Differential IDAC for PPG applications

A system, comprising:

• a detector configured to capture light and generate an electrical signal:
• a photoplethysmography (PPG) circuit coupled to the detector, the PPG circuit configured to receive the electrical signal and generate compensation current for ambient light components of the electrical signal, the PPG circuit comprising:
• a first reference resistor coupled to a voltage supply rail;
• a second reference resistor coupled to reference ground;
• a reference current source arranged between the first reference resistor and the second reference resistor;
• a first variable resistor coupled to the voltage supply rail, the first variable resistor having a first resistance value based on a first digital code;
• a second variable resistor coupled to the voltage supply rail, the second variable resistor having a second resistance value based on a second digital code;
• a p-channel transistor configured to source a first output current from the first variable resistor to a first output terminal;
• an n-channel transistor configured to source a second output current from the second variable resistor to a second output terminal;
• a first amplifier configured to cause a first voltage across the first variable resistor to equal a first voltage across the first reference resistor;
• and
• a second amplifier configured to cause a second voltage across the second variable resistor to equal a second voltage across the second reference resistor.

A method to generate a differential current to reduce an ambient light component in an electrical signal corresponding to a photoplethysmography (PPG) signal measurement, the method comprising:

• sourcing, by a p-channel transistor, a first output current from a first variable resistor to a first output terminal, the first variable resistor coupled to a voltage supply rail, the first variable resistor having a first resistance value based on a first digital code;
• sourcing, by an n-channel transistor, a second output current from a second variable resistor to a second output terminal, the second variable resistor coupled to the voltage supply rail, the second variable resistor having a second resistance value based on a second digital code;
• setting, by a first amplifier, a first voltage across the first variable resistor to equal a first voltage across a first reference resistor, the first reference resistor coupled to the voltage supply rail;
• and
• setting, by a second amplifier, a second voltage across the second variable resistor equal to a second voltage across a second reference resistor, the second reference resistor coupled to reference ground, a reference current source arranged between the first reference resistor and the second reference resistor.