OPTICAL RECEIVER FOR OPTICAL DIGITAL COMMUNICATION

摘要

PURPOSE:To always obtain an optimum amplification factor by providing a resistor whose resistance is higher than an input impedance of a preamplifier between an input of the preamplifier and a ground level point and supplying a bias current to the resistor so as to increase an input saturation current of the preamplifier. CONSTITUTION:A resistor R whose resistance is much higher than an input impedance of a preamplifier 12 is provided between an input of the preamplifier and a ground level point to supply a bias current IDC to the resistor R in a decreasing direction of an input current IIN. Thus, an input current versus output voltage characteristic shown in solid lines is shifted to the characteristic shown in broken lines and a saturation point P. is shifted to a point P1. As a result, a saturation current of the preamplifier 12 is improved by +IDC. In this case, it is required to take notice of a parasitic capacitance (capacitance between input and ground point of preamplifier 12) of a current source circuit and of an impedance (higher than input impedance of the preamplifier 12) of the current source circuit.