JP6862901B2 - Frequency ratio measuring device and physical quantity sensor - Google Patents

Description

The present invention relates to a frequency ratio measuring device and a physical quantity sensor.

A frequency delta-sigma-modulated signal output device that generates a delta-sigma-modulated signal, which is a signal corresponding to the ratio of the frequency of a reference signal (reference clock) to the frequency of a signal to be measured, is known.
The frequency delta sigma modulation signal output device has a frequency delta sigma modulator (hereinafter referred to as "FDSM (Frequency Delta Sigma Modulator)"), and the frequency delta sigma modulation of the signal to be measured using the reference signal by the FDSM. Then, a delta-sigma modulated signal is generated and output.

In this frequency delta-sigma modulation signal output device, periodic quantization noise called idle tone is generated. That is, the output signal of the FDSM is a signal in which an idle tone is superimposed on the baseband signal component of the signal to be measured.
Patent Document 1 discloses a frequency measuring device (frequency ratio measuring device) capable of suppressing idle tones by switching and using two FDSMs having different operating frequencies.

Japanese Unexamined Patent Publication No. 2011-89896

In the apparatus described in Patent Document 1, in order to drive at the optimum operating point, it is necessary to store information on the operating point at which the idle tone becomes large in advance and refer to the information sequentially. Moreover, when the operating point changes suddenly, it is difficult to follow it.

An object of the present invention is to provide a frequency ratio measuring device and a physical quantity sensor capable of easily and accurately suppressing the influence of quantization noise such as idle tone.

The present invention has been made to solve at least a part of the above-mentioned problems, and can be realized as the following forms or application examples.

The frequency ratio measuring device of the present invention is a frequency ratio measuring device that measures the frequency ratio between the measured signal and the reference signal based on the measured signal and a plurality of reference signals.
A plurality of frequencies to which the reference signal and the measured signal are input and one of the input reference signal and the measured signal is used for frequency delta sigma modulation of the other to generate a frequency delta sigma modulated signal. Delta sigma modulator and
A statistical processing unit that performs statistical processing using a plurality of data represented by the plurality of frequency delta-sigma modulated signals is provided.
The reference signals input to the plurality of frequency delta-sigma modulation units are characterized in that they have different frequencies from each other.
According to the present invention, the influence of quantization noise such as idle tone can be easily and accurately suppressed, and the measurement accuracy can be improved.

In the frequency ratio measuring device of the present invention, it is preferable that the statistical processing unit selects and outputs a median value from a plurality of data represented by the plurality of frequency delta-sigma modulated signals.
As a result, data that is greatly affected by idle tones can be excluded, data that is less affected by idle tones is expected to be selected, and the effects of quantization noise such as idle tones can be suppressed more accurately. The measurement accuracy can be improved.

In the frequency ratio measuring device of the present invention, the statistical processing unit refers to the data to which the statistical processing unit belongs from a combination of the data obtained by removing at least one from the plurality of data represented by the plurality of frequency delta-sigma modulated signals. It is preferable to select the set having the smallest variance and output the value obtained based on the data belonging to the set.
A group to which data having a large influence of idle tone belongs has a large variance of data belonging to the group. Therefore, by selecting the pair having the smallest variance, it is possible to exclude the pair to which the data having a large influence of the idle tone belongs, and it is expected that the pair to which only the data having a small influence of the idle tone belongs is selected. As a result, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved.

In the frequency ratio measuring apparatus of the present invention, it is preferable that the statistical processing unit obtains and outputs an average value of the data belonging to the set.
As a result, even if the set includes data having a large influence of the idle tone, it is possible to avoid selecting the data having a large influence of the idle tone alone, and more accurately the idle tone and the like can be obtained. The influence of quantization noise can be suppressed, and measurement accuracy can be improved.

In the frequency ratio measuring device of the present invention, the statistical processing unit compares the variance of the data belonging to the set with the threshold value, and if the variance is smaller than the threshold value, the average value of the data belonging to the set. When the variance is equal to or greater than the threshold value, it is preferable to select and output the median value from the plurality of data.
When the variance is smaller than the threshold, the pair with the smallest selected variance is likely to belong to only the data that are less affected by the idle tone. Therefore, by obtaining and outputting the average value of the data belonging to the set having the minimum variance, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved. it can.
Further, when the variance is equal to or more than the threshold value, it corresponds to the case where the set having the smallest selected variance cannot exclude the data having a large influence of the idle tone. Therefore, by selecting and outputting the median value from all the original data, it is expected that the data that is greatly affected by the idle tone can be excluded, and the data that is less affected by the idle tone is selected. The influence of quantization noise such as idle tone can be accurately suppressed, and the measurement accuracy can be improved.

In the frequency ratio measuring device of the present invention, the statistical processing unit compares the variance of the data belonging to the set with the threshold value, and if the variance is smaller than the threshold value, the average value of the data belonging to the set. When the variance is equal to or greater than the threshold value, it is preferable to select and output the median value from the data belonging to the set.
When the variance is smaller than the threshold, the pair with the smallest selected variance is likely to belong to only the data that are less affected by the idle tone. Therefore, by obtaining and outputting the average value of the data belonging to the set having the minimum variance, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved. it can.
Further, when the variance is equal to or more than the threshold value, it corresponds to the case where the set having the smallest selected variance cannot exclude the data having a large influence of the idle tone. Therefore, by selecting and outputting the median value from the data belonging to the set with the smallest variance, the data with a large influence of the idle tone can be excluded, and the data with a small influence of the idle tone is selected. Is expected, and the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved.

The frequency ratio measuring device of the present invention is a frequency ratio measuring device that measures the frequency ratio between the measured signal and the reference signal based on the measured signal and a plurality of reference signals.
A plurality of frequencies to which the reference signal and the measured signal are input and one of the input reference signal and the measured signal is used for frequency delta sigma modulation of the other to generate a frequency delta sigma modulated signal. Delta sigma modulator and
A selection unit for selecting any one of a plurality of data represented by the plurality of frequency delta-sigma modulated signals is provided.
The reference signals input to the plurality of frequency delta-sigma modulation units are characterized in that they have different frequencies from each other.
According to the present invention, the influence of quantization noise such as idle tone can be easily and accurately suppressed, and the measurement accuracy can be improved.

