TWI609671B - Signal detection method - Google Patents

Description

Signal detection method

The invention relates to a signal detecting method, in particular to a method for detecting a peak to peak interval (PPI) of a light volume change signal obtained by an optical blood volume (PPG) sensor. Signal detection method.

The Photoplethysmography (PPG) sensor is a physical phenomenon that utilizes a change in the amount of attenuation caused by light passing through a human body, thereby obtaining a light volume change signal associated with the change in the amount of attenuation. At present, optical blood volume sensors have been widely used in wearable devices to collect data on physiological conditions of the human body, thereby instantly detecting and recording information such as heartbeat or blood pressure. For example, when the optical blood volume sensor is applied to the wrist of a human body, since the blood vessel of the wrist has a significant volume change with the beating of the heart, the light volume change signal will be periodic and exhibiting ups and downs. The waveform, and the light volume change signal can calculate the heartbeat or other physiological state information of the human body. However, how to accurately obtain the peak-to-peak interval of the optical volume change signal of the optical blood volume sensor (Peak to Peak) Interval; PPI) has become an important issue.

Accordingly, it is an object of the present invention to provide a signal detecting method for accurately obtaining a peak-to-peak interval of a light volume change signal.

Therefore, the signal detecting method of the present invention is suitable for processing a light volume change signal obtained from a photoplethysmography (PPG) sensor, wherein the light volume change signal is a digital signal, and the signal detecting method includes the following: Step: (a) performing baseline filtering and band pass filtering on the optical volume change signal by a filter; (b) each of the optical volume change signals processed by the processor (a) by the processor (a) Sampling point, calculating a corresponding region slope value, defining that the light volume change signal includes N sampling points, N is a positive integer, and the slope value of the region corresponding to the i-th sampling point is related to the i-2th sampling point, I-1 sampling points, ith sampling points, i+1th sampling points, and i+2 sampling points, i is an integer from 0 to (N-1); (c) by the processor According to a threshold, when the slope value of the region corresponding to the i-th sampling point is greater than one-half of the threshold value, determining that the slope value of the region corresponding to the i-th sampling point is an area corresponding to the i-th sampling point Maximum slope value, the threshold value is related to the threshold corresponding to the i-1th sampling point And the corresponding i-th sampling point value of the slope region; and (d) by the processor in each zone of such sample points after the maximum slope value, Search for the sampling point corresponding to the slope value of the region from positive to negative, and determine that the sampling point corresponding to the slope value of the region is a peak position.

In some implementations, wherein in step (a), the bandpass filtering of the filter is to preserve a frequency band between 0.5 Hz and 4 Hz.

In some implementations, wherein in step (b), the slope value of the region corresponding to the i-th sampling point is equal to 3*S3+S1+3*S2+S4, wherein S1 is the i-th sampling The slope between the point and the i-1th sampling point, S2 is the slope between the i-1th sampling point and the i th sampling point, and S3 is the i th sampling point and the i+1th sampling point The slope between, S4 is the slope between the i+1th sampling point and the i+2th sampling point.

In some implementations, in step (c), the threshold value slope_threshold_i corresponding to the i-th sampling point, the threshold value slope_threshold_i-1 corresponding to the i-1th sampling point, and the corresponding i-th sampling The relationship of the region slope value input_slope of the point is as follows, slope_threshold_i=(slope_threshold_i-1+input_slope)/2.

In some implementations, wherein in step (d), the processor further searches for the sampling point corresponding to the slope value of the region from negative to positive in the sampling points after the maximum slope value of each region, and It is also decided that the sampling point corresponding to the region slope value from negative to positive is a trough position.

In some implementations, wherein, in step (c), when the processor When the slope value of the region corresponding to the ith sampling point is the maximum slope value of the region corresponding to the ith sampling point, the processor determines the slope value of the regions within a predetermined time after the ith sampling point. Neither will the slope of these areas be the maximum.

In some embodiments, wherein in step (c), the predetermined time is equal to 0.24 seconds.

In some implementations, wherein the time interval of each sampling point included in the light volume change signal is between 4 milliseconds and 40 milliseconds (ms).

The effect of the invention is that: by dynamically adjusting the threshold value, it is determined whether the slope value of each region is the maximum slope value of a region, and then searching and determining the locations of the sampling points according to the position of the maximum slope value of each region. The peak positions are such that the peak-to-peak spacing of the light volume change signal is correctly detected without interference from other factors.

