A photocurrent sensing circuit includes a logarithmic compression circuit;
a cancellation circuit logarithmically compressing a current
substantially equal in temperature coefficient of the photocurrent to
convert the same into a voltage, and performing an addition or a
subtraction on the converted voltage and a voltage converted from a
photocurrent by logarithmically compression; a logarithmic operation
circuit logarithmically compressing the voltage received from the
cancellation circuit to produce a first voltage, logarithmically
compressing a voltage proportional to a thermal voltage of the
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 the second
and third voltages with respect to the first voltage to produce a fourth
voltage; and an inverse logarithmic transformation circuit performing
inverse logarithmic transformation on the fourth voltage to output a
current.