In the frequency ratio measuring device of the present invention, it is preferable that the selection unit selects and outputs a median value from a plurality of data represented by the plurality of frequency delta-sigma modulation signals.
As a result, data that is greatly affected by idle tones can be excluded, data that is less affected by idle tones is expected to be selected, and the effects of quantization noise such as idle tones can be suppressed more accurately. The measurement accuracy can be improved.

In the frequency ratio measuring apparatus of the present invention, it is preferable to have a low-pass filter on the output side of the frequency delta-sigma modulation unit.
Thereby, the measurement accuracy can be further improved.

In the frequency ratio measuring device of the present invention, it is preferable to have a weighting unit for weighting the signal on the output side of the frequency delta-sigma modulation unit.
As a result, the measurement can be performed accurately.

The frequency ratio measuring device of the present invention preferably has a frequency dividing portion that divides a common signal to generate the plurality of reference signals.
Thereby, a plurality of reference signals can be generated from one clock signal (signal). As a result, the number of reference signal generators can be reduced and the power consumption can be reduced as compared with the case where a plurality of reference signal generators are used.

The physical quantity sensor of the present invention includes a detection unit that detects a physical quantity and
It is characterized by including the frequency ratio measuring device of the present invention in which the signal to be measured output from the detection unit is input.
According to the present invention, the influence of quantization noise such as idle tone can be easily and accurately suppressed, and the measurement accuracy can be improved.

It is a block diagram which shows 1st Embodiment of the frequency ratio measuring apparatus of this invention. It is a block diagram which shows the structural example of the frequency delta sigma modulation part of the frequency ratio measuring apparatus shown in FIG. It is a block diagram which shows the structural example of the frequency delta sigma modulation part of the frequency ratio measuring apparatus shown in FIG. It is a block diagram which shows the 2nd Embodiment of the frequency ratio measuring apparatus of this invention. It is a block diagram which shows the 3rd Embodiment of the frequency ratio measuring apparatus of this invention. It is a block diagram which shows the 4th Embodiment of the frequency ratio measuring apparatus of this invention. It is a figure which shows the internal structure of the detection part in embodiment of the acceleration sensor which is an example of the physical quantity sensor of this invention. FIG. 5 is a cross-sectional view taken along the line AA in FIG. It is a graph which shows the frequency (true value) of the signal to be measured in an experiment. It is a graph which shows the experimental result. It is a graph which shows the experimental result. It is a graph which shows the experimental result. It is a graph which shows the experimental result. It is a graph which shows the experimental result. It is a graph which shows the experimental result.

Hereinafter, the frequency ratio measuring device and the physical quantity sensor of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a first embodiment of the frequency ratio measuring device of the present invention. FIG. 2 is a block diagram showing a configuration example of a frequency delta sigma modulation unit of the frequency ratio measuring device shown in FIG. FIG. 3 is a block diagram showing a configuration example of a frequency delta sigma modulation unit of the frequency ratio measuring device shown in FIG.
In the following description, the case where the signal level is "Low" is also referred to as "0", and the case where the signal level is "High" is also referred to as "1".
First, an outline of the frequency ratio measuring device 1 will be described, and then a specific description will be given.

The frequency ratio measuring device 1 shown in FIG. 1 is a device that measures the frequency ratio of the measured signal and the reference signal based on the measured signal and a plurality of reference signals. The frequency ratio measuring device 1 receives a reference signal and a signal to be measured, and uses one of the input reference signal and the signal to be measured for frequency delta sigma modulation of the other to generate a frequency delta sigma modulated signal. It includes a plurality of frequency delta sigma modulation units 2 and a statistical processing unit 5 that performs statistical processing using a plurality of data represented by a plurality of frequency delta sigma modulation signals. The reference signals input to the plurality of frequency delta-sigma modulation units 2 have different frequencies from each other.
According to this frequency ratio measuring device 1, the influence of quantization noise such as idle tone can be easily and accurately suppressed, and the measurement accuracy can be improved.

Further, the statistical processing unit 5 selects and outputs a median value from a plurality of data represented by the plurality of frequency delta-sigma modulated signals.
As a result, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved. Hereinafter, a specific description will be given.

The frequency ratio measuring device 1 shown in FIG. 1 generates a value (or the value) corresponding to the ratio (frequency ratio) between the frequency of the reference signal (reference clock) Fs whose frequency is known and the frequency of the signal to be measured Fx. It is a device (circuit) that generates a count value (a signal indicating the count value) which is a value used for the purpose. That is, the measured value (output) of the frequency ratio measuring device 1 is the count value. Further, in the frequency ratio measuring device 1, both the direct counting method and the reciprocal counting method can be adopted. In the following, a direct counting method will be described as an example.

As shown in FIG. 1, the frequency ratio measuring device 1 includes a plurality of frequency delta sigma modulators 2 (hereinafter referred to as “FDSM (Frequency Delta Sigma Modulator)”), a plurality of low-pass filters 3 (filters), and a plurality of frequency ratio measuring devices 1. A plurality of scalers 4 which are an example of the weighting unit of the above and a statistical processing unit 5 are provided.

The number of FDSM2 is not particularly limited as long as it is plural, and is appropriately set according to various conditions, but in the present embodiment, it is three. However, in the configuration in which the statistical processing unit 5 selects the median value as in the present embodiment, the number of FDSM2s is preferably 3 or more. Thereby, the measurement accuracy can be improved. The upper limit of the number of FDSM2 is not particularly limited, but the number of FDSM2 is preferably 255 or less, and more preferably 15 or less. This is because the number of bits for handling the integrated value when calculating the average is suppressed to an increase of 4 bits or 8 bits from the number of bits when handling one data, and a multiple of 4 bits is used when handling digital data. This is because it is easy to handle as a unit unit of. Further, if the number of FDSM2s is too large, the circuit configuration becomes large and the power consumption increases.
The number of low-pass filters 3 and scalers 4 is the same as the number of FDSM2, respectively.

