PIR Signal Conditioning Circuit

Abstract

The present application discloses a PIR signal conditioning circuit, which includes a bias module, a chopper amplifier module, an analog-to-digital converter, a Fourier transform module, and a decision module. The bias module is configured to obtain an induction signal from a PIR sensor and a bias control word from the Fourier transform module, remove at least part of the DC component in the induction signal according to the bias control word, and output a bias waveform. The chopper amplifier module is configured to amplify the bias waveform to obtain a chopped waveform. The analog-to-digital converter is configured to sample the chopped waveform to obtain a sampled waveform in the digital domain. The Fourier transform module is configured to transform the sampled waveform into the frequency domain to obtain a detection waveform, output the zero-frequency component and non-zero frequency component in the detection waveform, and the zero-frequency component is used to determine the bias control word. The decision module is configured to determine whether there is a detection target according to the non-zero frequency component. The present application can improve the sensitivity of target detection based on PIR signals.

Description

Technical Field

[0001] The present application relates to the technical field of signal processing, and particularly relates to a PIR signal conditioning circuit. Background Art

[0002] The PIR sensor made by passive infrared (PIR) technology is simple to use and low in cost, and is quite popular in the market. The PIR technology utilizes the pyroelectric principle and the bright and dark areas achieved by the Fresnel lens to realize the perception of human movement. The pyroelectric principle determines that the human body signal sensed by the PIR sensor is a very weak low-frequency signal. Therefore, the signal conditioning circuit of the PIR sensor needs to have low flicker noise and an efficient signal detection method to ensure that the PIR sensor has a long detection distance.

[0003] In the existing technology, the method of using an operational amplifier and a band-pass filter to perform signal conditioning and then detecting in the time domain has the advantage of a simple circuit structure, but it has the problem of low sensitivity in some scenarios. Summary of the Invention

[0004] In view of this, the present application provides a PIR signal conditioning circuit to solve the problem of low sensitivity in traditional PIR signal conditioning schemes.

[0005] A PIR signal conditioning circuit provided by the present application includes a bias module, a chopper amplifier module, an analog-to-digital converter, a Fourier transform module, and a decision module;

[0006] The bias module is configured to obtain an induction signal from a PIR sensor and a bias control word from the Fourier transform module, remove at least part of the DC component in the induction signal according to the bias control word, and output a bias waveform;

[0007] The chopper amplifier module is configured to amplify the bias waveform to obtain a chopped waveform;

[0008] The analog-to-digital converter is configured to sample the chopped waveform to obtain a sampled waveform in the digital domain;

[0009] The Fourier transform module is configured to convert the sampled waveform to the frequency domain to obtain a detection waveform, output the zero-frequency component and the non-zero frequency component in the detection waveform, and the zero-frequency component is used to determine the bias control word;

[0010] The decision module is configured to determine whether there is a detection target according to the non-zero frequency component.

[0011] Optionally, the chopper amplifier module includes a clock source, a first inverter, a second inverter, and a low-noise amplifier; an input terminal of the first inverter is configured to receive the bias waveform, a control terminal is connected to an output terminal of the clock source, and an output terminal is connected to an input terminal of the low-noise amplifier; an input terminal of the second inverter is the output terminal of the low-noise amplifier, a control terminal is connected to the output terminal of the clock source, and an output terminal is configured to output the chopped waveform.

[0012] Optionally, the PIR signal conditioning circuit further includes a low-pass filter; the low-pass filter is disposed between the chopper amplifier module and the analog-to-digital converter.

[0013] Optionally, a sampling rate of the analog-to-digital converter is greater than twice a cut-off frequency of the low-pass filter.

[0014] Optionally, the analog-to-digital converter is further configured to sample the chopped waveform in a data segment of each time window, and send the sampled waveform to the Fourier transform module at an end of the time window, where a plurality of the time windows are consecutive before and after.

[0015] Optionally, the bias module is provided with a weighted accumulator; the weighted accumulator is configured to scale a zero-frequency component by a preset multiple and accumulate the result with a bias control word of a current time window as a bias control word in a next time window.

