Patent ID: 7839097

Claim:
A circuit comprising: a first and a second nodes which are adapted to be electrically coupled to a voltage source; a constant current source electrically coupled to said first node; a first resistance means electrically coupled in series between said constant current source and said second node; a third node coupled between said constant current source and said first resistance means; and a current regulation driving unit electrically coupled to said third node, said current regulation driving unit comprising: a noninverting operational amplifier (NOA) with its input terminal electrically coupled to said third node; a first field effect transistor (FET) with its gate terminal electrically coupled to said NOA's output terminal; a light emitting diode (LED) electrically coupled between said first node and said first FET's drain terminal; a fourth node electrically coupled to said NOA's feedback terminal and said first FET's source terminal; and a current sense resistance means electrically coupled between said fourth node and said second node, said current sense resistance means regulating said LED's electrical current while maintaining said NOA's non-inverting input voltage constant; wherein said first resistance means is a second FET; wherein said current sense resistance means comprises at least two FETs electrically coupled together in parallel, each of said at least two FETs being controlled by a digital signal; wherein said second FET is physically close to said at least two FETs; and wherein said second FET and said at least two FETs are substantially same devices.