An Analog Front-End with Automatic Gain Control for Galvanic-Coupled Human Body Communication

The channel loss of galvanic-coupled human body communication (GC-HBC) is greatly affected by human body activities or individual differences, which will cause large changes in the amplitude of the input signal received by the receiver. This requires the analog front-end to have the ability to adaptively adjust the circuit gain to ensure stable output of the amplified signal. In this regard, this paper proposes an analog front-end with automatic gain control for GC-HBC. This circuit uses a differential preamplifier circuit with high input impedance and a rear-stage automatic gain control circuit that uses voltage feedback to control gain. While achieving amplification of weak signals, it also meets the requirements for stable signal output. The measurement results show that it has an input impedance of
$> \mathbf{100}\mathbf{M}\mathbf{\Omega}$
, a maximum gain of 74dB, and a sensitivity of - 76dBm, effectively meeting the needs for capturing and amplifying weak signals. The loop stabilization time is
$156\mu\mathrm{s}$
, and the input dynamic range is 34dB, which can ensure stable output of the amplified signal amplitude when the input signal amplitude changes.