Proportional-Integral-Differential-Based Automatic Gain Control Circuit for Ultrasonic Ranging Systems

This paper presents a fully analog automatic gain control (AGC) circuit based on PID control for ultrasonic echo compensation. The AGC circuit is mainly composed of an amplifier, PID controller, sampling circuit and reference circuit. Junction field-effect transistors (JFETs) operating in nonsaturation regions, which are equivalent to voltage-controlled resistors, determine the gain of the amplifier. The PID controller in the feedback loop adjusts the equivalent resistance of JFETs according to the difference between the output of the AGC and a reference voltage. The proposed circuit is able to achieve large gain range operating at frequencies from 10 kHz to 2 MHz. Experimental results show that various ultrasonic echo sequences can be properly amplified to the set level with low distortion.