Cable cross talk suppression
Systems, methods, and devices are provided for suppressing cross-talk noise due to capacitive and/or inductive coupling in a medical sensor signal. For example, an embodiment of a patient monitor may include driving circuitry, an amplifier, and transient current discharge circuitry. When the driving circuitry drives an emitter to emit light into a patient, a detector may detect a portion of the light that passes through the patient, generating a detector signal. Cross-talk between the emitter driving signals and the detector signal may generate interference in the form of a transient current in the detector signal. Before the amplifier receives the detector signal, transient current discharge circuitry may discharge the transient current.
1. An electronic patient monitor comprising:
driving circuitry configured to generate an emitter control signal to cause an emitter of a medical sensor to emit light into a patient;
an amplifier configured to receive a detector signal generated when a detector of the medical sensor detects emitted light that passes through the patient; and
transient current discharge circuitry configured to discharge a transient current from the detector signal due to inductive coupling or capacitive coupling, or a combination thereof, of the emitter control signal with the detector signal, such that the transient current is at least partially discharged from the detector signal when the detector signal is received by the amplifier.
2. The patient monitor of claim 1 , wherein the transient current discharge circuitry comprises a switch configured to couple the detector signal to ground when the transient current occurs.
3. The patient monitor of claim 2 , wherein the switch is configured to couple the detector signal to ground for a period of time that begins before or when the emitter control signal is generated.
4. The patient monitor of claim 3 , wherein the period of time is less than 30 microseconds.
5. The patient monitor of claim 1 , comprising processing circuitry configured to control the driving circuitry and the transient current discharge circuitry, wherein the processing circuitry is configured to cause the transient current discharge circuitry to discharge the transient current from the detector signal when the processing circuitry causes the driving circuitry to generate the emitter control signal.
6. The patient monitor of claim 1 , wherein the emitter control signal is configured to cause the emitter to emit light for less than 200 microseconds.
7. The patient monitor of claim 1 , wherein the emitter control signal is configured to cause the emitter to emit light for 50 microseconds or less.
8. The patient monitor of claim 1 , wherein the detector signal is a current signal and wherein the amplifier comprises a transimpedance amplifier configured to convert the detector signal into a voltage signal via a transimpedance, wherein the transimpedance, in the absence of the transient current discharge circuitry, would not discharge the transient current before the emitter control signals varied to cause the emitter of the medical sensor to stop emitting light into the patient.
9. A method comprising:
providing an emitter control signal to an emitter to cause the emitter to emit light into a patient using emitter control circuitry; and
receiving into signal receiving circuitry a detector signal generated by a detector when the detector senses emitted light that passes through the patient, wherein:
when transient current is expected in the detector signal, the signal receiving circuitry couples the detector signal to ground to discharge the transient current; and
when the transient current is not expected in the detector signal, the signal receiving circuitry couples the detector signal to an amplifier.
10. The method of claim 9 , wherein the transient current is expected in the detector signal immediately after the emitter control signal is provided to the emitter.
11. The method of claim 9 , wherein the transient current is not expected in the detector signal after the detector signal has been coupled to ground for a period of time.
12. The method of claim 9 , wherein the emitter control signal comprises a driving current and the detector signal comprises a photocurrent, wherein the transient current in the detector signal is due to capacitive coupling or inductive coupling, or a combination thereof, of the photocurrent with the driving current.
13. The method of claim 12 , wherein the signal receiving circuitry couples the detector signal to an amplifier when the transient current is not expected in the detector signal, wherein the amplifier comprises a current-to-voltage converter.
14. The method of claim 9 , comprising determining when the transient current is expected in the detector signal using a processor and controlling the signal receiving circuitry to either couple the detector signal to ground or to the amplifier using a signal generated by the processor, wherein the emitter control signal is provided to the emitter using the emitter control circuitry under the control of the processor, wherein the transient current is determined to be expected when the processor causes the emitter control circuitry to provide the emitter control signal.
15. A system comprising:
a medical sensor capable of emitting light into a patient in response to an emitter driving current, detecting a portion of the emitted light that passes through the patient, and generating a photocurrent based on the detected light; and
a patient monitor capable of generating the emitter driving current, receiving the photocurrent, and discharging transient current in the photocurrent before converting the photocurrent to a voltage.
16. The system of claim 15 , comprising a patient cable capable of transmitting the emitter driving current to the medical sensor from the patient monitor and the photocurrent to the patient monitor from the medical sensor, wherein a differential capacitance between components capable of transmitting the emitter driving current and the photocurrent exceeds 3 pF.
17. The system of claim 15 , wherein the patient monitor is capable of coupling the photocurrent to ground for a period of time immediately after the medical sensor begins emitting light into the patient in response to the emitter driving current.
18. The system of claim 15 , wherein the patient monitor is capable of coupling the photocurrent to a current-to-voltage converter to convert the photocurrent to the voltage after the transient current in the photocurrent has been discharged.
19. The system of claim 15 , wherein the patient monitor is capable of converting the photocurrent to the voltage using a transimpedance amplifier having a transimpedance that exceeds 100 kΩ.
20. The system of claim 15 , wherein the patient monitor is capable of converting the photocurrent to the voltage using a transimpedance amplifier having a transimpedance of at least 100 kΩ.