Questions on the reverse design of the mixed circuit

Hi,
Recently,we revesed a mixed signal IC. I found the digital part is synthesized from behavioral level. It seems impossible for me to understand it. It is impossible to understand its function from gate level.I wonder how to analysis it?

Pl.s share your experence with me.

Thanks

If the digital part was synthesized it uses standard cell library. You don't need extract full schematic on transistor level. Remove all metal layers and divide the digital block into standard cells. Without metals the view is more clear. Extract (restore) schematic of every standard cell. Define logic function of every standard cell. Then extract (restore) connections. Draw schematic in standard cell symbols. Write Verilog model of every standard cell.
Simulate the circuit in mixed mode.
Compare result with specification. If any discrepancy check what can be wrong. May be you made mistake in standard cell, may be in their connection.
Good luck.

Fom said:

If the digital part was synthesized it uses standard cell library. You don't need extract full schematic on transistor level. Remove all metal layers and divide the digital block into standard cells. Without metals the view is more clear. Extract (restore) schematic of every standard cell. Define logic function of every standard cell. Then extract (restore) connections. Draw schematic in standard cell symbols. Write Verilog model of every standard cell.
Simulate the circuit in mixed mode.
Compare result with specification. If any discrepancy check what can be wrong. May be you made mistake in standard cell, may be in their connection.
Good luck.

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Thanks Fom, your reply is very helpful.

Would u pls. clarify the mixed mode simulation a bit more? you mean the mixed simulation is mixed gate level and transistor level? Then what simulation tool you can introduce to me? HSPICE can do it?

Firther, would you give me some advice on backend design? Alougth it is gate level, obviously, I can not use it to automaticly place and rute the layout.

Thanks

try to find a chance to stop reverse and start forward design, don't do that things wasting your time.

walker5678 said:

try to find a chance to stop reverse and start forward design, don't do that things wasting your time.

Click to expand...

Yes, I am trying to find the chance of forward design.
But, I don't think "do that things " is wasting my time. Many peiple has some misunderstanding on the "reverse deisgn". Few of them realized its posotive aspects.

Regards

I agree, that it's very likely, that a digital design of some complexity was defined by a behavourial description, but I wonder how you definitely found that it was designed that way. Cause you didn't understand the logic?

Assumed, you actually extracted the complete logic and it's (mainly) a synchronous one, it can be analyzed in terms of internal states, external signals and transitions. That's also a kind of (low level) behavioural description. The problem is, however, that the internal states may be grouped in many ways, allowing alternative high level descriptions.

Thus finding a meaningful high level description has a lot to do with intuitive understanding (respectively supposition) of the original design.