Long interconnect between digital and analog blocks

Long interconnect between digital and analog blcoks

Dear All:

Due to chip planning reason, I have separated the digital blocks and analog ones far away from each other. However, the digital control line must travel a quite long distance (~1mm) before they reach the analog parts. Such interconnects are mainly bit control signal (like VCO band control bit) that would be quiescent after the chip goes into steady state, and the transition speed is pretty low (tens of ns per transit), so their parasitics may not be a concern. I am wondering if this is feasible on-chip because I fear that the lines are broken during manufacturing or easy to break when chip power up. In addition, the line are multilevel metals with 4um width, and inverter buffers are inserted every 300um. Does anyone can help and provide experience?
Thanks in advance!

Re: Long interconnect between digital and analog blcoks

With no current load there should be no reason for
lines to fail. If there were, you would not be alone in a
foundry customer pitchfork mob. You might pay attention
to antenna rules though.

The only time I ever had a problem with >1000um runs
(and on finer pitch) was a bit of determinstic jitter from
coupling of adjacent minimum spaced lines. On an ASIC
that unfortunately spec'd jitter on the two signals in
question, sub-10-pS. The autorouter, run by an outsourced
digital core shop, did it; I just got the fun of finding and
fixing it after prototype delivery was blown. Run length
was 10X your inter-buffer distance (but I doubt that
rebuffering alone would have fixed the problem, only
reduced its magnitude). Separation, and placing a guard
between, did the job.

Concentrate on what happens if signals are jittery, on
how much noise pickup from nearest neighbor against
driver output impedance vs logic noise margin. I don't
think there's a problem, as long as you are not routing
RF or critical timing / low jitter stuff this way.

Re: Long interconnect between digital and analog blcoks

Thanks freebird, quite useful! I am routing only some control bits that have no RF or timing issue with regard to those 1mm long interconnects..

Re: Long interconnect between digital and analog blcoks

From time to time I have had to add these 'unusual' lines at the chip level. Antenna rules have to be observed. DRC rules as well, but that changes dramatically from technology to technology. You might pass all checks, you might fail a lot of rules.