JP2014059257A - Weak signal detection apparatus and weak signal detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a noise component sufficiently and to increase a SN ratio even if a signal is weak.SOLUTION: After modulating a benchmark signal by band diffusion, noise reduction is executed twice by having a first detection stage restoring a sensor signal including noise by back diffusion, and a second detection stage multiplying the restored signal and a reference signal of the benchmark signal for a phase detection.

Description

  The present invention relates to a weak signal detection device and a weak signal detection method capable of increasing the S / N ratio by removing noise from a weak signal detected by a sensor.

  When measuring weak signals such as weak radio waves and weak light from the detection signals detected by the sensor, it is necessary to reduce the noise component as much as possible to increase the SN ratio. Patent Document 1 discloses a device that detects a weak signal using a Hall element as a sensor. FIG. 8 shows a detection apparatus 100 described in Patent Document 1.

  As shown in FIG. 8, the detection apparatus 100 includes a wideband sensor 110 including a sensor element such as a Hall element, a wideband signal generator 120 that generates a wideband signal, and a wideband drive circuit 130 that drives the wideband sensor 110. And a demodulation circuit 140 for synchronously detecting the output signal from the broadband sensor 110 using the band spread signal output from the band spread signal generator 120. As the band spread signal generated by the band spread signal generator 120, for example, an M-sequence spread signal for performing spectrum spread is used, and the band spread drive circuit 130 drives the wide band sensor 110 by this band spread signal.

  A weak signal 150 to be measured is input to the broadband sensor 110 together with environmental noise 151 and element noise 152. The wideband sensor 110 is driven by a band spread signal generated by the band spread drive circuit 130 and outputs a band spread sensor signal. The band spread sensor signal is synchronously detected by the demodulation circuit 140 using the band spread signal from the band spread signal generator 120 and demodulated to obtain a measurement output 160.

  In such a structure, the broadband sensor 110 is driven by a spread spectrum signal by spread spectrum to obtain a sensor output from the broadband sensor 110 that has been spread spectrum, and is despread and demodulated to restore the original bandwidth. To do. At this time, since the noise spectrum is uncorrelated with the band spread signal, it is spread over a wide band and unnecessary components are removed and suppressed. For this reason, SN ratio can be made high.

WO2009-57626

  In the conventional detection apparatus 100 shown in FIG. 8, the noise output is controlled to be reduced by despreading and demodulating the sensor output from the wideband sensor 110 subjected to band spreading. In this control, the noise component is reduced. There is a limit to making it smaller. For this reason, when the signal to be detected is a weak signal such as a weak electric signal or weak light, it is difficult to increase the SN ratio and it is difficult to detect with high accuracy.

  The present invention has been made in consideration of such conventional problems, and even for weak signals such as weak radio waves and weak light, the noise component can be sufficiently reduced and the SN ratio is increased. It is an object of the present invention to provide a weak signal detection device and a weak signal detection method that can be used.

  In order to achieve the above object, the present invention provides a first detection step of modulating a reference signal by band spreading and then demodulating a sensor signal including noise by despreading, and a reference signal of the demodulated signal and the reference signal. And a second detection stage in which phase detection is performed by multiplying the two and the apparatus, and a method and a method for performing noise reduction twice.

  The weak signal detection apparatus according to the first aspect of the invention includes a modulation signal generation unit that generates a modulation signal by modulating a reference signal by band spreading, and a measurement target signal that is driven by the modulation signal from the modulation signal generation unit. A signal output to be output; a detection sensor for detecting a signal to be measured from the signal output device; a demodulated signal generator for demodulating the sensor signal from the detection sensor by despreading to generate a demodulated signal; and the reference signal And a phase sensitive detector for detecting a phase by multiplying the demodulated signal from the demodulated signal generator.

  3. The weak signal detection device according to claim 2, wherein a light source driving signal for driving the light emitting element is used as a reference signal, a modulation signal generating unit that generates a modulation signal by modulating the reference signal by band spreading, and the modulation signal generating unit. A light source driving circuit that is driven by a modulation signal from the light source to cause the light emitting element to emit light, a detection sensor that detects an optical signal obtained from the measurement object by irradiating the measurement object with light emitted from the light emitting element, and A demodulated signal generator that demodulates a sensor signal from a detection sensor by despreading to generate a demodulated signal, and a phase sensitive detector that performs phase detection by multiplying the reference signal of the reference signal and the demodulated signal from the demodulated signal generator And a detector.

