WO2015198470A1

WO2015198470A1 - Measurement device and measurement method

Info

Publication number: WO2015198470A1
Application number: PCT/JP2014/067157
Authority: WO
Inventors: 立石　潔; 渉小野寺; 佐藤　充
Original assignee: パイオニア株式会社
Priority date: 2014-06-27
Filing date: 2014-06-27
Publication date: 2015-12-30
Also published as: JPWO2015198470A1

Abstract

This measurement device is provided with an illuminating means (120) for illuminating a subject of measurement (200) with laser light, a light-receiving means (130) for receiving laser light scattered by said subject of measurement, a constraining means (150) for constraining the amplitude of an output signal from the light-receiving means to within prescribed bounds, and an outputting means (170) for outputting information regarding motion of the subject of measurement on the basis of a beat signal due to a laser-light Doppler shift in the output signal from the light-receiving means. Said measurement device minimizes the impact of mode hopping, allowing measurement to be performed in a suitable manner.

Description

Measuring apparatus and measuring method

The present invention relates to a technical field of a measurement apparatus and a measurement method for measuring information related to movement of a measurement target using light scattered in the measurement target.

In the semiconductor laser used in this type of measuring apparatus, the band gap changes due to the rise in the laser temperature, so that the oscillation wavelength gradually changes to a long wavelength as the temperature rises. When the temperature continues to rise, the oscillation wavelength suddenly jumps to the wavelength having the maximum gain on the long wavelength side at a certain timing. This phenomenon is called mode hopping, and is known to cause a measurement error in a measuring apparatus using optical Doppler, for example.

Patent Document 1 proposes a technique of controlling the temperature of a laser light source using a Peltier element in order to suppress the occurrence of the mode hop described above.

JP 2001-120509 A

However, in the technique described in Patent Document 1 described above, the power consumption of the Peltier element, which is a heat absorption means, is large, and in addition, a temperature sensor and a control IC are required, so there are many components and cost is low. There is a technical problem that is disadvantageous. Further, in order to suppress mode hops, it is necessary to strictly control the temperature with a temperature sensor and an endothermic means, and there is a technical problem that it is difficult to completely eliminate mode hops.

Examples of problems to be solved by the present invention include the above. An object of the present invention is to provide a measuring apparatus and a measuring method capable of suppressing an adverse effect of mode hops on measurement.

A measuring apparatus for solving the above problems includes an irradiating means for irradiating a measurement target with laser light, a light receiving means for receiving the laser light scattered by the measurement target, and an amplitude of an output signal of the light receiving means. Limiting means for limiting the value within a predetermined range; and output means for outputting information on the movement of the measurement target based on a beat signal resulting from the Doppler shift of the laser light included in the output signal of the light receiving means; Is provided.

A measurement method for solving the above problems includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output signal obtained in the light reception step The information on the movement of the measurement target is output based on a limiting process for limiting the amplitude of the laser beam to a predetermined range and a beat signal resulting from the Doppler shift of the laser light included in the output signal obtained in the light receiving process Output step.

It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 1st Example. It is a circuit diagram which shows the specific structure of a light receiving element and an I-IV converter. It is a block diagram which shows the specific structure of an amplitude limiter amplifier. It is a circuit diagram which shows the specific structure of an amplitude limiter part. It is a block diagram which shows the specific structure of a blood flow calculating part. It is a graph which shows the specific example of a blood flow spectrum. It is a graph (the 1) which shows an amplification signal and a blood flow output. It is a graph (the 2) which shows an amplification signal and a blood-flow output. It is a graph (the 3) which shows an amplification signal and a blood-flow output. It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 2nd Example. It is a block diagram which shows the specific structure of a limiter process part. It is a block diagram which shows the specific structure of a limit level adjustment part. It is a graph which shows the data which do not perform a limiter process, and a corresponding blood-flow output. It is a graph which shows the data which performed the limiter process, and corresponding blood-flow output. It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 3rd Example.

<1>
The measurement apparatus according to the present embodiment is configured to irradiate laser light onto a measurement target, light reception means that receives the laser light scattered by the measurement target, and an amplitude of an output signal of the light reception means. Limiting means for limiting to within the range, and output means for outputting information on the movement of the measurement target based on a beat signal resulting from the Doppler shift of the laser light included in the output signal of the light receiving means. .

According to the measurement apparatus according to the present embodiment, the laser beam is irradiated from the irradiation unit to the measurement target during the operation. The irradiation means is configured to include, for example, a semiconductor laser element or the like, and is disposed at a position where the measurement target can be efficiently irradiated with light when used. The measurement target is a fluid such as blood of a living body. However, the measurement target is not particularly limited, and may be other than fluid (for example, an individual) as long as it moves.

