JPH0357429A - Pulse detecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photoelectric pulse detection circuit used in electronic devices such as electronic wristwatches.

[Conventional technology]

Pulse detection is done by detecting vibrations in the arteries caused by the beating of the heart. A method for detecting heart sounds caused by heartbeats. Methods such as detecting changes in blood volume are used. In particular, small electronic devices use optical means to detect changes in blood volume.
An effective method is to measure pulse rate, etc. from the photoplethysmogram obtained by this method. For example, by providing a light emitting element such as an LED (light emitting diode) and a light receiving element such as a phototransistor, the finger is irradiated with light from the light emitting element, and the reflected light or transmitted light is incident on the light receiving element. Detects changes in blood volume due to blood pulsation as changes in the amount of light received,
A filter circuit is used to filter the optical pulse wave obtained by this. The pulse rate is measured by converting it into a signal corresponding to the pulse rate via an amplifier, waveform shaping circuit, etc.

However, in the method of measuring blood N changes using optical means, detection is performed using a light-receiving element such as a phototransistor, so light from a fluorescent lighting device or external light such as sunlight is received. It works.

[Problem to be solved by the invention]

As mentioned above, in the method of measuring blood volume changes using optical means, a disturbance signal can be obtained by intermittently blocking the upper part of the detection surface with extraneous light and an object that can block this light. I end up. It is necessary to distinguish between this disturbance signal and the photoelectric pulse wave signal obtained from the detected part to obtain a highly reliable detection result.

[Purpose of the invention]

The present invention aims to provide a pulse detection circuit that can obtain highly reliable pulse detection results in view of the above-mentioned {ff. [Means and effects for solving the five problems] In order to achieve the above object, the present invention includes a light receiving element, a first amplifying means for amplifying a signal obtained from the light receiving element, and a first amplifying means for amplifying a signal obtained from the light receiving element. The present invention is characterized by comprising comparison means for comparing the obtained signal with a second reference voltage higher in level than the base voltage supplied to the first amplification means.

According to the comparison means, it is possible to detect whether or not the detected part is placed on the detection surface, and has the effect of obtaining a pulse detection result with higher reliability.

C Embodiment] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In this embodiment, the pulse rate detection circuit of the present invention is provided in an electronic wristwatch, and the pulse rate is measured by placing a finger on a predetermined position of the electronic wristwatch. FIG. 2 is a diagram showing the external appearance of a part of the electronic wristwatch used in the present invention. In the figure, a watch case 1 includes a display section 2 for displaying the time, pulse rate, etc., a pulse detection window 3 for placing a finger, which is the detected section, and a pulse output sensor 4 below the window. Although not shown, various operation switches are provided to change the display. FIG. 3(A) is a diagram showing a pulse detection state where a finger is placed on the pulse detection window 3, and the pulse detection sensor 4 is a light emitting element such as an LED 5.
and a phototransistor 6 which is a light receiving element. FIG. 3(B) is a simulated sectional view when not in use, and is the same as the configuration shown in FIG. 3(^).

FIG. 1 is a diagram of a pulse detection circuit and a pulse calculation circuit, which are an embodiment of the present invention, provided in the above-mentioned electronic wristwatch.
The explanation will continue by comparing it with the waveform diagram output to each terminal shown in Figure 4. The pulse detection circuit uses LED4 which is a light emitting element.
and a phototransistor 6 as a light-receiving element; an LED drive stage 7 for controlling turning on and off of the LED 4; and a first one for amplifying the pulse detection signal output from the phototransistor 6. Pulse signal amplification which further amplifies the pulse signal of the 1,000 stage amplification stage 8 and the first amplification means 8 and extracts only the signal power of 2 to 4 Hz which is a certain part of the pulse signal. It consists of a filter means 9 and a comparator A2 for comparing the signal level of the first amplification means 8, and the pulse signal amplification. The pulse rate is calculated by a pulse calculation means lO which measures the pulse rate from the output signal of the filter means 9 and the output signal of the comparator A2. Although the pulse rate calculation stage 10 is not shown, it includes a central processing unit (hereinafter referred to as CPU) that includes time counting, control of operations corresponding to various switch inputs, and timing signal generation means for outputting various timing signals. 9).

When the pulse measurement state is set by inputting the operation switch, the pulse calculation means 10 provided in the CPU sends a signal to the LED driving means 7 to light up the LED, turn on the transfer game T2, and turn on the first The state is set so that a signal can be input to the amplification means 8. LEorg operating means 7 is NP
N Controls the transistor Tl to cause current to flow through the LED 5 to light it up.

The resistor R1 is inserted to control the current flowing to the LED 5. It is impossible to keep the LED 5 lit while detecting the pulse. Pulse driving method (
An intermittent drive such as that described in Japanese Utility Model Application Laid-open No. 53-76697 is conceivable.

When a finger is placed on the pulse detection window 3 as shown in FIG. The phototransistor 6 is excited by this light and a current flows, generating an electromotive force across R2, which is connected in series with the phototransistor 6 between the power supplies. This signal is output as a pulse signal shown in FIG. 4 ta+. The pulse signal (8)
Is the direct current cut off by capacitor CI and resistor R3? It passes through a pass filter and is further connected to a resistor R4 and a capacitor C via a transfer gate T2 which is on.
2, to an amplifier circuit consisting of a capacitor C3, resistors R5 and R6, and an operational amplifier Al. The DC component of the amplified signal fbl is canted by the capacitor C4, and the amplified signal fbl is input to the pulse signal amplification filter means 9.The pulse signal amplification filter 9 has a frequency of 2 to 4 Hz. It includes a high-pass filter for extracting only the pulse signal, a low-pass filter, and a circuit that amplifies and shapes the waveform to a rectangular wave that amplitudes between voltage a (OV=V3!~VDD), and generates the rectangular wave shown in Fig. 4 fdl. Outputs a pulse signal formatted as follows.

