Reflection photodetector and biological information measuring instrument

• US 6,198,951 B1
• Filed: 04/30/1999
• Issued: 03/06/2001
• Est. Priority Date: 09/05/1997
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Kondo, Yutaka, Baba, Norimitsu, Kurihara, Hajime, Kosuda, Tsukasa
• Primary Examiner(s): Lacyk, John P.
• Application Number:
  US09/297,438
• Time in Patent Office: 676 Days
• Field of Search: 600/322, 600/323, 600/336, 600/310, 600/316, 600/330, 600/340, 600/344
• US Class Current: 600/323
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

When emitted light from LED 31 is incident on photodiodes 32 and 33 with luminance Pa and Pb, currents ia and ib are generated according to luminance Pa and Pb. When outside light is incident through the finger tissues on photodiodes 32 and 33 with luminance Pc, current ic is produced. The current i1 (=ia+ic) generated by photodiode 32, and the current i2 (=−ib−ic) generated by photodiode 33, are added at node X, and the current ic corresponding to outside light is thus cancelled. In addition, photodiodes 32 and 33 are disposed at different distances from LED 31. As a result, the current flowing to opamp 34 is current ia corresponding to luminance Pa because luminance Pb is extremely low. The opamp 34 then applies a current voltage conversion to generate pulse wave signal Vm.

Claims

1. A reflection type photodetection apparatus, having a light emitting element for emitting light to a detected object, for detecting the intensity of light reflected by the detected object, said reflection type photodetection apparatus comprising:

a first photoelectric conversion element for receiving and converting light reflected by the detected object and externally-sourced light to a first electrical output signal;

a second photoelectric conversion element for receiving and converting externally-sourced light to a second electrical output signal; and

a difference means for detecting and outputting a difference signal representing a difference between the first output signal of the first photoelectric conversion element and the second output signal of the second photoelectric conversion element;

wherein the first photoelectric conversion element, second photoelectric conversion element, and light emitting element are arranged so that a distance from a photodetection center of the second photoelectric conversion element to a light emitting center of the light emitting element is different from a distance from the light emitting center of the light emitting element to a photodetection center of the first photoelectric conversion element, and

the first photoelectric conversion element and second photoelectric conversion element are positioned so that externally-sourced light reaches each with substantially equal intensity, such that the intensity of light reflected by the detected object can be detected without significant affect from externally-sourced light.

3. A biological information measuring apparatus having a reflection type photodetection apparatus as set forth in claim 1, wherein:

the light emitting element emits light to a detection site on a human body,

the difference signal outputted by the difference detection means represents pulsation in blood flow, and

based on the difference signal biological information indicative of a body condition is measured.

2. A reflected light detection method for detecting the intensity of light reflected by a detected object using a reflection type photodetection apparatus having a light emitting element for emitting light to the detected object, a first photoelectric conversion element for receiving and converting light to a first electrical signal, and a second photoelectric conversion element for receiving and converting light to a second electrical signal, said reflected light detection method comprising:

a step for emitting light from the light emitting element to the detected object;

a step for generating the first electrical signal by detecting and photoelectrically converting light reflected by the detected object and externally-sourced light by means of the first photoelectric conversion element;

a step for generating the second electrical signal by detecting and photoelectrically converting externally-sourced light by means of the second photoelectric conversion element; and

a step for detecting the intensity of the light reflected by the detected object, without significant affect from externally-source light, by calculating a difference between the first signal and second signal.

4. A biological information measuring apparatus comprising:

a light emitting means for emitting light to a detection site of a body, and a photodetection means for detecting light emitted by the light emitting means to the body and generating a body movement signal according to the detected light quantity, for measuring movement of the body based on the body movement signal;

wherein the body movement signal is generated based on the quantity of detected light in a wavelength range of 600 nm and above.

6. The biological information measuring apparatus as set forth in claim 4, wherein the wavelength of the light emitted from the light emitting means is 600 nm or above.

7. The biological information measuring apparatus as set forth in claim 4, wherein the wavelength of light received by the photodetection means from the light emitting means is 600 nm or above.

