| 摘要 |
PURPOSE:To eliminate probability that unstable operation of oscillation, etc., is caused while having small compressibility, by attaining constant gain amplification with an AGC control current suppressed to a constant value when a detection becomes below an inferior threshold level. CONSTITUTION:Controller 13 is provided between detector 11 detecting an output signal and buffer unit 12 converting this detected output into an adequate current value. The output signal is applied as an AGC control current to respective control amplifiers 2-1 to 2-n by way of detector 11 and buffer unit 12. At this time, controller 13 when the detection 11 output becomes below a fixed value controls buffer unit 12 to suppress the AGC control current to a constant value and, in consequence, the operation gain of the AGC amplifier decreases down to a constant value, so that the unstable-operation state can be avoided. Next, if a signal of more than the constant value arrives in this state, controller 13 detects that the detection 11 output becomes above the constant value and resets the above-mentioned suppression on buffer unit 12. As a result, the AGC control current increases and the AGC amplifier returns the original gain state, thereby starting the AGC operation. |
