Patent ID: 8248012

Claim:
A method of determining gain of a back-electromotive force (BEMF) amplifier in a circuit comprising an electric motor coupled in series with a sense resistor, the BEMF amplifier having a gain to be adjusted for generating an amplified replica signal of a first voltage drop on the sense resistor, and an adder for generating a difference signal between a second voltage drop on the electric motor and the amplified replica signal, the method comprising: setting the electric motor into a tri-state function mode and storing a first quasi steady-state value for BEMF from the difference signal; forcing a reference current through the electric motor and determining a first value of the gain of the BEMF amplifier for equaling the difference signal to the first quasi steady-state value; setting the electric motor into a tri-state function mode a second time and storing a second quasi steady-state value for BEMF from the difference signal; and increasing the first value of the gain by an amount proportional to a difference between the second quasi steady-state value and the first quasi steady-state value.