| 摘要 |
PURPOSE:To expand a dynamic range to a high light receiving level by increasing the resistance value of a non-linear resistor accompanying the fall of the light receiving level of a light receiving element, and making the non-linear resistor practically non-conductive at a minimum light receiving level. CONSTITUTION:The cathode of a diode PD is connected to power supply VB, and simultaneously, it is earthed through a capacitor C1. Besides, its anode is connected to the input terminal of a front end F/E by a transformer impedance amplifier through a forward resistor R and a coupling capacitor C2, and simultaneously, it is connected to the anode of a Schottky barrier diode D. In this case, the diode D is in a high resistance state, and a current (i) received by the photodiode PD flows mostly to the front end F/E. Accordingly, a junction point A is biased, and the Schottky barrier diode D is turned into a low resistance state, and suppresses its forward voltage, and restricts the current to the front end F/E. |
