| 摘要 |
PURPOSE:To eliminate the insercurity of operation due to a shot noise, by providing a circuit which stops rise in bias voltage within a weak light-input range to the light input break detecting circuit of an optical receiver which has an avalache photodiode. CONSTITUTION:The avalache photodiode APD is controlled so that the product of a light input and a multiplication rate is constant by increasing the bias voltage Vd within the range wherein the light input is weak. A bias voltage increasing circuit is connected to the APD by a buffer 28 which outputs a voltage V1 proportional to a photocurrent IP, error amplifiers 30 and 32, and DC-DC converter 34 to inrease a bias voltage Vd as the light input decreases. The bias voltage Vd is fed back to the amplifier 32 negatively to be balanced when V2=k.Vd. When the light input further decreases, a diode 31 conducts to limit the rise in bias voltage Vd. Thus, the insecurity of input break detection due to a shock noise is prevented. |
