Effect of ``Baseline Restoration'' on Signal-to-Noise Ratio in Pulse Amplitude Measurements

The effect of baseline restoration on signal-to-noise ratio in pulse-amplitude measurements is determined theoretically and experimentally. It is found that the signal-to-noise ratio with baseline restoration normalized to that without restoration is ηr/η=[1+α− 2α½kx(τ)]−½, where kx(τ) is the noise correlation factor at the output of the filter (amplifier), τ is the measurement interval, and α is the attenuation of noise power due to integration by the restorer capacitance and switch resistance (α=1 for fast restorer). Methods of calculation of correlation functions are outlined. A method for measurement of correlation functions by oscilloscope is described. The results are presented for the three commonly used filters: CR-RC filter, quasi-Gaussian filter, and delay-line filter. Baseline restoration is found to degrade the signal-to-noise ratio. The amount of this degradation can be reduced to negligible proportions in filters with long memory (such as CR-RC) by a small degree of integration in the restorer. Peak-to-peak amplitude measurement of double-differentiated signals performs, in effect, baseline restoration and, in addition, improves signal-to-noise ratio compared to peak-amplitude measurement.