| 摘要 |
PURPOSE:To prevent the generation of a differential waveform in the output of an equalizing amplifier at switching from a transmitting period to a receiving period by providing an offset cancelling circuit between a receiving transformer and the equalizing amplifier. CONSTITUTION:The offset cancelling circuit 17 is constituted of a capacitor 12 and a switch 13. An offset charging period Tc is formed during the period from the start of the receiving period Tr to the arrival of a receiving signal S12. An input offset voltage of is charged in the capacitor 12 by shorting the switch 13 during the period Tc. After the priod Tc, the switch 13 is opened. Since the receiving period Tr has been already started at that time, a switch 15 is shorted and a switch 14 is opened, so that an input signal S12 of the equalizing amplifier 12 is obtained by subtracting the of from a transmission/ reception signal S11 in the receiving priod Tr as shown in S12. Thereby, the output S13 of the amplifier 16 is prevented from the generation of a differential waveform which may be generated in an ordinary example. |
