Low-power CMOS active resistor independent on the threshold voltage

This paper presents a new linearity improvement technique for a CMOS active resistor. The method is based on the cancellation of the main odd-order nonlinear terms and bulk effect, using a parallel connection of two active resistors opposite excited, with different polarisation voltages. The resistor is designed to work for an extended range of the input voltages, and achieves an improvement in linearity about a magnitude order. The utilization area of this active resistor includes, but are not limited to active filters, switched capacitor circuits or medical applications. Its theoretical estimated performance, linearity error 0.35% for an input range of 500mV, was confirmed by SPICE simulations. The circuit draws a very small amount of current from a 3.3V voltage source, being suitable for low-power applications. The resistor was implemented in 0.35mu CMOS AMS technology and the layout area is about 60mum x 80mum.