[time-nuts] Re: [OT] MB506 pre-scaler module ??

[ed breya]

I think the very first prescaler IC I ever encountered, long ago, is the 
11C90. I believe it's heyday was in the 1980s - it appears it was near 
EOL by 1992. I discovered it in some junk 6 GHz synthesizer modules that 
used a PLLed VHF VCO and a power amplifier, that was then SRD/BPF 
multiplied up the rest of the way. Later, I found one used as a 
prescaler in a low cost frequency counter from the 80s or 90s.

A data sheet is here - it provides some more perspective on how these 
work, and their evolution.

https://pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/11C90.pdf

You can see that it is basically a high speed ECL 1/10 divider (or 1/11 
- dual modulus even) capable of DC to around 650 MHz. It also includes 
provision to connect it for self-biased clock input at the logic 
threshold for AC coupling without any other parts (except an input 
capacitor depending on lowest frequency needed). This made it possible 
to toggle with input levels a fair amount less than the normal ECL 
range. I think the later, improved technologies used more gain stages to 
get the higher sensitivities we see in the modern (1990s-present) types. 
There is of course a trade-off between speed and sensitivity, since more 
gain slows it down.

Anyway, if you thoroughly read the Functional Description on page 6, 
you'll see the story from the horse's mouth, so to speak. BTW I believe 
there is a typo in the second paragraph, where it says

"This feature ensures that the circuit will operate with clock waveforms 
having very slow rise and fall times, and thus, there is no maximum 
frequency restriction."

I think it was meant to say no "minimum" frequency restriction, which 
makes more sense, in context.

I think around here is where prescalers were becoming a distinct 
functional component class, more tailored to the huge emerging 
telecommunications markets - optimized for RF, and separate from the 
counters category, although used together. At heart, they are the same.

Enjoy the story.

Ed