Lilliputian dimensions associated with the submicron geometries of most digital and many analog processes result in much faster circuit operation. As ICs speed up, the rise and fall times of most pulse and function generators, which are typically 5 nsec, become inadequate for measuring time intervals lower than 20 nsec.
You can overcome this limitation with analog comparators or advanced CMOS logic gates, which create faster digital edges. Their rise and fall times are fast enough, but the signal levels include ground and VCC only. Designers have applied the submicron processes that high-speed digital circuits use to analog switches as well, so the turn-on and turn-off times for these switches also produce fast rise and fall times. What’s more, an SPDT (singlepole double-throw) switch can create pulses whose high and low levels are programmable.
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