Automatic Gain Control (AGC) for Radar, Drones & Self-Driving Tech

Looking for a smart way to keep your signal levels steady in radar or drone systems? This clever AGC (Automatic Gain Control) design uses a JFET as a voltage-controlled resistor to dynamically manage amplifier gain.

At the heart of the circuit is a non-inverting op-amp whose gain is controlled by the resistance between the JFET's drain and source. The op-amp output feeds a full-wave rectifier, which then drives an integrator. Acting as a low-pass filter, the integrator smooths out ripple for lower distortion and more consistent performance.

The op-amp + diode configuration delivers a rectified DC voltage proportional to the input signal. This voltage adjusts the JFET’s resistance, which in turn fine-tunes the amplifier’s gain to maintain a steady 0.2V peak-to-peak output—ideal for close-range detection.

Originally designed for radar-seeking systems, this robust AGC circuit is just as relevant today in autonomous vehicles and drones, where real-time responsiveness and stability are key.

📚 Source: C. Marco, “Automatic Gain Control Operates Over Two Decades,” Electronics, Aug. 16, 1973; reprinted in Circuits for Electronics Engineers, 1977.