[time-nuts] 74HC4046 receiver

[Bruce Griffiths]

John

How short a transition time do you want?
100ps or less is relatively easy with off the shelf parts as long as ECL
or CML are OK.
If you want a higher voltage swing can probably do 200ps or so with only
a few parts.
Tunnel diodes (they are still available) will easily achieve transition
times of a few tens of picosec albeit with a relatively low swing.
SRDs can be used to sharpen up slow (1ns or more) transitions.
One can always use a high current longtailed pair switching 100mA or
more into a 50 ohm load to keep the power supply transients within
reasonable bounds whilst achieving fast transition times.
This is the sort of output stage albeit with some series feedback in the
emitters (or III-V FET sources) used in most hp pulse generators with
fast transition times.

If you want to achieve very low jitter then cascading a couple of
limiter stages (longtailed pairs) with low pass filtered outputs which
in turn drive the output stage (AC04 or whatever) will be better than an
arbitrary Wenzel circuit feeding an AC04 at least for lower frequency
sinewaves (< 40MHz or so). Just select the filter capacitor values for
minimum jitter for the input frequency of interest.

Characterisation of the jitter of an AC04 when driven with different
amplitude sinewaves at the same frequency will be useful in optimising
such designs.

Bruce

John Ackermann N8UR wrote:
> After my experiments last weekend (which will continue...) I am 
> contemplating making up a simple circuit board with a Wenzel input 
> circuit driving a 74AC04 output, to provide a fast transition time 
> source that could be fed by a sine wave oscillator.  I suspect the '04 
> output rise time is about as fast as anything that we'd reasonably 
> homebrew, though I'd be happy to be proven wrong (Bruce???).
>
> I'm not considering turning this into a TAPR project, but I'll probably 
> end up with more PC boards than I need, so if anyone is interested in 
> getting a board (and sharing in the board cost), let me know.
>
> John
> ----
>
> Pete wrote:
>   
>> Bruce,
>>
>> The jitter measurements were made via the DTS PER function.
>> This looks only at CH1 & the reference is the DTS internal
>> 100MHz. OXCO. DTS-2075 jitter floor is < 3ps rms.
>>
>> The Fairchild & National parts have identical datasheets &
>> spec SIGin sensitivity as 133mV @ Vcc=6V. The Philips
>> version specs SIGin sensitivity as 35mV @ Vcc=6V.
>>
>> Fine idea to look at delta with 2ea 'AC04s driven from a
>> common source; I'll try it in the next day. Unfortunately, I
>> have no low jitter (<5ps) fast transition source to properly
>> drive the parts. It's still worth a look.
>>
>> Pete 
>>     
>
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