The pathological elements voltage mirror (VM) and current mirror (CM) have shown advantages in analog behavioral modeling and circuit synthesis, where many nullor-mirror equivalences have been explored to design and to transform voltage-mode circuits to current-mode ones and viceversa. However, both the VM and CM have not equivalents to perform automatic symbolic circuit analysis. In this manner, we introduce nullor-equivalents for these pathological elements allowing to include parasitics and to perform only symbolic nodal analysis. The nullor-equivalent of the CM is extended to provide multiple-outpus (MO-CM). Finally, two active filters containing VMs, CMs and MO-CMs are analysed to show the usefulness of the models.

A formulation method is introduced for the symbolic analysis of mixed-mode analog circuits consisting of opamps, current conveyors and/or current-feedback opamps. We show that by modeling all active devices using only nullors and grounded resistors, a reduced system of nodal equations can be formulated and solved by determinant decision diagrams. The nullor equivalents allow including parasitic elements as demonstrated in designing a universal filter.

A new nullor-based model to describe the behavior of Operational Transresistance Amplifiers (OTRAs) is introduced.The new model is composed of four nullors and three grounded resistors. As a consequence, standard nodal analysis can be applied to compute fully-symbolic small-signal characteristics of OTRA-based analog circuits, and the nullorbased OTRAs model can be used in CAD tools. In this manner, the fully-symbolic transfer functions of several application circuits, such as filters and oscillators can easily be approximated.

Abstract-We present the calculation of noise expressions of low voltage amplifiers by applying symbolic nodal analysis and using nullors. The nullor equivalents of the MOSFETs include only the dominant parasitic elements in order to generate a simplified symbolic noise expression, which provides a good insight to improve the design of low voltage amplifiers. The generated symbolic noise expressions are compared with HSPICE simulations, so that one can appreciate the good agreement with our proposed symbolic noise analysis approach.

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