  According to a third aspect of the present invention, there is provided a weak signal detecting device that generates a reference signal and a reference signal by periodically interrupting a weak light signal from a weak light emitter, and band-spreading the reference signal from the optical chopper A modulation signal generating unit that generates a modulation signal by modulating the detection signal, a detection sensor that detects a weak light signal from the weak light emitter modulated by the modulation signal from the modulation signal generation unit, and a detection sensor A demodulated signal generation unit that demodulates the sensor signal of the signal by despreading to generate a demodulated signal, and a phase sensitive detection unit that multiplies the reference signal from the optical chopper and the demodulated signal from the demodulated signal generation unit And.

  5. The weak signal detection device according to claim 4, wherein a detection sensor that receives a weak light signal from a weak light emitter and generates a reference signal and a reference signal, and modulates the reference signal from the detection sensor by modulation by band spreading. A modulation signal generation unit that generates a signal, a demodulation signal generation unit that demodulates the modulation signal from the modulation signal generation unit by despreading to generate a demodulation signal, a reference signal from the detection sensor, and the demodulation signal generation unit And a phase sensitive detector for detecting the phase by multiplying the demodulated signal from the signal.

  According to a fifth aspect of the present invention, the weak signal detection method generates a modulation signal by modulating the reference signal by band spreading, detects the measurement target signal driven based on the modulation signal, and then reverses the detected measurement target signal. A first detection stage for demodulating by spreading to generate a demodulated signal, and a second detection stage for phase detection by multiplying the reference signal of the reference signal and the demodulated signal are provided.

  The weak signal detection method according to claim 6 uses a light source driving signal for driving a light emitting element as a reference signal, modulates the reference signal by band spreading to generate a modulation signal, and drives the optical driving circuit by the modulation signal. After the light emitting element is caused to emit light and irradiate the measurement target, a light signal obtained from the measurement target is detected, a first detection step of demodulating the detected sensor signal by despreading to generate a demodulated signal, and And a second detection step of detecting a phase by multiplying a reference signal of a reference signal and the demodulated signal.

  The weak signal detection method according to claim 7, wherein a weak light signal from a weak light emitter is intermittently generated by an optical chopper to generate a reference signal and a reference signal, and the reference signal is modulated by band spreading to generate a modulation signal. A first detection stage in which a weak light signal from the weak light emitter is detected by being modulated by the modulation signal, and a demodulated signal is generated by demodulating the detected sensor signal by despreading; and a reference from the optical chopper And a second detection stage for phase detection by multiplying the signal and the demodulated signal.

  The weak signal detection method according to claim 8, wherein a weak light signal from a weak light emitter is received by a detection sensor as a reference signal and a reference signal, and the reference signal is modulated by band spreading to generate a modulation signal, A first detection stage that demodulates the modulated signal by despreading to generate a demodulated signal; and a second detection stage that multiplies the reference signal from the detection sensor and the demodulated signal to detect the phase. It is characterized by.

  According to the present invention, a phase detection is performed by multiplying a first detection step of modulating a reference signal by band spreading and then demodulating a sensor signal including noise by despreading, and the demodulated signal and a reference signal of the reference signal. Since the noise reduction is performed twice by configuring the second detection stage, the noise component can be sufficiently reduced even for weak signals such as weak radio waves and weak light, and the SN ratio can be increased. it can.

It is a block diagram which shows the weak signal detection apparatus of 1st Embodiment of this invention. It is a block diagram which shows the flow of the signal in 1st Embodiment. It is a graph which shows typically signal processing in the 1st detection stage. It is a graph which shows typically signal processing in the 2nd detection stage. It is a block diagram which shows the weak signal detection apparatus in 2nd Embodiment of this invention with the flow of a signal. It is a block diagram which shows the weak signal detection apparatus in 3rd Embodiment of this invention with the flow of a signal. It is a block diagram which shows the weak signal detection apparatus in 4th Embodiment of this invention with the flow of a signal. It is a block diagram which shows the conventional detection apparatus.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. In each embodiment, the same members are assigned the same reference numerals.

(First embodiment)
FIG. 1 is a block diagram of a weak signal detection apparatus 1 according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing a signal flow. The weak signal detection device 1 performs a first detection step of detecting a weak signal by noise compression limitation, and then performs a second detection step of band-limiting by a phase sensitive method, and performs noise reduction twice. There is a feature.