[0016] Optionally, the time window further includes a gap segment located before the data segment; the gap segment is configured to reserve a stable time for the sampled waveform.

[0017] Optionally, the non-zero frequency components include a plurality of frequency points, and each frequency point has a corresponding detection threshold; the decision module is further configured to determine that a current detection target exists when detecting that at least one frequency point is greater than the corresponding detection threshold.

[0018] Optionally, the decision module is further configured to, if no detection target is detected in a time window, perform a weighted summation on each frequency point and a corresponding detection threshold of the time window, and use a result of the weighted summation as a detection threshold of a next time window.

[0019] Optionally, a sum of weights of each frequency point and the corresponding detection threshold is 1.

[0020] In the above PIR signal conditioning circuit of the present application, the bias module eliminates as much as possible the strong DC component in the induction signal before the chopper amplifier module, which can prevent the DC component caused by the chopper error in the chopper amplifier module from leaking into the effective signal. The chopper amplifier module amplifies the bias waveform by dozens of decibels, which can improve the accuracy of subsequent components in signal processing. The Fourier transform module converts the sampled waveform into the frequency domain to obtain the detection waveform, so that the zero-frequency component represents the bias residue in the bias waveform. Using the magnitude of this zero-frequency component to correct the bias control word can improve the residual bias in the bias waveform in the next time window. The non-zero frequency components represent the effective signals detected by the PIR sensor and are used to determine whether there is a detection target. When the noise floor levels at different frequency points are inconsistent, using the non-zero frequency components in the frequency domain for detection can balance the false alarm and missed detection performance at the system level. Compared with the time-domain signal decision scheme, the sensitivity of target detection based on the PIR signal is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 is a schematic structural diagram of a PIR signal conditioning circuit according to an embodiment of the present application;

[0023] Figure 2 is a schematic structural diagram of a chopper amplifier module according to an embodiment of the present application;

[0024] Figure 3 is a schematic diagram of related waveforms according to an embodiment of the present application;

[0025] Figure 4 is a schematic structural diagram of a PIR signal conditioning circuit according to another embodiment of the present application;

[0026] Figure 5 is a schematic diagram of a time window according to an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application. Without conflict, the following various embodiments and their technical features can be combined with each other.

[0028] The first aspect of the present application provides a PIR signal conditioning circuit. Refer toFigure 1 As shown, the above PIR signal conditioning circuit includes a bias module 110, a chopper amplifier module 120, an analog-to-digital converter 130, a Fourier transform module 140, and a decision module 150. Specifically, the first input terminal of the bias module 110 is connected to the output terminal of the PIR sensor for accessing the induction signal of the PIR sensor, the second input terminal is connected to the first output terminal of the Fourier transform module 140, and the output terminal is sequentially connected to the input terminal of the Fourier transform module 140 through the chopper amplifier module 120 and the analog-to-digital converter 130; the second output terminal of the Fourier transform module 140 is connected to the first input terminal of the decision module 150; the second input terminal of the decision module 150 is used for accessing a detection threshold, and the output terminal is used for outputting an indication signal of the presence or absence of a target. Optionally, components such as the bias module 110, the chopper amplifier module 120, the analog-to-digital converter 130, the Fourier transform module 140, and the decision module 150 operate in consecutive time windows respectively, and the time windows of each component are aligned with each other.

[0029] The bias module 110 is used to obtain the induction signal (i.e., the PIR signal) from the PIR sensor and the bias control word from the Fourier transform module 130, remove at least part of the DC component (such as a strong DC component or a DC component greater than a certain current value) in the induction signal according to the bias control word, and output a bias waveform. Specifically, the bias module 110 mainly eliminates the strong DC component in the induction signal as much as possible before the chopper amplifier module 120 to effectively prevent the DC component caused by the chopper error in the chopper amplifier module 120 from leaking into the effective signal (such as a non-zero frequency component), affecting the system performance, where the bias amount in the bias module 110 is only determined by the bias control word, and the bias control word remains unchanged within a time window.

