Low-noise sensor system
A sensor system has a low-noise sensor controller providing communications between an active-temperature-regulated optical sensor and an external monitor. A low-noise sensor controller drives optical emitters, receives resulting detected signals after attenuation by a blood perfused tissue site and communicates the detector signals to the attached signal processor. An optically-isolated controller front-end receives and digitizes the detected signals. A controller serializer transmits the digitized detector signal to the processor via a single, shielded coaxial cable.
1. A low-noise sensor system comprising:
an optical sensor having emitters for transmitting optical radiation into a blood-perfused tissue site and detectors responsive to optical radiation after attenuation by pulsatile blood flow within the tissue site so as to generate sensor signals;
a sensor controller having an optically-isolated front-end that receives and digitizes the sensor signals, the sensor controller housed within the optical sensor; and
a serializer in communications with a shielded conductor so as to serially transmit the digitized sensor signals to an external monitor for deriving blood-related physiological parameters responsive to detector signals from the detector, the serializer housed within the optical sensor.
2. The low-noise sensor system according to claim 1 further comprising:
a DC power supply;
a battery;
a sensor-controller power output; and
a relay that connects the DC power supply to the battery in a recharge mode and that connects the battery to the sensor-controller power output in an operational mode.
3. The low-noise sensor system according to claim 2 wherein an interface between the sensor controller and the external monitor consists solely of three conductors including a DC power supply plus (+) conductor, a DC power supply minus (−) conductor and the shielded conductor.
4. The low-noise sensor system according to claim 3 further comprising:
a first thermoelectric cooler in thermodynamic communications with the emitters;
a second thermoelectric cooler in thermodynamic communications with the detectors; and
a temperature regulator that controls the thermoelectric coolers so as to maintain the emitters and detectors at predetermined temperatures.
5. The low-noise sensor system according to claim 4 wherein a sensor status is transmitted to the external monitor with sensor data through the interface.
6. The low-noise sensor system according to claim 5 further comprising a micro-controller that sequentially activates the emitters and controls emitter drive currents.
7. The low-noise sensor system according to claim 6 wherein the optically-isolated front-end further comprises:
a programmable gain amplifier that individually amplifies detector signals; and
an analog-to-digital converter (ADC) that digitizes the detector signals for transmission to the monitor.
8. A low-noise sensor method comprising:
attaching an optical sensor to a tissue site;
emitting multiple wavelengths of optical radiation into the tissue site;
detecting optical radiation after attenuation by pulsatile blood flow within the tissue site;
digitizing and serializing the detected optical radiation on the optical sensor;
serially transmitting the digitized detected optical radiation to a monitor; and
calculating physiological parameters based upon the digitized detected optical radiation.
9. The low-noise sensor method according to claim 8 further comprising independently thermos-electrically cooling emitters and detectors of the optical sensor.
10. The low-noise sensor method according to claim 9 further comprising:
providing a sensor controller that controls the digitizing and serial transmitting;
powering the sensor controller with a battery; and
intermittently charging the battery when not digitizing and serial transmitting.
11. The low-noise sensor method according to claim 10 further comprising providing a 3-wire interface between the sensor controller and an external monitor including a 2-wire interface for the charging and a 1-wire interface for the serial transmitting.
12. The low-noise sensor method according to claim 11 further comprising:
serializing a sensor status; and
combining the sensor status with sensor data for transmission to the monitor.
13. The low-noise sensor method according to claim 12 further comprising:
micro-controlling an emitter driver sequence and an emitter drive current.
14. The low-noise sensor method according to claim 13 further comprising optically-isolating the sensor controller.
15. A low noise sensor apparatus comprising:
an emitter means for illuminating a tissue site;
a detector means for receiving tissue site illumination after tissue site absorption and generating a detector signal in response;
a front-end means for amplifying and digitizing the detector signal; and
a serializing means for communicating the amplified and digitized detector signal to an external monitor;
wherein the emitter means, detector means, front-end means and serializing means are housed within the same sensor housing.
16. The low noise sensor apparatus according to claim 15 wherein the serializing means is configured to transmit a sensor status including sensor temperatures and accelerations to the external monitor via the serializer means.
17. The low noise sensor apparatus according to claim 16 further comprising a temperature regulating means in communications with the emitter means and the detector means.
18. The low noise sensor apparatus according to claim 17 further comprising a rechargeable battery powered means of providing low-noise power to at least the front-end means and serializer means.
19. The low noise sensor apparatus according to claim 18 comprising an optical isolation means for reducing noise for the front-end means.
20. The low noise sensor apparatus according to claim 19 comprising a three-wire isolation means disposed between at least the front-end means and the external monitor for reducing noise.