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 comprising a programmable gain amplifier, wherein the optically-isolated front-end is configured to:
receive the sensor signals;
individually amplify the sensor signals by the programmable gain amplifier; and
digitize the sensor signals;
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;
a DC power supply;
a sensor-controller power output; and
a battery, wherein the battery is configured to connect to the DC power supply and the sensor via a relay.
2. The low-noise sensor system according to claim 1 , wherein the relay is configured to:
connect the DC power supply to the battery in a recharge mode; and
connect 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 the 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:
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;
individually amplifying the detected optical radiation with a programmable gain amplifier;
digitizing the detected optical radiation;
serially transmitting, via a shielded conductor, the digitized detected optical radiation to a monitor;
providing a sensor controller that controls the digitizing and serial transmitting;
powering the sensor controller with a battery;
charging, via a relay, the battery with a power supply; and
calculating physiological parameters based upon the digitized detected optical radiation.
9. The low-noise sensor method according to claim 8 further comprising independently thermo-electrically cooling emitters and detectors of the optical sensor.
10. The low-noise sensor method according to claim 9 further comprising:
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;
a serializer means for communicating the amplified and digitized detector signal to an external monitor via a shielded conductor;
a rechargeable battery powered means for providing low-noise power to at least the front-end means; and
a power supply means for charging the rechargeable battery powered means via a relay means.
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 wherein the rechargeable battery powered means is configured to provide low-noise power to at least the 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.