Linear Active Resistor Based on CMOS Square-Root Circuits for VLSI Applications

The main advantages of the new proposed CMOS active resistor are the improved linearity, the small area consumption and the improved frequency response. An original technique for linearizing the I(V) characteristic of the active resistor is proposed, based on the utilization of a new linear differential amplifier and on a current-pass circuit. The linearization of the original differential structure is achieved by compensating the quadratic characteristic of the MOS transistor operating in the saturation region by original square-root circuits. The errors introduced by the second-order effects is estimated, while the frequency response of the circuit is very good as a result of biasing all MOS transistors in the saturation region and of the current-mode operation of the square-root circuits. The active resistor is implemented in 0.35mum CMOS technology, the SPICE simulation confirming the theoretical estimated results and showing a linearity error under a percent for an extended input range (plusmn400mV)and a small value of the supply voltage (plusmn2.5V)