[time-nuts] More on paralleling output gates

Magnus Danielson cfmd at bredband.net
Sun Apr 9 21:56:18 EDT 2006

From: "Robert Lutwak" <Lutwak at Alum.mit.edu>
Subject: Re: [time-nuts] More on paralleling output gates
Date: Sun, 9 Apr 2006 16:04:49 -0400
Message-ID: <001401c65c10$db4f3070$6400a8c0 at lutwakhome>

> I suspect you're just measuring the bandwidth of your 400 MHz oscilloscope.

He is close... tau of 1.1 ns should be expected from a 400 MHz.

I am sitting here and thinking "Hey, isn't those 3 x 50 Ohm sources in parallel
a impedance missmatch?". If you have a sufficiently long system (> 1/12 of the
risetime in cable-length which in this case would mean maybe 50 cm or so) we
must consider it as an impedance system and thus we should care less about the
bulk capacitance behaviour (which can be "cured" with a stronger source) but
rather with the source and load impedances relative the cable impedance.

I'd like to view the exercise as only mildly interesting. Better to find a
better source for that signal. If you feel like toying around more on that '04
then directly parallel the outputs into a single 47 Ohm resistor might be more


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