(a)~(d)‧‧‧ steps

PP1~PP6‧‧‧ sampling point

S1~S4‧‧‧ slope

M1~M6‧‧‧ position

P1~P6‧‧‧ position

Other features and advantages of the present invention will be apparent from the embodiments of the present invention. FIG. 1 is a flow chart illustrating the flow of steps of an embodiment of the signal detecting method of the present invention; FIG. FIG. 3 is a schematic view showing a state of the light volume change signal after the step (a) of the embodiment; Figure 4 is a schematic diagram showing how step (b) of the embodiment calculates a region slope value; and Figure 5 is a schematic diagram illustrating the peak positions determined by step (d) of the embodiment.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

Referring to FIG. 1, an embodiment of the signal detecting method of the present invention is suitable for processing a light volume change signal obtained from an optical blood volume (PPG) sensor, and the light volume change signal is a digital signal. More precisely, the PPG sensor first generates an analog light volume change signal, and then performs an analog digital conversion, and outputs the digital light volume change signal of the digital position. Moreover, the analog digital conversion of the optical volume change signal is not limited to being performed by the PPG sensor, but may be performed by other electronic devices. The light volume change signal includes N sampling points, which are sequentially the 0th sampling point, the 1st sampling point, the ith sampling point, the N-1th sampling point, and the N is a positive integer, and i is an integer from 0 to (N-1). In this embodiment, the time interval of each sampling point of the light volume change signal is 4 milliseconds (ms), that is, the light volume change signal is obtained by sampling at a sampling frequency of 250 Hz. In other embodiments, the sampling frequency can also be between 25 Hz and 250 Hz, also That is to say, the time interval of each sampling point of the light volume change signal is between 4 milliseconds and 40 milliseconds.

The signal detection method includes steps (a) to (d).

In step (a), the light volume change signal is subjected to baseline filtering and band pass filtering by a filter. In more detail, the band pass filtering performed by the filter retains the light volume change signal. A frequency band between 0.5 hertz (Hz) and 4 Hz, and filtering out a frequency band less than 0.5 Hz and greater than 4 Hz. Referring to FIG. 2 and FIG. 3, the horizontal axis of FIGS. 2 and 3 is a number, which is represented as the i-th sampling point, and the vertical axis is the relative magnitude of the amplitude, and the physical unit is, for example, a voltage representing the magnitude of the change in the light volume. For example, FIG. 2 is a primitive aspect of the digital volume change signal of the digit, with a phenomenon of baseline drift, and FIG. 3 is a view of the optical volume signal of the digit after baseline filtering and bandpass filtering. It is further added that the continuous fold lines shown in Fig. 2 and Fig. 3, in fact, should be composed of discontinuous sampling points if the horizontal axis is enlarged and viewed, as shown in Fig. 4.

Referring to FIG. 1, in step (b), a corresponding region slope value is calculated by a processor for each sampling point included in the light volume change signal processed in step (a), that is, the N sampling points. . And the slope value of the region corresponding to the ith sampling point is related to the i-2th sampling point, the i-1th sampling point, the ith sampling point, the i+1th sampling point, and the i+2th Sampling point. Referring again to FIG. 4, in more detail, the slope value of the region corresponding to the i-th sampling point PP3 is equal to 3*S3+S1+3*S2+S4, where S1 is the i-2th. The slope between the sample PP1 and the i-1th sampling point PP2, S2 is the slope between the i-1th sampling point PP2 and the i-th sampling point PP3, and S3 is the i-th sampling point PP3 and the i-th The slope between +1 sampling points PP4, S4 is the slope between the i+1th sampling point PP4 and the i+2th sampling point PP5.

Referring to FIG. 1, in step (c), the processor determines, according to a threshold, that the i-th sampling point is corresponding when the slope value of the region corresponding to the i-th sampling point is greater than one-half of the threshold value. The slope value of this region is the maximum slope value of a region corresponding to the i-th sampling point. The threshold value is related to the threshold value corresponding to the i-1th sampling point and the slope value of the region corresponding to the i-th sampling point. In more detail, the relationship between the threshold value slope_threshold_i corresponding to the i-th sampling point, the threshold value slope_threshold_i-1 corresponding to the i-1th sampling point, and the slope value input_slope of the region corresponding to the i-th sampling point is as follows. Slope_threshold_i=(slope_threshold_i-1+input_slope)/2, therefore, the threshold value is dynamically adjusted to determine whether the slope value of each region is the maximum slope value of a region. Referring to FIG. 5 again, FIG. 5 is similar to FIG. 2 or FIG. 3, wherein the horizontal axis is a number, which is represented as the i-th sampling point, and the vertical axis is the relative magnitude of the amplitude, and the physical unit is, for example, a voltage representing the amount of change of the light volume. The size, for example, the curve passing through the positions P1 to P6 is the light volume change signal (ie, a part of the N sampling points) processed through the step (a), and the other curve is the processed through the step (b). The area slope value, where the position M1~M6 on the curve passing through the positions P1~P6 is the corresponding area The sampling points of the maximum slope value of the domain.

Furthermore, in the step (c), when the processor determines that the slope value of the region corresponding to the i-th sampling point is the maximum slope value of the region corresponding to the i-th sampling point, the processor determines that the i-th The slope values of the regions within a predetermined time after the sampling point are not the maximum slopes of the regions. For example, if the light volume change signal is generated by the PPG sensor detecting the blood vessel of the human body, the heart rate of the human body is normally less than 250 beats per minute, and therefore, an area is determined by the processor. Within 60/250 = 0.24 seconds after the maximum slope value, the sampling points should not have the maximum slope value of the next region. Therefore, the processor directly determines the regions within the predetermined time (eg, 0.24 seconds). The slope value will not be the maximum value of the slope of the regions, or the processor may not determine whether the slope value of the regions is the maximum value of the slopes of the regions during the predetermined time (eg, 0.24 seconds) to save The resources of the operation processing.

