Tunable CMOS resistor circuit with improved linearity based on the arithmetical mean computation

An original active resistor structure using exclusively MOS devices working in the saturation region will be further presented. Performing the great advantage of an excellent linearity, obtained by a proper biasing of the differential core (using original translation and arithmetical mean blocks), the proposed circuit is designed for low-voltage low-power operation and allows a very good controllability of the equivalent resistance. The estimated linearity is obtained for an extended range of the differential input voltage and in the worst case of considering second-order effects that affect MOS transistors operation. The frequency response of the new active resistor is strongly increased by operating all MOS devices in the saturation region. The circuit is implemented in 0.35 μm CMOS technology on a die area of 30 μm × 40 μm, being supplied at ± 3.6 V . The active resistor presents a very good linearity (THD <; 0.8%) for an extended range of the input voltage ( - 2.5 V <; V_X - V_Y <; 2.5 V). The tuning range is extremely large comparing with the previous reported active resistors: ± (500 kO - 5 MΩ) , the circuit being able to simulate both positive and negative active resistances.