| 摘要 |
PURPOSE:To control an output to an adequate level at all times so that an amplification degree can be fixed for a necessary time by controlling an amplification degree of a differential amplifier during a sampling period of a signal, and fixing the amplification degree during a holding period. CONSTITUTION:A differential signal A from a head, inputted to terminals 101, 102 is impressed to input terminals 11, 12 of a differential amplifier 1 and input terminals 19, 20 of an envelope generating circuit 2. The envelope generating circuit 2 is a circuit for deriving an envelope signal of the differential signal A, and a derived envelope signal B is impressed to an input terminal 22 of an operating circuit 3, is conveted to a signal C which is necessary for controlling an amplification degree of the differential amplifier 1, is outputted from an output terminal 23, and is supplied to an analog signal input terminal 18 of a sample holding circuit 4. A sample hold command D is inputted to a command input terminal 17 through a terminal 105 from a controlling circuit of the outside, samples or holds the signal C impressed to the analog signal input terminal 18, and its output E is used for a control signal of an amplification degree control terminal 13 of the differential amplifier 1. |
