Delta-sigma modulator for outputting analog representation of physiological signal

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.