Further, in the frequency ratio measuring device 1, the low-pass filter 3 is electrically connected to the output side (second stage) of the FDSM 2 (hereinafter, also simply referred to as “connection”), and the scaler 4 is connected to the output side of the low-pass filter 3. Has been done. Further, three series circuits composed of the FDSM2, the low-pass filter 3 and the scaler 4 are connected in parallel. Then, the statistical processing unit 5 is connected to the output side of each scaler 4.
The order of the low-pass filter 3 and the scaler 4 may be reversed, and the low-pass filter 3 may be connected to the output side of the scaler 4. Further, the low-pass filter 3 may be connected to the output side of the statistical processing unit 5 instead of the position shown in the figure. In this case, the number of low-pass filters 3 can be reduced to one.

Further, the signal to be measured is input to each FDSM2, and the reference signal (reference clock) whose frequency is known is input to each FDSM2. However, the frequencies of the reference signals input to each FDSM2 are different from each other. Specifically, the reference signal CLK1 is input to the first FDSM2, the reference signal CLK2 is input to the second FDSM2, and the reference signal CLK3 is input to the third FDSM2. .. The frequency of the reference signal CLK1 and the frequency of the reference signal CLK2 are different, the frequency of the reference signal CLK1 and the frequency of the reference signal CLK3 are different, and the frequency of the reference signal CLK2 and the frequency of the reference signal CLK3 are different.
The method of generating the reference signal CLK1, the reference signal CLK2, and the reference signal CLK3 is not particularly limited, and for example, a common clock signal (signal) may be divided and generated, or each of them may be generated individually. May be good.

Further, the FDSM2 has a function of frequency-delta-sigma-modulating the signal to be measured based on the reference signal (using the reference signal) and generating a frequency delta-sigma-modulated signal (direct counting method). The reference signal may be frequency-delta-sigma-modulated based on the signal to be measured (using the signal to be measured) (reciprocal counting method).

The FDSM2 includes, for example, an FDSM that outputs an output signal in a bitstream format (hereinafter, also referred to as "FDSM having a bitstream configuration (bitstream type FDSM)"), and an FDSM that outputs an output signal in a datastream format (hereinafter, "" A data stream configuration FDSM (also referred to as a data stream type FDSM)) or the like can be used.
When using an FDSM having a bitstream configuration, other signal processing circuits can be simplified. Further, when the FDSM having a data stream configuration is used, it is possible to cope with a case where the frequency fluctuation is large.

Next, the FDSM2 having a data stream configuration and the FDSM2 having a bitstream configuration will be described. First, the FDSM2 having a data stream configuration will be described.
As shown in FIG. 2, the FDSM2 having a data stream configuration has an up counter 21 that counts the rising edge of the signal to be measured and outputs count data Dc indicating the count value, and count data synchronized with the rising edge of the reference signal. The first latch 22 that latches Dc and outputs the first data D1, the second latch 23 that latches the first data D1 and outputs the second data D2 in synchronization with the rising edge of the reference signal, and the first A subtractor 24 for generating output data OUT by subtracting the second data D2 from the data D1 is provided. The first latch 22 and the second latch 23 are composed of, for example, a D flip-flop circuit or the like.

The FDSM2 in this example is also called a first-order frequency delta-sigma modulator, which latches the count value of the measured signal twice by the reference signal, and uses the rising edge of the reference signal as a trigger to set the count value of the measured signal. Hold sequentially. In this example, it is assumed that the latch operation is performed at the rising edge, but the latch operation may be performed at both the falling edge and the rising / falling edge. Further, the subtractor 24 calculates the difference between the two held count values, and outputs the increment of the count value of the measured signal observed during one cycle of the reference signal with the passage of time without a dead period. When the frequency of the signal to be measured is fx and the frequency of the reference signal is fc, the frequency ratio is fx / fc. The FDSM2 outputs a frequency delta-sigma modulated signal indicating a frequency ratio as a digital signal sequence.
This digital signal string is called a data string / data stream. Further, a digital signal string represented by one bit, which will be described later, is called a bit string / bit stream.

Next, FDSM2 having a bitstream configuration will be described.
As shown in FIG. 3, the FDSM2 having a bit stream configuration synchronizes with the first latch 22 that latches the signal to be measured and outputs the first data d1 in synchronization with the rising edge of the reference signal, and synchronizes with the rising edge of the reference signal. Then, the second latch 23 that latches the first data d1 and outputs the second data d2, and the exclusive logic that calculates the exclusive OR of the first data d1 and the second data d2 to generate the output data OUT. A sum circuit 25 is provided. The first latch 22 and the second latch 23 are composed of, for example, a D flip-flop circuit or the like.

The difference between this FDSM2 and the FDSM2 having the data stream configuration is that in the FDSM2 having the data stream configuration, the count data Dc is held by the first latch 22, and the measured signal observed during one cycle of the reference signal. While the increment of the count data Dc obtained by counting the rising edge of is output as the output data OUT, in this FDSM2, the high or low state of the signal to be measured is held by the first latch 22, and the reference signal becomes a reference signal. It is a point to output the even / oddness of the number of inversions during one cycle transition as output data OUT (0 is output if the number of inversions is even, and 1 is output if the number of inversions is odd).

By the way, since one cycle of the measured signal is composed of two inversion transitions of High and Low, the degree of change of the change of the measured signal with respect to the reference signal on the output data OUT is determined by the FDSM2 of the data stream configuration. It is twice as much as the case where the count value is held in. Therefore, the behavior of the idle tone in the FDSM2 having the bitstream configuration matches the behavior when the signal under test having twice the frequency is input to the FDSM2 in the FDSM2 having the data stream configuration. Regarding the operation of the FDSM2 having a bitstream configuration, the frequency fx of the signal to be measured may be replaced with the frequency 2fx as necessary in consideration of the above-mentioned properties.

