Resistorless switched-capacitor current reference based on the MOSFET ZTC condition

The MOSFET Zero Temperature Coefficient (ZTC) condition is a strategy that can be used to implement low temperature sensitivity circuits, such as current and voltage references. This condition is usually analyzed using the strong inversion quadratic MOSFET model. In this work we use a different approach, based on a continuous MOSFET model that can predict its behavior from weak to strong inversion. Based on this analysis, we verify that the ZTC point occurs from moderate to strong inversion for any CMOS process, since this point must occur for gate-source voltages larger than one threshold voltage. Also, a resistorless switched capacitor current reference based on the ZTC condition (ZSCCR), presenting low temperature coefficient (TC), is presented. The ZSCCR is designed in a 180 nm process, resulting a reference current of 5.88 µA under a supply voltage of 1.8 V, and occuping a silicon area around 0.010mm². Results from circuit simulation show an effective temperature coefficient (TCeff ) of 60 ppm/°C from −45 to +85 °C and a power consumption of 63 µW.