Health monitoring systems and methods
Systems, methods and devices for reducing noise in health monitoring including monitoring systems, methods and/or devices receiving a health signal and/or having at least one electrode or sensor for health monitoring.
1. A device for monitoring a physiological parameter, the device being adapted to be adhered to the skin of a subject for the physiological parameter monitoring; the device comprising:
a substrate;
one or more light sources;
a light sensor;
circuitry for reducing errors caused by ambient light using a correlated double sampling technique; comprising:
first and second switches and;
first and second capacitors,
the first capacitor being in series with the light sensor, and the second capacitor being in parallel with the output, and the first and second switches being disposed between the output and ground to alternatively provide output or shunt to ground;
the first capacitor being C 1 , the second capacitor being C 2 , the first switch being S 1 , the second switch being S 2 and
when the one or more light sources are turned off, and switch S 1 is closed, and switch S 2 is open; charge proportional to the noise signal accumulates on C 1 , and then switch S 1 is opened and, then, the voltage on C 1 is equal to the noise signal voltage; and,
next, the light signal is measured; switch S 2 is closed, and charge is allowed to flow through C 1 and C 2 in series; and, then, S 2 is opened, and the voltage is held on C 2 until the next measurement cycle when the whole process is repeated; and,
if C 1 is much larger than C 2 , nearly all the voltage will appear on C 2 , and the voltage on C 2 will be equal to the noise-free signal (s); or, otherwise, the voltage on C 2 will be a linear combination of the previous C 2 voltage (p) and the noise-free signal: (C 2 *s+C 1 *p)/(C 1 +C 2 ).
2. A device according to claim 1 further including a resistor in parallel with the other circuit elements.
3. A device according to claim 1 wherein either one of:
a filtering effect is of applying a first-order, low-pass, IIR discrete-time filter to the light signal; or,
if this filtering effect is not desired, the voltage on C 2 is discharged to zero before the light signal is measured each cycle, the light signal being held on C 2 is: (C 2 *s)/(C 1 +C 2 ).
4. A device according to claim 1 ; one or more of:
a trans-impedance amplifier is used in place of a resistor;
a phototransistor in place of the light sensor; and
field effect transistors or FETs in place of the first and second switches; or
the output is followed by one or more of
additional buffering,
amplification,
filtering and
processing stages.