| 摘要 |
PURPOSE:To prevent an error in signal detection due to the variation in the amplitude of a received signal by adjusting automatically the amplitude of not a received multilevel signal, but a reproduced multilevel signal and a reference voltage for level decision making as to a multilevel digital communication system. CONSTITUTION:An operational amplifier 32 adjusts its output voltage, i.e. reference voltage 9 so that the center reference voltage 12 for level decision making is invariably the earth potential. Therefore, reference voltages 9-15 are invariably in constant proportion relation about the earth potential. An integrator output 28 is connected to not a variable gain amplifier, but the reference voltage 15. Consequently, an automatic control loop for the amplitude of a reproduced four- level signal 25 and reference voltages 10, 12, and 14 for level decision making is constituted. Namely, the reference voltages 9-15 are so adjusted that the reproduced four-level signal 25 has the same amplitude with the received four-level signal, and a reference voltage for level decision making which matches with the received four-level signal all the time is generated, so signal detection is performed correctly.
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