The laser light emitted from the irradiation means is scattered (specifically reflected and transmitted) in the object to be measured and then received by the light receiving means. The light receiving means includes, for example, a photodiode and outputs an output signal corresponding to the received light.

Here, particularly in the present embodiment, the amplitude of the output signal of the light receiving means is limited within a predetermined range by the limiting means. For this reason, the output signal is output in a state where, for example, a portion where the amplitude exceeds a predetermined range is cut. Here, the “predetermined range” is an amplitude range (in other words, an upper limit value of amplitude) set as a reference for amplitude limitation in order to suppress the influence caused by the mode hop as will be described later. is there. The predetermined range is set as a range in which the influence by the mode hop can be effectively suppressed by a prior simulation or the like. The predetermined range may be a fixed value, or may be a value that can be changed according to a measurement situation or the like.

The output signal of the light receiving means is used when outputting information related to the movement of the measurement target from the output means. Specifically, in the output means, information on the movement of the measurement target is obtained based on a beat signal resulting from a Doppler shift (hereinafter referred to as “optical Doppler” as appropriate) of the laser light included in the output signal of the light receiving means. Calculated. Here, “information relating to movement” is a broad concept including information that indirectly indicates such information in addition to the movement speed, movement amount, and movement direction of the measurement target.

When using optical Doppler to output information related to the movement of the object to be measured, for example, if a mode hop occurs due to a temperature rise of the irradiation means, an error may occur in the measurement result. Specifically, the amplitude value of the output signal of the light receiving means greatly fluctuates due to the mode hop (for example, the amplitude instantaneously becomes a very large value), which is unnecessary for the measurement result obtained from the output signal. Variation will occur.

However, in this embodiment, as described above, the amplitude of the output signal of the light receiving means is limited within a predetermined range. For this reason, even if a mode hop occurs, the fluctuation portion due to the mode hop is excluded from the output signal of the light receiving means. As a result, the output signal used when outputting the information related to the movement of the measurement target is in a state in which it is not influenced by mode hops at all or almost. Therefore, even in a situation where a mode hop occurs, information regarding the movement of the measurement target is output as accurate.

As described above, according to the measurement apparatus according to the present embodiment, it is possible to suppress the influence of mode hops and perform measurement accurately.

<2>
In one aspect of the measuring apparatus according to the present embodiment, the limiting unit changes the predetermined range according to the past amplitude of the output signal of the light receiving unit.

According to this aspect, information relating to the amplitude of the output signal of the light receiving means is stored and used for the subsequent amplitude limitation. More specifically, for example, the amplitude of the output signal of the light receiving means in the situation where the mode hop has not occurred immediately after the start of the operation is stored, and a predetermined coefficient (for example, 1.1, for example) is stored in the average value of the stored amplitude peaks. A value obtained by multiplying a coefficient for allowing a slight variation in the degree is set as the predetermined range.

As described above, if the predetermined range is variable, the amplitude of the output signal can be more appropriately limited as compared with the case where the predetermined range which is a fixed value is used. Specifically, the predetermined range is too large to remove the fluctuation part due to the mode hop from the output signal, or the predetermined range is too small to cause the part from the output signal not to cause the mode hop (i.e., for measurement). It is possible to prevent the removal of the portion to be used. Therefore, according to this aspect, it is possible to obtain a more accurate measurement result.

<3>
In another aspect of the measuring apparatus according to this embodiment, the limiting unit limits the amplitude at a stage before converting the output signal of the light receiving unit from an analog signal to a digital signal.

According to this aspect, since the amplitude of the output signal is limited in the state of an analog signal, the output signal after limitation is amplified in accordance with the D range of the subsequent A / D conversion, and the quantum by the A / D conversion is increased. Error can be reduced. As a result, the bit length of A / D conversion can be set small, and the cost of the A / D converter can be reduced.

<4>
In another aspect of the measuring apparatus according to this embodiment, the limiting unit limits the amplitude at a stage after the output signal of the light receiving unit is converted from an analog signal to a digital signal.

According to this aspect, since the amplitude of the output signal is limited by the state of the digital signal, it is possible to perform the highly accurate limiting process relatively easily by utilizing the characteristics of the digital signal.

<5>
In another aspect of the measuring apparatus according to the present embodiment, the limiting unit limits the amplitude in both the stage before and after the conversion of the output signal of the light receiving unit from an analog signal to a digital signal.

