[time-nuts] Distribution amplifier for 10MHz and 1 pps

[Julien Goodwin]

The 74S140 (dual 4-input NAND) is the classic TI TTL 50-ohm driver.
They're still available in DIP & SOIC.

I'm currently waiting on some boards to arrive so I can try SN74LVC1G17
as a more modern replacement that's much cheaper and smaller.

Once I've proven it I'll do a separate thread to the list about the
whole project, since it's on-topic.

On 18/3/19 1:27 pm, Bob kb8tq wrote:
> Hi
> 
> CMOS is good. The faster the better. Go to your favorite vendor and find whatever is “king” this month
> and that’s what you go with. HC has been around a *long* time and is about as slow as it gets in terms 
> of 5V CMOS ( yes, 4000 series is slower still …).  Faster means less delay in the gate (so lower variation
> in delay). It also turns out that faster means lower phase noise so lower jitter. 
> 
> Buffers are better than inverters, simply because they have higher output drive capability. One “favorite”
> are the x125 and x126 tri-state buffers. NC7SZ125 and NC7SZ126 are two examples. 
> 
> If you want to drive 50 ohms, you likely will need to parallel gates in order to handle the current. There is 
> an ongoing debate about source termination vs load termination vs “both termination” vs “don’t bother”. 
> I would suggest that terminating one end or the other is a … errr …. really good idea. 
> 
> Lots more information in the archives.
> 
> Bob
> 
>> On Mar 17, 2019, at 6:39 PM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
>>
>> I'm very curious, too.  Especially when I *just* built one using 74HC04N.  
>>
>> --------------------------------------- 
>> (Mr.) Taka Kamiya
>> I'm stuck in a wormhole....  Hello, worms! 
>>
>>    On Sunday, March 17, 2019, 4:01:26 PM EDT, Hal Murray <hmurray at megapathdsl.net> wrote:  
>>
>>
>>> For 1PPs the main goal is jitter and the selection of the ICs is very tricky 
>>
>> Could you please say more?  Do you mean logic family selection, or chip 
>> selection within a family?
>>
>> Most modern digital chips are CMOS with an input threshold of VCC/2.  I'd 
>> expect power supply noise to be important and families with faster switching 
>> times probably make more noise.
>>
>>
>> -- 
>> These are my opinions.  I hate spam.
>>
>>
>>
>>
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> 
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