Subnanosecond risetime pulse generators

Treats the design of solid-state pulse generators with risetimes less than 100 ps. These generators have been used in time-domain measurements on microwave components and materials to obtain frequency characteristics from time domain waveforms. A brief review of various sources including avalanche transistors, tunnel diodes, and step-recovery diodes (SRD´s) is given. The main feature is a description of a 60-ps risetime step generator with modifications for impulse and RF pulse outputs. In the step generator an avalanche transistor driver produces a 30-V step, which is successively sharpened by two SRD´s to a 20-V 60-ps risetime step. A trigger signal is provided by the first SRD followed by an internal 70-ns delay so that the faster pulse from the second SRD stage can be displayed on a sampling oscilloscope with no additional delay lines. The basic step can be differentiated to produce a 6-V 60-ps halfwidth impulse or filtered to generate a 1-V 500-ps wide RF burst with principal spectral amplitude in the 9-16 GHz frequency range. These generators provide a larger instantaneous spectral amplitude than the commonly used tunnel diode pulser.