Front end with offset-free symmetrical current source optimized for time domain impedance spectroscopy

摘要: Fast impedance measurements are often performed in time domain utilizing broad bandwidth excitation signals. Other than frequency harmonic distortion cannot be compensated which requires careful design of the analog front end. In order to minimize influence electrode polarization and noise, especially low-frequency measurements, current injection shows several advantages compared voltage application. Here, we show an active end based on a voltage-controlled source for wide range impedances. Using proper feedback, majority parasitic capacitances compensated. The ranges from dc 20 MHz magnitude below 5 kΩ. output is symmetric signal without dc-offset accomplished by combination conveyor inverter. An independent feedback loop compensates offset arising asymmetries within circuitry. We focused stability usage with small metal electrodes aqueous solutions. At monitor side two identical, high input difference amplifiers convert net through object dropping across into 50 Ω output. entire circuitry optimized step response making it suitable fast measurements.