According to this aspect, it is possible to enjoy both the gain for performing the limiting process in the analog stage and the gain for performing the limiting process in the digital stage, so that a very suitable measurement can be realized.

In this aspect, the restriction process is performed in two stages. Therefore, in the restriction process in the first analog stage, even if there is a restriction with a certain margin (that is, a component due to mode hops remains to some extent). It is desirable to perform a highly accurate restriction (that is, a restriction that can remove a component due to a mode hop as much as possible) in the restriction process in the last digital stage.

<6>
In another aspect of the measuring apparatus according to the present embodiment, the light receiving means outputs first and second photoelectric conversion element units that respectively convert the laser light into current and output, and the first photoelectric conversion element unit outputs A differential current output unit that outputs a differential current between a current to be output and a current output from the second photoelectric conversion element unit as a detection current.

According to this aspect, the two photoelectric conversion element portions are provided for converting laser light into current and outputting the current. Each of the first and second photoelectric conversion element units includes one or a plurality of photoelectric conversion elements (for example, photodiodes), and outputs a current according to the amount of input light.

More specifically, the first and second photoelectric conversion element units include, for example, a cathode of the first photoelectric conversion element unit and an anode of the second photoelectric conversion element unit, and an anode and a first photoelectric conversion element unit. The two photoelectric conversion element portions are connected in parallel so as to be connected. Alternatively, the first and second photoelectric conversion element portions are connected in series so that the cathodes or the anodes are connected to each other.

The differential current output unit outputs a differential current between the current output from the first photoelectric conversion element unit and the current output from the second photoelectric conversion element unit as a detection current. Accordingly, a current component corresponding to a steady light component included in the laser light (hereinafter referred to as a “DC (direct current) component” as appropriate) among the currents output from the first and second photoelectric conversion element units. A current mainly including a current component corresponding to a signal light component included in the laser light (hereinafter referred to as an “AC (alternate current) component” as appropriate) can be output as a detection current after being reduced or removed. That is, the DC component of the current output from the first photoelectric conversion element unit and the DC component of the current output from the second photoelectric conversion element unit can be canceled, and the AC corresponding to the signal light component included in the laser light. A detection current mainly including components can be output.

As a result, since the detection current contains little or no DC component, for example, a current-voltage conversion circuit that can be generated when the DC component contained in the detection current is relatively large (that is, the detection current is converted into a voltage). The gain of amplification by the current-voltage conversion circuit can be increased while avoiding the occurrence of the saturation phenomenon of the circuit).

Furthermore, according to this aspect, since a current mainly including an AC component corresponding to the signal light component included in the laser light can be output as the detection current, the S / N ratio (signal-to-noise) of the output signal can be output. ratio) can be improved. That is, according to this aspect, the DC component corresponding to the noise component included as the steady light component in the laser light out of the current output from each of the first and second photoelectric conversion element units is reduced or removed, Since the detection current mainly including the AC component corresponding to the signal component is output, the S / N ratio in the output signal can be improved.

<7>
The measurement method according to the present embodiment includes an irradiation process for irradiating a measurement target with laser light, a light reception process for receiving the laser light scattered by the measurement target, and an amplitude of an output signal obtained in the light reception process. An output for outputting information related to the movement of the measurement object based on a beat signal resulting from a Doppler shift of the laser light included in the output signal obtained in the light receiving step A process.

According to the measurement method of the present embodiment, it is possible to perform measurement accurately while suppressing the influence of mode hops, as in the measurement apparatus according to the present embodiment described above.

In the measurement method according to this embodiment, it is possible to adopt various aspects similar to the various aspects of the measurement apparatus according to this embodiment described above.

The operation and other gains of the measuring apparatus and measuring method according to the present embodiment will be described in more detail in the following examples.

Hereinafter, embodiments of the measuring apparatus and the measuring method will be described in detail with reference to the drawings. In the following, a case where the measurement device according to the present invention is configured as a blood flow measurement device that measures blood flow will be described as an example.

<First embodiment>
A measuring apparatus according to the first embodiment will be described with reference to FIGS.

<Overall configuration>
First, the overall configuration of the measuring apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of the measuring apparatus according to the first embodiment.

In FIG. 1, the measuring apparatus according to the present embodiment includes a laser driving unit 110, a semiconductor laser 120, a light receiving element 130, an IV conversion unit 140, an amplitude limiter amplifier 150, an A / D converter 160, and the like. The blood flow calculation unit 170 is provided.