Further, the frequency ratio measuring device 1 has a low-pass filter 3 on the output side of the frequency delta-sigma modulation unit 2. Thereby, the measurement accuracy can be further improved.
The low-pass filter 3 is not particularly limited, and examples thereof include a general low-pass filter, a lag lead filter, a lag filter, a moving average filter, and the like.
The low-pass filter 3 cuts off or reduces frequency components above a predetermined cutoff frequency (cutoff frequency). Thereby, the noise component contained in the signal output from FDSM2 can be removed or reduced.

Further, the frequency ratio measuring device 1 has a scaler 4 which is an example of a weighting unit for weighting a signal on the output side of the frequency delta-sigma modulation unit 2, strictly speaking, the output side of the low-pass filter 3. ing. As a result, the measurement can be performed accurately.
The scaler 4 has a function of weighting the signal output from the low-pass filter 3, that is, the frequency delta-sigma modulated signal.
This weighting is performed by multiplying the frequency delta sigma modulated signal, that is, the data represented by the frequency delta sigma modulated signal, and the weighting coefficient (magnification) of the scaler 4.

The weighting coefficient (magnification) of each scaler 4 is k1, k2, and k3, respectively, and the values thereof are appropriately set according to various conditions. In addition, k1, k2, and k3 may be larger than 1, may be 1, and may be smaller than 1, respectively.
Here, in the present embodiment, k1, k2, and k3 are preset so that when the frequency of the signal to be measured changes, the data (frequency ratio) represented by each frequency delta-sigma modulated signal all changes at the same ratio. Has been done. Therefore, the weighting for each frequency delta-sigma modulated signal is performed so that when the frequency of the signal to be measured changes, the frequency ratios represented by each frequency delta-sigma modulated signal all change at the same ratio. The "same ratio" includes not only the exact same ratio but also the case where the ratio differs within the range of 10% or less. Further, the weighting method is not limited to the above method.

In addition, the statistical processing unit 5 has a function of performing statistical processing. The statistical processing unit 5 performs statistical processing using three (plurality) data represented by three (plurality) frequency delta-sigma modulation signals output from the three (plurality) FDSM2s.
In the present embodiment, the statistical processing unit 5 selects (obtains) the median value from the three data and outputs it.
The median is the value located in the center (middle) when a finite number of data are arranged in ascending or descending order. However, when the number of data is an even number, the median value may be the average value of the two data closest to the center, or one of the two data may be selected as the median value. ..

In the present embodiment, since the number of data is three, the statistical processing unit 5 selects the second largest value among the three data, or if the two data have the same value, the value having the same value. And output. This output is a value corresponding to the frequency ratio of the reference signal and the signal to be measured (hereinafter, also referred to as “frequency ratio”), that is, a count value.
As described above, in the frequency ratio measuring device 1, the frequency ratio can be obtained by a simple and small-scale circuit configuration having the statistical processing unit 5 and by a simple statistical process of obtaining the median value.
Further, by obtaining the frequency ratio by selecting the median value, the influence of quantization noise such as idle tone can be suppressed, and the measurement accuracy can be improved.

The reason why the influence of the idle tone can be suppressed will be explained. First, the idle tone has a property that it becomes large when the reference signal is at a predetermined frequency and becomes small at other frequencies in the vicinity of the predetermined frequency. In addition, the idle tone is generated so as to protrude more to the plus side than the true value, or to protrude more to the minus side than the true value, and to occur in the direction (plus side or minus side). Is there?) Depends on the frequency, but it is difficult to know the change in the frequency in advance. Therefore, it is highly likely that one of the maximum value and the minimum value of the three data contains an idle tone having a large influence. By selecting the median value from the three data, it is possible to exclude the data having a large influence of the idle tone, and it is expected that the data having a small influence of the idle tone will be selected.
Further, when the number of data is 5 or more, for example, when the number of data is 5, the idle tone having a large influence on one of the maximum value and the minimum value of the five data is also the same. Is likely to be included. Therefore, by selecting any one of the three data excluding the maximum value and the minimum value, it is expected that the data having a large influence of the idle tone can be excluded. In the present embodiment, by selecting the median, the data having a large influence of the idle tone is excluded, and the probability that the data having a small influence of the idle tone is selected can be increased.

Next, the operation of the frequency ratio measuring device 1 will be described.
As shown in FIG. 1, a signal to be measured and reference signals CLK1, CLK2, and CLK3 are input to each FDSM2 of the frequency ratio measuring device 1. In this case, a common signal to be measured is input to each FDSM2. On the other hand, the frequencies of the reference signals CLK1, CLK2, and CLK3 are different from each other.

First, each FDSM2 performs the predetermined processing described above to generate a frequency delta-sigma modulated signal.
Each frequency delta-sigma modulated signal is subjected to predetermined processing by the corresponding low-pass filter 3, and is output from the corresponding low-pass filter 3.

The frequency delta-sigma modulated signal output from each low-pass filter 3 is weighted by the corresponding scaler 4, and is multiplied by k1, k2, and k3.
Each weighted frequency delta-sigma modulated signal is input to the statistical processing unit 5. The statistical processing unit 5 selects (obtains) the median value from the three data represented by the three frequency delta-sigma modulated signals, and outputs the median value. Each of the above-mentioned processes is sequentially performed at a predetermined timing.

Such a frequency ratio measuring device 1 can be configured by hardware that realizes the functions corresponding to the above-mentioned parts. Further, the frequency ratio measuring device 1 can also be configured by software by a program, a module, or the like that realizes the functions corresponding to the above-mentioned parts. Further, the frequency ratio measuring device 1 can be configured by combining hardware and software that realize the functions corresponding to the above-mentioned parts.

As described above, according to the frequency ratio measuring device 1, the influence of quantization noise such as idle tone can be easily and accurately suppressed, and the measurement accuracy can be improved.
Further, the statistical processing performed by the statistical processing unit 5 is to select (calculate) the median value in the present embodiment, but the present invention is not limited to this, and other examples include obtaining an average value.

