| 摘要 |
PURPOSE:To optimize the band of an optical receiver without replacement of the capacitor and the coil of an equalizing circuit by controlling an applied voltage to a diode connecting in parallel with a resistor determining the gain of an amplifier means to control a differentiating resistance of the diode. CONSTITUTION:The amplification band of a parallel feedback type preamplifier depends on a high frequency cut-off characteristic and its 3dB band f3dB is expressed in equation I, where C is a junction capacitance of a photodiode 1 and Zin is an input impedance. A transistor(TR) 11 and resistors 5, 6 whose resistance is respectively R2, R3 form an amplifier stage and its gain A is expressed in equation 11. As a DC control voltage VCONT applied to a diode 2 varies, a differentiating current of the diode 2 is changed. An open loop gain A of the preamplifier is expressed in equation III, where RD is a differentiating resistance of the diode 2. When the gain A in the equation III is substituted into the gain A in the equation I, since the band f3dB depends on the gain A (in equation III), the band f3dB is able to be controlled by the DC control voltage VCONT applied to the diode 2. |
