Automatic gain control system

An AGC system comprising:

• a. a demodulator of modulated signals containing spaced repetitive pulses representing a maximum carrier level,
• b. a first amplifier for said modulated signals whose output is coupled to said demodulator and whose gain is subject to electrical control, and
• c. a feedback network not requiring gating to produce a control voltage from said pulses suitable for automatic gain control of said first amplifier, said feedback network comprising:
• 1. a second amplifier coupled to the output of said demodulator having a threshold set at less than the maximum carrier level to produce output pulses consisting of portions of said repetitive pulses in excess of said threshold,
• 2. a third amplifier coupled to the output of said second amplifier for non-linearly amplifying said thresholded pulses as a function of their magnitude, said third amplifier having an output characteristic having an initial slope of one sign and reproducing said thresholded pulses in the output in a first current direction;
• followed by a change in slope in said output characteristic to one of opposite sign, continuing until the pulses in the output have a second, reversed current direction, said second sloping region providing a gain stabilizing action when said feedback loop is closed, said third amplifier having negligible output current in the absence of input current,
• 3. an integrating network comprising a storage capacitor shunting the output of said third amplifier for providing a smoothed gain control voltage from said non-linearly amplified thresholded pulses, and
• 4. means to couple said integrating network to said first amplifier to increase or decrease the gain thereof about a quiescent point as said third, non-linear amplifier supplies current to or withdraws current from said integrating network as a function of signal strength.