[0030] The chopper amplifier module 120 is used to amplify the bias waveform to obtain a chopped waveform. Specifically, the chopper amplifier module 120 can amplify the weak bias waveform by dozens of decibels to improve the accuracy of subsequent components in signal processing.

[0031] The analog-to-digital converter 130 is used to sample the chopped waveform to obtain a sampled waveform in the digital domain.

[0032] The Fourier transform module 140 is used to convert the sampling waveform into the frequency domain to obtain a detection waveform, and output the zero-frequency component and the non-zero-frequency component in the detection waveform, wherein the zero-frequency component is used to determine the bias control word. Specifically, in the detection waveform, the zero-frequency component can characterize the DC component in the sampling waveform, that is, the bias residue in the bias waveform. Using the magnitude of this zero-frequency component to correct the bias control word can improve the residual bias in the bias waveform in the next time window; the non-zero-frequency component characterizes the effective signal detected by the PIR sensor, and is compared with the corresponding threshold to determine whether there is a target in the current field of view of the PIR sensor.

[0033] The decision module 150 is used to determine whether a detection target exists according to the non-zero frequency component, so as to output an indication signal indicating whether a detection target exists or not.

[0034] In the above-mentioned PIR signal conditioning circuit, the bias module 110 eliminates the strong DC component in the sensing signal as much as possible before the chopper amplifier module 120, which can prevent the DC component caused by the chopping error in the chopper amplifier module 120 from leaking into the effective signal. The chopper amplifier module 120 amplifies the weak bias waveform by tens of decibels, which can improve the accuracy of subsequent components when performing signal processing. The Fourier transform module 140 converts the sampling waveform into the frequency domain to obtain a detection waveform, so that the zero-frequency component represents the bias residue in the bias waveform. Using the size of this zero-frequency component to correct the bias control word can improve the residual bias in the bias waveform in the next time window. The non-zero frequency component represents the effective signal detected by the PIR sensor and is used to determine whether there is a detection target. When the background noise levels at different frequency points are inconsistent, the use of non-zero frequency component detection in the frequency domain can balance the false alarm and missed detection performance at the system level. Compared with the time domain signal judgment scheme, its detection sensitivity can be higher.

[0035] In one embodiment, reference Figure 2 As shown, the chopping amplifier module 120 includes a clock source 121, a first inverter 122, a second inverter 123 and a low noise amplifier 124. The input end of the first inverter 122 is used to access the bias waveform, the control end is connected to the output end of the clock source 121, and the output end is connected to the input end of the low noise amplifier 124; the input end of the second inverter 123 is connected to the output end of the low noise amplifier 124, the control end is connected to the output end of the clock source 121, and the output end is used to output the chopping waveform.

[0036] Specifically, the clock source 121 is used to output a clock signal to the first inverter 122 and the second inverter 123. The clock signal includes a high level and a low level. The high level is the inversion period, which is used to indicate that the corresponding inverter (such as the first inverter 122 and the second inverter 123) inverts the input signal. The first inverter 122 is used to invert the input signal (i.e., the bias waveform) during the inversion period of the clock signal. The low-noise amplifier 124 is used to amplify the signal after the inversion process, for example, amplifying the bias waveform by several tens of decibels. The second inverter 123 is used to invert the input signal during the inversion period of the clock signal.

[0037] In the above chopping amplifier module 120, because the low-noise amplifier 124 inevitably has propagation delay, when the clock source 121 drives the first inverter 122 and the second inverter 123, glitches will appear on the chopped waveform, as Figure 3 shown. The periodic appearance of glitches will introduce rich harmonic components, and these harmonic components will modulate the phase noise of the clock source 121, resulting in the deterioration of the noise performance in the entire chopped waveform. Considering that the glitches in the chopped waveform are caused by the unsynchronized inversion of the first inverter 122 and the second inverter 123, the glitch amplitude is equal to twice the amplitude of the output waveform of the low-noise amplifier 124. Eliminating the residual bias in the bias waveform can reduce the glitch amplitude, which helps to avoid the deterioration of the noise performance in the chopped waveform and ensure that the system-level detection performance is not affected by the chopping mechanism. In addition, the clock source 121 needs to have a relatively low oscillation frequency to achieve low power consumption, and at the same time, the oscillation frequency must be much higher than the cut-off frequency of the low-pass filter 124 to ensure sufficient suppression of the glitches in the chopped waveform by the low-pass filter. Preferably, the oscillation frequency of the clock source 121 is greater than 10 times or greater than 100 times the cut-off frequency of the low-pass filter.

