Automatic power reduction in photoplethysmography and pulse oximetry systems

An apparatus comprising:

• a transmit circuit including a light source;
• a receive circuit including a photodetector and a transimpedance amplifier coupled to the photodetector;
• and
• a calibration circuit coupled to the transmit circuit and the receive circuit, the calibration circuit including:
• a current controller to set an operational current of the light source to a minimum value that results in a target output voltage of the receive circuit, wherein a gain of the transimpedance amplifier is to remain substantially constant during calibration of the receive circuit, the current controller including:
• a reference comparator to generate a first comparison signal based on a calibration output voltage of the receive circuit and a reference voltage, and
• a counter coupled to the reference comparator, the counter to generate a counter value based on the first comparison signal;
• and
• a logic gate coupled to the reference comparator, the logic gate to generate a completion notification in response to the calibration output voltage of the receive circuit exceeding the reference voltage.

A method comprising:

• transmitting outbound light from a light source of a transmit circuit;
• receiving inbound light at a photodetector of a receive circuit;
• amplifying, by a transimpedance amplifier of the receive circuit, an analog signal associated with the inbound light;
• generating, by a reference comparator, a comparison signal based on a calibration output voltage of the receive circuit and a reference voltage;
• generating, by a counter, a counter value based on the comparison signal;
• generating, by a logic gate, a completion notification in response to the calibration output voltage of the receive circuit exceeding the reference voltage;
• and
• setting, by a calibration circuit, an operational current of the light source to a minimum value that results in a target output voltage of the receive circuit, wherein the gain of the transimpedance amplifier remains substantially constant during calibration of the receive circuit.