Modulation and demodulation techniques for a health monitoring system

• US 10,219,754 B1
• Filed: 02/12/2015
• Issued: 03/05/2019
• Est. Priority Date: 09/09/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Lamego, Marcelo M.
• Primary Examiner(s): Nguyen, Hien
• Application Number:
  US14/621,268
• Time in Patent Office: 1,482 Days
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• 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
• CPC Class Codes: A61B 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

An electronic device includes one or more light sources for emitting light toward a body part of a user and one or more optical sensors for capturing light samples while each light source is turned on and for capturing dark samples while the light source(s) are turned off. A signal produced by the one or more optical sensors is demodulated produce multiple demodulated signals. Each demodulated signal is received by one or more decimation stages to produce a signal associated with each light source. Each signal associated with the light source(s) is analyzed to estimate or determine a physiological parameter of the user.

Claims

1. A method for estimating physiological parameters when modulated light from a first light source and a second light source is emitted toward a body part of a user, the method comprising:

determining a first multiplier value by;

turning on the first light source;

generating a first initial signal in response to capturing a first light sample corresponding to the first light source;

demodulating the first initial signal to produce first initial demodulated signals;

filtering and decimating the first initial demodulated signals; and

determining the first multiplier value based on the filtered and decimated first initial demodulated signals;

determining a second multiplier value by;

turning on the second light source;

generating a second initial signal in response to capturing a second light sample corresponding to the second light source;

demodulating the second initial signal to produce second initial demodulated signals;

filtering and decimating the second initial demodulated signals; and

determining the second multiplier value based on the filtered and decimated second initial demodulated signals;

capturing multiple light samples while the first light source and the second light source are turned on to emit modulated light toward the body part of the user and converting the multiple light samples into a captured signal;

demodulating the captured signal to produce multiple demodulated signals;

performing a first decimation stage by;

low pass filtering each demodulated signal; and

decimating each demodulated signal;

performing a second decimation stage after the first decimation stage by;

low pass filtering each demodulated signal; and

decimating each demodulated signal;

demultiplexing each demodulated signal after the second decimation stage to produce a first signal associated with the first light source and a second signal associated with the second light source;

multiplying the first signal by the first multiplier value using a first multiplier circuit to obtain a first conditioned signal;

multiplying the second signal by the second multiplier value using a second multiplier circuit to obtain a second conditioned signal; and

analyzing the first conditioned signal and the second conditioned signal to estimate the physiological parameter of the user.

2. The method as in claim 1, wherein the capturing multiple light samples comprises capturing multiple light samples while:

the first light source is turned on and the second light source is turned off;

the second light source is turned on and the first light source is turned off; and

the first light source and the second light source are turned off after being turned on.

3. The method as in claim 2, wherein the capturing multiple light samples further comprises capturing one or more light samples after the first light source is turned off and before the second light source is turned on.

4. The method as in claim 1, wherein the demodulating the captured signal to produce multiple demodulated signals comprises:

applying a first demodulation operation of a sine function to the captured signal; and

applying a second demodulation operation of a cosine function.

5. The method as in claim 2, wherein the multiple light samples comprise at least five light samples captured when the first light source is turned on and the second light source is turned off.

6. The method as in claim 1, wherein:

when the first light source is turned on, the first light source emits infrared light; and

when the second light source is turned on, the second light source emits visible light.