System for Precise Observations of Repetitive Picosecond Pulse Waveforms

Conventional sampling techniques yield minimum risetime in the oscillography of repetitive electrical waveforms. However, system timing uncertainties introduce drift and jitter errors, which are typically comparable in magnitude to the cathode-ray-oscilloscope risetime. By using two sampling oscilloscopes in cascade it is possible to reduce the drift by a factor of 10-3, down to a level of 10-14 seconds (during an averaging and recording time interval of 2 minutes). Successive sampling also allows accurate jitter filtering. With the aid of a tunnel-diode step generator the total system has a 10-90 percent risetime of 25 X 10-12 second, a step response that is closely integral Gaussian, a time-measurement uncertainty of about 10-13 second, and amplitude accuracy of 0.2 percent. Absolute time calibration is possible with a 3 X 10-14-second resetting capability. Applications include the measurement of the impulse-response functions of coaxial two-port networks in the 10-11-second range. Finally, it is shown that amplitude averaging of a sampled waveform with time jitter causes convolution error and loss of resolution.