[0038] In one example, as shown in Figure 4 the above PIR signal conditioning circuit further includes a low-pass filter 160; the low-pass filter 160 is disposed between the chopping amplifier module 120 and the analog-to-digital converter 130. The above low-pass filter 160 is used to perform low-pass filtering on the chopped waveform to suppress the high-frequency noise in the chopped waveform and the signal glitches introduced by the chopping amplifier circuit 120, and avoid sampling aliasing during the sampling process of the subsequent analog-to-digital converter 130; among them, the signal glitches introduced by the chopping amplifier circuit 120 are mainly caused by the signal delay between the first inverter 122 and the second inverter 123, that is, the delay of the low-noise amplifier 124. Therefore, the low-pass filter 160 adopts a second-order low-pass filter with a cut-off frequency of 5 - 10 Hz, which can effectively filter out the signal glitches introduced by the chopping amplifier circuit 120 in the chopped waveform.

[0039] Optionally, the sampling rate of the analog-to-digital converter 130 should be greater than twice the cut-off frequency of the low-pass filter 160 to avoid sampling aliasing during the sampling process of the analog-to-digital converter 130. Further, the sampling rate of the analog-to-digital converter 130 is 5 to 10 times the cut-off frequency of the low-pass filter 160, so that on the basis of anti-aliasing during the sampling process of the analog-to-digital converter 130, the corresponding circuit is easier to implement.

[0040] In one embodiment, the analog-to-digital converter 130 is further configured to sample the chopped waveform in the data segment of each time window and send the sampled waveform to the Fourier transform module at the end of the time window, where multiple time windows are consecutive before and after. For example, the time window can refer to Figure 5 As shown, it includes a gap segment and a data segment. All time windows are connected end to end. Each time window consists of a gap segment of M sample points followed by a data segment of N sample points. The sample points in the gap segment can be discarded, and the sample points in the data segment enter the Fourier transform module 140. M and N are preset positive integers; the sampled waveform obtained by sampling the analog-to-digital converter 130 can be segmented according to the time window. As Figure 5 Shown, at the end of each time window, the data segment of the sampled waveform within the current time window is immediately sent to the Fourier transform module 140 to be converted to the frequency domain to obtain the detection waveform. The length of the gap segment needs to be long enough to ensure that the sampled waveform after the bias control word of the bias module 110 is modified returns to stability. The number of sampling points N in the data segment can be lengths such as 16, 32, 64, 128, etc. The length of the time window can be set to about 1 second to 2 seconds to balance the detection ability and the response speed.

[0041] In one example, as Figure 4 Shown, the above-mentioned bias module 110 is provided with a weighted accumulator 112, that is, as Figure 4 Shown, the bias module 110 includes a bias processing unit 111 and a weighted accumulator 112. The first input end of the bias processing unit 111 is used to access the induction signal of the PIR sensor. The second input end is connected to the output end of the weighted accumulator 112, and the output end is connected to the input end of the chopping amplifier module 120. The input end of the weighted accumulator 112 is used to access the zero-frequency component.

[0042] The above-mentioned weighted accumulator 112 is used to access the zero-frequency component scaled by a preset multiple and accumulate it with the bias control word of the current time window as the bias control word in the next time window; the bias processing unit 111 is used to remove the strong DC component in the induction signal of the corresponding time window according to the bias control word and output the bias waveform.

[0043] Among them, the time window further includes a gap segment located before the data segment; the gap segment is used to reserve the stable time of the sampling waveform. The bias processing unit 111 can update the bias control word adopted by the corresponding time window during the length of the gap segment. Therefore, the length of the gap segment needs to be long enough to ensure that the processed waveform after the modification of the bias control word by the bias processing unit 111 returns to stability.