  As shown in FIG. 1, the weak signal detection apparatus 1 includes a modulation signal generation unit 2, a signal output device 3, a detection sensor 4, a demodulated signal generation unit 5, and a phase sensitive detection unit 6. The modulation signal generation unit 2, the signal output unit 3, the detection sensor 4, and the demodulated signal generation unit 5 perform the first detection stage, and the phase sensitive detection unit performs the second detection stage.

  As shown in FIGS. 1 and 2, the modulation signal generation unit 2 generates a modulation signal by spreading a reference signal 10 over a wide band and modulating it, and spread spectrum, frequency hopping, pseudo-random signal, FM modulation. The modulation signal 11 is generated by the above. In spread spectrum, either a direct spread method or a frequency spread method may be used. In the case of the direct spreading method, either an M-sequence spreading code or a PN pseudo code can be used as a pseudo random code.

  The signal output unit 3 receives the modulation signal 11 and is driven by the input modulation signal to generate the measurement target signal 13. The signal output unit 3 outputs the generated measurement target signal 13 to the noise space 14, and the detection sensor 4 receives and detects the measurement target signal that has passed through the noise space 14. The measurement target signal 13 that has passed through the noise space is in a state including noise 15 in the space, and is detected by the detection sensor 4 in this state. That is, the sensor signal detected by the detection sensor 4 is in a state where the measurement target signal 13 subjected to the band spread and the noise in the noise space 14 not subjected to the band spread are mixed. The sensor signal of the detection sensor 4 is output to the demodulated signal generator 5.

  The demodulated signal generator 5 demodulates the sensor signal from the detection sensor 4 to generate a demodulated signal 17. The demodulation of the sensor signal is performed by despreading, and demodulation is performed using the despreading code of the spreading code used in the modulation signal generation unit 2. In this demodulation, since the noise contained in the sensor signal has no correlation with the despread code, only the signal to be measured is restored and the demodulated signal 17 in which the noise is compressed is generated. Thus, the first detection stage is completed.

  FIG. 3 is a graph schematically showing signal processing in the first detection stage. In the normal signal state, the reference signal S and the noise N are mixed as shown in FIG. On the other hand, in this embodiment, the reference signal (measurement target signal) S is band-spread by spread spectrum as shown in FIG. The detection sensor 4 detects the band spread signal in a state including the noise N. Thereafter, the demodulated signal generator 5 despreads the sensor signal including the noise N. As a result, the noise N is compressed and the signal intensity of the noise N is reduced, so that the SN ratio can be improved.

  A second detection stage is performed following the first detection stage. In the second detection stage, the demodulated signal 17 generated by the demodulated signal generator 5 is output to the phase sensitive detector 6. In the phase sensitive detector 6, the phase detection is performed by multiplying the reference signal 18 of the reference signal 10 and the demodulated signal 17 from the demodulated signal generator 5. That is, the phase sensitive detector 6 performs phase detection by multiplying the demodulated signal 17 synchronized with the reference signal 18, and the phase sensitive detector 6 functions as a lock-in amplifier. For example, a signal having the same frequency as that of the reference signal 10 is used as the reference signal 18.

  After this phase detection, the output of the phase sensitive detector 6 is averaged by a low-pass filter to obtain a final output signal.

  FIG. 4 is a graph schematically showing signal processing in the second detection stage. FIG. 6A shows the demodulated signal F obtained in the first detection stage, in which the noise N is compressed by despreading. Phase detection is performed by multiplying the demodulated signal F by the reference signal of the phase sensitive detector 6. Since the band is limited by phase detection, the finally detected output signal has a noise N component dramatically reduced as shown in FIG. Thereby, SN ratio can be improved.

  In the weak signal detection of such an embodiment, after the reference signal 10 is modulated by band spreading such as spread spectrum to generate the measurement target signal 13, the measurement target signal 13 including noise is detected as a sensor signal. After performing the first detection step of despreading the sensor signal and compressing the noise, the phase sensitive detection unit 6 performs the second detection step of phase detection on the signal obtained in the first detection step. The reduction is doubled. For this reason, even if the detection target is a weak radio wave, the SN ratio of the detection can be increased, and the detection can be performed with high accuracy.

(Second Embodiment)
FIG. 5 is a block diagram showing a weak signal detection device 1A according to the second embodiment of the present invention together with a signal flow. The weak signal detection apparatus 1A of this embodiment is applied to detection of weak light, and performs noise reduction by double of the first detection stage and the second detection stage as in the first embodiment.

