Patent ID: 8278973

Claim:
A device comprising: a first terminal; a first driving circuit coupled to drive the first terminal; a control circuit coupled to the first driving circuit and including first and second circuit units, the second circuit unit changing a first impedance of the first driving circuit in stepwise manner in either direction of up and down to cause the first impedance of the driving circuit to approach or become substantially equal to a first reference value, and the second circuit unit producing a first detection signal when the first impedance of the first driving circuit has reached or crossed the first predetermined value at least two times, the first circuit unit responding to the first detection signal and terminating changing the first impedance of the first driving circuit, and a second terminal, and wherein the second circuit unit comprises: a second driving circuit coupled to the second terminal and indicative of a second impedance relative to the first impedance, a first comparator circuit comparing a voltage of the second terminal with a first predetermined voltage and generating a first comparing signal taking one of first and second logic levels based on a comparing result thereby, and at least three first flip-flop circuits connected such that an output node of a preceding one of the first flip-flop circuits is connected an input node of a succeeding one of the first flip-flop circuits, and leading one of the first flip-flop circuits receiving the first comparing signal at an input node thereof.