Methods and apparatus to produce fully isolated NPN-based bandgap reference

A bandgap reference circuit, comprising:

• a first circuit to generate a first current and a second circuit to generate a second current, wherein a control circuit forces the first and second currents to have a first magnitude, and wherein the first magnitude is proportional-to-temperature;
• a third circuit to generate a third current having a second magnitude, wherein the second magnitude is complementary-to-temperature, wherein the third current is based on a first voltage associated with the first circuit;
• and
• a fourth circuit comprising a transistor and a resistor, wherein adding the first and second magnitudes comprises generating a fifth current having the first magnitude in a fifth circuit and generating a sixth current having the second magnitude in a sixth circuit, wherein the fifth and sixth circuits sink current from the fourth circuit to form a third magnitude that is substantially constant over a change in temperature, wherein the fourth circuit generates a fourth current having the third magnitude and, wherein the transistor is to sense a second voltage indicative of the first voltage, and wherein the transistor turns on to cause the resistor to have a voltage indicative of the third magnitude.

A temperature measurement system, comprising:

• a first circuit to generate a first current and a second circuit to generate a second current, wherein a control circuit forces the first and second currents to have a first magnitude, and wherein the first magnitude is proportional-to-temperature;
• a third circuit to generate a third current having a second magnitude, wherein the second magnitude is complementary-to-temperature, and wherein the third current is based on a first voltage associated with the first circuit;
• and
• a fourth circuit comprising a transistor and a resistor to add the first and second magnitudes to form a third magnitude that is substantially constant over a change in temperature, wherein the fourth circuit generates a fourth current having the third magnitude and, wherein the transistor is to sense a second voltage indicative of the first voltage, and wherein the transistor turns on to cause the resistor to have a voltage indicative of the third magnitude;
• and
• a temperature sensing circuit coupled to the first and third currents and comparing the two currents.