Patent ID: 7129463

Claim:
A photocurrent sensing circuit having a stabilized feedback loop, the circuit comprising: a photocurrent generator including a photodiode generating the photocurrent in proportion to an amount of incident light and applying the photocurrent to an output node; a switching unit applying the photocurrent applied to a control node to a voltage-generating capacitor when a shutter signal is in a first state, and applying a predetermined current to the control node when the shutter signal is in a second state; and a circuit stabilizer applying the photocurrent applied to the output node to the control node, and always forming a feedback loop of the photodiode through the photocurrent applied to the output node, wherein the circuit stabilizer comprises: a first NMOS transistor forming the feedback loop of the photodiode in response to the photocurrent input to the output node when the predetermined current is applied to the control node, breaking the feedback loop and applying the photocurrent applied to the output node to the control node when the predetermined current is not applied to the control node; a second NMOS transistor always forming the feedback loop of the photodiode in response to the photocurrent applied to the output node; and a third NMOS transistor connected to the first and second transistors and the photodiode, and providing a current path for forming the feedback loop.