In article ,
Paul Burridge wrote:
What's the maximum multiplication factor it's practical and sensible
to attempt to achieve in one single stage of multiplication? (Say from
a 7Mhz square wave source with 5nS rise/fall times.)

Depends on what you call "practical".

I know that one type of atomic clock uses a one stage frequency multiplier
to go from about 10MHz to about 9.1GHz.

A slow edged square wave follows the 1/N rule to about the point where the
rise or fall time is equal to half a cycle of the harmonic frequency.
From that point up, the spectrum falls off at a rate of at least 1/n^2.
Usually it is faster than that.

If we assume that the 5nS rise time is the input to a stage, we can use a
fast transistor to effectively speed the edge up.
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