Delta-sigma modulator for outputting analog representation of physiological signal

• US 20050187453A1
• Filed: 02/25/2004
• Published: 08/25/2005
• Est. Priority Date: 02/25/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Petersen, Ethan, Chew, Bradford B., Shea, William
• Granted Patent: US 7,212,847 B2
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: H03M 7/3028 the quantiser being a single bit one
• CPC Class Codes: H03M 7/3042 the modulator being of the error feedback type, i.e. having loop filter stages in the feedback path only

Abstract

A method and apparatus for providing a substantially real-time representation of an analog representation of a physiological signal. The waveform signal from the sensor is converted into digital form. A delta-sigma modulator is used as a simple Digital-to-analog Converter (ADC). The output can then be provided through a simple hardware filter to give an analog output signal in nearly real-time, which can be used for other instruments, synchronization, display, etc.

Claims

1. A method for operating an physiological monitor comprising:

detecting a signal from a patient including a physiological waveform;

converting said waveform into digital form;

applying said waveform to a delta-sigma modulator; and

filtering said waveform to provide an analog waveform output.

2. The method of claim 1 further comprising demodulating said digital form of said waveform, wherein said delta-sigma modulator processes said waveform after said demodulation.

3. The method of claim 2 wherein said filtering is performed by a hardware filter coupled to an output of said delta-sigma modulator.

4. The method of claim 2 wherein said delta-sigma modulator provides a single bit output.

5. A method for operating an oximeter comprising:

detecting a signal from a patient including a pulse oximetry waveform;

converting said waveform into digital form;

demodulating said digital form of said waveform into red and IR signals;

applying one of said red and IR signals to a software delta-sigma modulator;

providing a single bit, serial output from said delta-sigma modulator;

filtering said single bit, serial output with a hardware filter.

6. An physiological monitor apparatus comprising:

an input for receiving from a patient a signal including a physiological waveform;

an analog-to-digital converter for converting said waveform into digital form;

a processor including a delta-sigma modulator configured to convert said waveform from digital into analog form;

a filter coupled to an output of said delta-sigma modulator for filtering said waveform.

7. The oximeter apparatus of claim 6 wherein said delta-sigma modulator is a software modulator that produces a serial, single bit output.

8. The oximeter apparatus of claim 6 wherein said filter is a hardware RC filter.

9. An oximeter apparatus comprising:

an input for receiving from a patient a signal including a pulse oximetry waveform;

an analog-to-digital converter for converting said waveform into digital form;

a processor including

a demodulator for separating said waveform into red and IR signals, and

a software delta-sigma modulator configured to convert one of said red and IR signals in digital form back into an analog signal by producing a serial, single bit output;

a hardware RC filter coupled to an output of said delta-sigma modulator for filtering said waveform.