Current Source Models: Historical Perspective

Post date: Aug 12, 2014 3:56:37 PM

Digital Implementation and analysis flows rely heavily on cell models. These models have evolved through the years. CCS and ECSM are two dominant models currently in use in the industry today. CCS stands for Composite Current Source. It is a part of liberty format released and endorsed by Synopsys Inc and is touted as first in the industry to deliver a complete open-source current based modeling solution for timing, noise and power.

1. High-Z interconnect
2. Receiver Miller effect
3. Dynamic IR-drop
4. Multi-voltage, and Dynamic Voltage and Frequency Scaling (DVFS) design
5. Driver weakening
6. Temperature inversion
7. Lithography induced variability

ECSM stands for Effective Current Source Model. It is liberty extension released in 2001 by Cadence Design Systems and is claimed as most complete open library format available and holistically models the effects of timing, noise, power, and variation. It was, indeed, first effort to model long wires with high impedance interconnects.

Accuracy of driver models in delay calculation during static analyses was primary technical reason behind the rise of these two current source models in early 2000s. ECSM was ahead of curve in modeling long wires with high impedance, when it was released in 2001. CCS leapfrogged with complete set of modeling in mid-2000s. ECSM caught up in the later part of decade.

These two formats have been released in open source to gain wider industry support. Extensions of ECSM are now released by the ECSM working group of the OMTAB (Open Modeling Technical Advisory Board) under SI2 . Whereas ownership of enhancing liberty format including CCS was given to LTAB (Liberty Technical Advisory Board) under IEEE-ISTO