Anti-common-mode noise design for amplifier circuit during weak voltage signal measurement

The quality of measurement instruments usually was determined by the quality of their front amplifier,so those amplifiers with higher input impedance and stronger ability of anti-noise were chosen for using in computing circuits and instrumental circuits.When weak voltage signal is needed to be measured accurately,the symmetry of the instrumental amplifiers is difficult to realize.The authors proposed to add negative feedback circuit with common-mode voltage in instrumental amplifiers to totally or partly offset the common-mode noise in the strong noise environment,and add following circuit at the input end to decrease the measurement error caused by the imbalance of inputting circuit when the signal need to be transmitted in a long distance.The experimental results proved that the improved instrumental amplifier can effectively restrain common-mode interference.