Pulse wave measurement device, pulse wave measurement system and signal processing method

Abstract

A pulse wave measurement device includes a storage unit and a subtractor. When a light emitting element alternately switches between a lighting state in which the light emitting element emits light into a body and a non-lighting state in which the light emitting element does not emit light, the storage unit stores a value of a first digital signal representing an output state of a light receiving element that receives light transmitted through or reflected by the body at timing of the lighting state, and a value of a second digital signal representing an output state of the light receiving element at timing of the non-lighting state. The subtractor subtracts the second digital signal value stored in the storage unit from the first digital signal value stored in the storage unit.

What is claimed: 
     
         1 . A pulse wave measurement device, comprising:
 a storage unit configured to store a value of a first digital signal, the first digital signal corresponding to an output signal of a light receiving element configured to receive light transmitted through or reflected by a target object when a light emitting element is emitting light, and a value of a second digital signal, the second digital signal corresponding to an output signal of the light receiving element when the light emitting element is not emitting light; and   a subtractor configured to calculate a correction value for the first digital signal by performing mathematical operations on the value of the second digital signal and the value of the first digital signal.   
     
     
         2 . The device according to  claim 1 , wherein the value of the second digital signal and the value of the first digital signal are stored in the storage unit before the subtractor subtracts the value of the second digital signal from the value of the first digital signal. 
     
     
         3 . The device according to  claim 1 , further comprising:
 a signal measurement circuit configured to measure the first and second digital signals from the light receiving element and store values of the first and second digital signals in the storage unit, wherein   the second digital signal is measured during a time when the light emitting element is not emitting light that is immediately before or after a time during which the light emitting element is emitting light and the first digital signal is measured, and   the subtractor is configured to subtract the value of the second digital signal from the value of the first digital signal.   
     
     
         4 . The device according to  claim 1 , further comprising:
 a signal measurement circuit configured to measure the first and second digital signals from the light receiving element and store values of the first and second digital signals in the storage unit, wherein   the subtractor is configured to subtract one half of a first value of the second digital signal measured before the first digital signal is measured and one half of a second value of the second digital signal measured after the first digital signal is measured from the value of the first digital signal.   
     
     
         5 . The device according to  claim 1 , further comprising:
 a signal measurement circuit configured to measure the first and second digital signals from the light receiving element and store values of the first and second digital signals in the storage unit, the signal measurement circuit being configured to measure a plurality of values of the second digital signal during each period before and after the light emitting element emits light, wherein   the subtractor is configured to average a subset of the plurality of values of the second digital signal to provide an averaged value of the second digital signal and subtract the averaged value of the second digital signal from the value of the first digital signal.   
     
     
         6 . The device according to  claim 1 , further comprising:
 a signal measurement circuit configured to measure the first and second digital signals from the light receiving element and store values of the first and second digital signals in the storage unit, the signal measurement circuit being configured to measure the second digital signal during only some periods during which the light emitting element is not emitting light.   
     
     
         7 . The device according to  claim 1  further comprising:
 a processor configured to calculate a pulse rate based on the correction value for the first digital signal output from the subtractor. 
 
     
     
         8 . The device according to  claim 1 , further comprising:
 an acceleration sensor configured to detect acceleration of the target object, wherein   the storage unit is further configured to store a value of a motion signal corresponding to acceleration of the target object when the first digital signal is measured.   
     
     
         9 . The device according to  claim 8 , wherein the subtractor is configured to subtract the value of the second digital signal and the value of the motion signal from the value of the first digital signal. 
     
     
         10 . The device according to  claim 1 , further comprising:
 a signal measurement circuit configured to measure the first digital signal and the second digital signal from the light receiving element and store the value of the first digital signal and the value of the second digital signal in the storage unit; and   a timing control circuit configured to control a timing at which the signal measurement circuit measures values of the first and second digital signals.   
     
     
         11 . The device according to  claim 1 , further comprising:
 a processor configured to:
 remove a high frequency noise component in a signal output from the subtractor and generates a pulse wave signal; and 
 detect a period of the pulse wave signal. 
   
     
     
         12 . The device according to  claim 1 , wherein the subtractor is a circuit configured to perform mathematical operations on the value of the first and the second digital signal. 
     
     
         13 . The device according to  claim 1 , wherein the subtractor is a processor programmed to perform mathematical operations on the value of the first and the second digital signal. 
     
     
         14 . The device according to  claim 1 , wherein the target object is a human body. 
     
     
         15 . The device according to  claim 1 , wherein the target object is a blood vessel.