Pulse sharpening in a uniform LC ladder network containing nonlinear ferroelectric capacitors

A new method of pulse sharpening is described in which the risetime of a high-voltage pulse is progressively reduced as it propagates along a uniform lumped-element delay line containing nonlinear ferroelectric capacitors. The capacitors are made from a barium-titanate-based ceramic dielectric whose relative permittivity reduces with applied voltage stress. The resultant drop in capacitance causes the phase velocity of an electrical pulse propagating on the delay line to increase with increasing pulse amplitude. Therefore, the time delay of each section of the line is also amplitude dependent, causing the crest of the pulse to catch up with the low-amplitude portion of its leading edge. In the experiment described, the risetime of the leading edge of a 28-kV voltage pulse was reduced from 280 to 50 ns as it propagated along a 15-section ladder network. It is found that the impedance of the ladder is amplitude dependent, and the problem of matching the line with a nonreactive linear load resistance is discussed. Techniques are described for characterizing the nonlinearity of the capacitors and also for measuring their loss.<
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