PULSE WAVE SENSOR

• US 20150366513A1
• Filed: 06/19/2015
• Published: 12/24/2015
• Est. Priority Date: 06/24/2014
• Status: Abandoned Application

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Terumoto, Koji
• Application Number:
  US14/744,571
• Publication Number:
  US 20150366513A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F

Abstract

A pulse wave sensor includes: an optical sensor unit configured to irradiate a living body with light emitted from a light emitting unit and detect light reflected from or transmitted through the living body with a light receiving unit to generate a current signal in accordance with a light reception intensity; a pulse driving unit configured to turn on or turn off the light emitting unit at a predetermined frame frequency and a predetermined duty rate; a current-voltage conversion circuit configured to convert the current signal into a voltage signal; and a detection circuit configured to extract an upper envelope and a lower envelope of the voltage signal and obtain a difference therebetween to generate a detection signal.

Claims

1. A pulse wave sensor comprising:

an optical sensor unit configured to irradiate a living body with light emitted from a light emitting unit and detect light reflected from or transmitted through the living body with a light receiving unit to generate a current signal in accordance with a light reception intensity;

a pulse driving unit configured to turn on or off the light emitting unit at a predetermined frame frequency and a predetermined duty rate;

a current/voltage conversion circuit configured to convert the current signal into a voltage signal; and

a detection circuit configured to extract an upper envelope and a lower envelope of the voltage signal and obtain a difference therebetween to generate a detection signal.

2. The pulse wave sensor of claim 1, wherein the detection circuit includes:

an upper envelope detector unit configured to extract an upper envelope signal from the voltage signal;

a lower envelope detector unit configured to extract a lower envelope signal from the voltage signal; and

a differential amplification unit configured to obtain a difference between the lower envelope signal and the upper envelope signal to generate the detection signal.

3. The pulse wave sensor of claim 2, wherein the upper envelope detector unit includes:

a first diode including an anode connected to an input terminal for the voltage signal and a cathode connected to an output terminal for the upper envelope signal; and

a first capacitor including a first terminal connected to an output terminal for the upper envelope signal and a second terminal connected to a terminal for applying a reference voltage.

4. The pulse wave sensor of claim 2, wherein the lower envelope detector unit includes:

a second diode including a cathode connected to an input terminal for the voltage signal and an anode connected to an output terminal for the lower envelope signal; and

a second capacitor including a first terminal connected to an output terminal for the lower envelope signal and a second terminal connected to a terminal for applying a reference voltage.

5. The pulse wave sensor of claim 2, wherein the detection circuit further includes

a level shifter unit configured to adjust a signal level of the upper envelope signal and the lower envelope signal to respectively match an input range of the differential amplification unit.

6. The pulse wave sensor of claim 5, wherein the level shifter unit is a high pass filter.

7. The pulse wave sensor of claim 1, wherein the current/voltage conversion unit is a trans-impedance amplifier.

8. The pulse wave sensor of claim 1, further including a band pass filter circuit configured to remove both low-frequency components and high-frequency components superimposed on the detection signal to generate a filtered signal.

9. The pulse wave sensor of claim 8, further including an amplifier circuit configured to amplify the filtered signal by a predetermined gain to generate an output signal.

10. The pulse wave sensor of claim 1, wherein a wavelength output from the light emitting unit falls within a visible light region where a wavelength is 600 nm or smaller.