CTAT generator using parasitic PNP device in deep sub-micron CMOS process

A method of generating a current that remains substantially constant over temperature from a bandgap reference voltage, comprising the steps of:

• a. providing a proportional to absolute temperature (PTAT) current;
• b. receiving the PTAT current by a first current mirror to provide a current proportional to the PTAT current;
• c. providing a first bias current;
• d. receiving the first bias current by a first transistor having a base, an emitter and a collector, the emitter coupled to receive the first bias current, the collector coupled to ground, and in accordance therewith providing a first base-emitter voltage and a first base current;
• e. receiving the first bias current by a first resistive circuit coupled between the base and emitter of the first transistor and in accordance therewith providing a current proportional to the base-emitter voltage of the first transistor;
• f. providing a second bias current;
• g. receiving the second bias current by a second transistor having a base, an emitter and a collector, the emitter coupled to receive the second bias current, the collector coupled to ground, and in accordance therewith providing a second base-emitter voltage and a second base current;
• h. receiving the second bias current by a second resistive circuit coupled between the emitter of the second transistor and the base of the first transistor and in accordance therewith providing a current proportional to the base-emitter voltage of the second transistor, the current provided by the first resistive circuit equals the current provided by the second resistive circuit;
• i. providing a bias voltage;
• j. receiving the bias voltage by a third and fourth transistor having a gate, a drain, and a source, the gate of the third and fourth transistor coupled to receive the bias voltage, the source of the third transistor coupled to the base of the first transistor, the source of the fourth transistor coupled to the base of the second transistor;
• k. receiving the current provided by to the first and second resistive circuit and first and second base current by a second current mirror, the first and second base current are equal and oppose such that the second base current eliminates the first base current, and in accordance therewith providing a current complementary to absolute temperature (CTAT);
• l. adjusting the first current mirror such that the slope with respect to temperature of the PTAT current is equal in magnitude and opposite in sign to the slope with respect to temperature of the CTAT current;
• and
• m. combining the PTAT and CTAT currents using a third current mirror coupled between the first and the second current mirrors to provide a current that remains substantially constant over temperature.