The laser driver 110 generates a current for driving the semiconductor laser 120.

The semiconductor laser 120 is a specific example of “irradiation means”, and irradiates the measurement target 200 (for example, skin of a living body) with laser light corresponding to the drive current generated in the laser drive unit 110. .

The light receiving element 130 is a specific example of “light receiving means”, and receives scattered light scattered by the blood 200 out of the laser light emitted from the semiconductor laser 120. The light receiving element 130 outputs a detection current according to the intensity of the received scattered light.

The IV converter 140 converts the detection current output from the light receiving element 130 into a voltage and outputs a detection voltage.

The amplitude limiter amplifier 150 is a specific example of “limiting means”, which performs a limiter process on the detected voltage, amplifies it, and outputs it as an amplified signal. The limiter process will be described in detail later.

The A / D converter 160 quantizes the input analog amplified signal and outputs it as digital data.

The blood flow calculation unit 170 is a specific example of “output means”, and outputs a blood flow (specifically, information related to movement of the blood 200 such as a flow rate) based on input data. The blood flow calculation unit 170 is configured as a DSP (Digital Signal Processor), for example, and can perform digital signal processing such as frequency analysis on input data.

<Description of operation>
Below, operation | movement of the measuring apparatus mentioned above is demonstrated in detail with reference to FIG.

In FIG. 1, during the operation of the measuring apparatus according to the present embodiment, first, the laser driving unit 110 generates a specified operating current that is equal to or higher than the threshold current of the semiconductor laser 120 and supplies it to the semiconductor laser 120. Thereby, the semiconductor laser 120 oscillates.

The semiconductor laser 120 is fixed to the measurement target 200 with a clip or the like (not shown) so as to emit laser light to the measurement target 200. When the measurement target 200 is living body skin, the irradiated laser light becomes scattered light scattered by a skin tissue that is a fixed object and scattered light scattered by red blood cells in a capillary that is a moving object, Both of them are received by the light receiving element 130.

Here, the scattered light scattered by the skin tissue is the reference light, and the scattered light scattered by the red blood cells is the scattered light that has caused an optical Doppler shift corresponding to the moving speed of the red blood cells. These two scattered lights cause interference due to the coherence of the laser light. The light receiving element 130 generates a detection current corresponding to the intensity of the optical beat signal as a result of this interference.

Similarly to the semiconductor laser 120, the light receiving element 130 is fixed to the measurement target 200 with a clip or the like (not shown) so as to receive the scattered light from the measurement target 200. The detection current corresponding to the optical beat signal detected by the light receiving element 130 is converted into a current voltage by the IV converter 140 and output as a detection voltage.

Hereinafter, specific configurations and operations of the light receiving element 130 and the IV converter 140 will be described with reference to FIG. FIG. 2 is a circuit diagram showing a specific configuration of the light receiving element and the I-∨ converter.

In FIG. 2, the light receiving element 130 according to the present embodiment includes two

light receiving elements

130a and 130b. The

light receiving elements

130a and 130b are specific examples of a “first photoelectric conversion element unit” and a “second photoelectric conversion element unit”, and are configured as, for example, a photodetector using a PIN semiconductor. The

light receiving elements

130a and 130b have cathodes connected to each other and are connected in series in opposite directions. If comprised in this way, DC component can be suppressed and AC component which is a signal component can be detected efficiently.

Specifically, a current component corresponding to a steady light component included in the input light (hereinafter referred to as “DC (direct current) component”) is reduced or removed from the current output from each of the

light receiving elements

130a and 130b. Thus, a current mainly including a current component corresponding to the signal light component included in the input light (hereinafter appropriately referred to as “AC (alternate current) component”) can be output as the detection current. That is, the DC component of the output current of the light receiving element 130a and the DC component of the current output of the light receiving element 130b can be canceled, and a detection current mainly including an AC component corresponding to the signal light component included in the input light is obtained. Can be output.

For example, assuming that the detection current of the light receiving element 130a is Id1 and the detection current of the light receiving element 130b is Id2, since both are connected in series with opposite polarities, the detection current is represented by the following formula (1).

Idt = Id2-Id1 (1)
Further, since the scattered light received by the light receiving element 130a and the scattered light received by the light receiving element 130b are different from each other, if the wavelength of the light is used as a reference length, the signal is approximately uncorrelated. Therefore, the intensity of the optical beat signal, which is a signal component, is multiplied by √2 by subtraction.

