The trend towards mostly battrey operated portable electronic equipments has increased the interest of researches in employing companding (compressing/expanding) circuits that operate at very low voltages and powers. Many functions in signal processing are modeled by nonlinear and differential equations whose implementation ca be done easily using current- mode companding circuits. Therefore, roposing analytic methods in static and dynamic companding networks and designing improved current-mode circuits and overcoming the problems of the existing circuits are essential. In this thesis, after reviewing the structures of companding circuits, a new general method in designing and analyzing current-mode companding networks is presented. The results help to use easily and more effectively the properties of these networks and to expand their usage.The presented analysis can also be used in automated CAD design approaches. Because of various advantages of floating gate MOS transistors, such a working in low voltages and low powers, and programibility, translinear loops based on these transistor is presented. These new loops are immune from body effect, have lower circuit complexity, do not need extra biasing circuits and have lower supply voltage. Since in companding circuits voltages at internal nodes are compressed and nonlinear with large signal behavior, using small signal linear model of circuits, like taylor series and Volterra series, leads to on inaccurate evaluation of circuit distortion. In this thesis, after reviewing the previous methods, by employing harmonic balance technique, a new algoritm for analyzing nonlinear behavior of companding circuits is presented. The proposed method can evaluate the distortion with more accuracy, in a greater number of harmonics and with less complexity. In addition, a noise analysis method based on the noise of element in the companding circuits is presented. The above mentioned methods can be used as a new computer aided design tool in designing of companding circuits.
