As two important bio-electrical signals

EEG and ECG have long been used important physiological

psychological indicators. To classify this kind of sensors from a technical point of view

such medical sensor electrodes can be divided into two categories: wet electrodes and dry electrodes

which in turn can be further divided into contact dry electrode and non-contact dry electrode. Although being used in most of the occasions

typical wet electrode is inconvenience with several drawbacks. The research of dry electrodes is a hot topic in the world right now

and most researches focus on contact dry electrode which features micro-needle penetration technology. To realize contact dry electrode based on ultra-high input impedance amplifier circuit

focus on introduction of impedance boosting technique using positive feedback are given

circuit design and analysis.