Signal conversion circuit, heart rate sensor and electronic device

A heart rate sensor, comprising a signal conversion circuit, wherein the signal conversion circuit comprises:

• a photoelectric conversion circuit, configured to convert an optical signal into a current signal, wherein the current signal in a first phase comprises a signal converted from a useful optical signal, a modulated optical signal and a background optical signal in the optical signal, and the current signal in a second phase comprises a signal converted from the background optical signal, the useful optical signal is an optical signal carrying target information;
• a differential signal conversion circuit, connected to the photoelectric conversion circuit, and configured to convert the current signal into a first differential signal and a second differential signal, wherein the first differential signal is an integration signal of the current signal in the first phase, and the second differential signal is an integration signal of the current signal in the second phase;
• and
• a subtraction amplifier, connected to the differential signal conversion circuit, and configured to subtract the second differential signal from the first differential signal and amplify an obtained difference value to generate a third differential signal;
• wherein the differential signal conversion circuit comprises a first differential signal generation circuit configured to integrate the current signal in the first phase;
• and a second differential signal generation circuit configured to integrate the current signal in the second phase, wherein the first differential signal generation circuit is connected in parallel with the second differential signal generation circuit;
• the first differential signal generation circuit comprises a first integration circuit and a second integration circuit, the second differential signal generation circuit comprises a third integration circuit and a fourth integration circuit, each of integration circuits comprises a capacitor and a switch, and the differential signal conversion circuit further comprises a first switch, a second switch, and a first transconductance amplifier, one end of the photoelectric conversion circuit is connected to a positive input end of the first transconductance amplifier through the first switch, and the other end of the photoelectric conversion circuit is connected to a negative input end of the first transconductance amplifier through the second switch, the positive input end of the first transconductance amplifier is connected to a negative output end of the first transconductance amplifier through the first integration circuit, the negative input end of the first transconductance amplifier is connected to a positive output end of the first transconductance amplifier through the second integration circuit, the third integration circuit is connected in parallel with the first integration circuit, and the fourth integration circuit is connected in parallel with the second integration circuit.