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. 2019 Aug 26;19(17):3698. doi: 10.3390/s19173698

Figure 1.

Figure 1

Figure 1

Illustration of multi-wavelength photoplethysmography (MW-PPG) sensing technologies: (a) prior works using a conventional spectrometer as the sensing device; (b) prior works using a photodiode as the sensing device in sequential sampling architecture; (c) the proposed work using the developed chip-scale MW-PPG sensors as the sensing device.