Integrated Photodiode Back Surface PPG Signal Strength
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Solution Overview
Problem
Conventional photoplethysmographic (PPG) systems face challenges in accurately determining pulse rate due to low signal strength caused by long path lengths of reflected and scattered light, which can be mitigated by reducing the distance between the light sensor and emitter, but this affects the depth of light penetration into the skin.
Innovation Solution
Integrating photodiodes directly onto the back surface of a PPG device, eliminating the need for a separate substrate and reducing the gap between windows and the active photodiode area, thereby enhancing signal strength without compromising light penetration depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lateral separation between the light sensor and light emitter is reduced to increase signal strength, then the PPG signal strength is improved, but the depth of light penetration into the skin is affected
Solution Approach 1:
The photodiode is inverted and integrated directly onto the back surface of the device, changing the spatial arrangement from lateral separation to vertical integration. This dimensional reconfiguration allows the light sensor to be positioned immediately adjacent to the light emitter in the same plane, reducing the optical path length while maintaining the vertical penetration depth into skin tissue through the back surface geometry
2Ease of manufacture
If a separate substrate is used to support the photodiode, then the device structure is more conventional and easier to manufacture, but the gap between windows and photodiode increases causing light loss and reduced measurement accuracy
Solution Approach 1:
The photodiode is merged directly with the back surface of the device, eliminating the separate substrate. The photodiode stackup is formed as an integrated component on the back surface, removing intermediate layers and reducing the optical gap between the light path and the sensor active area, thereby minimizing light loss and improving measurement accuracy
Solution Approach 2:
The separate substrate is extracted and removed from the optical path. By eliminating this intermediate component, the design achieves direct contact between the photodiode active area and the light path through the back surface windows, reducing unnecessary optical interfaces and associated light loss
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves measurement accuracy and reduces power consumption by minimizing light loss, allowing for more precise physiological signal detection without altering the depth of light penetration.
Implementation Method 1
A device can include one or more photodiodes located on a back surface of the device, where the photodiodes can be configured for measuring one or more optical properties
Data Source
AI summary
This relates to one or more integrated photodiodes on a back surface of a PPG device. The one or more integrated photodiodes can reduce the gap between one or more windows and the active area of the photodiode(s) to increase the PPG signal strength without affecting the depth of light penetration into skin tissue. In some examples, the photodiode stackup can contact the surface of the windows. In some examples, the photodiode stackups can exclude a separate substrate. In some examples, the photodiode stackup can be deposited on the inner surface of the windows opposite the outer surface of the device. In some examples, the photodiode stackup can be deposited on the back surface and/or outer surface of the device. In this manner, PPG sensors can be included in the device without the need for extra layers and measurement accuracy can be improved due to lower light loss.