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Author: Admin | 2025-04-27
Used for capturing the pin density = 8.610 by 8.610 Microns Table 4: Pin density comparison Multibit experiment: Number of bins with pin density more than 0.5 = 3.78 % Singe bit experiment: Number of bins with pin density more than 0.5 = 2.04 % Taking care of the high pin density: High pin density may result in high localized congestion over the multibit flops. There are different ways to avoid such issues, Cell padding Instance Padding Avoid placing multibit below power straps. IR/EM issue with MBIT: When the clock pin of the Multibit toggles, both the flops and their internal clock circuitry will draw current even though only one of them is changing the state. This can lead to high current getting drawn from the power rails. This requires a robust power network and an addition of Decoupling capacitors around the multibit flops. This also means that the short-circuit current requirement of multibit flops would be higher than a single bit flop in a localized region. One way to avoid IR/EM issue is to reserve space around the multibit flop by applying cell padding and removing the pad during de-caps insertion. Conformal checks: During RTL to synthesized netlist conformal checks, we need to instruct the tool to split the multibit flops into a single bit and do the verification. When the multibit conversion happens, the tools follow a particular naming convention with prefix and separator to identify the multibit flops. With these naming conventions, the multibit flops can be broken down into single bit flops during the conformal checks. Conclusion: Multibit flops offer a smart way to reduce the overall power of the design without impacting the timing. Usage of multibit flops reduces the leakage power and the dynamic power by reducing the clock tree cells and holding the buffers required in the design. It also helps in improving the density of the design by reducing the standard cell area, and thereby optimizing the block size. Authors: Upendra Somashekaraiah works as a Technical Manager at eInfochips, an Arrow company. He has more than 12 years of experience in ASIC
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