<Second Embodiment>
FIG. 4 is a block diagram showing a second embodiment of the frequency ratio measuring device of the present invention.
Hereinafter, the second embodiment will be described mainly on the differences from the above-described embodiment, and the description of the same items will be omitted.
The second embodiment is the same as the first embodiment except that the selection unit 6 is provided instead of the statistical processing unit 5.
First, an outline of the frequency ratio measuring device 1 will be described, and then a specific description will be given.

The frequency ratio measuring device 1 is a device that measures the frequency ratio of the measured signal and the reference signal based on the measured signal and a plurality of reference signals. The frequency ratio measuring device 1 receives a reference signal and a signal to be measured, and uses one of the input reference signal and the signal to be measured for frequency delta sigma modulation of the other to generate a frequency delta sigma modulated signal. It includes a plurality of frequency delta sigma modulation units 2 (FDSM) and a selection unit 6 that selects any one of a plurality of data represented by the plurality of frequency delta sigma modulation signals. The reference signals input to the plurality of frequency delta-sigma modulation units 2 have different frequencies from each other.
According to this frequency ratio measuring device 1, the influence of quantization noise such as idle tone can be easily and accurately suppressed, and the measurement accuracy can be improved.

Further, the selection unit 6 selects and outputs a median value from a plurality of data represented by the plurality of frequency delta-sigma modulation signals.
As a result, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved. Hereinafter, a specific description will be given.

As shown in FIG. 4, the frequency ratio measuring device 1 of the second embodiment includes a plurality of FDSM2s (three in the present embodiment), a plurality of low-pass filters 3 (three in the present embodiment), and a plurality of (three) FDSMs. In the embodiment, the scaler 4 (three) and the selection unit 6 are provided.
The selection unit 6 has a function of making a selection. The selection unit 6 selects any one of the three (plurality) data represented by the three (plurality) frequency delta-sigma modulation signals output from the three (plurality) FDSM2s.
In the present embodiment, the selection unit 6 selects (obtains) the median value from the three data and outputs it. That is, the selection unit 6 selects and outputs the second largest value among the three data, or if the two data have the same value, the value having the same value.

The second embodiment as described above can also exert the same effect as the above-described embodiment.
Further, the selection made by the selection unit 6 is to select the median value in the present embodiment, but the selection is not limited to this, and other examples include selecting the value closest to the average value.

<Third Embodiment>
FIG. 5 is a block diagram showing a third embodiment of the frequency ratio measuring device of the present invention.
Hereinafter, the third embodiment will be described mainly on the differences from the above-described embodiment, and the description of the same matters will be omitted.
The third embodiment is the same as the first embodiment except that the frequency dividing portion 7 is further provided.
That is, the frequency ratio measuring device 1 has a frequency dividing unit 7 that divides a common signal to generate a plurality of reference signals.
Thereby, a plurality of reference signals can be generated from one clock signal (signal). As a result, the number of reference signal generators can be reduced and the power consumption can be reduced as compared with the case where a plurality of reference signal generators are used. Hereinafter, a specific description will be given.

As shown in FIG. 5, the frequency ratio measuring device 1 of the third embodiment includes a frequency dividing portion 7, a plurality of FDSM2s (three in the present embodiment), and a plurality of (three in the present embodiment) low-pass filters. 3, a plurality of scalers 4 (three in this embodiment), and a statistical processing unit 5 are provided. The frequency dividing portion 7 is connected to the input side of each FDSM2.

The frequency dividing unit 7 has a function of dividing the frequency and generating a reference signal CLK1, a reference signal CLK2, and a reference signal CLK3.
The frequency dividing unit 7 has a frequency dividing device 71, a frequency dividing device 72, and a frequency dividing device 73 into which a common (one) clock signal (signal) which is a source signal of a reference signal is input. There is. Each of the frequency dividers 71, 72, and 73 is connected to the input side of the corresponding FDSM2.

Further, the frequency division ratio (n1) of the frequency divider 71, the frequency division ratio (n2) of the frequency divider 72, and the frequency division ratio (n3) of the frequency divider 73 are different from each other. As a result, reference signals CLK1, CLK2, and CLK3 having different frequencies can be generated. The frequency division ratios of the frequency dividers 71, 72, and 73 are appropriately set based on the frequency of the input clock signal and the frequencies of the generated reference signals CLK1, CLK2, and CLK3, respectively.

The third embodiment as described above can also exert the same effect as the above-described embodiment.
Further, in the third embodiment, three reference signals can be generated from one clock signal. As a result, the number of reference signal generators can be reduced and the power consumption can be reduced as compared with the case where three reference signal generators are used.
The third embodiment can also be applied to the second embodiment, the fourth embodiment and the fifth embodiment.

<Fourth Embodiment>
FIG. 6 is a block diagram showing a fourth embodiment of the frequency ratio measuring device of the present invention.
Hereinafter, the fourth embodiment will be described mainly on the differences from the above-described embodiment, and the description of the same items will be omitted.
The fourth embodiment is the same as the first embodiment described above, except that the configuration of the statistical processing unit 5 is different.
First, the outline of the statistical processing unit 5 will be described, and then, a specific description will be given.

In the fourth embodiment, the statistical processing unit 5 is a set in which the variance of the data to which the statistical processing unit 5 belongs is the smallest from the combination of data obtained by excluding at least one of the plurality of data represented by the plurality of frequency delta-sigma modulated signals. Is selected, and the value obtained based on the data belonging to the set having the smallest variance is output.
As a result, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved.

Further, in the fourth embodiment, the value obtained based on the data belonging to the set having the smallest variance is the average value of the data belonging to the set having the smallest variance. That is, the statistical processing unit 5 obtains and outputs the average value of the data belonging to the set having the smallest variance.
As a result, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved. Hereinafter, a specific description will be given.

