| 摘要 |
PROBLEM TO BE SOLVED: To shorten initial pull-in time at turning on of a power source, using a simple configuration without having to expand circuit scale. SOLUTION: When the power source is turned on, a decision part 9 outputs a switch control signal (m) to a changeover switch 7, selects the output signal of a sweep signal generator 6, generates a voltage sweep signal (h), which is increased from the minimum value of a gain control voltage range (p) to the maximum value, from a sweep signal generator 6 and supplies it to the gain control input terminal of a gain variable amplifier 1. Then, a difference (f) between an output level value (d) of an output signal (c) and a convergent value (e) of a target value is calculated, and at the time where f=0, a sweep voltage value (j) is detected and stored in a memory. After sweeping is completed, the voltage value stored in the memory is generated as a sweep voltage value (j) and supplied to the gain variable amplifier 1 as a gain control signal (b), afterwards a gain control voltage value (g) outputted from a control voltage generating part 5 is supplied, and original automatic gain control due to a closed loop control system is started.
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