System and method for temperature sensing using thermopile integrated with rigid printed circuit board

An electronic device comprising:

• an absolute temperature sensor configured to estimate a first temperature;
• a back crystal;
• an optical sensor comprising one or more photoemitters and one or more photodetectors;
• and
• a heat flux sensor comprising:
• a printed circuit board (PCB) comprising an optical spacer between the optical sensor and the back crystal of the electronic device, the PCB comprising a thermopile, wherein the thermopile comprises a plurality of thermocouples in series;
• a plurality of vias in the PCB comprising one or more first vias from a first layer of the PCB to a second layer of the PCB comprising a first conductive material with a first Seebeck coefficient and one or more second vias from the first layer of the PCB to the second layer of the PCB comprising a second conductive material with a second Seebeck coefficient, different from the first Seebeck coefficient;
• a plurality of conductive traces on the first layer of the PCB and on the second layer of the PCB, the plurality of conductive traces interconnecting the plurality of vias;
• and
• sensing circuitry coupled to the thermopile and configured to measure a voltage proportional to a temperature gradient between the first layer and the second layer of the PCB;
• and
• processing circuitry configured to estimate a second temperature at the optical sensor and/or at the back crystal using the voltage proportional to the temperature gradient and the first temperature.