Referring to FIG. 1, in step (d), the processor searches for the sampling point corresponding to the slope value of the corresponding region in the corresponding sampling point after the maximum slope value of each region, and determines the corresponding region. The slope value is a peak position from the positively negative negative sampling point. Referring again to FIG. 5, for example, via the step (c), the processor obtains the sampling points corresponding to the maximum slope value of the equal regions, that is, the positions M1 to M6. After the six sampling points of the positions M1~M6, the processor searches for and determines the sampling point corresponding to the positive slope of the region, that is, the position P1~P6, that is, the processor passes the step (d) Judging the peak position of the light volume change signal, and then correctly detecting Peak to Peak Interval (PPI) of the light volume change signal.

In addition, in this embodiment, the peak positions of the optical volume signals can be searched for and determined through the step (d). Similarly, in other embodiments, the maximum slope value of the processor in each region. In the subsequent sampling points, it is also possible to search for the sampling point corresponding to the slope value of the region from negative to positive, to determine the sampling point corresponding to the slope value of the region from negative to positive, that is, to search for and determine the light. The position of each trough of the volume change signal.

In summary, the signal detection method of the present invention dynamically adjusts the threshold value to determine whether the slope value of each region is the maximum slope value of a region, and then searches for and determines the position according to the maximum slope value of each region. The position of the peaks in the sampling points enables the peak-to-peak spacing of the light volume change signal to be correctly detected without interference from other factors, and thus can be applied to heart rate detection, diagnosis of cardiovascular conditions of the human body, or The data of the physiological state of the human body is collected, so that the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the simple equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still Within the scope of the invention patent.

(a)~(d)‧‧‧ steps

Claims (7)

A signal detection method is suitable for processing a light volume change signal obtained from an optical blood volume (PPG) sensor, wherein the light volume change signal is a digital signal, and the signal detection method comprises the following steps: a) performing baseline filtering and band pass filtering on the optical volume change signal by a filter; (b) each sampling point included in the optical volume change signal processed by the processor (a) by a processor, Calculating a corresponding region slope value, defining that the light volume change signal includes N sampling points, N is a positive integer, and the slope value of the region corresponding to the ith sampling point is related to the i-2th sampling point, the i-1 The sampling point, the i-th sampling point, the i+1th sampling point, and the i+2th sampling point, i is an integer from 0 to (N-1), and the slope of the region corresponding to the i-th sampling point The value is equal to 3*S3+S1+3*S2+S4, where S1 is the slope between the i-2th sampling point and the i-1th sampling point, and S2 is the i-1th sampling point and the i th The slope between the sampling points, S3 is the slope between the i-th sampling point and the i+1th sampling point, and S4 is the i+1th sampling point and the i+2 The slope between the points; (c) by the processor according to a threshold value, when the slope value of the region corresponding to the i-th sampling point is greater than one-half of the threshold value, determining the corresponding i-th sampling point The slope value of the region is a maximum slope value corresponding to an area of the i-th sampling point, and the threshold value is related to the threshold value corresponding to the i-1th sampling point and the slope value of the region corresponding to the i-th sampling point; and d) by the processor after the maximum slope value in each region In the sampling point, the sampling point corresponding to the slope value of the region is changed from positive to negative, and the sampling point corresponding to the slope value of the region is determined to be a peak position. The signal detecting method according to claim 1, wherein in the step (a), the band pass filtering performed by the filter is to retain the frequency band of the optical volume change signal between 0.5 Hz and 4 Hz. . The signal detecting method according to claim 2, wherein in step (c), the threshold value slope_threshold_i corresponding to the i-th sampling point, the threshold value slope_threshold_i-1 corresponding to the i-1th sampling point, and The relationship of the slope value input_slope of the region corresponding to the i-th sampling point is as follows, slope_threshold_i=(slope_threshold_i-1+input_slope)/2. The signal detecting method according to claim 3, wherein in the step (d), the processor searches for the corresponding region slope value from negative to positive in the sampling points after the maximum slope value of each region. The sampling point, and also determines that the sampling point corresponding to the region slope value from negative to positive is a trough position. The signal detecting method according to claim 3, wherein, in the step (c), the processor determines that the slope value of the region corresponding to the i-th sampling point is the maximum slope value of the region corresponding to the i-th sampling point. When the processor determines that the slope values of the regions within a predetermined time after the ith sampling point are not the maximum values of the regions. The signal detecting method according to claim 5, wherein in the step (c), the predetermined time is equal to 0.24 seconds. The signal detecting method according to claim 6, wherein the light volume change signal The time interval of each sample point included in the number is between 4 milliseconds and 40 milliseconds (ms).