Hybrid voltage reference circuit with threshold voltage variation compensation

A neural interface comprising:

• an electrode area including a plurality of electrodes configured to record or stimulate brain activity;
• and
• at least one thermal sensor configured to measure a temperature of the electrode area, wherein the at least one thermal sensor comprises a circuit including:
• a first MOS transistor configured to provide a zero-gate-voltage drain current to a set of transistors connected between the drain of the first MOS transistor and ground;
• wherein the set of transistors comprises:
• a second MOS transistor, configured to generate a first proportional to absolute temperature (PTAT) voltage;
• a bipolar junction transistor (BJT) configured to generate a complementary to absolute temperature (CTAT) voltage;
• and
• a third MOS transistor configured to generate a second PTAT voltage and connecting the set of transistors to ground;
• wherein the reference voltage is a sum of the first PTAT voltage, the second PTAT voltage, and the CTAT voltage;
• wherein the first MOS transistor and the third MOS transistor are of the same type of transistor;
• wherein a source-bulk voltage of the third MOS transistor is non-zero to increase a threshold voltage of the third MOS transistor;
• wherein the first PTAT voltage is independent of a threshold voltage of the second MOS transistor;
• and
• wherein a dependence of the second PTAT voltage on the threshold voltage of the third MOS transistor is opposite of a dependence of the CTAT voltage on a threshold voltage of the first MOS transistor.