Broadband sampling oscilloscope characterization with the “Nose-to-Nose” calibration procedure: a theoretical and practical analysis

In the past the “nose-to-nose” calibration procedure has been introduced as probably the most accurate method to determine the impulse response of broadband sampling oscilloscopes like the HP54124T. The method is based on the hypothesis “sampler kick-out equals oscilloscope impulse response”. This hypothesis was originally based on an intuitive approach and was later verified experimentally (comparison with power measurements) as well as with SPICE simulations. Until now, however, there was no generalized mathematical evidence supporting this basic hypothesis. In this paper a mathematical theory is developed, which starts from a generalized sampler equivalent scheme, and which shows that, under conditions which are valid in practice, the sampler kick-out indeed equals the sampler impulse response. Experimental results are reported concerning the accuracy and precision of the calibration procedure. These experiments involve the investigation of experiment repeatability, noise, sampler linearity and timebase effects