Heart rate detection system and wearable device using the same

A heart rate detection system, comprising:

• at least one light emitting unit, emitting a light to a user's body;
• a light sensor, sensing a reflected light of the light and accordingly generating a first electric signal;
• and
• a processor, coupled to the light sensor and the light emitting unit, configured to:
• convert the first electric signal from a time-domain signal to a frequency-domain signal;
• calculate a first noise signal according to a first equation, and subtract the first noise signal from the first electric signal of the frequency-domain signal;
• calculate a second noise signal according to a second equation, and subtract the second noise signal from the first electric signal of the frequency-domain signal having the first noise signal removed;
• convert the first electric signal of the frequency-domain signal having the first noise signal and the second noise signal removed to a second time-domain signal;
• execute a peak detection with respect to the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed according to a first sampling rate, and calculate a plurality of peak values of the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed;
• and
• calculate a plurality of time intervals among the peak values according to the first sampling rate and the peak values, and calculate a heart rate based on the time intervals;
• wherein the first equation is:
• Y
• ⁡
• [
• i
• ]
• =
• ∑
• j
• =
• 0
• M
• -
• 1
• ⁢
• X
• ⁡
• [
• i
• +
• j
• ]
• M
• ;
• wherein Y[i] is the first noise signal, X[i+j] is the first electric signal of the frequency-domain signal, and M is a sampling number;
• wherein the second equation is:
• S
• ⁡
• [
• i
• ]
• =
• ∑
• j
• =
• 0
• M
• -
• 1
• ⁢
• Z
• ⁡
• [
• i
• +
• j
• ]
• M
• ;
• wherein S[i] is the second noise signal, and Z[i+j] is the first electric signal of the frequency-domain signal having the first noise signal removed.