Low power voltage reference circuits

A voltage reference circuit comprising:

• a proportional to absolute temperature (PTAT) generation circuit configured to generate a PTAT current;
• a complimentary to absolute temperature (CTAT) generation circuit configured to generate a CTAT current;
• an output circuit configured to combine the PTAT current and the CTAT current to generate a reference voltage at an output of the voltage reference circuit;
• and
• wherein the CTAT generation circuit comprises
• a first p-type field-effect transistor (FET) having a source terminal coupled to a voltage supply, a gate terminal coupled to a ground connection at a first node, and a drain terminal coupled to the PTAT generation circuit and the ground connection at a second node, and
• a second p-type FET having a source terminal coupled to the voltage supply, a gate terminal coupled to the PTAT generation circuit at a third node, and a drain terminal coupled to the ground connection at the first node.

A voltage reference circuit comprising:

• a current mirror circuit coupled to a voltage supply;
• a proportional to absolute temperature (PTAT) generation circuit coupled to the current mirror circuit and to a ground connection;
• a complementary to absolute temperature (CTAT) generation circuit coupled to the voltage supply, the current mirror circuit, the PTAT generation circuit, and the ground connection;
• an output circuit coupled to the voltage supply, the current mirror circuit, the CTAT generation circuit, and the ground connection;
• a feedback loop that includes portions of the PTAT generation circuit and the CTAT generation circuit, wherein the feedback loop contributes to generation of a CTAT current;
• wherein all active devices in the voltage reference circuit are field-effect transistors (FETs);
• and
• wherein the voltage reference circuit does not include any operational amplifiers.