The paper presents an original approach of designing analog signal processing circuits, based on the re-using of the same functional core for implementing a multitude of circuit functions: signal gain with theoretical null distortions, signal squaring, voltage multiplying with very good linearity and simulation of a perfect linear resistor with both positive and negative equivalent resistance. The great advantages of the increased modularity and controllability and of the reduced design costs represent an immediate consequence of the multiple functions realized by the proposed structures. Because the most important circuit complexity is concentrated in implementing the core of the multifunctional structure, both circuit area and power consumption per each realized function can be strongly reduced using this method, especially for multifunctional structures that are able to implement an important number of functions. The proposed circuits are designed for a low-voltage low-power operation, being supplied at V-DD = 1.4V and consuming between 2 mu W and 15 mu W, depending on the implemented function.