter unit 20 and the sampling frequency fs. Perform the following calculation. The calculation result is output to the adjustment unit 50. In this embodiment, the measurement frequency fo takes into account the frequency conversion magnification m.

  The adjustment unit 50 receives the frequency fo, the frequency conversion magnification m, and the sampling frequency fs of the signal under measurement so that a desired operating point parameter value stored in advance in the storage unit 60 can be obtained according to a command supplied from the outside. Is selected. By appropriately combining these parameters, it is possible to set the circuit state more accurately to a desired operating point parameter value. Thereby, pattern noise can be better suppressed.

  In this configuration, the adjustment unit 50 may adjust a part of the frequency fo, the frequency conversion magnification m, and the sampling frequency fs of the signal under measurement (see FIGS. 29 and 30). Thereby, the adjustment becomes easier.

  (Example 6)

  FIG. 32 shows another embodiment. In the figure, parts corresponding to those in FIG. 31 are denoted by the same reference numerals, and description thereof will be omitted.

  In this embodiment, in the circuit configuration as shown in FIG. 29 to FIG. 31, the function of setting the circuit state (measured signal frequency fo, frequency conversion magnification m, sampling frequency fs) so as to be a desired operating point parameter. In addition, it has a function of sequentially detecting and determining operating point parameters in the output of the frequency measuring device. Thereby, it is possible to automatically adjust the frequency measuring device so as to be a combination of the measured signal frequency fo, the frequency conversion magnification m, and the sampling frequency fs, in which pattern noise is suppressed. The frequency divider / multiplier 40 is not an essential component in this embodiment.

  For this reason, in this embodiment, in addition to the previous embodiment, a control unit 80 for controlling the operation of each unit is provided. The detected operating point parameter value is sequentially compared with the data in the storage unit 60. Each function (indicated by a dotted line in FIG. 32) of the adjustment unit 50, the storage unit 60, the operating point calculation unit 70, and the control unit 80 is formed by a computer system.

  Next, an operation example of the frequency measuring apparatus according to the present embodiment will be described.

  When receiving an operating point parameter extraction command from a computer program or an operator, the control unit 80 causes the signal source 10, the frequency divider / multiplier 40, and the short gate time counter unit 20 to set initial values fo, m, and fs, respectively. The adjustment unit 50 is instructed. The m of the frequency divider / multiplier 40 apparently changes the frequency fo. Note that m is 1 when the frequency divider / multiplier 40 is not provided.

  The control unit 80 refers to the data in the storage unit 60, obtains an operating point parameter at which the pattern noise is equal to or lower than the reference level, selects fo (and m) corresponding to the sampling frequency fs, and sends the adjustment unit 50 to each unit Set parameters. As a result, a frequency measurement device that avoids pattern noise and performs frequency measurement by the short gate time count method can be obtained.

  As described above, in the embodiment of the present invention, the short gate time count frequency measuring device has a function of adjusting the operating point (ratio of the signal to be measured and the sampling frequency), so that pattern noise can be suppressed. , The SN ratio is improved.

  In addition, by suppressing the pattern noise, the design margin increases, so the number of taps of the low-pass filter can be reduced, and high-speed response can be realized. (High-speed response and decrease in the number of filter taps reduce the memory used. Means.)

  In addition, the adjustment function can suppress pattern noise that occurs when the operating point parameter is shifted. Since the performance is significantly improved at the same sampling frequency, the sampling frequency can be lowered and the power consumption is suppressed when the required performance is low.

  In addition, according to the embodiment of the present invention, a short gate time count frequency measuring device in which the operating point parameter is adjusted in advance is provided, so that it is not necessary to adjust the operating point parameter, so that the burden on the user is reduced. Can be good. Further, it is possible to provide a short gate time count type frequency frequency measuring device counter having a function of easy readjustment. In addition to reducing the burden on the user, the product life can be extended by simple adjustment.

  Since the frequency measuring apparatus of this system has a small circuit scale and is easy to mount, the device can be reduced in size, weight, and cost. For example, it is convenient to use various sensors using quartz for miniaturization / high resolution, AD conversion elements, and the like. Moreover, it is convenient to use for integration and platformization of various sensors using crystal. Moreover, it is convenient to use for a odor sensor, a gas sensor, a transducer array for a biosensor, or the like.

