With the development of science and technology, heartbeat detection function is employed in wearable electronic devices, which makes a light-emitting diode (LED) irradiate towards inner of a human body. The light penetrating through or reflected from the human body is sensed by using a photodiode or a phototransistor, and an optical signal (that is, a photoelectric current) sensed by the photodiode or phototransistor is converted into a voltage signal by using a heartbeat detection circuit.
An existing heartbeat detection circuit converts the photoelectric current flowing through the photodiode or the phototransistor into a voltage signal by using a transimpedance amplifier (TIA, which is also referred to as a current-to-voltage converter). However, the heartbeat signal has a very small amplitude, and is easy to be impacted by background light from the environment. The transimpedance amplifier is incapable of eliminating a background photoelectric current, and thus accuracy of judgment of the heartbeat signal is affected. Further, the transimpedance amplifier has a high power consumption, and is easy to be impact by noise. Therefore, an improvement to the existing heartbeat detection circuit is desired.