Using harmonic frequencies in 74ac logic as alternative to a "normal" vco/pll combination

[Fulcrum]

Using very fast 74ac(t) logic (I was thinking of a 74ac14 smTrigger/buffer)
One could filter out one of the harmonic frequencies that these chips
generate, using a very sharp filter.
I don't have a spectrum analyser to check it, but does anybody here have an
idea until what freq. harmonics are generated. I was able to receive signals
around 430+ MHz which was the 7th harmonic freq. from a 74ac14 buffering a
61Mhz square.

I was wondering how much higher one could go. (1600 MHz ???)

 

[raymund hofmann]

Using very fast 74ac(t) logic (I was thinking of a 74ac14 smTrigger/buffer)
One could filter out one of the harmonic frequencies that these chips
generate, using a very sharp filter.
I don't have a spectrum analyser to check it, but does anybody here have an
idea until what freq. harmonics are generated. I was able to receive signals
around 430+ MHz which was the 7th harmonic freq. from a 74ac14 buffering a
61Mhz square.

I was wondering how much higher one could go. (1600 MHz ???)

With AC Logic you may be able to generate Harmonics over 1GHz, especially if you
increase their power supply to the absolute maximum.
With ECLinPS TTL to ECL translator you will surely have harmonics up to a few
GHz.
But maybe it gets easier to design a VCO at the required Frequency than the
Filter for the Harmonic...
For the 25th Harmonic you have to adjust the Filter with a accuracy of less than
4%. And it has to have quite narrow passband to sufficiently suppress the next
uneven harmonic about 8% away.
And the power at the 25th Harmonic (even with ideal Waveform) is already quite
low (maybe -40Db with AC gate) compared to the base frequency.
And also is a LC VCO a kind of tuneable LC Filter ...

Raymund Hofmann