| 摘要 |
PROBLEM TO BE SOLVED: To obtain a gain switching circuit in which the gain of an amplifier mounted on a plug-in type package can be switched easily. SOLUTION: Packages 101a-101c are plugged into the backboard part 102 of a shelf 100 and connected therewith. Amplifiers 1a, 1b are mounted on the package 101a and comprise a plurality of CR series circuits 3, 4 having different negative feedback impedances. A relay 2 connects the CR series circuit 3 or 4 as the negative feedback circuit of the amplifier 1a or 1b when backboard connectors 6 of the backboard part 102 connection are wired to be supplied with power from a predetermined power supply B, otherwise connects the other of the CR series circuits as the negative feedback circuit of the amplifier 1a or 1b.
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