Patent ID: 7683955

Claim:
The photocurrent sensing circuit comprising: a first logarithmic compression circuit including a diode, and logarithmically compressing a photocurrent received from a light receiving element to convert said photocurrent into a voltage, using said diode; a cancellation circuit logarithmically compressing a current substantially equal in temperature coefficient of said photocurrent to convert said current into a voltage, and performing an addition or a subtraction on said converted voltage and the voltage converted by said first logarithmic compression circuit to output a resultant voltage; a logarithmic operation circuit logarithmically compressing the resultant voltage received from said cancellation circuit to produce a first voltage, logarithmically compressing a voltage proportional to a thermal voltage of said photocurrent to produce a second voltage, logarithmically compressing a current having thermal dependence of nearly zero to produce a third voltage and performing an addition or a subtraction of each of said second and third voltages with respect to said first voltage to produce a fourth voltage; and an inverse logarithmic transformation circuit performing inverse logarithmic transformation on said fourth voltage to output a current.