  The weak signal detection apparatus 1A of this embodiment drives the light emitting element 21 to irradiate the measurement target 25 with light, and the detection sensor 4 including the light receiving element receives and detects the optical signal from the measurement target 25. Is. In this embodiment, the modulation signal generation unit 2, the light source drive circuit 23, the light emitting element 21, the detection sensor 4, and the demodulation signal generation unit 5 perform the first detection stage, and the phase sensitive detection unit 6 performs the second detection stage.

  As the light emitting element 21, a light source such as a semiconductor laser (LD), a fixed laser, a gas laser, a light emitting diode (LED), or a flash lamp can be used. In this case, when an LD or LED is used as the light emitting element 21, it is easy to directly modulate the light source driving circuit 23. For this reason, a sine wave or a square wave can be oscillated as a reference signal of the phase sensitive detector 6 at 1 kHz or less, and then a lock-in amplifier can be applied with the spread signal. As the detection sensor 4, a high-speed response element such as a photomultiplier tube or APD (Abalanche Photodiode), or a light receiving element such as a Si diode or an InGaAs diode can be used.

  As the reference signal, a light source driving signal 22 for driving the light emitting element 21 is used. The modulation signal generator 2 modulates the light source drive signal 22 by band spreading. Band spreading can be performed by spread spectrum (SS spreading). The modulation signal generated by the spread spectrum is output to the light source drive signal 22, and the light source drive circuit 22 is driven by the input modulation signal to cause the light emitting element 21 to emit light.

  The light emitted from the light emitting element 21 is irradiated to the measurement object 25. An optical signal is generated from the measurement object 25 by irradiation of light from the light emitting element 21. When the measurement target is a lesion such as a cancer cell, excited single photooxygen is emitted by a photochemical reaction that is photoexcited to generate a weak light signal. Further, when the measurement target is a thick sample, a weak light signal transmitted through the measurement target is obtained. Although the weak optical signal from these measurement objects is detected by the detection sensor 4, the sensor signal detected by the detection sensor 4 includes noise.

  The sensor signal detected by the detection sensor 4 is output to the photocurrent / voltage conversion amplifier 26 and amplified, and then input to the demodulated signal generation unit 5. The demodulated signal generation unit 5 receives the diffusion synchronization signal 29 from the modulation signal generation unit 2 and demodulates the sensor signal from the detection sensor 4 by despreading. In this demodulation, since the noise included in the sensor signal has no correlation with the despread code, only the signal from the measurement target is restored, and a demodulated signal in which the noise is compressed is generated. Thus, the first detection stage is completed.

  In the second detection stage following the first detection stage, the demodulated signal generated by the demodulated signal generation section 5 is output to the phase sensitive detection section 6. The phase sensitive detection unit 6 performs phase detection by multiplying the reference signal 18 of the reference signal 10 and the demodulated signal from the demodulated signal generation unit 5. The phase sensitive detection unit 6 functions as a lock-in amplifier that detects the multiplication of the demodulated signal 17 synchronized with the reference signal 18 and detects the phase. The reference signal 18 is a signal having the same frequency as the light source drive signal 22.

  After this phase detection, the output of the phase sensitive detector 6 is averaged by a low-pass filter as indicated by reference numeral 27 to obtain a final output signal.

  In such weak signal detection, the light source drive signal 22 is modulated to drive the light emitting element 21, and the detection sensor 4 detects an optical signal including noise obtained from the measurement target 25 based on the light from the light emitting element 21. Then, after performing a first detection stage in which the sensor signal from the detection sensor 4 is despread to compress noise, a second detection is performed in which the phase sensitive detection unit 6 detects the phase of the signal obtained in the first detection stage. In order to perform the stage, the noise reduction is performed twice. For this reason, even if the optical signal obtained from the measurement object is a weak optical signal, the SN ratio can be increased and the signal can be detected with high accuracy.

  In this embodiment, the light emitting element 21 is used to detect a weak light signal emitted from the lesion by actively photoexciting the lesion such as cancer cells with high accuracy. Can be useful. When the measurement target is a thick sample, the weak light signal transmitted through the measurement target is detected with high accuracy, and thus can be suitably used for optical CT, mammography, and the like.

(Third embodiment)
FIG. 6 is a block diagram showing the weak signal detection device 1B according to the third embodiment of the present invention together with the signal flow. The weak signal detection apparatus 1B of this embodiment is also applied to detection of weak light, and performs double noise reduction in the first detection stage and the second detection stage.

