A low-voltage low power CMOS companding filter

CMOS companding filters exploit compressed I-V characteristics of MOSFETs and reduce voltage swings at internal nodes, thus allowing large dynamic range in low supply voltage environments. Companding filters replace g_m-c filters in low voltage environments for higher dynamic range. Square-root domain filters and log-domain filters belong to this class of companding filters. The former uses the quadratic law of MOSFETs in the strong inversion region. Low power, low voltage and high frequency building blocks are needed for improved performance filters in VLSI. In this paper, a current-mode square-root domain filter with a novel current-mode geometric-mean and current squarer circuit, based on an up-down MOS translinear loop is presented. The main advantages of the proposed circuits over others are low power, low voltage, less circuit complexity and less signal dependent errors without complex current injection. Further, it is operative at higher frequencies. The body effect is minimized due to the up-down voltage translinear loop and isolation of the currents eliminates the redundancy, if the same current is used repetitively. These filters find their applications in current-controlled oscillators and in the design of low power low voltage current-mode video frequency filters.