Patent ID: 8129672

Claim:
A photosensor device with dark current cancellation, comprising: a first photosensor, having a first dark current but not receiving any photo signal; a first current replication circuit, said first current replication circuit is coupled to said first photosensor, said first current replication circuit generates a replicated current based on said first dark current; a second photosensor coupled to said first current replication circuit for acquiring said replicated current, said second photosensor having a second dark current receives said photo signal to generate a photocurrent based on intensity of said photo signal, wherein said second dark current is equal to said replicated current, so that said second dark current is offset by said replicated current; a second current replication circuit, said second current replication circuit is coupled to said second photosensor, said second current replication circuit generates a charge current and a discharge current both based on said photocurrent; and a digital signal generator, coupled to said second current replication circuit, said digital signal generator generates a digital signal based on said charge current and said discharge current to perform charging and discharging functions, and an electricity characteristic of said digital signal is related to intensity of said photo signal.