Patent ID: 6838654

Claim:
An apparatus for comparing outputs of a first and a second photodetector, comprising: a first circuit path comprising a first transistor, a current from said first photodetector being supplied to the first circuit path; and a second circuit path comprising a second transistor, said two transistors connected to form a current mirror arrangement, said two transistors being such that the current mirror arrangement provides a signal that is an first amplified version of the output of the first photodetector; a third circuit path comprising a third transistor, a current from said second photodetector being supplied to the third circuit path; a fourth circuit path comprising a fourth transistor, said third and fourth transistors connected to form a current mirror arrangement, said third and fourth transistors being such that the current mirror arrangement provides for the second device an output signal that is a second amplified version of the output of the second photodetector; and a comparator directly comparing the first and second amplified versions of the outputs of the first and second photodetectors without negative feedback.