As shown in FIG. 6, the frequency ratio measuring device 1 of the fourth embodiment includes a plurality of (five in the present embodiment) FDSM2, a plurality of (five in the present embodiment) low-pass filters 3, and a plurality (the present). In the embodiment, five scalers 4) and a statistical processing unit 5 are provided. The weighting coefficients (magnifications) of each scaler 4 are k1, k2, k3, k4, and k5, respectively. Further, reference signal CLK1, reference signal CLK2, reference signal CLK3, reference signal CLK4, and reference signal CLK5 having different frequencies are input to each FDSM2.

The statistical processing unit 5 performs statistical processing using the five (plural) data represented by the five (plural) frequency delta-sigma modulated signals output from the five (plural) FDSM2s.
That is, the statistical processing unit 5 selects (obtains) the set having the smallest variance of the data to which it belongs from the combination of data excluding at least one of the five data, and selects the data belonging to that set. Output the value obtained based on. In the present embodiment, the statistical processing unit 5 obtains and outputs the average value of the data belonging to the set having the smallest variance. Here, the number of data in each set may be four cases, three cases, or two cases. That is, the minimum number of data in each set is two.
In this embodiment, the variance is used. For example, when the standard deviation is used and the set having the smallest standard deviation is selected, it is equivalent to selecting the set having the smallest variance. Therefore, the standard deviation Is also included in "selecting the set with the smallest variance".

Hereinafter, a case where a combination of data obtained by excluding one of the five data is used (a case where the number of data in each set is four) will be specifically described.
First, let the five data be "a1", "a2", "a3", "a4", and "a5". The combination of data obtained by excluding one of these five data is "a1, a2, a3, a4", "a1, a2, a3, a5", "a1, a2, a4, a5", "a1". , A3, a4, a5 "," a2, a3, a4, a5 ". "A1, a2, a3, a4" is set C1, "a1, a2, a3, a5" is set C2, "a1, a2, a4, a5" is set C3, "a1, a3, a4, a5" is set. C4, "a2, a3, a4, a5" is referred to as a set C5.

First, the statistical processing unit 5 obtains the variance of the data belonging to each of the set C1, the set C2, the set C3, the set C4, and the set C5. Then, the statistical processing unit 5 selects the set having the smallest variance from the sets C1 to the set C5.
Next, the statistical processing unit 5 obtains and outputs the average value of four data belonging to the selected set, that is, the set having the smallest variance. This output is a frequency ratio.

By obtaining the frequency ratio in this way, the influence of quantization noise such as idle tone can be suppressed, and the measurement accuracy can be improved.
The reason why the influence of the idle tone can be suppressed is that, due to the nature of the idle tone described in the first embodiment, among the five sets, the set to which the data having a large influence of the idle tone belongs is four belonging to the set. The data distribution is large. Therefore, by selecting the group with the smallest variance from the five groups, it is possible to exclude the group to which the data with a large influence of the idle tone belongs, and it is expected that the group to which only the data with a small influence of the idle tone belongs will be selected. Will be done.

The fourth embodiment as described above can also exert the same effect as the above-described embodiment.
Further, in the statistical processing performed by the statistical processing unit 5, variance is used in the present embodiment, but the present invention is not limited to this, and in addition to this, for example, in each set, each data is squared and added. , And selecting the set corresponding to the median of the added values.

<Fifth Embodiment>
Hereinafter, the fifth embodiment will be described mainly on the differences from the above-described embodiment, and the description of the same items will be omitted.
The fifth embodiment is the same as the fourth embodiment described above, except that the configuration of the statistical processing unit 5 is different. Further, since the block diagram of the frequency ratio measuring device 1 of the fifth embodiment is the same as the block diagram (FIG. 6) of the frequency ratio measuring device 1 of the fourth embodiment, in the description of the fifth embodiment, FIG. Refer to.

In the frequency ratio measuring device 1 of the fifth embodiment, the statistical processing unit 5 inputs five (plural) data represented by five (plural) frequency delta-sigma modulated signals output from the five (plural) FDSM2s. Use to perform statistical processing.
That is, the statistical processing unit 5 selects (obtains) the set having the smallest variance of the data to which it belongs from the combination of data obtained by excluding at least one of the five data. Then, the statistical processing unit 5 compares the variance of the data belonging to the selected set (the set having the smallest variance) with the threshold value, and if the variance is smaller than the threshold value, the data belonging to the set having the smallest variance Calculate the average value and output it. When the variance is equal to or greater than the threshold value, the statistical processing unit 5 selects (obtains) the median value from the original five data (all data) and outputs the data.
Further, when the variance is equal to or greater than the threshold value, the statistical processing unit 5 may select (find) the median value from the data belonging to the set having the smallest variance and output the data.
As a result, the influence of quantization noise such as idle tone can be suppressed more accurately, and the measurement accuracy can be improved.

Hereinafter, a case where a combination of data obtained by excluding one of the five data is used (a case where the number of data in each set is four) will be specifically described.
The statistical processing unit 5 first obtains a combination of data obtained by excluding one of the five data "a1", "a2", "a3", "a4", and "a5", and the five sets C1. For each of the set C2, the set C3, the set C4, and the set C5, the variance of the data belonging to the set is obtained. Then, the statistical processing unit 5 selects the set having the smallest variance from the sets C1 to the set C5.

Next, the statistical processing unit 5 obtains the variance of the data belonging to the selected set (the set having the smallest variance), and compares the obtained variance with the threshold value. The threshold value is appropriately set according to various conditions.
As a result of comparison, when the variance is smaller than the threshold value, the average value of the data belonging to the set having the smallest variance is obtained and output. This output is a frequency ratio.
Also, as a result of comparison, if the variance is greater than or equal to the threshold value, the median value is selected (obtained) from the original five data and output, or among the data belonging to the set with the smallest variance. From, select (obtain) the median value and output. This output is a frequency ratio.

By obtaining the frequency ratio in this way, the influence of quantization noise such as idle tone can be suppressed, and the measurement accuracy can be improved.
The reason why the influence of the idle tone can be suppressed is that, due to the nature of the idle tone described in the first embodiment, among the five sets, the set to which the data having a large influence of the idle tone belongs is four belonging to the set. The data distribution is large. Therefore, by selecting the group with the smallest variance from the five groups, it is possible to exclude the group to which the data with a large influence of the idle tone belongs, and it is expected that the group to which only the data with a small influence of the idle tone belongs will be selected. Will be done.