It is explanatory drawing explaining the structure of the frequency measurement apparatus of a short gate time count system. It is explanatory drawing explaining the structural example of a short gate time counter part. It is explanatory drawing explaining the other structural example of a short gate time counter part. It is a circuit diagram explaining the structural example of a low-pass filter (analog). It is a block diagram explaining the structural example of a low-pass filter (digital). It is explanatory drawing explaining the example of an output of a short gate time counter part. It is explanatory drawing explaining the example of an output of a low-pass filter. It is explanatory drawing explaining the measurement experiment of pattern noise. It is explanatory drawing explaining the example of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph explaining the example of a measurement of pattern noise. It is a graph which shows the relationship between an operating point parameter and a pattern noise level. It is explanatory drawing explaining the example which adjusted the frequency measuring apparatus of the short gate time count system with the operating point parameter. It is a circuit diagram explaining the example of the oscillation circuit used for a signal source. It is a graph which shows the example of an output of the low-pass filter before adjusting an operating point parameter. It is a graph which shows the output example of the low-pass filter after adjusting an operating point parameter. It is a graph which shows the other output example of the low-pass filter after adjusting an operating point parameter. It is a graph which shows the example of an output of a comparative example. It is a graph which shows the example where pattern noise came to generate | occur | produce with a time-dependent change. It is a graph which shows the example of an output of a low-pass filter after an operating point parameter readjustment. It is a graph which shows the other output example of the low-pass filter after an operating point parameter readjustment. It is explanatory drawing explaining the 1st example of a frequency measurement apparatus provided with an operating point parameter adjustment means. It is explanatory drawing explaining the 2nd example of a frequency measurement apparatus provided with an operating point parameter adjustment means. It is explanatory drawing explaining the 3rd example of a frequency measurement apparatus provided with an operating point parameter adjustment means. It is explanatory drawing explaining the 4th example of a frequency measurement apparatus provided with an operating point parameter adjustment means.

Explanation of symbols

10 signal source, 20 short gate time counter unit, 30 low-pass filter, 450 frequency divider / multiplier, 50 adjustment unit, 60 storage unit, 70 operating point calculation unit, 80 control unit

Claims (9)

A signal source for generating a signal under measurement in the form of a pulse train;
A gate time counter unit that continuously counts the signal under measurement at a sampling frequency of a short gate time and outputs a series of count values corresponding to the frequency of the signal under measurement;
A low-pass filter that removes a first frequency component from the series of count values and outputs a level signal corresponding to the frequency of the signal under measurement,
The frequency of the signal under measurement and the sampling frequency are selected based on a distribution characteristic of a frequency ratio versus a noise level between the frequency of the signal under measurement and the sampling frequency, which is obtained in advance. A frequency measurement device that reduces the noise level in the output.   The combination of the frequency of the signal under measurement and the sampling frequency is defined by an operating point parameter that is a value between 0 and 1 in the ratio a / b between the frequency a of the signal under measurement and the sampling frequency b. 2. The frequency measurement according to claim 1, wherein the frequency of the signal under measurement and the sampling frequency are set so that the value of the operating point parameter does not become a value near a predetermined rational number that increases a noise level. apparatus.   The frequency measurement apparatus according to claim 2, wherein the predetermined rational number includes any one of 1/1, 1/2, 1/3, 1/4, and 1/5.   The neighborhood value of the predetermined rational number is a value of the operating point parameter when a pattern noise level appearing in an output of the low-pass filter exceeds a reference value when the operating point parameter is variously set. Or the frequency measuring apparatus of 3. And a frequency adjustment unit for adjusting the frequency of the signal under measurement and / or the sampling frequency.
5. The frequency adjustment unit according to claim 2, wherein the frequency adjustment unit sets the frequency of the signal under measurement and the sampling frequency so that the value of the operating point parameter is separated from a value near a predetermined rational number. Frequency measuring device. Furthermore,
A frequency adjustment unit for adjusting the frequency of the signal under measurement and / or the sampling frequency;
An operating point calculation unit for calculating an operating point parameter from the output of the short gate time counter unit;
A storage unit for storing a range of operating point parameters excluding the vicinity of the predetermined rational number;
A control unit for controlling each unit,
The operating point calculation unit calculates the operating point parameter by obtaining an average value from a sequence of outputs of the short gate time counter unit within a certain section,
The control unit receives the operating point parameter calculated from the operating point calculating unit, and passes through the frequency adjusting unit so that the operating point parameter is within the range of the operating point parameter stored in the storage unit. The frequency measurement device according to claim 2, having a function of changing a frequency of a measurement signal or the sampling frequency. Furthermore,
An operating point calculation unit for calculating an operating point parameter from the output of the short gate time counter unit;
A storage unit for storing a range of operating point parameters excluding the vicinity of the predetermined rational number,
The frequency adjustment unit recalculates the frequency of the signal under measurement and the sampling frequency based on the operating point parameter when the operating point parameter calculated by the operating point calculating unit is in a range near the predetermined rational number. The frequency measuring device according to claim 5, which is adjusted.   The frequency adjustment unit includes at least one of a circuit constant including a circuit voltage of an oscillation circuit of the signal source, a frequency divider that divides the output of the signal source, a multiplier that multiplies the output of the signal source, and the sampling frequency. The frequency measuring device according to claim 5, wherein any one of the frequency measuring devices is adjusted.   A device using the frequency measuring device according to claim 1.

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