Pulse spectroscopy

1. An electronic fitness device comprising:

a housing including a bottom wall adapted to be positioned over the skin of a user;

a first optical transmitter positioned along the bottom wall, the first optical transmitter configured to transmit a first optical signal and a second optical signal, the first optical signal having a first wavelength;

an optical receiver positioned along the bottom wall, the optical receiver configured to receive the first and the second optical signals modulated by the skin of the user and generate first and second photoplethysmogram (PPG) signals resulting from the received first and the second optical signals, respectively, the first and the second optical signals traveling along the same path and each received optical signal containing a cardiac component associated with the user's heartbeat; and

a processing element in electronic communication with the first optical transmitter and the optical receiver, the processing element configured to:

control the first optical transmitter to transmit the first optical signal during a first period of time and the second optical signal during a second period of time,

receive the first and the second PPG signals from the optical receiver,

compare the first and the second PPG signals,

identify a common component present in the first and the second PPG signals based on the comparison,

determine a signal filter parameter based on the common component,

generate a first cardiac component from the first PPG signal based on the signal filter parameter,

generate a second cardiac component from the second PPG signal based on the signal filter parameter, and

determine blood-related physiological information based on the first and the second cardiac components.

2. The electronic fitness device of claim 1 , further comprising at least a first signal filter and a second signal filter, and wherein the processing element:

generates the first cardiac component by filtering the first PPG signal with the first signal filter using the signal filter parameter, and

generates the second cardiac component by filtering the second PPG signal with the second signal filter using the signal filter parameter.

3. The electronic fitness device of claim 2 , further comprising a second optical transmitter positioned along the bottom wall, the second optical transmitter configured to transmit a third optical signal having a second wavelength, wherein the processing element is further configured to:

control the second optical transmitter to transmit the third optical signal during a third period of time,

receive the third PPG signal from the optical receiver, and

filter the third PPG signal with a third signal filter to generate a third cardiac component using the signal filter parameter.

4. The electronic fitness device of claim 1 , wherein the processing element is further configured to utilize the signal filter parameter to generate a transfer function that is applied to each of at least a first signal filter and a second signal filter, and wherein the processing element:

generates the first cardiac component by filtering the first PPG signal with the first signal filter, and

generates the second cardiac component by filtering the second PPG signal with the second signal filter.

5. The electronic fitness device of claim 1 , wherein the signal filter parameter is a spectral parameter of the common component, and wherein the processing element:

generates the first cardiac component by filtering the first PPG signal with the first signal filter using the spectral parameter, and

generates the second cardiac component by filtering the second PPG signal with the second signal filter using the spectral parameter.

6. The electronic fitness device of claim 1 , wherein the signal filter parameter is a common waveform associated with the common component and the processing element:

generates the first cardiac component by comparing the first PPG signal with the common waveform, and

generates the second cardiac component by comparing the second PPG signal with the common waveform.

7. The electronic fitness device of claim 6 , further comprising a second optical transmitter positioned along the bottom wall, the second optical transmitter configured to transmit a third optical signal having a second wavelength, wherein the processing element is further configured to:

control the second optical transmitter to transmit the third optical signal during a third period of time,

receive the third PPG signal from the optical receiver, and

compare the third PPG signal with the common waveform to generate a third cardiac component, and

wherein the signal-to-noise ratio of the third PPG signal is lower than the signal-to-noise ratio of the first PPG signal.

8. The electronic fitness device of claim 1 , wherein the processing element is further configured to:

determine values of a plurality of filter coefficients for each of at least a first signal filter and a second signal filter using the signal filter parameter, each signal filter being a discrete-time, multi-tap time delay line filter with each tap configured using one of the plurality of filter coefficients,

periodically update the filter coefficients based on a feedback signal based on a difference between the first cardiac component and the second PPG signal.

9. The electronic fitness device of claim 8 , further comprising a second optical transmitter positioned along the bottom wall, the second optical transmitter configured to transmit a third optical signal having a second wavelength, wherein the processing element is further configured to:

control the second optical transmitter to transmit the third optical signal during a third period of time,

receive the third PPG signal from the optical receiver, and

filter the third PPG signal with a third signal filter to generate a third cardiac component.

10. The electronic fitness device of claim 1 , wherein the signal filter parameter is one of a filter coefficient, a waveform associated with the identified common component, or a spectral parameter of the identified common component.

11. The electronic fitness device of claim 1 , wherein the second optical signal has the first wavelength.

12. The electronic fitness device of claim 3 , wherein the second optical signal has a third wavelength, the third wavelength being different than the first wavelength of the first optical signal.