When the variance is smaller than the threshold value, it is highly probable that the pair with the smallest selected variance belongs to only the data to which the influence of the idle tone is small. Therefore, by obtaining and outputting the average value of the data belonging to the set having the minimum variance, the influence of the idle tone can be suppressed and the measurement accuracy can be improved.
Further, when the variance is equal to or more than the threshold value, it corresponds to the case where the set having the smallest selected variance cannot exclude the data having a large influence of the idle tone. Therefore, by selecting and outputting the median value from the original five data, the effect of suppressing the influence of the idle tone can be expected, and the measurement accuracy can be improved. The advantage of choosing the median is as described in the first embodiment.
Further, even if the median value is selected from the data belonging to the set having the minimum variance and output, the effect of suppressing the influence of the idle tone can be expected, and the measurement accuracy can be improved.
The fifth embodiment as described above can also exert the same effect as the above-described embodiment.

<Physical quantity sensor embodiment>
FIG. 7 is a diagram showing an internal structure of a detection unit in an embodiment of an acceleration sensor, which is an example of a physical quantity sensor of the present invention. FIG. 8 is a cross-sectional view taken along the line AA in FIG.
Hereinafter, an embodiment of an acceleration sensor, which is an example of a physical quantity sensor, will be described focusing on differences from the above-described embodiment, and the same matters will be omitted.

As shown in FIGS. 7 and 8, the acceleration sensor 100 (physical quantity sensor) of the present embodiment is output from the detection unit 200 for detecting acceleration, which is an example of a physical quantity (physical quantity related to vibration), and the detection unit 200. It is equipped with a frequency ratio measuring device 1 (see FIG. 1 and the like for the frequency ratio measuring device 1) to which a signal to be measured is input. The detection unit 200 and the frequency ratio measuring device 1 are electrically connected. Since the frequency ratio measuring device 1 has already been described, the description thereof will be omitted.

The detection unit 200 includes a flat plate-shaped base portion 210, a substantially rectangular flat plate-shaped movable portion 212 connected to the base portion 210 via a joint portion 211, and a physical quantity spanned between the base portion 210 and the movable portion 212. It includes an acceleration detection element 213, which is an example of a detection element, and a package 220 that houses at least each of the above components.
The detection unit 200 receives a drive signal applied to the excitation electrode of the acceleration detection element 213 via the external terminals 227 and 228, the internal terminals 224 and 225, the external connection terminals 214e and 214f, the connection terminals 210b and 210c, and the like. The vibrating beams 213a and 213b of the acceleration detection element 213 oscillate (resonate) at a predetermined frequency. Then, the detection unit 200 outputs the resonance frequency of the acceleration detection element 213, which changes according to the applied acceleration, as a signal to be measured (detection signal).

This measured signal is input to the frequency ratio measuring device 1, and the frequency ratio measuring device 1 operates as described in the above embodiment.
The number of detection units 200 is one in the present embodiment, but is not limited to this, and may be, for example, two or three. By providing three detection units 200 and crossing the detection axes of each detection unit 200 with each other, it is possible to detect the acceleration in each of the three detection axes orthogonal to each other.
Even with the acceleration sensor 100 as described above, the frequency ratio measuring device 1 included in the acceleration sensor 100 can exert the same effect as that of the above-described embodiment. As a result, the acceleration sensor 100 can accurately detect the acceleration.

In order to confirm the effect of the frequency ratio measuring device 1 described above, the following experiment was conducted.
FIG. 9 is a graph showing the frequency (true value) of the signal to be measured in the experiment. 10 to 15 are graphs showing the experimental results, respectively.

<Experimental method>
The frequency ratio of the signal under test and the reference signal was measured using a frequency ratio measuring device.
As the signal to be measured, a signal whose frequency changes from 180283.2 Hz to 180283.8 Hz was used. The frequency of this signal to be measured is called the "true value". The signal to be measured is as shown in FIG.
In addition, the frequency of the signal to be measured was obtained from the frequency ratio obtained by the measurement and graphed.
In addition, the variance of the difference from the true value was obtained for the frequency of the obtained signal to be measured. The smaller the dispersion, the more preferable.
Each example and each comparative example are as follows.

(Example 1)
The frequency ratio measuring device of the first embodiment having three FDSMs was used. The statistical processing unit of this frequency ratio measuring device obtains and outputs the average value of the three data.
As the reference signal, a signal obtained by dividing a signal having a frequency of 30 MHz by 126, a signal obtained by dividing the signal by 127, and a signal obtained by dividing the signal by 128 (three reference signals) were used.
The results are as shown in FIG.

(Example 2)
The frequency ratio measuring device of the first embodiment having three FDSMs was used. The statistical processing unit of this frequency ratio measuring device selects and outputs the median value from the three data.
As the reference signal, a signal obtained by dividing a signal having a frequency of 30 MHz by 126, a signal obtained by dividing the signal by 127, and a signal obtained by dividing the signal by 128 (three reference signals) were used.
The results are as shown in FIG.

(Comparative Example 1)
A frequency ratio measuring device having one FDSM was used.
As the reference signal, a signal (one reference signal) obtained by dividing a signal having a frequency of 30 MHz by 127 was used.
The results are as shown in FIG.

(Example 3)
The frequency ratio measuring device of the fourth embodiment having five FDSMs was used. The statistical processing unit of this frequency ratio measuring device selects the set having the smallest variance of the data to which it belongs from the combination of four data excluding one from the five data, and 4 belonging to that set. The average value of two data is calculated and output.
The reference signal is a signal having a frequency of 30 MHz divided by 125, a signal divided by 126, a signal divided by 127, a signal divided by 128, and a signal divided by 129. And (5 reference signals) were used.
The results are as shown in FIG.

