In this paper, a hybrid time-base (HTB) device for the coherent sampling oscilloscope is presented. The HTB device makes it possible to reduce the uncertainty of determining the time position of the sample in the horizontal channel of the sampling oscilloscope. For its functioning, the proposed HTB device requires that the system-under-test, in addition to the test signal, also has a synchronous reference clock – harmonic oscillation. It should be noted that both the test signal and the harmonic reference clock are sampled simultaneously. The harmonic reference clock is connected to one of the oscilloscope channels and a special algorithm processes the clock samples and adjusts the coherent sampling mode. Two techniques of determining the position of the sample on the time axis are combined in the HTB device – the “trigonometric”, when the position is calculated by the arccosine or arcsine formula of the reference clock sampling value, and the interpolation method, according to which the time position of the sample is found by averaging the positions of two adjacent samples, obtained using said “trigonometric” technique. Primary experimental studies have shown that using the HTB device can reduce jitter of the sampling oscilloscope by several times and the drift with constant time distortion components is practically absent in this device.
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