A stable CMOS current reference based on the ZTC operating point

This paper presents the design of a temperature stable, supply independent current reference in a 0.25 μm CMOS technology. A current with small temperature coefficient is derived by exploiting the zero temperature coefficient (ZTC) operating point of a MOS transistor. The transistor is used in a feedback loop to cancel the temperature dependence of a polysilicon resistor. It is shown that simple equations together with fast simulations of the ZTC point and a special temperature coefficient can quickly yield an accurate design. Measurements from 10 samples show an average current of 6 μA with a standard deviation of 2.3 %, a voltage dependence of 0.3 %/V whereas the temperature coefficient is approximately 130 ppm/°C measured over a temperature range from -40 °C to 125 °C. The circuit compares favorably with other published untrimmed current references.