Chopper Amplifier Circuit for Low-Noise Biopotential and Impedance Sensing

The patent applies periodic chopping action to modulate the input signal at a specific frequency (e.g., 60Hz). By periodically switching the signal path through capacitors and transistors, the biopotential and impedance signals are transformed into AC signals at the chopping frequency, which can then be amplified without being affected by 1/f noise that dominates at low frequencies.

The patent introduces an intermediary chopping circuit as a mediator between the input signal and the amplifier. This chopping circuit converts the DC or low-frequency input signals into AC signals at a higher frequency, allowing the amplifier to operate in a frequency range where 1/f noise is minimal, thus protecting the measurement from noise interference.

The patent designs a universal measuring apparatus that can perform both biopotential measurement and impedance measurement using the same hardware components. By controlling the switching elements (transistors Q1-Q4, capacitors C1-C2) in different configurations through the chopping circuit, the single device can adapt to measure different types of physiological signals without requiring separate dedicated circuits for each measurement type.

The patent employs dynamic switching control to reconfigure the measurement circuit on-the-fly. The chopping circuit dynamically changes the connection topology by switching transistors and capacitors based on the selected measurement mode (biopotential or impedance), allowing the device to adapt its configuration without physical reconfiguration or additional fixed circuits for each mode.