Design of Real-Time Automatic Gain Control Circuit for Ultra-Low-Frequency (ULF) Communications

This paper demonstrates a real-time automatic gain control (AGC) circuit based on peak detection module for very low frequency (3KHz $\sim30$ kHz) communications. Operating timing of the AGC circuit is controlled by the FPGA board, while voltage selection module is adaptively switched according to the output of the peak detection circuit. Experiments of the implemented AGC circuit shows that four levels of automatic gain adjustment, i.e. 20 dB, 10 dB, 0 dB and -10 dB, can be realized for the input signal amplitude within 30 mV to 1.5 V. The measured settling time of the fabricated circuit is reduced to 54 $\mu$s, which is only 1.25% of that of the traditional AGC circuit (4.3 ms).