System and method for powering a wireless sensor device
A system and method for powering a wireless sensor device are disclosed. In a first aspect, the wireless sensor device comprises at least two electrodes configured to be attached to a body and at least two leads coupled to the at least two electrodes. The wireless sensor device also includes a system on chip (SoC) coupled to the at least two leads and a portable power source (V batt ) coupled to the SoC. When the at least two electrodes are attached to the body, a difference in resistance is measured between the at least two leads by the SoC and the difference in resistance is utilized by the SoC to enable the portable power source to activate the wireless sensor device.
1. A wireless sensor device comprising:
at least two electrodes configured to be attached to a body;
at least two leads coupled to the at least two electrodes;
a system on chip (SoC) coupled to the at least two leads, wherein the SoC includes a reset generation logic coupled to both a voltage comparator and an internal reset pin and further includes a latch logic coupled to both an output of the voltage comparator and a SoC internal power supply; and
a portable power source (V batt ) coupled to the SoC, wherein when the latch logic is enabled by the voltage comparator, the SoC internal power supply is coupled to the portable power source;
wherein when the at least two electrodes are attached to the body, a difference in resistance is measured between the at least two leads by the SoC using the voltage comparator, wherein after the latch logic is enabled and a predetermined time period occurs, the reset generation logic de-asserts the internal reset in to allow the wireless sensor device to turn on.
2. The wireless sensor device of claim 1 , wherein the SoC further includes a voltage comparator, wherein one of the at least two leads is coupled to a first voltage input of the voltage comparator and a reference voltage is coupled to a second voltage input of the voltage comparator, wherein when a sensing voltage provided to the first voltage input is less than the reference voltage the wireless sensor device is in a first state and when the sensing voltage provided to the first voltage input is greater than the reference voltage the wireless sensor device is in a second state, wherein determination of one of the first and second states enables the portable power source to activate the wireless sensor device.
3. The wireless sensor device of claim 2 , wherein after the at least two electrodes are attached to the body and a contact resistance (R c ) is measured by the SoC, power is provided to the wireless sensor device when the wireless sensor device is in one of the first and second states.
4. The wireless sensor device of claim 2 , wherein the SoC further includes a reset logic coupled to an output of the voltage comparator and a SoC internal power supply (VDD 0 ) coupled to the reset logic, wherein when the reset logic is enabled by the voltage comparator, the SoC internal power supply is coupled to the portable power source.
5. The wireless sensor device of claim 4 , wherein the SoC further includes a counter block coupled to the reset logic and a clock input coupled to the counter block, wherein after the reset logic is enabled and a maximum count is achieved by the counter block, the counter block transitions to a logical high output level to allow the wireless sensor device to turn on.
6. The wireless sensor device of claim 1 , wherein when the latch logic and the reset generation logic are reset, the SoC internal power supply is disabled and the internal reset pin is asserted to turn off the wireless sensor device.
7. The wireless sensor device of claim 1 , wherein the SoC further includes a first protection resistor (R 1 ) and a first biasing resistor (R 3 ) which are both coupled to one of the at least two leads, a second protection resistor (R 2 ) and a second biasing resistor (R 4 ) which are both coupled to another of the at least two leads, and a differential amplifier coupled to the at least two leads, wherein the differential amplifier provides a bias current (I bias ), wherein the first and second biasing resistors (R 3 and R 4 ) have a resistance and the differential amplifier has a bias current (I bias ) to allow a maximum input swing for the differential amplifier.
8. The wireless sensor device of claim 1 , wherein the at least two electrodes are configured to be attached to the body using a hydrogel.
9. A method for powering a wireless sensor device, the method comprising:
attaching at least two electrodes to a body;
coupling at least two leads to the at least two electrodes;
coupling a system on chip (SoC) to the at least two leads, wherein the SoC includes a reset generation logic coupled to both a voltage comparator and an internal reset in and further includes a latch logic coupled to both an output of the voltage comparator and a SoC internal power supply;
coupling a portable power source (V batt ) to the SoC, wherein when the latch logic is enabled by the voltage comparator, the SoC internal power supply is coupled to the portable power source;
measuring a difference in resistance between the at least two leads by the SoC using the voltage comparator when the at least two electrodes are attached to the body, wherein after the latch logic is enabled and a predetermined time period occurs, the reset generation logic de-asserts the internal reset in to allow the wireless sensor device to turn on.
10. The method of claim 9 , wherein the SoC includes a voltage comparator, the method further comprising:
coupling one of the at least two leads to a first voltage input of the voltage comparator; and
coupling a reference voltage to a second voltage input of the voltage comparator;
wherein when a sensing voltage provided to the first voltage input is less than the reference voltage the wireless sensor device is in a first state and when the sensing voltage provided to the first voltage input is greater than the reference voltage the device is in a second state;
wherein determination of one of the first and second states enables the portable power source to activate the wireless sensor device.
11. The method of claim 10 , further comprising:
measuring a contact resistance (R c ) by the SoC after attaching the at least two electrodes to the body; and
providing power to the wireless sensor device when the wireless sensor device is in one of the first and second states.
12. The method of claim 9 , wherein when the latch logic and the reset generation logic are reset, the SoC internal power supply is disabled and the internal reset pin is asserted to turn off the wireless sensor device.
13. The method of claim 9 , wherein the SoC further includes a first protection resistor (R 1 ) and a first biasing resistor (R 3 ) which are both coupled to one of the at least two leads, a second protection resistor (R 2 ) and a second biasing resistor (R 4 ) which are both coupled to another of the at least two leads, and a differential amplifier coupled to the at least two leads, wherein the differential amplifier provides a bias current (I bias ), wherein the first and second biasing resistors (R 3 and R 4 ) have a large-resistance and the differential amplifier has a small bias current (I bias ) to allow a maximum input swing for the differential amplifier.
14. The method of claim 13 , wherein when the sensing voltage provided to the first voltage input is less than the reference voltage, the sensing voltage is represented by the equation 0.5V batt +I bias ×R 4 .
15. The method of claim 13 , wherein when the sensing voltage provided to the first voltage input is greater than the reference voltage, the sensing voltage is represented by the equation 0.5V batt +R 4 /(R 1 +R c +R 2 +R 4 )×0.5V batt .
16. The method of claim 9 , further comprising:
configuring the at least two electrodes to be attached to the body using a hydrogel.