Equivalent-time sampling and real-time digital oscillography interpolation

Two methods for increasing the sampling rate in digital oscilloscopes are analyzed. The equivalent-time sampling is carried out via measuring and accumulating a series of oscillograms with a random phase and leads to nonuniform sampling. As a result, for few accumulations, the output noise level increases and the effective number of bits decreases. Interpolation in digital oscilloscopes is performed by sin x/x functions and its errors are determined by the length of the interpolating FIR filter. A table for choosing the filter length, depending on the interpolation coefficient and the normalized band of the reconstruction filter is presented. Obtaining a high interpolation coefficient requires considerable computational power.