Automatic gain controller

An automatic gain controller for controlling an amplifier to produce an output signal of constant amplitude regardless of the amplitude of an input signal to the amplifier comprising:

• signal detecting means receiving an output signal having a varying amplitude from an amplifier for converting the output signal into a DC current changing in amplitude according to the amplitude of the output signal;
• first and second time-constant controlling means connected in parallel and receiving the DC current to produce first and second pure DC components with different time-response characteristics;
• voltage subtracting means receiving the first and second pure DC components for subtracting the second pure DC component from the first pure DC component to produce a resultant voltage;
• voltage comparing means for comparing the resultant voltage with a predetermined reference voltage to produce a comparison signal;
• voltage sinking means for discharging the first pure DC component and resultant voltage;
• switching means for selectively controlling transmission of the first pure DC component to an output control voltage amplifying means of said automatic gain controller and to said voltage sinking means in response to the comparison signal;
• and
• control voltage amplifying means receiving the first pure DC component when said switching means is open to produce an amplified output signal supplied to the amplifier for regulating gain of the amplifier.