[0044] In one embodiment, the non-zero frequency components include multiple frequency points, and each frequency point has a corresponding detection threshold; the decision module 150 is further configured to determine that a detection target exists currently when at least one frequency point is detected to be greater than the corresponding detection threshold. The thresholds of each frequency point are set independently. When the background noise levels of different frequency points are inconsistent (the characteristic that the background noise levels of different frequency points are inconsistent comes from flicker noise and the low-pass filter. The former presents a 1 / f characteristic in frequency, that is, the lower the frequency, the greater the noise, and the latter has in-band fluctuation characteristics. These two reasons will both cause the background noise levels of different frequency points to be different), it can balance the false alarm and missed detection performance at the system level. Compared with the related time-domain decision scheme, the detection sensitivity of the target detection scheme according to the frequency-domain frequency points in this embodiment can be higher.

[0045] Optionally, the non-zero frequency components include multiple frequency points within one time window, and each frequency point has a corresponding detection threshold. Therefore, each time window has a corresponding threshold sequence, and the threshold sequence includes the detection thresholds corresponding to the respective frequency points within the corresponding time window.

[0046] In one example, the decision module 150 is further configured to, if no detection target is detected in a time window, perform a weighted sum of each frequency point and the corresponding detection threshold of this time window, and use the result of the weighted sum as the detection threshold of the next time window. For example, the weights of k frequency points (A1 to Ak) in time window n are a1, a2,..., ak in sequence, and the weights of the detection thresholds corresponding to the k frequency points (B1 to Bk) are b1, b2,..., bk in sequence. Then the detection threshold in time window n+1 can be the weighted sum of each frequency point and the corresponding detection threshold, and the corresponding detection thresholds can include: a1*A1 + b1*B1, a2*A2 + b2*B2,..., ak*AK + bk*BK. This example can update the threshold sequence to make the threshold sequence more accurate. The threshold sequence corresponding to the first time window is the initial threshold sequence, and the initial threshold sequence can be obtained through testing and solidified into the circuit in advance.

[0047] Optionally, the sum of the weights of each frequency point and the corresponding detection threshold is 1; as described above, the weights of k frequency points in time window n are a1, a2,..., ak in sequence, and the weights of the detection thresholds corresponding to the k frequency points are b1, b2,..., bk in sequence. Then a1 + b1 = 1, a2 + b2 = 1,..., ak + bk = 1.

[0048] In the above PIR signal conditioning circuit, the bias module 110 eliminates the strong DC component in the sensing signal as much as possible before the chopper amplifier module 120, which can prevent the DC component caused by the chopping error in the chopper amplifier module 120 from leaking into the effective signal. The chopper amplifier module 120 amplifies the weak bias waveform by tens of decibels, which can improve the accuracy of subsequent components when performing signal processing. The Fourier transform module 140 converts the sampling waveform into the frequency domain to obtain a detection waveform, so that the zero-frequency component represents the bias residue in the bias waveform. Using the size of this zero-frequency component to correct the bias control word can improve the residual bias in the bias waveform in the next time window. The non-zero frequency component represents the effective signal detected by the PIR sensor and is used to determine whether there is a detection target. When the background noise levels at different frequency points are inconsistent, the use of non-zero frequency component detection in the frequency domain can balance the false alarm and missed detection performance at the system level. Compared with the time domain signal judgment scheme, its detection sensitivity is higher.

[0049] Although the present application has been shown and described with respect to one or more implementations, equivalent variations and modifications will occur to those skilled in the art based on reading and understanding of this specification and the accompanying drawings. The present application includes all such modifications and variations and is limited only by the scope of the appended claims. In particular, with respect to the various functions performed by the above-mentioned components, the terms used to describe such components are intended to correspond to any component (unless otherwise indicated) that performs the specified function of the component (e.g., it is functionally equivalent), even if it is not structurally equivalent to the disclosed structure that performs the functions in the exemplary implementation of this specification shown herein.

