Heart rate and blood oxygen monitoring system

• US 10,123,711 B2
• Filed: 01/10/2013
• Issued: 11/13/2018
• Est. Priority Date: 01/10/2012
• Status: Active Grant

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Mehta, Arpit, Olsen, Richard I., Christman, Daniel S.
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Liu, Chu Chuan (JJ)
• Application Number:
  US14/371,174
• Publication Number:
  US 20150011851A1
• Time in Patent Office: 2,133 Days
• CPC Class Codes: A61B 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/6898 Portable consumer electronic devices, e.g. music players, telephones, tablet computers
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

An integrated circuit device includes an insulating body provided with a number of electrically conductive leads and having a surface provided with a red LED aperture, an IR LED aperture and a photodetector aperture. The insulating body also includes an optical isolator optically separating the photodetector aperture from the red LED aperture and the IR LED aperture. A red LED is aligned with the red LED aperture, an IR LED is aligned with the IR LED aperture, and a photodetector is aligned with the photodetector aperture.

Claims

1. An electronic device with heart rate monitor comprising:

a body including a planar infrared (IR) transmissive surface comprising a plastic or glass;

a digital processor located within the body;

a display screen supported by the body;

an IR light emitting diode (LED) aligned with the IR transmissive surface;

LED driving circuitry coupled to the IR LED;

an IR photodetector aligned with the IR transmissive surface, where the IR transmissive surface serves as a window for the IR LED and the IR photodetector such that a finger placed on the IR transmissive surface over the IR LED and the IR photodetector will reflect IR light from the IR LED back to the IR photodetector through the window;

a filtering and amplification stage having an input coupled to the IR photodetector;

an analog-to-digital converter (ADC) having an analog input coupled to an output of the filtering and amplification stage and a digital output; and

memory coupled to the digital processor including code segments executable by the digital processor for;

(a) continuously determining if a signal has been acquired from the IR detector until a signal has been acquired;

(b) filtering the acquired signal, determining if it is strong enough for processing and, if not, increasing the IR LED strength and returning to operation (a);

(c) detecting if a finger has been placed on the IR transmissive surface and, if not, returning to operation (b);

(d) capturing raw data from the ADC and storing the raw data in a data log;

(e) checking the data log and, if N seconds of raw data has not been captured, returning to operation (b);

(f) performing a Fast Fourier Transform (FFT) of the raw data to develop FFT data;

(g) processing the FFT data for at least one of window, averaging and noise rejection to develop processed FFT data;

(h) determining a confidence level in the processed FFT data and, if the confidence level is not above a threshold, returning to operation (b);

(i) calculating a heart rate from the processed FFT data; and

(j) at least one of displaying and storing the heart rate.

2. An electronic device with heart rate monitor as recited in claim 1 wherein the electronic device is a portable digital device and further comprises a wireless connection to a network.

3. An electronic device with heart rate monitor as recited in claim 2 wherein the network is at least one of a cellular telephone network and the Internet.

4. An electronic device with heart rate monitor as recited in claim 3 wherein the electronic device is one of a cellular telephone and a computer tablet.

5. A combination heart rate monitor and blood oxygen monitoring circuit comprising:

a red LED and an IR LED;

a time multiplexer pulsing the red LED and the IR LED on and off in regular intervals;

a red photodetector and an IR photodetector positioned to receive light emitted by the red LED and the IR LED that is reflected from a finger positioned proximate to the red LED, the IR LED, the red photodetector and the IR photodetector;

a filtering and amplification stage coupled to the red photodetector and the IR photodetector to process signals developed from the light reflected by the finger;

control circuitry receiving feedback from the filtering and amplification stage and controlling the currents to the red LED and the IR LED to control the intensity of the light that they emit;

an analog-to-digital converter (ADC) having an analog input coupled to an output of the filtering and amplification stage and having a digital output;

registers for storing digital output of the ADC;

a digital signal processor (DSP) coupled to the registers for processing data stored therein; and

memory coupled to the DSP including code segments executable by the DSP for;

(a) continuously determining if a finger has been detected until a finger is detected;

(b) determining if a red LED source or an IR LED source is detected;

(c) if a red LED source has been detected, determining if its signal strength is high enough and, if not, increasing a red LED drive current;

(d) if an IR LED source has been detected, determining if its signal strength is high enough and, if not, increasing an IR LED drive current;

(e) capturing red data and IR data when both the red signal strength and the IR signal strength are high enough;

(f) performing a Fast Fourier Transform (FFT) of the captured red data and captured IR data to develop FFT data;

(g) processing the FFT data for at least one of window, averaging, and noise rejection to develop processed FFT data;

(h) determining a confidence level in the processed FFT data and, if the confidence level is not above a threshold, returning to operation (a);

(i) calculating the blood oxygen level from the processed FFT data;

(j) calculating the heart rate as the fundamental frequency from the processed FFT data; and

(k) at least one of displaying and storing the heart rate and the blood oxygen level.

6. A combination heart rate and blood oxygen monitoring circuit as recited in claim 5 wherein the filtering and amplification stage includes a series connection of a transimpedance amplifier (TIA) and a programmable gain amplifier (PGA).