Method and apparatus for demodulating signals in a pulse oximetry system

• US 7,221,971 B2
• Filed: 12/19/2005
• Issued: 05/22/2007
• Est. Priority Date: 04/14/1997
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Weber, Walter M., Al-Ali, Ammar, Diab, Mohamed K.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US11/311,213
• Publication Number:
  US 20060161056A1
• Time in Patent Office: 519 Days
• Field of Search: 600/310, 600/322, 600/323, 600/336, 600/500, 600/502
• US Class Current: 600/336
• CPC Class Codes: A61B 2560/0242 adapted to measure environmental factors, e.g. temperature, pollution
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7217 of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker
• 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 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: H04J 14/08 Time-division multiplex systems
• CPC Class Codes: H04J 3/10 Arrangements for reducing cross-talk between channels

Abstract

A method and an apparatus measure blood oxygenation in a subject. A first signal source applies a first input signal during a first time interval. A second signal source applies a second input signal during a second time interval. A detector detects a first parametric signal responsive to the first input signal passing through a portion of the subject having blood therein. The detector also detects a second parametric signal responsive to the second input signal passing through the portion of the subject. The detector generates a detector output signal responsive to the first and second parametric signals. A signal processor receives the detector output signal and demodulates the detector output signal by applying a first demodulation signal to a signal responsive to the detector output signal to generate a first output signal responsive to the first parametric signal. The signal processor applies a second demodulation signal to the signal responsive to the detector output signal to generate a second output signal responsive to the second parametric signal. The first demodulation signal and the second demodulation signal both include at least a first component having a first frequency and a first amplitude and a second component having a second frequency and a second amplitude. The second frequency is a harmonic of the first frequency. The second amplitude is related to the first amplitude to minimize crosstalk from the first parametric signal to the second output signal and to minimize crosstalk from the second parametric signal to the first output signal.

Claims

1. An apparatus comprising:

a detector;

a modulation signal generator configured to generate a first sequence of pulses having a duty cycle Q at a sampling frequency fs;

a first emitter that emits first electromagnetic energy in response to said first sequence of pulses, said detector configured to receive said first electromagnetic energy and to generate a detector output signal; and

a processor configured to demodulate digital samples obtained at least in part from said detector output signal, said processor configured to identify undesired frequency components in said detector signal caused by ambient electromagnetic energy detected by said detector and to determine fs and said Q at least in part to reduce interference from said undesired frequency components, said processor further configured to compute a physiological parameter using data obtained from said digital samples.

2. The apparatus of claim 1, wherein said physiological parameter comprises blood oxygenation.

3. The apparatus of claim 1, wherein said physiological parameter comprises pulse rate.

4. The apparatus of claim 1, further comprising a second emitter that emits second electromagnetic energy in response to a second sequence of pulses, wherein said detector is configured to receive said second electromagnetic energy and to generate said detector output signal responsive to said first and second electromagnetic energy.

5. The apparatus of claim 1, wherein said processor is further configured to demodulate an output signal corresponding to noise produced by said detector.