Use of frequency division multiplexing for optical cardiac signals

An electronic wearable device comprising:

• a housing including a bottom wall configured to contact a user's skin;
• a plurality of modulators, each modulator configured to output one of a plurality of modulated electronic signals, each modulated electronic signal having a predetermined carrier frequency;
• a plurality of optical transmitters positioned on the bottom wall and configured to output a plurality of optical signals, each optical transmitter coupled with one of the plurality of modulators and configured to receive one of the modulated electronic signals and output an optical signal into a user's skin that corresponds to the carrier frequency of the modulated electronic signal;
• an optical receiver positioned on the bottom wall and configured to receive the plurality of optical signals from the user's skin as a broadband electronic signal including optical signals associated with at least two carrier frequencies, and output the broadband electronic signal;
• and
• a plurality of receive processor circuits, each receive processor circuit and configured to receive the broadband electronic signal and output one of a plurality of photoplethysmogram (PPG) electronic signals corresponding to the one of the plurality of optical signals.

An electronic wearable device comprising:

• a housing including a bottom wall configured to contact a user's skin;
• a first modulator configured to output a first modulated electronic signal having a first carrier frequency;
• a second modulator configured to output a second modulated electronic signal having a second carrier frequency;
• a first optical transmitter coupled with the first modulator, positioned on the bottom wall and configured to output a first optical signal based on the first modulated electronic signal, the first optical signal output into the user's skin and having the first carrier frequency;
• a second optical transmitter coupled with the second modulator, positioned on the bottom wall and configured to output a second optical signal based on the second modulated electronic signal, the second optical signal output into the user's skin and having the second carrier frequency;
• an optical receiver positioned on the bottom wall and configured to receive the first optical signal and the second optical signal from the user's skin as an analog broadband electronic signal including the first optical signal and the second optical signal associated with the first carrier frequency and the second carrier frequency, respectively, and output the analog broadband electronic signal;
• an analog to digital converter configured to receive the analog broadband electronic signal and output the broadband electronic signal as a stream of digital data values corresponding to the first optical signal and the second optical signal;
• a memory element configured to store the first carrier frequency as corresponding to the first optical signal and the second carrier frequency as corresponding to the second optical signal;
• and
• a processor coupled with the analog to digital converter and the memory element, the processor configured to:
• receive the digital broadband electronic signal having the first carrier frequency components and the second carrier frequency components,
• generate a first filtered electronic signal and a second filtered electronic signal having the first carrier frequency and the second carrier frequency, respectively,
• demodulate the first filtered electronic signal and the second filtered electronic signal by extracting the amplitude of the first carrier frequency and the second carrier frequency, respectively, and
• output a first PPG electronic signal and a second PPG electronic signal corresponding to the demodulated first filtered electronic signal and the demodulated second filtered electronic signal, respectively.