| 摘要 |
PURPOSE:To convert a digital signal with high precision without increase bits in number by controlling the gain of a variable gain amplifier so that an analog signal is within the dynamic range of an AD converter. CONSTITUTION:Reflected light from an optical fiber F is incident to an avalanche photodiode APD through a photocoupler COP to be converted there into an electric signal, which is amplified by an amplifier AMP1. The output of the AMP1 is further inputted to the variable gain amplifier AMP2 and then inputted to an AD converter A/D. Then, the digital signal from the converter A/D is added by an adder ADD several times and its output is inputted to a microprocessor PRO, which finds and stores its mean value in memories M1-M3. Said operation is repeated and when the storing operation to the memories M1- M3 is completed, data are read out of the memories M1-M3 and concatenated at a data concatenation part CON, whose output is inputted to a display device DIS to display such a receive waveform that the ending point and starting point of dynamic ranges are coincident. |
