[sdiy] Nanosecond delays - the clean or dirty method?

Jay Schwichtenberg jschwich53 at comcast.net
Thu Feb 25 20:16:17 CET 2021


One thing I would be worried a bought is if the RC circuit effecting 
other chips on the CE line?

Might be a buffered signal going to the cartridge and in that case would 
be OK.

If you are doing a PCB seems like you might be able to add some SMT for 
the delay. You can use both top and bottom of the PCB with SMT stuff.

Good luck.
Jay S

On 2/25/2021 7:56 AM, Steve Lenham wrote:
> I need to delay the Chip Enable signal to a RAM IC by a tiny amount - 
> around 25ns. I'm building a replacement memory cart for a vintage 
> unit, and this is necessary to allow the use of a battery-free F-RAM 
> for storage (some F-RAMs have certain timing quirks).
>
> I know that the proper way to do this would be to insert one or more 
> pairs of inverters to delay the signal by a few propagation delays, 
> but that needs, like, another chip.
>
> The DIRTY way to do it is to add a tiny RC delay. I tried 1K5 and 22pF 
> and it worked perfectly, delaying the edge by about 50ns and solving 
> my problem.
>
> I'm well aware of the dangers of slow pulse edges and would never 
> consider this for something more lengthy without adding a Schmitt 
> buffer, but am curious as to whether it is still seen as irredeemably 
> bad practice for a tiny nudge such as this. I'm sure I have seen it 
> done in various vintage schematics.
>
> Any thoughts would be appeciated!
>
> Cheers,
>
> Steve L.
> Benden Sound Technology
>
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