[sdiy] Re: ripple counters

[asfi at eol.ca]

mark verbos writes: 

> Hi everybody, 
> 
> I'm planning to build a voltage controlled delay using the Sigma Delta 
> technique, with 4164 RAMs similar to the one on Batz's page or the Delta 
> Labs stuff. I'm putting together the clocking section and I was planning 
> to use a 4040 or a pair of 4024s to count the RAMs, but I'm wondering if 
> the fact that they're ripple counters will screw the circuit up. So my 
> question is.... How long do they actually have chaos between steps and is 
> it enough to confuse the RAM in something like this? Obviously it will 
> depend on how fast the circuit is clocked, but what is the breaking point? 
> The data sheet claims that the 4040 can go up to 6MHz. Should I just use 
> 40193s to be safe? They only claim to go up to 8 MHz. Plus, they only have 
> 4 outs each, so it will take more chips. Anyone have experience with this?

I haven't looked at the timing requirements for the circuit so I can't say 
whether a ripple counter would be OK. But in a nutshell, metal-gate CMOS 
(the 4000 series) = slow as molasses in January. 

The 74HC(T)4040 would be a far better bet, if timing allows an async 
counter. 

If you do need to go synchronous, there's the 74HC590, though you'll need a 
little extra glue for it. 

 - Colin Hinz
 Toronto, Canada