We propose a novel CMOS differential voltage-controlled equivalent active resistor based on a modified common-source cross-coupled pair. The equivalent resistance exhibited by the circuit can be tuned to be either positive or negative through the tail current, which is controlled by a bias voltage. The complete cell comprises four transistors, two resistors in addition to the bias voltage, and tail current source. Application to the design of oscillators is demonstrated by theoretical analysis, circuit simulations, and verified experimentally through measurements on prototypes implemented using discrete transistors.
PROPOSED DIFFERENTIAL RESISTORConsider the proposed active resistor circuit shown in Figure 1A where NMOS transistors M 1a,b form a cross-coupled differential pair biased by the tail current I b . These two transistors are connected to the common-gate PMOS transistors M 2a,b . Compared with the conventional cross-coupled differential pair, in the proposed active resistor, the gates of the Int J Circ Theor Appl. 2019;47:175-185.wileyonlinelibrary.com/journal/cta