| 摘要 |
PURPOSE:To omit a gain control circuit for lots of devices provided with a two-way communication function by providing an automatic gain control circuit and an automatic level control circuit utilizing an AGC voltage of the gain control to one device. CONSTITUTION:Each input/output level of a transmission circuit 39, a reception circuit 36, a transmission circuit 34 and a reception circuit 42 is decided to a prescribed level in advance. Suppose that the 1st device 30 is in the reception state. Then the automatic gain control circuit 35 controls the level of an input signal so that the input level of the reception circuit 36 is a desired level. In transmitting a signal from the 1st device 30, the transmission level is controlled by an AGC voltage of a memory 37. That is, the loss between the 1st and 2nd devices 30 and 31 is proportional to the AGC voltage when data are transmitted and received between the 1st and 2nd devices 30, 31.
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