A method is proposed to find the individual impulse response of broad-band sampling oscilloscopes (HP54124T, 50 GHz bandwidth). The method is based on the fact that, when the oscilloscope is sampling a dc voltage, pulses are launched from the sampler towards the input connector. These pulses contain information on the scope's characteristic and can be measured by a second oscilloscope. This type of measurement is called a ''nose-to-nose'' calibration. Applying deconvolution techniques to the result of this measurement, the characteristic of the two scopes can be found, assuming that the two scopes are identical. To avoid relying on this assumption, three oscilloscopes can be used. The nose-to-nose is then applied three times, with a different pair of scopes connected together each time. The individual characteristics of the three sampling oscilloscopes are then calculated. Both SPICE simulations and close correspondence between swept-sine measurements and this method indicate that it is probably the most accurate method available at this moment to calibrate broadband sampling oscilloscopes. Several measurement uncertainties and practical problems are identified. The phase contribution of the sampling aperture can never be determined by this method, but there is strong evidence that the effect is negligible. Practical measurement problems are related to linearity of the samplers, additive noise, time-base jitter, and time-base drift.