(Example 4)
The frequency ratio measuring device of the fifth embodiment having five FDSMs was used. The statistical processing unit of this frequency ratio measuring device selects the set having the smallest variance of the data to which it belongs from the combination of four data excluding one from the five data. Then, the statistical processing unit compares the variance of the four data belonging to the set with the threshold, and if the variance is ^{smaller than the threshold (10-5} ), finds the average value of the four data belonging to the set. If the variance is ^{equal to or greater than the threshold (10-5} ), the median value is selected from the original five data and output.
The reference signal is a signal having a frequency of 30 MHz divided by 125, a signal divided by 126, a signal divided by 127, a signal divided by 128, and a signal divided by 129. And (5 reference signals) were used.
The results are as shown in FIG.

(Comparative Example 2)
A frequency ratio measuring device similar to that of the fifth embodiment in which the number of FDSMs is five was used. The statistical processing unit of this frequency ratio measuring device performs the same processing as in the fourth embodiment.
However, as the reference signal, a signal having a frequency of 30 MHz divided by 128 and five signals (reference signals) out of phase with each other were used.
The results are as shown in FIG.

<Experimental results>
Variance of the difference from the true value of Example 1: 0.641 × 10 ^-4
Variance of the difference from the true value of Example 2: 0.257 × 10 ^-4
Variance of the difference from the true value of Comparative Example 1: 0.852 × 10 ^-4
Variance of the difference from the true value of Example 3: 0.199 × 10 ^-4
Variance of the difference from the true value of Example 4: 0.178 × 10 ^-4
Variance of the difference from the true value of Comparative Example 2: 1.364 × 10 ^-4
From the above experimental results, in Examples 1 to 4, the variance of the difference from the true value is small, and in particular, in Examples 2, 3 and 4, the variance of the difference from the true value is very small, and the measurement accuracy is good. It turns out. This is because the influence of the idle tone is suppressed.

Although the frequency ratio measuring device and the physical quantity sensor of the present invention have been described above based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is an arbitrary configuration having the same function. Can be replaced with one. Moreover, other arbitrary components may be added.
Further, the present invention may be a combination of any two or more configurations (features) of each of the above-described embodiments.

Further, in the above-described embodiment, the acceleration sensor has been described as an example of the physical quantity sensor, but in the present invention, the physical quantity sensor can be used as long as it can detect the change in the physical quantity as the frequency change. In addition, the present invention includes, for example, a mass sensor, an ultrasonic sensor, an angular acceleration sensor, a capacitance sensor, and the like.
Further, the physical quantity sensor of the present invention is, for example, various electronic devices such as an inclinometer, a seismometer, a navigation device, an attitude control device, a game controller, a mobile phone, a smartphone, a digital still camera, and various mobile objects such as an automobile. Etc. can be applied. That is, in the present invention, it is possible to provide an electronic device provided with the physical quantity sensor of the present invention, a mobile body provided with the physical quantity sensor of the present invention, and the like.

1 ... Frequency ratio measuring device, 2 ... FDSM (frequency delta sigma modulator), 3 ... Low pass filter, 4 ... Scaler, 5 ... Statistical processing unit, 6 ... Selection unit, 7 ... Frequency division unit, 21 ... Up counter, 22 ... 1st latch, 23 ... 2nd latch, 24 ... subtractor, 25 ... exclusive OR circuit, 71 ... frequency divider, 72 ... frequency divider, 73 ... frequency divider, 100 ... acceleration sensor, 200 ... detection Part, 210 ... Base part, 210b ... Connection terminal, 210c ... Connection terminal, 211 ... Joint part, 212 ... Movable part, 213 ... Accelerometer detection element, 213a ... Vibration beam, 213b ... Vibration beam, 214e ... External connection terminal, 214f ... External connection terminal, 220 ... Package, 224 ... Internal terminal, 225 ... Internal terminal, 227 ... External terminal, 228 ... External terminal

Claims (8)

A frequency ratio measuring device that measures the frequency ratio between the measured signal and the reference signal based on the measured signal and a plurality of reference signals.
A plurality of frequencies to which the reference signal and the measured signal are input and one of the input reference signal and the measured signal is used for frequency delta sigma modulation of the other to generate a frequency delta sigma modulated signal. Delta sigma modulator and
A statistical processing unit that performs statistical processing using a plurality of data represented by the plurality of frequency delta-sigma modulated signals is provided.
The reference signals input to the plurality of frequency delta-sigma modulators have different frequencies from each other .
The statistical processing unit selects the set having the smallest dispersion of the data to which the data belongs from the combination of the data excluding at least one from the plurality of data represented by the plurality of frequency delta-sigma modulated signals. , A frequency ratio measuring device characterized by outputting a value obtained based on the data belonging to the set. The frequency ratio measuring device according to claim 1 , wherein the statistical processing unit obtains and outputs an average value of the data belonging to the set. The statistical processing unit compares the variance of the data belonging to the set with the threshold, and if the variance is smaller than the threshold, obtains and outputs the average value of the data belonging to the set, and the variance is calculated. for more than the threshold value, from among the plurality of data, the frequency ratio measuring apparatus according to claim 1 for selecting and outputting the median value. The statistical processing unit compares the variance of the data belonging to the set with the threshold, and if the variance is smaller than the threshold, obtains and outputs the average value of the data belonging to the set, and the variance is calculated. for more than the threshold value, from among the data belonging to the group, the frequency ratio measuring apparatus according to claim 1 for selecting and outputting the median value. The frequency ratio measuring device according to any one of claims 1 to 4 , which has a low-pass filter on the output side of the frequency delta-sigma modulation unit. The frequency ratio measuring device according to any one of claims 1 to 5 , further comprising a weighting unit that weights a signal on the output side of the frequency delta-sigma modulation unit. The frequency ratio measuring device according to any one of claims 1 to 6 , further comprising a frequency dividing portion that divides a common signal to generate the plurality of reference signals. A detector that detects physical quantities and
A physical quantity sensor comprising the frequency ratio measuring device according to any one of claims 1 to 7 , wherein a signal to be measured output from the detection unit is input.

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