PIR signal conditioning circuit

Abstract

The invention discloses a PIR signal conditioning circuit. The PIR signal conditioning circuit comprises a bias module, a chopping amplification module, an analog-to-digital converter, a Fourier transform module and a judgment module, the bias module is used for acquiring an induction signal from a PIR sensor and a bias control word from the Fourier transform module, removing at least part of direct current components in the induction signal according to the bias control word, and outputting a bias waveform; the chopping amplification module is used for amplifying the bias waveform to obtain a chopping waveform; the analog-to-digital converter is used for sampling the chopping waveform to obtain a sampling waveform of a digital domain; the Fourier transform module is used for converting the sampling waveform into a frequency domain to obtain a detection waveform and outputting a zero frequency component and a non-zero frequency component in the detection waveform, and the zero frequency component is used for determining the bias control word; and the judgment module is used for determining whether a detection target exists or not according to the non-zero frequency component. According to the invention, the sensitivity of target detection according to the PIR signal can be improved.

Description

Technical Field

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

[0002] Passive infrared (PIR) sensors made with passive infrared (PIR) technology are easy to use, low-cost, and very popular in the market. PIR technology uses the pyroelectric principle to superimpose the bright and dark areas of the Fresnel lens to realize the perception of human movement. The pyroelectric principle determines that the human signal perceived 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 longer detection distance.

[0003] In the existing technology, an operational amplifier and a bandpass filter are used to implement detection in the time domain after signal conditioning. This method 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 of traditional PIR signal conditioning solutions.

[0005] The present application provides a PIR signal conditioning circuit, comprising 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 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;

[0007] The chopping wave amplification module is used to amplify the bias waveform to obtain a chopping wave waveform;

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

[0009] 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;

[0010] The judgment module is used to determine whether a detection target exists according to the non-zero frequency component.

[0011] Optionally, the chopping amplification 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 connected to 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 chopping waveform.

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

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

[0014] Optionally, the analog-to-digital converter is further 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.

[0015] Optionally, 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 with the bias control word of the current time window as the bias control word in the next time window.

[0016] Optionally, the time window further includes a gap segment located before the data segment; the gap segment is used to reserve stabilization time for the sampling waveform.

[0017] Optionally, 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 the corresponding detection threshold.

[0018] Optionally, the judgment module is further configured to perform weighted summation on each frequency point and a 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 for the next time window.

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

[0020] In the above-mentioned PIR signal conditioning circuit of the present application, the bias module eliminates the strong DC component in the sensing signal as much as possible before the chopper amplifier module, which can prevent the DC component caused by the chopping error in the chopper amplifier module from leaking into the effective signal. The chopper amplifier module amplifies the bias waveform by tens of decibels, which can improve the accuracy of subsequent components when performing signal processing. The Fourier transform module 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 sensitivity for 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 drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

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

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

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

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

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

[0027] The technical solutions in the embodiments of the present application are clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application. In the absence of conflict, the following 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. Figure 1 As shown, the above-mentioned 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 end of the bias module 110 is connected to the output end of the PIR sensor for accessing the sensing signal of the PIR sensor, the second input end is connected to the first output end of the Fourier transform module 140, and the output end is connected to the input end of the Fourier transform module 140 through the chopper amplifier module 120 and the analog-to-digital converter 130 in sequence; the second output end of the Fourier transform module 140 is connected to the first input end of the decision module 150; the second input end of the decision module 150 is used to access the detection threshold, and the output end is used to output an indication signal of the presence or absence of the target. Optionally, the 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 respectively work in each continuous time window, and the time windows of each component are aligned with each other.

[0029] The bias module 110 is used to obtain the sensing signal (i.e., 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 (e.g., a strong DC component, or a DC component greater than a certain current value) in the sensing signal according to the bias control word, and output a bias waveform. Specifically, the bias module mainly eliminates the strong DC component in the sensing signal as much as possible before the chopper amplifier module 120, so as to effectively prevent the DC component caused by the chopping error in the chopper amplifier module 120 from leaking into the effective signal (e.g., non-zero frequency component) and affecting the system performance, wherein 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 chopper waveform. Specifically, the chopper amplifier module 120 can amplify the weak bias waveform by tens of decibels to improve the accuracy of subsequent components when performing 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 for at least the corresponding inverter (such as the first inverter 122 and the second inverter 123) to invert 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 inverted signal, for example, to amplify the bias waveform by 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-mentioned chopper amplifier module 120, because the low noise amplifier 124 inevitably has a propagation delay, when the clock source 121 drives the first inverter 122 and the second inverter 123, glitches will appear on the chopper waveform, such as Figure 3 As shown, the periodic appearance of glitches will introduce abundant harmonic components, which will modulate the phase noise of the clock source 121, resulting in deterioration of the noise performance in the entire chopping waveform. Considering that the glitches in the chopping 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 amplitude of the glitches, help avoid the deterioration of the noise performance in the chopping 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 lower oscillation frequency to achieve low power consumption, and the oscillation frequency must be much higher than the cutoff frequency of the low-pass filter 124 to ensure that the low-pass filter has sufficient suppression of the glitches in the chopping waveform. Preferably, the oscillation frequency of the clock source 121 is greater than 10 times the cutoff frequency of the low-pass filter or greater than 100 times the cutoff frequency of the low-pass filter.

