CDC synchronizer

[stevenv07]

Hello everyone,

Does anyone know if tsmc provides cdc synchronizer (2 FF synchronizer) for 28nm library?

Thanks in advance!
Steve.

 

[oratie]

It provides metastability hardened flops, that should be used in (2 FF synchronizer) . Cell name is *SYN*

 

[stevenv07]

@oratie: I've found the cell name *SYN* in the library which is a scan FF with the name "SDFSYNSND2...". I wonder why the normal DFF (w/o scan) has no synchronizing cell type.
Do you know how many clock cycle does it take to transfer the input data to the output? (one or two clock cycles?).

Thanks so much!
Steve.

 

[oratie]

I do not know, why TSMC did not provide non-scan version. Logically this *SYN* flop is equivalent to the normal scan-flop. Just transitor size/ratio was modified to provide better metastability immunity.

 

[FvM]

Do you know how many clock cycle does it take to transfer the input data to the output? (one or two clock cycles?).

The purpose of a 2 FF synchronizer is to get a stable copy of an asynchronous single bit input signal. It does not transfer data (e.g. multi-bit entities or bit streams) consistently between clock domains.

In synchronous logic, each FF delays an input signal by one clock cycle. So does the 2 FF synchronizer.