On the other hand, since the DC current is canceled by subtraction, saturation can be prevented even if the detection sensitivity of Amp1 and Amp2 which are transimpedance amplifiers is set high. Specifically, the resistance values of the feedback resistors Rf1 and Rf2 can be set high, and the current-voltage conversion sensitivity is improved. As a result, a high detection S / N (Signal-to-Noise ratio) is obtained.

The non-inverting input terminals of Amp1 and Amp2 are grounded. Due to the negative feedback action of the feedback resistors Rf1 and Rf2 of Amp1 and Amp2, the non-inversion terminal and the inversion terminal are in an imaginary shoot state and have approximately the same potential. Therefore, the anode of the light receiving element 130a and the anode of the light receiving element 130b are at the same potential, and the P light receiving element 130a and the light receiving element 130b operate in a so-called power generation mode. With this power generation mode, dark current is suppressed, and noise increase due to dark current fluctuation can be suppressed.

The detection voltage Vd1 of Amp1 and the detection voltage Vd2 of Amp2 are as shown in the following formulas (2) and (3).

Vd1 = Rf1 · Idt (2)
Vd2 = Rf2 · (−Idt) (3)
Amp3 differentially amplifies the detection voltage of Amp1 and Amp2 and outputs it as Vout. This differential amplification removes common mode noise such as power supply noise and hum.

Here, when the resistance value is set so that Ra1 = Ra2 = Ra and Rb1 = Rb2 = Rb, Vout is expressed by the following formula (4).

Vout = (Rb / Ra) (Vd1-Vd2) (4)
From the above equations (2), (3), and (4), when the resistance value is set so that Rf1 = Rf2 = Rf, Vout is expressed by the following equation (5).

Vout = 2Rf (Rb / Ra) Idt (5)
From the above equation (5), it can be seen that the detection voltage Vout corresponding to the intensity of the optical beat signal as the signal component can be obtained.

Returning to FIG. 1, the detection voltage output from the IV converter 140 is input to the amplitude limiter amplifier 150 and output as an amplified signal. Hereinafter, a specific configuration and operation of the amplitude limiter amplifier 150 will be described with reference to FIGS. FIG. 3 is a block diagram showing a specific configuration of the amplitude limiter amplifier. FIG. 4 is a circuit diagram showing a specific configuration of the amplitude limiter unit.

In FIG. 3, the detection voltage input to the amplitude limiter amplifier 150 is first input to the variable amplifier 151. A gain setting value is input to the control terminal of the variable amplifier 151 from an external CPU (not shown). The variable amplifier 151 amplifies the detection voltage with a specified gain according to the gain setting value, and outputs the amplified detection voltage to the BPF unit 152.

The BPF unit 152 constitutes a band pass filter for suppressing low frequency noise such as a hum signal and high frequency noise from the SW power source. The output of BPF 152 is input to the amplitude limiter unit 153.

As shown in FIG. 4, the amplitude limiter unit 153 includes a resistor Ri and diodes D1 and D2. The resistor Ri is set to be larger than the on-resistances of the diodes D1 and D2, thereby limiting the signal amplitude exceeding the forward voltage of the diodes D1 and D2. Thus, the amplitude limiter unit 153 constitutes a so-called diode limiter. The output of the amplitude limiter unit 153 is input to the AC amplifier 154.

The AC amplifier 154 amplifies the signal so as to obtain an appropriate amplitude with respect to the D range of A / D conversion, and outputs it as an amplified signal. Specifically, when the input D range of the A / D converter 160 is ± 1.4V and the diode limit amplitude is ± 0.7V, the gain of the AC amplifier may be set to double.

Returning to FIG. 1 again, the amplified signal that is the output of the amplitude limiter amplifier 150 is input to the A / D converter 160. The A / D converter 160 quantizes the input amplified signal at a specified sampling frequency and outputs data as a digital value.

The data output from the A / D converter 160 is subjected to digital signal processing by the blood flow calculation unit 170, and information relating to blood flow is output. Below, the specific structure and operation | movement of the blood flow calculating part 170 are demonstrated with reference to FIG.5 and FIG.6. FIG. 5 is a block diagram showing a specific configuration of the blood flow calculation unit. FIG. 6 is a graph showing a specific example of a blood flow spectrum.

In FIG. 5, data input to the blood flow calculation unit 170 is first input to the Hanning window processing unit 171. The Hanning window processing unit 171 executes Hanning window processing as preprocessing for FFT (Fast Fourier Transform).

The FFT processing unit 172 performs frequency analysis on the data limited by the window function by FFT processing.

The square calculation unit 173 performs complex conjugate processing on the frequency analysis data, and acquires the power spectrum P (f).