[0038] In one example, reference Figure 4 As shown, the PIR signal conditioning circuit further includes a low-pass filter 160; the low-pass filter 160 is arranged between the chopper amplifier module 120 and the analog-to-digital converter 130. The low-pass filter 160 is used to perform low-pass filtering on the chopper waveform to suppress the high-frequency noise in the chopper waveform and the signal glitches introduced by the chopper amplifier circuit 120, so as to avoid sampling aliasing in the subsequent analog-to-digital converter 130 during the sampling process; wherein the signal glitches introduced by the chopper 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, so the low-pass filter 160 adopts a second-order low-pass filter with a cut-off frequency of 5 to 10 Hz, which can effectively filter out the signal glitches introduced by the chopper amplifier circuit 120 in the chopper waveform.

[0039] Optionally, the sampling rate of the analog-to-digital converter 130 is greater than 2 times the cutoff 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 cutoff frequency of the low-pass filter, so that the analog-to-digital converter 130 can resist aliasing during the sampling process, and the corresponding circuit can be more easily implemented.

[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, wherein the multiple time windows are consecutive, for example, the time windows can refer to Figure 5 As shown, it includes gap segments and data segments, all time windows are connected end to end, and each time window is composed of a gap segment of M sample points followed by a data segment of N sample points, wherein the sample points of the gap segment can be discarded, and the sample points of the data segment enter the Fourier transform module 140, where M and N are preset positive integers; the sampling waveform obtained by the analog-to-digital converter 130 can be segmented according to the time window, such as Figure 5 As shown, at the end of each time window, the data segment of the sampling waveform in the current time window is immediately sent to the Fourier transform module 140 for conversion into the frequency domain to obtain a detection waveform, wherein the length of the gap segment needs to be long enough to ensure that the sampling waveform modified by the bias control word of the bias module 110 is stable, the number of sampling points N in the data segment can be 16, 32, 64, 128, etc., and the time window length can be set at about 1 second to 2 seconds to balance the detection capability and response speed.

[0041] In one example, if Figure 4 As shown, the above-mentioned bias module 110 is provided with a weighted accumulator 112, that is, Figure 4 As shown, the bias module 110 includes a bias processing unit 111 and a weighted accumulator 112, wherein a first input end of the bias processing unit 111 is used to access the sensing signal of the PIR sensor, a 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 chopper amplifier module 120, and the input end of the weighted accumulator 112 is used to access the zero-frequency component.

[0042] The weighted accumulator 112 is used to access the zero-frequency component after scaling by a preset multiple and add it to 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 induced signal of the corresponding time window according to the bias control word and output a bias waveform.

[0043] The time window also includes a gap segment before the data segment; the gap segment is used to reserve the stabilization time of the sampled waveform. The bias processing unit 111 can update the bias control word used in the corresponding time window at the gap segment length, so the gap segment length needs to be long enough to ensure that the processed waveform after the bias control word of the bias processing unit 111 is modified is stable.

[0044] In one embodiment, the non-zero frequency component includes multiple frequency points, each frequency point has a corresponding detection threshold; the decision module 150 is also used to determine that there is a detection target when at least one frequency point is detected to be greater than the corresponding detection threshold. The threshold of each frequency point is set independently, which can balance the false alarm and missed detection performance of the system level when the noise floor levels of different frequency points are inconsistent (the inconsistent noise floor levels of different frequency points are derived from flicker noise and low-pass filters. The former presents a 1 / f characteristic in frequency, that is, the lower the frequency, the greater the noise, and the latter has an in-band fluctuation characteristic. Both of these reasons will lead to different noise floor levels at different frequency points). Compared with the relevant time domain decision scheme, the detection sensitivity of the scheme for target detection based on the frequency domain frequency points in this embodiment can be higher.

[0045] Optionally, the non-zero frequency component includes multiple frequency points in a time window, each frequency point has a corresponding detection threshold, and thus each time window has a corresponding threshold sequence, which includes the detection threshold corresponding to each frequency point in the corresponding time window.

[0046] In one example, if the detection target is not detected in a time window, the judgment module 150 is also used to perform weighted summation of each frequency point and the corresponding detection threshold in the time window, and use the result of the weighted summation as the detection threshold of the next time window. For example, the weights of the k frequency points (A1 to Ak) in the time window n are a1, a2, ..., ak, and the weights of the detection thresholds (B1 to Bk) corresponding to the k frequency points are b1, b2, ..., bk, respectively. Then, the detection threshold in the time window n+1 can be the weighted summation of each frequency point and the corresponding detection threshold, and the corresponding detection threshold 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, which can be obtained by 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 mentioned above, the weights of the k frequency points in the time window n are a1, a2, ..., ak, and the weights of the detection thresholds corresponding to the k frequency points are b1, b2, ..., bk, 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 specification 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 terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, which are 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 therefore cannot be understood as a limitation on 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 understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0052] In this application, the word "exemplary" is used to mean "used as an example, illustration or description". Any embodiment described as "exemplary" in this application is not necessarily to be construed as being more preferred or more advantageous than other embodiments. In order to enable any technician in the field to implement and use the present application, the present application provides the above description. In the above description, various details are listed for the purpose of explanation. It should be understood that a person of ordinary skill in the art can recognize that the present application can be implemented without using these specific details. In other embodiments, well-known structures and processes will not be elaborated in detail to avoid unnecessary details that make the description of the present application obscure. Therefore, the present application is not intended to be limited to the embodiments shown, but is consistent with the widest range of 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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