Passive detection of pulse
First Claim
1. A body-mountable device comprising:
- a photodiode;
a photodiode voltage source, wherein the photodiode voltage source applies a voltage to the photodiode such that the photodiode is reverse biased, wherein a photodiode current through the photodiode is related to light received from a portion of subsurface vasculature;
a current-mode digital-to-analog converter (DAC), wherein the current-mode DAC sources or sinks a DAC current;
a current mirror, wherein the current mirror has an input current path and an output current path, wherein the current mirror provides an output current in the output current path that is related to an input current in the input current path, wherein the photodiode and current-mode DAC are connected in parallel to the input current path of the current mirror such that the input current is related to the photodiode current and DAC current; and
output electronics coupled to the output current path of the current mirror, wherein the output electronics provides a digital output related to the output current in the output current path of the current mirror.
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Abstract
A body-mountable light sensing device includes a photodiode configured to receive light from a portion of subsurface vasculature and electronics configured to operate the photodiode to measure the received light. The electronics include a photodiode voltage source configured to reverse bias the photodiode, a current mirror, and a sigma-delta modulator configured to generate a digital output related to the received light and having a high resolution while using low power. The digital output could be used to determine a pulse rate or other properties of blood in the portion of subsurface vasculature by detecting absorption of ambient light by blood in the portion of subsurface vasculature. Components of the body-mountable device could be embedded in a polymeric material configured for mounting to a surface of an eye. The digital output and/or related information could be wirelessly communicated by the body-mountable device.
19 Citations
19 Claims
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1. A body-mountable device comprising:
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a photodiode; a photodiode voltage source, wherein the photodiode voltage source applies a voltage to the photodiode such that the photodiode is reverse biased, wherein a photodiode current through the photodiode is related to light received from a portion of subsurface vasculature; a current-mode digital-to-analog converter (DAC), wherein the current-mode DAC sources or sinks a DAC current; a current mirror, wherein the current mirror has an input current path and an output current path, wherein the current mirror provides an output current in the output current path that is related to an input current in the input current path, wherein the photodiode and current-mode DAC are connected in parallel to the input current path of the current mirror such that the input current is related to the photodiode current and DAC current; and output electronics coupled to the output current path of the current mirror, wherein the output electronics provides a digital output related to the output current in the output current path of the current mirror. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method, comprising:
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receiving, by a photodiode in a body-mountable device, light from a portion of sub surface vasculature; applying, by a photodiode voltage source in the body-mountable device, a voltage to the photodiode such that the photodiode is reverse biased, wherein a photodiode current through the photodiode is related to the light received from the portion of subsurface vasculature; providing, by a current-mode digital-to-analog converter (DAC) in the body-mountable device, a DAC current; providing, by a current mirror in the body-mountable device, an output current in an output current path of the current mirror, wherein the output current is related to an input current in an input current path of the current mirror, and wherein the photodiode and current-mode DAC are connected in parallel to the input current path of the current mirror such that the input current is related to the photodiode current and DAC current; and generating a digital output related to the output current in the output current path of the current mirror. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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Specification