The quality and effectiveness of biomedical measurement systems have a strong dependence of the variations of the electrode-tissue impedance. The reason is that the contact quality of the biomedical system with tissue through electrodes, depicted in Fig. a, might change significantly and lead to considerable measurement errors.
Therefore, an impedance measurement system is essential for the signal integrity of the entire biomedical system. Especially, in long-term biomedical measurements, a continuous-time impedance monitoring is mandatory.
The principle of bio-impedance measurement is injecting differential current into the body and measuring the resulting differential voltage which varies proportionally with the tissue impedance being measured.