  The weak signal detection apparatus 1 </ b> B of this embodiment detects a weak light signal from the weak light emitter 31 that emits light by a chemical reaction or the like, and is arranged so that the light chopper 32 faces the weak light emitter 31. The optical chopper 32 has a plurality of slits 32a formed on the circumference, and is driven to rotate at a predetermined angular velocity. As a result, the light chopper 32 periodically interrupts the light from the weak light emitter 31 to generate the reference signal 10 and the reference signal 18. The reference signal 10 is sent to the modulation signal generation unit 2 side, and the reference signal 18 is sent to the phase sensitive detection unit 6 side.

  The modulation signal generation unit 2 includes an optical shutter 33. The optical shutter 33 is formed by an electromagnet and a spring, and is disposed on the optical path of the reference signal 10. The optical shutter 33 band-spreads the reference signal 10 from the weak light emitter 31 and applies pseudo-random modulation. Band spreading can be performed by spread spectrum. The reference signal 10 from the weak light emitter 31 modulated by the optical shutter 33 passes through the space, and is detected by the detection sensor 4 including a light receiving element. The sensor signal detected by the detection sensor 4 includes noise.

  After the detection sensor 4 detects the reference signal 10 from the weak light emitter 31, it is the same as in the second embodiment, and the sensor signal detected by the detection sensor 4 is output to the photocurrent / voltage conversion amplifier 26 and amplified. Then, it is input to the demodulated signal generator 5 and demodulated by despreading. At this time, since the noise included in the sensor signal has no correlation with the despread code, only the reference signal 10 from the weak light emitter 31 is restored, and a demodulated signal in which the noise is compressed is generated. This ends the first detection stage.

  In the second detection stage following the first detection stage, the reference signal 18 from the optical chopper 32 and the demodulated signal generated by the demodulated signal generation section 5 are input to the phase sensitive detection section 6, and the reference signal is detected by the phase sensitive detection section 6. Phase detection (lock-in amplifier) is performed by multiplying 18 and the demodulated signal from the demodulated signal generator 5. After this phase detection 19, the output of the phase sensitive detection unit 6 is averaged by a low-pass filter as indicated by reference numeral 27 to obtain a final output signal.

  In such a weak signal detection, the characteristic that the weak light emitter 31 emits light is used, the optical chopper 32 generates the reference signal 10 by the weak light signal from the weak light emitter 31, and the reference signal 10 is band-spread. Thereafter, the detection sensor 4 detects an optical signal including noise, despreads the sensor signal from the detection sensor 4 and compresses the noise (first detection stage), and then the signal obtained in the first detection stage Since the phase sensitive detection unit 6 performs phase detection (second detection stage), noise reduction is performed twice. For this reason, even if the light signal emitted from the weak light emitter 31 is a weak light signal, the SN ratio can be increased and can be detected with high accuracy. In addition, since the weak light emitter 31 utilizes the characteristic that the light emitter 31 emits light by itself, the detection that does not require the light emitting element 21 as in the second embodiment is possible.

(Fourth embodiment)
FIG. 7 is a block diagram showing a weak signal detection apparatus 1C according to the fourth embodiment of the present invention together with a signal flow. The weak signal detection apparatus 1C of this embodiment also detects weak light using the characteristic that the weak light emitter 31 emits light by itself, and performs double noise reduction in the first detection stage and the second detection stage.

  As shown in FIG. 7, the optical signal emitted by the weak light emitter 31 itself is detected by the detection sensor 4 including a light receiving element. The detection sensor 4 receives the optical signal from the weak light emitter 31 to generate a standard signal and a reference signal. The modulation signal generator 2 includes a semiconductor switch 41 and modulates the reference signal by band spreading such as spectrum spreading. The modulated reference signal is amplified by the photoelectric voltage conversion amplifier 26 and then demodulated by despreading by the demodulated signal generation unit 5 to generate a demodulated signal. The demodulated signal is multiplied by a reference signal from the detection sensor 4 by the phase sensitive detection unit 6 to perform phase detection, averaged by a low-pass filter (reference numeral 27), and becomes a final output signal.

  Also in this embodiment, since the double noise reduction of the first detection stage and the second detection stage is performed, the SN ratio is increased even if the light signal emitted from the weak light emitter 31 is a weak light signal. Can be detected with high accuracy.

DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C Weak signal detection apparatus 2 Modulation signal generation part 3 Signal output device 4 Detection sensor 5 Demodulation signal generation part 6 Phase sensitive detection part 10 Reference signal 13 Measurement object signal 14 Noise space 15 Noise 17 Demodulation signal 18 Reference Signal 21 Light emitting element 22 Light source drive signal 23 Light source drive circuit 25 Measurement object 31 Weak light emitter 32 Optical chopper 33 Optical shutter

Claims (8)

A modulation signal generation unit that generates a modulation signal by modulating a reference signal by band spreading;
A signal output that is driven by the modulation signal from the modulation signal generator and outputs a measurement target signal;
A detection sensor for detecting a signal to be measured from the signal output device;
A demodulated signal generator for demodulating the sensor signal from the detection sensor by despreading to generate a demodulated signal;
A weak signal detection apparatus comprising: a phase sensitive detection unit that performs phase detection by multiplying a reference signal of the reference signal and a demodulated signal from the demodulated signal generation unit. A light source driving signal for driving the light emitting element as a reference signal, a modulation signal generating unit that generates a modulation signal by modulating the reference signal by band spreading;
A light source driving circuit that is driven by a modulation signal from the modulation signal generation unit to emit light from the light emitting element;
A detection sensor for detecting an optical signal obtained from the measurement target by irradiating the measurement target with light emitted from the light emitting element;
A demodulated signal generator for demodulating the sensor signal from the detection sensor by despreading to generate a demodulated signal;
A weak signal detection apparatus comprising: a phase sensitive detection unit that performs phase detection by multiplying a reference signal of the reference signal and a demodulated signal from the demodulated signal generation unit. An optical chopper that periodically generates a reference signal and a reference signal by intermittently and intermittently weak light signals from the weak light emitter;
A modulation signal generation unit that generates a modulation signal by modulating the reference signal from the optical chopper by band spreading;
A detection sensor for detecting a weak light signal from the weak light emitter in a state modulated by a modulation signal from the modulation signal generation unit;
A demodulated signal generator for demodulating the sensor signal from the detection sensor by despreading to generate a demodulated signal;
A weak signal detection apparatus comprising: a phase sensitive detection unit that performs phase detection by multiplying a reference signal from the optical chopper and a demodulation signal from the demodulation signal generation unit. A detection sensor that receives a weak light signal from a weak light emitter and generates a reference signal and a reference signal;
A modulation signal generation unit that modulates the reference signal from the detection sensor by band spreading to generate a modulation signal;
A demodulated signal generating unit that demodulates the modulated signal from the modulated signal generating unit by despreading to generate a demodulated signal;
A weak signal detection apparatus comprising: a phase sensitive detection unit that performs phase detection by multiplying a reference signal from the detection sensor and a demodulation signal from the demodulation signal generation unit. A reference signal is modulated by band spreading to generate a modulated signal, a measurement target signal driven based on the modulated signal is detected, and then the detected measurement target signal is demodulated by despreading to generate a demodulated signal. 1 detection stage;
A weak signal detection method comprising: a second detection step of performing phase detection by multiplying a reference signal of the reference signal and the demodulated signal. A light source driving signal for driving the light emitting element is used as a reference signal, the reference signal is modulated by band spreading to generate a modulation signal, and the light driving element is driven by the modulation signal to cause the light emitting element to emit light and to be measured A first detection stage that detects an optical signal obtained from the measurement target, demodulates the detected sensor signal by despreading, and generates a demodulated signal;
A weak signal detection method comprising: a second detection step of performing phase detection by multiplying a reference signal of the reference signal and the demodulated signal. A weak light signal from a weak light emitter is intermittently generated by an optical chopper to generate a reference signal and a reference signal, a modulation signal is generated by modulating the reference signal by band spreading, and a weak light signal from the weak light emitter is generated. A first detection stage that is modulated and detected by the modulation signal and demodulates the detected sensor signal by despreading to generate a demodulated signal;
A weak signal detection method comprising: a second detection step of phase detection by multiplying a reference signal from the optical chopper and the demodulated signal. A weak light signal from a weak light emitter is received by a detection sensor and used as a reference signal and a reference signal. The reference signal is modulated by band spreading to generate a modulated signal, and the modulated signal is demodulated by despreading and demodulated signal. A first detection stage that generates
A weak signal detection method comprising: a second detection step of phase detection by multiplying a reference signal from the detection sensor and the demodulated signal.

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