Delta-sigma modulator for outputting analog representation of physiological signal

• US 7,212,847 B2
• Filed: 02/25/2004
• Issued: 05/01/2007
• Est. Priority Date: 02/25/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Petersen, Ethan, Chew, Bradford B., Shea, William
• Primary Examiner(s): Winakur; Eric F.
• Application Number:
  US10/787,853
• Publication Number:
  US 20050187453A1
• Time in Patent Office: 1,161 Days
• Field of Search: 600/309, 600/310, 600/316, 600/323, 600/300, 600/324, 600/500
• US Class Current: 600/323
• 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 is provided. The waveform signal from the sensor is converted into digital form. A delta-sigma modulator is used as a simple Digital-to-analog Converter (DAC). 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 a physiological monitor comprising:

detecting an analog signal from a patient, wherein the analog signal comprises at least one modulated physiological waveform;

converting the analog signal into a digital signal;

demodulating the digital signal to produce at least two demodulated physiological signals;

applying at least one of the demodulated physiological signals to a delta-sigma modulator to provide at least one physiological waveform; and

filtering the at least one physiological waveform to provide a real-time analog filtered physiological waveform output, wherein the analog filtered physiological waveform is real-time relative to the time of detecting the analog signal from the patient to the time of providing the analog filtered physiological waveform output.

2. The method of claim 1 wherein filtering at least one physiological waveform comprises passing the at least one physiological waveform through a hardware filter.

3. The method of claim 1 wherein the delta-sigma modulator is configured to provide a single bit output.

4. The method of claim 1, wherein the at least one modulated physiological waveform comprises a representation of an IR signal returned from a physiological sensor and a red signal returned from a physiological sensor.

5. The method of claim 1, wherein converting the analog signal into a digital signal comprises passing the analog signal through an analog-to-digital converter (ADC).

6. The method of claim 1, wherein the demodulated waveform comprises a representation of an IR signal received from a physiological sensor.

7. The method of claim 1, wherein the delta-sigma modulator is configured to provide second order noise shaping of the demodulated physiological signals.

8. The method of claim 1, wherein the delta-sigma modulator is configured to output a serial bit stream having a given frequency.

9. The method of claim 1, wherein the hardware filter comprises an RC filter.

10. A method for operating an oximeter comprising:

detecting an analog signal from a patient, wherein the analog signal comprises at least one pulse oximetry waveform;

converting the analog signal into a digital signal;

demodulating the digital signal to produce a red signal and an IR signal;

applying one of the red signal and the IR signal to a software delta-sigma modulator, wherein the software delta sigma modulator is configured to provide a single bit, serial output; and

filtering the single bit, serial output with a hardware filter to provide a real-time analog waveform output, wherein the analog waveform is real-time relative to the time of detecting the analog signal from the patient to the time of providing the analog filtered physiological waveform output.

11. The method of claim 10, wherein the at least one pulse oximetry waveform comprises a representation of an IR signal returned from a physiological sensor or a red signal returned from a physiological sensor.

12. The method of claim 10, comprising configuring the software delta-sigma modulator to provide second order noise shaping of one of the red signal and the IR signal.

13. The method of claim 10, wherein the hardware filter comprises an RC filter.

14. A physiological monitor apparatus comprising:

an input configured to receive an analog signal from a patient, wherein the analog signal comprises a physiological waveform;

an analog-to-digital converter configured to convert the analog signal into a digital form of the physiological waveform;

a processor including a delta-sigma modulator configured to convert the digital form of the physiological waveform into an analog form of the physiological waveform, and wherein the delta-sigma modulator is configured to output the analog form of the physiological waveform; and

a filter configured to receive and filter the analog form of the physiological waveform and to output a real-time waveform, wherein the real-time waveform is real-time relative to the time analog signal received from the patient to the time the real-time waveform is output.

15. The physiological monitor apparatus of claim 14 wherein the delta-sigma modulator comprises a software modulator that produces a serial, single bit output.

16. The physiological monitor apparatus of claim 14 wherein the filter is a hardware RC filter.

17. The method of claim 14, wherein the delta-sigma modulator is configured to output a serial bit stream having a given frequency.

18. An oximeter apparatus comprising:

an input configured to receive a signal, wherein the signal comprises a pulse oximetry waveform, and wherein the pulse oximetry waveform is representative of data gathered from a sensor coupled to a patient;

an analog-to-digital converter configured to convert the pulse oximetry waveform into a digital form of the pulse oximetry waveform;

a processor, comprising;

a demodulator configured to separate the digital form of the pulse oximetry waveform into a red digital signal and an IR digital signal; and

a software delta-sigma modulator configured to convert one of the red digital signal and the IR digital signal into an analog signal, wherein the analog signal is a serial, single bit output;

a hardware RC filter configured to filter the serial, single bit output of the software delta-sigma modulator and to output a filtered signal in real-time, wherein the filtered signal is real-time relative to the time the input receives the signal to the time the filtered signal is output; and

an output configured to provide the real-time filtered signal to a host.

19. The method of claim 18, wherein the serial, single bit output has a given frequency.