High input impedance differential pre-amplifier circuit of ultrasonic flowmeter

The invention relates to a high input impedance differential motion preamplifier circuit for an ultrasonic flowmeter, which comprises a high voltage protection circuit, a CMRR alignment circuit, and an amplifying circuit consisting of an integrated operational amplifier. The input signal from an ultrasonic probe is inputted into the high voltage protection circuit through an input signal terminal,the high voltage protection circuit is directly or indirectly connected with the CMRR alignment circuit, the CMRR alignment circuit can regulate the resistance balance of the preamplifier circuit toensure the high attenuation of a common mode signal, and the AC input impedance of the preamplifier is improved through the positive feedback characteristic of the amplifier. The high input impedancedifferential motion preamplifier circuit for the ultrasonic flowmeter has the advantages of obtaining a high input voltage signal from the probe and absorbing little power from the probe, and consequently ensuring the improved