The first moment integration unit 174 multiplies the obtained power spectrum P (f) by the frequency vector f, and further integrates it within the specified band to obtain Σ {f · P (f)}.

The LPF unit 175 removes the high-frequency component of the Σ {f · P (f)} signal and multiplies it by a specified gain. Thereby, a blood flow output is obtained.

As shown in FIG. 6, when the blood flow is low, that is, when the velocity of blood cells, which are scatterers flowing in the capillary, is slow, the power spectrum P (f) of the optical beat signal is indicated by a dotted line in the figure. Thus, the low frequency component is included more than the high frequency component. On the other hand, when the blood flow is high, that is, when the flow velocity of blood cells, which are scatterers flowing in the capillaries, is fast, the power spectrum P (f) of the optical beat signal has the characteristics shown by the solid line in the figure. As a result, the high frequency component is contained more than the low frequency component.

Thus, when the moving body is fast, the Doppler shift amount of scattered light increases. Therefore, in the frequency spectrum of the optical beat signal, components in a high frequency region are further increased, and the characteristics as shown in FIG. 6 are exhibited.

Note that the blood flow calculation unit 170 performs calculation to efficiently detect the power spectrum change of the optical beat signal. In this embodiment, a method using frequency analysis by FFT has been described, but the present invention is not limited to this method.

<Effects on mode hops>
Next, effects obtained by the measuring apparatus according to the present embodiment will be described with reference to FIGS. 7 to 9 are graphs showing the amplified signal and the blood flow output, respectively. Note that the horizontal axis of the graphs shown in FIGS. 7 to 9 is time, which corresponds to 0 to 27 seconds.

The waveform shown in FIG. 7 is an example of a waveform obtained when the semiconductor laser 120 is stably oscillating in a single mode, that is, when no mode hop occurs. In this case, since no mode hop occurs, almost no noise is present in the amplified signal. For this reason, an accurate blood flow output is obtained without performing the amplitude limiter process.

The waveform shown in FIG. 8 is an example of a waveform obtained when the semiconductor laser 120 is in an unstable oscillation state due to mode hopping. In this case, as can be seen from comparison with FIG. 7, a lot of noise is present in the amplified signal due to the occurrence of mode hops. For this reason, if the amplitude limiter process is not performed, the pulse wave of the blood flow output is disturbed.

The waveform shown in FIG. 9 is an example of a waveform obtained when the semiconductor laser 120 is in an unstable oscillation state due to mode hops, as in FIG. 8, but the amplitude limiter processing according to this embodiment is performed. Demodulating. For this reason, the noise component is suppressed by the amplitude limiting action of the amplitude limiter amplifier 150. As a result, the disturbance of the pulse wave in the blood flow output is suppressed to a minimum, and a waveform close to a state in which mode hopping is not performed (that is, no noise) is obtained as in the case of FIG.

As described above, according to the measurement apparatus of the first embodiment, even if noise due to the mode hop of the semiconductor laser 120 occurs, the influence can be suppressed and more accurate blood flow measurement can be performed. It is. Further, if the mode hop itself of the semiconductor laser 120 is to be removed, it is required to introduce an expensive temperature control system or the like. However, in this embodiment, it is not necessary to remove the mode hop itself. realizable. Furthermore, if a temperature control system with high power consumption is not required, battery driving is possible, and the apparatus can be miniaturized.

<Second embodiment>
Next, a measuring apparatus according to the second embodiment will be described with reference to FIGS. The second embodiment is different from the first embodiment described above only in part of the configuration and operation, and many parts are the same as the first embodiment. For this reason, below, a different part from 1st Example is demonstrated in detail, and description is abbreviate | omitted suitably about the overlapping part.

<Overall configuration>
The overall configuration of the measuring apparatus according to the second embodiment will be described with reference to FIG. FIG. 10 is a block diagram showing the overall configuration of the measuring apparatus according to the second embodiment.

In FIG. 10, the measurement apparatus according to the second embodiment includes a laser driving unit 110, a semiconductor laser 120, a light receiving element 130, an IV conversion unit 140, an amplifier 155, an A / D converter 160, The blood flow calculation unit 170 and the limiter processing unit 180 are provided. In other words, in the measuring apparatus according to the second embodiment, the part that performs the limiter process of the amplitude limiter amplifier 150 (see FIG. 1) according to the first embodiment serves as a limiter processing unit 180 in the subsequent stage of the A / D converter 160. It is provided independently.

