[time-nuts] Frequency Divider
bruce.griffiths at xtra.co.nz
Thu Apr 2 12:31:46 UTC 2009
John Ackermann N8UR wrote:
> Hal Murray wrote:
>>> Start with a buffer amp and then a decent Schmidt trigger.
>> If you have a clean input signal, a Schmitt trigger doesn't solve any
>> problems. It does help if you have a slowly rising signal such that noise
>> might be significant while the signal is near threshold. A 10 MHz sine wave
>> is slow relative to AC logic.
>> Since we were recently speaking of LPROs, their user manual has a section on
>> how to convert 10 MHz sine waves into TTL signals. None of their suggestions
>> used Schmitt triggers.
>> This feels like the sort of thing that should have been hashed out here by
>> now. Is it time to start a FAQ?
> The TADD-2 uses an input circuit published by Wenzel in their "Waveform
> Conversion" document at http://www.wenzel.com/documents/waveform.html.
> I haven't measured its standalone jitter, but its input sensitivity is
> great -- it will reliably trigger a CMOS gate from an input at least
> down to -10 dBm, maybe lower (I don't recall the exact limits I found
> when I tested). If you build this, note one thing -- with the 100 ohm
> emitter resistor specified, the square wave output is more like 6V than
> 5V p-p. I use 120 ohms instead to get a 5 volt output.
> While the Wenzel circuit requires a modest handful of discrete
> components, I think it's the most useful solution by a pretty clear
> margin for our typical requirement of driving a single-ended logic gate
> from an HF source.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
One could also use a PECL to TTL level translator.
JPL have used ECL dividers throughout to produce 10MHz, 1MHz and 100KHz
outputs from the 100MHz signal derived from a Hydrogen maser:
Where TTL outputs are required an ECL to TTl translator followed by a
discrete amplifier to drive TTL levels in a 50 ohm load was used.
More information about the time-nuts