LOW-NOISE LUMPED-ELEMENT TIMING FILTERS WITH RISE-TIME INVARIANT CROSSOVER TIMES

Herein are described low-noise, lumped-element pulse-shaping filters that produce output pulses with zero-crossing times that are invariant with changes in input pulse amplitude and invariant with changes in input pulse rise time for input pulses with linearly increasing leading edges. Design equations and circuit diagrams are given. In addition, equations are derived that show that, in general, the noise-caused timing variance is inversely proportional to the crossover time, provided the crossover time occurs during the linearly increasing leading edge. The noise-caused timing variances of these lumped-element filters are only a few percent worse than the best that can be achieved for the same crossover time with a conventional delay-line constant-fraction filter in cascade with a resistance-capacitance low-pass filter. Neither delay lines nor delay-line approximates are used in these filters.