[0050] That is, the above description is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of the present application, such as the mutual combination of technical features between the embodiments, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

[0051] In addition, in the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present application. In addition, for structural elements with the same or similar characteristics, the present application may use the same or different reference numerals for identification. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically defined.

[0052] In the present application, the term "exemplary" is used to mean "serving as an example, illustration, or explanation". Any embodiment described as "exemplary" in the present application is not necessarily to be construed as more preferred or more advantageous than other embodiments. The above description is given so that any person skilled in the art can make and use the present application. In the above description, various details are set forth for purposes of explanation. It should be understood that those of ordinary skill in the art can recognize that the present application can be practiced without these specific details. In other embodiments, well-known structures and processes are not elaborated in detail so as not to obscure the description of the present application with unnecessary details. Therefore, the present application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope that conforms to the principles and features disclosed in the present application.

Claims

1. A PIR signal conditioning circuit, characterized in that: The PIR signal conditioning circuit includes a bias module, a chopper amplifier module, an analog-to-digital converter, a Fourier transform module and a decision module; The bias module is used to obtain the sensing signal from the PIR sensor and the bias control word from the Fourier transform module, remove at least part of the DC component in the sensing signal according to the bias control word, and output a bias waveform; The chopping wave amplification module is used to amplify the bias waveform to obtain a chopping wave waveform; The analog-to-digital converter is used to sample the chopped waveform to obtain a sampled waveform in the digital domain; The Fourier transform module is used to convert the sampling waveform into the frequency domain to obtain a detection waveform, and output a zero-frequency component and a non-zero-frequency component in the detection waveform, wherein the zero-frequency component is used to determine the bias control word; The judgment module is used to determine whether a detection target exists according to the non-zero frequency component.

2. The PIR signal conditioning circuit according to claim 1, characterized in that: The chopping amplifier module includes a clock source, a first inverter, a second inverter and a low noise amplifier; The input end of the first inverter is used to access the bias waveform, the control end is connected to the output end of the clock source, and the output end is connected to the input end of the low noise amplifier; the input end of the second inverter is the output end of the low noise amplifier, the control end is connected to the output end of the clock source, and the output end is used to output the chopped waveform.

3. The PIR signal conditioning circuit according to claim 2, characterized in that: The PIR signal conditioning circuit also includes a low-pass filter; the low-pass filter is arranged between the chopping amplifier module and the analog-to-digital converter.

4. The PIR signal conditioning circuit according to claim 3, characterized in that: The sampling rate of the analog-to-digital converter is greater than twice the cut-off frequency of the low-pass filter.

5. The PIR signal conditioning circuit according to claim 1, characterized in that: The analog-to-digital converter is also used to sample the chopped waveform in a data segment of each time window, and send the sampled waveform to the Fourier transform module at the end of the time window, wherein a plurality of the time windows are consecutive.

6. The PIR signal conditioning circuit according to claim 5, characterized in that: The bias module is provided with a weighted accumulator; The weighted accumulator is used to accumulate the zero-frequency component scaled by a preset multiple and the bias control word of the current time window as the bias control word in the next time window.

7. The PIR signal conditioning circuit according to claim 6, characterized in that: The time window also includes a gap segment located before the data segment; the gap segment is used to reserve a stabilization time for the sampling waveform.

8. The PIR signal conditioning circuit according to claim 5, characterized in that: The non-zero frequency component includes multiple frequency points, each frequency point has a corresponding detection threshold; The judgment module is also used to determine that a detection target currently exists when it is detected that at least one frequency point is greater than a corresponding detection threshold.

9. The PIR signal conditioning circuit according to claim 5, characterized in that: The decision module is also used to perform weighted summation of each frequency point and the corresponding detection threshold in a time window if no detection target is detected in the time window, and use the result of the weighted summation as the detection threshold of the next time window.

10. The PIR signal conditioning circuit according to claim 9, characterized in that: The sum of the weights of each frequency point and the corresponding detection threshold is 1.

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