EVALUATION OF THE ULTRASONIC PREAMPLIFIER NOISE VOLTAGE DENSITY

Abstract

Analysis of the noise voltage density evaluation procedures of the ultrasonic preamplifier is presented. Ultrasonic testing is demanding low noise reception channel. Techniques and equipment for ultrasonic preamplifier's noise performance evaluation are suggested. Equipment used and measurement technologies applied are described. One of the techniques suggested allows estimating the preamplifier noise with only impedance measurement results available. Sine wave correlation technique was used in the impedance measurement procedure. Another technique, not demanding the spectrum analyzer, was suggested, which uses the analog-to-digital converter (ADC) sampling and the Fourier transform to obtain the noise spectral density. Experimental results for the measured complex gain and the equivalent input noise of the preamplifier are presented. Comparison with traditional noise estimation procedure, using the spectrum analyzer is given. Both direct measurement techniques (ADC record Fourier analysis based and spectrum analyzer) indicated good match. Noise whiteness was estimated: in a region of operation frequencies, 5–7 MHz, noise can be considered as white.