Patent ID: 7342451

Claim:
A circuit for producing a pair of currents having a ratio proportional to the natural logarithm of an input signal, comprising: a differential pair of transistors, each one of the transistors having a control electrode for controlling carriers between a first electrode thereof and a second electrode thereof, the first electrodes of the pair being fed a common current, the control electrode of a first one of the pair of transistors being adapted for connection to a first reference potential; a control circuit for controlling the control electrode of the second one of the pair of transistors to a second potential; a current feedback circuit fed by a first current passing through the second electrode of one of the pair of transistors for producing a corresponding feedback current; a translinear loop, fed by the input signal and the feedback current, for producing a second current through the second electrode of another one of the pair of transistors proportional to the natural logarithm of the input signal; and wherein the first and second currents provide the pair of currents having the ratio proportional to the natural logarithm of the input signal.