The limiter processing unit 180 limits the amplitude of the digital data input from the A / D converter 160 by digital signal processing, and outputs it to the blood flow calculation unit 170 as limit data.

Note that, unlike the amplitude limiter amplifier 150 according to the first embodiment, the amplifier 155 does not limit the amplitude by analog processing, but amplifies the detection voltage input from the IV conversion unit 140 to obtain an amplified signal. Output to the A / D converter 160.

<Specific Configuration of Limiter Processing Unit>
Next, a specific configuration of the limiter processing unit 180 will be described with reference to FIG. FIG. 11 is a block diagram showing a specific configuration of the limiter processing unit.

In FIG. 11, the data input to the limiter processing unit 180 is first input to the positive side level comparison unit 181. The positive level comparing unit 181 compares the input data with a limit level (that is, a predetermined amplitude limit value). When the input data is larger than the limit level, the first data switching unit 182 switches the input data to the limit level. Similarly, the limit level is inverted in sign by the -1 time processing unit 183 and compared with the input data in the negative side level comparison unit 184. When the input data is smaller than the limit level multiplied by −1 (that is, when the negative amplitude is large), the second data switching unit 185 replaces the input data with the limit level multiplied by −1. As a result, the amplitude of the input data is limited according to the limit level and output as limit data.

<Limit level adjustment unit>
The limiter processing unit 180 described above may be configured as a variable limiter processing unit by including a limit level adjustment unit. Below, a limit level adjustment part is demonstrated with reference to FIG. FIG. 12 is a block diagram showing a specific configuration of the limit level adjustment unit.

12, the limit level adjustment unit 190 is provided between the A / D converter 160 and the limiter processing unit 180. The data input to the limit level adjustment unit 190 is accumulated n points in the buffering unit 191. Note that n, which is the number of accumulated data, may be selected, for example, the number of data necessary for the FFT processing in the blood flow calculation unit 170.

The peak detector 192 detects the peak value of the accumulated data. The LPF unit 193 averages the peak amounts detected by the peak detection unit 192. For this reason, the output of the LPF unit 193 is an average value of peak amounts.

The gain multiplying unit 194 multiplies the average value of the peak amount, which is the output of the LPF unit 193, by a predetermined gain (for example, 1.1 times). The upper limit setting unit 195 compares the output of the gain multiplication unit 194 with a predetermined upper limit value (that is, a limit level). If the upper limit setting unit 195 is larger than the predetermined upper limit value, the upper limit setting unit 195 is replaced with the predetermined upper limit value and output as a variable limit level. The On the other hand, when it is not larger than the predetermined upper limit value, it is output as a variable limit level as it is.

On the other hand, the output of the buffering unit 191 is also input to the limiter processing unit 180. The limiter processing unit 180 compares the buffered data with the variable limit level, and executes a process of replacing the data exceeding the variable limit level with the variable limit level. This process is the same as the process executed by the limiter processing unit 180 described with reference to FIG.

<Effects on mode hops>
Next, effects obtained by the measuring apparatus according to the second embodiment will be described with reference to FIGS. FIG. 13 is a graph showing data not subjected to limiter processing and the corresponding blood flow output. FIG. 14 is a graph showing data subjected to limiter processing and the corresponding blood flow output.

In FIG. 13 and FIG. 14, the limit data at the time of executing the limiter process is limited in waveform by the variable limit level as compared with the data when the limiter process is not performed, and is generated due to the mode hop noise of the semiconductor laser 120. It can be seen that the impulse waveform is removed.

Note that the variable limit level realized by the limit level adjusting unit 190 is an appropriate limiter level according to the amplitude of the data. Specifically, when the data amplitude level during normal operation is low, the limiter level is automatically lowered. On the other hand, when the amplitude level of data during normal operation is high, the limiter level automatically increases. Therefore, an appropriate limiter level can always be selected regardless of fluctuations in the amplitude level of data during normal operation. . With this configuration, the blood flow output can be output as a more appropriate waveform.

Incidentally, in the example shown in FIGS. 13 and 14, when the limiter process is not performed, a false pulse wave with a period shorter than 0.5 seconds is detected. On the other hand, when the limiter process is executed, a false pulse wave having a period shorter than 0.5 seconds is suppressed.

As described above, according to the measuring apparatus according to the second embodiment, as in the first embodiment, even if noise due to mode hops occurs, the influence is suppressed and more accurate blood flow measurement is performed. Is possible.

