出版社：Faculty of Humanities, Kaunas University of Technology
其他摘要：The noise model for first stages of ultrasonic system is developed. The aim is to obtain low noise factor for input stages, particularly for preamplifier. The air-coupled composite ultrasonic transducer is used as the signal source. The transducer impedance is measured experimentally and equivalent Butterworth-Van Dyke dual-circuit model generated. The last have been merged with the preamplifier noise model and equations for noise spectral density and noise factor calculation developed. Analysis has indicated that lowest noise factor (NF=1,9 dB) for transducer used is obtained for operational amplifier LMH6624 at frequency f=500 kHz and input termination resistance RT=10 kΩ. Simulation results indicate increase of noise factor if input termination resistance RT is reduced.Ill.8, bibl.8 (in Lithuanian; summaries in English, Russian and Lithuanian).
