The new design of AGC circuit for the sinusoidal oscillator with wide oscillation frequency range

The typical automatic gain control (AGC) schemes are not suitable for the sinusoidal oscillator with wide oscillation frequency range. To solve this problem, the up-down counter, multiplying digital-to-analog converter, and high-speed comparators are employed to achieve the proposed AGC circuit, which corrects the complex roots of the overall system automatically to the imaginary axis of the complex frequency plane. The negative feedback technique with digital hardware is applied on the loop gain control. No low-pass filter is needed to detect the oscillation amplitude. Thus, this technique is suitable for the sinusoidal oscillator with wide oscillation frequency range. The oscillation frequencies ranging from 7 Hz to 1 MHz are tested with the proposed AGC circuit. The experimental results demonstrate the static characteristics and dynamic responses of the overall system.