A Weak-Inversion Cmos Analog Multiplier/Divider Circuit

A structure that has a weak-inversion biased MOS transistor at its core which can be used to build analog multipliers, dividers, squarers or square rooters is presented. It relies on the exponential dependence of the drain current to the gate-to-source voltage of a MOS transistor that is biased in the weak-inversion region. The proposed circuit produces at the output a current proportional to the gate-to-source voltage that has, conversely, a logarithmic dependence on the drain current, which is set to be the input current. Given that linear operations in the log-domain correspond to exponentiations, multiplications or divisions in the antilog-domain, the proposed structure serves as a building block for analog multipliers, dividers and many other non-linear circuits.