Two novel nonlinear circuits that exhibit an all-positive pinched hysteresis loop are proposed. These circuits employ two NMOS transistors, one of which operates in its triode region, in addition to two first-order filter sections. We show the equivalency to a charge-controlled resistance (memristance) in a decremental state via detailed analysis. Simulation and experimental results verify the proposed theory.
IntroductionPinched hysteresis was proposed to be a signature of memristive devices [1,2], yet it can also be observed in several other nonlinear devices such as nonlinear inductors (capacitors) with quadratic-type current (voltage) dependence [3]. Finding a general model for pinched hysteresis behavior was attempted in [4] for specific devices labeled as memristors [5]. In [6] and from a simplified mathematical point of view, the following model was proposed and shown to exhibit a pinched hysteresis behavior which can fit both chargecontrolled and flux-controlled memristance definitions:where if ( ) = V( ) and ( ) = ( ), the chargecontrolled memristance is obtained, while for the alternative setting ( ) = ( ) and ( ) = V( ), the flux-controlled memristance is obtained. In (1), the constants and are scaling and integration time constants, respectively. Note that circuit realization of this model for the purpose of emulating its pinched hysteresis behavior in non-solid-state devices requires a multiplier block, an integrator block, and an adder [6]. Several other emulator circuits have recently been proposed in the literature [7][8][9][10][11][12][13]. It is important to note that (1) is nonlinear due to the multiplication term and that pinched hysteresis cannot appear in a linear system. It is also possible to include other forms of nonlinearity that apply to the shaping of the loop as a result of shaping the applied excitation. This means replacing ( ) in (1) more generally with ( ( )). Pinched hysteresis loop is generally observed as a result of applying a bipolar sinusoidal voltage or current excitation signal and is thus symmetrical around the origin. Nonsymmetrical loops can also be obtained when the pinch point is shifted away from the origin. However, an all-positive pinched loop, to the best of our knowledge, has not been demonstrated before. It is the purpose of this work to introduce two simple circuits where this behavior is observed. We rely on the inherent nonlinearity of a MOS transistor to perform the multiplication operation required by (1) in order to obtain a charge-controlled memristance. Recall that a MOS transistor current-voltage relation can be described by