Difference Between CCS and NLDM

What is CCS and NLDM:

CCS stands for Composit Current Sourse Model, and NLDM stands for Non-Linear Delay Model. Both CCS & NLDM are delay models used in timing analyze.

Difference between CCS & NLDM:

• NLDM uses a voltage source for driver modeling
• CCS uses a current source for driver modeling

Why prefer CCS to NLDM:

The issues with NLDM modeling is that, when the drive resistance RD becomes much less than Znet(network load impedance), then ideal condition arises i.e Vout=Vin. Which is impossible in practical conditions.

So with NLDM modeling parameters like the cell delay calculation, skew calculation will be inaccurate.

That is the reason why we prefer CCS to NLDM