Further, the output signal of the first amplifier circuit 8 shown in FIG. 4 Tol is input to the comparator A2. The input signal on one side of comparator A2 is 1/2Va as shown by the broken line in Fig. 4.
Input a reference voltage V■ for comparison, which has a slightly higher level than o. 4('b) which is the output signal of the first amplifying means 8 as shown in FIG. 4Q)l? (solid line) is
Outputs the signal.

Next, as shown in FIG. 3(B), although the pulse detection window 3 is in a state where the pulse can be detected, the finger, which is the detected part, is not placed on the pulse detection window 3, and external light is transmitted to the phototransistor 6. Let's discuss the case where the beam is irradiated.

External light such as light from a lighting device such as a fluorescent lamp or sunlight is directly irradiated to the phototransistor 6 and excited, generating an electromotive force at both ends of R2 inserted in series.
It outputs an almost flat signal at a certain level as shown in Figure 4 (when the external light of al is irradiated without being blocked.The signal level changes depending on the amount of light irradiated.This signal is output from the capacitor CI Since the DC component is canted and input to the first amplifying means 8, as shown in FIG.
is output from the amplification means 8. This signal is processed by the pulse signal amplification and filter stage 9, which includes a filter that extracts only the 2 to 4 Hz component of the pulse signal, and an amplification and waveform shaping circuit, as described above. A slight change in the amount of light coming from the sunlight causes a noise signal to be output as shown in FIG. 4 (d+). Also, the output signal of the first amplification means 8 shown in FIG. Since the potential level is lower than that of VIIEF, a low level signal is output as shown in FIG. 4 tel.The pulse signal amplification shown in FIG. The output signal of converter A shown in Fig. 4 (Cl)
The output signal of 2 is passed through the AND game port 2 to
The signal shown in is input to the pulse calculation means 10 provided in the C P Ull, and the period of the signal is measured and converted into the number of pulses per minute. As shown in the operation description above, in this embodiment, when detecting the pulse rate, changes in the blood flowing through the finger, which is the part to be measured, are detected using an LED 5 and a phototransistor 6 that receives changes in the amount of reflected or transmitted light. The pulse signal detected by the phototransistor 6 is amplified by the first amplification circuit 8, and further pulse signal amplification. Filter means 9
A signal of 2 to 4 Hz, which is the pulse signal component, is extracted through the , but is the pulse of the finger being measured? Even when the external light is not properly placed on the bay window 3 and a large amount of external light hits the phototransistor 6, the 2-4HzO disturbance noise contained in the external light is also output as a signal in the pulse signal amplification and 1,000-stage filter 9 described above. Resulting in. The DC component of the signal detected by the phototransistor 6 is cut off by the capacitor C1, and the signal integrated by the resistor R4 and capacitor C2 is amplified by the first amplifier circuit 8, so that the output of the first amplifier circuit 8 is Figure 4 shows when the finger being measured is correctly placed on the pulse detection window 3 and when it is not)
As shown in , completely different signals are output, and comparator A2 outputs 1/2VoD, which is the reference voltage of amplifier AI.
By comparing the pulse rate with the slightly higher value ■■, it is possible to detect whether the finger, which is the part to be measured, is correctly placed on the pulse detection window 3.

It goes without saying that the embodiments of the present invention are not limited to those used in the above-mentioned electronic wristwatches, but can be used in other electronic devices with pulse rate monitors that have a light emitting element and a light receiving element. In addition, the AND gate 12 judges whether or not the finger is placed correctly, but the CPU II judges whether the finger is placed correctly or not.
The operation control may be performed to determine whether or not to perform pulse rate detection while checking the output level of step 2.

〔Effect of the invention〕

As described above in detail, according to the present invention, when detecting the pulse rate, the measured pulse rate is determined by detecting whether or not the finger, which is the part to be measured, is correctly placed on a part of the detection sensor. It is possible to obtain detection results with higher reliability.

[Brief explanation of drawings]

Fig. 1 is a diagram of a pulse detection circuit and a pulse calculation circuit according to an embodiment of the present invention, Fig. 2 is an external view of a part of an electronic wristwatch, and Fig. 3 (A) is a diagram of a pulse detection window. Figure 3 (B) is a cross-sectional view of the pulse detection window when not in use, and Figure 4 is a waveform diagram output to each terminal shown in Figure 1. . 1...Watch case 2...Display section 3...Pulse detection window 4...Pulse detection sensor 5...LED 6...Phototransistor 7...LED driving means 8...No. 1 amplification means 9...pulse signal amplification. Filter means 10... Pulse calculation means 11... CPU 12... AND gate AI. A2...Operational amplifier Rl-R6...Resistance 01-C4...Capacitor T1...NPN }Resistor T2...Transfer gate or higher

Claims (1)

[Claims] In a photoelectric pulse detection circuit comprising a detection sensor comprising a light emitting element and a light receiving element, an amplification means and a filter means for amplifying the signal of the light receiving element, and a pulse calculation means for converting into a pulse rate. . A pulse detection circuit comprising a comparator for comparing an intermediate signal of the amplification means with a reference voltage higher than a reference voltage of the amplification means.