| 摘要 |
PURPOSE:To simplify amplitude measurement by providing an AGC circuit with a detection circuit which detects the output of a variable gain amplifier, a comparator circuit which compares its output with a reference voltage, a reversible counter which provides addition or subtraction according to the output of the comparator, and a D/A converter. CONSTITUTION:An AGC circuit consists of variable gain amplifier 1, detector 2 for output level detection, direct-current amplifier 3 for AGC loop feedback, reference voltage input terminal 4, comparator 5, reversible counter 6, D/A converter 7, and switch S. In this constitution, switch S is closed to make detector 2 detect the output level of amplifier 1 and comparator 5 makes a comparison between a detection output and reference voltage to make counter 6 increase or decrease its count value, which applied to amplifier 1 via converter 7, thereby exercising gain control. With switch S opened next, an AGC loop is turned OFF to fix a gain when switch S is closed. Consequently, the ON-OFF switching of AGC and a gain adjustment can be done by one stage, so that the circuit will be simplified. |