<Third embodiment>
Next, a measuring apparatus according to the third embodiment will be described with reference to FIG. The third embodiment differs from the first and second embodiments described above only in part of the configuration and operation, and many parts are the same as the first and second embodiments. For this reason, below, a different part from 1st and 2nd Example is demonstrated in detail, and description shall be abbreviate | omitted suitably about the overlapping part.

<Overall configuration>
The overall configuration of the measuring apparatus according to the third embodiment will be described with reference to FIG. FIG. 15 is a block diagram showing the overall configuration of the measuring apparatus according to the third embodiment.

15, the measurement apparatus according to the third embodiment includes a laser driving unit 110, a semiconductor laser 120, a light receiving element 130, an IV conversion unit 140, an analog amplitude limiter 150b, an amplifier 155, an A / A A D converter 160, a variable limiter processing unit 180b, and a blood flow calculation unit 170 are provided. That is, in the measurement apparatus according to the third embodiment, the analog amplitude limiter 150b and the variable limiter processing unit 180b that perform the limiter process are provided in each of the front stage and the rear stage of the A / D converter 160.

Similar to the amplitude limiter amplifier 150 (see FIG. 1) according to the first embodiment, the analog amplitude limiter 150b performs amplitude limitation by analog signal processing on the detection voltage output from the IV conversion unit 140. . The amplitude limitation in the analog amplitude limiter 150b is executed using a fixed limit level.

By limiting the amplitude by analog signal processing, it is possible to realize amplification to the amplitude in accordance with the D range of the A / D converter 160 in the subsequent amplification processing in the amplifier 155, and to reduce the quantization error. Become.

On the other hand, the variable limiter processing unit 180b performs amplitude limitation by digital signal processing on the data output from the A / D converter 160, similarly to the limiter processing unit 180 (see FIG. 10) according to the second embodiment. Unlike the analog amplitude limiter 150b, the amplitude limit in the variable limiter processing unit 180b is executed using a variable limit level.

∙ In the amplitude limit by digital signal processing, the limit level can be made variable to limit the amplitude more precisely. For this reason, more appropriate limit processing can be executed, and the influence of mode hop noise can be suppressed more appropriately.

As described above, according to the measuring apparatus according to the third embodiment, the limit process is performed by both the analog signal process and the digital signal process, and thus blood flow measurement can be more suitably performed. is there.

The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification. The method is also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 110 Laser drive part 120 Semiconductor laser 130 Light receiving element 140 IV conversion part 150 Amplitude limiter amplifier 151 Variable amplifier 152 BPF part 153 Amplitude limiter 154 AC amplifier 155 Amplifier 160 A / D converter 170 Blood flow calculation part 171 Hanning window process part 172 FFT processing unit 173 square calculation unit 174 primary moment integration unit 175 LPF unit 180 limiter processing unit 181 positive side level comparison unit 182 first data switching unit 183 -1 times processing unit 184 negative side level comparison unit 185 second data switching Unit 190 limit level adjustment unit 191 buffering unit 192 peak detection unit 193 LPF unit 194 gain multiplication unit 195 upper limit setting unit 200 object to be measured

Claims

Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Limiting means for limiting the amplitude of the output signal of the light receiving means within a predetermined range;
And an output means for outputting information relating to the movement of the object to be measured based on a beat signal resulting from a Doppler shift of the laser light included in an output signal of the light receiving means.
2. The measuring apparatus according to claim 1, wherein the limiting unit changes the predetermined range in accordance with a past amplitude of an output signal of the light receiving unit.
3. The measuring apparatus according to claim 1, wherein the limiting unit limits the amplitude before converting the output signal of the light receiving unit from an analog signal to a digital signal.
3. The measuring apparatus according to claim 1, wherein the limiting means limits the amplitude at a stage after the output signal of the light receiving means is converted from an analog signal to a digital signal.
3. The measuring apparatus according to claim 1, wherein the limiting unit limits the amplitude in both a stage before and after a step of converting an output signal of the light receiving unit from an analog signal to a digital signal. .
The light receiving means is
First and second photoelectric conversion element units for converting the laser light into current and outputting the current,
6. A differential current output unit that outputs a differential current between a current output from the first photoelectric conversion element unit and a current output from the second photoelectric conversion element unit as a detection current. The measuring apparatus as described in any one of.
An irradiation step of irradiating a measurement target with laser light;
A light receiving step for receiving the laser light scattered by the measurement object;
A limiting step of limiting the amplitude of the output signal obtained in the light receiving step within a predetermined range;
An output step of outputting information relating to the movement of the measurement target based on a beat signal resulting from a Doppler shift of the laser light included in the output signal obtained in the light receiving step.