Design and Implementation of Adaptive Signal Conditioning Based on Programmable Gain Amplifier for Dynamic Range Multi-Frequency Bioimpedance Measurements

This research presents the design and experimental evaluation of an adaptive analog front-end (AFE) system for voltage acquisition in bioimpedance applications. The proposed architecture integrates a first-order high-pass filter, a programmable gain amplifier (PGA) with 16 gain variation range 0.13 to 10 times, and a Sallen-Key second-order low-pass filter. PGA gain is controlled in real-time based on RMS voltage of input signal analysis using a 12-bit ADC on an STM32F446RE microcontroller with a sampling rate of 1.5 MSPS. The system accommodates input signals ranging from 6 mV to 8.97 V, with automatic biasing to mid-supply (1.65 V) for unipolar ADC operation. To validate the functional performance and signal integrity of the system, a series of characterization experiments were conducted covering frequency response, accuracy, and repeatability aspects. Frequency response testing confirmed a flat passband between 100 Hz and 100 kHz, ensuring compatibility with bioimpedance signals in the 1–100 kHz range. Error measurements yielded percentage errors below 3% across frequencies and gain settings, with excellent linearity (R^2=0.99994) at 1 kHz. Repeatability tests demonstrated stable performance, and standard deviation remained below 0.3 mV at mid to high range frequencies. The use of MCP6002 op-amps (GBWP = 1 MHz) introduces slight degradation at higher gains and frequencies, which is consistent with expected bandwidth limitations. Overall, the system provides a compact, reliable, and precise analog front-end solution for real-time voltage acquisition in dynamic bioimpedance monitoring systems.