8. A biological information measuring apparatus as set forth in claim 4, further comprising:

a frequency analysis means for frequency analyzing the body movement signal generated by the photodetection means, and generating a body movement spectrum; and

a pitch detection means for extracting a fundamental frequency based on the body movement spectrum generated by the frequency analysis means, and detecting a body movement pitch of the body based on the extracted fundamental frequency.

5. A biological information measurement method for emitting light to a detection site of a body, comprising:

detecting the emitted light to the body;

generating a body movement signal based on the detected light quantity, and measuring movement of the body based on the body movement signal; and

generating the body movement signal based on the quantity of detected light in a wavelength range of 600 nm and above.

9. A biological information measuring apparatus comprising:

a body movement detection means, having a first light emitting means for emitting light to a detection site on a body, for detecting light emitted by the first light emitting means to the body, and generating a body movement signal according to the amount of detected light;

a pulse wave detection means, having a second light emitting means for emitting light to a detection site on the body, for detecting light emitted by the second light emitting means to the body, and generating a pulse wave signal according to the amount of detected light; and

a biological information generating means for generating biological information indicative of a body condition based on the body movement signal and pulse wave signal;

wherein the body movement detection means generates the body movement signal based on the quantity of detected light in a wavelength range of 600 nm or greater, and

the pulse wave detection means generates the pulse wave signal based on the quantity of detected light in a wavelength range of 600 nm or below.

11. The biological information measuring apparatus as set forth in claim 9, wherein the biological information generating means comprises a comparison operator for comparing the body movement signal and pulse wave signal, and generating biological information based on the result of the comparison.

12. The biological information measuring apparatus as set forth in claim 11, wherein the comparison operator subtracts the body movement signal from the pulse wave signal, and outputs a difference signal.

13. The biological information measuring apparatus as set forth in claim 12, wherein the biological information generating means frequency analyzes the difference signal output by the comparison operator to generate pulse wave analysis data from which the body movement component is removed, and generates biological information for the body based on the pulse wave analysis data.

14. The biological information measuring apparatus as set forth in claim 12, wherein the biological information generating means applies an autocorrelation function to the difference signal output by the comparison operator to generate autocorrelated pulse wave data, and generates biological information based on the autocorrelated pulse wave data.

15. The biological information measuring apparatus as set forth in claim 12, wherein the biological information generating means detects a degree of irregularity in body movement based on the body movement signal,

determines whether to perform an autocorrelation operation based on the result of the degree of irregularity detection,

applies an autocorrelation function to the difference signal output by the comparison operator to generate autocorrelated pulse wave data if an autocorrelation operation is to be performed, and

generates biological information based on the autocorrelated pulse wave data, or

generates biological information based on the difference signal if an autocorrelation operation is not performed.

16. The biological information measuring apparatus as set forth in claim 12, wherein a photodetection means of the body movement detection means is a first photodiode for outputting a first electrical signal according to the amount of light detected by the first photodiode;

a photodetection means of the pulse wave detection means is a second photodiode for outputting a second electrical signal according to the amount of light detected by the second photodiode; and

the comparison operator outputs the difference signal from a node connected in series with the first photodiode and second photodiode.

10. A biological information measurement method for measuring biological information indicative of a body condition, said method comprising:

a step for emitting light to a detection site on the body, detecting the light emitted to the detection site on the body, and generating a body movement signal according to the amount of detected light, where the amount of detected light measured is in a wavelength range of 600 nm or above;

a step for emitting light to a detection site on the body, detecting the light emitted to the detection site on the body, and generating a pulse wave signal according to the amount of detected light, where the amount of detected light measured is in a wavelength range of 600 nm or below; and

a step for generating biological information indicative of a body condition based on the body movement signal and pulse wave signal.

17. A biological information measuring apparatus comprising:

light emitting means for emitting light to a wrist or arm; and

photodetection means for detecting light emitted by the light emitting means to the body and generating a pulse wave signal according to the amount of detected light;

wherein biological information for the body is generated based on a pulse wave signal measured in a 500 nm to 600 nm wavelength range and a body movement signal measured in a wavelength range of 600 nm and above.

18. The biological information measuring apparatus as set forth in claim 17, wherein the primary wavelength of light emitted by the light emitting means is 500 nm to 600 nm.

19. The biological information measuring apparatus as set forth in claim 17, wherein the primary wavelength of light detected by the photodetection means is 500 nm to 600 nm.