Electroencephalogram（ EEG） is an important diagnostic medical information

currently non-contact dry electrode has advantages of simple to use and less susceptible to environmental constraints in acquisition of EEG signals

thus it has broad application prospects

and has become a hot research topic worldwide. Because human skin has high impedance

thus require non-contact dry electrode has high input impedance. In order to increase input impedance

use depth of series of negative feedback voltage to achieve amplifier circuit of ultra-high input impedance

and give design and analysis of circuit. Depth voltage series negative feedback preamplifier can provide up 2. 6 × 1011Ω input impedance

which helps non-contact dry electrodes for signal acquisition.